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Gyung-jin Park - One of the best experts on this subject based on the ideXlab platform.
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optimization of the loading path for the tube hydroforming process
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 2016Co-Authors: Hwanhak Jang, Youngmyung Lee, Gyung-jin ParkAbstract:In general, hydroforming optimization aims to make a desired shape of a plastically deformed structure under dynamic forces. The automotive industry has shown great interest in tube hydroforming, which is a metal-forming process. The forces from the hydraulic fluid are utilized to deform a tube. The internal pressures and the axial feedings (of the axial forces) determine the quality of the deformed product. In this research, an optimization process is employed to evaluate the appropriate external forces but defects are prevented. The equivalent Static Loads method for non-linear Static response structural optimization is used for the optimization process because the tube-hydroforming process is analysed by non-linear dynamic response analysis. The equivalent Static Loads are the Static Loads that generate the same response field as that of non-linear dynamic analysis and are utilized as the loading conditions in linear Static response optimization. A novel process is added to the original equivalent stat...
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nonlinear dynamic response topology optimization using the equivalent Static Loads method
Computer Methods in Applied Mechanics and Engineering, 2015Co-Authors: Hyunah Lee, Gyung-jin ParkAbstract:Abstract A novel method for nonlinear dynamic response topology optimization is proposed using the equivalent Static Loads (ESLs) method. The ESLs are the Loads that generate the same response field of linear Static analysis as that of nonlinear dynamic analysis at each time step. In the proposed procedure, nonlinear dynamic analysis is performed, ESLs are made and linear Static topology optimization is carried out with the ESLs. The process cyclically proceeds until the convergence criterion, which is specifically defined for this problem, is satisfied. Since the density method for topology optimization is utilized, the low-density finite elements can cause mesh distortion in nonlinear dynamic analysis. Transformation variables are introduced for a new update method for the incorporating process of the topology results into nonlinear dynamic analysis. Also, a new objective function is proposed to minimize the peaks of the time dependent transient responses. A couple of standard problems and a practical problem are solved to validate the proposed method.
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shape optimization of the workpiece in the forging process using equivalent Static Loads
Finite Elements in Analysis and Design, 2013Co-Authors: Jaejun Lee, Uijin Jung, Gyung-jin ParkAbstract:The forging process, which is the shaping of a workpiece using compressive Loads, is a representative plastic manufacturing process and typically consists of a multi-step process with a preforming process. The workpiece shape is an important factor because it influences the quality of the final product. After the forging process, defects such as an unfilled area, flash and crack can occur, and the effective strains may not be evenly distributed. Shape optimization of the workpiece is nonlinear dynamic response optimization because nonlinearities are involved in the analysis of the forging process. Many researches are performed to predetermine the workpiece shape using conventional methods. It is well known that the conventional methods are quite costly due to repeated nonlinear analysis for the calculation of function and sensitivity information. In this paper, the equivalent Static Loads method for non linear Static response structural optimization (ESLSO) is employed to determine the workpiece shape which leads to the desired final shape and even distribution of the effective strain. Equivalent Static Loads (ESLs) are defined as the Static Loads for linear analysis, which generate the same response field as that of nonlinear analysis. In ESLSO, the dynamic Loads for nonlinear analysis are transformed to ESLs. The ESLs, which have the characteristics of nonlinearities and dynamic Loads, are utilized as the loading conditions in linear Static response optimization. The design is updated from the results of linear Static response optimization using ESLs. Nonlinear analysis is carried out with the updated design, and the process proceeds in a cyclic manner until the convergence criteria of the design variables are satisfied. Two kinds of ESLs are proposed and they are the ESLs for the displacements and the ESLs for the effective strains. Examples of the forging process are formulated and solved.
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dynamic response topology optimization in the time domain using equivalent Static Loads
AIAA Journal, 2012Co-Authors: Hyeyoun Jang, Hyeongrae Lee, Jaiki Lee, Gyung-jin ParkAbstract:Most topology optimization techniques find the optimal layout of a structure under Static Loads. Some studies are focused on dynamic response topology optimization because the dynamic forces act in the real world. Dynamic response topology optimization is solved in the time or frequency domain. A method for dynamic response topology optimization in the time domain is proposed using equivalent Static Loads. Equivalent Static Loads are Static Loads that generate the same displacement field as dynamic Loads at each time step. The equivalent Static Loads are made by multiplying the linear stiffness matrix and the displacement field from dynamic analysis and used as multiple loading conditions for linear Static topology optimization. The results of topology optimization are utilized in dynamic analysis again and a cyclic process is utilized until the convergence criterion is satisfied. The paradigm of the method was originally developed for size and shape optimizations. A new objective function is defined to minimize the peaks of the compliance in the time domain and a convergence criterion is newly defined considering that there are many design variables in topology optimization. The developed method is verified by solving some examples and the results are discussed.
