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Author: Hesham Kamel Ibrahim
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The complicated nature of the physical crash processes of complex vehicle structures makes design optimization for crashworthiness a very challenging task. Moreover, large scale and highly nonlinear nature of crashworthiness simulations of vehicle structure make it impractical to conduct direct optimization on the full nonlinear model of the structure. The main objective of the thesis is to present a systematic and practical methodology to conduct vehicle crashworthiness design optimization efficiently at early stages of design. The thesis includes four main parts. In the first part, an efficient and practical methodology for design optimization of vehicle structures under frontal impact for crashworthiness improvement is presented. The proposed methodology is based on identifying the main vehicle structural part contributing most to the total amount of impact energy absorbed in the whole vehicle structure. The computationally efficient surrogate model of expensive nonlinear finite element simulation of this major vehicle part is developed and then integrated with gradient based optimization algorithm to maximize its absorbed impact energy while guarding against increase in its weight. In the second part, a methodology for deriving the important relation between minimum structural weight and maximum impact energy is presented. The proposed methodology is based on the principle of the Pareto front and multiobjective optimization. The methodology enables the designer to evaluate the crashworthiness performance of any suggested design easily and effectively. Moreover, the methodology provides different optimum designs from which the designer can easily select the optimum design variables to improve the performance of the initial design. In the third part, the crashworthiness behavior of simple thin walled structures and vehicle structural components made of magnesium due to its light weight is examined and a new methodology for material design optimization is presented. The proposed methodology adds material type as design variables to formal size design variables. Direct optimization using the genetic algorithm is conducted to find the optimum material combination and part's thicknesses to improve the crashworthiness performance of the vehicle structure. Finally in the fourth part, the effect of imperfection on crush elements performance is studied. Different imperfection configurations are proposed to improve the crashworthiness performance of crush elements. The genetic algorithm is directly combined with nonlinear finite elements models to search for optimum imperfection values. The results show that the crashworthiness performance of crush elements can be greatly improved through introduction of proper imperfection. Using the proposed methodologies, the current research presents a fundamental and systematic study to conduct design optimization of vehicle structures practically and efficiently.
Author: Hesham Kamel Ibrahim
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The complicated nature of the physical crash processes of complex vehicle structures makes design optimization for crashworthiness a very challenging task. Moreover, large scale and highly nonlinear nature of crashworthiness simulations of vehicle structure make it impractical to conduct direct optimization on the full nonlinear model of the structure. The main objective of the thesis is to present a systematic and practical methodology to conduct vehicle crashworthiness design optimization efficiently at early stages of design. The thesis includes four main parts. In the first part, an efficient and practical methodology for design optimization of vehicle structures under frontal impact for crashworthiness improvement is presented. The proposed methodology is based on identifying the main vehicle structural part contributing most to the total amount of impact energy absorbed in the whole vehicle structure. The computationally efficient surrogate model of expensive nonlinear finite element simulation of this major vehicle part is developed and then integrated with gradient based optimization algorithm to maximize its absorbed impact energy while guarding against increase in its weight. In the second part, a methodology for deriving the important relation between minimum structural weight and maximum impact energy is presented. The proposed methodology is based on the principle of the Pareto front and multiobjective optimization. The methodology enables the designer to evaluate the crashworthiness performance of any suggested design easily and effectively. Moreover, the methodology provides different optimum designs from which the designer can easily select the optimum design variables to improve the performance of the initial design. In the third part, the crashworthiness behavior of simple thin walled structures and vehicle structural components made of magnesium due to its light weight is examined and a new methodology for material design optimization is presented. The proposed methodology adds material type as design variables to formal size design variables. Direct optimization using the genetic algorithm is conducted to find the optimum material combination and part's thicknesses to improve the crashworthiness performance of the vehicle structure. Finally in the fourth part, the effect of imperfection on crush elements performance is studied. Different imperfection configurations are proposed to improve the crashworthiness performance of crush elements. The genetic algorithm is directly combined with nonlinear finite elements models to search for optimum imperfection values. The results show that the crashworthiness performance of crush elements can be greatly improved through introduction of proper imperfection. Using the proposed methodologies, the current research presents a fundamental and systematic study to conduct design optimization of vehicle structures practically and efficiently.
