scholarly journals SPLASHNIK-THE TAYLOR MODEL BASIN DISPOSABLE WAVE BUOY

2011 ◽  
Vol 1 (7) ◽  
pp. 6
Author(s):  
Wilbur Marks ◽  
Robert G. Tuckerman
Keyword(s):  
Fixed Point ◽  
Energy Spectrum ◽  
Wave Spectrum ◽  
The State ◽  
Measuring System ◽  
Vertical Acceleration ◽  
Height Distribution ◽  
Taylor Model ◽  
Wave Measurement ◽  
The Waves

In connection with full scale ship trials, it is often necessary to have a description of the state of the sea which may be used as a scale against which to measure ship performance. Visual observations of waves have proven to be unreliable in the past and are, in any event, not sufficiently detailed to be adequately descriptive, for many problems. Hindcasting** the state of the sea depends on wind information (speed, duration, area of sea covered, and rate of growth and/or decay) obtained from six hourly weather maps. The wind data is used in conjunction with certain empirical^theoretical formulations to produce an energy spectrum of waves at the place and time of interest. The energy spectrum is a good descriptive tool, because it gives information on the energy content of the wave frequencies present and provides an estimate of the height distribution of the waves as well as certain other statistical quantities. However, hindcasting the wave spectrum is unsatisfactory for two reasons: 1) estimation of the wind field from sparse observations spaced six hours apart is highly subjective, and 2), no specific energy spectrum formulation has as yet been verified. There is still another method for description of the seaway. If the waves at a fixed point can be measured for a sufficient length of time, then this sample record can be converted into a wave (energy) spectrum that will adequately characterize the state of the sea. There are many systems that will measure waves, but the requirement that wave measurements complement simultaneous ship motions measurements, in all states of sea, eliminates most of the known instruments. In particular, it is required that the waves be observed at a fixed point for a period of hours, while the ship conducts certain maneuvers which may remove it several miles from the point of observation. This means that the wave measurement system must be physically divorced from the ship. Furthermore, many tests will be made in heavy seas so that it will not be practical to seek out the instrument and recover it. As a consequence of the conditions imposed by the particular problem stated here, the wave measuring system must be able to: 1. Telemeter information to the ship for at least 7 hours at a distance of at least 8 nautical miles, 2. Be launched from the deck of a ship in waves perhaps 25 feet high, and 3. Be inexpensively constructed ($125.00 - $150.00) so as to be expendable. Since investigation revealed that no known instrument had embodied in it all three of these features, it was decided to design and build an appropriate system, at the David Taylor Model Basin. After some consideration of the imposed conditions, it was decided that a small floating buoy (SPLASHNIK) which measures apparent vertical acceleration and telemeters the information back to the ship could be designed to fulfill the requirements. The intent of this paper is to describe the SPLASHNIK system, the data reduction method, some experimental verification of the method, and some proposed improvements. It should be noted that this technique of wave measurement (recording of vertical acceleration) is not new. In fact, one instrument described by Dorrestein (1957) is somewhat similar to the SPLASHNIK and has been in operation for several years. Other institutions are also known to be experimenting with accelerometer wave buoys. However, several basic design differences make the SPLASHNIK especially useful as a tool in the study of ship behavior. A drawing of the SPLASHNIK appears in Figure 1.

Determination of the Wave Spectrum From Observed Motions of a Vehicle in a Seaway

1967 ◽  
Vol 11 (03) ◽  
pp. 199-208
Author(s):  
Wilbur Marks
Keyword(s):  
Wave Spectrum ◽  
Full Scale ◽  
The State ◽  
Vertical Acceleration ◽  
Time Histories

If, during full-scale trials, it is not possible to measure the state of the sea with a reliable wavemeter, then certain motion records may be combined to achieve the same end. The derivation of the wave spectrum from the time histories of pitch, heave (vertical acceleration), and bow immersion is presented. The problem of the conversion of acceleration to displacement is discussed. The method is applied to the particular case of the hydrofoil boat Sea Legs.

Wave groups and spectral shape in ice

2020 ◽  
Author(s):  
Johannes Gemmrich ◽  
Jim Thomson ◽  
Todd Mudge
Keyword(s):  
Spectral Characteristics ◽  
Wave Spectrum ◽  
Height Distribution ◽  
Wave Groups ◽  
Ice Coverage ◽  
Frequency Components ◽  
Ice Conditions ◽  
Wave Groupiness ◽  
Group Structures ◽  
The Waves

