Variable Stiffness Structure Research Articles

Curvilinear fiber optimization tools for aeroelastic design of composite wings

The aeroelastic design of composite wings modeled as thin-walled beams is investigated through the use of curvilinear fiber. The structural model considers non-classical effects such as transverse shear, warping restraint, rotary inertia, nonuniform torsional model and also aerodynamic loads based on Wagner's function. In this paper, a linear spanwise variation of the fiber orientation resulting in a variable-stiffness structure is used to optimize the wing for maximum aeroelastic instability speed purpose, while manufacturing constraints are incorporated. Numerical results indicate improvements of aeroelastic stability of variable-stiffness wings over conventional, constant-stiffness ones.

Generating realistic laminate fiber angle distributions for optimal variable stiffness laminates

The advent of advanced fiber placement technology has made it possible, through the use of fiber steering, to exploit the anisotropic properties of composite materials to a larger extent than was previously possible. Spatial variation of stiffness can be induced by steering composite fibers in curvilinear paths to give beneficial load and stiffness distribution patterns. Buckling of composite panels is one area where fiber steering has been proven to be very effective. Fiber angles and predefined fiber angle variations are used in most of the research on fiber steered composites reported in the literature, however, from an optimization point of view it is attractive to design such variable stiffness (VS) structures in terms of lamination parameters (LPs). This results in a two-step design approach. In the first step a VS composite is designed in terms of LPs, and in the second step the LPs are converted into fiber angle distributions for each layer in the laminate. A methodology is proposed to convert a known LP distribution for a VS composite laminate into a realistic design in terms of fiber angles, with minimum loss of structural performance, whilst satisfying a constraint on in-plane fiber angle curvature. The proposed conversion process is formulated as an optimization problem and can be used for any number of equi-thickness plies. The methodology was tested by converting a known optimal LP design for a sample structure, a square plate under bi-axial compression into a fiber angle design. The effect of the in-plane curvature constraint, the number of layers in the laminate, and the choice of objective function for the conversion process were studied for a balanced symmetric lay-up.

Pressurized artificial muscles

Pressurized artificial muscles are reviewed. These actuators consist of stiff reinforcing fibers surrounding an elastomeric bladder and operate using a pressurized internal fluid. The pressurized artificial muscles, known as McKibben actuators or flexible matrix composite actuators, can be applied to a wide array of applications, including prosthetics/orthotics, robots, morphing wing technologies, and variable stiffness structures. Analytical models for predicting the response behavior have used both virtual work methods and continuum mechanics. Various nonlinear control algorithms have been developed, including sliding mode control (SMC), adaptive control, neural networks, etc. In addition to traditional fluid-driving methods, innovative techniques such as chemical and electrical driving techniques are reviewed. With improved manufacturing techniques, the operational life of pressurized artificial muscles has been significantly extended, thus making them suitable for a vast range of potential applications.

Mechanical Properties Analysis of Combined Structure of Suspension Platform of Suspended Access Equipment

Based on the theory of structural mechanics, it has established that a simplified mechanical model of suspension platform of ZLP800 suspended access equipment (SAE) in this paper. Under the two common combinations we could calculate and comparatively analyse deflection of variable stiffness structure of suspension platform. On this basis, 15m span suspension platform module combination was obtained by the enumeration method. Moreover, by deflection calculations of the platform structure in different combinations，we could obtain the best module combination so as to provide a theoretical basis for the design of large span suspension platform.

Force Tracking Control of Fluidic Flexible Matrix Composite Variable Stiffness Structures

Active valve control is investigated for force tracking of fluidic flexible matrix composite (F2MC) variable stiffness structures through analytical and experimental studies. F2MC structures are based upon fluid-filled flexible matrix composite tubes, and previous investigations have shown that several orders of magnitude change in stiffness can theoretically be achieved by opening and closing the inlet valve to the tubes. In this article, a simple analytical model of the F2MC system is developed that captures the dynamics of the composite tube, the servovalve, and the flow of the fluid through the valve. A combined observer/ regulator control system is determined using linearized equations of motion and is applied to the non-linear system. Analysis and experimental results demonstrate that the F2MC system can track a desired force—displacement curve using active valve control.

307 剛性切替柔軟機構による可変剛性構造の最適設計(GS-12 設計工学)

307 剛性切替柔軟機構による可変剛性構造の最適設計(GS-12 設計工学)

Morphing skins

AbstractA review of morphing concepts with a strong focus on morphing skins is presented. Morphing technology on aircraft has found increased interest over the last decade because it is likely to enhance performance and efficiency over a wider range of flight conditions. For example, a radical change in configuration, i.e. wing geometry in flight may improve overall flight performance when cruise and dash are important considerations. Although many morphing aircraft concepts have been elaborated only a few deal with the problems relating to a smooth and continuous cover that simultaneously deforms and carries loads. It is found that anisotropic and variable stiffness structures offer potential for shape change and small area increase on aircraft wings. Concepts herein focus on those structures where primary loads are transmitted in the spanwise direction and a morphing function is achieved via chordwise flexibility. To meet desirable shape changes, stiffnesses can either be tailored or actively controlled to guarantee flexibility in the chordwise (or spanwise) direction with tailored actuation forces. Hence, corrugated structures, segmented structures, reinforced elastomers or flexible matrix composite tubes embedded in a low modulus membrane are all possible structures for morphing skins. For large wing area changes a particularly attractive solution could adopt deployable structures as no internal stresses are generated when their surface area is increased.

