Some Experimental Results with Ship Model Acceleration Waves

1981 ◽  
Vol 25 (03) ◽  
pp. 181-190
Author(s):  
S. M. Çalisal
Keyword(s):  
Survey Methods ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Pitching Moment ◽  
Total Resistance ◽  
Acceleration Waves ◽  
Acceleration Potential ◽  
Initial Acceleration ◽  
Theoretical Results ◽  
Independent Model

The wave resistance of a ship moving at a constant speed can be calculated using information obtained from its wave pattern. One of the basic assumptions in wave survey methods is t1he existence of a time-independent model speed. In towing tanks initial acceleration is unavoidable. Wehausen (1964) showed that the effect of initial acceleration on wave resistance has a decaying and oscillating character. Çalişal (1977) gave the general form of the initial acceleration potential and showed the existence of a two-dimensional wave of the formζT=AcTsin[14k0(x−cT)+ϕ(t)]+0(cT)−2(1)To study the validity of the theoretical results, some experiments were performed. The variation of the measured spectra and the frequencies within the recorded total resistance pitching moment are of interest. Results indicate that models should travel a distance proportional to the square of the Froude number before wave data collection can begin, that the predicted encounter frequency exists in the recorded total resistance and pitching moment signals, and that special effort is required to avoid initial acceleration waves due to wall effects.

Effect of Initial Acceleration on Ship Wave Pattern and Wake Survey Methods

1977 ◽  
Vol 21 (04) ◽  
pp. 239-247
Author(s):  
S. Calisal
Keyword(s):  
Survey Methods ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Acceleration Wave ◽  
Ship Wave ◽  
Initial Acceleration ◽  
Wake Survey

Wave resistance calculations based on wave survey methods assume a constant ship velocity. The possible effects of initial acceleration are studied for different wave survey methods, and a procedure for determining the existence of an initial acceleration wave is proposed.

scholarly journals Continuity with respect to the speed for optimal ship forms based on Michell's formula

2021 ◽  
Vol 0 (0) ◽  
pp. 0
Author(s):  
Julien Dambrine ◽  
Morgan Pierre
Keyword(s):  
Drag Coefficient ◽  
Froude Number ◽  
Nonnegative Function ◽  
Wave Resistance ◽  
Viscous Drag ◽  
Total Resistance ◽  
Hull Design ◽  
Bulbous Bow ◽  
Two Parameters ◽  
Theoretical Results

<p style='text-indent:20px;'>We consider a ship hull design problem based on Michell's wave resistance. The half hull is represented by a nonnegative function and we seek the function whose domain of definition has a given area and which minimizes the total resistance for a given speed and a given volume. We show that the optimal hull depends only on two parameters without dimension, the viscous drag coefficient and the Froude number of the area of the support. We prove that, up to uniqueness, the optimal hull depends continuously on these two parameters. Moreover, the contribution of Michell's wave resistance vanishes as either the Froude number or the drag coefficient goes to infinity. Numerical simulations confirm the theoretical results for large Froude numbers. For Froude numbers typically smaller than <inline-formula><tex-math id="M1">\begin{document}$ 1 $\end{document}</tex-math></inline-formula>, the famous bulbous bow is numerically recovered. For intermediate Froude numbers, a "sinking" phenomenon occurs. It can be related to the nonexistence of a minimizer.</p>

scholarly journals Hydrodynamic Forces Exerting on an Oscillating Cylinder under Translational Motion in Water Covered by Compressed Ice

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 822
Author(s):  
Yury Stepanyants ◽  
Izolda Sturova
Keyword(s):  
Lift Force ◽  
Wave Motion ◽  
Translational Motion ◽  
Added Mass ◽  
Hydrodynamic Forces ◽  
Wave Resistance ◽  
Translational Velocity ◽  
Damping Coefficients ◽  
Incompressible Ideal Fluid ◽  
Theoretical Results