<p>The reduction of arctic summer ice coverage has prompted a renewed interest in the physics of wave-ice interactions. Progress has been made on the observational, theoretical and modeling aspects of waves in the presence of ice.</p><p>This presentation will address our recent observational studies of spectral wave properties in the marginal ice zone, and in ice covered seas. Waves propagating through ice are attenuated and scattered, resulting in a pronounced change of the shape of the wave spectrum. In particular, the strong attenuation of the high frequency components affects wave steepness and the spectral bandwidth, and thus wave groupiness and the crest height distribution.</p><p>We present data for various ice conditions, obtained from drifting SWIFT buoys, a moored ADCP and moored inverted echosounders. All observations show well developed group structures of the waves. However, for different datasets we obtain opposite dependencies between wave groupiness and wave spectral characteristics. This suggests that depending on ice condition, both, the linear mechanism of wave superposition, or wave nonlinarites can be responsible for the wave group enhancement in ice. These mechanisms will be discussed.</p>

Wave adjustment: general concept and examples

2015 ◽  
Vol 779 ◽  
pp. 514-543 ◽  
Author(s):  
G. M. Reznik
Keyword(s):  
Free Surface ◽  
State Vector ◽  
Wave Spectrum ◽  
Initial Perturbation ◽  
Three Dimensional ◽  
The State ◽  
Physical Parameters ◽  
Fast Wave ◽  
Group Speed ◽  
The Waves

We formulate a general theory of wave adjustment applicable to any physical system (not necessarily a hydrodynamic one), which, being linearized, possesses linear invariants and a complete system of waves harmonically depending on the time $t$. The invariants are determined by the initial conditions and are zero for the waves, which, therefore, do not transport and affect the invariants. The evolution of such a system can be represented naturally as the sum of a stationary component with non-zero invariants and a non-steady wave part with zero invariants. If the linear system is disturbed by a small perturbation (linear or nonlinear), then the state vector of the system is split into slow balanced and fast wave components. Various scenarios of the wave adjustment are demonstrated with fairly simple hydrodynamic models. The simplest scenario, called ‘fast radiation’, takes place when the waves rapidly (their group speed $c_{gr}$ greatly exceeds the slow flow velocity $U$) radiate away from the initial perturbation and do not interact effectively with the slow component. As a result, at large times, after the waves propagate away, the residual flow is slow and described by a balanced model. The scenario is exemplified by the three-dimensional non-rotating barotropic flow with a free surface. A more complicated scenario, called ‘nonlinear trapping’, occurs if oscillations with small group speed $c_{gr}\leqslant U$ are present in the wave spectrum. In this case, after nonlinear wave adjustment, the state vector is a superposition of the slow balanced component and oscillations with small $c_{gr}$ trapped by this component. An example of this situation is the geostrophic adjustment of a three-dimensional rotating barotropic layer with a free surface. In the third scenario, called ‘incomplete splitting’, the wave adjustment is accompanied by non-stationary boundary layers arising near rigid and internal boundaries at large times. The thickness of such a layer tends to zero and cross-gradients of physical parameters in the layer tend to infinity as $t\rightarrow \infty$. The layer is an infinite number of wave modes whose group speed tends to zero as the mode number tends to infinity. In such a system, complete splitting of motion into fast and slow components is impossible even in the linear approximation. The scenario is illustrated by an example of stratified non-rotating flow between two rigid lids. The above scenarios describe, at least, the majority of known cases of wave adjustment.

Measurement of the Pulverized Coal Concentration by Measuring the Time Delay of Ultrasonic with Digital Correlation Method

2013 ◽  
Vol 333-335 ◽  
pp. 359-364
Author(s):  
Ke Wang
Keyword(s):  
Time Delay ◽  
Power Plant ◽  
Correlation Method ◽  
The State ◽  
Pulverized Coal ◽  
Measuring System ◽  
Digital Correlation ◽  
Coal Boiler ◽  
Key Parameter

The pulverized coal concentration in blast pipe in front of firebox is one key parameter in coal boiler used in a power plant; it will affect the state of burning in firebox. This paper proposes a new digital correlation method to measure the time delay of ultrasonic for measuring the pulverized coal concentration. The principle of measurement is discussed in detail and the measuring system is designed.

Experimental Study on New Wave Measurement Using Passive Underwater Acoustics

2008 ◽  
Author(s):  
Jing Li ◽  
Dingyong Yu ◽  
Huaxing Liu
Keyword(s):  
Virtual Instrument ◽  
Low Cost ◽  
Measuring System ◽  
Time Data ◽  
Significant Wave ◽  
Wave Measurement ◽  
Wave Heights ◽  
Mean Wave Period ◽  
Passive Acoustic ◽  
User Friendly

The passive acoustic-based wave measurement via hydrophones is presented in this paper. It has the potential to measure non-intrusively, implement with low cost and with higher resolution. Details of experiments, real-time data recording and processing are described respectively. Particularly, the portable data acquisition system based on virtual instrument technique is designed to make the in situ measurement convenient and user-friendly. Special emphasis is put on FFT filtering technique to band pass the signal fast and efficiently. The key wave parameters, i.e. the mean wave period and the significant wave height, can be obtained from the comparatively safe and stable underwater by means of submerged hydrophones. Considering the pressure sensor has been widely used in the ocean wave measurement, it is deployed simultaneously to test the feasibility of the new system. The result shows that the present measuring system can give satisfactory measurement of significant wave heights and average wave periods in shallow water despite of the little deviation.

