Search

This paper traces the development of Ambiguity Function Analysis as applied to underwater acoustic signal processing. Based on Woodward's time-frequency correlation function (Woodward, 1953) the dependence of range and Doppler resolution is illustrated for a number of signal waveforms in a white noise background. The effect of unwanted signals (clutter) and noise on the ambiguity function is discussed in detail. An approach to the solution of the more difficult problem of ambiguity function synthesis is suggested.

Resistance to penetration of water is an important requirement for materials used in hydrospace application. In this paper the effects of hydrostatic pressure on the permeability and swelling of elastomers and plastics, and correlations between swelling and permeability are discussed from the theoretical and practical points of view. It is shown that hydrostatic pressure can have various effects on the permeability of polymeric materials to water and other permeants, depending on the exposure conditions and the permeation mechanism. On one hand a decrease in permeability with increasing hydrostatic pressure was observed for butyl rubber exposed to pressurized water on the upstream side and to an environment of low water vapour pressure on the downsteam side. Other materials such as polyethylene, polyurethane and nylon exhibited either a similar decrease or no change in permeability with increasing hydrostatic pressure. On the other hand it is well known that water flow through porous materials, and through non-porous materials used for desalination processes, such as cellulose acetate, increases considerably with increasing hydrostatic pressure. These differences in behaviour, and more complicated correlations, are explained on the basis of thermodynamic considerations. It is also shown that hydrostatic pressure does not increase the swelling of rubbers exposed in the ocean and that there is no simple correlation between swelling and permeability. The reasons for this are discussed. From the practical point of view it follows that: 1. 1. Exposure of hydrophones to great depth will not aggravate those problems which are caused by water permeation through their rubber boots. 2. 2. Materials intended in applications where imperviousness is important cannot be chosen on the basis of swelling tests. 3. 3. In order to predict the extent of water penetration through a barrier material, knowledge of the mechanism of permeation and the exposure conditions is necessary.

INTRODUCTION INOR6ANIC, non-metallic materials have found applications in marine structures for many years. Some of these materials have outstanding resistance to deterioration in the sea and are transparent. Silica-glass windows are standard items in the periscopes of submarines. Some of these materials are extremely resistant to compression stresses and are sufficiently rigid to offer high resistance to elastic buckling in thin shells under external pressure. Light-bulbs are surprisingly resistant to external pressure. Also some have low specific gravities. Hollow glass spheres are furnishing buoyancy in deep oceanography at modest cost. A number of improvements are being made in glasses and ceramics, and in their processes that improve their tensile strength, bending strength, resistance to impact and resistance to stress--corrosion cracking. Also, in the last five years, there has been a great increase in efforts to use these materials in sophisticated marine applications, such as in capsules for manned vehicles and for moored habitats, for deep submergence. The incentive is to exploit the favourable trade-offs of structures made of these materials with regard to allowable depths, buoyancy, durability and cost. These efforts on the development of materials and on their deep submergence uses are intimately conected. It has become evident that the latter goal can be attained more effectively by accelerating and exploiting the former. The purpose of this paper is to summarize advances being made in these related fields.

The Annapolis Laboratory of the Naval Ship Research and Development Center has installed an ocean pressure laboratory to simulate the effects of the ocean environment on machinery components for deep diving submersibles and bottom-operating equipments. The heart of the complex is a unique 10ft diameter test tank having a static pressure capability of 12,000psi and a cyclic capability of 4000psi (rate of 1 cycle/minute) for 2 × 106 cycles. The paper presents some highlights of the design, fabrication and acceptance testing of the large tank including the metallurgical problems associated with the use of HY-100 forgings.

This paper presents an overview of the present state of technology for reinforced plastic materials related to the ocean engineering field. Typical marine applications are described. Information and references are presented on fabrication and properties of high-strength, filament-wound plastic materials, pertinent to deep-depth pressure hull and bouyancy applications. Problem areas are discussed and future composite material improvements are projected. Much of the data presented has been developed through an extensive R & D programme sponsored by the Naval Ship Systems Command.

With the recent development of techniques for hatching, feeding, and maintaining large quantities of barnacle larvae under controlled laboratory conditions, a wide variety of studies relating to fouling and antifouling problems are now possible. In this paper, investigations currently under way at the Naval Applied Science Laboratory and the Osborn Laboratories of Marine Sciences, New York Aquarium, are discussed. These include a new bioassay approach for evaluating toxic coatings, a discussion of some factors that may influence marine fouling, and a programme of research on the adhesive substances produced by metamorphosed and growing barnacles and by barnacle larvae.

Based on extensive experiments with a number of different body shapes in clay-water mixtures, the drag formulation of Eq. 4 for Bingham plastic materials has been verified. Thus the occurrence of a yield stress is such as to increase the drag coefficient of a body shape above that experienced in Newtonian fluid flow (at a corresponding Reynolds number) by an amount proportional to τ y /ϱV 2 . The increase can be quite considerable, as indicated in Figs. 1 and 3. Furthermore, as apparent from Fig. 2, the non-Newtonian fluid effect is larger for bodies of blunt cross-sectional shape. Thus a body of extreme bluntness (the disc) undergoes a drag increase over two and a half times that experienced by an f = 4 ellipsoid. As a cylindrical body (placed normal to the flow) a strut could thus be expected to suffer a drag increase due to yield stress appreciably larger than that of a circular member. The drag results indicated here have heretofore not be available. They show that, for bodies or structures in relative motion with non-Newtonian fluids, forces can arise which are greatly in excess of those to be expected for conventional fluids. Since near-bottom materials are likely to be non-Newtonian in character—thus clay-water mixtures behave as Bingham plastics—these considerations are significant for near-bottom ocean and off-shore work. Although the basic research (Pazwash, 1970) supporting the paper was extensive, much still remains to be learned on this matter and many unanswered questions are evident.