scholarly journals WIND WAVES TRANSMISSION THROUGH POROUS BREAKWATER

1980 ◽  
Vol 1 (17) ◽  
pp. 18
Author(s):  
Stanislaw R. Massel ◽  
Piotr Butowski
Keyword(s):  
Average Rate ◽  
Wind Waves ◽  
Mass Term ◽  
Momentum Equation ◽  
Solid Particles ◽  
Long Waves ◽  
Experimental Investigations ◽  
Inertia Force ◽  
Rigorous Approach ◽  
In Series

Rubble - mound breakwaters are designed to protect exposed marine areas from excessive wave activity. The resulting interaction of the incident waves with the rubble units is extremely complex due to the variable reflective and frietional properties of the permeable structure. In the past decade considerable effort has been expended to derive rational methods for of such type structure. The theoretical and experimental investigations have been focused especoialy on the prediction of the reflection and transmission of regular waves incident to breakwater. Sollitt and Cross /^^^Z/ presented the analytical approach to the problem based on the assumption that the original nonlinear governing equation of the wave motion into porous media may be replaced by a linear one so as to give the same average rate of dissipation/Lorentz approximation/. Under the assumption that severe wave conditions for most breakwaters correspond to relatively long waves, the considerably simple solutions were developed by Kondo and Toma /1972/ and in series of papers by Madsen and co-authors /\97k, 1977, 1978/. Madsen s solutions follows rather a physical than mathematical rigorous approach to the problem. The momentum equation evaluated him explains the influence of the inertia force associated with the unsteady flow around the solid particles. Very careful analytical examination of this problem for the long waves past the narrow gaps and holes has been presented by Mei at al. /197**/. The study indicate that apparent mass term can be ignored in most practical cases.

scholarly journals EXPERIMENTAL STUDIES OF FORCES ON PILES

2000 ◽  
Vol 1 (4) ◽  
pp. 25 ◽  
Author(s):  
J. R. Morison ◽  
J. W. Johnson ◽  
M. P. O'Brien
Keyword(s):  
Surface Waves ◽  
Drag Force ◽  
Experimental Studies ◽  
Mass Term ◽  
Fluid Particle ◽  
Experimental Investigations ◽  
Inertia Force ◽  
Fluid Density ◽  
Virtual Mass ◽  
The Moment

In the design of a pile structure exposed to surface waves of a given height and period, some of the factors involved in the problem and studied herein are the size, shape and spacing of the piles and the moment distribution on uniform and non-uniform piles. Theoretical and experimental investigations have shown that the force exerted by surface waves on a pile consists of two components — a drag force and an inertia force. The drag force is proportional to the fluid density, the projected area and the square of the fluid particle velocity. The inertia force, including the virtual mass, is proportional to the fluid density, the volume of the object and the fluid particle acceleration. The virtual mass is the apparent increase of the displaced mass of fluid necessary to account for the increase in force resulting from the acceleration of the fluid relative to the object. This factor is included in the coefficient of mass term in the force calculations.

Wave Buoy Performance in Short and Long Waves, Evaluated Using Tests on a Hexapod

2018 ◽  
Author(s):  
Sanne van Essen ◽  
Kevin Ewans ◽  
Jason McConochie
Keyword(s):  
Degrees Of Freedom ◽  
Wind Waves ◽  
Long Waves ◽  
Normal Operation ◽  
Period Range ◽  
Multiple Degrees Of Freedom ◽  
Hydrodynamic Response ◽  
Vertical Displacements ◽  
Internal Integration ◽  
Offshore Wave

Offshore wave conditions can be measured using wave buoys, which are generally designed for wind waves. Longer waves (swell or bound second-order waves) are very relevant for certain maritime structures. The accuracy of the instrumentation in a typical wave buoy in long and short waves was therefore studied, and it was investigated if the buoy can be applied in longer waves. A Waverider buoy was placed on a hexapod, which applied regular and irregular prescribed motions in multiple degrees of freedom. The hydrodynamic response of the buoy in waves and the effect of its mooring system were not evaluated; the buoy was assumed to follow the orbital motions of a wave and to rotate with its slope. The tests showed that the buoy sensors measure accelerations and rotations with periods between 1.5 and 35 s very well. Vertical displacements derived from the accelerations by the buoy are accurate for the period range of 2 to 20 s. In longer waves, the motions are significantly underestimated, even though the accelerations are accurately measured. This will not lead to large errors in normal operation, as the energy of such long waves is generally low. This explains why the buoy also performs well when it is subjected to irregular motions (less than 2% error in the significant wave height of a half-hour measurement in realistic irregular sea states with peak periods between 5 and 20 s can be expected). It can be concluded that the buoy accurately measures accelerations. The accuracy of the derived displacements decreases when very long swell wave energy (> 20 s) is present. Review of the internal integration procedure may be considered when there is a specific interest in measuring longer waves.

