scholarly journals WAVE-FORMED RIPPLES IN NEARSHORE SANDS

1976 ◽  
Vol 1 (15) ◽  
pp. 122 ◽  
Author(s):  
John R. Dingler ◽  
Douglas L. Inman
Keyword(s):  
Wave Motion ◽  
Wave Spectrum ◽  
Fine Sand ◽  
Wave Form ◽  
Flow Sheet ◽  
Sheet Flow ◽  
Stress Criterion ◽  
Relative Stress ◽  
La Jolla ◽  
Relict Ripples

Ripples are generated and modified by wind-generated waves and their profiles are controlled by the nature of the near-bottom wave motion and by the size of the bed material. Wave-formed ripples develop under a definable set of conditions called the ripple regime. The ripple regime is bounded by those conditions that initiate grain motion, low-wave intensity, and by those that cause the disappearance of ripples, onset of sheet flow. Sheet flow occurs when intense wave motion causes several grain layers to be in motion. Three distinct ripple types occur in nearshbre areas of fine sand - relict ripples, vortex ripples, and transition ripples. Vortex and transition ripples lie within the active ripple regime, whereas relict ripples do not. Ripples in fine sand were studied in the field at La Jolla, California, where profiles were obtained using a newly developed high-resolution sonar capable of vertical resolution of the order of one millimeter. Simultaneous profile and wave-pressure measurements permit correlation of the ripple profiles with individual waves and with the wave spectrum. The sonar, with its rapid scan capability (^ one meter per second), gives instantaneous measurement of the actively changing bed features in nearshore waters. The combination of bottom scans and wavepressure measurements extends previous wave-ripple studies to include all of the nearshore ripple regime. The relation between the wave and ripple data from this study is best shown by plotting ripple steepness n/A against the wave form of the Shields relative stress criterion 0. Vortex ripples (n /\ ^_ 0.15) occur for 0 values less than 40 but greater than the minimum value which is determined by the onset of grain motion.

PROPELLER NOISE FROM A LIGHT AIRCRAFT FOR LOW-FREQUENCY MEASUREMENTS OF THE SPEED OF SOUND IN A MARINE SEDIMENT

2002 ◽  
Vol 10 (04) ◽  
pp. 445-464 ◽  
Author(s):  
MICHAEL J. BUCKINGHAM ◽  
ERIC M. GIDDENS ◽  
FERNANDO SIMONET ◽  
THOMAS R. HAHN
Keyword(s):  
Water Column ◽  
Speed Of Sound ◽  
Low Frequency ◽  
Deep Ocean ◽  
Fine Sand ◽  
P Wave ◽  
Difference Frequency ◽  
S Wave ◽  
Low Frequencies ◽  
La Jolla

The sound from a light aircraft in flight is generated primarily by the propeller, which produces a sequence of harmonics in the frequency band between about 80 Hz and 1 kHz. Such an airborne sound source has potential in underwater acoustics applications, including inversion procedures for determining the wave properties of marine sediments. A series of experiments has recently been performed off the coast of La Jolla, California, in which a light aircraft was flown over a sensor station located in a shallow (approximately 15 m deep) ocean channel. The sound from the aircraft was monitored with a microphone above the sea surface, a vertical array of eight hydrophones in the water column, and two sensors, a hydrophone and a bender intended for detecting shear waves, buried 75 cm deep in the very-fine-sand sediment. The propeller harmonics were detected on all the sensors, although the s-wave was masked by the p-wave on the buried bender. Significant Doppler shifts of the order of 17%, were observed on the microphone as the aircraft approached and departed from the sensor station. Doppler shifting was also evident in the hydrophone data from the water column and the sediment, but to a lesser extent than in the atmosphere. The magnitude of the Doppler shift depends on the local speed of sound in the medium in which the sensor is located. A technique is described in which the Doppler difference frequency between aircraft approach and departure is used to determine the speed of sound at low-frequencies (80 Hz to 1 kHz) in each of the three environments, the atmosphere, the ocean and the sediment. Several experimental results are presented, including the speed of sound in the very fine sand sediment at a nominal frequency of 600 Hz, which was found from the Doppler difference frequency of the seventh propeller harmonic to be 1617 m/s.

scholarly journals Calculations of near-field emissions in frequency-domain into time-dependent data with arbitrary wave form transient perturbations

2012 ◽  
Vol 1 (2) ◽  
pp. 26
Author(s):  
Y. Liu ◽  
B. Ravelo ◽  
J. Ben Hadj Slama
Keyword(s):  
Time Domain ◽  
Near Field ◽  
Wave Spectrum ◽  
Computational Method ◽  
Time Dependent ◽  
Dependent Data ◽  
Wave Form ◽  
Frequency Dependent ◽  
Transient Electromagnetic ◽  
The Time Domain

