Wave Reduction by S-Catamaran at Supercritical Speeds

2003 ◽  
Vol 47 (02) ◽  
pp. 145-154
Author(s):  
Xue-Nong Chen ◽  
Som D. Sharma ◽  
Norbert Stuntz
Keyword(s):  
Model Experiment ◽  
Wave Resistance ◽  
Practical Reasons ◽  
Trial And Error ◽  
Resistance Reduction ◽  
Design Speed ◽  
Yaw Angle ◽  
Twin Hulls ◽  
The Waves ◽  
The Ideal

The S-catamaran is a catamaran with twin hulls that are slightly curved in an S-form and arranged at a mean yaw angle but mirror symmetric to their common longitudinal centerplane. Theoretical studies (Chen & Sharma 1997, Chen 1997) show that by proper choice of the sectional area curve, separation, curvature, and yaw the waves generated by the component hulls cancel each other at a supercritical design speed, and consequently the wave wake and wave resistance can be substantially reduced. Theoretically, an almost complete elimination of the waves would be conceivable for an S-catamaran. To verify this theory, a model experiment with an S-catamaran was recently carried out in the VBD. The S-catamaran (Chen & Sharma 1997) was designed to have the same length and displacement as the VBD model series M601, which was developed and tested much earlier in the VBD by Heuser (1973). Despite certain deviations from the ideal form for practical reasons, the wave resistance of the new curved-yawed-hull catamaran with and without skeg was numerically found to be less than that of an equivalent straight-unyawed-hull catamaran by 50% and 30%, respectively. Now, the new design, albeit without skeg, has been validated by a model experiment. In comparison with a reference catamaran of the series M601, up to 28% wave-resistance reduction was achieved in the experiment, although not in the originally designed configuration but at a reduced yaw angle found by trial and error.

Optimization of the Hybrid Ship Transport Factor through Retrofitted Wave Cancelling Side-Hull Expansions and Bow Bulb

2015 ◽  
Author(s):  
Manivannan Kandasamy ◽  
Ping C. Wu ◽  
Scott Bartlett ◽  
Loc Nguyen ◽  
Frederick Stern
Keyword(s):  
High Performance ◽  
Negative Impact ◽  
Fiscal Year ◽  
Hull Form ◽  
Transport Factor ◽  
Resistance Reduction ◽  
The Us ◽  
Us Navy ◽  
Speed Range ◽  
Design Speed

The US Navy is currently considering the introduction of a Flight III variant beginning with DDG-123 in Fiscal Year 2016. The new design incorporates a new combat system and associated power and cooling upgrades. The overall system improvements increase the payload of the ship and the resulting increased displacement has a negative impact on the service life allowance for range, fuel consumption and sea-keeping characteristics. The present objective is to increase the hull displacement without resistance and sea-keeping penalty and with minimal modifications to the baseline DTMB-5415 design (open literature surrogate of the existing DDG-51 hull form) by using retrofitted blisters in the form of side hull expansions and a bow-bulb. The investigation makes use of high-performance CFD computing for analysis of wave cancellation mechanisms. A candidate modified 5415 design with both blisters and bow bulb shows a resistance reduction of ~11% w.r.t.the baseline 5415 in the design speed range of 15-19 knots, even though the displacement is increased by 8%, such that the transport factor is increased by 19%.

A Slender-Ship Theory of Wave Resistance

1983 ◽  
Vol 27 (01) ◽  
pp. 13-33
Author(s):  
Francis Noblesse
Keyword(s):  
Froude Number ◽  
Wave Resistance ◽  
Successive Approximations ◽  
Zeroth Order ◽  
Remarkable Effect ◽  
Ship Wave ◽  
First Order ◽  
Wigley Hull ◽  
Low Froude Number ◽  
The Waves

