Produktion und Systeme
Refine
Year of publication
Document Type
- Article (398)
- conference proceeding (article) (341)
- Part of a Book (54)
- Book (36)
- conference proceeding (presentation, abstract) (27)
- Report (22)
- conference talk (18)
- conference proceeding (volume) (13)
- Doctoral Thesis (9)
- Patent (6)
Is part of the Bibliography
- no (937)
Keywords
- Produktionsplanung (19)
- additive manufacturing (15)
- Hierarchische Produktionsplanung (12)
- PPS (11)
- Simulation (11)
- Ablaufplanung (9)
- BEHAVIOR (9)
- Enterprise-Resource-Planning (9)
- elemental semiconductors (9)
- simulation (9)
Institute
- Fakultät Maschinenbau (413)
- Fakultät Informatik und Mathematik (166)
- Fakultät Elektro- und Informationstechnik (163)
- Fakultät Angewandte Natur- und Kulturwissenschaften (117)
- Fakultät Betriebswirtschaft (84)
- Labor Intelligente Materialien und Strukturen (73)
- Mechatronics Research Unit (MRU) (71)
- Technologie-Campus Neustadt an der Donau (71)
- Labor Faserverbundtechnik (LFT) (63)
- Labor Laser-Materialbearbeitung (LMP) (58)
Begutachtungsstatus
- peer-reviewed (338)
- begutachtet (4)
"Gazellen" - schnell wachsende Jungunternehmen: Definitionen, Forschungsrichtungen und Implikationen
(2012)
Schnell wachsende Jungunternehmen – bildlich als “Gazellen“ bezeichnet – sind von großer Bedeutung für die positiven ökonomischen Effekte, die man mit Entrepreneurship verbindet. Dennoch ist der Begriff der "Gazelle" in der Literatur noch nicht annähernd einheitlich definiert. Dieser Beitrag macht mit den wesentlichen Begriffsdefinitionen vertraut und unterzieht diese einer kritischen Würdigung. Es werden vier grundsätzliche Forschungsrichtungen identifiziert, die sich um das Thema “Gazellen“ etabliert haben: (1) phänomenologische Beschreibungen, (2) volkswirtschaftliche Wirkungen, (3) Rahmenbedingungen ihrer Entstehung (externe Erfolgsfaktoren), sowie (4) Gründungs- und Wachstumsmanagement (interne Erfolgsfaktoren). Ein Überblick über die Literatur soll einen vertiefenden Einstieg in die Thematik erleichtern. Abschließend werden definitorische Forderungen, Probleme bei der Auswahl von Stichproben und Empfehlungen für die zukünftige Erforschung von schnell wachsenden Jungunternehmen formuliert.
19F Gas Flow Measurement of C3F7H During Constant Flow and High Frequency Oscillatory Ventilation
(2013)
The aim of the current study is the development of MRI methods that enable the investigation of gas flow mechanisms during high frequency oscillatory ventilation. This work includes flow measurements during three constant flows (19.9, 30.6 and 41.4 L min-1) and the comparison to direct numerical simulations (DNS) using a second-order-acurate finite-volume method and to data measured with a volume flow meter. 19F-MRI, DNS and flow meter data are in good agreement. Flow measurements during HFOV of 4 Hz were successfully performed and velocity profiles could be recorded at different phases of the ventilation cycle.
Distinct electron and hole quasi-Fermi potentials, øf,n and øf,p, are included into a one-dimensional SOI MOSFET model that accounts for finite inversion and depletion layer thicknesses. The inclusion of øf,n, øf,p in the nonlinear analytical model is demonstrated to describe phenomena like kink effect and the multistable-charge-controlled-memory effect (MCCM) in SOI MOSFETs. The calculation of øf,p(t) depends on the device history and generation/recombination rates.
New structural sheet metal parts are developed in an iterative, time-consuming manner. To improve the reproducibility and speed up the iterative drawability assessment, we propose a novel low-dimensional multi-fidelity inspired machine learning architecture. The approach utilizes the results of low-fidelity and high-fidelity finite element deep drawing simulation schemes. It hereby relies not only on parameters, but also on additional features to improve the generalization ability and applicability of the drawability assessment compared to classical approaches. Using the machine learning approach on a generated data set for a wide range of different cross-die drawing configurations, a classifier is trained to distinguish between drawable and non-drawable setups. Furthermore, two regression models, one for drawable and one for non-drawable designs are developed that rank designs by drawability. At instantaneous evaluation time, classification scores of high accuracy as well as regression scores of high quality for both regressors are achieved. The presented models can substitute low-fidelity finite element models due to their low evaluation times while at the same time, their predictive quality is close to high-fidelity models. This approach may enable fast and efficient assessments of designs in early development phases at the accuracy of a later design phase in the future.
A family of CMOS low- to high-voltage output interface circuits based on a standard, unmodified low-voltage CMOS technology is described. Using only thin-oxide high-voltage (HV) devices with reduced V/sub GS/ (gate-to-source voltage) swing, it makes use of level-shift techniques to meet the constraints on the gate control signals. These static circuits permit the full output voltage swing of V/sub DDH/, while keeping the V/sub GS/ swing of the output devices within the safety limits, including during HV supply transients. Using a standard 2- mu m n-well CMOS technology, reliable, reproducible V/sub DS/ breakdown voltages as high as 120 V and 80 V have been obtained for HV-nMOS and HV-pMOS devices, respectively.< >
This article takes stock of 99 journals dedicated to the field of entrepreneurship research and examines their evaluations and impact. It compares several journal quality assessments, the Australian ERA 2010, ABDC 2010 and UQ 2011 lists, with other international rankings and with highly regarded impact measurements. In a following section, the H-Index and the HC-Index for journals are introduced. The H-Indices are Google Scholar based impact measurements which can be easily executed by anyone. The results for the entrepreneurship journals H-Indices are compared with other impact factors and with journal rankings from Australia and elsewhere. Results reveal that rankings are incomplete in regard to entrepreneurship journals and that many rankings are inconsistent when compared to impact measurements. This holds true even for the ERA and the ABDC 2010 lists, even though these are among the most appropriate lists.
A Bibliometric Based Review on Social Entrepreneurship and its Establishment as a Field of Research
(2013)
This paper provides an overview on the state of art of research on social entrepreneurship and the establishment of this topic in the academic world. It uses scientometric methods, especially bibliometrics, in measuring the maturity of social entrepreneurship research. The empirical part reveals the increasing number of
literature, the institutionalization of social entrepreneurship in seven dimensions, the emergence of thematic clusters, and methodological issue. The paper makes concrete suggestions on how to overcome methodological challenges at the boarder of advanced
qualitative and early quantitative research designs. Using Harzing’s “Publish or Perish” software this article furthermore provides a ranking of the 20 most cited academic contributions in social entrepreneurship. Surprisingly, almost half of the most cited
papers have not been published in journals but in books, rising doubts on the current (over-)rating of journal publications.
In fatigue strength assessment, the methods based on ideal elastic stresses according to Basquin and the less established method based on elastic-plastic stress quantities according to Manson, Coffin and Morrow are applied. The former calculates loads using linear-elastic stresses, the latter requires elasticplastic evaluation parameters, such as stresses and strains. These can be determined by finite element analysis (FEA) with a linear-elastic constitutive law, and subsequent conversion to elastic-plastic loads, using the macro support formula by Neuber. In this contribution, an alternative approach to approximate elastic-plastic parameters proposed by Glinka is compared to the the strain-life method using Neuber's formula, as well as the stress-life method of Basquin. Several component tests on 42CrMoS4-QT specimens are investigated. To determine the input data for the fatigue strength evaluations, the entire test setup is computed by FEA. The nodal displacements from these validated full-model simulations are used as boundary conditions for a submodel simulation of a notch, whose results serve as input for the fatigue strength assessments. It is shown that all approaches provide a reliable assessment of components. Our key result is that the strain-life method using the concept by Glinka for notch stress computation, yields improved results in fatigue strength assessments.
