• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.2
• /
• pp.127-136
• /
• 1996

Dynamic analysis of a three-axle heavy truck is carried out with rigid body model and flexible body model. To see the effects of chassis flexibility, the chassis is modeled as flexible body. The mass matrix, stiffness matrix, and vibration normal modes of the chassis are obtained by a finite element analysis program, and four vibration normal modes are used in the flexible body model. The vehicle model consisting of a frame, a cab, suspensions, an engine, a deck, a seat, and tires, has total 77 degrees of freedom. The result shows that the peaked acceleration in the flexible model is lower than that of the rigid body model.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2009.04a
• /
• pp.259-262
• /
• 2009

지진이나 충돌 등과 같은 동적 하중은 하중 속도에 따라 재료의 파괴 거동이 변하기 때문에 하중 속도는 하중의 위치나 크기와 더불어 재료의 파괴 거동을 결정짓는 중요한 요소 중 하나이다. 특히 콘크리트와 같은 취성재료의 경우 재료의 속도 의존적 거동에 의해 가해진 하중으로부터 발생된 균열의 형상이나 진행 형태가 변하므로 전체 구조물의 거동에도 큰 영향을 끼친다. 따라서 취성재료를 이용한 속도 의존적 파괴 거동에 관한 연구는 그 중요성에 의해 다양한 방법으로 진행되어져 왔으나, 해석을 통한 빠른 하중에서의 파괴 거동 해석은 대부분 무시되어왔다. 하지만 최근 폭발과 같은 매우 빠른 하중에서의 재료의 파괴 거동 대한 관심이 증대되고 있고, 그에 관한 연구의 필요성도 점차 커지고 있다. 따라서 본 연구에서는 irregular lattice model의 하나인 rigid-body-spring networks(RBSN)를 이용하여 취성 재료의 파괴 거동해석에 적합한 수치 해석 모델을 개발하였다. 동적 해석을 위해 각 요소에 질량을 부여하고, 각 요소의 거동은 시간 적분에 의하여 계산된다. 이를 이용하여 빠른 하중에서의 취성 재료의 파괴 거동 특성을 분석하고 기존 실험과의 비교를 통해 수치 해석 모델의 타당성을 입증하였다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.9
• /
• pp.2165-2172
• /
• 1995

Optimization of mesh discretization has been proposed to improve the accuracy of limit analysis solution of collapse load by using the Rigid Body Spring Model(R. B. S. M) under the plane strain condition. Moreover, the fracture behaviour of materials was investigated by employing the fracture mechanism of a spring connecting the triangular rigid body element. It has been clarified that the collapse load and the geometry of slip boundary for optimized mesh discretization were close to those of the slip line solution. Further, the wedge-shaped fracture of a cylinder under a lateral load and the central fracture of a strip in the drawing process were well simulated.

• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.8
• /
• pp.108-114
• /
• 1997

A simple and efficient method is presented for the dynamics of interconnected flexible beams having large rigid body rotations. A simple mass matrix is obtained by interpolating the displacements in the global inertia frame, and the elastic force is also simply computed by using linear finite element technique with the moving frame attached to the beam. For the beams connected by revolute joints, kinematic constraints and relative rotations between the beans are not required and the equations of motions are time integrated by a simple ODE technique. Numerical simulations are conducted to demonstrate the accuracy and efficiency of the present technique.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.04a
• /
• pp.340-346
• /
• 2013

This paper describes a helicopter vibration induced by main rotor in forward flight. The hub loads in the fixed frame, which are dominant source of helicopter vibration, are obtained by multi-blade summation of rotating blades loadings. The components of 3/rev, 4/rev, and 5/rev blades loadings are transmitted by blades to 4/rev hub loads in the fixed frame. The vertical vibrations of helicopter at pilot seat and copilot seat are calculated through rigid body transfer functions considering airframe to be rigid body. The blades are assumed to be elastic and undergo the flap, lag, and torsion motion and free wake aerodynamic model is used to calculate the precise blade loadings in the analysis. The 4/rev vertical vibration responses are analyzed from rotating blade loadings and fixed hub loadings.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.10a
• /
• pp.159-166
• /
• 2001

