Yoshiki Sugawara

Quantitative Validation of Dynamic Stiffening Represented by Absolute Nodal Coordinate Formulation

In recent years, various flexible structures which undergo large deformations are often applied to deployment mechanisms of space applications due to the requirements for a large structure. It is necessary to grasp their complex behaviors before the launch to escape failures as much as possible. The dynamics due to the large deformations and the overall motions are especially quite important. To overcome the difficulties of ground check about their dynamics, a powerful numerical analysis method is required strongly. In the past decade Absolute Nodal Coordinate Formulation (ANCF) method has been developed for the flexible multibody systems with large deformation and various applications have been applied to ANCF for practical use. However, there are not enough researches which validate the method by the comparison with experimental data. Especially, there are few study which conducts a quantitative validation of ANCF about overall motion with large deformation. In this paper, dynamic stiffening is focused on as one of the important overall motion. A mathematical model of two dimensional simple flexible beam is constructed based on ANCF. To simulate the dynamic stiffening by the derived model, the flexible beam is rotated horizontally in a certain angular velocity and the time history of the deformation is analyzed. Then, the results of the numerical analysis are compared with the data of corresponding experiments quantitatively.© 2009 ASME

Improvement on Evaluating Axial Elastic Force in Bernoulli-Euler Beam Based on the Absolute Nodal Coordinate Formulation by Accurate Mean Axial Strain Measure

This paper presents an improved formulation of axial elastic force in three-dimensional Bernoulli-Euler beam element based on the absolute nodal coordinate formulation. An accurate measure of mean axial strain for evaluating the axial elastic forces characterizes the presented formulation. The presented formulation evaluates the mean axial strain accurately by calculating the length of deformed beam element along its neutral axis. A comparison of the conventional formulations of the axial elastic force and the presented formulation is performed in some numerical examples which contain large bending deformation of flexible beam. As a result, it is verified that the presented formulation can express large deformation accurately with smaller number of elements than the conventional formulation which calculates the mean axial strain with straight-line distance between both element nodes. Moreover, it is also verified that the presented formulation can avoid excessive increase in computing time to simulate the dynamic behavior of flexible beam.Copyright

A Controller Design for Flexible Multibody System by the Use of Absolute Nodal Coordinate Formulation

In the past decade, Absolute Nodal Coordinate Formulation (ANCF), which is kind of a finite element method, has been developed for flexible multibody systems with large deformation and large rotation. Almost all studies for ANCF are dedicated to the development of expression ability of flexible multibody system’s behaviors, for example, a study of expansion of ANCF to three dimensional beam, the improvement of computational performance for numerical analysis and so on. On the other hand, there are few studies which extract controllers from the mathematical expressions derived by ANCF. The main aim of this study is to propose a controller design procedure by the use of the mathematical expression which is derived by ANCF. A flexible beam is introduced as a controlled object and the control torque is applied to the one end of the beam. Control objective is to rotate the beam to the desired position and suppress the residual vibration of the beam. In order to derive the mathematical expression for controller design, a kind of ANCF which uses continuum mechanics approach is employed. It is shown that some assumptions and manipulations of the mathematical expression derived by that method result in the linear equation of motion with some uncertainties and the resultant equation has a form suitable for controller design based on μ synthesis framework which is one of the robust control design method. Using μ synthesis framework, controllers are derived for some design parameters and the derived controllers are applied to the controlled object. The validity of the procedure for controller design is shown by numerical simulations and the possibilities and future works of the proposed controller design procedure by the use of mathematical expression by ANCF is discussed.Copyright

Parametric Instability in Metallic Bellows Subjected to Seismic Excitation

This paper investigates the parametric instability of a metallic bellows filled with fluid and subjected to the variance of dynamic internal pressure due to an earthquake. The axial stiffness of the bellows varies due to the variation in internal static fluid pressure, and this stiffness variation induces a parametric instability in the bellows. A finite element model describing a bellows connected to a pipe is developed to examine the question of whether parametric instability is excited in such bellows by earthquake motion, which is not the harmonic vibration. Numerical simulations and experiments were carried out using the acceleration recorded by past recorded actual earthquakes. We find that indeed parametric instability may appear in the bellows when the natural frequency of the pipe is close to the predominant frequency component of the earthquake, though the earthquake motion is not harmonic.Copyright

Control of Deployment Mechanism for Space Application by Compliance Control and Complementary System Representation

Recently, deployment system is often required for satellite to execute various missions. Such a deployment system consists of two functions. One is the deployment mechanism to deploy the components from folded configurations and the other is latch mechanisms to fix the deployed components in desired configuration. Deployment systems are often subjected to failure due to mechanical load by launch rocket and vacuum metalizing by space high vacuum environment. To escape such failures, deployment system without latch mechanism is sometimes used in space applications. Behaviour of such a system includes continuous flexible dynamics and discrete impact dynamics and degrades the attitude control performance of a satellite. To improve such performance degradation, compliance control is implemented to attitude control of satellite. Compliance control is often applied for the control which includes contact state, but it is not easy to get precise information of contact forces and torques of the motion with impact dynamics by conventional force sensor system, which arise in very short period. Especially such a measurement is very difficult in space applications in which slow control timing is preferred for reliability of the system and saving of power. Therefore, it is difficult to use compliance control for the system with impact dynamics effectively in space applications. In this paper, complementary system representation is utilized to implement compliance control more effectively for simple satellite model, and validity of proposed method is shown by simulation.

System Design and Control Aspect of a Novel Satellite Concept “Panel Extension Satellite (PETSAT)”

Abstract A novel concept of satellite design, named “PETSAT,” is proposed and its system design and control aspect is discussed in this paper. In this concept, a satellite is made of several “Functional Panels” such as “Communication panel,” “Attitude control panel,” “Thruster panel,” and “Mission Panel,” each of which has a special dedicated function. By connecting these panels by reliable connection mechanism in “plug-in” fashion, the total integrated system as a whole has a satellite function. The satellite is configured by multiple panels with hinges, which poses unique problems on system design, information management and dynamics and control, such as design of function distributions into panels, inter-/intra-panel communication systems architecture, moment of inertia management, flexibility, distributed control and so on. The paper will describe the basic concept of PETSAT, result of system design and subsystem development with focus on information management system and Attitude Control Panel. In-orbit demonstration plan which is now scheduled in 2008 − 2009 will also be given.