Verification and Validation of URANS Wave Resistance for Air Cushion Vehicles, and Comparison With Linear Theory

2011 ◽  
Vol 55 (04) ◽  
pp. 249-267
Author(s):  
S. Bhushan ◽  
F. Stern ◽  
L. J. Doctors
Keyword(s):  
Experimental Data ◽  
Shallow Water ◽  
Froude Number ◽  
Linear Theory ◽  
Nonlinear Theory ◽  
Pressure Level ◽  
Sinkage And Trim ◽  
Air Cushion ◽  
Air Cushion Vehicles ◽  
Straight Ahead

Verification and validation of URANS wave-resistance predictions for straight-ahead and yawed air-cushion vehicles in calm deep and shallow water are performed. The nonlinear and linear theories are compared to explicate their trends for large cushion pressures, water depth, and cushion dimensions, and the nonlinear theory sinkage and trim trends are discussed. The grid-verification study shows monotonically converged solutions with averaged uncertainty of 4% and 10% for straight-ahead motion in deep and shallow water, respectively. URANS predictions agree with the experimental data to within 6% and 9% for straight-ahead deep and shallow water simulations, respectively. The smooth-edged cushion-pressure simulations predict lower resistance than the sharp-edged case, whereas no significant dependence is obtained for Reynolds number and turbulence modeling. URANS predicts attenuation in the resistance secondary hump as the cushion-pressure level increases. On the other hand, the linear theory does not account for the effect of cushion-pressure level. The linear and nonlinear theories compare within 4.5% for static cushion-pressure-to length ratios less than 0.025 and Froude number greater than 0.5 for both deep and shallow water. The nonlinear theory predicts the effect of water depth better than the linear theory, when compared with the experiments. Both the theories agree well in predicting the decrease in resistance with the decrease in cushion width. The nonlinear theory does not show unrealistically large resistance and side force for sharp-edged cushion pressure for yawed cases, as observed in the linear theory. However, both the theories compare well for the resistance and side-force predictions for the smooth-edged cushion pressure, where the results agree within 10% of the deep-water experimental data. The nonlinear theory predictions for the sinkage and trim are in good agreement with the experimental data, but sinkage is overpredicted and trim is underpredicted. URANS wave-elevation patterns display transverse and diverging waves, which compare well with the Kelvin waves for Froude number less than 0.6 and greater than 1.0, respectively. URANS predicts breaking waves for large cushion pressures for Froude number less than 0.6.

Waves and Wave Resistance for Air-Cushion Vehicles with Time-Dependent Cushion Pressures

1978 ◽  
Vol 22 (03) ◽  
pp. 170-177
Author(s):  
H. J. Haussling ◽  
R. T. Van Eseltine
Keyword(s):  
Shallow Water ◽  
Froude Number ◽  
Water Depth ◽  
Critical Frequency ◽  
Wave Resistance ◽  
Time Dependent ◽  
Length Ratio ◽  
Wave Patterns ◽  
Air Cushion ◽  
Air Cushion Vehicles

Wave patterns and wave resistance are computed for air-cushion vehicles with time-dependent cushion pressures moving at uniform speed over deep and shallow water. The effect of beam-to-length ratio, Froude number, and water depth on the resistance is investigated. The resistance is found to exhibit a distinctive behavior at a critical frequency. This behavior corresponds to a singularity in the resistance at the critical frequency. The importance of this behavior is found to diminish with decreasing beam-to-length ratio and increasing Froude number.

Comparison Between Theoretical Predictions of Wave Resistance and Experimental Data for the Wigley Hull

1983 ◽  
Vol 27 (04) ◽  
pp. 215-226
Author(s):  
C. Y. Chen ◽  
F. Noblesse
Keyword(s):  
Experimental Data ◽  
Froude Number ◽  
Resistance Coefficient ◽  
Wave Resistance ◽  
Number Range ◽  
Theoretical Predictions ◽  
Wigley Hull ◽  
Sinkage And Trim ◽  
Theoretical Results ◽  
Good Agreement