This paper is devoted on the application of the computational method for calculating the transient electromagnetic (EM) near-field (NF) radiated by electronic structures from the frequency-dependent data for the arbitrary wave form perturbations i(t). The method proposed is based on the fast Fourier transform (FFT). The different steps illustrating the principle of the method is described. It is composed of three successive steps: the synchronization of the input excitation spectrum I(f) and the given frequency data H0(f), the convolution of the two inputs data and then, the determination of the time-domain emissions H(t). The feasibility of the method is verified with standard EM 3D simulations. In addition to this method, an extraction technique of the time-dependent z-transversal EM NF component Xz(t) from the frequency-dependent x- and y- longitudinal components Hx(f) and Hy(f) is also presented. This technique is based on the conjugation of the plane wave spectrum (PWS) transform and FFT. The feasibility of the method is verified with a set of dipole radiations. The method introduced in this paper is particularly useful for the investigation of time-domain emissions for EMC applications by considering transient EM interferences (EMIs).

scholarly journals DIELECTRIC OIL`S TEST MACHINE WISH VOLTAGE RISE ELECTRONIC MODULE

2021 ◽  
pp. 103-108
Author(s):  
Igor Bogatirov ◽  
Helena Ponuzhdayeva ◽  
Denis Koliushko ◽  
Serhii Rudenko ◽  
Alexander Istomin
Keyword(s):  
High Voltage ◽  
Dielectric Breakdown ◽  
Sine Wave ◽  
Wave Form ◽  
Test Machine ◽  
Flow Sheet ◽  
Voltage Measurement ◽  
Voltage Step ◽  
Voltage Rise ◽  
Pulse Width Modulator

For test operations according to the liquid dielectric breakdown voltage measurement method we use high voltage machines that consist of high-voltage step-up transformer, voltage rise block, test cell with electrodes and so on. Described dielectric oil's test machine UIM – 90 with electromechanical voltage rise block. Cause of hard requirements in specification documents about voltage sine wave form on cell's electrodes, we performed field tests for UIM – 90 that help to evaluate the mains voltage impact on the test voltage distortion and measurement accuracy. Was discovered that during usage of electromechanical voltage rise block voltage steps disrupt sine wave’s form proportionally to step-up transformer’s transformation coefficient. Performed analysis of this block’s construction and established that usage of ЛАТР and mechanical voltage controller could lead to additional sine’s wave disruption. Decided to develop electronic voltage rise block which will allow to get rid of mains influence on test data. Created the algorithm of wave shaping from microcontroller, which generates voltage ramp to the amplifier representing pulse width modulator, then to the step-up transformers cascade. Proposed to use additional transformer for level matching of amplifier’s output voltage and main high voltage transformer’s input voltage. Presented flow sheet for UIM – 90 with electronic voltage step-up block and cascading start ofstep-up transformers. Provided voltage oscillograph trace and it spectrograph on the main transformer’s primary side, received due to the implementation of developed electronic voltage step-up block, prove that voltage sine wave form  doesn’t rely on mains quality. After upgraded UIM – 90 and it world analogues technical parameters analysis we could make a conclusion about it competitive capability on global level.

scholarly journals On Frequency and Spatial Periodicity of the Waves of the Anomalous Amplitude in the Ocean

2019 ◽  
Keyword(s):  
Wave Packet ◽  
Wave Motion ◽  
Simple Calculation ◽  
Physical Reality ◽  
Wave Form ◽  
Laboratory System ◽  
Strong Wind ◽  
Average Value ◽  
Wind Exposure ◽  
The Waves

The paper shows that the waves of anomalous amplitude are long-lived formations. They drift in the direction of the wave motion with the group velocity of the wave packet, which is half the phase velocity of the main wave. The swing of the wave (the distance from the hump to the trough) of the anomalous amplitude is more than three times the average value of the sweep of the wave motion. The modulation instability of this wave form a perturbation spectrum, the energy of which is twice the energy of the main wave in the developed process mode. The spatial size of the wave packet practically does not change, the amplitude of the swing in the maximum first increases, then gradually decreases. The number of such waves in areas of strong wind exposure is much larger than the statistics of random interference processes allow. This is due to the influence of the main wave (its amplitude remains noticeably greater than the amplitudes of each of the modes of the wave packet) on the behavior of each pair of modes from the wave packet of the perturbation. In the laboratory system, the duration of the anomalous wave coincides qualitatively with the time of existence of the Peregrin autowave. Although the Peregrin autowave corresponds to a different physical reality, where the dispersion of the wave is weak. Gravitational surface waves have a strong dispersion, and the NSE equation in this case is noticeably modified. However, in rest system of the wave packet (moving relative to the laboratory system) the abnormal amplitude wave lifetime is much longer. The distance that the wave packet travels with a persisting anomalous sweep is at least equal to several hundred wavelengths and can reach hundreds of kilometers. A simple calculation of such waves by means of space monitoring due to the small viewing area (frame) may be inaccurate. Once formed, such waves are able to drift over considerable distances. However, they may well get into the next frame of view. That is, estimates of the number of such waves can be overestimated.

