Ui-Jin Jung

A Preliminary Study on the Optimal Shape Design of the Axisymmetric Forging Component Using Equivalent Static Loads

: s에서의 등가정하중 f : 목적함수 g : 부등제한조건 m : 평균값 S : 표준편차 e : 유효변형률 Key Words : Equivalent Static Loads(등가정하중), Shape Optimization(형상최적설계), Forging(단조), Preform(예비성형체) 초록: 본 논문은 등가정하중을 이용하여 단조공정의 예비성형체 및 빌렛의 형상설계를 위한 최적화 방법을 제안한다. 단조공정에서 예비성형체의 형상은 최종 성형품의 품질을 결정하는데 중요한 역할을 한다. 본 연구는 빌렛 및 예비성형체의 형상을 설계하기 위하여 등가정하중법을 사용하였다. 등가정하중법은 비선형 동적하중을 등가정하중으로 변환하고 여기서 구한 등가정하중을 이용하여 선형 응답 최적화를 수행하는 방법이다. 설계변수의 갱신은 선형 응답 최적화와 비선형 해석을 통하여 이루어진다. 본 논문에 포함된 예제는 원하는 단조품의 생산을 위한 최적의 예비성형체와 빌렛의 형상을 도출하여 제안한 방법의 유용성을 검증한다. 비선형 해석과 선형 응답 최적화는 각각 LS-DYNA와 NASTRAN을 사용하였다. Abstract: An optimization method is proposed for preform and billet shape designs in the forging process by using the Equivalent Static Loads (ESLs). The preform shape is an important factor in the forging process because the quality of the final forging is significantly influenced by it. The ESLSO is used to determine the shape of the preform. In the ESLSO, nonlinear dynamic loads are transformed to the ESLs and linear response optimization is performed using the ESLs. The design is updated in linear response optimization and nonlinear analysis is performed with the updated design. The examples in this paper show that optimization using the ESLs is useful and the design results are satisfactory. Consequently, the optimal preform and billet shapes which produce the desired final shape have been obtained. Nonlinear analysis and linear response optimization of the forging process are performed using the commercial software LS-DYNA and NASTRAN, respectively.

A Preliminary Study on the Optimal Preform Design in the Forging Process Using Equivalent Static Loads

The forging process is the shaping of a workpiece using dynamic loads and typically consists of the multi-step process with the preforming process. Defects such as flash and unfilling occur and the distribution of effective strains is not even in the workpiece after the forging process. An optimized preform is necessary for reduction of the defects in the desired final forging. Optimization of the forging process is nonlinear dynamic response optimization because nonlinearities are involved in the analysis. When the conventional method is utilized in optimization of the forging process, the cost is extremely high due to repeated nonlinear analyses for function and sensitivity calculation. In this paper, the equivalent static loads method for non linear static response structural optimization (ESLSO) is employed to determine the preform shape which leads to reduction of the unfilled area and even distribution of the effective strain in the final forging shape. ESLSO is a structural optimization method where nonlinear dynamic loads are transformed to equivalent static loads (ESLs). ESLs are defined as the loads for linear analysis, which generate the same response field as that of nonlinear analysis. 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 solved using these ESLs and the results are discussed.

Simulation of Rollover Crashes and Passenger Injury Assessment for a Wheeled Armored Vehicle

A wheeled armored vehicle is a military vehicle that has been developed to enhance combat capabilities and mobility for the army. The wheeled armored vehicle has a high center of gravity, and it operates on unpaved and sloped roads. Therefore, this vehicle has a high risk of rollover crashes. To design the interior of the military vehicle, the crews safety during rollover crashes is an important factor. However, actual vehicle tests for design are extremely expensive. In this paper, nonlinear dynamic analysis is performed to simulate the rollover crashes and the passenger injury is assessed for a wheeled armored vehicle. The scope of this research is the rollover condition, FE modeling of the wheeled armored vehicle and the dummy, arrangement of dummies, assessment of passenger injuries, and simulation model for rollover crashes.

Preliminary Study on Structural Optimization with Control Variables Using Equivalent Static Loads for Spring-damper Control Systems

:Ⓒ 비례궤환이득 Key Words: Equivalent Static Loads(등가정하중), Structural Optimization(구조최적설계), Control Variable(제어변수) 초록: 본 논문은 등가정하중을 이용하여 제어시스템을 포함한 구조물의 설계를 위한 최적화 방법을 제안한다. 지난 연구는 구조물과 제어시스템 최적설계를 독립적으로 분리하여 수행하였고, 구조물과 제어시스템을 동시에 최적화하여도 제어시스템의 제어변수는 정상상태에서만 최적화하여 성능을 향상시켰다. 하지만 제어변수는 모든 시간영역에서 최적화해야 한다. 즉, 제어시스템의 해석은 과도상태에서 수행해야 한다. 본 연구에서는 새로운 등가정하중을 이용하여 제어변수를 포함하는 제어시스템 구조물의 최적설계를 위한 방법을 제시하였다. 등가정하중은 동적하중이 구조물에 작용할 때 발생하는 임의 시간에서의 변위장과 동일한 변위장을 만들어내는 정하중을 의미한다. 이렇게 계산된 등가정하중을 이용하여 설계영역에서 선형정적응답 최적설계를 진행한다. 몇 가지 예제를 통해 새로운 등가정하중을 적용한 동적응답 최적설계방법의 유용성을 확인하였다. Abstract An optimization method is proposed for the simultaneous design of structural and control systems using the equivalent static loads. In the past researches, the control parameters of such feedback gains are obtained to improve some performance in the steady-state. However, the actuators which have position and velocity feedback gains should be designed to exhibit a good performance in the time domain. In other words, the system analysis should be conducted for the transient-state in dynamic manner. In this research, a new equivalent static loads method is presented to treat the control variables as the design variables. The equivalent static loads (ESLs) set is defined as a static load set which generates the same displacement field as that from dynamic loads at a certain time. The calculated sets of ESLs are applied as multiple loading conditions in the optimization process. Several examples are solved to validate the proposed method.