The concept of Industrial Revolution 4.0 (IR4.0) has sparked the urgency of many manufacturers to revisit their manufacturing processes and search for opportunities to further improved their production output. Unfortunately, it is difficult to improve a process with inadequate data. Many of the SMEs in developing countries are still using manufacturing machines from the yesteryears which do not have computational and connectivity capabilities. Therefore, we developed an end-to-end Internet-of-Things (IoT) solution, which reliably tracks the production performance of manufacturing machines. This paper elaborates on the designs and the rationale behind it. As of the writing of this paper, our IoT system has been deployed in real manufacturing environment and has been running for approximately 90 days on a 24/7 basis without data lost.
A Graphical User Interface for Simulating Resin-Transfer-Molding Combining LS-DYNA and OpenFOAM
(2015)
The paper describes parts of the joint research project Swim-RTM including several industrial and academic partners. Its goal is to combine LS-DYNA and the open-source CFD solver OpenFOAM to simulate the production process of continuous fiber-reinforced plastics, particularly the resin-transfer-molding (RTM) process, in which the layers of dry fabric (unidirectional or woven) are formed in the mold (draping) and then filled with liquid resin with high pressure at injection points. Through a combined analysis of both the structural mechanical and the fluid dynamical phases, a better prediction and thereby optimization of the textile components properties as well as injection points can be achieved, improving the manufacturing process. The draping simulation of the fabric layers is carried out with LS-DYNA, while the injection simulation of the matrix material is performed in full 3D with OpenFOAM. A key question in this research project is how local porosities can be derived from the structural computation in the draping step. The purpose of the presented subproject is to develop a graphical user interface (GUI) to enable the simulation of the entire RTM process of long-fiber-reinforced components including the transfer of results between the draping and injection phases. The complete simulation task is relatively complex and involves several software packages, meaning a high effort for the user to get familiarized with. To circumvent this, the GUI aims at requiring from the user only the minimum necessary input data, creating and running the simulation and mapping tasks in the background, and showing graphically all demanded intermediate and final results. For the draping step several current fabric materials such as *MAT_034, *MAT_234, *MAT_235, *MAT_249 are available. Several modelling techniques for the composite setup are also conceivable, including a workflow similar to metal forming applications. In the injection step the fabric is modelled as a porous medium and different transport models and liquid resin types are at hand. For the data transfer between the draping and injection models, i.e. the mapping of data between shell and volume meshes within the developed GUI, first the OpenFOAM volume mesh is converted to LS-DYNA format and the necessary passing parameters are extracted from the output files, then the mapping tool DYNAmap [3] from DYNAmore GmbH is invoked, and finally the OpenFOAM command files are created. After the injection simulation is started and successfully terminated, information, such as the distribution of air inclusions or the shear stress distribution to analyze the reorientation of component fibers, is available and can be transferred from the 3D fluid mesh to an LS-DYNA shell mesh for further computations, for instance a crash simulation. This backward data mapping between volume and shell meshes can then be performed inside the GUI.
Mechanical properties of biological tissue represent important diagnostic information and are of histological and pathological relevance. Malignant tumors are significantly stiffer and more immobile than surrounding healthy tissue. Hard calcifications in vessels occur due to arteriosclerosis. The problem is, that such information is usually not available or can only be obtained by manual palpation, which is subjective and limited in sensitivity. It requires intuitive assessment and does not allow quantitative documentation. Unfortunately, none of the established medical imaging equipment such as magnetic resonance imaging (MRI) or X-ray computed tomography (CT) can provide direct measure of tissue elasticity. On the one hand a suitable sensor is required for quantitative measurement of mechanical tissue properties. On the other hand there is also some need for a realistic haptic display of such tissue properties. Suitable actuator arrays with high spatial resolution acting in real time are required. A haptic sensor actuator system is presented in this paper including a sensitive sensor part and an actuator array for different applications. The mechanical consistency of an object is to be locally specified using a sensor system and represented perceptibly in a remote position on an actuator system for the user. The sensor system uses ultrasound (US) elastography, whereas the actuator array is based on electrorheological (ER) fluids.
The performance of thermal conductivity vacuum gauges can be improved by a well-designed geometry. The lower measurement range limit is determined by the size of the active sensing area and the thermal conduction heat losses through the supporting structures. The upper measurement range is limited by the distance between the heated element and the cold reference plane. Silicon based MEMS-technology gives the possibility to fabricate both sensing structures with suitable areas out of low thermal conductive materials and narrow gaps in order to extend the measurement range in both directions. In this work we present a MEMS-process to fabricate high thermal resistance sensor structures. The rectangular sensitive areas are anchored by four beams and are structured out of low thermal conductive PECVD-siliconnitride films with 1 µm in thickness. The metallic heating structure is completely embedded in the SiN-layer. Both sensitive area and its support beams were released from the silicon bulk material by anisotropic underetching. In this way a free-supporting structure with a gap of 150 μm to the silicon substrate was formed. The influence of the filament geometry and temperature was systematically investigated to determine the properties of the chips as thermal conductivity vacuum gauges. The temperature of the sensitive area was held constant by a self-balancing bridge circuit and the heating power was measured by a Δ-Σ-ADC. The average solid state thermal conductivity is in the order of 106WK1. The measuring range of the most sensitive structures covers 8 orders of magnitude from 105 mbar to 1000mbar.
A Krylov subspace projection method which provides simultaneous solutions of the Helmholtz equation at multiple frequencies in one solution step is presented. The projector is obtained with an unsymmetric block Lanczos algorithm applied to a transfer function derived from a finite element discretization. This approach is equivalent to a matrix-valued Padé approximation of the transfer function. The proposed method is an extension of the formulation presented in [J. Comput. Acoust. 8 (2000) 223] to unsymmetric systems and allows the treatment of a much wider range of practical problems, including near-field and fluid–structure interaction computations
This article describes a systematic literature search of research articles on the topics of ecological sustainability and production planning. Over 900 research articles deal intensively with these topics. These articles were catalogued and included in a database. They can be evaluated with an analysis tool, developed by the research group. The tool is available free of charge via a website of the research group.
A management system for dynamic and interorganizational design processes in chemical engineering
(2004)
Design processes in chemical engineering are hard to manage. The design process is highly creative, many design alternatives are explored, and both unexpected and planned feedback occurs frequently. Thus, it is inherently difficult to manage the workflow in design processes, i.e., to coordinate the effort of experts working on tasks such as creation of flow diagrams, steady-state and dynamic simulations, etc. Conventional project and workflow management systems support the management of design processes only to a limited extent. In contrast, the management system AHEAD is designed specifically for dynamic design processes. In addition, AHEAD supports the management of interorganizational design processes. A subprocess may be delegated to a contractor, which receives information only about those parts of the overall process that are relevant for the contract. The management systems of the client and the contractor are coupled at run time such that both systems maintain up-to-date state information. The contract may be changed at any time according to the rules of a pre-defined change protocol. To validate this approach to the management of dynamic and interorganizational design processes, the AHEAD system has been applied to a comprehensive case study, namely the conceptual design and basic engineering of a chemical plant for producing polyamide 6.
