A wing rock is known to be a self-excited rolling oscillation of a delta wing that is induced by unsteady aerodynamic forces. In this study, free-to-roll simulations are carried out by incorporating time-accurate computational fluid dynamics with an equation of motion of a wing. A limit cycle oscillation and the histogram of a hysteresis in the rolling moment, which has four peaks within one cycle, are successfully simulated. The strength of the leading-edge vortices at a fixed roll angle is rather different from that during the wing rock especially at large angular velocities and that causes the characteristics behavior of the unsteady moments.
A study on rendezvous docking control of the HOPE is presented. The HOPE is the Japanese version of unmanned space shuttle, which requires the automatic rendezvous docking guidance algorithm. In this paper, the thruster combination algorithm is implemented by using linear programming (LP) method for minimum fuel consumption. The automatic guidance algorithms for three approaching phases are developed. The numerical simulation by these algorithms showed good result. The thruster combination algorithm by LP, the determination algorithm of the thruster firing timing by C-W-Hill’s equation, and the technique for implementing the simulation are explained in detail.
Detonation initiation in a liquid-fuel pulse detonation engine (PDE) was experimentally investigated. The PDE at Hiroshima University consisted of an initiator and a main combustor. The initiator was filled with liquid-fuel-oxygen mixture, and the main combustor was filled with liquid-fuel-air mixture. The experiments were carried out with varying the volume of the initiator and of the injected liquid-fuel-oxygen mixture. It was found that the predominant factor to initiate a detonation wave of liquid-fuel-air mixture was the volume of the overflowed liquid-fuel-oxygen mixture from the initiator into the main combustor. That is, we found that the minimum overflowed volume for the detonation initiation existed.
The behavior of drag and lift acting on a pair of circular cylinders arranged side by side near the critical Reynolds number were investigated in a low speed wind tunnel. When the gap between the cylinders is greater than about a cylinder diameter, the drag and lift of both cylinders are similar to each cylinder in variation respectively. The variations of drag and lift are similar to that of a single cylinder. The lift acts in the direction which two cylinders always repel each other. When the gap is smaller than about 1/2 diameters, the different variations of drag and lift between two cylinders are observed near the critical Re. When the gap is 1/4 diameters, one cylinder experiences negative lift and maximum drag near the critical Re. The negative lift is generated because the boundary layer transition occurs in the early stage on the surface of gap side of one cylinder compared with the outer side.
This study is concerned with an effective damage identification method for composite laminated plates with multiple site damage using a successive iteration method of bounding domain. First we use a flexibility method to determine the subdomains of composite laminated plate which contain damage areas. The subdomains are subdivided into smaller subdomains using a successive iteration method of bounding domain, and finally we determine the areas of the multiple site damage. In order to reduce computational time and number of design variables, we use the domain decomposition finite element technique to get frequencies and mode shapes of the whole domain by assembling subdomain frequencies and subdomain mode shapes. For a numerical example, the damage identification is conducted for a composite laminated plate with multiple site damage. As the result, it is revealed that the present damage identification method is effective and computationally efficient.
This paper presents a method of designing and keeping the approach trajectory for a space robot (chaser) flying around a troubled satellite (target) on a circular orbit around the earth. The approach trajectory is designed by considering orbital dynamics of the chaser represented by the Hill’s equation. The extended Kalman filter is employed to estimate state and control variables that are not available for measurement. An optimal feedback control scheme for the thrust is proposed to maintain trajectory in the presence of disturbances. Simulation results that verify the trajectory keeping capability of the proposed thrust control are also presented.
Ordinary displacement meter tracks the motion of specific points in a solid to give Lagrangian description of displacement. This paper proposes Eulerian type displacement meter which gives Eulerian description of displacement and shows that PC mouse, which is now an indispensable computer input device, is on its own an excellent Eulerian displacement meter. While in computer environments, mouse moves on the fixed pad and it measures its own movement, in this study, the movement of the object is measured by the mouse fixed in space. It is shown that the true strain is obtained by dividing the difference of the readings of two Eulerian meters by their separation distance. It can also give Lagrangian description if it tracks the target strip attached to the gauge point. Uniaxial tensile tests of rubber and membrane materials have been conducted and their elongation has been measured successfully by the present method.
Magnetic force acting on a model fixed at the center of the JAXA 60cm MSBS was measured with an industry manufactured balance system when MSBS control coil currents were varied. At the same time, magnetic field intensity was also measured with 11 Hall sensors, which were arranged around the MSBS test section. From relations between coil currents and its corresponding controlled magnetic forces, regressive curves were given and maximum deviation from the curves was evaluated. From relations between Hall sensor outputs and the magnetic forces, regressive curves and deviation were also obtained. Obtained results show Hall sensor outputs are much better indexes of balance than the coil currents. The maximum deviations were reduced to a half or one-third times as much as those evaluated using the control coil currents. However, when couples acting on the model are controlled, they are not effective to reduce hysteresis phenomenon in the relation. The deviation can be reduced by decreasing the range of calibration. Then, the error of the balance of the MSBS was reduced to about 1% of the calibration range.