1,235 research outputs found
CRITICAL REVIEW OF THE CURRENT ASSESSMENT APPROACHES FOR FRONTAL CRASH COMPATIBILITY REGARDING THE EVALUATION OF STRUCTURAL INTERACTION
No full textThe assessment of structural interaction has been identified as the main challenge of the unresolved problem of frontal crash compatibility. With this background, two questions are raised: Does a better structural interaction correspond with higher safety and crash compatibility? Are current test approaches able to evaluate structural properties? Considering the structural mechanics of collisions, it is hypothesized that a poor structural interaction does not necessarily result in lower safety and should be considered together with compartment strength and restraint systems. This hypothesis is confirmed by reviewing some crash results from other studies. A spring-mass vehicle model is also used to verify the hypothesis. Finally, a comprehensive simulation study is conducted to find the answers to the two questions. For this study three different variations of a vehicle model are created, which represent different structural properties of the passenger car fleet. The crash performance of these models is analyzed in different car-to-car and car-to-barrier tests. Results of the car-to-car tests show that better structural interaction often makes the vehicle more aggressive. Generally, better structural interaction increases crash pulse and reduces intrusions. Depending on vehicle design and crash configuration, the intrusions or the crash pulse become more important as to why good or poor structural interaction cannot be overall related to more crash compatibility or occupant safety. Our criticism of the current assessment approaches for frontal crash compatibility is the establishment of a direct link between good structural interaction and higher safety. These approaches do not consider the effect of higher crash pulses due to the better structural interaction. Our recommendation is to assess the partner protection through metrics about intrusions and crash pulse of the partner, without direct assessment of the structural interaction. Instead, the test configuration should be able to reflect structural properties in intrusions or crash pulse. Results of the car-to-barrier tests show that the Progressive Deformable Barrier can reflect structural issues correctly. However, the developed metrics for this barrier result in incomprehensive interpretations. Results of the tests with other barriers are inconsistent with the structural properties of the vehicles. Finally, an exemplary test concept with the Advanced European Mobile Deformable Barrier is presented as an alternative assessment approach. Simulation results of the proposed assessment approach show good consistency with the crash performance of the vehicles in the car-to-car tests. Combination of this test concept with the Full-Width Rigid Barrier test can be used to assess the safety and crash compatibility of passenger cars
Hybrid Strategy Coupling EGO and CMA-ES for Structural Topology Optimization in Statics and Crashworthiness
No full textTopology Optimization (TO) represents a relevant tool in the design of
mechanical structures and, as such, it is currently used inmany industrial applications.
However, many TO optimization techniques are still questionable when applied to
crashworthiness optimization problems due to their complexity and lack of gradient
information. The aim of this work is to describe the Hybrid Kriging-assisted Level
Set Method (HKG-LSM) and test its performance in the optimization of mechanical
structures consisting of ensembles of beams subjected to both static and dynamic
loads. The algorithm adopts a low-dimensional parametrization introduced by the
Evolutionary Level Set Method (EA-LSM) for structural Topology Optimization
and couples the Efficient Global Optimization (EGO) and the Covariance Matrix
Adaptation Evolution Strategy (CMA-ES) to converge towards the optimum within
a fixed budget of evaluations. It takes advantage of the explorative capabilities of
EGO ensuring a fast convergence at the beginning of the optimization procedure,
as well as the flexibility and robustness of CMA-ES to exploit promising regions
of the search space Precisely, HKG-LSM first uses the Kriging-based method for
Level Set Topology Optimization (KG-LSM) and afterwards switches to the EALSM
using CMA-ES, whose parameters are initialized based on the previous model.
