http://www.dynalook.com daily 1 2009-03-06T17:29:14Z http://www.dynalook.com/Personally/af02_v10_elsaesser_trw.pdf Components for occupant restraint systems usually undergo structural analysis before hardware prototypes are made. In most cases the simulation is nonlinear in geometry, material and boundary conditions. Additionally, the load case often is highly dynamic. For this purpose explicit FEM is a suitable tool. It is well known, that the accuracy of deformations and especially stresses has to be checked carefully in some cases. Therefore, a comparison of different modeling approaches has been performed for basic analytical load cases. The examined variations included: Shell and solid mesh, different degrees of discretization, element formulations. All models have been run in LS-DYNA, some selected ones as well in PAMCRASH and ABAQUS Standard, for reasons of comparison. Two basic load cases have been examined: a) Prismatic cantilever beam with rectangular cross section, under a single force load. b) Circular plate, fixed at the boundary, under pressure load. These two models have been chosen in order to have an analytical solution to compare the numerical results with. All models have been run under linear conditions: Elastic, isotropic material behaviour and small deformations. The solution of each variation has been compared to the analytical one. No publisher admin 2009-09-17T11:06:47Z File http://www.dynalook.com/Personally/gothenburg2002.pdf Detailed finite element side impact dummy models of the USSID and EUROSID have been developed in cooperation with the German Association for Automotive Research (FAT) dur- ing the last 5 years. Both models are validated using tests at material and component levels as well as fully assembled models. The development of the LS-DYNA dummy models has been performed by the authors. Both models are used by nearly all car manufacturers worldwide which use LS-DYNA for occupant safety simulations. EuroNCAP (European New Car Assessment Program) announced recently a modified testing protocol for side impact assessment using the ES-2 dummy instead of the EUROSID-1 dummy. The ES-2 dummy is identical in many parts with the EUROSID-1 dummy but shows different behavior in experiments. Hence, the development of a model for the ES-2 dummy is of great interest for the automotive engineers working in the field of passive safety. The FAT has launched a project similar to the previous one to develop an ES-2 model. Due to urgent need of the model in the industry a tight schedule is given for the development. The first release of the model is already available. DYNAmore GmbH is responsible for the de- veloping the LS-DYNA models. This paper summarizes experiences gained during the vali- dation of the EUROSID-1 and USSID model and describes the tests performed to validate the ES-2 model. Finally, the performance of the first version of the ES-2 model and the schedule for the project is presented. No publisher admin 2009-09-17T11:07:29Z File http://www.dynalook.com/Personally/70.pdf A coupled finite element and mesh-free method for the solid and structure analysis has been proposed. This method is developed to minimize the mesh distortion problems encountered in the finite element analysis and to reduce the high CPU cost associated with the mesh-free computation. To couple the mesh-free method with the LS-DYNA, an interface constraint has been developed. This interface constraint is introduced onto the interfaces between finite element and mesh-free zones, and mesh-free and mesh- free zones. The completeness condition is imposed in the solution approximation to achieve the desired consistency across the interfaces. To satisfy the linear exactness in the mesh-free Galerkin approximation of the Dirichlet boundary value problem, two integration constraints have been developed. A local boundary integration scheme has been proposed to satisfy the first integration constraint and to eliminate the possible hourglass modes. The interface constraint is further extended to the essential boundaries to meet the second integration constraint and to reduce the computation time on the imposition of essential boundary conditions. Several examples are solved to evaluate the numerical performance. No publisher admin 2009-09-17T11:07:42Z File http://www.dynalook.com/Personally/60.pdf A new particle element has been added to LS-DYNA. It is based on Smoothed Particle Hydrodynamics theory. SPH is a meshless lagrangian numerical technique used to modelize the fluid equations of motion. SPH has proved to be useful in certain class of problems where large mesh distortions occur such as high velocity impact, crash simulations or compressible fluid dynamics. First, the basis principles of the SPH method will be introduced. Then, the model of perforation of a bullet through a thin plate will be presented. Two models are realised: one is made of lagrangian brick elements only, and the second one uses SPH elements for the plate. Finally, a discussion is proposed on the different methods used to deal with the penetration problem. No publisher admin 2009-09-17T11:07:51Z File http://www.dynalook.com/Personally/46.pdf This paper evaluates a Successive Response Surface Method (SRSM) specifically developed for simulation-based design optimization, e.g. that of explicit nonlinear dynamics in crashworthiness design. Linear response surfaces are constructed in a subregion of the design space using a design of experiments approach with a D-optimal experimental design. To