Author: Ann-Britt Ryberg
Publisher: Linköping University Electronic Press
ISBN: 9176854825
Category :
Languages : en
Pages : 63
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Book Description
Multidisciplinary design optimization (MDO) can be used in computer aided engineering (CAE) to efficiently improve and balance performance of automotive structures. However, large-scale MDO is not yet generally integrated within automotive product development due to several challenges, of which excessive computing times is the most important one. In this thesis, a metamodel-based MDO process that fits normal company organizations and CAE-based development processes is presented. The introduction of global metamodels offers means to increase computational efficiency and distribute work without implementing complicated multi-level MDO methods. The presented MDO process is proven to be efficient for thickness optimization studies with the objective to minimize mass. It can also be used for spot weld optimization if the models are prepared correctly. A comparison of different methods reveals that topology optimization, which requires less model preparation and computational effort, is an alternative if load cases involving simulations of linear systems are judged to be of major importance. A technical challenge when performing metamodel-based design optimization is lack of accuracy for metamodels representing complex responses including discontinuities, which are common in for example crashworthiness applications. The decision boundary from a support vector machine (SVM) can be used to identify the border between different types of deformation behaviour. In this thesis, this information is used to improve the accuracy of feedforward neural network metamodels. Three different approaches are tested; to split the design space and fit separate metamodels for the different regions, to add estimated guiding samples to the fitting set along the boundary before a global metamodel is fitted, and to use a special SVM-based sequential sampling method. Substantial improvements in accuracy are observed, and it is found that implementing SVM-based sequential sampling and estimated guiding samples can result in successful optimization studies for cases where more conventional methods fail.
Author: K. Hamza
Publisher:
ISBN:
Category :
Languages : en
Pages : 8
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Book Description
A new method for crashworthiness optimization of vehicle structures is presented, where an early design exploration is done by the optimization of an "equivalent" mechanism approximating a vehicle structure. An equivalent mechanism is a network of rigid links with lumped mass connected by prismatic and revolute joints with nonlinear springs approximating aggregated behaviors of structural members. A number of finite element (FE) models of the thin-walled beams with typical cross sections and wall thicknesses are analyzed to build a surrogate model that maps a property of nonlinear spring to the corresponding FE model. Using the surrogate model, an equivalent mechanism is optimized for given design objectives by selecting the properties of the nonlinear springs among the values that can be realized by an FE model. After the optimization, the component FE models corresponding to the optimal spring properties are "assembled" into a FE model of an entire structure, which is further modified for final tuning. Two case studies of a vehicle front substructure are presented, which demonstrate the approach can help obtain a better design with far less computational resources than the direct optimization of a FE model.
Author: Norman Jones
Publisher: Butterworth-Heinemann
ISBN:
Category : Science
Languages : en
Pages : 472
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Book Description
Author: Prasad Tapkir
Publisher:
ISBN:
Category :
Languages : en
Pages : 202
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Book Description
The passenger safety is one of the most important factors in the automotive industries. At the same time, in order to improve the overall efficiency of passenger cars, lightweight structures are preferred while designing the vehicle structures. Among various structural optimization techniques, topology optimization techniques are usually preferred to address the issue of crashworthiness. The hybrid cellular automaton (HCA) is a truly nonlinear explicit topology design method developed for obtaining conceptual designs of crashworthy vehicle components. In comparison to linear implicit methods, such as equivalent static loads, and partially nonlinear implicit methods, the HCA method fully captures all the relevant aspect of a fully nonlinear, transient dynamic crash simulation. Traditionally, the focus of the HCA method has been on designing load paths in the crash component that increase the uniform internal energy absorption ability; thus far, other relevant crashworthiness indicators such as peak crushing force and displacement have been less studied. The objective of this research is to extend the HCA method to synthesize load paths to obtain the different acceleration-displacement profiles, which allow reduced peak crushing force as well as reduced penetration during a crash event. To achieve this goal, this work introduces the concept of achieving uniform energy distribution at variable design simulation times. In the proposed work, the design time is used as a new design parameter in topology optimization. The desired volume fraction of the final design and the design time provided two dimensional design space for topology optimization, which is followed by the formulation of design of experiments (DOEs). The nonlinear analyses of the corresponding DOEs are performed using nonlinear explicit code LS-DYNA, which is followed by topology synthesis in HCA. The performance of the resulting structures showed that the short design times lead to design obtained by linear optimizers, while long simulation times lead to designs obtained by the traditional HCA method. To achieve the target crucial crash responses such as maximum acceleration and maximum displacement of the structure under the dynamic load, the geological predictor has been implemented. The concept of design time is further developed to improve structural performance of a vehicle component under the multiple loads using the method of multi-design time. Finally, the design time is implemented to generated merged designs by performing binary operations on topology-optimized designs. Numerical example of the simplified front frame is utilized to demonstrate the capabilities of the proposed approach.
