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Organisationseinheit der BAM
- 7 Bauwerkssicherheit (2)
- 2 Prozess- und Anlagensicherheit (1)
- 2.3 Einstufung von Gefahrstoffen und -gütern (1)
- 6 Materialchemie (1)
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- 9 Komponentensicherheit (1)
- 9.3 Schweißtechnische Fertigungsverfahren (1)
The present study documents the results of an
inter-disciplinary model project that was planned with the
aim of developing an innovative winter covering system
for marble statuaries located on the Schlossbru¨cke (Berlin).
Such a system would need to fulfil the various requirements
for structural stability, aesthetics, climate and practical
use. This applied research represents the first complex
scientific study of the sustainability of a winter covering
system. The study is characterised by the use of complex
scientific instruments such as special laboratory analysis
and numerical simulation tools. The interaction between
the environment and the artefacts in connection with the
innovative winter covering structures were studied by
extensive climatic monitoring.
Many self-accelerating decomposition temperatures (SADTs) of solid organic peroxides and self-reactive substances have been determined with the UN test method H.4, which is a scaled down test in a small Dewar vessel. For solid organic peroxides and solid self-reactive substances Fierz has questioned this procedure in a recent paper. Fierz concluded that the Dewar test results should not be extrapolated to beyond 8 l packages, owing to the thermal insulation value of solids. On the other hand, long term experience with the test, with a great variety of solid organic peroxides and self-reactive substances show about equal critical temperatures in the small Dewar vessel and on 50 kg scale. In the present work, we first checked, by numerical simulations, the Dewar scale versus the larger scale, in a way comparable with Fierz method: both scales are simulated by spheres, consisting of a number of annular layers, for the large scale the usual external heat loss term is used but for the small scale the outside heat transfer is strongly limited. The outcome of these simulations, covering a variety of physical parameters, supports the concerns expressed by Fierz. After this, we performed accurate cooling and heating experiments with solid organic peroxide in the usual Dewar vessel, provided with a large set of thermocouples. The results of these experiments showed that the simulation model for the Dewar vessel has to be changed from a spherical analogue to a short cylinder of solid material with heat exchange mainly via its top (Utop 3.5 W/(m2 K), overall heat transfer coefficient) and some heat exchange (Uside 0.29 W/(m2 K)) through its cylindrical and bottom part. With this modified cylinder model (being neither an infinitely long cylinder nor a slab) of the Dewar vessel, we found that the UN method H.4 enables an accurate prediction of the SADT, with small deviations of 0 ± 2.5 °C. Further, by performing a truly three-dimensional (3D) finite element calculation in FEMLAB, the new heat characteristics of the Dewar vessel as well as a 50 kg package of dilauroyl peroxide, a solid organic peroxide, were checked. The outcome was compared with the critical ambient temperatures known for various package sizes, which agreed well.
Miscanthus x Giganteus (Miscanthus) energy crop was examined at laboratory scale to assess its self-heating and self-ignition risks during storage. Chipped Miscanthus (18 mm) from February and March harvests, in 2012, were assessed as well as ground Miscanthus (3 mm) from the March harvest. February and March crops had moisture contents of 41.6 and 20.2%, respectively. Self-ignition temperatures were independent of moisture although moisture did affect the time from the beginning of storage until storage temperature was reached. Ground Miscanthus had lower self-ignition temperatures than chipped Miscanthus. Isothermal respirometric tests carried out showed increase risk of self-heating in the February crop compared to the March crop due to increased microbial activity. Numerical simulations were used to determine critical enhanced start temperatures, e.g. caused by microbial decomposition, of the stored Miscanthus. Safe storage conditions have been derived from the investigations. The numerical simulations demonstrated that self-ignition was possible in Miscanthus chip piles with a height greater than 6 m if there was significant heat release from microbiological activity. Reliable assessment of self-heating and self-ignition risks in large scale Miscanthus energy crop clamps or piles are required to prevent losses due to decomposition and fire damage.
In recent years, it was shown that the introduction of additional oscillating and permanent magnetic fields to laser beam and laser-arc hybrid welding can bring several beneficial effects.
Examples are a contactless weld pool support for metals of high thickness suffering from severe drop-out when being welded conventionally or an enhanced stirring to improve the mixing of added filler material in the depth of the weld pool to guarantee homogeneous resulting mechanical properties of the weld. The latest research results show the applicability to various metal types over a wide range of thicknesses and welding conditions. The observations made were demonstrated in numerous experimental studies and a deep understanding of the interaction of the underlying physical mechanisms was extracted from numerical calculations.
An effective protection of structures against impact from detonation of high explosives (HE) necessitate certain design specifications to be met. In the event of an explosion, accidental or intentional, any damage in its neighborhood (especially, for example, to the structures of strategic importance) should remain as low as possible. The behavior of a structure under the shock loading from an explosion will determine the extent of the damage. The investigation of the relevant phenomena that occur during the event of an explosion is the objective of this study.
In accordance with the test parameters, numerical simulations were performed and results were compared with those from field tests. The deformation of the wall under shock impact was simulated by implementing the appropriate interaction of fluid and structure. Moreover, the numerical pressure-time histories in front of the wall were compared with the ones measured in the field by means of piezoelectric pressure gauges, providing a validation for the shock waves’ propagation.
