Undesired Waves Research Articles

Documentation of damping capacity of metallic, ceramic and metal-matrix composite materials

High-damping materials allow undesirable mechanical vibration and wave propagation to be passively suppressed. This proves valuable in the control of noise and the enhancement of vehicle and instrument stability. Accordingly, metallurgists are continually working toward the development of high-damping metals (hidamets) and high-damping metal-matrix composites (MMCs). MMCs become particularly attractive in weight-critical applications when the matrix and reinforcement phases are combined to provide high-damping and low-density characteristics. In selecting the constituents for an MMC, one would like to have damping capacity data for several prospective component materials. Based upon data which have been published in the scientific literature, a concise documentation is given of the damping capacity of materials by three categories: (a) metals and alloys, (b) ceramic materials, and (c) MMCs.

Performance of the star-shaped flyer in the study of brittle materials: Three dimensional computer simulations and experimental observations

A three dimensional finite element computer simulation has been performed to assess the effects of release waves in normal impact soft-recovery experiments when a star-shaped flyer plate is used. Their effects on the monitored velocity-time profiles have been identified and their implications in the interpretation of wave spreading and spall signal events highlighted. The calculation shows that the star-shaped flyer plate indeed minimizes the magnitude of edge effects. The major perturbation to the one-dimensional response within the central region of the target plate results from spherical waves emanating from the corners of the star-shaped plate. Experimental evidence of the development of a damage ring located in coincidence with the eight entrant corners of the flyer plate is reported. Microscopy studies performed in the intact recovered samples revealed that this damage ring eliminates undesired boundary release waves within the central region of the specimen. Consequently, the observed damage in compression and tension within this region can be attributed primarily to the conditions arising from a state of uniaxial strain.

PSEUDOREFLECTION PROFILING METHOD: AN EFFICIENT COMPLEMENT TO CDP METHOD1

AbstractA method for pseudoreflection profiling (PRP) is presented. By using transmission seismograms, this method produces time sections similar to those obtained using the common depth point (CDP) method.Pseudoreflection profiles are obtained using the following procedure. Equivalent transmission responses at sites on soft deposits are derived by Wiener filter estimation using seismograms acquired on the sites and on the basement rock. These responses are substituted into the Claerbout‐Kunetz equation to obtain the pseudoreflection profiles.A 3D subsurface model is produced when the PRP method is applied to explosion seismograms. The time sections thus obtained are consistent with those obtained using the CDP method in a neighbouring area. The maximum station interval for obtaining coherent profiles with this method is estimated to be one quarter of the wavelength of the transmitted waves.This technique should be used in combination with another method such as the CDP method because it has two weak points: the velocity structure cannot be obtained directly and undesirable waves cannot be eliminated through processing.

Null beam forming by phase control of selected elements in phased-array antennas

In phased-array antennas, nulls of the radiation pattern can be formed in the direction of undesired wave by controlling only the phase excitation without affecting the main beam. However, the computation time becomes very large when an antenna with a large number of elements is analyzed and it becomes very difficult to counteract the variation of wave boundary instantly. Here, based on the exact calculation of phase value by the method of plane-wave synthesis, the foremen-tioned elements are selected which contribute more to the null formation, and the method of controlling only the phase of the selected elements is presented. Using this method, the computation time can be reduced. Moreover, the depth of nulls and the gain of the main beam obtained in this way is the same as that produced by controlling the phase of all the antenna elements. As a result of numerical simulation and experiments of null forming in the phased-array antenna using a 5-bit phase shifter, deep nulls with the level of less than -40 dB could be formed without decreasing the gain of the main beam.

