• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집A
• /
• pp.499-504
• /
• 2000

Since large space structures(LSS) such as a space station, a solar power station satellite, etc., are theoretically distributed parameter and infinite-dimensional system, they have to be modeled into large finite-dimensional systems for control system design. Besides, there are fundamental problems in active vibration control of the large flexible structures. For example, a modeled large finite-dimensional system must be controlled with a much smaller dimensional controller. This causes the spillover phenomenon which degrades the control performances and reduces the stability margin. Furthermore, it may destabilize the entire feedback control system. In this paper, we proposed a novel control method for spillover suppression in the control of large flexible structures by using eigenstructure assignment. Its effectiveness in spillover suppression is investigated and verified by the numerical experiments using an example of the simply supported flexible beam which is modeled to have four controlled modes and eight uncontrolled modes.

• 한국해양공학회지
• /
• 제27권3호
• /
• pp.29-35
• /
• 2013

The exploration areas for maritime resources such as oil and natural gas have gradually moved to deep sea areas. It has become difficult to use existing fixed marine structures, which are very costly to build, because that have reached the uppermost economic limit. Therefore, floating marine structures and flexible marine structures are preferred. In particular, slender bodies such as risers and pipes are important parts of ocean depth marine structures. These slender bodies have more flexible structural characteristics in deep water areas because their overall length becomes longer and thediameter/length slenderness ratio gets smaller. In addition, the dynamic behavior of slender bodies becomes complicated as external forces such as tides and waves act on it directly. In this study, in order to solve these problems, we performed model tests in a 2-D wave basin using flexible slender bodies with different modulus of elasticity values. As a result, we compiled statistics and compared the behaviors of flexible slender bodies with respect to the effect of the modulus of elasticity. We expect that the results could be used as reference data for the design of structures with flexible elements.

• 한국정밀공학회지
• /
• 제21권2호
• /
• pp.67-73
• /
• 2004

Some of Spacecraft's structures are flexible so that a certain expected disturbance can easily excite a low frequency vibration on these structures, having very low natural damping. Such vibration will degrade the performance of the system, which should to be kept in a specific shape or attitude against the undesired vibration. In this paper, LQG/LTR controller is developed using an additional dynamic model to increase the performance of the frequency responses at low frequency area. This study presents that the LQG/LTR design was an effective controller for the flexible structure.

• 대한기계학회논문집
• /
• 제18권7호
• /
• pp.1674-1684
• /
• 1994

An efficient iterative method is presented for the dynamic analysis of bodies moving on flexible structures. In contrast to traditional approaches, the nominal motion of the body is considered here as an unknown. The correct contact forces between the bodies and the flexible structures are computed by an iterative method reducing the specially defined error vectors to zero, and thus satisfying the constraints between the bodies and the structures. Even thought only simple equations of motions and simple time integrators are adopted, the correct solutions are economically obtained and the Timoshenko paradox is completely resolved. Numerical simulations are conducted demonstrate the accuracy and reliability of the solution and to compare the results with the reference.

• 대한기계학회논문집
• /
• 제19권7호
• /
• pp.1657-1664
• /
• 1995

For dynamic analysis of flexible structures, classical linear modeling has been widely used due to its several good aspects. However, it was found that the modeling often lost its accuracy. So, it is important to know the valid range of the modeling before it is used. more complicated modelings are needed to obtain reliable results only outside the valid range of the classical linear modeling. In this study, some rigid body motions of flexible structures which lead to the failure of the classical linear modeling are investigated. Hybrid deformation variable modeling, which is proved to be accurate in previous studies, is used to figure out the valid range of the classical linear modeling through numerical examples.

• 대한기계학회논문집 C: 기술과 교육
• /
• 제3권2호
• /
• pp.97-106
• /
• 2015

Flexible structures are often important components of mechanical assemblies in motion. A flexible structure sometimes must go through assembly steps that cause it to be in a pre-stressed condition when in the starting position for operation. A virtual prototype of the assembly must also bring the model of the flexible structure into the same pre-stressed condition in order to obtain accurate simulation results. This case study is presented regarding the simulation of a constant velocity joint, with a focus on the flexible boot. The case study demonstrates that careful definition of the initial conditions of the boot and flexible body contacts yields high-fidelity simulation results.

• Earthquakes and Structures
• /
• 제4권2호
• /
• pp.133-155
• /
• 2013

The earthquake responses are studied for the tall flexible structures such as TV towers when the vertical eccentricities between the discrete nodes and the corresponding centroids of investigated lumps are considered. In practical analyses, the tall flexible structures can be made into a spatial-discrete system of some certain length of beam elements with different lengths and cross-sectional areas. These elements are used to construct the investigated lumps in this paper. The different cross-sectional areas and the different lengths of two adjacent elements lead to the appearance of vertical eccentricity between the discrete node and the centroid of investigated lump within the same investigated lump. Firstly, the governing equations are established for a typical investigated lump. Secondly, the calculating formulae of the forces and moments acting on the investigated lump are derived and provided. Finally the new dynamic equilibrium equations with modified mass matrix and assemblage of stiffness matrix have been derived for the stick MDOF model based on beam theory when the existing vertical eccentricities are considered. Numerical results demonstrate that these vertical eccentricities should be considered in order to obtain the accurate earthquake responses for the tall flexible structures.

• 한국소음진동공학회논문집
• /
• 제19권4호
• /
• pp.400-408
• /
• 2009

이 논문에서는 제어 가능한 ER 마운트를 이용한 유연 구조물의 진동제어 성능을 실험적으로 고찰하였다. 압착 모드형 ER 마운트를 설계하고, 전기장 인가에 따른 댐핑력 특성을 실험적으로 평가하였다. 제작된 ER 마운트를 빔과 프레임 형태의 유연 구조물에 적용하였고, 최적 제어기를 사용하여 시간 영역과 주파수 영역에서 진동제어 성능을 평가하였다.

• 소음진동
• /
• 제11권1호
• /
• pp.68-75
• /
• 2001

A method for actively controlling dynamic reaction forces in flexible structures subject to persistent excitations is presented. Since reaction forces are not directly measured in flexible structures, reaction forces are estimated by using the Kalman filter. The estimated reaction force is used as an error signal in the adaptive feedforward disturbance cancellation controller. In order to compensate the static effect of the truncated modes in the reaction forces, the residual flexibility matrix is used with the Kalman filter. The paper presents the formulation of the reaction forces in conjunction with the Kalman filter estimator and the adaptive feedforward controller. The results show that the dynamic reaction forces at its supports in a flexible beam test rir are well suppressed.

• 제어로봇시스템학회논문지
• /
• 제6권11호
• /
• pp.955-962
• /
• 2000

Although large space structures(LSS) such as a space station, a solar power station satellite, etc., are theoretically distributed parameter and infinite-dimensional systems, they have to be modeled into a lumped parameter and large finite-dimensional system for control system design. Besides, there remains the fundamental problem that the modeled large finite-dimensional system must be controled with a much smaller dimensional controller due to the limitation of computing resources. This causes the spillover phenomenon which degrades control performances and reduces the stability margin. Furthermore, it may destabilize the entire feedback control system. In this paper, we propose a novel spillover suppression method in the active vibration control of large flexible structures by using eigenstructure assignment. Its validity and effectiveness are investigated and verified by the numerical experiments using a simply supported flexible beam, which is modeled to have four controlled modes and eight uncontrolled modes.