This paper addresses simultaneous optimal design of adaptive truss structures, in which we compromise structural and control systems while taking into account structural layout, shape and control systems. The problem becomes nonconvex discrete optimization problem in terms of continuous and discrete design variables. Noticing that the nonconvex problem can be approximated by a convex one by adding a semidefinite positive function, so-called a convexifying function, to make the constraint convex, first, we solve this nonconvex problem using successive LMI optimization in cross-sectional area of truss members and state feedback gains. Second, we solve this discrete problem using genetic algorithm for simultaneous optimization of layout of truss structures. In this way, a hybrid method combining successive LMI optimization and genetic algorithm is used in this study. A numerical example of a simple structure is provided to demonstrate the effectiveness of the proposed method.
Effects of the asymmetric injectors on a compressible shear layer were investigated experimentally. The sine-, triangle- and square-waved splitter plates were used for the asymmetric injectors and the amplitude and wavelength of the splitter plates were varied. It was found that regardless of wave shapes, the growth rate increased by the asymmetric injectors. Increase in the amplitude led to increase in the growth rate and the maximum growth rate was gotten when the wavelength is equal to 11.5 or 15.3mm. The sine-wave gave maximum growth rate when other parameters were fixed. The vortex structures induced by asymmetric injectors were investigated by the numerical simulation. Although the complex vortex structures were induced in shear flow, the large-scale streamwise vortex structures, that is, the rib structures winding around the vortex cores were observed in the shear layer and caused time averaged streamwise vortex structure which increased growth rates. As a result, it was suggested that asymmetric injectors could induce the secondary instability of the double shear flow.
Influence of the ion slip effect on the MHD flow control of plasma flow around a blunt body is examined by means of two-dimensional numerical simulation. In order to understand the ion slip effect fundamentally, the calorically perfect gas model is adopted and it is assumed that the electron and ion Hall parameters can take any value and be distributed uniformly inside the bow shock. Numerical results confirm that the ion slip effect reduces the influences of MHD flow control. When the ion slip parameter βeβi becomes large, the electrical current density around the blunt body decreases in inverse proportion to the value of (1+βeβi). For the MHD interaction parameter with Q = 10, the maximum electrical current density with the ion slip effect (the electron Hall parameter βe = 10, the ion Hall parameter βi = 0.1) decreases by 44% in comparison with that of the case without ion slip effect (βe = 10, βi = 0).
The steady state of dipolar magnetic field expansion is examined by injecting a plasma jet from the center of the dipolar magnetic field (magnetic inflation). An effective magnetic inflation is essential for the realization of a magneto plasma sail (MPS), which produces a propulsive force by the interaction between the solar wind and an artificial dipolar magnetic field that is inflated by the plasma jet injected from the spacecraft. During the process of magnetic inflation, the finite Larmor radius effect is of practical significance since rL/LB is considerably greater than unity in a region far from the center of the dipolar magnetic field. The simulation result obtained using the ideal magnetohydrodynamics (MHD) model is overestimated, namely, it shows that the inflated magnetic field decays according to |B| ∝ r-2.0 since the magnetic field is frozen into the plasma jet. In comparison with the MHD result, the results obtained using the hybrid particle-in-cell code are more accurate. These results show that the inflated magnetic field decays according to |B| ∝ r-2.3 under the condition βin = 1 since the finite ion Larmor radius effect decreases the flow of magnetic flux with respect to the flow of plasma jet.
The present paper discusses a structural health monitoring method of CFRP structures based on a impact force identification. In the first part, an experimental identification method of impact force is developed where the relation between force histories and strain responses is determined experimentally. By employing this relation, the impact force is identified for CFRP laminated plates involving impact damages under a drop-weight impact test. It is shown that the identified force history agrees well with the experimental one even when the impact damage is induced. Next, the impact damage monitoring method is proposed. When the information on the maximum impact force is obtained, the occurrence of the impact damage can be predicted easily from the shape of force history, and the damage size can also be estimated using the experimental relation between the damage size and the maximum impact force. Thus, structural health can be evaluated automatically, by monitoring the impact force from the sensor response in real time, and great improvement of the structure safety becomes possible.
This study deals with co-planar orbital transfer of a satellite using a tether extension/retrieval mechanism. By controlling the pitch motion of the tether system, the designated velocity increment for the orbital transfer can be achieved at a prescribed position in orbit. First, this paper shows the governing equations of motion of the system by taking into consideration of the tether mass. Then, to achieve the specified tether length, pitch angle, and pitch angular rate at the designated position, this paper proposes two feedback control techniques to reduce the system's state errors: one for the pitch angular momentum error and the other for the pitch angle and pitch angular rate errors. Finally, numerical simulations demonstrate that the proposed methods can successfully achieve the designated states at the specified final position in the orbit.