This paper presents the calculation of the hydrodynamic forces exerted on an oscillating circular cylinder when it moves perpendicular to its axis in infinitely deep water covered by compressed ice. The cylinder can oscillate both horizontally and vertically in the course of its translational motion. In the linear approximation, a solution is found for the steady wave motion generated by the cylinder within the hydrodynamic set of equations for the incompressible ideal fluid. It is shown that, depending on the rate of ice compression, both normal and anomalous dispersion can occur in the system. In the latter case, the group velocity can be opposite to the phase velocity in a certain range of wavenumbers. The dependences of the hydrodynamic loads exerted on the cylinder (the added mass, damping coefficients, wave resistance and lift force) on the translational velocity and frequency of oscillation were studied. It was shown that there is a possibility of the appearance of negative values for the damping coefficients at the relatively big cylinder velocity; then, the wave resistance decreases with the increase in cylinder velocity. The theoretical results were underpinned by the numerical calculations for the real parameters of ice and cylinder motion.

scholarly journals The wave pattern of a doublet in a stream

1928 ◽  
Vol 121 (788) ◽  
pp. 515-523 ◽  
Keyword(s):  
Surface Effect ◽  
Ideal Point ◽  
Finite Size ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Point Of View ◽  
The Body ◽  
Surface Elevation ◽  
More Care ◽  
Forced Waves

The following paper is a study of the surface waves caused by a doublet in a uniform stream, and in particular the variation in the pattern with the velocity of the stream or the depth of the doublet. In most recent work on this subject attention has been directed more to the wave resistance, which can be evaluated with less difficulty than is involved in a detailed study of the waves; in fact, it would seem that it is not necessary for that purpose to know the surface elevation completely, but only certain significant terms at large distances from the disturbance. Recent experimental work has shown con­siderable agreement between theoretical expressions for wave resistance and results for ship models of simple form, and attempts have been made at a similar comparison for the surface elevation in the neighbourhood of the ship. In the latter respect it may be necessary to examine expressions for the surface elevation with more care, as they are not quite determinate; any suitable free disturbance may be superposed upon the forced waves. For instance, it is well known that in a frictionless liquid a possible solution is one which gives waves in advance as well as in the rear of the ship, and the practical solution is obtained by superposing free waves which annul those in advance, or by some equivalent artifice. This process is simple and definite for an ideal point disturbance, but for a body of finite size or a distributed disturbance the complete surface elevation in the neighbourhood of the body requires more careful specification as regards the local part due to each element. It had been intended to consider some expressions specially from this point of view, but as the matter stands at present it would entail a very great amount of numerical calculation, and the present paper is limited to a much simpler problem although also involving considerable computation. A horizontal doublet of given moment is at a depth f below the surface of a stream of velocity c ; the surface effect may be described as a local disturbance symmetrical fore and aft of the doublet together with waves to the rear. Two points are made in the following work.

Development and Assessment of a Total Resistance Optimized Bow for the AE 36

1994 ◽  
Vol 31 (02) ◽  
pp. 149-160
Author(s):  
Donald C. Wyatt ◽  
Peter A. Chang
Keyword(s):  
Experimental Data ◽  
Optimization Procedure ◽  
Wave Resistance ◽  
Scale Model ◽  
Optimization Approach ◽  
Nonlinear Constraints ◽  
Total Resistance ◽  
Hull Form ◽  
Final Design ◽  
Resistance Data

A numerically optimized bow design is developed to reduce the total resistance of a 23 000 ton ammunition ship (AE 36) at a speed of 22 knots. An optimization approach using slender-ship theory for the prediction of wave resistance is developed and applied. The new optimization procedure is an improvement over previous optimization methodologies in that it allows the use of nonlinear constraints which assure that the final design remains within practical limits from construction and operational perspectives. Analytic predictions indicate that the AE 36 optimized with this procedure will achieve a 40% reduction in wave resistance and a 33% reduction in total resistance at 22 knots relative to a Kracht elliptical bulb bow design. The optimization success is assessed by the analysis of 25th scale model resistance data collected at the David Taylor Research Center deepwater towing basin. The experimental data indicate that the optimized hull form yields a 51% reduction in wave resistance and a 12% reduction in total resistance for the vessel at 22 knots relative to the Kracht bulb bow design. Similarly encouraging results are also observed when comparisons are made with data collected on two other conventionally designed AE 36 designs.