scholarly journals APPLICATIONS ON NONLINEAR WAVE COMBINATION

1986 ◽  
Vol 1 (20) ◽  
pp. 26
Author(s):  
J.T. Juang
Keyword(s):  
Wave Height ◽  
Taiwan Strait ◽  
Western Coast ◽  
Linear Wave ◽  
Wave System ◽  
Height Distribution ◽  
Wave Height Distribution ◽  
Local Wave ◽  
Source Wave ◽  
The Waves

Due to the special bathymetry in Taiwan Strait, the waves off the western coast of Taiwan are considered to be composed of two-source wave system. One propagates from the central part of the Strait named main wave, and the other is generated by the local wind known as local wave which occurs along the shore. After the combination and the transformation procedure from these two-nonlinear-source wave system, the wave height distribution in Taiwan Strait should be modified. A comparison of the wave height distributions based on the present proposed method with the field data indicates that the present method yields a better result than other theorems. Furthermore, the result of application of two non-linear wave theorem to wave prediction are also presented.

scholarly journals Rejection of the biophoton hypothesis on the origin of photoreceptor dark noise

2019 ◽  
Vol 151 (7) ◽  
pp. 887-897 ◽  
Author(s):  
Victor I. Govardovskii ◽  
Luba A. Astakhova ◽  
Alexander Yu. Rotov ◽  
Michael L. Firsov
Keyword(s):  
Absolute Intensity ◽  
Light Signal ◽  
Measuring System ◽  
Single Photons ◽  
Dark Noise ◽  
Acipenser Ruthenus ◽  
Perfusion Chamber ◽  
The Waves ◽  
Sterlet Acipenser Ruthenus ◽  
Synchronous Accumulation

Rod photoreceptors of the vertebrate retina produce, in darkness, spontaneous discrete current waves virtually identical to responses to single photons. The waves comprise an irreducible source of noise (discrete dark noise) that may limit the threshold sensitivity of vision. The waves obviously originate from acts of random activation of single rhodopsin molecules. Until recently, it was generally accepted that the activation occurs due to the rhodopsin thermal motion. Yet, a few years ago it was proposed that rhodopsin molecules are activated not by heat but rather by real photons generated within the retina by chemiluminescence. Using a high-sensitive photomultiplier, we measured intensities of biophoton emission from isolated retinas and eyecups of frogs (Rana ridibunda) and fish (sterlet, Acipenser ruthenus). Retinal samples were placed in a perfusion chamber and emitted photons collected by a high-aperture quartz lens. The collected light was sent to the photomultiplier cathode through a rotating chopper so that a long-lasting synchronous accumulation of the light signal was possible. The absolute intensity of bio-emission was estimated by the response of the measuring system to a calibrated light source. The intensity of the source, in turn, was quantified by measuring rhodopsin bleaching with single-rod microspectrophotometry. We also measured the frequency of discrete dark waves in rods of the two species with suction pipette recordings. Expressed as the rate constant of rhodopsin activation, it was 1.2 × 10−11/s in frogs and 7.6 × 10−11/s in sterlets. Approximately two thirds of retinal samples of each species produced reliably measurable biophoton emissions. However, its intensity was ≥100 times lower than necessary to produce the discrete dark noise. We argue that this is just a lower estimate of the discrepancy between the hypothesis and experiment. We conclude that the biophoton hypothesis on the origin of discrete dark noise in photoreceptors must be rejected.

scholarly journals Effect of Surface Topography Parameters on Friction and Wear of Random Rough Surface

Materials ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 2762 ◽  
Author(s):  
Ruimin Shi ◽  
Bukang Wang ◽  
Zhiwei Yan ◽  
Zongyan Wang ◽  
Lei Dong
Keyword(s):  
Surface Topography ◽  
Fluid Dynamic ◽  
Dynamic Pressure ◽  
Functional Characterization ◽  
Three Dimensional ◽  
Measuring System ◽  
Height Distribution ◽  
Worn Surface ◽  
The Relationship

In order to explore the relationship between the surface topography parameters and friction properties of a rough contact interface under fluid dynamic pressure lubrication conditions, friction experiments were carried out. The three-dimensional surface topography of specimens was measured and characterized with a profile microscopy measuring system and scanning electron microscope. The friction coefficient showed a trend of decreasing first and then increasing with the increase in some surface topography parameters at lower pressure, such as the surface height arithmetic mean Sa, surface height distribution kurtosis Sku, surface volume average volume Vvv, and surface center area average void volume Vvc, which are the ISO 25178 international standard parameters. The effects of surface topographic parameters on friction were analyzed and the wear mechanism of the worn surface was presented. The wear characteristics of the samples were mainly characterized as strain fatigue, grinding, and scraping. The results provide a theoretical basis for the functional characterization of surface topography.

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