Experimental study of bore run-up

1989 ◽  
Vol 206 ◽  
pp. 563-578 ◽  
Author(s):  
Harry H. Yeh ◽  
Abdulhamid Ghazali ◽  
Ingunn Marton
Keyword(s):  
Water Wave ◽  
Wave Motion ◽  
Exchange Process ◽  
Propagation Speed ◽  
Transition Process ◽  
Wave Form ◽  
Momentum Exchange ◽  
Undular Bore ◽  
Run Up ◽  
Sloping Beach

Bore propagation near the shoreline, the transition from bore to wave run-up, and the ensuing run-up motion on a uniformly sloping beach are investigated experimentally. As a bore approaches the shoreline, the propagation speed first decelerates by compressing its wave form and then suddenly accelerates at the shoreline. Although this behaviour is qualitatively in agreement with the inviscid shallow-water wave prediction (often called the ‘bore collapse’ phenomenon), unlike the genuine bore-collapse phenomenon, the acceleration is caused by the ‘momentum exchange’ process, i.e. collision of the bore against the initially quiescent water along the shoreline. Owing to this momentum exchange, a single bore motion degenerates into two successive run-up water masses; one involves a turbulent run-up water motion followed by the original incident wave motion. The transition process from undular bore to wave run-up appears to be different from that of a fully developed bore. The bore front overturns directly onto the dry beach surface, and the run-up is characterized by a thin splashed-up flow layer.

scholarly journals FIELD MEASUREMENTS OF NEARSHORE VELOCITIES

1974 ◽  
Vol 1 (14) ◽  
pp. 30
Author(s):  
David A. Huntley ◽  
Anthony J. Bowen
Keyword(s):  
Wave Motion ◽  
Field Measurements ◽  
Wave Form ◽  
Edge Waves ◽  
Free Standing ◽  
Frequency Wave ◽  
Storm Waves ◽  
Circulation Patterns ◽  
Two Component ◽  
Base Side

Two component electromagnetic flowmeters are being used as the basis of an apparatus to measure nearshore velocities on natural beaches. The flowmeters are mounted on free standing tripods, 1 m. base side and 0.3 m. high, to measure the two components of horizontal flow, and have been used in depths of up to 4 m. and up to 150 m. from the shoreline. The apparatus has proved both flexible and reliable on beaches ranging from steep shingle (slope ^ 0.13) to very shallow sand (slope'*' 0.01) and under a wide variety of wave conditions, including full storm waves on a beach of intermediate slope ( ^ 0.04). Results show that a single flowmeter can be used on a tidal beach to measure the variation of the flow field along a line perpendicular to the shoreline. In this way edge waves and steady nearshore circulation patterns have been detected. If several flowmeters are placed on a line perpendicular to the shoreline, the progress of individual waves can be followed as they pass over each flowmeter in turn, and hence propagation speeds, changes of wave form and the development of lower frequency wave motion close to the shoreline can be studied.

scholarly journals Determination of Reaction Forces of a Deck Crane in Wave Motion Using Screw Theory

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Andrej Cibicik ◽  
Geir O. Tysse ◽  
Olav Egeland
Keyword(s):  
Wave Motion ◽  
Screw Theory ◽  
Equations Of Motion ◽  
Wave Spectrum ◽  
Force Response ◽  
Plücker Coordinates ◽  
Angular Velocities ◽  
Reaction Forces ◽  
Response Amplitude Operators

In this paper, we present a method for calculating reaction forces for a crane mounted on a ship moving in waves. The method is used to calculate the reaction forces between the crane base and the vessel deck. This includes the case where the crane is mounted on the platform that keeps the base of the crane horizontal when the vessel is moving in roll and pitch. The wave motion of the ship is modeled with force response amplitude operators (RAOs) based on the JONSWAP wave spectrum. The combined equations of motion for a vessel and a crane are derived using Kane’s equations of motion, where velocities and angular velocities are formulated in terms of twists, and the associated partial velocities and partial angular velocities are given as lines in Plücker coordinates. The unknown reaction forces are represented as wrenches and are determined using screw transformations. The method is used to study the effect of the roll and pitch compensation platform in numerical simulations. The efficiency of the platform is evaluated in terms of the magnitude of reaction forces and crane payload sway angles.