The hazards for passengers during vehicle fires result from the increasing temperature and the emitted smoke gases. A fire was set on a car to investigate the development of temperature and of gaseous fire products in the passenger compartment. The study was based on a full-scale test with a reconstructed scene of a serious car fire. The aim of this work was to identify the conditions for self-rescuing of passengers during a car fire.
A dummy, equipped with several thermocouples, was placed on the driver’s seat. Also, the smoke gases were continuously collected through a removable probe sensor corresponding to the nose of the dummy in the passenger compartment and analyzed using Fourier transform infrared spectroscopy. Additionally, several car components were investigated in the smoke density chamber (smoke emission and smoke gas composition). It was found that the toxic gases already reached hazardous levels by 5 min, while the temperatures at the dummy were at that time less than 80 °C. The toxicity of smoke gases was assessed using the
fractional effective dose concept. The various experimentally parameters (temperature and smoke gas composition) were implemented into numerical simulations with fire dynamics simulator. Both the experimental data and the numerical simulations are presented and discussed.
Self-ignition of deposited combustibles is a possible reason for excessive fires occurring on deposits for recycling materials or on waste dumps. Two series of experiments were performed to assess the hazard of self-ignition: hot storage tests with different homogeneous mixtures of combustible material and inert material and tests with pockets of combustible material embedded in inert matter. In the first test series considerable exothermicity (ΔT>60K) was observed for mass fractions of combustible material as low as 2.5%. In the second series it could be shown that the heat transfer from a pocket of burning material through the inert matter can ignite a second pocket of combustible matter.
Based on the experimental data, numerical simulations were performed to predict self-ignition on real-scale waste deposits. For a deposit of specific size and shape, the influence of the ambient temperature on the occurrence of self-ignition has been investigated.
In a bus depot fire in Germany 69 buses were destroyed in 2011. The fire started in one bus. Investigations after the fire showed that most likely a technical defect was the cause of the fire. The fire spread very rapidly to the other buses. The bus depot was in a building, which was also completely destroyed. In recent years several fires occurred in bus depots in Germany. All these fires showed the same rapid fire development, though the 2011 fire was the most severe with a property loss of about 22 million Euro. Operation interruption also is a key issue after these fires. The fire development and fire spread was investigated numerically after the fire with FDS 5 (NIST). The predicted fire spread was in good agreement with the timeline, which could be reconstructed after the fire: a video was made by a monitored location nearby.
Reasons for the rapid fire development and spread were investigated as well as fire safety measures in the building as smoke and heat Ventilation. Extensive experimental investigations of bus materials showed that these materials have poor fire performance compared with materials of other transport vehicles, e.g. trains. The poor fire performance of the bus materials affect directly the fire and smoke development in bus fires. As well as the real cases as the numerical calculations show that is nearly impossible to save the building or other buses in a building, which is used as a bus depot if one bus is already fully in fire. Often the bus fires Start in the engine compartment. Onboard suppression Systems can significantly reduce the hazard of these fires. Different fire safety measures are discussed and recommendations are derived from the investigations to reduce the hazard of bus depot fires.
Fires on waste dumps, surface landfills, Underground stowing or storage facilities of Recycling factories may have multiple harmful effects on individuals on site and on environment.
Possibly several tens of thousands of tons flare up plunging vast areas in smoke and releasing large amounts of flue gases. Experience shows that fire fighting takes days or even weeks and moreover, as long as hidden glowing nests exist fires may break out repeatedly weeks or months later. In the light of this, fire prevention is much easier to manage than extinction. It is of internst to identify the geometrical and physical conditions under which the mid-term or long-term storage of recycling materials can be performed avoiding self-ignition. Our Guideline presents a novel method developed at BAM which combines experimental tests on lab-scale with numerical simulations in Order to obtain permissible geometries of deposits and storage times at which self-ignition can be certainly avoided (Berger 2010).
Guided waves are increasingly a subject of great interest in nondestructive testing. An example of research in this field is the development of a novel procedure for ultrasonic testing of wheelset-axles using guided waves, which requires to treat the wheelset-axle as a thick walled cylinder with varying thickness. In order to describe ultrasound propagation in a waveguide with non-constant thickness, a multimodal approach, which allows to avoid extensive mesh-based numerical calculations, seems to be promising. The method treats the modes of a corresponding waveguide with constant thickness as a base in which an arbitrary sound field can be expressed. Since the local sound field at any given position in the waveguide with varying thickness will be a combination of these base modes, the problem is reduced to solving the differential equation that governs the evolution of the coefficients in the mode spectrum along the waveguide. Once the description of the sound field along the waveguide is obtained, the time dependence is added by multiplication with a simple oscillating term. Simulations of pulse propagation through the waveguide can then be constructed by adding up a sufficient number of mono-frequent continuous wave solutions. As an early stage in developing a simulation tool for sound propagation in thick walled cylinders with varying thickness, the multimodal approach was implemented and tested for the simple case of plate geometries. In this work, an overview of the simulations carried out for plates with non-constant thickness is presented. The performance of the algorithm based on the multimodal approach and the obtained results are compared to those of mesh-based simulation tools.