On the numerical dispersion relation of equatorial waves

Numerical dispersion relations for equatorial wave modes are computed two ways: from equations for the pressure, p, and for the meridional velocity, v. These are compared with both the continuous and the analytic finite difference dispersion relations for the u‐v‐p system of equations on an Arakawa C‐grid derived by D. W. Moore (personal communication, 1990). For a particular meridional wave structure and grid resolution, the dispersion relation is approximated more accurately via the finite‐difference form of the v‐equation than by either the p‐equation or the u‐v‐p system. However, the finite difference v‐equation possesses an undesirable wave solution which has unbounded u and p, and it also lacks the equatorial Kelvin wave. On the other hand, the p‐equation, is found to possess additional numerical solutions due to the conversion of the apparent singularities of the continuous equation at the inertial latitudes (yil = ±σ/β) into regular singularities of the discrete equation due to numerical truncation. These additional solutions are well separated in dispersion space from the equatorial ones except at selected frequencies. The frequencies at which the wavelengths of these additional solutions to the p‐equation approach the continuous dispersion relations are found to be sensitive to the distance from the inertial latitude to the nearest gridpoint.

Systems theory and the active control of duct noise

The behavior of an acoustical system may be represented using either a transfer function or impulse response. This representation enables an electrical model of the acoustical system to be created. The output of this model may be used to drive an acoustical source and produce a secondary wave to cancel an undesired primary wave. A system identification process generates the required model using an adaptive parameter estimation scheme. A variety of alternatives are available for the model structure as well as the parameter estimation scheme. These include a finite impulse response (FIR) or infinite impulse response (IIR) digital filter with parameters obtained using a least‐mean‐square (LMS) or recursive least‐mean‐square (RLMS) adaptive algorithm, respectively. Since the process is one of adaptive control, the filtered‐X or filtered‐U algorithm can be used to compensate for various transfer functions, identified on an off‐line or on‐line basis, following the adaptive model. Results will be presented from ...

Single element cantilever mounted shear wave transducer

A single element cantilever mounted shear wave transducer which takes advantage of the transverse vibration of a piezoceramic bimorph element mounted as a cantilever on a heavy slug. A gasket material between the slug and an inner holding tube assists in avoiding the propagation of undesirable compressional wave energy into transmission medium surrounding the transducer. Electrical isolation is achieved by wrapping the inner tube with a ground shield to which the ground wire is attached. A second layer of gasket material between the inner and an outer tube further inhibits the propagation of compressional wave energy into the transmission medium. A flexible potting compound seals the open end of the tubes including the bimorph element and serves as the active face of the transducer.

400 MHz SAW IF Filter for Satellite Broadcast Receiver without Any Adjustments

A UHF SAW filter for satellite broadcast receivers has been developed. Features are high center frequency to suppress the image interference, sufficiently flat group delay for linear FM detection and unnecessary any adjustments for tuning. The influence of electrode resistance on the insertion loss, and the triple transit echo caused by wave reflection is investigated in extended Smith's equivalent circuit model, and is effectively applied as an independent design parameter of the radiation and the load conductance. In cosequence the interdigital transducers with the wide aperture stretched nonoverlapped electrodes are efficiently verified to suppress undesired surface wave diffraction and reflection effects without any increase in the insertion loss, and to be able to omit the conventional tuning coils and the intentional impedance mismatching.

New Miniaturized SAW Device in Low Frequency Range for SAW Video DOC System in Home VTR

A new dropout compensation method called the SAW video DOC system has been developed, corresponding to the stream of high density magnetic recording. The purpose is to improve the signal-to-noise ratio and the characteristic of dropout compensation for the palyback signal in home video tape recorders. A wide band SAW device in low frequency range of the key device in the system is miniaturized and practically can-packaged by newly developed techniques: the reduction of finger pairs, new ultraviolet curable polymeric resin and suppression of undesired wave response. In consequence, almost complete dropout compensatin and improvement of the 2.5 dB signal-to-noise ratio can be achieved in a playback video signal.

