• Title/Summary/Keyword: Computer-assisted numerical analysis

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Multi-Objective Optimization of Electromagnetic Device Based on Design Sensitivity Analysis and Reliability Analysis (설계 민감도와 신뢰도 분석에 근거한 전자기기의 다목적 최적화)

  • Ren, Ziyan;Zhang, Dianhai;Park, Chanhyuk;Koh, Chang Seop
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.1
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    • pp.49-56
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    • 2013
  • In this paper, for constrained optimization problem, one multi-objective optimization algorithm that ensures both performance robustness and constraint feasibility is proposed when uncertainties are involved in design variables. In the proposed algorithm, the gradient index of objective function assisted by design sensitivity with the help of finite element method is applied to evaluate robustness; the reliability calculated by the sensitivity-assisted Monte Carlo simulation method is used to assess the feasibility of constraint function. As a demonstration, the performance and numerical efficiency of the proposed method is investigated through application to the optimal design of TEAM problem 22--a superconducting magnetic energy storage system.

Optimal Design of Inverse Electromagnetic Problems with Uncertain Design Parameters Assisted by Reliability and Design Sensitivity Analysis

  • Ren, Ziyan;Um, Doojong;Koh, Chang-Seop
    • Journal of Magnetics
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    • v.19 no.3
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    • pp.266-272
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    • 2014
  • In this paper, we suggest reliability as a metric to evaluate the robustness of a design for the optimal design of electromagnetic devices, with respect to constraints under the uncertainties in design variables. For fast numerical efficiency, we applied the sensitivity-assisted Monte Carlo simulation (S-MCS) method to perform reliability calculation. Furthermore, we incorporated the S-MCS with single-objective and multi-objective particle swarm optimization algorithms to achieve reliability-based optimal designs, undertaking probabilistic constraint and multi-objective optimization approaches, respectively. We validated the performance of the developed optimization algorithms through application to the optimal design of a superconducting magnetic energy storage system.

A New Sensitivity-Based Reliability Calculation Algorithm in the Optimal Design of Electromagnetic Devices

  • Ren, Ziyan;Zhang, Dianhai;Koh, Chang Seop
    • Journal of Electrical Engineering and Technology
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    • v.8 no.2
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    • pp.331-338
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    • 2013
  • A new reliability calculation method is proposed based on design sensitivity analysis by the finite element method for nonlinear performance constraints in the optimal design of electromagnetic devices. In the proposed method, the reliability of a given design is calculated by using the Monte Carlo simulation (MCS) method after approximating a constraint function to a linear one in the confidence interval with the help of its sensitivity information. The validity and numerical efficiency of the proposed sensitivity-assisted MCS method are investigated by comparing its numerical results with those obtained by using the conventional MCS method and the first-order reliability method for analytic functions and the TEAM Workshop Problem 22.

Thermal Flow Analysis of an Engine Room using a Porous Media Model for Imitating Flow Rate Reduction at Outlet of Industrial Machines (다공성 매질 모델 기반 출구유량 감소 모사 기법을 이용한 산업기계용 엔진룸 열유동해석)

  • Choi, Yo Han;Yoo, Il Hoon;Lee, Chul-Hee
    • Journal of Drive and Control
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    • v.19 no.1
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    • pp.62-68
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    • 2022
  • Considering the characteristics of industrial machines that lack vehicle-induced wind, forced convection by a cooling fan is mostly required. Therefore, numerical analysis of an engine room is usually performed to examine the cooling performance in the room. However, most engine rooms consist of a number of parts and components at specific positions, leading to high costs for numerical modeling and simulation. In this paper, a new methodology for three-dimensional computer-assisted design simplification was proposed, especially for the pile of components and parts at the engine room outlet. A porous media model and regression analysis were used to derive a meta-model for imitating the flow rate reduction at the outlet by the pile. The results showed that the fitted model was reasonable considering the coefficient of determination. The final numerical model of the engine room was then used to simulate the velocity distribution by changing the mass flow rate at the outlet. The results showed that both velocity distributions were significantly changed in each case and the meta-model was valid in imitating the flow rate reduction by some piles of components and parts.

Dynamic response of railway bridges traversed simultaneously by opposing moving trains

  • Rezvani, Mohammad Ali;Vesali, Farzad;Eghbali, Atefeh
    • Structural Engineering and Mechanics
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    • v.46 no.5
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    • pp.713-734
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    • 2013
  • Bridges are vital components of the railroads. High speed of travel, the periodic and oscillatory nature of the loads and the comparable vehicle bridge weight ratio distinguish the railway bridges from the road bridges. The close proximity between estimations by some numerical methods and the measured data for the bridge-vehicle dynamic response under the moving load conditions has boosted the confidence in the numerical analyses. However, there is hardly any report regarding the responses of the railway bridges under the effect of the trains entering from the opposite directions while running at unequal speed and having dissimilar geometries. It is the purpose of this article to present an analytical method for the dynamic analysis of the railway bridges under the influence of two opposing series of moving loads. The bridge structural damping and many modes of vibrations are included. The concept of modal superposition is used to solve for the system motion equations. The method of solution is indeed a computer assisted analytical solution. It solves for the system motion equations and gives output in terms of the bridge deflection. Some case studies are also considered for the validation of the proposed method. Furthermore, the effects of varying some parameters such as the distance between the bogies, and the bogie wheelset distance are studied. Also, the conditions of resonance and cancellation in the dynamic response for a variety of vehicle-bridge specifications are investigated.