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Technical overview of the equivalent Static Loads method for non-linear Static response structural optimization
Structural and Multidisciplinary Optimization, 2011Co-Authors: Gyung-jin ParkAbstract:Linear Static response structural optimization has been developed fairly well by using the finite element method for linear Static analysis. However, development is extremely slow for structural optimization where a non linear Static analysis technique is required. Optimization methods using equivalent Static Loads (ESLs) have been proposed to solve various structural optimization disciplines. The disciplines include linear dynamic response optimization, structural optimization for multi-body dynamic systems, structural optimization for flexible multi-body dynamic systems, nonlinear Static response optimization and nonlinear dynamic response optimization. The ESL is defined as the Static load that generates the same displacement field by an analysis which is not linear Static. An analysis that is not linear Static is carried out to evaluate the displacement field. ESLs are evaluated from the displacement field, linear Static response optimization is performed by using the ESLs, and the design is updated. This process proceeds in a cyclic manner. A variety of problems have been solved by the ESLs methods. In this paper, the methods are completely overviewed. Various case studies are demonstrated and future research of the methods is discussed.
W. S. Choi - One of the best experts on this subject based on the ideXlab platform.
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Structural optimization using equivalent Static Loads at all time intervals
Computer Methods in Applied Mechanics and Engineering, 2002Co-Authors: W. S. Choi, Gyung-jin ParkAbstract:A quasi-Static structural optimization for elastic structures under dynamic Loads is presented. An equivalent Static load (ESL) set is defined as a Static load set, which generates the same displacement field as that from a dynamic load at a certain time. Multiple ESL sets calculated at all the time intervals are employed to represent the various states of the structure under the dynamic load. They can cover all the critical states that might happen at arbitrary times. The continuous characteristics of a dynamic load are considered by multiple Static load sets. The calculated sets of ESLs are utilized as a multiple loading condition in the optimization process. A design cycle is defined as a circulated process between an analysis domain and a design domain. The analysis domain gives the loading condition needed in the design domain. The design domain gives a new updated design to be verified by the analysis domain in the next design cycle. The design cycles are iterated until the design converges. Structural optimization with dynamic Loads is tangible by the proposed method. Standard example problems are solved to verify the validity of the method.
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structural optimization under equivalent Static Loads transformed from dynamic Loads based on displacement
Computers & Structures, 2001Co-Authors: B S Kang, W. S. Choi, Gyung-jin ParkAbstract:Abstract All Loads in the real world act dynamically on structures. Since dynamic Loads are extremely difficult to handle in analysis and design, Static Loads are utilized with dynamic factors. The dynamic factors are generally determined from design codes or experience. Therefore, Static Loads may not give accurate solutions in analysis and design. An analytical method based on modal analysis in finite element analysis is proposed for the transformation of dynamic Loads into equivalent Static load sets. Equivalent Static load sets are calculated to generate an identical displacement field in a structure with that from dynamic Loads at a certain time. The process is derived mathematically and evaluated. The method is verified through numerical tests. Various characteristics are identified to match the dynamic and Static behaviors. For example, the opposite direction of a dynamic load should be considered due to the vibrational response. A dynamic load is transformed into multiple equivalent Static load sets according to the number of critical times. The places of the equivalent Static Loads can be different from those of the dynamic Loads. An optimization method is defined to use the equivalent Static Loads. The developed optimization process has the same effect as dynamic optimization which uses the dynamic Loads directly. Standard examples are solved and the results are discussed.
