Ki-Jong Park

Occupant analysis and seat design to reduce neck injury from rear end impact

Occupant injury from rear end impact is rapidly becoming one of the most aggravating traffic safety problems with high human suffering and societal costs. Although rear end impact occurs at a relatively low speed, it may cause permanent disability due to neck injuries resulting from an abrupt moment, shear force, and tension/compression force at the occipital condyles. The analysis is performed for a combined occupant-seat model response, using the SAFE (Safety Analysis For occupant crash Environment) computer program. A simulation model is established to match the sled tests. A parameter study is conducted for various physical and mechanical properties. Seat design has been carried out based on the design of experiment (DOE) process with respect to five parameters: seat back collapse angle, joint stiffness between the seat back and seat cushion, headrest stiffness, the clearance between the occupants head and headrest, and friction coefficient of the seat back. An orthogonal array is employed for the DOE. A good design has been found from the results of the experiment. It is found that reductions of the seat back collapse angle and joint stiffness are the most effective for preventing neck injuries.

Structural Optimization for Non-Linear Behavior Using Equivalent Static Loads by Proportional Transformation of Loads

1. Abstract Nonlinear Response Optimization using the Equivalent Static Loads (NROESL) method/algorithm is proposed to perform optimization of non-linear response structures. The conventional method spends most of the design time on nonlinear analysis. The NROESL algorithm makes the equivalent static load cases for each response and repeatedly performs linear response optimization and uses them as multiple loading conditions. The equivalent static loads are defined as the loads in linear analysis, which generate the same response fields as those in non-linear analysis. The algorithm is validated for the convergence and the optimality. The NROESL algorithm is applied to several structural problems with geometric and/or material nonlinearity. Conventional optimization with sensitivity analysis using the finite difference method is also applied to the same examples. The results of the optimizations are compared. The proposed NROESL method is found to be very efficient and good solutions are derived.

Structural Optimization of Truss with Non-Linear Response Using Equivalent Linear Loads

A numerical method and algorithms is proposed to perform optimization of non-linear response structures. An analytical and numerical method based finite element method is also proposed for the transformation of non-linear response into linear response. Loads transformed from this method are defined as the equivalent linear loads. With the loads and the transformed response, linear static optimization is performed for nonlinear response structure with geometric and/or material non-linearity. The results of the optimization are compared with them of typical non-linear response optimization using finite difference method. The proposed method is very efficient and derives good solution.

Impact Analysis of a Full Model Doublet-Type Spacer Grid in the Fuel Assembly of a PWR

A spacer grid is one of the main structural components in the fuel assembly of a Pressurized Light Water Reactor (PWR). It supports fuel rods and maintains geometry from external impact loads. In ICONE10, a paper was published for impact analysis of a partial model spacer grid. A five by five grid model was established and the analysis results were discussed. At this moment, a full model with a sixteen by sixteen grid is analyzed for impact analysis. This grid has a new doublet-type shape. The finite element model with 16×16 grid cells is established for nonlinear analysis. It is composed of inner straps, outer straps, guide thimbles, etc. The model is considered the aspects of welding and the contacts between the components. The critical impact load that leads to plastic deformation is identified. Nonlinear finite element analysis is carried out by a software system called ABAQUS/EXPLICIT. The results are discussed in the context of the previous results from the partial model and incorporation of the analysis results into the design change is discussed.Copyright

Impact Analysis of a Dipper-Type and Multi Spring-Type Fuel Rod Support Grid Assemblies in PWR

A spacer grid is one of the main structural components in a fuel assembly of a Pressurized light Water Reactor (PWR). It supports fuel rods, guides cooling water, and maintains geometry from external impact loads. A simulation is performed for the strength of a spacer grid under impact load. The critical impact load that leads to plastic deformation is identified by a free-fall test. A finite element model is established for the nonlinear simulation of the test. The simulation model is tuned based on the free-fall test. The model considers the aspects of welding and the contacts between components. Nonlinear finite element analysis is carried out by a software system called LS/DYNA3D. The results are discussed from a design viewpoint.Copyright

Structural Shape Optimization under Static Loads Transformed from Dynamic Loads

In structural optimization, static loads are generally utilized although real external forces are dynamic. Dynamic loads have been considered in only small-scale problems. Recently, an algorithm for dynamic response optimization using transformation of dynamic loads into equivalent static loads has been proposed. The transformation is conducted to match the displacement fields from dynamic and static analyses. The algorithm can be applied to large-scale problems. However, the application has been limited to size optimization. The present study applies the algorithm to shape optimization. Because the number of degrees of freedom of finite element models is usually very large in shape optimization, it is difficult to conduct dynamic response optimization with the conventional methods that directly threat dynamic response in the time domain. The optimization process is carried out via interfacing an optimization system and an analysis system for structural dynamics. Various examples are solved to verify the algorithm. The results are compared to the results from static loads. It is found that the algorithm using static loads transformed from dynamic loads based on displacement is valid even for very large-scale problems such as shape optimization.