scholarly journals SCOUR AROUND A CIRCULAR CYLINDER DUE TO WAVE MOTION

1970 ◽  
Vol 1 (12) ◽  
pp. 79
Author(s):  
Donald R. Wells ◽  
Robert M. Sorenson
Keyword(s):  
Circular Cylinder ◽  
Wave Motion ◽  
Oscillatory Flow ◽  
Fine Sand ◽  
Time Interval ◽  
Relative Depth ◽  
Incipient Motion ◽  
Critical Flow Velocity ◽  
Time Required ◽  
Influential Parameters

A vertical circular cylinder to simulate a pile was installed in the Texas A&M Hydrodynamics Lab two dimensional wave tank along with a built up section containing a horizontal bed of fine sand This was subjected to monochromatic waves of differing characteristics and conditions for mcipi ent motion were observed for each of three sands Also, the magnitude and pattern of ultimate scour and the time interval required to reach this state were measured for six different conditions of wave steepness and relative depth These results were related to influential parameters, including wave, pile and sediment character istics, and developed by dimensional analysis with consideration of the literature pertaining to past work on the movement of sediment by oscillatory flow Conclusions regarding the critical flow velocity for incipient motion, the effect of the above parameters on incipient motion and ultimate scour depth, the time required tor maximum scour, the significance of eddies generated by the pile, and the catalytic action of the pile in causing the initiation of scour are presented The above conclusions are also generally discussed in light of the difficulties involved in extend ing the results to prototype conditions.

Design of an intermediate high voltage EM for 3-D studies of biological material and its integration with a system for remote access

1995 ◽  
Vol 53 ◽  
pp. 66-67 ◽  
Author(s):  
Mark H. Ellisman
Keyword(s):  
High Voltage ◽  
High Performance ◽  
Remote Access ◽  
3 Dimensional ◽  
Voltage Electron ◽  
Remote Operation ◽  
High Voltage Electron Microscope ◽  
La Jolla ◽  
Performance Computing ◽  
Advanced Version

The increased availability of High Performance Computing and Communications (HPCC) offers scientists and students the potential for effective remote interactive use of centralized, specialized, and expensive instrumentation and computers. Examples of instruments capable of remote operation that may be usefully controlled from a distance are increasing. Some in current use include telescopes, networks of remote geophysical sensing devices and more recently, the intermediate high voltage electron microscope developed at the San Diego Microscopy and Imaging Resource (SDMIR) in La Jolla. In this presentation the imaging capabilities of a specially designed JEOL 4000EX IVEM will be described. This instrument was developed mainly to facilitate the extraction of 3-dimensional information from thick sections. In addition, progress will be described on a project now underway to develop a more advanced version of the Telemicroscopy software we previously demonstrated as a tool to for providing remote access to this IVEM (Mercurio et al., 1992; Fan et al., 1992).

Visual-Neural Correlate of Speechreading Ability in Normal-Hearing Adults

1982 ◽  
Vol 25 (4) ◽  
pp. 521-527 ◽  
Author(s):  
David C. Shepherd
Keyword(s):  
Normal Hearing ◽  
Wave Form ◽  
Firing Time ◽  
Neural Firing ◽  
Neural Correlate ◽  
Retest Reliability ◽  
Repeated Word ◽  
Negative Peak ◽  
The Stability ◽  
Test Retest Reliability

In 1977, Shepherd and colleagues reported significant correlations (–.90, –.91) between speechreading scores and the latency of a selected negative peak (VN 130 measure) on the averaged visual electroencephalic wave form. The primary purpose of this current study was to examine the stability, or repeatability, of this relation between these cognitive and neurophysiologic measures over a period of several months and thus support its test-retest reliability. Repeated speechreading word and sentence scores were gathered during three test-retest sessions from each of 20 normal-hearing adults. An average of 56 days occurred from the end of one to the beginning of another speechreading sessions. During each of four other test-retest sessions, averaged visual electroencephalic responses (AVER s ) were evoked from each subject. An average of 49 clays intervened between AVER sessions. Product-moment correlations computed among repeated word scores and VN l30 measures ranged from –.61 to –.89. Based on these findings, it was concluded that the VN l30 measure of visual neural firing time is a reliable correlate of speech-reading in normal-hearing adults.

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