Vibration Control of Variable Rigidity Frame Structure by Magnetic Clutch

There are many studies on base isolation and seismic isolation of structures. In order to clarify experimentally, the efficiency of variable stiffness control that has been considered using numerical simulation, a variable stiffness structure using a clutch system was made. A simple on-off control with a clutch mechanism of a variable stiffness structure to the magnitudes of acceleration has been proposed. This control method was examined in the research.Using this method, when the vibration acceleration amplitude is large, the clutch is connected to the additional structure saving potential energy in the additional structure, and when the vibration acceleration amplitude decreases, the clutch is disconnected from the additional structure releasing the potential energy at once and attenuating the displacement amplitude of vibration, so that the vibration can be decreased effectively.

Design of variable-stiffness conical shells for maximum fundamental eigenfrequency

Fiber-reinforced composite conical shells with given geometry and material properties are optimized for maximum fundamental frequency. The shells are assumed to be built using an advanced tow-placement machine, which allows in-plane steering of the fibers, resulting in a variable-stiffness structure. In this paper, different path definitions for variable-stiffness shells are provided and used to optimize conical shells for maximum fundamental frequency, while manufacturing constraints that apply for tow placement are taken into account in the process. The influence of manufacturing constraints on the performance is shown; and improvements of variable-stiffness conical shells over conventional, constant-stiffness shells are demonstrated.

Optimal Semi-active Control and Non-linear Dynamic Response of Variable Stiffness Structures

In this paper we study the semi-active control of structural systems by means of variable stiffness devices, and the resulting non-linear dynamics of the controlled system. In particular, the study is applied to base-excited single-degree-of-freedom systems, controlled by variable ON–OFF elastic devices and subjected to simple motion conditions: free vibrations following initial conditions and stationary response to harmonic input. A performance index, which, in the case of base-excited structures, assumes an original dual formulation following the relative or absolute approaches, has been proposed for instantaneous optimal control. The study includes both the optimal control design and the observation of the resulting non-linear dynamics of the controlled system. The dynamic behavior of the controlled non-linear system is studied with respect to the parameters which characterize the algorithms, the control device, and the input. In this way, also by means of significant (and original) analytical solutions of the equations of motion, the optimal formulation of the algorithms, some particular behaviors of the controlled systems, and the performances of the control approach are shown and explained for the different control strategies.

414 ソフトニング可変剛性構造体の最適設計(GS-12 設計工学,研究発表講演)

414 ソフトニング可変剛性構造体の最適設計(GS-12 設計工学,研究発表講演)

Response Control of Variable Stiffness Structure Using Electromagnetic Clutch

Vibration control method of a variable stiffness structure using an electromagnetic clutch is shown. The control effect is predicted by numerical simulation. On the basis of this result, an experiment is carried out using an actual apparatus to confirm the effect of the variable stiffness structure using the electromagnetic clutch.

Conceptual design and dynamics modeling of a cooperative dual-arm cam-lock manipulator

SUMMARYThis paper presents the conceptual designs, kinematics and dynamics modeling of a cooperative re-configurable Dual-Arm Cam-Lock Manipulator. A cam-lock manipulator is a robotics structure with a pair of multi-degree of freedom planar arms jointed together at a shared base. This manipulator is designed to be capable of performing a wide variety of tasks by automatically re-configuring itself to form a variable geometry, stiffness, damping, and workspace robotics structure by the virtue of a novel link/joint design along i''s arms, labeled as the cam-lock design. The kinematics and dynamics of this manipulator is described using admissible variables (i.e., variables that define the constrained admissible motion). Along with the dynamic relations of this manipulator, a generic equation was also developed for the joint servo system.

Control algorithm for estimating future responses of active variable stiffness structure : K. Yamada & T. Kobori, Earthquake Engineering & Structural Dynamics, 24(8), 1995, pp 1085–1099

Control algorithm for estimating future responses of active variable stiffness structure : K. Yamada & T. Kobori, Earthquake Engineering & Structural Dynamics, 24(8), 1995, pp 1085–1099

Control algorithm for estimating future responses of active variable stiffness structure

AbstractA control algorithm has been developed for controlling Active Variable Stiffness (AVS) structures. This algorithm analyses information of an observed seismic excitation, estimates the future structural responses and determines how to alter the structure stiffness. An objective structure is assumed to possess N on‐off elements whose states are controlled by the proposed algorithm. That is, at a given moment tk, (1) seismic excitation information is expressed by an Auto Regressive (AR) model as the identification model; (2) future excitation information is predicted using the AR model; (3) future responses due to predicted excitation are estimated; (4) based on the initial condition at tk, the responses of 2N possible structural states from tk, to tk+L are calculated; (5) the state which minimizes the input energy during tL is selected; and (6) immediately after tk, on‐off elements are set up and subjected to the selected states. The effectiveness of the induced algorithm is confirmed by numerical experiments on a model of a three‐storey building under sine and seismic excitations.