Wave Resistance and Wave Patterns of Thin Ships

1976 ◽  
Vol 20 (01) ◽  
pp. 1-6
Author(s):  
Joseph B. Keller ◽  
Daljit S. Ahluwalia
Keyword(s):  
Transverse Wave ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Kelvin Waves ◽  
Profile Curve ◽  
Cylindrical Waves ◽  
Straight Line ◽  
Starting Point ◽  
Wave Patterns ◽  
Similar Pair

The wave resistance R and wave height h(x, z) are evaluated asymptotically for small Froude number F = U(gL)−½ for a slender hull of any shape. Michell's theory for a thin ship of length L moving with constant speed U along a straight line is the starting point. It is found that asymptotically R and h depend only upon four properties of the ship—the slope of the hull and the slope of the profile curve of the hull at the waterline at bow and stern. Simple formulas are obtained for R and h in terms of these slopes. The wave pattern consists of four waves—a longitudinal and a transverse wave from the bow and a similar pair from the stern. Their phases are the same as those of Kelvin waves due to pressure points at the bow and stern, and they also decay with distance like cylindrical waves. However, their amplitudes have different angular variations from those of Kelvin waves.

scholarly journals Research on a method of hull form design based on wave-making resistance optimization

2012 ◽  
Vol 19 (3) ◽  
pp. 16-25 ◽  
Author(s):  
Jianglong Sun ◽  
Xujian Lv ◽  
Weibin Liu ◽  
Hanwen Ning ◽  
Xianwen Chen
Keyword(s):  
Cross Section ◽  
Frictional Resistance ◽  
Wave Resistance ◽  
Total Resistance ◽  
Hull Form ◽  
Mathematical Procedure ◽  
Result Show ◽  
Form Design ◽  
Hull Form Design ◽  
Resistance Performance

ABSTRACT In this paper, we consider an optimization of the hull shape in order to minimize the total resistance of a ship. The total resistance is assumed to be the sum of the wave resistance computed on the basis of the thin-ship theory and the frictional resistance. Smoothness of hull lines is proved with mathematical procedure, in which differentials of the hull lines functions are analyzed. The wave-making resistance optimization, involving a genetic algorithm, uses Michell integral to calculate wave resistance. A certain hull form is generated by the method using cross section information of a modified DTMB model ship 5415 and a comparative experiment is carried out. Experimental and calculation result show that the method is of good adaptability for designing certain types of ships with excellent resistance performance.

Improvements in the Prediction of the Characteristic Wave Pattern of Blunt Ships With Potential Codes

2013 ◽  
Author(s):  
Johannes Will ◽  
Jakob Christiansen
Keyword(s):  
Software Development ◽  
Viscous Flow ◽  
Potential Flow ◽  
Wave Pattern ◽  
Wave Resistance ◽  
Characteristic Wave ◽  
Ship Building

Potential flow solvers have been and still are the work horses of computational wave resistance determination. Having matured over more then two decades they seem to have reached their limit of improvement. While the main focus of today’s software development lies on viscous flow solvers, the development of potential codes must not be disregarded, but they should instead be keep up to date with respect to the requirements of today’s and future ship building markets as well as hardware and software capabilities.

Viscosity, Wake, and Ship Waves

1970 ◽  
Vol 14 (04) ◽  
pp. 207-240
Author(s):  
Roger Brard
Keyword(s):  
Wave Pattern ◽  
Viscous Resistance ◽  
Total Resistance ◽  
Wave Analysis ◽  
Ship Waves ◽  
Wake Survey

In this paper a theory of the effect of viscosity on ship waves is presented. It is shown that the wake affects the singularities kinematically equivalent to the hull and generates waves which modify the resulting wave pattern. The theory may explain why the estimate of the viscous resistance obtained by means of a wake survey and the estimate of the wavemaking resistance obtained by means of a wave analysis do not add up, in general, to the total resistance measured by using a dynamometer. The discrepancy seems to be due essentially to the existence of a wavemaking viscous resistance.

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