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Seongnam, South Korea

Choi J.,Seoul National University | Ryu H.S.,FunctionBay Inc. | Kim C.W.,Konkuk University | Choi J.H.,Kyung Hee University
Multibody System Dynamics | Year: 2010

Dynamic analysis of many mechanical systems often involves contacts among rigid bodies. When calculating the contact force with a compliant contact force model, a penetration depth and a contact reference frame (a contact point and normal and tangent directions) should be determined from the geometrical information of the rigid body surfaces. In order to improve the speed and robustness of the contact analysis, this paper proposes a contact search algorithm for surfaces composed of triangles. This algorithm is divided into two parts, the pre-search and the detailed search. In the pre-search, a bounding box tree and an overlap test are used to find intersecting triangle pairs, and triangle connectivity information is used to identify and separate multiple contact regions. Then an efficient and robust detailed search algorithm is proposed, where the penetration depth and contact reference frame are determined from the results of the pre-search. Finally, the contact force for each contact region is calculated from a modified compliant contact force model. Numerical examples are also presented to illustrate the accuracy and performance. © 2009 Springer Science+Business Media B.V. Source


Choi J.,FunctionBay Inc. | Kim S.S.,Seoul National University | Rhim S.S.,Kyung Hee University | Choi J.H.,Kyung Hee University
International Journal of Automotive Technology | Year: 2012

This study uses an elastohydrodynamic lubrication model coupled with multi-flexible-body dynamics (MFBD) to analyze dynamic bearing lubrication characteristics, such as pressure distribution and oil film thickness. To solve the coupled fluid-structure interaction system, this study uses an MFBD solver and an elastohydrodynamics module. The elastohydrodynamics module passes its force and torque data to the MFBD solver, which can solve general dynamic systems that include rigid and flexible bodies, joints, forces, and contact elements. The MFBD solver analyzes the positions, velocities, and accelerations of the multi-flexible-body system while incorporating the pressure distribution results of the elastohydrodynamics module. The MFBD solver then passes the position and velocity information back to the elastohydrodynamics solver, which reanalyzes the force, torque, and pressure distribution. This iteration is continued throughout the analysis time period. Other functions, such as mesh grid control and oil hole and groove effects, are also implemented. Numerical examples for bearing lubrication systems are demonstrated. © 2012 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg. Source


Choi J.,FunctionBay Inc. | Choi J.H.,Kyung Hee University
Proceedings of the ASME Design Engineering Technical Conference | Year: 2013

The contact analysis of multi-flexible-body dynamics (MFBD) has been an important issue in the area of computational dynamics because the realistic dynamic analysis of many mechanical systems includes the contacts among rigid and flexible bodies. But, until now, the contact analysis in the multi-flexible-body dynamics has still remained as a big, challenging area. Especially, the most of contact algorithms have been developed based on the facetted triangles. As a result, the contact force based on the facetted surface was not accurate and smooth because the geometrical error is already included in the contact surface representation stage. This kind of error can be very important in the precise mechanism such as gear contact or cam-valve contact problems. In order to resolve this problem, this study suggests a cubic spline surface representation method and related contact algorithms. The proposed contact algorithms are using the compliant contact force model based on the Hertzian contact theory. In order to evaluate the smooth contact force, the penetration depth and contact normal directions are evaluated by using the cubic spline surface interpolation. Also, for the robust and efficient contact algorithm development, the contact algorithms are divided into four main parts which are a surface representation, a pre-search, a detailed search and a contact force generation. In the surface representation part, we propose a smooth surface representation method which can be used for smooth rigid and flexible bodies. In the pre-search, the algorithm performs collision detection and composes the expected contact pairs for the detailed search. In the detailed search, the penetration depth and contact reference frame are calculated with the cubic spline surface interpolation in order to generate the accurate and smooth contact force. Finally in the contact force generation part, we evaluate the contact force and Jacobian matrix for the implicit time integrator. Copyright © 2013 by ASME. Source


Choi J.,FunctionBay Inc. | Rhim S.,Kyung Hee University | Choi J.H.,Kyung Hee University
International Journal of Non-Linear Mechanics | Year: 2013

The analysis of multi-flexible-body dynamics (MFBD) has been an important issue in the area of computational dynamics. Also, dynamic analysis of many mechanical systems often involves contacts among rigid and flexible bodies. But, until now, the contact analysis in the multi-flexible-body dynamics has still remains a big, challenging area. In order to simulate the contact phenomena, this study uses a compliant contact force model based on the Hertzian contact theory. When generating the contact force with a compliant contact force model, a penetration depth and a contact reference frame (a contact point and normal and tangent directions) must be determined from the geometrical information of the rigid and flexible body surfaces. For robust and efficient general purpose contact algorithms, the contact algorithms are divided into four main parts which are a surface representation, a pre-search, and a detailed search and a contact force generation. In the surface representation part, we propose a general surface representation method which can be used for complex rigid and flexible bodies. In the pre-search, the algorithm performs collision detection and composes the input data sets for the detailed search. Then, in the detailed search, the penetration depth and contact reference frame are calculated in order to generate the contact force by using the compliant contact force model. Finally, in the contact force generation part, we evaluate the contact force and the Jacobian matrix which can be used for the implicit integrator. The new general purpose contact algorithm is called GGEOM (General GEOMetry) contact, because it can use general rigid and flexible geometries. © 2013 Elsevier Ltd. All rights reserved. Source


Choi J.,FunctionBay Inc. | Kim S.S.,Seoul National University | Choi J.H.,Kyung Hee University
5th Asian Conference on Multibody Dynamics 2010, ACMD 2010 | Year: 2014

This study deals with the modeling and analysis method for the elastohydrodynamic lubrication system such as journal bearing coupled with flexible multibody dynamics (or Multi-Flexible-Body Dynamics, MFBD) in order to analyze dynamic bearing lubrication characteristics such as pressure distribution and oil film thickness. In order to solve coupled fluid-structure interaction system, this study uses two main parts. The one is the MFBD solver and the other is elastohydrodynamic module. The elastohydrodynamic lubrication module developed in this study transmits the force and torque data to the MFBD solver which can solve general dynamic systems that include lots of rigid and flexible bodies, joints, forces, and contact elements. And then, the MFBD solver analyses the position, velocity, and accelerations of the flexible multibody system with the pressure distribution results of the elastohydrodynamic module. And the MFBD solver transmits the position and velocity information to the elastohydrodynamic solver continuously. Moreover, other functions such as mesh grid control and oil hole and groove effects are implemented. Finally, numerical examples for bearing lubrication systems are demonstrated. Copyright (c) 2010 by JSME. Source

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