Showing papers on "Added mass published in 1985"
TL;DR: In this paper, the radiation coupling between all oscillators is represented by a partitioned matrix composed of the radiation admittance matrix for the pressure distributions, the radiation impedance matrix for oscillating bodies, and a radiation coupling matrix between the bodies and the pressure distribution.
138 citations
TL;DR: An infinite element based on the doubly asymptotic approximation (DAA) for finite element analysis of fluid is presented in this article, where finite elements model the region near the solid infinite elements account for the effects of the outer fluid on the inner region.
Abstract: An infinite element based on the doubly asymptotic approximation (DAA) for use in finite element analysis of fluid—structure interactions is presented Fluid finite elements model the region near the solid Infinite elements account for the effects of the outer fluid on the inner region The DAA‐based infinite elements involve an approximate calculation of the added mass using static mapped infinite elements, plus a consistent damping term Simple test analyses for a range of fluid properties demonstrate the performance of the solution technique The analyses of a Helmholtz resonator (open pipe) and a circular plate in water indicate the practical use of the solution approach
62 citations
TL;DR: In this article, a numerical method for calculating the two-dimensional hydrodynamic coefficients of one or two infinitely long, arbitrary cylinders forced to oscillate in or below the free water surface is described.
40 citations
TL;DR: In this paper, a linear theory is developed in the time domain for vertical motions of an axisymmetric cylinder floating in the free surface, and the velocity potential is obtained numerically from a discretized boundary-integral-equation on the body surface, using a Galerkin method.
Abstract: A linear theory is developed in the time domain for vertical motions of an axisymmetric cylinder floating in the free surface. The velocity potential is obtained numerically from a discretized boundary-integral-equation on the body surface, using a Galerkin method. The solution proceeds in time steps, but the coefficient matrix is identical at each step and can be inverted at the outset.Free-surface effects are absent in the limits of zero and infinite time. The added mass is determined in both cases for a broad range of cylinder depths. For a semi-infinite cylinder the added mass is obtained by extrapolation.An impulse-response function is used to describe the free-surface effects in the time domain. An oscillatory error observed for small cylinder depths is related to the irregular frequencies of the solution in the frequency domain. Fourier transforms of the impulse-response function are compared with direct computations of the damping and added-mass coefficients in the frequency domain. The impulse-response function is also used to compute the free motion of an unrestrained cylinder, following an initial displacement or acceleration.
35 citations
TL;DR: Two new derivations of Darwin's theorem on the equality of the added mass for translation of a body moving in an ideal fluid of infinite extent and the drift mass are given in this paper.
Abstract: Two new derivations of Darwin's theorem on the equality of the added mass for translation of a body moving in an ideal fluid of infinite extent and the drift mass are given. The first is based on the idea of time lag, used by Rayleigh (1876), Ursell (1953), and Longuet-Higgins (1953) to study fluid drift. The second is truly elementary, relying only on the concept of continuity and Newton's second law of motion. A geometrical interpretation of the result in the first derivation is given, and a few examples are provided.
29 citations
TL;DR: In this paper, it is known that the typical six-equation two-fluid model of two-phase flow possesses complex characteristics, exhibits unbounded instabilities in the short-wavelength limit, and constitutes an ill...
Abstract: It is known that the typical six-equation two-fluid model of two-phase flow possesses complex characteristics, exhibits unbounded instabilities in the short-wavelength limit, and constitutes an ill...
18 citations
TL;DR: In this article, a three-dimensional finite element analysis has been used to simulate the coupled static and dynamic behaviour of compliant ocean structures, which are assumed to be in the Morison regime.
17 citations
TL;DR: In this article, a mixed numerical model is developed to simulate wave motion in rubble-mound structures, where the mixed model utilizes a combined finite difference method of characteristics scheme to integrate the unsteady continuity and momentum equations in the x-t plane to obtain the internal water levels while the two-dimensional properties of the flow are found from a finite element solution for the internal flow domain, x-y plane, at any time t. The model is applied to the Sines breakwater in order to check the dynamic stability of the seaward slope under severe wave attack.
Abstract: A mixed numerical model is developed to simulate wave motion in rubble‐mound structures. The mixed model utilizes a combined finite difference method of characteristics scheme to integrate the unsteady continuity and momentum equations in the x-t plane to obtain the internal water levels while the two‐dimensional properties of the flow are found from a finite element solution for the internal flow domain, x-y plane, at any time t. The two‐dimensional solution is used to update pressure distribution coefficient and hydraulic conductivity values in the x-t plane. The model is applied to the Sines breakwater in order to check the dynamic stability of the seaward slope under severe wave attack. The predicted values for the internal water surface are found to be in fair agreement with a physical model measurement. Furthermore, the model indicates a lower factor of safety than the traditional analysis. Special provisions are included in the model to account for added mass and to detect and correct for internal ...
13 citations
TL;DR: In this article, the problem of computing the vibration modes of a structure vibrating in a fluid is examined with specific application to ship hulls, and the effects of the extra coefficients in the mass matrix arising from added mass on the various methods of eigensolution are discussed.
