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Showing papers in "Journal of Ship Research in 1973"


Journal ArticleDOI
TL;DR: In this paper, the authors discussed the prediction of the extreme values of a stationary random process having an arbitrary bandwidth spectrum and derived formulas to predict extreme values for a given number of observations and time by applying order statistics.
Abstract: Paper discusses the prediction of the extreme values of a stationary random process having an arbitrary bandwidth spectrum. Formulas to predict the extreme values are derived for a given number of observations and time by applying order statistics, and the effect of bandwidth of spectrum on the extreme values is discussed. The most probable extreme value and the extreme value for a preassigned probability of being exceeded are obtained. The estimation formulas are applied to predict the extreme value of the pitching motion and acceleration of a ship in irregular seas and waves generated in a towing tank. It is found that the extreme values observed in model experiments fall fairly well in the vicinity of the predicted most probable values.

86 citations


Journal ArticleDOI
TL;DR: In this article, a general numerical procedure is described for finding a blockage coefficient when the cross section takes an arbitary shape, and some asymptotic formulae, valid for a broad range of shiplike cross sections, are also derived for cases where the clearance below the ship is small.
Abstract: Each cross section of a ship has a blockage coefficient which is uniquely dependent on its shape. A general numerical procedure is described for finding this coefficient when the cross section takes an arbitary shape. Some asymptotic formulae, valid for a broad range of shiplike cross sections, are also derived for cases where the clearance below the ship is small.

47 citations


Journal ArticleDOI
Cesar Farell1

46 citations


Journal ArticleDOI
TL;DR: In this article, the mathematical solution to the diffraction problem is obtained on the basis of the linearized long-wave approximation for a shiplike body with beam-to-length ratio approximately equal to 0.2.
Abstract: Exciting forces and moments due to plane incident waves on a stationary platform are studied in the report. The platform is a vertical cylinder with a finite draft and elliptical cross section. The mathematical solution to the diffraction problem is obtained on the basis of the linearized long-wave approximation. Numerical results via Mathieu functions are presented for a shiplike body with beam-to-length ratio approximately equal to 0.2. Various draft-to-depth ratios and angles of incidence are considered. Results have been checked with the limiting case of a circular cylinder for the long-wavelength range. Aside from its own practical interest, the present theory provides a basis for comparison with other approximate theories of slender-body type and serves as a prelude to the corresponding calculations for arbitrary wavelengths. (Author)

38 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the viscous resistance of a spheroid model by means of wake surveys together with total resistance measurements, and found that the proximity of the free surface greatly influences the visco-viscous resistance.
Abstract: Towing-tank measurements of the viscous resistance of a spheroid model by means of wake surveys together with total resistance measurements show that the proximity of the free surface greatly influences the viscous resistance, which becomes much larger than the deep-submergence resistance as the spheroid approaches the free surface. Wind tunnel measurements reveal a similar effect of a rigid wall on the viscous drage of a body. The values of the wave resistance obtained as the difference between the measured values of total resistance and viscous resistance are found to be in agreement, for the range of Froude numbers investigated, with the analytical results obtained neglecting viscous effects and linearizing the free-surface boundary condition, but satisfying exactly the boundary condition on the surface of the body.

16 citations


Journal ArticleDOI
TL;DR: In this paper, the results of a digital computer simulation of a nonlinear random process are described, and the results obtained by objective statistical test procedures indicate that the distribution of maxima of the nonlinear process is not Rayleigh in a substantial portion of the parameter range of interest.
Abstract: The methods and results of a digital computer simulation of a nonlinear random process are described. The process was one of the simpler analytical models for ship roll. The main objective of the simulation was to obtain "empirical" data on the distribution of roll maxima, and to test these data against the corresponding theoretical distribution for a random Gaussian (linear) process. Effect was made to confine the variation of parameters within ranges appropriate to ship rolling. Within this range of parameters, the frequency band of response is sufficiently narrow that the theoretical distribution of maxima of the corresponding linear process tends toward the Rayleigh. The results obtained by objective statistical test procedures indicate that the distribution of maxima of the nonlinear process is not Rayleigh in a substantial portion of the parameter range of interest. However, it was possible to conclude from the results that the Rayleigh assumption is reasonable for an important class of engineering predictions; that of the prediction of average, "significant" and "1/10 highest" maxima from a knowledge of the spectrum of roll.

15 citations


Journal ArticleDOI
TL;DR: In this article, a procedure for predicting the performance of a propeller numerically to within the accuracy of tunnel and open-water model tests is described, given the geometry of the propeller, ship speed, wake fraction distribution and rpm, the thrust and torque characteristics are calculated.
Abstract: A procedure is described for predicting the performance of a propeller numerically to within the accuracy of tunnel and open-water model tests. Given the geometry of the propeller, ship speed, wake fraction distribution and rpm, the thrust and torque characteristics are calculated. The procedure gives good results not only for "normal" propellers but also for such abnormal cases as a variable-pitch propeller operating at off-design pitches. The possibility exists of extension of the method for calculation of spindle torques, stresses, and cavitation inception.