Structural optimization often requires the evaluation of design sensitivities. The Semi Aanalytic method(SAM) for computing sensitivity is popular in shape optimization because this method has several advantages. But when relatively large rigid body motions are identified for individual elements, the SA method shows severe inaccuracy. In this paper, the improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes. Moreover, the error of the SA method caused by numerical difference scheme is alleviated by using a series approximation for the sensitivity derivatives and considering the higher order terms. Finally, this paper shows that the refined SA method including the iterative method improves the results of sensitivity analysis in dynamic problems.

• Journal of the Society of Naval Architects of Korea
• /
• v.40 no.2
• /
• pp.28-33
• /
• 2003

This study is performed to evaluate and design the dynamic characteristics of the onboard machinery with resilient mounts. To avoid resonance with onboard machinery and external force, it is necessary to calculate natural frequencies of the resilient mounting system more accurately. Natural frequencies of on board machinery are determined by rigid body properties(mass, moment of inertia, center of mass) of machinery and stiffness of mounts. But it is very difficult to calculate rigid body properties theoretically. And stiffness properties of rubber mounts vary with dynamic displacement, pre load, frequency and temperature, and so on. In this study, we have identified rigid body properties using experimental modal analysis and estimated dynamic stiffness of rubber mount for onboard machinery using measured vibration response during seatrial. We measured displacement excitation through deck under mounts and evaluated relationship between modes of resilient mounting system and main excitation sources of a ship.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.900-910
• /
• 2000

This study have been performed to investigate the dynamic behavior of the Korean High Speed Train(KHST) during the conceptual design process. This study gets a focus on the analysis of the rigid model, for which the yaw damper layout is modified in a nonlinear limit cycle analysis. In this study, influences of the system parameters such as stiffness of suspension and connection elements as well as damping coefficients were studied and an optimized parameter set is achieved. Throughout the dynamic calculation of KHST on the straight and the curved track, vibration accelerations in car body, ride comforts and wheel rail forces are investigated. Finally the vibration characteristics from rigid car body are compared with those due to the influence of elastic car body.

• Journal of computational fluids engineering
• /
• v.20 no.2
• /
• pp.103-108
• /
• 2015

Fluid-body interaction analysis of floating body with six degree-of-freedom motion is presented. In this study, three-dimensional incompressible Navier-Stokes equations are employed as a governing equation. The numerical method is based on a finite-volume approach on a cartesian grid together with a fractional-step method. To represent the body motion, the immersed boundary method for direct forcing is employed. In order to simulate the coupled six degree-of-freedom motion, Euler's equations based on rigid body dynamics are utilized. To represent the complex body shape, level-set based algorithm is utilized. In order to describe the free surface motion, the volume of fluid method utilizing the tangent of hyperbola for interface capturing scheme is employed. This study showed three different continuums(air, water and body) are simultaneously simulated by newly developed code. To demonstrate the applicability of the current approach, two different problems(dam-breaking with stationary obstacle and water entry) are simulated and all results are validated.

• Structural Engineering and Mechanics
• /
• v.2 no.4
• /
• pp.327-343
• /
• 1994

This is the second part of the paper (Rojek and Kleiber 1993) devoted to nonlinear dynamic analysis of structures consisting of rigid and deformable parts. The first part contains a theoretical formulation of nonlinear equations of motion for the coupled system as well as a solution algorithm. The second part presents the computer implementation of the equations derived in the first part with a short review of the capabilities of the computer program used and the library of finite elements. Details of material nonlinearity treatment are also given. The paper is illustrated by discussing a practical problem of a safety cab analysis for an agricultural tractor.