Parameter Design in Optimal Control Problems for Linear Dynamic Systems Using a Canonical Form

Control problems in dynamic systems require an optimal selection of input trajectories and system parameters. In this paper, a novel procedure for optimization of a linear dynamic system is proposed that simultaneously solves the parameter design problem and the optimal control problem using a specific system state transformation. Also, the proposed procedure includes structural design constraints within the control system. A direct optimal control method is also examined to compare it with the proposed method. The limitations and advantages of both methods are discussed in terms of the number of states and inputs. Consequently, linear dynamic system examples are optimized under various constraints and the merits of the proposed method are examined.

Optimization of the Television Packing System Using Equivalent Static Loads

최근 새로운 제품을 개발 하는데 허용되는 시간이 점점 짧아지고 있는 추세이다. 직접 실험을 수행할 경우 시제품을 제작하는 데 소요되는 시간이 추가적으로 필요하기 때문에 최근에는 컴퓨터 시뮬레이션으로 실험을 대체하는 추세이다. 그러나 시뮬레이션 역시 제품의 불안정한 상황을 모두 모사하는데 상당한 시간과 노력이 필요하다. 따라서 시뮬레이션에 소요되는 Key Words: Equivalent Static Loads(등가정하중), Shape Optimization(형상최적화), Structural Optimization(구조최적설계), Topology Optimization(위상최적화), Packing Design(포장재 설계) 초록: 텔레비전의 운송 중 발생 가능한 낙하상황을 설정하고, 낙하충격으로부터 텔레비전을 보호할 수 있는 텔레비전 포장재의 최적설계를 수행하였다. 텔레비전 포장재의 최적설계는 등가정하중법을 이용하여 비선형동적응답 구조최적설계를 수행하였으며, 포장재의 최적설계 과정을 본 연구에서 제안하였다. 개념설계 단계에서 등가정하중법을 적용한 위상최적설계를 수행하였으며 상세설계 단계에서 가상모델을 사용한 응력등가정하중법을 이용하여 형상최적설계를 수행하였다. 응력등가정하중은 비선형동적응답 해석의 변위장뿐만 아니라 응력반응장과 동일한 선형해석반응장을 유발하는 선형정적하중이다. 즉, 비선형동적응답 해석에서의 응력반응장을 구조최적설계에서 제한조건을 설정할 수 있는 것이다. 실제 예제를 통해 등가정하중법을 적용한 최적설계 과정의 유용성을 검증하였다. 텔레비전 포장재 낙하 테스트는 LS-DYNA를 사용하였으며 구조최적설계는 NASTRAN을 사용하였다. Abstract: A nonlinear dynamic response structural optimization process is proposed for the television (TV) packing system that protects the damage from a drop situation using the equivalent static loads (ESLs). Topology optimization using ESLs is carried out for conceptual design, and shape optimization using stress ESLs for a virtual model is performed for detailed design. Stress ESLs are static loads that generate the same displacement as well as the stress fields of linear static analysis as those of nonlinear dynamic analysis. Thus, the response of nonlinear dynamic analysis can be utilized as a constraint in the linear static structural optimization. An actual example is solved to validate the process. The drop test of a television packaging system is analyzed by LS-DYNA, and NASTRAN is used for optimization.

A New Method for Simultaneous Optimization of a Structure With Active and Passive Control Variables

An optimization method is proposed for the simultaneous design of structural and control systems using the equivalent static loads. The two structural and control systems are not completely independent and need to be considered in a unified fashion. Furthermore, an integrated system design is unavoidable to exhibit a good performance in the time domain. The analysis for the integrated system is conducted for the transient-state in a dynamic manner. The constraints for the structural and control systems are defined in the time domain as well. Therefore, a physically small scale problem in structural analysis easily becomes quite a large scale in an optimization problem. A new equivalent static loads (ESLs) method, which deals with the structural design variables as well as the control design variables, is proposed to solve physically large scale problems. A finite element dynamic equation is defined with control forces and a dynamic response optimization problem is formulated. Linear static response optimization is carried out with the ESLs. The control forces for the linear static response optimization are considered as design variables. Shape variables are utilized to handle the design variables for the control forces. Several examples are solved to validate the proposed method.Copyright

Structural Optimization of the Mobile Harbor Carne Considering Sea State

The mobile harbor is a new concept system to solve the problems of a port. These problems are that container ships cannot be anchored at the dock because they have become larger or the waiting times of anchoring the ships are increased due to heavy container traffic. A new system is designed to carry out the loading and unloading of containers between the mobile harbor and the container ship using the mobile harbor crane at sea. The crane plays an important role when transferring the containers. In this research, various types of the mobile harbor crane are proposed and structural optimization for each type of the crane is carried out. The loading conditions consider the rolling and pitching conditions of the unstable sea state and the wind force are considered. The constraints are mainly the regulations made by the Korean Register of Shipping. The structure of the crane is optimized to minimize the mass while various constraints are satisfied.