Solids Distribution in Sediment-Laden Open-Channel Flow: Experiment and Prediction

2020 ◽  
Author(s):  
Václav Matoušek ◽  
Jan Krupička ◽  
Tomáš Picek ◽  
Štěpán Zrostlik
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Transport Model ◽  
Plane Surface ◽  
Open Channel Flow ◽  
Solid Particles ◽  
Experimental Results ◽  
Transport Layer ◽  
Experimental Investigations ◽  
Solids Concentration

Abstract Solid-liquid flow is studied in an open channel with a mobile bed at the condition of intense transport of solids. It is flow of high-concentrated mixture of coarse sediment and water over a plane surface of the bed eroded due to high bed shear. In the flow, solid particles are non-uniformly distributed across the flow depth. The flow develops a transport layer, adjacent to the the top of the bed, in which transported particles interact with each other. Results are presented of experimental investigations of the sediment-laden open-channel flow in a recirculating titling flume. The experiments included measurements (using ultrasonic techniques) of the distribution of solids velocity across the transport layer. The related distribution of solids concentration was deduced from the measured distribution of velocity and from other measured flow quantities. Since recently, a direct measurement of the solids distribution across the transport layer has been added to the experiments using a measuring technique svideo camera and a laser sheet. This work discusses results of combined measurements of the distributions of solids concentration and velocity in steady uniform turbulent flow for two lightweight solids fractions and various flow conditions (a broad range of the bed Shields parameter, discharge of solids, discharge of mixture, and the longitudinal slope of the bed). Furthermore, the camera-based measuring method and the deducing method for a determination of solids distribution are discussed and their results compared to show a good agreement in a majority of the test runs. The experimental results are compared with predictions of a recently developed bed-load transport model. Among other outputs, the model predicts the position of the top of the transport layer and the local velocity of sediment particles at this position. The presented model predictions agree well with experimental results based on the measured distibutions.

Low-Frequency Oscillations Within the Hambantota Port During the Southwest Monsoon, 2019

2020 ◽  
Author(s):  
Zhenjun Zheng ◽  
Xiaozhou Ma ◽  
Xuezhi Huang ◽  
Yujin Dong ◽  
Guohai Dong
Keyword(s):  
Wind Waves ◽  
Low Frequency ◽  
Southwest Monsoon ◽  
Long Waves ◽  
Frequency Wave ◽  
Low Frequency Oscillations ◽  
Mild Slope Equation ◽  
Spectrum Density ◽  
Forcing Mechanisms ◽  
Low Frequency Waves

Abstract Long waves with periods greater than tens of seconds propagating into a harbor may be trapped and significantly amplified, thereby resulting in detrimental effects on port operations. The water surface elevation in the Hambantota Port, Sri Lanka, was measured to investigate the low-frequency oscillations and their forcing mechanisms. Results show that the port is protected well from short waves with periods less than 30 s; however, the protection against long waves with periods larger than 30 s is inadequate. The spectral analyses identified four dominant periods within the low-frequency wave range. Modal analysis based on the extended mild-slope equation shows that the measured spectrum density for some dominant periods is low because the measurement point is close to the corresponding modal lines. Correlation analysis shows that low-frequency oscillations inside the Hambantota Port are excited directly by the low-frequency waves contained within the incident waves. The low-frequency waves outside the Hambantota Port are generated from the higher-frequency gravity waves (swell and wind waves) due to nonlinear interactions. Empirical formula is adopted to estimate the low-frequency wave height outside the Hambantota Port.