14 citations


Journal Article
TL;DR: In this article, the Direct Search Design Algorithm and the Golden Search are used to produce an automated optimal dimensional synthesis procedure for the structural design of submersible, frame reinforced, circular shells.
Abstract: The Direct Search Design Algorithm and the Golden Search are utilized to produce an automated optimal dimensional synthesis procedure for the structural design of submersible, frame reinforced, circular shells. Using this procedure it was found that the shell weight/weight displaced ratio is independent of the diameter of the shell and the optimal shell dimensions are proportional to the diameter. Between frame shell buckling is generally the most important instability failure mode in optimal designs. Where significant out-of-roundness (eccentricity) of the shell exists, frame yield normally also controls the design. High-strength steels were found to be effective primarily by reducing the adverse effect of eccentricity and by controlling plating yield for shells under relatively high pressure.

12 citations



Journal ArticleDOI
TL;DR: In this article, a mathematical model used in previous Davidson Laboratory adaptations of linearized unsteady lifting surface theory to marine propellers has been revised by removing the so-called "staircase" approximation of the blade wake and replacing it by an exact helicoidal blade wake.
Abstract: : The mathematical model used in previous Davidson Laboratory adaptations of linearized unsteady lifting surface theory to marine propellers has been revised by removing the so-called 'staircase' approximation of the blade wake and replacing it by an 'exact' helicoidal blade wake. A new numerical procedure and program based on the present model has been developed to evaluate the steady and unsteady blade loading distributions, which are used to determine the bearing forces and moments. Systematic calculations of these forces and moments for a series of propellers show better agreement on the whole with experimental measurements than did the earlier calculations for the same series. In addition, the chordwise loading distributions are much smoother than obtained previously. However, the quantitative improvement must be weighed against the considerable increase in computer time over the old method.

12 citations



Journal ArticleDOI
TL;DR: In this article, the effects of the stimulators were accounted for by considering the virtual origin of the turbulent boundary layer, and a shallower viscous-resistance curve than expected was found, which was attributed to the effect of the trailing vortices formed over the surface of the model.
Abstract: A reflex and a normal model of a typical bulbous-bow tanker were fitted with different types of stimulators and tested in a wind tunnel and a towing tank respectively. The effects of the stimulators were accounted for by considering the virtual origin of the turbulent boundary layer. A shallower viscous-resistance curve than expected was found, which was partly attributed to the effects of the trailing vortices formed over the surface of the model. Both the friction and pressure distributions were measured for the relfex model. Equations proposed for the viscous, frictional, and pressure resistance coefficients over the model Reynolds number range did not correlate satisfactorily when extrapolated to full-scale reynolds numbers.

Journal ArticleDOI
TL;DR: In this paper, the problem of choosing orthogonal, curvilinear, coordinate systems for use in boundary-layer calculations on arbitrary three-dimensional bodies is considered in some detail.
Abstract: : The problem of choosing orthogonal, curvilinear, coordinate systems for use in boundary-layer calculations on arbitrary three-dimensional bodies is considered in some detail. A general method for the practical evaluation of the various geometrical properties of the coordinates occurring in the three-dimensional boundary-layer equations is described. A particular coordinate system which appears to be the most convenient one for ship hulls is then proposed and analyzed further.

Journal ArticleDOI
TL;DR: In this article, a solution for the motion of an air-cushion vehicle (ACV) starting from rest under the action of a propulsor of given thrust-speed characteristics is presented.
Abstract: This paper presents the solution for the motion of an air-cushion vehicle (ACV) starting from rest under the action of a propulsor of given thrust-speed characteristics. The wave resistance is based on linearized potential theory, while the aerodynamic drag components are assumed to be strictly quasi-steady. The problem is treated in two different ways: calculating the wave resistance in a truly unsteady manner, and on the simplified quasi-steady basis. The results show that the shape of the propeller characteristics has only a minor effect on the velocity pattern. However, the effect of overloading the ACV is shown to have crucial effects on its ability to surpass the critical depth hump. In this respect, the simpler quasi-steady calculations lead to unnecessarily pessimistic estimates of the acceleration margin. Under certain circumstances in relatively shallow water, the quasi-steady analysis would suggest that the ACV could not overcome the critical hump, while the more elaborate unsteady calculations show that it has indeed adequate power to reach its final cruising speed.

Journal ArticleDOI
TL;DR: Turbulent boundary layer calculation scheme is presented which combines the Cumpsty-Head-Smith three-dimensional turbulent boundary layer method, under the small cross flow approximation, with the Tuck-von Kerczek slender body potential flow at zero Froude number as discussed by the authors.
Abstract: Turbulent boundary layer calculation scheme is presented which combines the Cumpsty-Head-Smith three-dimensional turbulent boundary layer calculation method, under the small cross flow approximation, with the Tuck-von Kerczek slender body potential flow at zero Froude number. A sample calculation for the Lucy Ashton double model conforming to the experiments of Joubert and Matheson is presented.

