RESEARCH

Reliability Analysis and Fatigue

	Stochastic response surface: The stochastic response surface (SRS) approach models the performance function as the sum of elementary functions (bases) of stochastic input parameters and is particularly useful in computationally intensive applications. Either Monte Carlo simulation or moment-based methods are then applied to the SRS for reliability analyses. This research presents an efficient shape optimization technique that addresses the efficiency/ effectiveness issues based on SRS constructed using local sensitivities and model outputs at heuristically selected collocation points. Go to top
	Tail modeling: It is generally accepted that using central models (e.g., FORM, response surfaces) for estimating large percentiles such as those required in reliability constraint calculations can lead to significant inaccuracies in the reliability analysis results. In this research, we develop an approach for the reliability-based design optimization of highly safe structural systems where a tail model is used for computing the reliability constraint during design optimization. The tail model is an adaptation of a powerful result from extreme value theory in statistics related to the distribution of exceedances. The conditional excess distribution above a certain threshold is approximated using the generalized Pareto distribution (GPD). The tail modeling technique is utilized to approximate the probability of failure in reliability analysis. Go to top
	Load tolerance design under fatigue reliability: In this research, we develop an efficient technique to estimate the load tolerance, which shows a capacity of the current design, a future reference for design upgrade, maintenance and control. A reliability-based load design method is applied in fatigue reliability design, which provides the load tolerance for a structure subject to the fatigue failure mode. Go to top

Sensitivity Analysis Using Meshfree Method

Nonlinear sensitivity analysis: Design sensitivity analysis is an essential process in the gradient-based optimum control technique. In this research activity, the continuum-based design sensitivity formulation is developed for such structural problems as linear elasticity, nonlinear elasticity, elastoplasticity, frictional contact problem, and transient dynamics. It is shown through various numerical examples that accurate sensitivity information greatly reduces design optimization cycles and provides fast convergence. Go to top

Meshfree method: Conventional finite element method has been struggled by limitation in the solution smoothness and mesh distortion in large deformation problems. The meshfree method is developed to overcome the above-mentioned two issues by removing elements in domain discretization and adopting global approximation of field variables. In this research, we develop linear/nonlinear structural analysis tools using meshfree method. This development is strongly connected with design optimization. Go to top

Manufacturing Process Simulation and Design

	Die shape design: Numerical simulation of the manufacturing process is complicated because the material experiences large deformation as well as complicated frictional contact with fixtures. In this research activity, an accurate numerical simulation technology is developed for manufacturing process analysis. Such technical aspects as large-deformation elastoplasticity, frictional contact, implicit time integration, and springback estimation are considered. In addition to the simulation, a design technology is developed such that the springback is compensated by changing the die shape design. Go to top
	Chatter vibration control: In high-speed tooling process, chatter vibration becomes a bottleneck in increasing manufacturing speed. In order to damp out the unwanted vibration, several fingers are inserted into the tool, which looses energy due to the friction between interface. In this research activity, the optimum configuration of the fingers are investigated, including number of finger slots and the internal radius of the finger. Go to top
	Micro-molding: In this research activity, we investigate the micro-molding of bulk amorphous metals to achieve low cost fabrication of complex 3D components at the micro and meso scales. The behavior of these materials under high strain rates in the temperature range between the glass transition temperature and melting temperature is studied. The goal is to demonstrate that it is possible to mass produce high strength, high precision, high aspect ratio metallic components, with feature sizes of microns or less using a relatively inexpensive and uncomplicated process suitable for wide spread implementation. Go to top

Wear and Tribology

Wear modeling: It is desirable to design engineering components for infinite life, unfortunately, in systems where parts are in intimate contact and relative motion wear is inevitable such designs are difficult to realize. Wear predictions are typically made using contact pressures and slip calculated from the first wear cycle and do not account for the changes in the geometry during life. The objective is to identify critical material wear factors in the oscillating metal-on-metal wear problem, measure these parameters using a simple and inexpensive reciprocating flat geometry wear test and to use these measurements coupled with finite element analysis to predict the wear profile of an experiment with a different wear geometry. Go to top

Micro/nano-indentation and scratch: Mechanical properties of material in small scales are quite different from those of bulk materials. Micrometric indentation and scratch is a convenient way to study the mechanical properties of thin coatings. A numerical approach that studies the behavior of elasto-plastic thin metal (aluminum alloys and gold) films is developed. The numerical results are compared with experimental results with good agreements. Go to top

Modeling and Design

	Open-Ocean-Aquaculture Cage: The ever increasing demands of the world population on ocean resources have resulted in severe over-fishing in many parts of the world. Open-ocean-aquaculture (OOA) is one area that shows great promise to meet the needs of US markets and reduce the need to import fish from abroad. In this research, we developed inflatable OOA cage using flexible members. Lightweight inflatables will greatly decrease the cost of cage transportation, deployment, assembly, and maintenance. A semi-rigid, inflatable, tensegrity-structure design, maintains divergence volume, which is critical for fish health and aquaculture success. The inflated cage retains the system integrity by using pressurized water instead of air. Go to top
	Electrodynamic maglev suspension design: A maglev system uses magnetic fields to levitate and accelerate a vehicle along a track. Maglev technology can be applied to launch vehicles and spacecrafts. Maglev system is composed of a vehicle (cradle) with permanent magnets and a rail with coils in it. A moving cradle with a special configuration of high-strength permanent magnets generates passive magnetic levitation when it moves over multi-loops of wire embedded in the track underneath. The system is configured so that the resulting magnetic forces are decomposed into driving forces and lifting forces. The feasibility of the system as a proof-of-concept model of a new launch assistant vehicle for space crafts is examined, by identifying the dynamic characteristics of magnetic-levitation system with computational motion analysis. Go to top
	Eulerian shape optimization with a fixed grid: Eulerian shape design uses advantages from both conventional shape design and topology design. It can remove mesh distortion problem in the conventional shape optimization and maintain geometric information while finite elements are fixed. The geometric model is placed over regularly meshed finite elements. Finite elements that belong inside the geometric model have a full magnitude of shape density, while those outside the model have a zero magnitude of shape density (a void). Go to top

Noise, Vibration, and Harshness Design

Structure-induced noise and vibration control is an important area of research for reducing the noise level generated by various structural parts. In this research activity, the finite element and boundary element methods are used to simulate low-frequency vibration of a vehicle and noise level in the passenger compartment. By developing an adjoint design sensitivity formulation, design optimization of a future commercial vehicle has been achieved in which the noise level is reduced by 60% compared to the initial design. Go to top

High-frequency vibro-acoustic design: At high frequency ranges, structural-acoustic simulation using conventional finite element or boundary element methods is impractical because of excessive number of elements. an energy finite element method has been developed by using statistical conservation of vibration energy. Even if this research is in its early stage, a feasibility study of controlling power flow using design sensitivity analysis show promising results. Go to top