Mapping the Domain of Electronic Repair Shops: A Field Study in Fault Diagnosis

1995 ◽  
Vol 39 (9) ◽  
pp. 464-468 ◽  
Author(s):  
Dal Vernon C. Reising ◽  
Penelope M. Sanderson
Keyword(s):  
Fault Diagnosis ◽  
Concept Maps ◽  
Field Work ◽  
Problem Definition ◽  
Experimental Investigations ◽  
Simple Explanation ◽  
Field Observations ◽  
Multiple Faults ◽  
Technological Advances ◽  
In Series

Recent experimental research has indicated that different multiple faults impose differing levels of objective and subjective difficulty on human troubleshooters. Technological advances suggest that systems are becoming more complex and integrated, in which case multiple components will fail. Operators will have to be able to deal with these more complex failures. In this paper we report field work conducted in order to build and substantiate a model of the factors influencing fault diagnosis in the field. By conducting field observations and by constructing concept maps, we investigated how expert troubleshooters handle the difficulty associated with diagnosing multiple faults. The troubleshooters were expert electronic technicians in departmental repair shops on a large university campus. The end product of the research is a model of fault diagnosis that is grounded in field data. Our results suggest that diagnostic difficulty arises from several factors: (1) organizational structure, (2) technicians' strategies for fault diagnosis, and (3) equipment design. The field observations and concept maps indicate that technicians approach the diagnostic task with standard, ritualistic methods that they have developed over years of experience. They generally go through two phases of troubleshooting: (1) the problem definition phase and (2) what we call the At-the-Equipment-TroubleShooting (AETS) phase. Technicians also reason about multiple failures in series, considering one simple explanation at a time. Our principal conclusion is that in real-world settings the three previously mentioned factors have evolved to avoid situations in which technicians must engage in prolonged functional reasoning. These findings will be used (1) to develop further the model of fault diagnosis, and (2) to guide future experimental investigations studying the influences of fault diagnosis.

Approximate Calculation of the Laminar Boundary Layer

1949 ◽  
Vol 1 (3) ◽  
pp. 245-280 ◽  
Author(s):  
B. Thwaites
Keyword(s):  
Boundary Layer ◽  
Laminar Boundary Layer ◽  
Applied Mathematics ◽  
Equations Of Motion ◽  
Momentum Equation ◽  
Solid Boundary ◽  
Approximate Methods ◽  
Principal Characteristics ◽  
Two Dimensional Flow ◽  
In Series

The steady two-dimensional flow of viscous incompressible fluid in the boundary layer along a solid boundary, which is governed by Prandtl's approximation to the full equations of motion, presents a problem which in general is as intractable as any in applied mathematics. The problem, however, has such an immediate and necessary application that approximate methods of varying accuracy which go beyond the formal processes of expansions in series and so on, have been devised for the rapid calculation of the principal characteristics of the laminar boundary-layer, the variation of pressure along the surface being known. Such methods usually represent approximately the boundary-layer velocity distribution at any point by one of a known family of distributions whose spacing along the surface is determined by some means, often by the use of Kármán's momentum equation.

Gas Dynamics of the Temperature-Determined Stirling Cycle

1981 ◽  
Vol 23 (4) ◽  
pp. 207-216 ◽  
Author(s):  
A. J. Organ
Keyword(s):  
Angular Speed ◽  
Momentum Equation ◽  
Operating Conditions ◽  
Working Fluid ◽  
Gradient Term ◽  
Unexpected Finding ◽  
State Variables ◽  
Frictional Drag ◽  
Stirling Cycle ◽  
In Series

The Stirling cycle machine is modelled as a number of sections of duct in series, some tapered, some parallel. The working fluid assumes the temperature of the adjacent metal wall. Flow is defined by two conservation equations (mass and momentum) and the equation of state, p = ρRT. Friction is taken into account by using the steady-state correlation between friction factor, local instantaneous Reynolds number, and local hydraulic radius. The formulation permits frictional drag and frictional reheating to interact more or less as they do during operation of a Stirling cycle machine at high rotational speeds. The equations are converted to characteristic form and solved numerically with pressure, p, and velocity, u, as state variables rather than the more usual a (acoustic speed) and u. This formulation paves the way for a full characteristics solution incorporating the energy equation but avoiding the entropy gradient term ∂s/∂x which is inappropriate to conditions within the Stirling machine. The paper includes a Mach-line net plotted by computer for the first revolutions of the crankshaft after start-up. Indicator diagrams are presented corresponding to different angular speeds. It is found that the indicator diagram for the compression space is not greatly affected by angular speed, while that for the expansion space changes from positive, via figure-of-eight to negative over a relatively narrow speed range. An attempt is made to explain this unexpected finding in terms of the momentum equation for constant area flow with a severe temperature gradient. A comparison is included between the computed results and those predicted for the same operating conditions by the Schmidt isothermal analysis.

scholarly journals Application of Polyhedral Spherical Packing Precipitation Technology in Water Plant Reform

