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2004 ASME/JSME Pressure Vessels and Piping Conference

作者： Marler, R. Timothy Yang, Jingzhou Rao, S.S. Center for Computer Aided Design University of Iowa Iowa City IA 52242 Department of Mechanical Engineering University of Miami Coral Gables FL 33124

In an engineering design process, it is often desirable or even necessary to find a feasible starting point before finding the actual optimal design. The identification of unapparent feasible points provides problem insight with little computational cost. In addition, some optimization algorithms either require, or function more efficiently with, an initial point that satisfies all constraints. The advantages of using an initial feasible design are especially evident with complex structural problems and with problems that involve potential safety concerns such as the design of large pressure vessels. Although some methods are available, literature concerning the development and use of feasible-point determination is scarce. In this paper, fuzzy function theory is used to develop a novel, simple, and efficient algorithm for determining a feasible point by starting with a potentially infeasible point. Each constraint is written in fuzzy form with a newly developed membership function. The resulting optimization problem is easily solved using conventional techniques. This approach is applied to structural and manufacturing problems, including the design of a general pressure vessel. When compared with an established method, the new approach is successful and more than twenty-five times faster with larger problems.

关键词： Fuzzy control

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design sensitivity analysis and optimization of high frequency radiation problems using energy finite element method and energy boundary element method

Design sensitivity analysis and optimization of high frequen...

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Collection of Technical Papers - 10th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference

作者： Choi, Kyung K. Dong, Jun Vlahopoulos, Nickolas Wang, Aimin Zhang, Weiguo Department of Mechanical and Industrial Engineering Center for Computer-Aided Design University of Iowa Iowa City IA 52242 United States Department of Naval Architecture and Marine Engineering University of Michigan Ann Arbor MI 48109 United States

ISBN: (纸本)1563477165

This paper presents a continuum design sensitivity analysis (DSA) and optimization of high frequency radiation problems using the Energy Finite Element Method (EFEM) and Energy Boundary Element Method (EBEM). The noise radiated from the vibrating structure at a high frequency range is obtained through a sequential procedure. The structural EFEM calculates structural energy distribution, which is then used as the boundary condition for EBEM to calculate the energy density at a far-field observation point. For DSA, the direct differentiation method calculates the sensitivity of the exterior noise through the sensitivity of the structural energy density obtained from EFEM. The adjoint variable method calculates the adjoint load from an acoustic EBEM re-analysis, and the adjoint response is obtained from a structural EFEM re-analysis. The sensitivity information is obtained by carrying out numerical integration only on the structural FE part. The proposed DSA approach has been applied in the design of automotive and naval structures to search for the best material layout to achieve lowest noise level at high frequency.

关键词： Machine design

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Fatigue reliability based optimal replacement decision of mechanical components

Fatigue reliability based optimal replacement decision of me...

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2004 ASME/JSME Pressure Vessels and Piping Conference

作者： Tang, Jun Park, Young Ho Center for Computer-Aided Design College of Engineering University of Iowa Iowa City IA 52242 United States Department of Mechanical Engineering College of Engineering New Mexico State University Las Cruces NM 88003 United States

This paper introduces a maintenance decision-making strategy in the general area of replacement and reliability of mechanical components. The decision-making strategy involves the optimization of replacement interval based on fatigue failure of mechanical components. This new approach is based on the cumulative damage distribution function for evaluating mean fatigue life. By using the approach, the analytical expressions for the mean and the variance of the cumulative damage distribution under both stationary narrow-band and stationary wide-band random process are provided. The mean value and variance of the fatigue life distribution are thus evaluated to determine the optimal replacement intervals under fatigue failure. An algorithm of evaluating the mean and standard deviation of fatigue life is also presented. Therefore, the reliability of a component under random cyclic loading for a specified duration is quantified accordingly. Even though the new method introduces a great deal of complexity in the analytical models, this method can efficiently determine replacement intervals for component whose operating costs increases with use and replacement intervals for component subject to failure induced by the random process. An example is presented to demonstrate the application of the present method.

关键词： Reliability

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Dislocation Dynamics in Semiconductor Thin Film-Substrate Systems

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MRS Online Proceedings Library 2004年第1期795卷 529-534页

作者： E. H. Tan L. Z. Sun Department of Civil and Environmental Engineering Center for Computer-Aided Design The University of Iowa Iowa City U.S.A.

A discrete dislocation dynamics model is developed to establish the equations of motion for three-dimensional interacting dislocation loops in the semiconductor thin film–substrate system. The film is assumed to be an elastic layer and is perfectly bonded with another elastic substrate. Dislocation loops are discretized into segments, each of which is represented by a parametric space curve of specific shape functions and associated degree of freedom. The dislocation stress field is calculated as an essential ingredient in the dislocation dynamics method. Dislocation dynamics and interaction with film surface/interface are simulated.

