Resonance scattering of sound by a small gaseous object of arbitrary form

The acoustic scattering amplitude for a dilute gaseous object of arbitrary form in a liquid medium is determined self-consistently for the case of linear dimension small as compared to the wavelength. A scatterer of bulk modulus β, and density p, in a medium of bulk modulus II and density p may exhibit monopole resonance scattering at a frequency w,= (4πβoC / pV)l, in which V is the volume and C is the capacitance in electrostatic units of a conducting replica of the scatterer. The criterion for occurrence of the resonance phenomenon is 3Fβo/β 1 is minimum for a sphere. Dipole scattering is given in terms of the polarizability dyadic of a nonconducting replica of dielectric constant p/po, and is negligibly small in a neighborhood of the resonance frequency.The Office of Naval Research under Contract Nonr-1367(00), NR 261-102

Inclusion of transverse shear deformation in the exact buckling and vibration analysis of composite plate assemblies

The problem considered is the development of the necessary plate stiffnesses for use in the general purpose program VICONOPT for buckling and vibration of composite plate assemblies. The required stiffnesses include the effects of transverse shear deformation and are for sinusoidal response along the plate length as required in VICONOPT. The method is based on the exact solution of the plate differential equations for a composite laminate having fully populated A, B, and D stiffness matrices which leads to an ordinary differential equation of tenth order

Exact methods for modal transient response analysis including feedback control

This paper presents a modal method for the analysis of controlled structural systems that retains the uncoupled nature of the classical transient response analysis of a structure subjected to a prescribed time-varying load. The control force is expanded as a Taylor series that remains on the right side of the equations, and it does not lead to a computational approach that requires coupling between modes on the left side. Retaining a sufficient number of terms in the series produces a solution to the modal equations that is accurate to machine precision. The approach is particularly attractive for large problems in which standard matrix exponential methods become computationally prohibitive. Numerical results are presented to show the accuracy and efficiency of the proposed approach for dynamic feedback compensation of a truss structure with local member modes in the controller bandwidth

Axisymmetric shell analysis of the space shuttle solid rocket booster field joint

The Space Shuttle Challenger (STS 51-L) accident led to an intense investigation of the structural behavior of the solid rocket booster (SRB) tang and clevis field joints. Results are presented of axisymmetric shell analyses that parametrically assess the structural behavior of SRB field joints subjected to quasi-steady-state internal pressure loading for both the original joint flown on mission STS 51-L and the redesigned joint flown for the first time after the STS 51-L accident on the Space Shuttle Discovery. Discussion of axisymmetric shell modeling issues and details is presented and a generic method for simulating contact between adjacent shells of revolution is described. Results are presented that identify the performance trends of the joints for a wide range of joint parameters. An important finding is that the redesigned joint exhibits significantly smaller O-ring gap changes and much less sensitivity to joint clearances than the original joint. For a wide range of joint parameters, the result presented indicate that the redesigned joint provides a much better pressure seal than the original joint

Experimental Observations of Aerodynamic and Heating Test on Insulating Heat Shields

Several different types of insulating heat shields have been subjected to aerodynamic tests and radiant-heating tests in order to obtain a better insight into the problems involved when the primary structure of m aerodynamically heated vehicle is substantially cooler than the exposed external surface. One of the main problems was considered to be a proper allowance for thermal expansion caused by these large temperature differences, so that undue distortion or thermal stresses would not occur in either the outer shield or the underlying structure. corrugated outer skin with suitably designed expansion joints was a feature of all the specimens tested

Bumpy Fruit of Papaya as Related to Boron Deficiency

Externally deformed papaya fruits with "bumpy" skin surfaces have been present in the papaya industry for many years. A relationship between bumpy fruit and boron deficiency has been established in other studies. Studies relating to boron have not been reported under the "rocky" Hawaiian soil conditions. Since studies on boron nutrition under Hawaiian soil conditions have not been reported, this study has two objectives. The first is to determine if there are differences in boron tissue levels between affected and unaffected trees under field conditions. The second is to determine the application rate of boron at which the milky exudate can be eliminated

A Preliminary Study of Pitch Inflection in the Speech of Preschool Children

Individual and group studies of the language development of children have largely centered about the meaningful content including vocabulary, the production of speech sounds, and growth in the use of the sentence. Practically no studies have been made of the expressive side of language development including pitch variation, vocal quality, accent and emphasis, and the temporal organization of the language units