• International Journal of Precision Engineering and Manufacturing
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• 제6권4호
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• pp.55-59
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• 2005

This paper presents a feasibility study whether Shida's constitutive equation being widely used for plain carbon steel in steel manufacturing industry can be extended to alloy steels with a due carbon equivalent model. T,he constitutive relation of the alloy steels (SAE9254, AISI52100 and AISI4140) is measured using hot deformation simulator (GLEEBLE 3500C) at high temperatures ($800^{\circ}C{\~}1000^{\circ}C$) within strain rates of $0.05{\~}40\;s^{-1}$. It has been found the predicted flow stress behavior (constitutive relation) of AISI52100 steel is in agreement with the measured one. On the other hand, the measured flow stress behavior of SAE9254 and AISI4140 steel partly concords with the predicted one when material experiences relatively high strain rate ($10{\~}40\;s^{-1}$) deformation at low temperature ($800^{\circ}C$). It can be deduced that, for AISI52100 steel, Shida's equation with the carbon equivalent model can be applicable directly to the roughing and intermediate finishing stand in hot rolling process for calculating the roll force and torque.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.584-589
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• 2001

This paper presents the dynamic parameter design optimization of a suspension seat system using the genetic algorithm. At first, an equivalent 1-D.O.F. mass-spring-damper model of a suspension seat system was constructed for the purpose of its vibration analysis. Vertical vibration response and transmissibility of the equivalent model due to base excitations, which are defined in the ISO's seat vibration test codes, were computed. Furthermore, seat vibration test, that is ISO's damping test, was carried out in order to investigate the validity of the equivalent suspension seat model. Both analytical and experimental results showed good agreement each other. For the design optimization, the acceleration transmissibility of the suspension seat model was adopted as an object function. A simple genetic algorithm was used to search the optimum values of the design variables, suspension stiffness and damping coefficient. Finally, vibration ride performance test results showed that the optimum suspension parameters gives the lowest vibration transmissibility. Accordingly the genetic algorithm and the equivalent suspension seat modelling can be successfully adopted in the vibration ride quality optimization of a suspension seat system.

• Composites Research
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• 제28권2호
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• pp.58-64
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• 2015

본 논문에서는 샌드위치 복합재 패널로 제작되는 사용후 핵연료 수송용기 충격완충체의 유효등가 유한 요소모델을 제시하는데 목적을 둔다. 샌드위치 복합재 패널은 금속재 면재와 각각 우레탄 폼, 발사목 그리고 레드우드 심재로 구성되었다. 충격완충체의 유효등가 유한요소 모델은 샌드위치 복합재 패널의 저속충격 시험과 해석결과와의 비교를 통해 제시되었으며, LS-DYNA 3D를 사용한 동적 외연 유한요소해석에 의해 수행되었다. 시험과 해석 결과, 충격완충체 샌드위치 패널의 유한요소 모델은 적층쉘 요소의 면재와 솔리드요소의 심재를 사용한 기존의 혼합모델링 기법에 비해 면재와 심재 모두 솔리드 요소를 적용하는 방법이 더 정확한 결과를 나타냄을 확인하였다. 이때 발사목과 레드우드 심재는 요소제거 기능을 갖는 솔리드 요소로 모델링 되는 것이 추천되어진다.

• 한국기계가공학회지
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• 제19권3호
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• pp.77-85
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• 2020

In this study, we proposed a method to replace the solid finite element model of the boiler membrane wall for coal-fired power plants using an equivalent shell model. The application of a bending load to the membrane wall creates greater displacement at both ends of the central portion when compared with the middle when an isotropic elastic constant is used in the shell model. This is inconsistent with the results of the solid model where the central portion is uniformly deformed. Here, we presented a method to determine the orthotropic elastic constants of the shell model in terms of bending stiffness and vibration characteristics to solve this problem. Our analysis of the orthotropic shell model showed that the error ratio was 0.9% for the maximum displacement due to the bending load, 0.3% for the first natural frequency, and 2.5% for the second natural frequency when compared with the solid model. In conclusion, a complicated boiler membrane wall composed of a large number of pipes and fins can be replaced with a simple shell model that shows equivalent bending stiffness and vibration characteristics using our proposed method.

• 대한기계학회논문집A
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• 제24권2호
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• pp.506-517
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• 2000

One dimensional performance model has been used for the design of torque converter. The model is based on the concept of constant mean flow path and constant flow angle. These constant-assumed para meters make the design procedure to be simple. In practice, some parameters are usually replaced with geometric raw data and, the constant experiential correction factors have been used to minimize the design error. These factors have no definite physical meaning and so they cannot be applied confidently to the other design condition. In this study, the detail dynamic model of torque converter is presented to establish the theoretical background of correction factors. To verify the validity of theoretical model, steady state performance test was carried out on the several input speed. The oil temperature effect on the performance is analysed and adjusted. The constant equivalent flow angles are determined at a part of performance region by comparing the theoretical model and the test data. The sensitivity of correction factors to the input speeds are studied and the change of torus flow is presented.