A new slender-ship theory of wave resistance is presented. Specifically, a sequence of explicit slender-ship wave-resistance approximations is obtained. These approximations are associated with successive approximations in a slender-ship iterative procedure for solving a new (nonlinear integro-differential) equation for the velocity potential of the flow caused by the ship. The zeroth, first, and second-order slender-ship approximations are given explicitly and examined in some detail. The zeroth-order slender-ship wave-resistance approximation, r(0) is obtained by simply taking the (disturbance) potential, ϕ, as the trivial zeroth-order slender-ship approximation ϕ(0) = 0 in the expression for the Kochin free-wave amplitude function; the classical wave-resistance formulas of Michell [1]2 and Hogner [2] correspond to particular cases of this simple approximation. The low-speed wave-resistance formulas proposed by Guevel [3], Baba [4], Maruo [5], and Kayo [6] are essentially equivalent (for most practical purposes) to the first-order slender-ship low-Froude-number approximation, rlF(1), which is a particular case of the first-order slender-ship approximation r(1): specifically, the first-order slender-ship wave-resistance approximation r(1) is obtained by approximating the potential ϕ in the expression for the Kochin function by the first-order slender-ship potential ϕ1 whereas the low-Froude-number approximation rlF(1) is associated with the zero-Froude-number limit ϕ0(1) of the potentialϕ(1). A major difference between the first-order slender-ship potential ϕ(1) and its zero-Froude-number limit ϕ0(1) resides in the waves that are included in the potential ϕ(1) but are ignored in the zero-Froude-number potential ϕ0(1). Results of calculations by C. Y. Chen for the Wigley hull show that the waves in the potential ϕ(1) have a remarkable effect upon the wave resistance, in particular causing a large phase shift of the wave-resistance curve toward higher values of the Froude number. As a result, the first-order slender-ship wave-resistance approximation in significantly better agreement with experimental data than the low-Froude-number approximation rlF(1) and the approximations r(0) and rM.

Stern Flap–Waterjet–Hull Interactions and Mechanism: A Case of Waterjet-Propelled Trimaran With Stern Flap

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Lei Zhang ◽  
Jianing Zhang ◽  
Yuchen Shang
Keyword(s):  
High Efficiency ◽  
Navier Stokes ◽  
Local Effects ◽  
Resistance Components ◽  
Leading Role ◽  
Resistance Reduction ◽  
Sinkage And Trim ◽  
Improved Performance ◽  
Design Speed ◽  
Pressure Resistance

Abstract To research the stern flap (SF) and waterjet–hull interaction, unsteady Reynolds-averaged Navier–Stokes (URANS) simulations for a waterjet-propelled trimaran considering sinkage and trim are performed. Uncertainty analysis of the numerical results for the bare hull (BH) model is presented. At the design speed Froude number (Fr) of 0.6 and under displacement state, the model-scaled trimaran, installed with stern flaps of varied angle and length, tests the BH and self-propulsion (SP) performance based on URANS simulations. For the resistance, the global effects due to motions and the local effects of SF, waterjets (WJ), and the coupled term between SF and WJ on the hull are separately analyzed. Taking the waterjet propulsion system into account, an SP model with reasonable stern flap effectively reduces the trim, the resistance acting on the hull and the waterjet thrust deduction which contributes to energy-saving and high-efficiency propulsion. The mechanism of the improved performance of the waterjet-propelled trimaran with stern flaps is discussed. For the resistance increment, the global effects, the local effects of SF and WJ are the major reason for resistance increase, and the nonlinear coupled term of local effects contributes to the resistance reduction most. In addition, the different resistance components of frictional, hydrostatic, and hydrodynamic are separately researched, which shows that the pressure resistance components plays a leading role in the total resistance reduction in the SP model with the suitable SF.

scholarly journals Wave resistance : some cases of unsymmetrical forms

1926 ◽  
Vol 110 (754) ◽  
pp. 233-241 ◽  
Keyword(s):  
Mathematical Problem ◽  
Dynamical Theory ◽  
Wave Resistance ◽  
Experimental Results ◽  
General Effect ◽  
Surrounding Water ◽  
Order Of Magnitude ◽  
To Come ◽  
The Waves ◽  
Two Bodies