2019 ◽  
pp. 10-17
Author(s):  
LI Ya wen ◽  
Cheng Sheng gao ◽  
Li Ru yi
Keyword(s):  
Rural Areas ◽  
Engineering Application ◽  
Sphere Packing ◽  
Solid Particles ◽  
Inertia Force ◽  
Spherical Packing ◽  
Sedimentation Tank ◽  
Inclined Tube ◽  
New City ◽  
Pass Through

On the basis of micro flocculation interception sedimentation technology, polyhedral spherical packing is used as intercepting material in sedimentation tank. The process utilizes the characteristics of polyhedral sphere to make flocs and water move relatively, and continuously change the direction of water flow to produce turbulent vortices. When water moves in a vorticity, solid particles move relative to the flow along the radial direction under the action of centrifugal inertia force, which provides for the radial collision of particles with different scales along the vortices. Under these conditions, the micro flocs collide and aggregate continuously as they pass through the blades, and the concentration of alum in the water is increased. Finally, the precipitation is removed under the action of gravity. The process is applied to the reconstruction of Miluo New City Waterworks, and the original inclined pipe sedimentation tank is retained and put into operation. The results show that the turbidity of effluent from polyhedral spherical sedimentation tank can reach below 2NTU, while that from inclined tube sedimentation tank is above 2NTU. The treatment effect of polyhedral sphere on low turbidity water is better than that of inclined tube, which provides a reference for the transformation of small and medium-sized water plants in rural areas. Keywords: Polyhedral sphere packing; Interception sedimentation; Technological transformation; Engineering application

Influence of following, regular and irregular long waves on wind-wave growth with fetch: an experimental study

2021 ◽  
Author(s):  
Antoine Villefer ◽  
Michel Benoit ◽  
Damien Violeau ◽  
Christopher Luneau ◽  
Hubert Branger
Keyword(s):  
Wave Energy ◽  
Wind Wave ◽  
Wind Waves ◽  
Peak Frequency ◽  
Long Waves ◽  
Specific Method ◽  
Wave Growth ◽  
Wind Velocities ◽  
Series Of Experiments ◽  
Frequency Variations

AbstractA series of experiments were conducted in a wind-wave tank facility in Marseilles (France) to study the effects of preexisting swell conditions (represented by long mechanically-generated waves) on wind-wave growth with fetch. Both monochromatic and irregular (JONSWAP-type) long wave conditions with different values of wave steepness have been generated in the presence of a constant wind forcing, for several wind velocities. A spectral analysis of temporal wave signals combined with airflow measurements allowed to study the evolution of both wave systems with the aim of identifying the interaction mechanisms transportable to prototype scale. In particular, a specific method is used to separate the two wave systems in the measured bimodal spectra. In fetch-limited conditions, pure wind-wave growth is in accordance with anterior experiments, but differs from the prototype scale in terms of energy and frequency variations with fetch. Monochromatic long waves are shown to reduce the energy of the wind-waves significantly, as it was observed in anterior laboratory experiments. The addition of JONSWAP-type long waves instead results in a downshift of the wind-wave peak frequency but no significant energy reduction. Overall, it is observed that the presence of long waves affects the wind-wave energy and frequency variations with fetch. Finally, in the presence of JONSWAP-type long waves, variations of wind-wave energy and peak frequency with fetch appear in close agreement with the wind-wave growth observed at prototype scale both in terms of variations and nondimensional magnitude.

Experimental Investigations of the Self-Controlled Synchronous Motor Connected to a Three-Phase Line Commutated SCR Inverter

2016 ◽  
Vol 7 (1) ◽  
pp. 1
Author(s):  
Tapan Kumar Chakraborty
Keyword(s):  
Steady State ◽  
Synchronous Motor ◽  
The Self ◽  
Experimental Investigations ◽  
Phase Line ◽  
Three Phase ◽  
In Series ◽  
Terminal Voltage ◽  
Excitation Winding ◽  
Steady State Performance

<p>This paper concerns the experimental investigations of the three-phase line commutated SCR inverter fed synchronous motor.  The fabricated system consists of a line-commuted inverter, a three-phase synchronous motor with the excitation winding connected in series to the inverter input, a terminal voltage sensor and a gate-pulse generating circuit. The firing pulses for SCRs of the inverter are generated by the microprocessor in proper sequence with the help of synchronizing signal derived from the terminal voltages of the synchronous machine. The steady state performance characteristics are obtained experimentally using the fabricated system. The experimental results show that a three-phase synchronous motor supplied by a line commutated inverter with the excitation winding connected in series to the dc link provide  excellent characteristics of the conventional dc series motor.</p>

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