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Showing papers on "Added mass published in 1982"


01 Jan 1982
TL;DR: In this article, the authors present a survey of the analytical background including the definition of added mass, the structure of the added mass matrix and other effects such as the influence of viscosity, fluid compressibility and the proximity of solid and free surface boundaries.
Abstract: This report reviews the existing state of knowledge concerning the evaluation of the forces imposed on a body in a fluid due to acceleration of either the body or the fluid. It concentrates on those fluid inertial forces due to acceleration rather than on the drag/lift forces due to steady motion. The first part of the report presents a survey of the analytical background including the definition of added mass, the structure of the added mass matrix and other effects such as the influence of viscosity, fluid compressibility and the proximity of solid and free surface boundaries. Then the existing data base from experiments and potential flow calculations is reviewed. Approximate empirical methods for bodies of complex geometry are explored in a preliminary way. The possible dramatic effects of the proximity of the ocean bottom are further highlighted. The confused state of affairs regarding the possibly major effects of viscosity in certain regimes of frequency and Reynolds number is discussed. Finally a number of recommendations stemming from ocean engineering problems are put forward.

304 citations


Journal ArticleDOI
TL;DR: In this paper, the added mass and damping coefficients associated with the periodic motions of a floating hemisphere are derived for two physically distinct cases of heave and surge, where these nautical terms refer respectively to a vertical or horizontal oscillation of the body.
Abstract: The object of this paper is to derive the added mass and damping coefficients associated with the periodic motions of a floating hemisphere. Two physically distinct cases are considered; namely those of heave and surge, where these nautical terms refer respectively to a vertical or horizontal oscillation of the body. Computations have been done and the values found for the various force coefficients are presented in tabulated form. A brief derivation of the long- and short-wave asymptotics of these coefficients has also been included.

241 citations


Journal ArticleDOI
TL;DR: In this article, the authors used strobe photography to measure the kinematics of a sphere moving via saltation along the bed of an open channel flow, and showed that the forces of bouyancy, added mass, and drag could predict the particle motion.
Abstract: An evaluation of the fluid forces exerted on a bed load particle is presented. The study used strobe photography to measure the kinematics of a sphere moving via saltation along the bed of an open channel flow. The experiment showed that the forces of bouyancy, added mass, and drag could predict the particle motion. The added mass force included an unusual component due to the mean shear of the open channel flow.

44 citations


Journal ArticleDOI
TL;DR: In this article, the authors find the equivalent external forces and moments exerted on the fluid [Ref. 7, Eqs. (3.46 and 3.47) and they find that there exist an added inertia tensor, principal axes and a center of added mass.
Abstract: Reference , A., Flight Mechanics, Vol. 1: "Theory of Flight Paths," Pergamon Press, New York, 1962, Chap. 9, pp. 149-189. solid body inertia tensor ([#]), principal axes, and mass center, there exist an added inertia tensor ([>!]), principal axes, and a center of added mass. Referring to Ibrahim, we find the equivalent external forces and moments exerted on the fluid [Ref. 7, Eqs. (3.46) and (3.47)] are

22 citations


Journal ArticleDOI
TL;DR: In this paper, a terradynamic penetrator is considered and some interaction characteristics such as the added mass and the interaction pressure distribution are calculated, and the magnitude of added mass is found to be small compared to the penetrator's mass.
Abstract: The motion of a terradynamic penetrator is formulated, and some interaction characteristics as the added mass and the interaction pressure distribution are calculated. The magnitude of the added mass is found to be small compared to the penetrator’s mass. The expression for the interaction pressure is shown to be composed of a static and a dynamic term. The calculated stresses and masses can be used for the dynamic analysis of the penetrator’s structure.

8 citations


01 Feb 1982
TL;DR: In this paper, a panel source distribution was used to derive the added mass matrix of a vibrating hull, which was formulated by taking a constant source strength per finite element on the wetted hull surface.
Abstract: Instead of using a finite element model of the surrounding fluid, a panel source distribution has been used to derive the added mass matrix of a vibrating hull. This source distribution is formulated by taking a constant source strength per finite element on the wetted hull surface. With this method, the boundary conditions are satisfied exactly on the hull surface and at infinity. The boundary condition on the free surface is taken as the high frequency limit. In this way, the calculations are restricted to an integration over the hull surface. Consequently, less computer effort is needed than by using a finite element representation of the fluid, and a more exact result is obtained. For ellipsoids, performing rigid body vibrations, the numerical results are compared with the exact results. A fast convergence is shown for a moderate finite element grid of the wetted surface.