The use of non-conventional materials is nowadays of much interest in scientific community. Magneto-rheological elastomers are hybrid materials, which in presence of magnetic fields state a change in their mechanical properties. They are composed by an elastomeric matrix with embedded magnetic particles. One of the most attractive features of these materials is that as soon as the magnetic field is removed from the material, the original mechanical properties are completely recovered, with negligible differences in comparison to the original state. This paper focuses on the study of magnetic characteristics of these smart materials, such as relative permeability and demagnetizing factors, for samples with different volume concentration of ferromagnetic particles.
A solution methodology is introduced for the efficient computation of the acoustic field over restricted domains and for a frequency window. Typically, such partial field solutions include, for example, surfaces enclosing the radiating structure or even single points in the computational domain. The multiple-frequency partial-field (MFPF) method starts out by reformulating the finite element matrix system into a suitable shifted form. The DtN map is used as a radiation boundary condition and is interpreted as a low rank update of the matrix problem. The shifted standard form is then approximated by a rational matrix-valued Padé approximant and solved simultaneously over a frequency range. To obtain the Padé approximation, a banded unsymmetric Lanczos process is applied on the standard shifted form exploiting the matrix Padé-via-Lanczos connection. Numerical examples show the feasibility of the outlined procedure.
We derive a new 3D model for magnetic particle imaging (MPI) that is able to incorporate realistic magnetic fields in the reconstruction process. In real MPI scanners, the generated magnetic fields have distortions that lead to deformed magnetic low-field volumes with the shapes of ellipsoids or bananas instead of ideal field-free points (FFP) or lines (FFL), respectively. Most of the common model-based reconstruction schemes in MPI use however the idealized assumption of an ideal FFP or FFL topology and, thus, generate artifacts in the reconstruction. Our model-based approach is able to deal with these distortions and can generally be applied to dynamic magnetic fields that are approximately parallel to their velocity field. We show how this new 3D model can be discretized and inverted algebraically in order to recover the magnetic particle concentration. To model and describe the magnetic fields, we use decompositions of the fields in spherical harmonics. We complement the description of the new model with several simulations and experiments, exploring the effects of magnetic fields distortion and reconstruction parameters on the reconstruction.
An analytical model for dual-gate-controlled SOI MOSFETs is presented, assuming uniformly doped p-silicon films. It is restricted to electron inversion layers and depletion regions, neglecting hole densities. It allows to account for the spatial description of electronic quantities in the silicon film. Due to the non-linearities of the semiconductor equations the model parameters must be extracted iteratively. Some applications are presented to demonstrate the usefulness of the model.
A new approach to coat PA12 powders with laser-generated nanoparticles for selective laser sintering
(2018)
The modification of selective laser sintering (SLS) powder materials by nanoadditives offers the possibility to adapt the powder properties to the laser sintering process or the resulting part properties. To avoid agglomeration of the nanofiller, a new approach in which surfactant-free laser-generated colloidal nanoparticles are adsorbed onto the polymer surface directly in an aqueous solution is demonstrated. Based on this novel approach, polyamide 12 (PA12) powders are decorated with metal and oxide nanoparticles and processed via SLS. Electron microscopy and confocal laser scanning imaging are utilized to analyze the dispersion of the filler.
The concept and some steps in the development of a new actuator system which enables the haptic perception of mechanically inhomogeneous virtual objects are introduced. The system consists of a two-dimensional planar array of actuator elements containing an electrorheological (ER) fluid. When a user presses his fingers onto the surface of the actuator array, he perceives locally variable resistance forces generated by vertical pistons which slide in the ER fluid through the gaps between electrode pairs. The voltage in each actuator element can be individually controlled by a novel sophisticated switching technology based on optoelectric gallium arsenide elements. The haptic information which is represented at the actuator array can be transferred from a corresponding sensor system based on ultrasonic elastography. The combined sensor-actuator system may serve as a technology platform for various applications in virtual reality, like telemedicine where the information on the consistency of tissue of a real patient is detected by the sensor part and recorded by the actuator part at a remote location.
A one-dimensional analytical model for dual-gate-controlled SOI MOSFETs is presented and applied to a stacked p-channel MOSFET fabricated by epitaxial lateral overgrowth (ELO). The authors found and modeled a nonlinear dependence of front-gate threshold voltage on back-gate voltage if threshold is defined by a constant current instead of a constant silicon-surface potential. It is demonstrated by comparison of subthreshold slopes that surface potentials are not pinned to the onset of strong inversion or accumulation. Accurate one-dimensional modeling is a necessity for device characterization and a precondition for general SOI models for circuit simulation.< >
Due to a constantly growing interest in construction robots, guidance on the design and management for its development process is needed to employ the best practice know-how and accelerate efficient development and marketisation. The development of construction robots usually involves stakeholders from the construction sector, non-construction sectors, and investors. A systematic design management method can help to integrate the needs and aims of different stakeholders and team members during the development process. Therefore, a procedure model for the development of construction robots is proposed as an integrative guidance on how to systematically conceptualise engineer requirements and to design, develop, implement, evaluate, manage, and mature the designs of construction robots. Several recent projects have been used by the authors to test and verify parts of the proposed cyclic method. In addition, the authors explain how the proposed model has been composed of an adapted set of proven principles and methodologies from the systems engineering and management field and highlight the specific concepts for developing and testing the construction robots. The application of the procedure model revealed that the concept and method are feasible and, in principle, can provide a comprehensive and practical guide on the steps forward. A unique characteristic of the proposed procedure model is the core principle which allows the evolvement over time with each cycle of use. In addition, interchangeable elements can be inserted into the procedure model depending on the region, type of robot, and technical readiness level.
A lot of dental alloys are available on the market. Among these alloys, there are the conventional alloys, the so called casting alloys used without ceramics, the bonding alloys used with high fusing ceramics and the universal alloys used without or with low fusing ceramics. It is im portant to know the physical and mechanical properties of these materials but also their biocompatibility and their resistance to corrosion. Dental alloys are generally placed in the mouth for many years, they must not induce adverse biological reactions such as gingival swelling and erythema, mucosal pain and lichenoid reactions. Although these troubles are often caused not by the materials itself (1, 2), they can be induced by the metallic ions released during their corrosion. In order to decrease the risks to the health, it is necessary to study the corrosion of the dental alloys. Currently, the ISO 10271 Standard (3), describes 3 different corrosion tests: a static immersion test (chemical corrosion), an electrochemic al test and a tarnish test. However, there are no indications yet about the possible interpretation of test results. In this paper, we propose a method to compare and classify the dental alloys in relation to their chemical and electrochemical corrosion results. METHODS: The material tested are pure metals such as gold, palladium, silver, copper and zinc as well as dental alloys which are commercially sold (see Table 1). 54 different materials have been tested. A minimum of four samples of each material were tested by electrochemic al corrosio n and a minimum of three in chemical test. The samples were cast and prepared as indicated by the manufacturer and by the ISO 10271. For the electrochemical test, the samples are in the form of disks 11 mm in diameter. They are tested with a potentiostat/galvanostat Voltalab Model 21. For the chemical test, the samples are rectangular with the dimensions 35X10X1.7 mm. The solution used and the operating conditions are described in the ISO 10271. The concentration of metallic ions released is measured by Induced Coupled Plasma
The 0-1 multidimensional knapsack problem (MKP) is a well-known combinatorial optimization problem with several real-life applications, for example, in project selection. Genetic algorithms (GA) are effective heuristics for solving the 0-1 MKP. Multiple individual GAs with specific characteristics have been proposed in literature. However, so far, these approaches have only been partially compared in multiple studies with unequal conditions. Therefore, to identify the “best” genetic algorithm, this article reviews and compares 11 existing GAs. The authors' tests provide detailed information on the GAs themselves as well as their performance. The authors validated fitness values and required computation times in varying problem types and environments. Results demonstrate the superiority of one GA.