Author: Andrew Eric Parrish
Publisher:
ISBN:
Category : Automobiles
Languages : en
Pages :
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Book Description
This study uses numerical design optimization with advanced metamodeling techniques to investigate the effects of material substitution and dummy models on crashworthiness characteristics of automotive structures. A full-scale Dodge Neon LS-DYNA finite element model is used in all structural analysis and optimization calculations. Optimization is performed using vehicle-based responses for multiple crash scenarios and occupant-based responses for one crash scenario. An AZ31 magnesium alloy is substituted for the baseline steel in twenty-two vehicle parts. Five base metamodels and an Optimized Ensemble metamodel are used to develop global surrogate models of crash-induced responses. Magnesium alloy is found to maintain or improve vehicle crashworthiness with an approximate 50% reduction in selected part mass using vehicle-based responses while dummy-based designs show less percentage decrease in weight. Vehicle-based responses selected to approximate dummy injury metrics do not show the same relative change compared to dummy-based responses.
Author: Hamidreza Zarei
Publisher: Cuvillier Verlag
ISBN: 3867275424
Category :
Languages : en
Pages : 123
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Author: Satyajeet Suresh Shinde
Publisher:
ISBN:
Category : Automatic control
Languages : en
Pages : 188
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Book Description
Crashworthiness design is gaining more importance in the automotive industry due to high competition and tight safety norms. Further there is a need for light weight structures in the automotive design. Structural optimization in last two decades have been widely explored to improve existing designs or conceive new designs with better crashworthiness and reduced mass. Although many gradient based and heuristic methods for topology and topometry based crashworthiness design are available these days, most of them result in stiff structures that are suitable only for a set of vehicle components in which maximizing the energy absorption or minimizing the intrusion is the main concern. However, there are some other components in a vehicle structure that should have characteristics of both stiffness and flexibility. Moreover, the load paths within the structure and potential buckle modes also play an important role in efficient functioning of such components. For example, the front bumper, side frame rails, steering column, and occupant protection devices like the knee bolster should all exhibit controlled deformation and collapse behavior. This investigation introduces a methodology to design dynamically crushed thin-walled tubular structures for crashworthiness applications. Due to their low cost, high energy absorption efficiency, and capacity to withstand long strokes, thin-walled tubular structures are extensively used in the automotive industry. Tubular structures subjected to impact loading may undergo three modes of deformation: progressive crushing/buckling, dynamic plastic buckling, and global bending or Euler-type buckling. Of these, progressive buckling is the most desirable mode of collapse because it leads to a desirable deformation characteristic, low peak reaction force, and higher energy absorption efficiency. Progressive buckling is generally observed under pure axial loading; however, during an actual crash event, tubular structures are often subjected to oblique impact loads in which Euler-type buckling is the dominating mode of deformation. This undesired behavior severely reduces the energy absorption capability of the tubular structure. The design methodology presented in this paper relies on the ability of a compliant mechanism to transfer displacement and/or force from an input to desired output port locations. The suitable output port locations are utilized to enforce desired buckle zones, mitigating the natural Euler-type buckling effect. The problem addressed in this investigation is to find the thickness distribution of a thin-walled structure and the output port locations that maximizes the energy absorption while maintaining the peak reaction force at a prescribed limit. The underlying design for thickness distribution follows a uniform mutual potential energy density under a dynamic impact event. Nonlinear explicit finite element code LS-DYNA is used to simulate tubular structures under crash loading. Biologically inspired hybrid cellular automaton (HCA) method is used to drive the design process. Results are demonstrated on long straight and S-rail tubes subject to oblique loading, achieving progressive crushing in most cases.
Author:
Publisher: SAE International
ISBN: 9780898830651
Category : Automobiles
Languages : en
Pages : 283
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Author: Axel Schumacher
Publisher: Springer
ISBN: 3319679880
Category : Science
Languages : en
Pages : 2101
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Book Description
The volume includes papers from the WSCMO conference in Braunschweig 2017 presenting research of all aspects of the optimal design of structures as well as multidisciplinary design optimization where the involved disciplines deal with the analysis of solids, fluids or other field problems. Also presented are practical applications of optimization methods and the corresponding software development in all branches of technology.