7 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a continuous equations of motion for a cable system undergoing change of length, where hydrodynamic forces were incorporated as added mass and velocity-squared drag The nonlinear equations were solved using method of weighted residuals, orthogonal collocation.
Abstract: Ocean cable systems are particularly vulnerable to failure during deployment and retrieval operations due to dynamic effects imposed by ship motion and time dependent changes in hydrodynamic forces, cable length, area, and tension The continuous equations of motion for a cable system undergoing change of length were developed, where hydrodynamic forces were incorporated as added mass and velocity-squared drag The nonlinear equations were solved using method of weighted residuals, orthogonal collocation Residual quantities were not treated directly; rather, an approximation procedure for spatial derivatives was developed resulting in broader application for the solution technique Numerical results were compared with two sets of available experimental data Both experiments involved laboratory-scale cable systems in a one-dimensional variable length configuration and in two-dimensional fixed length configurations Analytic and experimental results were in reasonable agreement with some differences attributed to defining coefficient of drag as a constant, modeling difficulties, and low-order numerical approximation

6 citations


Patent
10 Jun 1982
TL;DR: In this paper, the authors propose to enlarge a damping factor of vibration in a structure as well as to secure a damped vibration effect for a wide range of frequency, by adding mass to the structure, while making controlling force act on between the added mass and the structure according to vibrations in the structure.
Abstract: PURPOSE:To enlarge a damping factor of vibration in a structure as well as to secure a damped vibration effect for a wide range of frequency, by adding mass to the structure, while making controlling force act on between the added mass and the structure according to vibrations in the structure. CONSTITUTION:When external force P acts on a building 1 by way of a wind or the foundation, a vibration is excited to the building 1. Vibro-acceleration in the building 1 is detected by an accelerometer 3, fed to a control unit 5 and given to an actuator 6 via an integrator, a speed signal amplifier and a power amplifier. At this actuator 6, there is produced controlling force in proportion to a roof velocity, between an added mass and the building 1, causing the vibration damping of the building 1 to grow large. Also in an interspace between the building 1 and the added mass 2, a displacement meter 4 detecting a relative displacement is installed, emitting a relative displacement signal, through which the actuator 6 is energized and the controlling force proportional to the relative displacement is produced.

5 citations


Journal ArticleDOI
TL;DR: In this article, the fundamental critical speed of a shaft in a viscous fluid was analyzed, and it was shown that the critical speed decreases for large viscosity of the fluid and when the fluid fills an annulus between the shaft and a cylindrical wall.
Abstract: Analytical results on the fundamental critical speed of a shaft in a viscous fluid are presented. When the fluid is set in motion by the shaft whirling, dynamic forces imposed by the fluid on the shaft are obtained by solving the two-dimensional Navier -Stokes equations under appropriate boundary conditions and on the assumption of small amplitude of the whirling motion. Added mass coefficients of the fluid and viscous damping coefficients are determined using these dynamic forces, and accordingly the equations of whirling motion of the shaft are derived. The critical speed of the shaft are found by solving these equations of whirl motion. In this analysis, configurations of the shaft are assumed to be a uniform elastic beam or a diskattached elastic beam, whose both ends are simply supported by bearings. For the latter case, an experimental study was made in order to confirm the analytical results. From this study, it was revealed that the critical speed decreases for large viscosity of the fluid, and when the fluid fills an annulus between the shaft and a cylindrical wall, the critical speed decreases for small annular gap width.

4 citations


Journal ArticleDOI
TL;DR: In this paper, the drag and added mass coefficients of a truss leg of an ocean platform are obtained by using the forced-oscillation technique in a still water, and higher order forces and lift forces are also measured.

2 citations


Journal ArticleDOI
TL;DR: It is shown that the method leads to a structural solution which is identical to the coupled fluid-structure solution provided that the fluid is discretized sufficiently to retain the requisite spectral fidelity.

Journal ArticleDOI
L. Hambro1
TL;DR: In this paper, a method is presented for treating mechanical systems with arbitrary holonomic constraints by differentiating the constraints twice, which is used to compute the motions when a jacket is launched from a barge and is in good agreement with model experiments.


Journal Article
TL;DR: In this paper, the authors considered the sway added mass of a rectangular cylinder in a restricted water by applying Hamilton's principle as the frequency tends to zero and derived an approximate formula for the cases of the cylinder swaying at the center of a narrow or wide canal relative to a cylinder, at off-center location in a canal, and in the restricted water with a single wall.
Abstract: In this paper, the sway added mass of a rectangular cylinder in a restricted water is considered by applying Hamilton's principle as the frequency tends to zero. The present method is an extension of Isshiki's method proposed in 1978. In the present method, it is assumed that the fluid velocity distribution in each subdomain of the fluid can be represented by higher order polynomials while Isshiki assumed linear velocity distribution. The fluid flow is assumed as a rotational motion in the present analysis. However, the results obtained from the present method show good agreement with Bai's numerical results for the case of large clearances between a canal wall and a cylinder. From Kelvin's minimum energy theorem, we can see that the value of sway added mass obtained from the present method approaches the upper bound. The approximate formula obtained in the present study takes a simple form which consists of the dimensions of the canal and the cylinder. The present formulae are derived for the cases of a rectangular cylinder swaying at the center of a narrow or wide canal relative to a cylinder, at off-center location in a canal, and in the restricted water with a single wall. From the results of numerical calculation, it is concluded that the sway added mass in restricted waters is more affected by water depth than clearance between a wall and a cylinder.