Acoustical and Engineering Properties of Sediments


Book Description

As part of a program of in situ acoustical measurements in ocean sediments, an experimental investigation was started in order to examine the feasibility of measuring shear wave speed, shear wave attenuation, and bulk density by using instruments similar to the compressional wave profilometer developed previously. Measurements were made of the shear wave speed and attenuation in high porosity koalinite clay as the clay consolidated over a period of time. Experimential and theoretical investigation of the measurement of bulk density by acoustical means indicates that the radiation impedance of a driven piezoelectric ceramic transducer can be determined by measuring the electrical input to the transducer. Preliminary measurements of these parameters are reported. As an adjunct to the other measurements, physical properties of the sediments used in the laboratory measurements were determined and are reported.




Physics of Sound in Marine Sediments


Book Description

The phenomenon of sound transmissions through marine sediments is of extreme interest to both the United States civilian and Navy research communities. Both communities have conducted research within the field of this phenomenon approaching it from different perspectives. The academic research community has approached it as a technique for studying sedimentary and crustal structures of the ocean basins. The Navy research community has approached it as an additional variable in the predictability of sound trans mission through oceanic waters. In order to join these diverse talents, with the principal aim of bringing into sharp focus the state-of-the-science in the problems relating to the behavior of sound in marine sediments, the Office of Naval Research organized and sponsored an invited symposium on this subject. The papers published in this volume are the results of this symposium and mark the frontiers in the state-of-the-art. The symposia series were based on five research areas identified by ONR as being particularly suitable for critical review and for the appraisal of future research trends. These areas include: 1. Physics of Sound in Marine Sediments, 2. Physical and Engineering Properties of Deep-Sea Sediments, 3. The Role of Bottom Currents in Sea Floor Geological Processes, 4. Nephelometry and the Optical Properties of the Ocean I'laters, S. Natural Gases in Marine Sediments and Their Mode of Distribution. These five areas also form some of the research priorities of the ONR program in Marine Geology and Geophysics.




Deep-Sea Sediments


Book Description

As part of its continuing program to stimulate superior basic research in the marine environment, the Office of Naval Research, Ocean Science and Technology Division, sponsored a series of closed seminar-workshops in 1972-1973. Each seminar focused upon one re search area of marine geology which is relatively new and in need of a critical evaluation and accelerated support. The subjects areas chosen for the seminars were: 1. natural gases in marine sediments and their mode of distribution, 2. nephelometry and the optical properties of ocean waters, 3. physical and engineering properties of deep-sea sediments, and 4. physics of sound in marine sediments. The objectives of each seminar-workshop were to bring into sharper focus the state-of-the-science within each subject area, to effect some degree of coordination among the investigators working within each of these areas and to provide the Ocean Science and Technology Division guidance for national program support. This volume.contains most of the papers presented at the semi nar on the physical and engineering properties of deep-sea sediments. The seminar was held at Airlie House, Airlie, Virginia on April 24- 27, 1973 and was organized and chaired by A. Inderbitzen. The at tendees were invited from among the leading investigators in this field from both the engineering and scientific disciplines. Each attendee was requested to prepare a paper within his area of spe ciality.




Sediment Acoustics


Book Description

Sediment Acoustics describes the development of a mathematical model to be used to predict the propagation characteristics of acoustic waves in marine sediments. The model is based on the classical theory of Maurice Biot. Over the past 20 years, R.D. Stoll has published many technical papers covering various stages of development and different applications of Biot's theory. This work is summarized in one reference volume for the first time and presents enough introductory material so that researchers and students may use the model without extensive literature searches. Scientists working in the areas of acoustical oceanography, marine seismology, and ocean engineering will find this monograph useful in predicting the wave velocity and attenuation of seafloor sediments based on the geology of an area and such measurable physical properties as porosity and geostatic stress. A simple, interactive computer program is given as an aid in calculating velocity and attenuation, and a number of examples from recent field experiments are presented so that the predictions of the model may be compared with the "ground truth."




Studies of Sediment Shear Waves, Acoustical Impedance, and Engineering Properties


Book Description

Compressional wave speed and attenuation have been meausred in situ with the ARL/UT compressional wave profilometer. As an extension of this work, studies have been made of the feasibility of measuring shear wave speed and attenuation, as well as sediment bulk density in situ, using similar techniques. Various transducer configurations have been constructed and tested. Preliminary data have been measured using some of the transducers. Concurrent measurements of engineering properties enable comparisons to be made with acoustic properties. Instruments have been contructed to measure several sediment engineering parameters including Atterberg limits and vane shear strength.




Acoustical Properties of Sediments


Book Description

The work consisted of (1) final development of the ARL:UT profilometer recorder and transducer to enable the in situ measurement of compressional wave, shear wave, acoustic impedance, and static shear strength of ocean bottom sediments during geophysical coring, and (2) laboratory acoustical measurements on artificial sediments to test predictions of the Hovem model when the pore fluid viscosity is varied. The new profilometer recorder and transducer are described in detail as well as the microcomputer band playback system. Data obtained from the laboratory measurements are displayed.




Acoustic Properties of Sediments at Weapons Test Ranges of the Naval Undersea Warfare Engineering Station, Keyport, Washington


Book Description

Estimates are made of sound absorption and sound speed characteristics of sediments at the Dabob Bay and Keyport Shallow Water ranges operated by the Naval Undersea Warfare Engineering Station using empirical models developed by Hamilton and mean grain size and porosity data measured in samples collected by the authors. Data reported by earlier investigators permit estimates to be made also for sediments at the Nanoose and Jervis Inlet ranges. The purpose is to provide information which can be used in the design and evaluation of acoustic imaging devices which maybe able to ease the problems of locating and recovery of torpedoes which became buried in the sediments. Field and laboratory procedures are described. Also reported are the results of measured sound speeds in a number of the gravity core samples The most common surficial sediment is a soft, saturated silty-clay mud. For such sediments the sound absorption coefficient alpha in dB per meter should be given approximately by alpha = 0.1 where F is the sound frequency in kHz. It is concluded that sound absorption in these sediments, although not small, should not preclude the short range use of an acoustic imaging system operating at moderate frequencies. The possibility and the consequences of the existence of of gassy sediments is discussed.







Marine Research


Book Description




Acoustics of the Seabed as a Poroelastic Medium


Book Description

This book presents a concise description of the acoustics of ocean sediment acoustics, including the latest developments that address the discrepancies between theoretical models and experimental measurements. This work should be of interest to ocean acoustic engineers and physicists, as well as graduate students and course instructors. The seabed is neither a liquid nor a solid, but a fluid saturated porous material that obeys the wave equations of a poroelastic medium, which are significantly more complicated than the equations of either a liquid or a solid. This volume presents a model of seabed acoustics with input parameters that allow the model to cover a wide range of sediment types. The author includes example reflection and transmission curves which may be used as typical for a range of sediment types. The contents of this book will allow the reader to understand the physical processes involved in the reflection, propagation, and attenuation of sound and shear waves in ocean sediments and to model the acoustic properties for a wide range of applications.