Within the research, a minimum compliance cantilever beam test case is used to
validate the presented strategy at different dimensionalities, up to 15 variables. The
method is then applied to a 15-variables 2D crash test case, consisting of a cylindrical
pole impact on a rectangular beam fixed at both ends. Results show that HKG-LSM
performs well in terms of convergence speed and hence represents a valuable option
in real-world applications with limited computational resources
Surrogate modeling in design optimization of structures with discontinuous responses: A new approach for ill-posed problems in crashworthiness design
No full textAdvances in computational technology have resulted in the dramatic reduction of computational time for crashworthiness analysis, hence enabling its structural design optimization. Surrogate modeling has been shown to further reduce computational effort as well as to smooth noisy responses. Crashworthiness optimization problems are, though, ill posed as they include nonlinear, noncontinuous and noisy responses. This violates the Hadamard conditions for well-posed problems and therefore the applicability of gradient-based algorithms is limited. Here, discontinuities in the responses with respect to the design variables will be handled that result in large changes in the system functions with only small changes in the design variables using a novel surrogate modeling technique. The applicability of typical global surrogate models is limited when critical discontinuities are present. An efficient method has been developed here to identify the number of discontinuities and their position in the design domain. Previous works assume a said number of discontinuities; here though, the number of discontinuities is not given a priori. The discontinuities are identified by examining the relative difference in the response value of samples in immediate proximity of each other. Samples in the same continuous subdomain are clustered and a support vector machine for classification is exploited to locate discontinuities. Local approximations are then used for the continuous subspaces between the discontinuities. Lastly, a surrogate-based design optimization is carried out. Starting with a two-bar truss, demonstrating a snap-through discontinuity, this method is shown to account for such discontinuities. This is then integrated into an optimization framework. Further academic example, namely a six-bar truss is modeled using the open-source framework Kratos Multiphysics and then optimized, showing the applicability of the method to problems with multiple discontinuities. Finally, a crash-absorbing tube is optimized that is impacted with an angle resulting in a noncontinuous design space: desired axial crushing and undesirable global buckling. After summarizing the results, advantages and possible limitations are discussed
Correction: Dermal Exposure Assessment to Pesticides in Farming Systems in Developing Countries: Comparison of Models. Int. J. Environ. Res. Public Health 2015, 12, 4670–4696
No full textWe wish to make the following changes to the published article [1], agreed upon by all authors. Claudia R. Binder has withdrawn her co-authorship. The corrected author list should therefore read: Camilo Lesmes-Fabian.[...
Kriging-guided level set method for crash topology optimization
No full textCrashworthiness optimization problems are characterized by strong nonlinearities and discontinuities.
Hence, gradient-based methods cannot be used and alternative approaches have
to be considered. Here, a novel, kriging-based method for level set topology optimization is
proposed and validated on a crash test case. Compared to CMA-ES, this method demonstrates
to be efficient in terms of convergence speed and promising in the context of crash topology optimization
Die Ringer-Kunst des Fabian von Auerswald /
No full textIn portfolio."Gedruckt zu Wittemberg durch Hans Lufft. M.D.XXXIX."--Colophon.85 full-page woodcuts by Lucas Cranach the Younger, representing the author in his 85 wrestling positions.Facsimile of the edition of 1539 with title: Ringen Kunst: fünff und achtzig Stücke, zu Ehren Kurfürstlichen Gnaden zu Sachsen [etc.] Durch Fabian von Auerswald zugericht.Mode of access: Internet
Kriging-assisted topology optimization of crash structures
No full textOver the recent decades, Topology Optimization (TO) has become an important tool in the design and analysis of mechanical structures. Although structural TO is already used in many industrial applications, it needs much more investigation in the context of vehicle crashworthiness. Indeed, crashworthiness optimization problems present strong nonlinearities and discontinuities, and gradient-based methods are of limited use. The aim of this work is to present an in-depth analysis of the novel Kriging-Assisted Level Set Method (KG-LSM) for TO. It is based on an adaptive optimization strategy using the Kriging surrogate model and a modified version of the Expected Improvement (EI) as the update criterion, which allows for embedding opportune constraints. The adopted representation using Moving Morphable Components (MMCs) significantly reduces the dimensionality of the problem, enabling an efficient use of surrogate-based optimization techniques. A minimum compliance cantilever beam test case of different dimensionalities is used to validate the presented strategy, as well as identify its potential and limits. The method is then applied to a 2D crash test case, involving a cylindrical pole impact on a rectangular beam fixed at both ends. Compared to the state-of-the-art Covariance Matrix Adaptation Evolution Strategy (CMA-ES), the KG-LSM optimization algorithm demonstrates to be efficient in terms of convergence speed and performance of the optimized designs
Finite-Elemente-basierte Bestimmung der Antwortspektren viskoelastischer Materialien bei gemäßigter Stoßbelastung
No full textThis work investigates by means of the finite element method the behaviour of viscoelastic materials subjected to an impact loading by a non-deformable sphere. The results are presented in form of dimensionless parameters; hence, the complexity of the problem is significantly reduced. Thus, it is possible to represent the governing relations through so-called master curves in accessible two-dimensional graphs. For the scaling of the dimensional problem parameters the time history of the impactor’s penetration is used together with the analytical solution for the impact event in case of a purely elastic half-space according to Heinrich Hertz. Thus, a comparatively small initial velocity is used which results in a rather long contact duration. Consequently, a part of the energy introduced by the impactor may be dissipated through viscoelastic processes.