The mechanical and microstructural investigation of polymer parts (polyamide 12) fabricated by Selective Laser Sintering as part of a Round Robin initiative is presented. The paper focuses on the microstructural analysis of the Round Robin samples and their evaluation regarding their effect on mechanical properties with respect to each other. Therefore optical microscopy on microtomed samples, X-ray computed tomography and Differential Scanning Calorimetry is used to determine the morphology of residual particle cores and of internal pores.
The mechanical properties of polymer parts built by Selective Laser Sintering are strongly related to the internal microstructure which differs with the applied production parameters. The paper focuses on the back tracing of the pore morphology of laser sintered polyamide-12 samples to the process parameters. Therefore, a data base is used which is supplied by a Round Robin initiative and includes mechanical tensile tests and the microstructural analysis of the pore morphology of several different sample charges built with different machines. The pore morphologies (porosity, pore density, pore shape and pore arrangement) measured by X-ray computed tomography are compared and discussed regarding the employed parameters and the resulting mechanical properties. The investigations point out that pore density is a superior indicator than porosity for mechanical issues. This is especially valid along the build direction since pore morphology has shown to be strongly anisotropic. Moreover, the analysis revealed that pore density is strongly affected by the process temperature, which is proved to be essential for the fabrication of mechanical robust parts using Selective Laser Sintering.
Friction has long been an important issue in multibody dynamics. Static friction models apply appropriate regularization techniques to convert the stick inequality and the non-smooth stick-slip transition of Coulomb’s approach into a continuous and smooth function of the sliding velocity. However, a regularized friction force is not able to maintain long-term stick. That is why, dynamic friction models were developed in the last decades. The friction force depends herein not
only on the sliding velocity but also on internal states. The probably best known representative, the LuGre friction model, is based on a fictitious bristle but realizes a too simple approximation. The recently published second order dynamic friction model describes the dynamics of a fictitious bristle more accurately. Its performance is compared here to stick-slip friction models, developed and launched not long ago by commercial multibody software packages.
A simulation analysis of Independent Requirements Consumption in Master Production Scheduling
(2012)
This poster presents purpose and function of the Independent Requirements Consumption in Master Production Scheduling and gives recommendations for its application. The approach of hierarchical production planning and its planning problems are explained. The problem of new customer requirements information between planning periods and solving options are shown. The solving option of Independent Requirements Consumption is focus of this poster. The algorithm of the Independent Requirements Consumption that is implemented in commercial Enterprise Resource Planning (ERP) systems like the SAP system is analyzed. The methods for analyzing the effects of the Independent Requirements Consumption are outlined. The scenarios for simulation studies are stated and compared to similar investigations. The simulation studies were performed on a simulation system at IPF that contains both a production planning and control system and a production. The extent of simulation analyses outreaches similar investigations, especially because of the variety of scenarios. For scenarios in which capacity is available to a sufficient extent, advice for setting the Independent Requirements Consumption parameters is given. It is pointed out that with production constrained scenarios, the necessity to level out production leads to problems. An algorithm to determine necessary inventory levels is presented. It is stated that straight advice for Independent Requirements Consumption parameter settings might not be possible with production constrained scenarios. Further analyses with production constrained scenarios as well as investigations concerning safety stocks in combination with Independent Requirements Consumption are current and future research topics at the Innovation Center for Production Logistics and Factory Planning.
In this paper, we propose a micro-periodic inventory replenishment policy for quickly perishable goods with fixed and known lifetime of items, deterministic lead time, fixed given order cycle, mixed issuing policies (FIFO and LIFO), age-based stock, imperfect items and target customer service level under random demand. The inventory policy is based on time of day (morning, midday, afternoon or evening). The results of our simulation study show that the proposed micro-periodic inventory policy leads to waste reduction of 66% as well as a partial decrease in cost compared to inventory policy with planning on a daily basis.
Lines are one of the basic features that are used to characterise the content of an image and to detect objects. Unlike edges or segmented blobs, lines are not only an accumulation of certain feature pixels but can also be described in an easy and exact mathematical way. Besides a lot of different detection methods, the Hough transform has gained much attention in recent years. With increasing processing power and continuous development, computer vision algorithms get more powerful with respect to speed, robustness and accuracy. But there still arise problems when searching for the best parameters for an algorithm or when characterising and evaluating the results of feature detection tasks. It is often difficult to estimate the accuracy of an algorithm and the influences of the parameter selection. Highly interdependent parameters and preprocessing steps continually lead to only hardly comprehensible results. Therefore, instead of pure trial and error and subjective ratings, a systematic assessment with a hard, numerical evaluation criterion is suggested. The paper at hand deals with the latter ones by using a human-generated ground truth to approach the problem. Thereby, the accuracy of the surveyed Kernel-based Hough transform algorithm was improved by a factor of three. These results are used for the tracking of cylindrical markers and to reconstruct their spatial arrangement for a biomedical research application.
Ablaufoptimierung in einer Halbleiterfertigung (Scheduling Optimization in Semiconductor Industry
(2022)
A rule-based, iterative approach is often used for the scheduling of automated plants. In this study, a wet bench from the semiconductor industry is used to show the potential that is lost as a result and how the scheduling can be optimized. Furthermore, it is investigated how adjustments to the plant design can further reduce the average cycle time.
Age-diverse work teams are being advocated as an important management tool to enhance performance and productively employ older workers. However, this advice is not founded on empirical evidence. There are very few studies that look at the relation between performance and age diversity of work teams. This lack of evidence is mainly due to a lack of available data. Information on performance and worker composition of a productive unit is available almost exclusively on the plant level in matched employer-employee data sets. But on the plant level/age heterogeneity of the workforce does not tell much about age diversity on the level where co-operation/teamwork takes place (work teams, departments, etc.). If all of the older workers work in the administration whereas all the young employees work in the production, the firm's workforce may be highly age-diverse, but work teams and departments are age-homogeneous. This problem notwithstanding, Grund and Westergård-Nielsen (2005) look at the relation between productivity and the standard deviation of workers’ age in a sample of 7,000 Danish firms. They find a hump-shaped relation.
Laser transmission welding is a well-known joining technology for thermoplastics, providing reliable and hermetical sealing without adhesives or particle formation. The main advantages of laser-based energy input - high precision, no additional adhesive and no particle emission - are essential for medical and optical applications. To obtain sufficient absorption in visually transparent polymers, thulium fibre lasers emitting in the polymers’ intrinsic absorption spectrum are used. Optics with high numerical aperture provide large intensity gradients inside the specimen, enabling selective fusing in the joining zone. Although the basic feasibility has already been demonstrated, the welding process lacks stability and productivity.
Aim of this work is the determination of optimized settings for a fast and reliable welding process. Thus, the interplay of process parameters as well as their impact on the seam are analysed by thermal simulations. Calculated settings are verified by welding tests with COC, PA6 and PETG, using a fixed-focus optics and a 3D laser scanner with up to 200 mm/s feed rate.
The aim of this study is to compare two different standardized testing procedures, tensile testing and Mode-I double cantilever beam (DCB) testing, to evaluate a possible correlation between the dominant failure in glass fibre-reinforced plastics and their according acoustic emissions (AE). AE is processed by using a burst collection of all recorded transient signals and is further analysed with the k-means clustering algorithm. To generate damage related AE, a series of experiments for tensile testing and Mode-I DCB testing is performed on 16-layer glass fibre/epoxy specimens with a cross-ply lay-up for tensile and an unidirectional lay-up for Mode-I DCB testing. Three sensors at tensile testing and one sensor at Mode-I DCB testing gather AE data. The results of clustered burst signals show a good accordance between both testing procedures, with a similar weighted peak frequency (WPF) range in each classified cluster. In total, three different clusters are determined. An assignment of these three clusters to the three dominant damage mechanisms, visually observed by microscopy, is suggested.