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transformation of dynamic Loads into equivalent Static Loads based on modal analysis
International Journal for Numerical Methods in Engineering, 1999Co-Authors: W. S. Choi, Gyung-jin ParkAbstract:All the forces in the real-world act dynamically on structures. Since dynamic Loads are extremely difficult to handle in analysis and design, Static Loads are usually utilized with dynamic factors. Static Loads are especially exploited well in structural optimization where many analyses are carried out. However, the dynamic factors are not determined logically. Therefore, structural engineers often come up with unreliable solutions. An analytical method based on modal analysis is proposed for the transformation of dynamic Loads into Equivalent Static Loads (ESLs). The ESLs are calculated to generate an identical displacement field with that from dynamic Loads at a certain time. The process is derived and evaluated mathematically by using the modal analysis. Since the exact solution is extremely expensive, some approximation methods are proposed. Error analyses have been conducted for the approximation methods. Standard examples for structural design are selected and solved by the proposed method. Applications of the method to structural optimization are discussed. Copyright © John Wiley & Sons, Ltd.
Hyunah Lee - One of the best experts on this subject based on the ideXlab platform.
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nonlinear dynamic response topology optimization using the equivalent Static Loads method
Computer Methods in Applied Mechanics and Engineering, 2015Co-Authors: Hyunah Lee, Gyung-jin ParkAbstract:Abstract A novel method for nonlinear dynamic response topology optimization is proposed using the equivalent Static Loads (ESLs) method. The ESLs are the Loads that generate the same response field of linear Static analysis as that of nonlinear dynamic analysis at each time step. In the proposed procedure, nonlinear dynamic analysis is performed, ESLs are made and linear Static topology optimization is carried out with the ESLs. The process cyclically proceeds until the convergence criterion, which is specifically defined for this problem, is satisfied. Since the density method for topology optimization is utilized, the low-density finite elements can cause mesh distortion in nonlinear dynamic analysis. Transformation variables are introduced for a new update method for the incorporating process of the topology results into nonlinear dynamic analysis. Also, a new objective function is proposed to minimize the peaks of the time dependent transient responses. A couple of standard problems and a practical problem are solved to validate the proposed method.
Rostock Univ. Fachbereich Maschinenbau Und Schiffstechnik - One of the best experts on this subject based on the ideXlab platform.
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Untersuchungen zur Betriebsfestigkeit schiffbaulicher Schweisskonstruktionen bei verschiedenen Randombelastungen. Anlagen Abschlussbericht
1995Co-Authors: Naubereit H., Friedrich P., Bakczewitz F., Rostock Univ. Fachbereich Maschinenbau Und SchiffstechnikAbstract:The wave-induced strains of the shipp's hull structural elements are interrupted during the lay time in the port. During loading and unloading the smooth water strains are varying. These variations of strains influence the fatigue life of structural elements. So welded cruciform specimens made of steel D 36 have been investigated unter unchanged random loading, random loading with Static Loads, random loading with Static Loads and single peak Loads and random loading with alternating Static Loads. The experimental results are compared with the calculated fatigue life to the nominal strain concept and the local strain concept. For the calculation of the stress concentration factor the FE-programme ANSYS has been applied. Also single edge cracks made of steel D 36 have been investigated under the above mentioned loadings. The experimental results are compared with the calculated crack lengths according to the linear and nonlinear concept. Connection of transverse bulkhead longitudinal stiffeners with one- side- and double connection have been investigated under Static Loads and random loading. The linear and nonlinear computation of stress distribution and the calculation of the concentration factor the FE-programme ANSYS has been applied. The experimental results under Static Loads show that the computation of the linear stress distribution can be predicted with sufficient accuracy. Results under random loading show that the crack initiation life is comparable with the calculated fatigue life according to the nominal strain concept and the local strain concept. The nonlinear calculated crack lengths are comparable with the experimental crack lengths for these complex structures. Final welded single edge cracks made of steel D 36 without and with natural stress have been investigated under the above-mentioned loadings. The experimental results are compared with the calculated crack lengths according to a nonlinear mixed mode concept. (orig.)SIGLEAvailable from TIB Hannover: F95B1016+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman
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Untersuchungen zur Betriebsfestigkeit schiffbaulicher Schweisskonstruktionen bei verschiedenen Randombelastungen Abschlussbericht
1995Co-Authors: Naubereit H., Friedrich P., Bakczewitz F., Rostock Univ. Fachbereich Maschinenbau Und SchiffstechnikAbstract:The wave-induced strains of the ship's hull structural elements are interrupted during the lay time in the port. During loading and unloading the smooth water strains are varying. These variations of strains influence the fatigue life of structural elements. So welded cruciform specimens made of steel D 36 have been investigated under unchanged random loading, random loading with Static Loads, random loading with Static Loads and single peak Loads and random loading with alternating Static Loads. The experimental results are compared with the calculated fatigue life to the nominal strain concept and the local strain concept. For the calculation of the stress concentration factor the FE-programm ANSYS has been applied. Also single edge cracks made of steel D 36 have been investigated under the above mentioned loadings. The experimental results are compared with the calculated crack lengths according to the linear and nonlinear concept. Connection of transverse bulkhead longitudinal stiffeners with one- side- and double connection have been investigated under Static Loads and random loading. The linear and nonlinear computation of stress distribution and the calculation of the concentration factor the FE-programm ANSYS has been applied. The experimental results under Static Loads show that the computation of the linear stress distribution can be predicted with sufficient accuracy. Results under random loading show that the crack initiation life is comparable with the calculated fatigue life according to the nominal strain concept and the local strain concept. The nonlinear calculated crack lengths are comparable with the experimental crack lengths for these complex structures. Final welded single edge cracks made of steel D 36 without and with natural stress have been investigated under the above-mentioned loadings. The experimental results are compared with the calculated crack lengths according to a nonlinear mixed mode concept. (orig.)SIGLEAvailable from TIB Hannover: F95B1015+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman
Yongil Kim - One of the best experts on this subject based on the ideXlab platform.
