Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Mechanical and Aerospace Engineering." Includes bibliographical references (p. 141-147).

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (January 23, 2007) Includes bibliographical references.

The large ductile deformation response of stiffened plates subjected to blast loads is investigated and simplified methods of analysis of such response are developed. Simplification is derived from modelling stiffened plates as singly symmetric beams or as grillages thereof. These beams are further assumed to behave in a rigid, perfectly plastic manner and to have piecewise linear bending moment-axial force capacity interaction relations, otherwise known as yield curves. A blast loaded, one-way stiffened plate is modelled as a singly symmetric beam comprised of one stiffener and its tributary plating, and subjected to a uniformly distributed line load. For a stiffened plate having edges fully restrained against rotations and translations, both transverse and in-plane, use of the piecewise linear yield curve divides the response of the beam model into two distinct phases: an initial small displacement phase wherein the beam responds as a plastic hinge mechanism, and a final large displacement phase wherein the beam responds as a plastic string. If the line load is restricted to be a blast-type pulse, such response is governed by linear differential equations and so may be solved in closed form. Examples of a one-way stiffened plate subjected to various blast-type pulses demonstrate good agreement between the present rigid-plastic formulation and elastic-plastic beam finite element and finite strip solutions. The response of a one-way stiffened plate is alternatively analysed by approximating it as a sequence of instantaneous mode responses. An instantaneous mode is analogous to a normal mode of linear vibration, but because of system nonlinearity exists for only the instant and deformed configuration considered. The instantaneous mode shapes are determined by an extremum principle which maximizes the rate of change of the stiffened plate's kinetic energy. This approximate rigid-plastic response is not solved in closed form but rather by a semi-analytical time-stepping algorithm. Instantaneous mode solutions compare very well with the closed-form results. The instantaneous mode analysis is extended to the case of two-way stiffened plates, which are modelled by grillages of singly symmetric beams. For two examples of blast loaded two-way stiffened plates, instantaneous mode solutions are compared to results from super finite element analyses. In one of these examples the comparison between analyses is extremely good; in the other, although the magnitudes of displacement response differ between the analyses, the predicted durations and mechanisms of response are in agreement. Incomplete fixity of a stiffened plate's edges is accounted for in the beam and grillage models by way of rigid-plastic links connecting the beams to their rigid supports. Like the beams, these links are assumed to have piecewise linear yield curves, but with reduced bending moment and axial force capacities. The instantaneous mode solution is modified accordingly, and its results again compare well with those of beam finite element analyses. Modifications to the closed-form and instantaneous mode solutions to account for strain rate sensitivity of the panel material are presented. In the closed-form solution, such modification takes the form of an effective dynamic yield stress to be used throughout the rigid-plastic analysis. In the time-stepping instantaneous mode solution, a dynamic yield stress is calculated at each time step and used within that time step only. With these modifications in place, the responses of rate-sensitive one-way stiffened plates predicted by the present analyses once again compare well with finite element and finite strip solutions. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

In this investigation a method is suggested for determining the dynamic, elastic response of a thin hemispherical shell subjected to a head-on attack by the initial shock wave of an underwater explosion. The shell which is fastened to the end of a fixed, semi-infinite tube of the same radius is surrounded by a high density fluid similar to water, and the internal cavity of the shell is filled with a low density fluid similar to air. The initial shock wave moves through the high density fluid. In the neighborhood of the obstacle, the shock front propagates in the direction of the axis of the semi-infinite tube and makes initial contact with the obstruction at the tip of the hemisphere at time equal to 0+. The following basic assumptions are used to define the mathematical model for the physical problem. The shock wave is considered to be a plane pressure pulse with exponential decay, the surrounding fluid is treated as if it were an acoustic medium, and the low density fluid is assumed to exert a constant pressure over the interior surface of the shell. The thin, hemispherical shell is regarded as being constructed of an isotropic, homogeneous, Hookean material of constant thickness. This shell experiences only small displacements. Moreover, in this model, the hemispherical shell is attached to a rigid, semi-infinite tube in such a way that the normal and in-plane displacements of the middle surface of the shell and the slope of the middle surface of the shell in the longitudinal direction are all zero at the shell-tube connection. The investigation for the solution to this axisymmetric problem, in which the mathematical formulations on the displacements of the shell and the velocity potential of the fluid are coupled, is begun with the separation of the displacements of the middle surface of the shell into two parts, ( )_M and ( )_B displacements. These are then shown to be analogous to the "membrane" and "pure bending" displacements familiar in the theory of static shells. The governing equations and the determinative conditions for the ( )_M displacements are found to be independent of the ( )_B displacements, while in the ( )_B formulation the ( )_M displacements are found to appear only in the determinative conditions. An approximate solution which is valid for small time and in which Poisson's ratio and the in-plane inertia term are assumed to be zero is obtained for the ( )_M displacements. A complementary solution for the ( )_B displacements which is valid in the neighborhood of the shell-tube connection is determined by using geometric and kinematic approximations in the ( )_B formulation. Approximate solutions for the displacements of the middle surface of the shell are then formulated by combining the ( )_M and ( )_B expressions above with the assumptions (valid only for the stated small time range) that the ( )_B contribution to the in-plane displacement is negligible over the entire shell and that the ( )_B contribution to the normal displacement is negligible except in the region near the shell-tube connection. Numerical results are calculated for a steel shell immersed in sea water and these results are presented in the form of tables and plots. / Ph. D.