converge to an optimum, a domain reduction scheme is utilized. The scheme requires only one user-defined parameter, namely the size of the initial subregion. During optimization, the size of this region is adapted using a move reversal criterion to counter oscillation and a move distance criterion to gauge accuracy. To test its robustness, the results using the method are compared to SQP results of a selection of the well-known Hock and Schittkowski problems. Although convergence to a small tolerance is slow when compared to SQP, the SRSM method does remarkably well for these sometimes pathological analytical problems. The second test concerns three engineering problems sampled from the nonlinear structural dynamics field to investigate the method’s handling of numerical noise and non-linearity. It is shown that, despite its simplicity, the SRSM method converges stably and is relatively insensitive to its only user-required input parameter. No publisher admin 2009-09-17T11:07:58Z File http://www.dynalook.com/Personally/45.pdf In the past years more and more complex materials, e. g. plastic and metallic foams, honey-comb materials, different types of glues, epoxy-glass materials etc., were incorporated in a wide range of products, particularly in the automotive industry. For the modeling of such materials within nonlinear dynamic problems numerous material models are available in LS-DYNA. However, the application of these material models require the knowledge of the ma-terial parameters describing the behavior of the specific material. The accuracy of the Finite-Element simulations depend authoritatively on the quality of the involved material parame-ters. In order to obtain these material parameters the calibration of the model is necessary through comparison with experimental data. The main objective of this paper is to demonstrate the calibration of a nonlinear material model by minimizing the difference of the model response and the experimental tests. As an example, a low density styrofoam is considered which is described by a material model with strain rate effects (Fu-Chang Model (LS-DYNA, 1999)). The minimization problem is solved via the Response Surface Method (Myers, 1995) using the commercial optimization code LS-OPT. No publisher admin 2009-09-17T11:08:16Z File http://www.dynalook.com/Personally/44.pdf This paper describes the multidisciplinary design optimization of a full vehicle to minimize mass while complying with crashworthiness and Noise, Vibration and Harshness (NVH) constraints. A full frontal impact is used for the crashworthiness simulation in the nonlinear dynamics code, LS-DYNA. The NVH constraints are evaluated from an implicit modal analysis of a body-in-white vehicle model using LS- DYNA. Seven design variables describe the structural components of which the thickness can be varied. The components are the aprons, shotguns, rails, cradle rails and the cradle cross member. The crashworthiness constraints relate to crush energy and displacement, while the torsional frequency characteristics are obtained from the modal analysis. The Multidisciplinary Feasible (Fully Integrated) formulation, in which full sharing of the variable sets is employed, is used as the reference case. In an attempt to investigate global optimality, three starting designs are used. Based on a Design of Experiments analysis of variance of the fully-shared variable results for each starting design, discipline-specific variables are selected from the full set using the sensitivity of the disciplinary responses. The optimizer used in all cases is the Successive Response Surface Method as implemented in LS-OPT. It is shown that partial sharing of the variables not only reduces the computational cost in finding an optimum due to fewer, more sensitive variables, but also leads to a better result. The mass of the vehicle is reduced by 4.7% when starting from an existing baseline design, and by 2.5% and 1.1% when starting from a lightest and heaviest starting design respectively. No publisher admin 2009-09-17T11:08:28Z File http://www.dynalook.com/Personally/43.pdf This paper evaluates the use of a response surface optimization algorithm for structural material or parameter identification. The algorithm used is the Successive Response Surface Method (SRSM) as implemented in LS-OPT. Two methods are used in the formulation of the optimization problem. The first is to minimize the maximum deviation of the distance function between the simulated and experimental results at selected points, while the second approach minimizes the more standard least squares residual form of the distance function, effectively providing a compromised match over all the parameters selected. SRSM uses a trust region that is adapted using a heuristic contraction and panning approach. The method has only one user-required parameter, the size of the initial trust region. To illustrate the robustness of SRSM as a material identification tool, three test cases are presented. The first concerns the identification of the power-law material parameters of a simple tensile test specimen. The second test case determines the leakage coefficient-pressure load curve of an airbag given experimental kinematic data of a chest form impacting the airbag. The third test case involves material identification of a rate- dependent low-density foam material. It is shown that SRSM essentially converges within 10 iterations for all the test cases, and that the two distance function minimization approaches