The paper deals with the investigation of magneto-sensitive elastomers (MSE) and their application in technical actuator systems. MSE consist of an elastic matrix containing suspended magnetically soft and/or hard particles. Additionally, they can also contain silicone oil, graphite particles, thermoplastic components, etc., in various concentrations in order to tune specific properties such as viscosity, conductivity and thermoelasticity, respectively. The focuses of investigations are the beneficial properties of MSE in prototypes for locomotion and manipulation purposes that possess an integrated sensor function. The research follows the principle of a model-based design, i.e. the working steps are ideation, mathematical modelling, material characterization as well as building first functional models (prototypes). The developed apedal (without legs) and non-wheeled locomotion systems use the interplay between material deformations and the mechanical motion in connection with the issues of control and stability. Non-linear friction phenomena lead to a monotonous forward motion of the systems. The aim of this study is the design of such mechanical structures, which reduce the control costs. The investigations deal with the movement and control of ‘intelligent’ mechanisms, for which the magnetically field-controlled particle-matrix interactions provide an appropriate approach. The presented grippers enclose partially gripped objects, which is an advantage for handling sensitive objects. Form-fit grippers with adaptable contour at the contact area enable a uniform pressure distribution on the surface of gripped objects. Furthermore, with the possibility of active shape adaptation, objects with significantly differing geometries can be gripped. To realise the desired active shape adaptation, the effect of field-induced plasticity of MSE is used. The first developed prototypes mainly confirm the functional principles as such without direct application. For this, besides the ability of locomotion and manipulation itself, further technological possibilities have to be added to the systems. The first steps are therefore being taken towards integrated MSE based adaptive sensor systems.
The paper deals with the investigation of magneto-sensitive elastomers(MSE) and their application in technical actuator systems. MSE consist of an elasticmatrix containing suspended magnetically soft and/or hard particles. Additionally,they can also contain silicone oil, graphite particles, thermoplastic components, etc.,in various concentrations in order to tune specific properties such as viscosity, con-ductivity and thermoelasticity, respectively. The focuses of investigations are thebeneficial properties of MSE in prototypes for locomotion and manipulation purposesthat possess an integrated sensor function. The research follows the principle of amodel-based design, i.e. the working steps are ideation, mathematical modelling,material characterization as well as building first functional models (prototypes). Thedeveloped apedal (without legs) and non-wheeled locomotion systems use the inter-play between material deformations and the mechanical motion in connection with theissues of control and stability. Non-linear friction phenomena lead to a monotonousforward motion of the systems. The aim of this study is the design of such mechanicalstructures, which reduce the control costs. The investigations deal with the movementand control of‘intelligent’mechanisms, for which the magnetically field-controlledparticle-matrix interactions provide an appropriate approach. The presented grippersenclose partially gripped objects, which is an advantage for handling sensitive objects.Form-fit grippers with adaptable contour at the contact area enable a uniform pressuredistribution on the surface of gripped objects. Furthermore, with the possibility ofactive shape adaptation, objects with significantly differing geometries can be gripped.To realise the desired active shape adaptation, the effect of field-induced plasticity ofMSE is used. The first developed prototypes mainly confirm the functional principles assuch without direct application. For this, besides the ability of locomotion andmanipulation itself, further technological possibilities have to be added to the systems.
The sustainable development of processes is currently an important topic in industry and science. Various interest groups and other factors like resource shortages or a lack of skilled workers drive this trend. In the area of Production and Operation Management, the integration of sustainable aspects is also becoming more and more important. However, mainly ecological aspects are considered. Thus, this contribution expands the previous research by the integration of social aspects. For this, we limit our research to the Master Production Scheduling as part of operational production planning. In the context of sustainability, the Global Reporting Initiative (GRI) Standard has established itself for companies and other organisations to report on their sustainability activities. It is the first and most widely adopted global standards for sustainability reporting. The aim of this standard is to measure the sustainable performance and in this way, sustainability activities can be oriented to specific performance indicators. Accordingly, the GRI standard enables concrete initiatives to improve social, environmental and economic conditions for everyone. The modular standard comprises 36 standard modules. For this paper, the 19 social modules were analysed and relevant indicators that could be influenced by the Master Production Scheduling were identified. One of the important indicators from the GRI standard for our research question is the use of employees, measured in terms of hiring and employee turnover. The long-term employee commitment and thus low fluctuation will become a competitive advantage in the future, which is enhanced by the demographic change and the lack of skilled workers. In order to integrate these aspects based on the GRI standard, the classic formulation of Master Production Scheduling is extended. For this a control of the employee utilization within concrete utilization intervals as well as dependent processing times due to different exhaustion effects were integrated. Additionally, in order to take into account the requirements of a flexible production and to model the use of employees, aspects of personnel requirements planning are considered as well, which enable the build-up and reduction of capacity. As a result, social and economic consequences of related production scenarios are presented. In this context, a conflict of targets arises especially with macroeconomic fluctuations. On the one hand, shortages and inventories should be avoided from an economic point of view. On the other hand, a low and constant work intensity as well as a constant number of staff should be preferred for long-term employee commitment. Accordingly, the ability of the model to examine these questions, which will become more and more important for industrial enterprises in the future, becomes clear. Furthermore, it can be seen that it is possible to improve social aspects by adapted production planning without neglecting economic targets.
This article illustrates the problem of deficient working conditions like high work intensity and underlines the possibilities of production planning and control to improve them. However, an included literature search presents that previous approaches have predominantly considered social aspects within a short planning horizon and that there is a need for a long-term consideration. To address this research gap a linear optimization model for Master Production Scheduling is presented, which has been extended by basic aspects of personnel requirements planning and a control of personnel work intensity. The results show that improvements in working conditions can be achieved through adapted production planning without an automatically increase in costs. However , challenges in quantifying the corresponding social correlations are identified as well.
Bedarfe von Kunden nach Produkten und von der Produktion nach Teilen werden in Unternehmen sehr häutig prognostiziert und ihre Ergebnisse werden in der operativen Produktionsplanung und -Steuerung intensiv genutzt. Bei regelmäßigen und konstanten Bedarfsverläufen wird bevorzugt die exponentielle Glättung 1. Ordnung eingesetzt. Zur Sicherung einer gleichbleibenden Prognosequalität ist sein Glättungsparameter im Zeitablauf anzupassen. Eine Automatisierung wird vorgeschlagen und analysiert.
Adaptive surface microstructures are used extensively in nature to control various surface properties such as wettability, adhesion, self-cleaning, drag reduction, etc. Regulation of these properties can be achieved with the appropriate employment of a multitude of smart materials, whose characteristics/response can be controlled by noncontact stimuli, e.g., light, heat, or magnetic field. One of the very promising magneto-regulable smart materials are magnetoactive elastomers (MAEs). They are comprised of a compliant polymer matrix with embedded micrometer-sized ferromagnetic particles. The particles interact with each other and a magnetic field. This results in remarkable tunability of the physical properties of MAEs. This paper reports a fast, resilient, and tailored method for direct surface micromachining of MAEs that enables micro-structuring without mechanical contact between the tool and the material, bypassing the usual constraints of conventional fabrication methods. It is shown that it is possible to fabricate a large variety of different microstructure geometries whose precision is limited predominantly by the size of magnetic particles. Lamellar structures with a high aspect ratio (up to 6:1) oriented either perpendicularly to the surface, can be strongly bent by applying magnetic fields in the range of 0–250 mT.