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Compact modeling of environmentally induced radiation effects on electrical devices

Compact modeling of environmentally induced radiation effect...

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IEEE Conference on Aerospace

作者： X. Huang A.M. Francis A.B. Lostetter H.A. Mantooth Mixed-Signal Computer-Aided Design Laboratory Department of Electrical Engineering University of Arkansas Fayetteville AR USA

This paper presents the feasibility of formalizing a compact modeling methodology for environmentally induced radiation effects, and of implementing that methodology into the Paragon compact modeling tool. For demonstration purposes, the paper focuses on two specific radiation effects implemented in a MOSFET device model. These two effects were chosen in order to illustrate two differing forms of model development. The first form takes existing device models and modifies the equations and/or variables already existing within that model to achieve the required results (behavioral modification). The second form adds completely new equations and variables to existing device models (behavioral augmentation). The MOSFET (1) threshold voltage shift due to total ionizing dosage (TID) and (2) leakage current increase due to TID, are two major device effects that fulfill both of these requirements. Voltage shift and leakage current are critical design issues in rad-hard electronics and space environments. The threshold voltage shift effects are implemented through the modification of device model equations, while leakage current increases are implemented with added behavioral macros to the model topology, thus fulfilling the second requirement. The use of the modified compact MOSFET model is illustrated in the simulation of an op-amp based filter. Gain and frequency shifts can be observed and compared as the circuit absorbs differing amounts of TID.

关键词： Radiation effects MOSFET circuits Equations Leakage current Threshold voltage Radiation hardening Circuit topology Circuit simulation Operational amplifiers Filters

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Effects of impact angle on cone crack formation in impact-loaded soda-lime glass

Effects of impact angle on cone crack formation in impact-lo...

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Advances in Fracture and Failure Prevention: Proceedings of the Fifth International Conference on Fracture and Strength of Solids (FEOFS2003): Second International Conference on Physics and Chemistry of Fracture and Failure Prevention (2nd ICPCF)

作者： Kim, Moon-Saeng Shin, Hyung-Seop Lee, Hyeon-Chul Kim, Ho-Jong School of Mechanical Engineering Pusan National University Pusan 609-735 Korea Republic of School of Mechanical Engineering Andong National University Kyungbuk 760-749 Korea Republic of Department of Computer Aided Design Doowon Technical College Ansung Kyunggi 456-718 Korea Republic of

In order to investigate the possibility of punching process of brittle material by ball impact, effects of impact angle on cone crack formation in impact-loaded soda-lime glass were evaluated experimentally. Evaluated were also contact area between specimen and sealing, and the optimal condition for cone crack formation in glass plates by impact with small steel balls. It has been found that lateral and radial cracks gradually developed asymmetrically. However, the perfect cone cracks were found to develop almost symmetrically. As the impact angle increased, the growth rate of cone cracks decreased. Regardless of the impact angle, the PMMA sealing was more effective for perfect cone formation than Aluminum and Polyurethane sealing. Thus, the application for industrial technology for hole (or nozzle) punching process of the brittle materials is expected to be feasible, based upon proper selection of sealing materials.

关键词： Brittleness

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Finite Element Simulation of the Tool Steel Stress Response As Used In a Hot Forging

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AIP Conference Proceedings 2004年第1期712卷 560-565页

作者： David Hjertsén Johnny Sjöström Jens Bergström Mats Näsström *Department of Computer Aided Design Luleå University of Technology SE‐ 971 87 Luleå Sweden **Department of Materials Engineering Karlstad University SE‐651 88 Karlstad Sweden

Hot‐work forging tools are subjected to severe and complex loading conditions (cyclic stress/strain conditions, varying strain rates, varying temperature, environmental damage), leading to short die life. There is also a temperature and time dependant material response to consider. Presently, hot‐forging of a steel crankshaft is approached by a combined experimental and numerical simulation study of a hot‐work tool *** forging conditions were investigated by thermal measurements and damage analysis. Laboratory testing by isothermal fatigue in the temperature range 200 – 600 °C was performed. An elasto‐plastic kinematic and isotropic hardening model (according to Chaboche) was used to model the material behaviour where the material parameters were derived from the experimental part. Viscoplastic effects are not accounted for in the material model as they have minor influence on the stress‐strain relation in the experimental setup. The model was implemented in a FEM program (***) using a semi‐implicit time integration scheme according to Shih and Ortiz, and evaluated by modelling of the isothermal fatigue *** FE‐results managed to describe the materials general behavior, the correlation between the experimental simulated values were however not satisfactory due to influence of factors in the parameter derivation. Important features of the material behaviour are the cyclic softening and its dependence of the temperature, and also the strain path history. The long‐term goal is to fully analyze the hot‐forging die in service by numerical simulation and to study the influence of manufacturing processes on die properties.