• 한국생산제조학회지
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• 제22권4호
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• pp.673-679
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• 2013

This study investigates the strength durability of an automotive front bumper subjected to vibrations during driving. Through structural analyses,the maximum equivalent stresses of models 1 and 2 were found to be 187.09 and 278.4 MPa, respectively. The maximum deformations of models 1 and 2 were 1.3772 and 2.675 mm, respectively. As model 1 shows less deformation than model 2, itis stronger than model 2. Models 1and 2 show natural frequencies within 230 Hz as the range of the maximum harmonic response frequency. Models 1 and 2 have maximum amplitude displacements of 0.105 and 0.154 mm at critical frequencies of 159 and 110 Hz, respectively. As model 1 has a higher critical frequency than model 2, it has more strength durability than model 2. This study result can be effectively utilized for the design of a front bumper by investigating prevention against damage and its strength durability.

• 대한기계학회논문집B
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• 제37권8호
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• pp.775-780
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• 2013

일반적으로 전기자동차(Electric Vehicle, EV)의 배터리로는 리튬-이온 전지가 많이 사용된다. 리튬-이온 전지는 충전이 가능한 이차 전지의 일종으로 마이크로 스케일의 극판과 분리막이 반복하여 적층된 구조를 가지고 있다. 이와 같은 미세구조로 인해 상세해석모형을 적용하는 것은 지나치게 많은 비용이 소모되는 일이다. 본 연구에서는 리튬-이온 전지를 하나의 등가물성으로 나타내는 방법을 제시하고 있으며, 185.3Ah 전지와 20Ah 전지에 이를 적용하여 그 결과를 이전자료와 비교하고 있다. 또한 집중용량법을 적용한 계산 결과를 함께 제시하여 유한요소법(FEM)이나 유한체적법(FVM)의 사용 없이 손쉽게 전지의 열적 거동을 확인할 수 있는 방법을 제시하였다.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1323-1338
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• 2006

An analytical method to estimate the coupled frequencies of the circular plate submerged in fluid is developed using the finite Fourier-Bessel series expansion and Rayleigh-Ritz method. To verify the validity of the analytical method developed, finite element method is used and the frequency comparisons between them are found to be in good agreement. For the perforated plate submerged in fluid, it is almost impossible to develop a finite element model due to the necessity of the fine meshing of the plate and the fluid at the same time. This necessitates the use of solid plate with equivalent material properties. Unfortunately the effective elastic constants suggested by the ASME code are found to be not valid for the modal analysis. Therefore in this study the equivalent material properties of perforated plate are suggested by performing several finite element analyses with respect to the ligament efficiencies.

• International Journal of Precision Engineering and Manufacturing
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• 제7권2호
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• pp.46-51
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• 2006

In this study, the electromagnetic characteristic of a flat-type two-dimensional proportional solenoid were analyzed by the magnetic reluctance method. The magnetic equivalent circuit equation for the solenoid was derived by modeling the reluctance of air gaps and magnetic structural components such as pole core, armature and yoke. It was solved iteratively because of the nonlinear magnetization properties of iron parts. The solutions showed good agreement with experimental data. Based on the magnetic equivalent circuit equation, the influence of design parameters on force-to-armature displacement curves was mathematically derived and experimentally verified. In this way, dominant design parameters could be analytically determined.

• 대한기계학회논문집A
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• 제31권6호
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• pp.718-724
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• 2007

Some of gas turbine model of 7F-Class has constructed and is operating with units domestically. Non-destructive testing (NDT) is one of the methods being used to inspect damage $1^{st}$ stage bucket and review damage trends. We also analyze damage configuration and microstructure according to material and compare with pape of electric power research institute (EPRI). The damaged mode could be determined by leveraging failure analysis. Especially, configuration uprate of bucket is not only to prevent damage during operation but also avoid domestic manufacturing by the competitors. Modifications were mainly concentrated on surfaces such as cooling hole and bucket tips. Analyzing of bucket damage, the earlier model of 7F-Class used with one cycle with equivalent operation hour (EOH), has various cracking of the bucket surface. Bucket damage of new model is centered on tip area (54%) as analyzed by EPRI research. We conclude that improving bucket configuration would increase repair rate on the bucket tip.