This effect is utilised by protective equipment designed to minimise the forces occurring in unintentional impact situations. Thus, it is necessary to tune the viscoelastic material behaviour to the impact event such that a minimal loading due to the deceleration of the impactor is obtained. On the other hand, a too large penetration of the impactor owing to the increase inmaterial compliance during contact must be prevented. The consideration of these two conflicting design criteria is realised in thiswork by a multi-objective optimisation. Moreover, the response spectra can be used for the determination of unknown model parameters of a viscoelastic material sample by means of impact experiments. This application may be utilised e.g. in the quality control of viscoelastic products. The procedure developed in this work is validated by laboratory experiments using polyurethane foams.In der vorliegenden Arbeit wird mit Hilfe der Finiten-Elemente-Methode das Verhalten von linear viskoelastischen Materialien untersucht, die einer Stoßbelastung durch eine nicht deformierbare Kugel ausgesetzt sind. Die Darstellung der Ergebnisse erfolgt in Form von dimensionslosen Parametern, wodurch die Komplexität des Problems deutlich reduziert
wird. Damit ist es möglich, die Zusammenhänge als sogenannte Master Curves in übersichtlichen zwei-dimensionalen Diagrammen zu repräsentieren. Zur Skalierung der dimensionsbehafteten Problemgrößen wird sowohl der Zeitverlauf der Eindringung des Impaktors verwendet als auch auf die analytische Lösung nach Heinrich Hertz für den Stoßvorgang im Falle eines rein elastischen Halbraums zurückgegriffen. Aus diesem Grund wird eine relativ geringe Anfangsgeschwindigkeit verwendet, welche eine entsprechend
lange Kontaktzeit zur Folge hat. Somit ist es möglich, aufgrund von viskoelastischen Prozessen einen Teil der durch den Impaktor eingebrachten Energie zu dissipieren. Dieser Vorgang wird bei Protektoren ausgenutzt, die im Fall einer ungewollten Stoßbelastung die auftretenden Kräfte minimieren sollen. Deshalb ist es notwendig, das viskoelastische Materialverhalten so auf die Belastung abzustimmen, dass eine minimale Belastung infolge der Abbremsung des Impaktors erreicht wird. Auf der anderen Seite darf die über die Kontaktzeit zunehmende Nachgiebigkeit des Materials nicht zu einer zu großen Penetration des Impaktors führen. Die Erfüllung dieser konträren Designkriterien wird in dieser Arbeit mit Hilfe einer Pareto-Optimierung gelöst. Darüberhinaus können die Antwortspektren auch zur Bestimmung unbekannter Modellparameter einer viskoelastischen Materialprobe mit Hilfe von Stoßexperimenten verwendet werden. Diese Anwendung kommt zum Beispiel bei der Qualitätskontrolle von viskoelastischen Produkten zum Einsatz. Die in dieser Arbeit entwickelte Vorgehensweise wird mit Hilfe von Labor-Experimenten an Polyurethan-Schaumstoffen validiert
An Alternative Approach to Boundary Element Methods via the Fourier Transform
No full textIn general, the use of Boundary Element Methods (BEM) is restricted to physical cases for which a fundamental solution can be obtained. For simple differential operators (e.g. isotropic elasticity) these special solutions are known in their explicit form. Hence, the realization of the BEM is straight forward. For more complicated problems (e.g. anisotropic materials), we can only construct the fundamental solution numerically. This is normally done before the actual problem is tackled; the values of the fundamental solutions are stored in a table and all values needed later are interpolated from these entries. The drawbacks of this approach lie in the high amount of storage capacity, which is required, and in numerically errors due to interpolation especially near the singularity of the fundamental solution. Hence, an alternative BEM, the Fourier BEM, was proposed in Duddeck (2002) which is based on boundary integral equations (BIE) obtained via Fourier transform. It can be applied to all problems as long as the differential operator is linear and has constant coefficients.
