宮﨑 康行

This paper gives an overview of the currently planned on-orbit space verification experimental device complex composed of multiple inflatable demonstration units, proposed by the authors' group. The compact device named SIMPLE is designed to be suitable for one of the shared experimental installations that constitute a single experimental block attached to the Exposed Facility of Kibo Japanese Experimental Module (JEM) of ISS. The SIMPLE mission was accepted by JAXA as the candidate of the secondary application of the Exposed Facility of JEM at the end of last year.

The present study develops a new three-dimensional Timoshenko beam finite element (FE) whose length can be varied during transient dynamic analyses. The variable-length element enables the dynamic deployment analysis of exible appendages with non-negligible bending stiffness. In addition, the developed scheme employs an implicit time integration whereby energy and momentum in the system is properly conserved, and no artificial numerical damping is introduced. As a result, the scheme makes it possible to evaluate the impact of structural damping on the system's dynamics. The developed beam element is then used in an FE model of a solar sailcraft currently developed in Japan, and its deployment dynamics is analyzed allowing for the bending stiffness of the bundled membranes, as well as the effect of some realistic design imperfections. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

A design challenge in large membrane space structures is to apply pretension as uniformly as possible throughout the membrane, without increasing structural mass and volume. The present paper begins with a brief review of existing designs of membranes surrounded by catenary cables and shear compliant borders. The paper then introduces weblike cables that surround the membrane, and analyzes the consequent reduction in mass and volume. In addition, a series of quasi-static finite element analyses demonstrates the attenuation of wrinkles by the web cables when support points are perturbed. The paper concludes that the proposed design preserves a biaxially prestressed membrane even in disturbed conditions, with a minimal suspension-cable mass and volume. (c) 2006 Elsevier Ltd. All rights reserved.

A numerical structural model of a thin-film sail that simulates the deformation caused by solar-radiation pressure is developed, using a geometrically nonlinear finite element method (FEM). By using the finite element presented in this study, the force and moment exerted on an arbitrarily shaped solar sail subjected to solar pressure can be calculated accurately. In addition, it is shown that the sail deformation due to a solar-pressure load can be approximated by the deformation caused by the corresponding uniform gas-pressure load. This finding will significantly simplify analyses to improve attitude controller design as well as structural design of sailcraft, because commercially available ITEM software can be used for the analyses.

This paper proposes a new finite element method of frictional impact of elastic bodies. The formulation introduces a contact frame that is placed in between contacting bodies and represents the contact surface. The nonpenetration condition and the slip-stick condition are defined between the contacting body and the contact frame with the aid of the independent localized Lagrange multipliers representing the contact forces. The position of the contact frame and the local coordinate of the contacting node along the contact frame are also treated as the independent variable, which enables the exact satisfaction of the constraint conditions without the deficiency or redundant constraint. The energy and momentum conservation algorithm is applied to the proposed impact system. For the case of frictional impact, the linear momentum is exactly conserved and the angular momentum is approximately conserved with negligible error. Copyright (c) 2006 John Wiley & Sons, Ltd.

Once a membrane starts vibrating, suppressing the vibration is very difficult. Thus, the present study primarily aims at isolating a membrane from major disturbance sources, that is, from support structures. The present study introduces weblike suspension cables around a membrane and develops in theory a vibration-isolation strategy applied only along the cables. First, collocated small actuators/sensors are attached at the interfaces of the cables and the membrane to realize a distributed cable-tension control. Second, linear theory-based localized controllers are designed for suspension-cable substructural models. The feedback laws for these two kinds of controllers are derived employing a partitioned equation of motion. The resultant control system is lightweight, simple, low order, robust, and redundant. A series of transient analyses using a geometrically nonlinear finite-element method corroborates the effectiveness of the proposed vibration-isolation strategy.

This paper reviews conventional wrinkle models for anisotropic membrane and shows the relation between the models. A new wrinkle model is proposed which assumes virtual shear as well as virtual elongation of the membrane to estimate the real strain in the wrinkled region. This model coincides with the other models if the virtual shear and elongation is determined so that the strain energy is minimized. Another wrinkle/slack model is proposed for the dynamic analysis of thin isotropic membrane undergoing large overall motion with wrinkle and slack. It can take into account the residual compressive stress in the wrinkled and slack regions, i.e. the stiffness in the post-buckling state. It is shown that the proposed model is a generalization of the conventional ones. Finite element formulation of the proposed model is described. Furthermore, the energy momentum conservation framework is constructed for the proposed membrane element, which achieves the unconditionally stable time integration. The total of the proposed method enables us to compute the overall motion of thin isotropic membrane such as the deployment of folded membrane, which has been one of the most difficult problems in aerospace engineering. Copyright (c) 2005 John Wiley & Sons, Ltd.

