Cezary Bojanowski

Multi-objective optimisation and sensitivity analysis of a paratransit bus structure for rollover and side impact tests

Paratransit buses are heavily used in the United States. A paratransit bus consists of custom passenger compartments mounted onto separate cutaway chassis. The lack of dedicated national crashworthiness standards, along with different construction methods used by paratransit fleet manufacturers, can result in a wide variance of passenger compartment structural strength. In August 2007, the Florida Department of Transportation (FDOT), to ensure adequate crashworthiness performance, introduced a standard stipulating that newly acquired buses must be tested for rollover and side impact conditions. The rollover test is performed using a tilt table test according to UN-ECE Regulation 66. The side impact test involves the impact of a bus by a common sport utility vehicle or pickup truck. In the current study, an original finite element model of a paratransit bus was used in LS-DYNA® simulations of both the rollover and the side impact testing procedures per FDOT standard. Using LS-OPT®, a metamodel-based approach was used to perform multi-objective optimisation of the bus structure for the rollover and the side impact tests. The linear ANOVA and the Sobols indices approach were used for sensitivity analysis. The structural components of the bus having the greatest influence on the bus performance in the simulated test scenarios were identified. The simulation results show that the original bus design would pass the FDOT testing procedure. However, appropriate redistribution of the mass can noticeably increase its strength for the side impact case.

Principles of Verification and Validation

This paper discusses the concepts of verification and validation in computational mechanics with special attention to structural fire engineering, by referring to recently published papers and guides on V&V that define some best practices and show directions for future development. The perspective of an analyst, who develops computational models, makes runs, and analyses numerical results mostly using software based on the finite element method, is presented. The considerations emphasize practical problems encountered in the V&V process, potential sources of errors and uncertainties, the importance of sensitivity study, new ideas regarding the relationship between validation and verification, differences between calibration and validation, new aspects of the validation metrics, and guides for designing validation experiments. The discussion is illustrated by computational problem examples.

Development of a Computational Approach to Detect Instability and Incipient Motion of Large Riprap Rocks

Computational fluid dynamics (CFD) has progressed to the point where flow problems can be solved in domains containing solid objects with complex, irregular geometry in relative motion along arbitrary paths through the fluid domain. The solvers incorporate moving mesh and mesh morphing techniques. With this new CFD capability the detailed stress distribution created by flow over the surface of a moving solid and the capability of computational structural mechanics (CSM) software to solve for both small and large displacements of solids from applied loads, it is now possible to solve a wide variety of fluid structure interaction (FSI) problems by coupling the two types of software. This paper presents development of procedures to couple STAR-CCM+® CFD software to LS-DYNA® CSM software to solve FSI problems. An initial application of the coupled software to FSI analysis of incipient motion of large riprap rocks is described. Two cases were used to test the coupling. The first has a rock layer in a channel with no bridge structures, and the second has an abutment corner that contracts the flow. Three representative rocks were included in the coupling and the approximate inlet flow velocity required to lift a rock and move it downstream was determined.

Influence of Multi-Dimension Heat Conduction on Heat Flux Calculation for HFIR LEU Analysis

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Comparison of response variation of THOR and Hybrid III dummy Models in a controlled rollover impact model

ABSTRACT Several dynamic rollover test procedures have been developed over the years; however, the repeatability of test results is often questioned. Also, there can be sensitivity of test and simulation results to small variations in the initial conditions. The objective of this study is to evaluate the response variation of three different crash dummy finite element (FE) models (two versions of a 50th percentile male Hybrid III (HIII) and a Test Device for Human Occupant Restraint (THOR) dummy) in a simulation of a controlled rollover test, using a late model vehicle FE model. A baseline model was established with each dummy, and then a global sensitivity analysis was performed for each dummy varying vehicle design and crash parameters. The simplified HIII dummy model was very sensitive to small variations in the initial conditions of the test. Both the THOR and detailed HIII models gave very consistent results presenting similar trends in the sensitivity analysis.

Example Validation of Numerical Modeling of Blast Loading

This paper reports a follow-up feasibility study on different approaches for numerical modeling of blast loads, implemented recently in a few commercial programs based on finite element method and explicit time integration. Four approaches have been considered including: explicit blast wave representation using fluid-structure interaction (FSI) with 2D and 3D multi-material arbitrary Lagrangian-Eulerian (ALE) formulations, direct application of empirical explosive blast loads on structures, and the most recent, combined method, in which direct empirical loading is applied to a reduced ALE domain. Each of these approaches has its own strengths and weaknesses, although the last one seems to be the most universal. Based on the published experimental data, a benchmark problem was selected, which considers a pressure loading exerted by explosion of near field hemispherical charges on a rigid steel plate. The comparison is done in terms of pressure peaks (overpressure) and time histories of reflected pressure, and reflected specific impulses.