The blast loading on a structure is a function of the incident blast wave characteristics, that is, overpressure and dynamic pressure. But the most damaging effect to the guy cable from a nuclear explosion would be the dynamic pressure caused by the high winds which follow the chock front. This dynamic pressure reaches its maximum value very rapidly, almost zero time after the passage of the shock front, and then decays exponentially as shown by equation (17). The work of this thesis has been the investigation of a guy cable under blast loading by correcting the tension during each small time interval. The results from this procedure are considerably smaller than those in the analytical work of Mr. D. A. Ball. From this point of view, we know that the tension of the cable in such a problem can not be considered as constant. / Master of Science

Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004. / Includes bibliographical references (leaves 73-76). / The recent trend of using fine water mist systems to replace the legacy HALON- 1301 fire suppression systems warrants further study into other applications of the water mist systems. Preliminary research and investigation indicates that fine mists (20-25 pm droplet size) may reduce peak overpressures of a shock wave traveling through a space. Such pressure reductions could be used to mitigate the destructive effects of a shock wave (initiated by an explosive device) traveling through a structure. Currently these blast mitigation effects have only been demonstrated in small-scale shock tube tests and computer simulations. Uncertainty exists as to the scalability of such a system. The intention of this research is to investigate the applicability of such a blast mitigation system for shipboard use. Study into the degree of mitigation necessary to make a system practical for shipboard installation was conducted. In addition, a theoretical study of the mechanisms of blast mitigation using water mists was completed. Preliminary design of a full-scale system was examined. / (cont.) Given the recent trend toward tumblehome hull forms in future Naval Combatant designs, there exists strong applicability of this system in the "dead" spaces created by the shaping of the tumblehome hull. Further work is needed in numerical modeling and laboratory testing of specific phases of the mitigation. The end goal is a feasible design of a blast mitigation system to be used in the outermost spaces of Naval Combatants to protect interior vital system spaces. / by Julie A. Kitchenka. / S.M. / Nav.E.

The Australian Maritime Engineering Cooperative Research Centre, and its partner organisation initiated this research effort. In particular, BHP and the Defence Science and Technology Organisation held the principal interest, as this research effort was a part of the investigation into the utilisation of X-80 steel in naval platforms. After some initial considerations, this research effort focussed on the development of X-80 steel blast tolerant transverse bulkheads. Unfortunately, due to the Australian Maritime Engineering Cooperative Research Centre not being re-funded after June 2000 and other project factors, the planned blast tests were not conducted, hence this research effort focussed on the tools needed for the formation of optimised blast tolerant transverse bulkheads rather than on the development of a single structural arrangement. Design criteria were formed from the worst case operational requirements for a transverse bulkhead, which would experience a 150 kg equivalent blast load at 8 m from the source. Since the development of any optimised blast tolerant structure had to be carried out using finite element analysis, material constants for X-80 steel under high strain rates were obtained. These material constants were implemented in the finite element analysis and the appropriate solid element size was evolved. The behaviour and effects of stress waves and high strain rates were considered and the literature reviewed, in particular consideration was given to joint structures and weld areas effects on the entire structural response to a blast load. Furthermore, to support the design criteria, rupture prediction and determination methodologies have been investigated and recommendations developed about their relevance. Since the response of transverse bulkheads is significantly affected by their joint and stiffener arrangements, separate investigations of these structures were undertaken. The outcomes of these investigations led to improvements in the blast tolerance behaviour of joints and stiffeners, which also improved the overall response of the transverse bulkhead to air blast loads. Finally, an optimisation procedure was developed that met all the design criteria and its relevant requirements. This optimisation procedure was implemented with the available data, to show the potential to develop optimised X-80 steel blast tolerant transverse bulkheads. Due to the constraints mentioned above the optimisation procedure was restricted, but did show progression towards more effective blast tolerant transverse bulkhead designs. Factors, such as double skin bulkheads, maximising plate separation, and the use of higher yield steel all showed to be beneficial in the development of optimal X-80 steel blast tolerant transverse bulkheads, when compared to the ANZACclass D-36 steel transverse bulkheads.

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