Additive Fertigung hat sich in zahlreichen industriellen Anwendungen etabliert und bildet eine wichtige Schlüsseltechnologie. Im Gegensatz zu metallischen Werkstoffen, haben additiv gefertigte Bauteile aus Kunststoffen geringere Festigkeit und Steifigkeit, sodass sich ihre Verwendung als lasttragende Strukturen schwierig gestaltet. Insbesondere der Einsatz von endlosen Verstärkungsfasern kann die mechanischen Eigenschaften additiv gefertigter Strukturen signifikant verbessern und die Fertigung hochbelastbarer Faserverbundstrukturen im 3D-Druckverfahren ermöglichen. Daher gilt es aktuell notwendige Anlagen und Prozessketten für den Fertigungsprozess aber auch Vorgehensweisen für die belastungsoptimierte Auslegung der Faserverläufe innerhalb des Bauteils zu entwickeln, um so das Themengebiet „Endlosfaserverstärkter 3D-Druck“ weiter voranzutreiben. Für mehr räumliche Freiheit bei der Positionierung der Druckbahnen können industrieroboterbasierte Systeme eingesetzt werden, um so das Potenzial gerichteter Bauweise von Faserverbundstrukturen auch im additiven Fertigungsprozess vollumfänglich ausschöpfen zu können. Dabei ermöglicht ihr Einsatz auch eine räumliche Ablage der Faserverstärkung, wobei für die Materialablage ein geeigneter 3D-Druckkopf erforderlich ist. Für die Implementierung der Faserverstärkung ist zudem eine dem Lastfall entsprechende Auslegung des Bauteils sowie die Ermittlung einer sinnvollen Faserpositionierung innerhalb des Bauteils erforderlich, wobei unterschiedliche Variablen aus den Bereichen Material, Struktur und Fertigungsprozess berücksichtigt werden müssen. Im Rahmen des Vortrages werden die Herausforderungen der Technologieentwicklung des endlosfaserverstärkten 3D-Drucks aufgegriffen sowie auf eine belastungsorientierte Faserpositionierung näher eingegangen. Aktuelle Erkenntnisse werden diskutiert sowie eine Entwurfsmethodik für die Prozesspfadgenerierung vorgeschlagen.
In the paper first results regarding the realisation of gradient and multi-material parts manufactured by Laser Beam Melting in powder bed of metals and polymers are published. Gradient properties of additively manufactured metal parts can be achieved by varying the composition of alloying components in the powder and adapting process strategies. As an alternative to atomizing pre-alloyed materials, mixtures of different powders are investigated. For realizing multi-material-parts from polymers, at first relevant material properties concerning compatibility have to be analysed. Therefore the paper shows the main requirements for compatibility between different materials and also first results regarding the compatibility of polymer powders and possible combinations for the manufacturing of multi-material components by laser beam melting of polymers.
Shape memory materials fulfill an important role in both actuation and mechanical coupling between actuators and associated dynamic systems. The simplest techniques are thermally based and in addition to the more common shape memory alloys there are also shape memory polymers. These have similar characteristics to those of their metallic cousins, but there the relationship stops. The basic physical principles are very different and this paper attempts to outline the current state-of-the-art to those already involved with the technology and perhaps open a fresh chapter in smart materials to those who are new to it.
Ageing and Productivty
(2009)
Altern und Produktivität
(2006)
Der Zusammenhang zwischen Alter und Leistungsfähigkeit von Beschäftigten wird in den verschiedensten Disziplinen untersucht - mit zum Teil recht unterschiedlichen Ergebnissen. Dieser Beitrag gibt einen Überblick über die Literatur und diskutiert die Notwendigkeit einer neuen Sicht der Produktivitätsmessung. Bisherige Studien beschäftigen sich mit der Messung der individuellen Produktivität. In einer modernen arbeitsteiligen Gesellschaft realisiert sich die Arbeitsproduktivität allerdings weniger in der Einzelperson als vielmehr im Zusammenwirken von jüngeren (innovativen, flexiblen?) und älteren (erfahrenen?) Mitarbeitern.
Altern und Produktivität
(2009)
This paper describes a very-high-speed integrated-circuit hardware description language (VHDL)-based analog-node model, an associated driver component for the mixed-signal event-driven (MixED) simulation technique, and some primitive device models applied to radio-frequency integrated circuits. With the presented MixED method, analog circuits are modeled as a composition of controlled sources. Unlike other VHDL-based analog simulation methods, these MixED sources compute not only a real number representing an output voltage but also an output impedance. This allows the outputs of several MiXED sources to be connected in order to drive the same node signal n . The voltage of this record-type signal is automatically computed at its element n . u by resolution functions in compliance with Kirchhoff's current law. The data structure of the node signal n , its self-defined resolution functions, and an associated driver component are presented and discussed to meet different simulation requirements, such as speed, versatility, current accuracy, and adaptive time stepping. Several examples demonstrate how to behaviorally model mixed-signal components with this method with an emphasis on the simulation of a heterodyne receiver. Simulation speeds are compared to VHDL-AMS tools.
An analytical model for the spatial distribution of potential, electric field and carrier densities is presented, assuming uniform doping density and constant quasi-Fermi potentials in the direction of modeling. Starting from the current relations a differential equation respecting two-dimensional effects is developed and solved approximately by decomposition in three regions with different preconditions: (a) flatband region, (b) constant spacecharge density and (c) strong inversion or accumulation. Inaccuracies arise mainly from violated preconditions at the interfaces between the different regions. Two-dimensional effects are respected in the analytical model of (b) only but they influence region (c) by means of boundary conditions at the interface of (b) and (c).
The investigations of this paper are focused to region (c). This part of our model is identical to the model of Hauser and Littlejohn[1]. They integrated a simplified form of the semiconductor-Poisson equation twice but were restricted to one-dimensional applications and thermal equilibrium. Our derivation allows for large electric fields and current densities perpendicular to the direction of modeling. From analytical considerations confirmed by numerical experiments we suggest preference to the gradual channel condition, with x and y defined according to Fig. 1. This definition allows the potentials to vary significantly with respect to y. We found that this holds for the quasi-Fermi potentials also. Furthermore an empirical model for the maximum width of strong-inversion layers in uniformly doped silicon films is presented in eqn (46).
An experimental study of the properties of magnetoinductive waves in the presence of retardation
(2006)
Magnetoinductive (MI) waves owe their existence to the magnetic coupling between metamaterial elements. First experiments confirming the existence of MI waves were carried out on capacitively loaded loops and Swiss Rolls about three orders of magnitude smaller than the operating wavelengths (5–15 m) so that the radiation effects did not play any significant role. In the present paper MI waves are studied experimentally on various types of split ring resonators of about 1 cm diameter operating in the microwave region between 1 and 2 GHz. Our results prove that retardation has a significant effect upon the propagation of MI waves.
Anhand zweier Beispiele wird ein interaktives System vorgestellt, mit welchem Live-Messungen an elektronischen Bauteilen und Schaltungen im Hörsaal durchgeführt werden können. Das System basiert auf dem USB-Messgerät „Analog Discovery 2“ der Firma Digilent, erweitert um eine Adapterplatine mit Steckbrett und eine Webcam.
Zunächst werden drei Aspekte erläutert, in welchen ein solches System positive Auswirkungen auf den Kompetenzerwerb haben kann: Praxisbezug, Aktivierung und Vernetzung. Anschließend werden die zwei Beispiele ausgeführt. In Beispiel 1 wird die persönliche Alltagserfahrung mit Akkus über interaktive Clicker-Fragen und begleitende Messungen mit dem Modell der linearen Quelle verknüpft. Die Studierenden lernen, oberflächliche Lösungen wie die Messung der Leerlaufspannung zu hinterfragen und das Verhalten realer Quellen anhand der gemessenen I-U-Kennlinien zu verstehen. Beispiel 2 zeigt kurz die Möglichkeiten auf, den abstrakten Formalismus der komplexen Wechselstromrechnung am Beispiel des Serienschwingkreises im Zeit- und Frequenzbereich
messtechnisch erlebbar zu machen.