The first step to derive the Fourier transformed BIE consistsin a rigorous mathematical formulation via distribution theory, which was developed by Schwartz(1950/51) at the end of the 1940s and which is still the mathematical basis for the treatment of partial differential equations, e.g. Hörmander (1990). In the context of BEM, this theory offers a straightforward approach towards the discussion of singularities normally encountered in the BIE. Distribution theory is able to handle all kind of singularities (jumps, weak, strong and hyper singular values) occurring in the BEM formulations and it is the adequate approach for the discussion of the corresponding integrations. In fact it can be shown by this approach, cf. Duddeck (2002), that all strong and hyper singular components are vanishing. In addition, the distribution theory enlarges the applicability of Fourier transform leading to alternative formulations for linear differential equations with constant coefficients. All differentiations are converted to multiplications; the differential operator becomes a simple algebraic expression, which can easily be inverted. This inverse differential operator is the Fourier transform of the fundamental solution.
In the approach discussed here, this Fourier fundamental solution and not the fundamental solution itself is taken for the computation of all entries to the BEM-matrices. Based on Parseval's formula, which states the equivalence of energy expressions in the Fourier and the original space, alternative BIE can be derived in the Fourier space leading to the same entries for the matrices. Thus for the Fourier BEM, every term should be established in the Fourier space. Because a Galerkin approach leads to symmetric matrices and does not require a second integration in the Fourier BEM, this approach was preferred to the conventional collocation BEM. The trial and the test functions can be easily transformed to the Fourier space as long as they are defined on straight elements. Otherwise a numerical approach can be selected.
In this paper, the method is applied to thin plate problems according to Kirchhoff's theory. The differential operator is of fourth order leading to highly singular integral equations. Although these singularities are quite complex, it can be shown easily that all strong and hyper singular terms are vanishing in both, the original and the Fourier transformed space. In the small example, all integrals were solved analytically, thus -- in contrast to other publications, e.g. Maucher and Hartmann (1999) -- no numerical errors, i.e. artificial oscillations, are occuring at the corners of a rectangular plate
Fabian lernt "schwimmen"
No full textMit der Absicht, eine Brücke zwischen deutschsprachiger Literatur und Humanistischer Psychologie zu konstruieren, geht die vorliegende Arbeit der Frage nach, ob es möglich ist, eine fiktive Person, die vor dem Hintergrund der Weltwirtschaftskrise von 1929 im Verlauf einer Romanhandlung arbeitslos geworden ist, durch Anwendung einer humanistischen Therapieform wieder in die Arbeitswelt zu integrieren. Die fiktive Person ist Jakob Fabian aus Erich Kästners neusachlichem Zeitroman Fabian. Die Geschichte eines Moralisten, erschienen 1931, und bei der humanistischen Therapieform handelt es sich um den „Klientenzentrierten Ansatz“ nach Carl Rogers. Die zentrale Forschungsfrage wird in zwei großen Schritten beantwortet: Im ersten Schritt werden themenrelevante Aspekte hinsichtlich Roman, Autor sowie Protagonist erläutert und analysiert, bis die Romanfigur Jakob Fabian zum Klienten Jakob Fabian wird und ein Anamnesebericht über diesen vorliegt. Basierend darauf, werden mit dem Ergebnis der beruflichen Rehabilitation im zweiten Schritt klientenzentriert-orientierte Therapiegespräche in einem realen Setting durchgeführt und transkribiert. Das Konzept dieser Arbeit kann als Modell auf weitere Arbeitslosenromane der Weimarer Republik angewendet werden. Zusätzlich besteht auch die Möglichkeit, das Setting an Beratungssituationen anzupassen.With the intention of constructing a bridge between German literature and “Humanistic Psychology”, the present thesis analyses the question, whether it is possible to reintegrate a fictitious man into the working environment by applying a humanistic type of therapy, who, against the background of the world economic crisis of 1929, in the course of a novel's plot has lost his job. Jakob Fabian is the fictional character in Erich Kästner’s new objectivity period novel Fabian. The story of a moralist, pub-lished in 1931, and the humanistic therapeutic method is the Rogerian Client-centered approach. The core issue is answered in two major steps: In the first step, issue-specific aspects regarding novel, author and protagonist are explained and analysed until the fictional character Jakob Fabian turns into the client Jakob Fabian and until an anamnesis report is available. Based on this, with the outcome of vocational rehabilitation in the second step, client-centred-oriented therapy sessions are conducted in a real setting and transcribed. The concept of this work can also be used as a model for other novels about unemployment during the Weimar Republic. In addition, it is also possible to adjust the setting of advisory situations
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