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nonlinear dynamic response structural optimization using equivalent Static Loads
Computer Methods in Applied Mechanics and Engineering, 2010Co-Authors: Yongil Kim, Gyung-jin ParkAbstract:It is well known that nonlinear dynamic response optimization using a conventional optimization algorithm is fairly difficult and expensive for the gradient or non-gradient based optimization methods because many nonlinear dynamic analyses are required. Therefore, it is quite difficult to find practical large scale examples with many design variables and constraints for nonlinear dynamic response structural optimization. The equivalent Static Loads (ESLs) method is newly proposed and applied to nonlinear dynamic response optimization. The equivalent Static Loads are defined as the linear Static load sets which generate the same response field in linear Static analysis as that from nonlinear dynamic analysis. The ESLs are made from the results of nonlinear dynamic analysis and used as external forces in linear Static response optimization. Then the same response from nonlinear dynamic analysis can be considered throughout linear Static response optimization. The updated design from linear response optimization is used again in nonlinear dynamic analysis and the process proceeds in a cyclic manner until the convergence criteria are satisfied. Several examples are solved to validate the method. The results are compared to those of the conventional method with sensitivity analysis using the finite difference method.
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nonlinear dynamic response structural optimization of a joined wing using equivalent Static Loads
49th AIAA ASME ASCE AHS ASC Structures Structural Dynamics and Materials Conference <br> 16th AIAA ASME AHS Adaptive Structures Conference<br, 2008Co-Authors: Yongil Kim, Gyung-jin Park, Raymond M Kolonay, Maxwell Blair, Robert A. CanfieldAbstract:The joined-wing configuration that was published by Wolkovich in 1986 has been studied by many researchers (Wolkovich, J., "The Joined-Wing: An Overview," Journal of Aircraft, Vol. 23, No. 3, 1986, pp. 161―178. doi: 10.2514/3.45285). Thejoined-wing airplane is defined as an airplane that incorporates tandem wings arranged to form diamond shapes from both the top and front views. The joined wing can lead to increased aerodynamic performances as well as a reduction in the structural weight. However, the joined wing has high geometric nonlinearity under the gust load. The gust load acts as a dynamic load. Therefore, nonlinear dynamic (transient) behavior of the joined wing should be considered in structural optimization. In previous research, linear dynamic response optimization and nonlinear Static response optimization were performed. It is well known that conventional nonlinear dynamic response optimization is extremely expensive. Therefore, in this research, nonlinear dynamic response optimization of a joined wing is carried out by using equivalent Static Loads. The concept of equivalent Static Loads is expanded and newly proposed for nonlinear dynamic response optimization. Equivalent Static Loads are the load sets that generate the same response field in linear Static analysis as that in nonlinear dynamic analysis. Therefore, nonlinear dynamic response optimization can be conducted by repeated use of linear response optimization. For the verification of efficiency of the proposed method, a simple nonlinear dynamic response optimization problem is introduced. The problem is solved by using both the equivalent Static Loads method and the conventional method with sensitivity analysis using the finite difference method. The procedure for nonlinear dynamic response optimization of a joined wing using equivalent Static Loads is explained, and the optimum results are discussed.