A number of theoretical predictions of the wave-resistance coefficient of the Wigley hull are compared with one another and with available experimental data, to which corrections for sinkage and trim are applied. The averages of eleven sets of experimental data (corrected for sinkage and trim) and of eleven sets of theoretical results for large values of the Froude number, specifically for F 0.266, 0.313, 0.350, 0.402, 0.452, and 0.482, are found to be in fairly good agreement, in spite of considerable scatter in both the experimental data and the numerical results. Furthermore, several sets of theoretical results are fairly close to the average experimental data and the average theoretical predictions for these large values of the Froude number. Discrepancies between theoretical predictions and experimental measurements for small values of the Froude number, specifically for F = 0.18, 0.20, 0.22, 0.24, and 0.266, generally are much larger than for the above-defined high-Froude-number range. However, a notable exception to this general finding is provided by the first-order slender-ship approximation evaluated in Chen and Noblesse [1],3 which is in fairly good agreement with the average experimental data over the entire range of values of Froude number considered in this study.

Spilling breakers in shallow water: applications to Favre waves and to the shoaling and breaking of solitary waves

2016 ◽  
Vol 808 ◽  
pp. 441-468 ◽  
Author(s):  
S. L. Gavrilyuk ◽  
V. Yu. Liapidevskii ◽  
A. A. Chesnokov
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Shallow Water ◽  
Froude Number ◽  
Fluid Velocity ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Undular Bore ◽  
Characteristic Wavelength ◽  
Good Agreement

A two-layer long-wave approximation of the homogeneous Euler equations for a free-surface flow evolving over mild slopes is derived. The upper layer is turbulent and is described by depth-averaged equations for the layer thickness, average fluid velocity and fluid turbulent energy. The lower layer is almost potential and can be described by Serre–Su–Gardner–Green–Naghdi equations (a second-order shallow water approximation with respect to the parameter $H/L$, where $H$ is a characteristic water depth and $L$ is a characteristic wavelength). A simple model for vertical turbulent mixing is proposed governing the interaction between these layers. Stationary supercritical solutions to this model are first constructed, containing, in particular, a local turbulent subcritical zone at the forward slope of the wave. The non-stationary model was then numerically solved and compared with experimental data for the following two problems. The first one is the study of surface waves resulting from the interaction of a uniform free-surface flow with an immobile wall (the water hammer problem with a free surface). These waves are sometimes called ‘Favre waves’ in homage to Henry Favre and his contribution to the study of this phenomenon. When the Froude number is between 1 and approximately 1.3, an undular bore appears. The characteristics of the leading wave in an undular bore are in good agreement with experimental data by Favre (Ondes de Translation dans les Canaux Découverts, 1935, Dunod) and Treske (J. Hydraul Res., vol. 32 (3), 1994, pp. 355–370). When the Froude number is between 1.3 and 1.4, the transition from an undular bore to a breaking (monotone) bore occurs. The shoaling and breaking of a solitary wave propagating in a long channel (300 m) of mild slope (1/60) was then studied. Good agreement with experimental data by Hsiao et al. (Coast. Engng, vol. 55, 2008, pp. 975–988) for the wave profile evolution was found.

On the Squat of a Ship

1984 ◽  
Vol 28 (02) ◽  
pp. 107-117 ◽  
Author(s):  
P. M. Naghdi ◽  
M. B. Rubin
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Differential Equations ◽  
Froude Number ◽  
Steady State Solution ◽  
State Solution ◽  
Inviscid Fluid ◽  
Two Dimensional ◽  
Sinkage And Trim

The problem of the squat of a "two-dimensional" ship is solved using a nonlinear steady-state solution of the differential equations of the theory of a directed fluid sheet. Particular attention is focused on the prediction of the sinkage and trim of the ship, and the results for a model ship qualitatively agree with available experimental data. Specifically, the solution presented here predicts the experimentally observed dependence of the sinkage and trim on the equilibrium depth of the water (regarded here as an incompressible, inviscid fluid), and predicts a nonzero drag for subcritical ship speeds (corresponding to the values of depth Froude number F < 1). The solution also exhibits certain detailed features of the sinkage curves which apparently were not observed in the experiments mentioned above. In this connection, additional relevant experiments are suggested.

scholarly journals Exhaust Noise Reduction by Application of Expanded Collecting System in Pneumatic Tools and Machines

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1592
Author(s):  
Dominik Gryboś ◽  
Jacek S. Leszczyński ◽  
Dorota Czopek ◽  
Jerzy Wiciak
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Noise Reduction ◽  
Sound Pressure ◽  
Acoustic Pressure ◽  
Pressure Level ◽  
Computational Results ◽  
Noise Measurements ◽  
Exhaust Noise ◽  
Collecting System