Die in Flugvorausrichtung weisenden Bauteile von Luftfahrzeugen sind oftmals durch Einschläge aufgrund von Vogelschlag, Hagel oder aufgewirbelten Kleinteilen gefährdet. Diese Einschläge, sogenannte Impacts, weisen bei faserverstärkten Kunststoffen ein stark krümmungs- und materialabhängiges Verhalten und Schadensausmaß auf. Impact-Schädigungen führen oftmals zu hohen Reparaturkosten, welche durch eine genauere Kenntnis des Schadens verringert werden können. Zur Klassifizierung dieser Schädigungen steht dabei vor allem das auftretende Frequenz signal des Impacts im Fokus der Untersuchungen.
Im vorliegenden Artikel werden Vorarbeiten zur Entwicklung eines Betriebsdatenverwaltungssystems für Intralogistikanlagen des Herstellers TGW Software Services beschrieben. Das beschriebene Vorgehen umfasst dabei im Wesentlichen vier Schritte.
Zunächst wird der aktuelle Stand in der Software des betrachteten Unternehmens hinsichtlich des Sammelns, Speicherns und Auswertens von Betriebsdaten analysiert.
Daran schließt sich eine Anforderungsanalyse für die Betriebsdatenverwaltung an. Zusammen mit den betroffenen Entwicklungsleitern werden die grundlegenden Ziele und Grenzen der zu entwickelnden Betriebsdatenverwaltung definiert. Es werden Quellen von Anforderungen für die Komponente gesammelt und alle funktionalen und nichtfunktionalen Anforderungen anhand dieser Quellen erarbeitet.
Basierend darauf wird ein erstes Modell erstellt, das die Entitäten, Beziehungen und Abläufe, die sich aus den ermittelten funktionalen Anforderungen ergeben, in konsolidierter Form zusammenfasst. Dieses wird zusammen mit einigen Überlegungen, die zu diesem Modell geführt haben, beschrieben.
Zuletzt werden dann verschiedene mögliche Konzepte zum grundlegenden technischen Aufbau einer Implementierung der Betriebsdatenverwaltung diskutiert, um schließlich anhand der definierten Qualitätsziele eine Empfehlung für einen Konzeptvorschlag abzugeben.
Ressourcenbelegungsplanungsprobleme haben fast immer exponentiell wachsende Lösungsräaume. Ausnahmen sind einfachste Ressourcenbelegungsplanungsprobleme die sich im wesentlichen durch Sortierverfahren optimal lösen lassen.
Dadurch sind Ressourcenbelegungsplanungsprobleme NP-vollständig. Nach der Literatur haben Lösungsräume von einigen NP-vollständigen
Optimierungsproblemen günstige Eigenschaften, die Metaheuristiken, wie genetische Algorithmen und lokale Suche, ausnutzen, um in vertretbarer
Rechenzeit gute Lösungen zu finden. Zu Ihrer Erkennung gibt es in der Literatur etablierte Analysemöglichkeiten. Sie werden in dieser Arbeit auf die Ressourcenbelegungsplanung übertragen und ihre Wirkung bzw. die auftretenden Schwierigkeiten werden anhand von einfachen Problemen aufgezeigt.
Nach dem Aufbau eines Mehrkörper-Simulationsmodells muss dieses auf Richtigkeit, Funktionalität und Wirtschaftlichkeit getestet werden. Die Ermittlung der Gleichgewichtslage stellt dabei eine erste Plausibilitäts-Kontrolle dar. Eine Linearisierung mit anschließender Analyse der Eigendynamik liefert Aussagen über die Frequenzen und das Dämpfungsverhalten des Modells. Einfache Erregersignale ermöglichen einen ersten Einblick in das nichtlineare dynamische Verhalten des Modells. Modell-Parameter, die nicht genau bekannt sind, können durch gezielte Variationen plausibel geschätzt oder über eine Optimierung sogar mit optimalen Werten belegt werden. Nach all diesen Tests steht das Mehrkörper- Simulationsmodell dann für praktischeUntersuchungen zurVerfügung, die neben reinen Zeitsimulationen auch Methoden der Inversen Kinematik und der Inversen Dynamik mit einschließen.
In this paper, the movement behavior of amoeboid locomotion system is investigated and the theoretical proof of the locomotion of the system is provided with the finite element method. It is shown that not only the speed of locomotion but also its direction can be influenced by the drive frequency. Depending on the drive frequency, a movement from the home position and a subsequent movement in opposite directions can be achieved. In addition, high speeds of movement can be achieved in a limited frequency range.
In practical use cases, simulation engineers are confronted with uncertainties in the simulation parameters. Normally, trust in a model is built from experience, practical assumptions, and parameter studies. This approach, though, is based on the assumption that few parameter combinations are sufficient to represent the whole design space. This lacks an appraisable mathematical basis.
To get insights into which parameters most strongly affect the results, a global sensitivity analysis can be conducted [2, 3]. The results are utilized to rank the most influential parameters and to filter less relevant ones. This gives feedback which improved set of input data will lead to more certainty in the simulation results. To enable this in the framework of multi-fidelity analysis and optimization, we compare here global sensitivities and uncertainties of the implicit One-Step approach (low-fidelity) with those of the explicit multi-step deep drawing approach (high-fidelity).
Effective coupling between two remote optical waveguides without branching sections can be achieved in a three-guide system with multimode central waveguide. We investigate the nonlinear power switching of c.w. laser radiation by such radiatively coupled waveguides. It is shown that effective all-optical switches with spatially well separated input/output channels can be realized although the influence of multimode interference on the switching characteristics becomes more pronounced for increasing thickness of the central guide. Different coupling regimes are specified, and the changes in switching characteristics during the transformation from one regime to another is studied. Numerical calculations for the critical power are compared with an approximate analytical expression. It is also shown that, at a moderate input power, a small number of modes determines the switching behavior.
By simultaneous laser beam melting (SLBM), different polymer powders can be processed to multi-material parts, which offers the potential to enlarge the field of application for conventional LBM. In a SLBM process, a powder bed consisting of different polymers and therefore with different melting and crystallization temperatures is deposited. Besides the use of infrared emitters for preheating the lower melting polymer, a CO2 laser distributes the necessary preheating temperature of the higher melting polymer. In the last step, a thulium fibre laser distributes the energy necessary for melting the two preheated powders simultaneously. In order to analyze the temperature gradients of the process on the powder surface and in deeper layers, a high-resolution thermal imaging system and thermocouples are used.
Analysis of the Acoustic Emission Failure Frequencies of Glass Fiber Reinforced Composite Components
(2017)
Powder based Additive Manufacturing technologies offer huge potential for building parts with almost no geometrical restrictions, but both the process controlling as well as the part properties are strongly dependent on different material characteristics of the material, like the flowability. In this work, different weight percentages of nano-scaled silica dioxide particles (Aerosil®) are admixed to pure polyethylene and polypropylene powder and the resulting flowability is determined. Besides using the Hausner ratio as standardized value, the degree of coverage is introduced as a new characteristic to quantify the powder flowability. The degrees of coverage are compared to the Hausner ratios to allow a discussion and evaluation about the different characteristic values. Additionally, tensile bars consisting of polypropylene are generated to determine the porosity by cross sections and the mechanical part properties by tensile testing. As mechanical part properties, the tensile strength and elongation at break are determined and the effects of different powder flowability on these properties are analyzed.
