The flow in the cross-flow separation of an axisymmetric paraboloid at 30, 40 and 50 deg angle of attack has been investigated experimentally by smoke visualization technique and hot wire anemometer. Reynolds numbers are 9.0×103 and 1.8×104 referred to the base diameter. Laser light sheet method is used in studying the structure of the vortices in cross-sectional flow. The development of streamwise vortices in each section of the body is visualized. X-type probe was used to measure three dimensional velocity fields over the axisymmetric paraboloid. Velocity fluctuations at sampling time of 4 kHz have been also evaluated. The extent of longitudinal vortices, such as main, primary-and secondary vortices, and the change of r.m.s. value in various cross-sections are presented. The variation of vortex patterns is shown for each cross-section, angle of attack and Reynolds numbers. It has been confirmed that each streamwise vortex is related to the velocity fluctuations.
This paper deals with the problem of dynamic stability of cross-ply laminated cylindrical shells subjected to static and periodic hydrostatic pressure. First, the axially symmetric motion of the shell under loading is determined. Subsequently, certain perturbations are superimposed on this motion, and their behavior in time is investigated. The symmetric state of motion of the shell is called stable if the perturbations remain bounded. The solutions for the prebuckling motion and the perurbated motion are obtained by the use of Galerkin's method. Stability regions are examined by utilizing Mathieu's equation. The inevitability of dynamically unstable behavior is proved analytically and the effects of various factors, such as fundamental natural frequency, amplitude of vibration and dynamic unstable mode, are clarified.
The inverse technique has been developed for the problem of force histories identification of point impact forces on orthotropic laminated plates. In a previous paper, the authors presented a simple method for identification of multiple impact forces acting on simply supported orthotropic laminated plates. The method utilized measured values of acceleration to predict point impact forces which resulted in the laminated plate response. This paper describes an attempt to extend the method to clamped orthotropic laminated plates and identify force histgries of point impact forces. In addition, this paper explores an iterative method to identify accurately force histories using a reduced number of measurement points. Several numerical examples are performed to ascertain effectiveness of the method to clamped laminated plates, the effect of the number of measurement points on the identification results for boundary conditions and validity of the iterative method.
The variable geometry trusses (VGTs) can purposefully vary their geometric configuration as well as their physical properties. The VGTs consist of repetition of a truss unit in which some of the truss members can vary their lengths continuously using actuators. In this paper, it is considered to obtain the global optimum geometry of twodimensional VGT of multiple units for maximizing structural stiffness against the external static load. Multi-degree of freedom of the VGT makes it difficult to obtain the global optimum geometry out of many local optima using the traditional gradient-based algorithms. To overcome this difficulty, we have proposed a tnneling method, which is one of the approaches for global optimization. From the result of numerical examples, the efficiency and reliability of the proposed method are discussed in comparison with the parametric results.