Numerical Model for Cerebrovascular Hemodynamics with Indocyanine Green Fluorescence Videoangiography

  • Hwayeong Cheon;Young-Je Son;Sung Bae Park;Pyoung-Seop Shim;Joo-Hiuk Son;Hee-Jin Yang
    • Journal of Korean Neurosurgical Society
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    • v.66 no.4
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    • pp.382-392
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    • 2023
  • Objective : The use of indocyanine green videoangiography (ICG-VA) to assess blood flow in the brain during cerebrovascular surgery has been increasing. Clinical studies on ICG-VA have predominantly focused on qualitative analysis. However, quantitative analysis numerical modelling for time profiling enables a more accurate evaluation of blood flow kinetics. In this study, we established a multiple exponential modified Gaussian (multi-EMG) model for quantitative ICG-VA to understand accurately the status of cerebral hemodynamics. Methods : We obtained clinical data of cerebral blood flow acquired the quantitative analysis ICG-VA during cerebrovascular surgery. Varied asymmetric peak functions were compared to find the most matching function form with clinical data by using a nonlinear regression algorithm. To verify the result of the nonlinear regression, the mode function was applied to various types of data. Results : The proposed multi-EMG model is well fitted to the clinical data. Because the primary parameters-growth and decay rates, and peak center and heights-of the model are characteristics of model function, they provide accurate reference values for assessing cerebral hemodynamics in various conditions. In addition, the primary parameters can be estimated on the curves with partially missed data. The accuracy of the model estimation was verified by a repeated curve fitting method using manipulation of missing data. Conclusion : The multi-EMG model can possibly serve as a universal model for cerebral hemodynamics in a comparison with other asymmetric peak functions. According to the results, the model can be helpful for clinical research assessment of cerebrovascular hemodynamics in a clinical setting.

A New Reliability-Based Optimal Design Algorithm of Electromagnetic Problems with Uncertain Variables: Multi-objective Approach

  • Ren, Ziyan;Peng, Baoyang;Liu, Yang;Zhao, Guoxin;Koh, Chang-Seop
    • Journal of Electrical Engineering and Technology
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    • v.13 no.2
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    • pp.704-710
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    • 2018
  • For the optimal design of electromagnetic device involving uncertainties in design variables, this paper proposes a new reliability-based optimal design algorithm for multiple constraints problems. Through optimizing the nominal objective function and maximizing the minimum reliability, a set of global optimal reliable solutions representing different reliability levels are obtained by the multi-objective particle swarm optimization algorithm. Applying the sensitivity-assisted Monte Carlo simulation method, the numerical efficiency of optimization procedure is guaranteed. The proposed reliability-based algorithm supplying multi-reliable solutions is investigated through applications to analytic examples and the optimal design of two electromagnetic problems.

A Dual-Scale Analysis of Macroscopic Resin Flow in Vacuum Assisted Resin Transfer Molding Process (VARTM공정에서의 거시적 수지 유동의 Dual-Scale 분석)

  • 박윤희;강문구;이우일
    • Composites Research
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    • v.15 no.6
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    • pp.1-7
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    • 2002
  • In VARTM process where a sacrificial medium is used to facilitate the resin flow, the velocity of resin varies drastically between the sacrificial medium and the fiber preform. Although the thickness-to-length ratio of a VARTM product is usually small, a 3-D analysis is prerequisite to analyze the lead-lag flow in the two different media. The problem associated with the full 3-D analysis is the CPU time. A full 3-D numerical mesh comprising large number of nodes requires an impractical CPU time on average computer platforms. In this study, a dual-scale analysis technique was developed. The flow analysis for the entire calculation domain was conducted in 2.5-D, and the 3-D analysis was performed for a small area of special concern. In some numerical examples, the local 3-D analysis could discover an eccentric flow pattern as well as the lead-lag flow that will inevitably be neglected in 2.5-D simulations. The global-local analysis technique practiced in this study can be used to analyze the intricate flow of resin through non-uniform media in affordable CPU times.

MAC Schemes for Best Effort Service in Wireless MAN: Design and Performance Analysis (무선 MAN에서 Best Effort 서비스를 위한 MAC 방식의 설계 및 성능 분석)

  • Park, Jin-Kyung;Shin, Woo-Cheol;Ha, Jun;Choi, Cheon-Won
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.43 no.11 s.353
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    • pp.128-140
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    • 2006
  • In the IEEE 802.16 Wireless MAN standard specifies the air interface of fixed point-to-multipoint broadband wireless access systems providing multiple services. Among the service classes supported between the base station and subscriber stations in the wireless MAN, the best effort service class is ranked on the lowest position in priority and is assisted by a MAC scheme based on reservation ALOHA. The wireless MAN standard, however, does not reveal every detail of the MAC scheme but only describes the skeleton of the MAC scheme. Focusing on the amount of resource that a subscriber demands by a request and the amount of resource that the base grants to a request we thus present a number of resource demand rules and resource grant rules. Also, we construct a candidate MAC scheme by implanting a pair of resource demand and grant rules into the skeleton of the MAC scheme. Meanwhile a difficult situation for the best effort service is expected wherein only scarce resource is available after most of the resource is already preempted by other services. Perceiving such a situation, we evaluate the throughput and delay performance of each candidate MAC scheme. Especially we develop an analytical method to approximately calculate the throughput in the saturated environment. From the numerical results, we observe that the candidate MAC scheme which adopts the non-gated exhaustive demand rule paired with the full grant rule attains superior performance at the expense of the fairness.