Laser transmission welding is a non-contact and efficient process technology for joining thermoplastic polymers. In the conventional process, laser sources in the wavelength range of 1 μm are usually used. Therefore, most of the laser radiation is transmitted through the upper joining partner and absorbed only in the lower joining partner. As a result, the possibilities to influence the temperature field especially in the upper joining partner are limited. To overcome these limitations, an additional thulium fiber-laser with a wavelength of 1.94 μm is used in this study and coaxially aligned with a diode laser. The use of an additional thulium fiber-laser leads to a significant absorption in the upper joining partner. Through this approach, it is shown that the temperature field and the weld seam geometry can be influenced by using these two different discrete laser wavelengths. Depending on the intensity distribution of both lasers, an increase of the size of the heat affected zone in the upper joining partner can be observed. In order to develop a better process understanding, a thermal finite element model is built up and verified by comparing the calculated size of the heat affected zone for different process parameters with the experimental data. The model is able to represent the influence of both laser sources on the temperature field and is used to calculate characteristics of the temperature field, such as maximum temperatures or cooling rates. The characteristics are then used to explain the weld seam morphology, such as occurrence and size of spherulitic structures in the weld seam.
Laser transmission welding is a well-known joining technology for welding thermoplastics. Although the process is already used industrially, fundamental process-structure-property relationships are not fully understood and are therefore the subject of current research. One aspect of these mentioned process-structure-property relationships is the interaction between the temperature field during the welding process, the weld seam morphology of semi-crystalline thermoplastics, and the weld seam strength. In this study, the influence of the line energy on the weld seam morphology of polypropylenes is analyzed. For this purpose, the size of spherulites in the weld seam is investigated, as well as different occurring phases of polypropylene (a- and b-phase). It is shown that both the spherulite size of the a-phase and the amount of b-phase increase with increasing line energy. For the explanation and discussion of the results, a temperature-dependent thermal simulation model is used to derive characteristic attributes of the temperature field (maximum temperatures, cooling rates, temperature gradients).
Die Wirtschaftsinformatik, die von den Mitgliedern des Arbeitskreises Wirtschaftsinformatik an Fachhochschulen im deutschsprachigen Raum vertreten wird, basiert auf drei Säulen, nämlich der Informatik, der Betriebswirtschaft und der Wirtschaftsinformatik selbst, worunter Systeme zur Steuerung betriebswirtschaftlicher Prozesse verstanden werden – dies entspricht auch der Empfehlung der Gesellschaft für Informatik und liegt den Evaluierungen der Akkreditierungsverfahren zugrunde. Diese Säulen inkludieren fast zwangsläufig eine substantielle Heterogenität an Projekten mit der industriellen Praxis wie auch in der Forschung. Die Einreichungen zur Tagung bestätigten diese Erwartung. Beispiele sind mehrere Arbeiten zur „Datenbank SAP HANA“, zu (allgemeinen) Entwicklungsthemen wie zum „Datenbank-Join“ oder der „Internetsuche“ und zu IT-Systemen wie beispielsweise „Fünf Jahre produktiver Einsatz eines man- dantenfähigen Data-Warehouse-Systems“. Andere Arbeiten befassen sich mit eher technischen Themen wie mobilen (End-)Geräten wie „Plattformunabhängiges, mobiles, integriertes Hochwassermeldesystem für Mittelhessen“ oder „Electronic vs. Mobile Banking“ und der Nutzung von Cloud wie beim „Aufbau einer ‚Private Cloud‘ mit OpenStack“. Mehrere Arbeiten befassen sich mit der IT-Unterstützung logistischer Fragestellungen wie die „Ermittlung von prognoserelevanten Absatzzahlen in der Praxis eines großen Lebensmittelkonzerns“, mit Prozessen wie „Business Process Excellence und der Zusammenhang mit dem Unternehmenserfolg“ sowie mit Management wie „Faktoren für nachhaltigen Unternehmenserfolg“.
Damping of impulsively generated coherent acoustic oscillations in a femtosecond laser-heated thin germanium film is measured as a function of fluence by means of ultrafast x-ray diffraction. By simultaneously measuring picosecond strain dynamics in the film and in the unexcited silicon substrate, we separate anharmonic damping from acoustic transmission through the buried interface. The measured damping rate and its dependence on the calculated temperature of the thermal bath is consistent with estimated four-body, elastic dephasing times (T2) for 7-GHz longitudinal acoustic phonons in germanium.
The current analyses present results of running ductile fracture propagation in high strength X100 line pipe steels under the influence of anisotropy. Mechanical anisotropy is commonly available in pipe products as a result of the manufacturing process, especially, those subjected to hot/cold-worked deformation. The outcomes of the present analyses show that its effect on the behavior of running ductile fracture in cracked pipes undergoing depressurization is meaningful. For instance, the Crack-Tip Opening Angle (CTOA) not only exhibits a strong dependence to the pipe's diameter size, but also to the material's anisotropy nature when compared to a hypothetical isotropic material. Moreover, laboratory scale tests such as those performed on Battelle Drop Weight Tear (BDWT) samples provide useful information about initiation of ductile crack propagation when the anisotropy features are taken into account in the material description.
The direct magnetoelectric (ME) effect is investigated in a planar structure comprising mechanically coupled layers of a magnetostrictive fibrous composite (MFC) and a piezoelectric ceramics (lead zirconate titanate, PZT). The MFC is an array of Ni-wires with a diameter of 200 mu m that are aligned parallel to each other in a single layer. The wires are separated by a distance of 250 or 500 mu m and fixed in a polyamide matrix. The structure was placed in a tangential constant field H and was excited by an alternating magnetic field h parallel to H, while the voltage generated by the PZT layer was measured. The resulting field dependences of the magnetization M(H) and the magnetostriction lambda(H) were determined by the orientation of the field H in the plane of the structure and the distance between the Ni-wires. The ME coupling coefficient of the structure decreased from 4.8 to 0.25 V/A when the orientation of H was changed from parallel to perpendicular to Ni-wires. With an increase in the excitation field amplitude h, a nonlinear ME effect in the output voltage, namely frequency doubling, was observed. The frequency and field dependences of the efficiency of the ME transduction in the MFC-piezoelectric heterostructure are well described by the existing theory.
Application of a Krylov subspace method for an efficient solution of acoustic transfer functions
(2021)
Solving acoustic radiation problems, arising from systems including fluid–structure interaction, is of interest in many engineering applications. Computing frequency response functions over a large frequency range is a concern in such applications. A method which solves the Helmholtz equation for multiple frequencies in one step is the matrix-Padé-via-Lanczos connection for unsymmetric systems, as presented by Wagner et al. [1]. The present work is based on Ref. [1] and presents a method for efficiently computing frequency responses over a frequency range for coupled structural-acoustic problems, where the structure and the acoustic near field are discretized with finite elements and an analytical Dirichlet-to-Neumann map approximates the far field. The method is based on a Krylov-subspace projection technique which derives a matrix-valued Padé approximation for a restricted area in the near field and the pressure field on a spherical boundary. On the spherical boundary, where the finite domain is truncated, the non-local modified Dirichlet-to-Neumann operator is applied as a low-rank update matrix. The present contribution extends this method and incorporates new techniques for a more stable model reduction through the Lanczos algorithm and a novel weighted adaptive windowing technique. Further, structural damping is incorporated, for computing the acoustic radiation of a harmonically excited plate. These computed results are compared with acoustic measurements in an anechoic chamber and verified with computational results obtained with a commercial code that uses the perfectly matched layer method.