1. One of the chief features of interest in curves showing the variation of wave resistance with velocity is the occurrence of oscillations about a mean curve, which may be regarded as due to interference between the waves produced by the front and rear portions of the model. In various comparisons made between theoretical curves and such suitable experimental results as are available, the greatest divergence is perhaps in the magnitude of these oscillations, the theore­tical curves showing effects many times greater than similar experimental results. There are, no doubt, many approximations in the hydro-dynamical theory which preclude too close a comparison between theoretical and experimental results in any particular case, but it seems fairly certain that the divergence in question must be largely due to neglecting the effects of fluid friction. For several reasons it is useless to attempt at present a direct introduction of vis­cosity into the mathematical problem, but a consideration of its general effect suggests one or two calculations which may be of interest The direct effect of viscosity upon waves already formed may be assumed to be relatively small; the important influence is one which makes the rear portion of the model less effective in generating waves than the front portion. We may imagine this as due to the skin friction decreasing the general relative velocity of model and surrounding water as we pass from the fore end to the aft end ; or we may picture the so-called friction belt surrounding the model, and may consider the general effect as equivalent to a smoothing out of the curve of the rear portion of the model. Without pursuing these speculations further, they suggest calculations which can be made for models in frictionless liquid when the form of the model is unsymmetrical in this manner ; and the particular point to be examined is the effect of such modification upon the magnitude of the inter­ference phenomena. The first sections compare, in this respect, two bodies entirely submerged in the liquid. The form in each case is a surface of revolution ; one is symmetrical fore and aft and has sharp pointed ends, while in the other the rear portion is cut away so as to come to a fine point. By inspection of the expressions for the wave resistance it is seen that the oscillating terms are of a lower order of magnitude in the latter than in the former case.

scholarly journals Needles, China Cups, Books, and the Construction of the Victorian Feminine Ideal in Rhoda Broughton’S Not Wisely, but too Well and Elizabeth Gaskell’S North and South

2012 ◽  
Vol 47 (1) ◽  
pp. 47-60
Author(s):  
Agnieszka Setecka
Keyword(s):  
Middle Class ◽  
Economic Status ◽  
Material Objects ◽  
Practical Reasons ◽  
Reality Effect ◽  
Class Status ◽  
Elements Of Style ◽  
And Function ◽  
North And South ◽  
The Ideal

Abstract Considering Victorian presentation of women as angelic, that is, spiritual, beings, it is rather surprising how much their presence was manifested by material objects. Baskets of needlework, tea equipage and novels lying around in a parlour were an unmistakable sign of the house being occupied by women. Indeed, my contention is, the objects did not clutter Victorian interiors, either real or imagined, merely for practical reasons or to produce the “reality effect.” They are a material representation of the immaterial and function as metaphors for angelic women’s spiritual qualities. Rather than functioning merely as details to enhance the illusion of the real (and thus as elements of style) or simply reflecting the Victorian world (and thus as empty forms), material objects are essential in constructing a middle-class (feminine) identity. My paper concentrates on Rhoda Broughton’s Not wisely, but too well and Elizabeth Gaskell’s North and South with an attempt to show how objects help construct a feminine ideal and, simultaneously, reveal the ideal to be just a construction. Broughton’s Kate Chester and Gaskell’s Margaret Hale find themselves in situations where their middle-class status might be compromised. Still, they both manage to reassert their position through effectively manipulating the signs of middle-class respectability. The “flimsy and useless” things they surround themselves with point to their “essentially feminine” qualities. Yet, the very superfluity of the objects reveals their relation to the characters’ economic status. They are, then, the site where the material and immaterial meet, where the borders between the economic world and the domestic world blur.

Sexe-Invloeden Bij De Beoordeling Van Stem En Uitspraak

1981 ◽  
Vol 9 ◽  
pp. 146-156
Author(s):  
L.W.A. van Herpt ◽  
W.P.F. Fagel
Keyword(s):  
Rating Scales ◽  
Rating Scale ◽  
Female Voice ◽  
Practical Reasons ◽  
Male Voice ◽  
Male And Female ◽  
Female Speech ◽  
Male Speaker ◽  
Pencil And Paper ◽  
The Ideal

In an attempt to develop a standardized instrument to measure subjective voice and pronunciation quality a sample op 35 bipolar seven-point scales was selected and tested for reliability among raters by a preliminary pencil-and-paper investigation. Different groups of subjects were asked to rate the ideal male voice, the ideal female voice, and their own voice on each of the 35 items. The contribution of different subject factors to the variance in the ratings of each concept on each scale separately was established. One of those factors was sex of the rater. For practical reasons, we want this nascent instrument to be equally applicable for male and female speakers. We therefore studied the differences between mean ratings for ideal male speaker and ideal female speaker on each of the scales as well. The results show (1) many significant differences between perceived ideal male and ideal female voice, which qualitatively are rather inde-pendent of the sex of the informant; quantitatively female raters show a tendency to make smaller differences between male and female ideal speaker on the rating scales; (2) male and female raters often differ significantly in their judgment of ideal male voice alone or of ideal female voice alone; where this is the case, the mean judgment of the female raters practically always stands on a more 'extreme' point of the rating scale; (3) male and female raters often differ significantly in the ratings of their own voice; in general, the differences between own voice ratings by males and females on the 35 rating scales are qualitatively the same as those between ratings of male and female ideal voice respectively. These results were compared with Kramer's (1977) study on perceptions of (typical) male and female speech. It is concluded that the same stereo-types play a part in our subject's ideal and self ratings as in the 'typical speech' ratings of Kramer's subjects.