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A Method for Solving computer-aided Product design Optimization Problem Based on Back Propagation Neural Network

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Chinese Journal of Chemical engineering 2004年第4期12卷 510-514页

作者：周祥何小荣陈丙珍 Department of Chemical Engineering Tsinghua University Beijing 100084 China Department of Chemical Engineering Tsinghua University Beijing 100084 Chinaecause of the powerful mapping ability back propagation neural network (BP-NN) has been employed in computer-aided product design (CAPD) to establish the property prediction model. The backward problem in CAPD is to search for the appropriate structure or composition of the product with desired property which is an optimization problem. In this paper a global optimization method of using the a BB algorithm to solve the backward problem is presented. In particular a convex lower bounding function is constructed for the objective function formulated with BP-NN model and the calculation of the key parameter a is implemented by recurring to the interval Hessian matrix of the objective function. Two case studies involving the design of dopamine β-hydroxylase (DβH) inhibitors and linear low density polyethylene (LLDPE) nano composites are investigated using the proposed method.

Because of the powerful mapping ability, back propagation neural network (BP-NN) has been employed in computer-aided product design (CAPD) to establish the property prediction model. The backward problem in CAPD is to search for the appropriate structure or composition of the product with desired property, which is an optimization problem. In this paper, a global optimization method of using the a BB algorithm to solve the backward problem is presented. In particular, a convex lower bounding function is constructed for the objective function formulated with BP-NN model, and the calculation of the key parameter a is implemented by recurring to the interval Hessian matrix of the objective function. Two case studies involving the design of dopamine β-hydroxylase (DβH) inhibitors and linear low density polyethylene (LLDPE) nano composites are investigated using the proposed method.

关键词： computer-aided product design (CAPD) back propagation neural network (BP-NN) a BB algorithm convex lower bounding function interval Hessian matrix

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Finite deformation micromechanical analysis of textile-reinforced plastics

Finite deformation micromechanical analysis of textile-reinf...

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2003 ASME International Mechanical engineering Congress

作者： Swan, Colby C. Kim, HyungJoo Department of Civil Engineering Center for Computer-Aided Design University of Iowa Iowa City IA 52242 United States Center for Computer-Aided Design University of Iowa Iowa City IA 52242 United States

ISBN: (纸本)0791837297

Nonlinear elastic stiffness behaviors of plain-weave textile-reinforced composites are considered in this work by modeling finite deformation effects at two scales: (1) at the fiber diameter scale within yarns (∼10 microns);(2) at the yarn diameter scale within woven textiles (∼1000 microns). To capture the effect of heterogeneous microscale stress and strain fields, symmetric, conjugate, stress and strain measures are first established. A transversely isotropic hyperelasticity model is then presented for modeling finite deformation behaviors of yarns. After the free parameters of this model are estimated using unit cell analysis at the fiber-diameter scale, it is then incorporated into plain-weave textile unit cell model. The textile mode is then subjected to finite strain deformation-controlled loading to quantify nonlinearity in stiffness behaviors.

关键词： Reinforced plastics

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An efficient methodology for fatigue reliability analysis of mechanical components based on the stress-life prediction approach

An efficient methodology for fatigue reliability analysis of...

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2003 ASME Pressure Vessels and Piping Conference

作者： Tang, Jun Park, Young Ho Center For Computer-Aided Design College of Engineering University of Iowa Iowa City IA 52242 United States Department of Mechanical Engineering College Of Engineering New Mexico State University Las Cruces NM 88003 United States

An efficient methodology for fatigue reliability assessment and its corresponding fatigue life prediction of mechanical components using the First-Order Reliability Method (FORM) is developed in this paper. Using the proposed method, a family of reliability defined S-N curves, called R-S-N curves, can be constructed. In exploring the ability to predict spectral fatigue life and assessing the corresponding reliability under a specified dynamics environment, the theoretical background and the algorithm of a simple approach for reliability analysis will first be introduced based on fatigue failure modes of mechanical components. It will then be explained how this integrated method will carry out the spectral fatigue damage and failure reliability analysis. By using this proposed methodology, mechanical component fatigue reliability can be predicted according to different mission requirements.

关键词： Fatigue of materials

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