Acoustic member mounting means for use in typewriters

First Page

Method for identifying weak sands

A method and apparatus for obtaining improved measurements of shear waves in low-velocity lossy formations surrounding a borehole. The method comprises forming an interface between the borehole wall and a solid homogeneous material having a lower velocity than the formation. The geometry and velocity of the homogeneous material provide enhancement of the shear waves at the interface and thereby minimize the effect of interference from undesired compressional waves. Further improvement is obtained by using shear waves whose particles move perpendicular to the travel of the wave, parallel to the plane of the waves and perpendicular to the surface of the material. These are commonly referred to as SV shear waves.

Seismic field recording technique

A method for removing an undesired surface wave from a reflected wave in a method for seismic exploration is accomplished by placing first and second detector arrays at a location on the surface of the earth in the direction of movement of the surface wave. The array has a length less than the length of the shortest wave length of the interfering wave to be eliminated. Signals from both arrays are recorded and processed by first adding the received signals to form a first output, subtracting added signals to form a second output, shifting one of the output signals by 90°, adjusting its amplitude and subtracting the phase shifted and adjust signal from the remaining signal thereby removing the surface wave.

Frequency independent directionally sensitive array in seismic surveying

A novel array of vertically and horizontally spaced hydrophones is shown which is capable of high ratio of desired signal to noise because of good directional sensitivity when used with any seismic source. Alternatively, a novel directionally sensitive array of vertically and horizontally spaced seismic sources is disclosed for use in seismic surveying with any spread of hydrophones or geophones, again attaining a high ratio of desired signal to noise. A reception pattern (in the first case) and a radiation pattern (in the second place) is produced which essentially eliminates reception or radiation at all frequencies except for waves within a predetermined angle with respect to the array. The sensitivity is essentially constant within such angle for all frequencies and essentially zero outside it. This permits the array geometry to be adjusted so that there is high attenuation of undesired seismic waves, whether these be due to noise or other random waves, or are signal-generated waves from the seismic source but traveling in an undesired direction.

Tests in support of LMFBR

Tests in support of LMFBR projects for potential incidents involving a hypothetical core disruptive accident or sodium-water interactions in steam generators have two possible goals: (1) to evaluate the integrity of the primary containment after the design is frozen or (2) to investigate design options in support of primary containment design. The test planning approach differs depending on the goal. The Fast Flux Test Facility tests had the first goal, the current Clinch River Breeder Reactor tests have the second goal. This paper discusses test planning, sources for simulating loads, modeling, and instrumentation. The main source described involves controlled venting of explosive gases. The source avoids generation of undesirable shock waves and facilitates calibration because the reaction rate of the explosive is independent of the response. It is indicated that the test program requiring the least time and cost involves a mixture of three types of models: small simple models, small complex models, and large complex models. Instrumentation is discussed that is required for validation of loading, response measurements for comparison with calculations, and response measurements on critical members where predictions are not possible.

REMARKS ON WAVENUMBER FILTERING IN THE FIELD

For many years exploration seismologists have endeavored to carry out wavenumber filtering by using a multiplicity of geophones per trace in order to attenuate undesired waves and to intensify the signal. In a similar manner, wavenumber filtering is carried out very often at the place of origin of seismic energy by shooting from several shotholes or by combining several elements of a nondynamite source in a suitable manner. The following consideration refers to receivers (geophones or hydrophones) as well as to emitters (shots and other sources of energy); for simplicity, in the following, the term “geophones” stands for all kinds of receivers and sources of energy.

HAMMER REFLECTION SEISMICS IN ENGINEERING GEOPHYSICS

A major problem in exploiting the reflection method in engineering geophysics lies in the difficulty of separating the various superimposed arrivals at short record times. Velocity filtering is used in the present study as a means of identifying the reflection arrivals by removing the undesirable waves and leaving a substantially usable reflection record, even at very short record times. Special circuitry has been developed to sense the time lag of positive zero crossings of the signal at two separate geophones, and to record only those arrivals whose phase shift is smaller than an arbitrarily set amount. This circuitry has been incorporated into a standard hammer‐type engineering seismograph. Fundamentals of analysis of an expanding reflection spread are reviewed, and field examples are shown to demonstrate the abilities and limitations of the present technique.