In this paper, we demonstrate how to reduce the noise level of expanded air from pneumatic tools. Instead of a muffler, we propose the expanded collecting system, where the air expands through the pneumatic tube and expansion collector. We have elaborated a mathematical model which illustrates the dynamics of the air flow, as well as the acoustic pressure at the end of the tube. The computational results were compared with experimental data to check the air dynamics and sound pressure. Moreover, the study presents the methodology of noise measurement generated in a pneumatic screwdriver in a quiet back room and on a window-fitting stand in a production hall. In addition, we have performed noise measurements for the pneumatic screwdriver and the pneumatic screwdriver on an industrial scale. These measurements prove the noise reduction of the pneumatic tools when the expanded collecting system is used. When the expanded collecting system was applied to the screwdriver, the measured Sound Pressure Level (SPL) decreased from 87 to 80 dB(A).

scholarly journals Modelling Weirs in Two-Dimensional Shallow Water Models

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2152
Author(s):  
Gonzalo García-Alén ◽  
Olalla García-Fonte ◽  
Luis Cea ◽  
Luís Pena ◽  
Jerónimo Puertas
Keyword(s):  
Experimental Data ◽  
Shallow Water ◽  
Shallow Water Equations ◽  
Water Model ◽  
Two Dimensional ◽  
Shallow Water Model ◽  
Experimental Dataset ◽  
River Hydraulics ◽  
Shallow Water Models ◽  
Water Models

2D models based on the shallow water equations are widely used in river hydraulics. However, these models can present deficiencies in those cases in which their intrinsic hypotheses are not fulfilled. One of these cases is in the presence of weirs. In this work we present an experimental dataset including 194 experiments in nine different weirs. The experimental data are compared to the numerical results obtained with a 2D shallow water model in order to quantify the discrepancies that exist due to the non-fulfillment of the hydrostatic pressure hypotheses. The experimental dataset presented can be used for the validation of other modelling approaches.

A Simple Approach to the Study of Wave Patterns

2014 ◽  
Vol 156 (A3) ◽  
Keyword(s):  
Numerical Methods ◽  
Shallow Water ◽  
Froude Number ◽  
Critical Speed ◽  
Graphical Method ◽  
Three Dimensional ◽  
Simple Approach ◽  
Critical Depth ◽  
Simple Manner ◽  
Wave Patterns

The paper revisits some pioneering work of Sir Thomas Havelock on wave patterns with particular attention focused on his graphical method of analysis. Motivated by a desire to explore this method further using numerical methods, it is extended in a simple manner to give three-dimensional illustrations of the wave patterns of a point disturbance in deep and shallow water. All results are confined to the sub- and trans-critical regimes with some obtained very close to the critical Depth Froude Number. Some conclusions are drawn on the wave types produced when operating close to the critical speed and their decay with distance off.

Characteristics of Hydraulic Shock Waves in an Inclined Chute Contraction - Experiments

2009 ◽  
Vol 25 (1) ◽  
pp. 129-136 ◽  
Author(s):  
C.-D. Jan ◽  
C.-J. Chang ◽  
J.-S. Lai ◽  
W.-D. Guo
Keyword(s):  
Experimental Data ◽  
Shock Waves ◽  
Froude Number ◽  
Inclination Angle ◽  
Laboratory Experiments ◽  
Deflection Angle ◽  
Experimental Results ◽  
Regression Analyses ◽  
Hydraulic Shock ◽  
Empirical Relations

AbstractThis paper presents the experimental results of the characteristics of hydraulic shock waves in an inclined chute contraction with consideration of the effects of sidewall deflection angle φ, bottom inclination angle θ and approach Froude number Fr0. Seventeen runs of laboratory experiments were conducted in the range of 27.45° ≤φ ≤ 40.17°, 6.22° ≤ θ ≤ 25.38° and 1.04 ≤ Fr0 ≤ 3.51. Based on the experimental data, three empirical dimensionless relations for the shock angle, maximum shockwave height, and corresponding position of maximum shockwave were obtained by regression analyses, respectively. These empirical relations would be useful for hydraulic engineers in designing chute contraction structures.

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