A bubble collapse phenomenon in water is photographically investigated using a high-speed framing camera (200, 000 frames/sec).The bubble was generated by focusing the beam of a pulsed ruby laser (22 nsec, 0.88 J, 40MW). It was found that the total collapse time of the bubble (initially 2.5mm in radius) is about 200 μsec, providing a reasonably good agreement with the collapse time 227 μsec obtained through the RAYLEIGH's analytical solution.
Usable range of reduced frequency are investigated for some of representative unsteady numerical lifting surface theories. They are three current methods and one new method developed in this paper. The former three methods, containing two doublet lattice methods and DAVIES' method, reveal their own defects. The proposed method consists of asymptotic expansion of the kernel function and appropriate treatment of the singularities. A whole lifting surface is divided into many chordwise strips, through a spanwise Semi-Circle-Method (SCM). A special care is taken for the "singular strip" in which the control point is contained. It is found that the present method improves remarkably defects of the above three methods.
In this paper the elastoplastic analysis of uniform bars with initial deflection under opposite tension loads at the center of both ends is presented. It was found that the problem is too complicated to examine fundamental aspects of behavior of such bars, because of the transcendental implicit result from the strict solution, the derivation of which is described in Appendix. Whereas the column problems under axial compressive load have been investigated by many researchers, in those cases an approximate method where the equilibrium is considered only at the midpoint of the bar, contributed considerably to clarify the features of the problem with sufficient accuracy. We applied the same approximate approach to get the solution showing clearly the behavior of uniform bars initially curved and subjected to opposite tension loads at both ends. It is remarkable that in cases where the initial deflection and the slenderness ratio are restricted in some limit, only one side of bars becomes plastic before the entire cross-section reaches the ultimate state of uniform tensile stress along the total length of the bars, although the change of stress distribution is rather complicated These cases are treated in this report. The remaining cases where both sides of bars become plastic and consequently the unloading in the plastic region must be considered, will be reported in the forthcoming papers.
On the basis of the preceding paper, the authors construct a simplified model of cylindrical shells under axial step loading and analyze its behavior by an energy approach. This model uses only linear springs, each of which provides for one corresponding mechanical property a simple and clear representation which is not available from the customary nonlinear spring models.
A probabilistic approach is used in investigating the dynamic response of cylindrical shells with general imperfections to axial compressive step loading. Assuming initial imperfections in the form of a white noise of zero mean and normal distribution, the problem is formulated on the basis of linear shell theory and solved for simply supported and clamped boundary conditions. The spatial stationarity property of the deformation is verified through analytical and numerical calculations, and the behavior of the shells just after application of the loading and the effect of boundary conditions are shown.
In general, the laminated composite structures exhibit the coupling effect due to the anisotropy and the unsymmetric lamination. In the present paper, such coupling effects on the buckling stresses in the cross-ply and angle-ply laminated cylindrical shells subjected to axial compression are considered. That is, the effects of stacking sequence, number of lamination, boundary conditions and buckling modes on the buckling stresses are analysed by use of the equilibrium equation or of the energy method based on the DONNELL-type expressions. The analytical predictions are verified by carrying out the buckling experiments on the thirteen kinds of carbon-fiber/epoxy (CFRP) laminated cylinders. The experiments show a good agreement with the analytical results. It is found that the coupling effects of laminates rapidly die out as the number of layers, N, increases and the buckling stresses become close to higher values for homogeneous orthotropic cylinders. The buckling stresses in antisymmetric laminates with N=2 are especially much decreased.