A Submerged Body with Zero Wave Resistance

1989 ◽  
Vol 33 (02) ◽  
pp. 81-83
Author(s):  
E.O Tuck
Keyword(s):  
Wave Resistance ◽  
Slender Body ◽  
Lower Resistance ◽  
Submerged Body ◽  
Design Speed

A slender body consisting of a submerged finned spheroid is shown to have zero wave resistance at a design speed, and lower resistance than either the spheroid alone or the fin alone in a range of speeds around design speed

Effect of Wake on Wave Resistance

1972 ◽  
Vol 16 (02) ◽  
pp. 93-112
Author(s):  
Sander Calisal
Keyword(s):  
Boundary Layer ◽  
Froude Number ◽  
Wave Resistance ◽  
Survey Method ◽  
Viscous Resistance ◽  
Total Resistance ◽  
Ship Model ◽  
A Value ◽  
Design Speed ◽  
Minimum Resistance

Suction is applied to the boundary layer of a ship model designed to be of minimum resistance for a Froude number V/(Lg)1/2= 0.289. The total resistance with suction is measured and the wave resistance is calculated by a wave-survey method. For the design speed the wave resistance is observed to remain almost constant up to a certain suction value and then to increase linearly with suction. The remaining viscous resistance, calculated by subtracting the directly measured wave resistance from the total resistance, decreases by the application of suction to a value lower than the values given by ITTC 57 and Schoenherr curves.

Experimental Study on Self-Made Similar Material of Soft Rock

2016 ◽  
Vol 717 ◽  
pp. 140-146 ◽  
Author(s):  
Jian Guang Li ◽  
Yang Wu ◽  
Yong Yan Wang ◽  
Nan Qin ◽  
Wei Xing Wang
Keyword(s):  
Model Experiment ◽  
Mechanical Characteristics ◽  
Soft Rock ◽  
Material Model ◽  
Similar Material ◽  
Advantages And Disadvantages ◽  
Mixed Mortar ◽  
Cementing Agent ◽  
Physical And Mechanical Characteristics ◽  
The Ideal

Similar material of soft rock used at domestic and abroad are analyzed and compared and researched the advantages and disadvantages of them. Self-made similar material of soft rock mixed with cement, plaster mixed mortar as a cementing agent and sand, rubber powder as aggregate were analyzed and compared. After analyzed multi physical and mechanical characteristics, different ratios of specimens were verified by adjusting the ratio of different materials in similar material to obtain the ideal similar material of soft rock. It was provided reference for similar material model experiment of soft rock.

On steady non-breaking downstream waves and the wave resistance – Stokes’ method

2017 ◽  
Vol 815 ◽  
pp. 388-414
Author(s):  
Dmitri V. Maklakov ◽  
Alexander G. Petrov
Keyword(s):  
Integral Equations ◽  
Wave Amplitude ◽  
Wave Resistance ◽  
Quadratic System ◽  
System Of Equations ◽  
Two Dimensional ◽  
Method Of Integral Equations ◽  
Analytical Formulae ◽  
The Mean ◽  
The Waves

In this work, we have obtained explicit analytical formulae expressing the wave resistance of a two-dimensional body in terms of geometric parameters of nonlinear downstream waves. The formulae have been constructed in the form of high-order asymptotic expansions in powers of the wave amplitude with coefficients depending on the mean depth. To obtain these expansions, the second Stokes method has been used. The analysis represents the next step of the research carried out in Maklakov & Petrov (J. Fluid Mech., vol. 776, 2015, pp. 290–315), where the properties of the waves have been computed by a numerical method of integral equations. In the present work, we have derived a quadratic system of equations with respect to the coefficients of the second Stokes method and developed an effective computer algorithm for solving the system. Comparison with previous numerical results obtained by the method of integral equations has been made.

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