Journal ArticleDOI
TL;DR: In this paper, elastic and plastic limit analyses of a web frame of a 225,000-dwt tanker are presented. And the results of these different approaches are discussed and compared, and three different methods are used to examine the behavior of the frame under the same loading conditions.
Abstract: Elastic and plastic limit analyses of a web frame of a 225,000-dwt tanker are preseneted. In the elastic range, three different methods are used to examine the behavior of the frame under the same loading conditions. Beyond the elastic range, plastic limit analysis is performed to investigate the collapse mechanisms and the corresponding collapse pressures. The results of these different approaches are discussed and compared.

Journal ArticleDOI
TL;DR: In this article, an analysis based on lifting surface theory has been developed for evaluation of the vibratory velocity field induced by an operating marine propeller in both uniform and nonuniform inflow fields.
Abstract: : An analysis based on lifting surface theory has been developed for evaluation of the vibratory velocity field induced by an operating marine propeller in both uniform and nonuniform inflow fields. The analysis demonstrates how in the case of nonuniform flow the velocity at any field point is made up of a large number of combinations of the frequency constituents of the loading function with those of the space function. A numerical procedure has been developed adaptable to a high-speed digital computer and the existing program, which evaluates the steady and unsteady propeller loadings, the resulting hydrodynamic forces and moments and the pressure field, has been extended to include evaluation of the velocity field as well. The program could become a versatile and useful tool for the ship researcher or designer.

Journal Article
TL;DR: In this paper, a correlation of the maximum pressure that obtains in the flat-plate hydrodynamic impact problem due to "trapped air" is presented, which becomes a similarity relation so that it is possible to scale impacts.
Abstract: A correlation is presented of the maximum pressure that obtains in the flat-plate hydrodynamic impact problem due to "trapped air." For large plates this becomes a similarity relation so that it is possible to scale impacts.

Journal ArticleDOI
TL;DR: In this article, a general method for determining the stresses around two openings of any shape in a large plate of elastic isotropic material is presented, based on the complex variable approach combined with the Schwarz successive approximation technique.
Abstract: A general method is presented for determining the stresses around two openings of any shape in a large plate of elastic isotropic material. The two openings can have individual boundary reinforcements. The method is based on the complex variable approach combined with the Schwarz successive-approximation technique. As an illustration of the method, the stresses are computed for the case of a small circular opening near a large circular opening, the amounts of reinforcing material on these two openings were varied to determine the optimum reinforcement. Several cases that frequently occur in ship construction are included.

Journal ArticleDOI
TL;DR: In this article, the maximum stresses in a spherical shell are obtained which is lifted or towed by a cable or any mechanical power hoist, and a nonlinear relaxation technique in conjection with finite difference approximations is introduced for the numerical integration.
Abstract: : The maximum stresses in a spherical shell are obtained which is lifted or towed by a cable or any mechanical power hoist. In view of the highly localized nature of the maximum stress induced in a spherical shell due to local loading, the nonlinear (large deflection) shallow shell theory is adopted for the analysis. A nonlinear relaxation technique in conjection with finite difference approximations is introduced for the numerical integration. Results obtained here are presented in the graphic form which may be readily used by engineers in practical design. (Author)

Journal ArticleDOI
TL;DR: In this paper, an analysis of the free vibrations of simply-supported and clamped, web-stiffened, circular, cylindrical sandwich shells is presented, which includes the effect of translatory and rotatory inertia in each layer of the sandwich.
Abstract: : An analysis is presented of the free vibrations of simply-supported and clamped, web-stiffened, circular, cylindrical sandwich shells. The mathematical model formulated includes the effect of translatory and rotatory inertia in each layer of the sandwich, and treats the two face layers as thin shells in which the classical (Donnell) theory of shells applies. Shear deformations, however, are permitted in the core, which is treated as a layer of inhomogeneous, orthotropic material. In the analysis, the discrete nature of the webs is maintained, except for the inclusion of an average secondary shear modulus induced by the bending of the webs and faces. Equations are also developed for the free vibrations of the corresponding homogeneously cored sandwich shells, in order to investigate the effect of smearing-out or averaging a given web-stiffened core. A Galerkin procedure is employed to determine the natural frequencies from a variational functional generated by means of Hamilton's principle. (Author)

Journal ArticleDOI
TL;DR: For a flat plate moving in a dilute polymer solution, effects on boundary-layer characteristics, shear stress, drag reduction and maximum drag reduction are considered for polymers which satisfy the Meyer-Elata law as discussed by the authors.
Abstract: For a flat plate moving in a dilute polymer solution, effects on boundary-layer characteristics, shear stress, drag reduction and maximum drag reduction are considered for polymers which satisfy the Meyer-Elata law. Results are derived from a model in which the velocity profiles satisfy the law-of-the-wall and a velocity-defect law, and the polymer has no effect in the range in which the latter law is valid. It is also assumed that the polymer affects the law of variation of the mixing length, and a family of velocity profiles representing this effect is adopted. This model then yields a curve of maximum drag reduction as well as a two-parameter family of curves of drag reduction, consequences of the nonoverlapping or overlapping of the two velocity-profile laws. The results are compared with those of Granville for drag reduction, and with the predicted curve of Virk-Granville and an experimental result of Levy and Davis for maximum drag reduction.