This paper shows numerical analysis on dynamic deployment behaviors of membrane structure models embedding inflatable tubes. To treat their nonlinearity, one kind of nonlinear elasto-dynamic analysis methods characterized by modified stiffness matrix is applied. Analyzed models were proposed for future membrane structure systems inspired by insects' metamorphoses. In this paper, we focus on a balance between two kinds of deployment forces: centrifugal forces due to rotation of a central satellite and extension forces due to inflation of embedded tubes. We present numerical results of deployment behaviors of rectangular and hexagonal membrane models. Details of the numerical method are also discussed. Numerical results of the rectangular membrane model provide that there exist minimum values of maximum strain energy of membrane elements at appropriate gas filling time for each rotation rate. This means that we could control deployment behaviors by regulation of inflation rate of embedded tubes and rotation rate of a central satellite bus. Numerical results of the hexagonal membrane model provide that the case of deployment with gas injection shows more smooth deployment behavior without local deformation. In the case of deployment without gas injection there appears to be local deformation with high strain energy density. Copyright © 2006 by ASME.

The present study addresses vibration mitigation of membrane structures the boundaries of which are surrounded by weblike perimeter cables. This proposed membrane design realizes significant structural mass reduction when compared to the conventional catenary design. A key dynamic characteristic of the proposed structure is that support perturbations propagated into the outer perimeter cables have a minor effect on the vibration frequencies of the membrane. This property has been exploited in the development of vibration mitigation strategies using active control. This is corroborated by carrying out nonlinear transient analysis which accounts for the effect of wrinkles in the membrane. The results confirm that disturbances emanating from the support structures can be isolated by the outer perimeter cables while maintaining the interior membrane in a wrinkle-free taut condition. A simple active control law has been developed and applied to only the outer perimeter cables. Numerical simulations show that the combination of the web-cable girded membranes and the proposed vibration mitigation strategy can provide sufficient damping for both in-plane and out-of-plane vibrations.

A new concept of redundant space structures using multicellular inflatable elements is proposed, and the results of basic analyses on simple multicellular models are reported. Much effort has been devoted to methods for sufficiently hardening the inflatable elements in space to tolerate damage sustained from space debris, especially with respect to rigidization of a membrane; however, if the structures are redundant, they do not need to be as stiff and strong as those without redundancy. Deflections of two kinds of multicellular cantilever inflatable tubes are numerically investigated. First, nonrigidized tubes are analyzed by the modified Euler-Bernoulli beam theory. Second, rigidized tubes with slackening effects of the membrane are simulated using the modified nonlinear finite element method. The results show that multicellular tubes can be redundant against problems with pressurization and can be as stiff and as strong as monocellular models with less internal gas. In the multicellular rigidized inflatable tubes, maintaining a small amount of internal pressure is quite effective to prevent the deformation of the cross section, which causes a drop in stiffness and strength. Therefore, adopting a redundant system is effective both for rigidized and nonrigidized inflatable elements.

An analytical solution is presented for the spatially large deformation of a thin elastic rod (spatial elastica) which is naturally straight and uniform with equal principal stiffnesses and is subjected to terminal loads. The elastica can suffer not only flexure and torsion as in the classical Kirchhoff theory, but also extension and shear. The present solution is expressed in integral form and described in terms of only four parameters. This solution;clears the difficulty with-the polar singularity in the use of Euler angles. Hence, the numerical analysis is possible for various boundary value problems with no limitation. In this paper we study the post-buckling behavior of an elastica under the terminal twist and uniaxial end-shortening, and give a theoretical explanation to commonly observed phenomena such as secondary bifurcation, formation of a kink, snap-through behavior. The contact problem is analyzed in the case where the elastica contacts with itself and forms a kink. These results are available for other analysis, e.g., based on finite element approximations. (C) 1997 Elsevier Science Ltd.