produce similar results. No publisher admin 2009-09-17T11:08:39Z File http://www.dynalook.com/Personally/42.pdf The purpose of this study is to develop a methodology for springback compensation in sheet metal stamping operations. An optimization method is employed to minimize the difference between the simulation results and the intended design. This procedure results in an optimized die shape. LS-DYNA, LS-OPT and TrueGrid are used to input original tool geometry, material, and process parameters, identify design variables, perform springback simulations, and output optimized tool geometry. It is found that springback trends are consistent with changes in the die shape, which provides an effective strategy for springback compensation. The standard NUMISHEET’96 S-Rail is used as a benchmark example in this study. No publisher admin 2009-09-17T11:09:00Z File http://www.dynalook.com/Personally/41.pdf This paper evaluates the robustness of LS-OPT for response surface and design sensitivity-based optimization. The methodology uses linear response surfaces constructed in a subregion of the design space. These are constructed using either a design of experiments approach with a D-optimal experimental design or the available analytical or numerical gradient. The approach utilizes a domain reduction scheme to converge to an optimum. The scheme requires only one user-defined parameter, namely the size of the initial subregion. To test its robustness, the results using the method are compared to SQP results of a selection of the well-known Hock and Schittkowski problems. Although convergence to a small tolerance is predictably slow when compared to SQP, LS-OPT does remarkably well for these, sometimes pathological, analytical problems. No publisher admin 2009-09-17T11:09:14Z File http://www.dynalook.com/Personally/30.pdf This paper discusses two new fluid solvers that will be included with releases of LS-DYNA after LS960. The first one is a new compressible solver based upon the Space-Time Conservation Element and Solution Element Method (or the CE/SE method for short), and the second one is an incompressible fluid FEM solver. No publisher admin 2009-09-17T11:09:29Z File http://www.dynalook.com/Personally/20.pdf LSTC is committed to building an implicit capability into LS-DYNA that is as capable as the flagship explicit capability. Over the years LSTC has added many different types of constraint handling capabilities in explicit that now have to be handled by implicit. The vast majority of these constraints are equality constraints imposed on the linear or nonlinear solution required at each time step. We will describe a new approach for handling equality constraints that has allowed us to robustly process them without placing unnecessary restrictions on how the user poses the constraints. Our new approach effectively and efficiently processes the constraints for the linear, nonlinear, and eigenvalue problems that have to be solved by the users of Implicit LS-DYNA. We compute a transformation based on the Jacobian matrix of the constraint equations and apply that transformation to form a reduced stiffness and, if necessary, reduced mass matrices. The transformation is also used to transforms vectors from the unconstrained space to the constrained space and back again. The only restriction placed on the structure of the constraint matrix is that it is full rank. We will also highlight the various constraints now supported for implicit solution in LS-DYNA v. 970 and demonstrate the solution of some problems illustrating these constraint features. No publisher admin 2009-09-17T11:10:24Z File http://www.dynalook.com/Personally/forming_parameters_maker_zhu.pdf LS-DYNA has been widely used to study automotive crash. Default input parameters are generally chosen to give efficient, accurate crash simulation results. These defaults are not necessarily optimal for metal forming simulations. The following presents a standard procedure for conducting metal forming simulations with LS-DYNA. Recommended input parameters are identified in boldface type and included in boxed keyword input syntax for quick reference. A boldface zero value is entered for required input data which is model specific, such as the termination time term. No publisher admin 2009-09-17T11:10:42Z File http://www.dynalook.com/Personally/af02_v4_rzesnitzek_dc.pdf The purpose of this paper is to explore some interesting aspects of stochastic opti- mization and to propose a two-stage optimization process for highly nonlinear automotive crash problems. In the first stage of this process, a preliminary stochastic optimization is conducted with a large number of design variables. The stochastic optimization serves the dual purpose of obtaining a (nearly) optimal solution, which need not be close to the initial design, and of identifying a small set of design variables relevant to the optimization problem. In the second stage, a deterministic optimization using only the set of relevant design variables is conducted. The result of the preceding stochastic optimization is used as the starting point for the deterministic optimization. This procedure is demonstrated with a van-component model (previously introduced in [1]) used for crash calculations. LS-OPT [4] is used due to its ability to perform both stochastic (Latin Hypercube) and deterministic optimization. No publisher admin 2009-09-17T11:10:56Z File http://www.dynalook.com/Personally/T4-paper_Goetheburg_1999.pdf No publisher admin 2009-09-17T11:11:12Z File