Abstract: SUMMARY The problem of computing the vibration modes of a structure vibrating in a fluid is examined with specific application to ship hulls. In particular, methods which take proper account of the three-dimensional nature of the water movements are described. Fluid singularities involving either a line doublet on the intersection of the water surface with the plane of symmetry or distributed sources on retracted boundaries are particularly effective at modelling the fluid flow and appear to give better numerical efficiencies than finite element or boundary element methods. The effects of the extra coefficients in the mass matrix arising from added mass on the various methods of eigensolution are discussed.
13 citations
10 citations
01 Jan 1985
Abstract: The hydrodynamics of ships floating alongside one another at small separation distance is studied. Nonlinear and viscous effects are accounted for in the narrow gap between the ships, and the solution in this domain is matched to a linear outer solution using the method of matched asymptotic expansions. The matching equations are nonlinear ordinary differential equations that are solved numerically. Finally the forces on a ship carrying out forced harmonic oscillations are calculated. The nonlinear forces are compared with the linear added mass and damping forces. .
31 May 1985
TL;DR: In this article, the aerodynamic-thermodynamic models for predicting the vertical motion of free balloon systems were criticised, and the authors proposed a new aerodynamic drag coefficient model based on Froude number and fractional volume as well as Reynolds number.
Abstract: : This paper critiques existing aerodynamic-thermodynamic models for predicting the vertical motion of free balloon systems It demonstrates that: a) the aerodynamic drag coefficient model should be based on Froude number and fractional volume as well as Reynolds number; b) there has been a widespread error in definition of the instantaneous mass of the balloon film involved in the heat transfer process; c) the gas bubble cannot be modelled as a sphere; d) the gas bubble is asymmetrical except when near or at its natural ceiling altitude; and e) the actual gas bubble shape, and most probably the added mass, is directly related to the type of gore pattern Finally, a procedure is proposed for the analysis of actual flight data to enable the development of a practical, but also theoretically sound, model of the aerodynamic drag coefficient of a zero-pressure, free balloon- and subsequent refinement of the heat transfer models for direct and reflected solar energy
TL;DR: In this article, a linearized approximation for both the convective inertia terms and the nonlinear terms involved in the fluid constitutive law is used, which is transformed to a coordinate system in such a way as to result in a linear diffusion-type equation for the vorticity in the Newtonian case, and for the viscoelastic case.
TL;DR: In this article, the added mass and damping coefficients of a toroidal body undergoing a forced, periodic heaving motion were derived for the RS-35 design of ring-hulled semisubmersible platform.
Abstract: This paper describes the calculation of the added-mass and damping coefficients of a submerged toroidal body that is undergoing a forced, periodic heaving motion. The velocity potential of the motion is expressed as an infinite sum of toroidal multipole potentials, and the problem is solved in a manner analogous to Ursell's classical solution for a submerged circular cylinder in two dimensions. When the torus is ‘slender’, in the sense that its tubular radius is small compared with its overall diameter, relatively simple closed-form asymptotic approximations for the addedmass and damping coefficients are obtained. This work is motivated by the proposed RS-35 design of ring-hulled semisubmersible platform.
TL;DR: In this paper, a mathematical model of the submersible operation is built on the equation of a six degree freedom motion of a rigid body, where gravity force, buoyancy, hydrodynamic forces and thrusts are considered as external forces in the model.
Abstract: Maneuverability of the MURS 300 Mark II (a Remotely Operated Vehicle), developed for inspecting underwater parts of hydroelectric dam facilities, is discussed in this paper based on the results of the computer simulation and the water tank test.A mathematical model of the submersible operation is built on the equation of a six degree freedom motion of a rigid body. Gravity force, buoyancy, hydrodynamic forces and thrusts are considered as external forces in the model. Cable tension is not included because of its negligibly small force in calm water. Hydrodynamic forces, drag, lift, added mass and so on are determined by the wind tunnel test and the water tank test.Thrusts are also measured in a water tank test. Being equipped with neither tail wing nor stabilizer, ROVs are usually characterized with their relatively poor directional stability. If a step input of thrust is added, ROVs are unlikely to move on a straight track without supplemental manipulation of thrusters.An automatic heading control system can be a solution to improve directional stability of ROVs.In case of the MURS 300 Mark II, a step input of its foward thrust causes its ascending because of the center of its horizontal thrust located slightly below its gravity center unless an automatic depth control system is installed. Given a rectangular pulse thrust, the MURS 300 Mark II equipped with automatic heading and depth control systems automatically returns to an original place where an operator sets a joystick in a neutral position.This operational characteristic of the MURS 300 Mark II is quite useful for underwater structure inspections. The results of a full scale experiment performed in a water tank agree to and prove the computer simulation outputs.
TL;DR: In this paper, a sliding behavior of a rigid body in the water during earthquakes was studied and the displacement calculated from the horizontal and vertical base accelerations showed relatively good agreement to the measured value, while the added mass of which inertia force corresponded to the hydrodynamic pressures on the model block were almost the same values as those measured by Euler's method.
Abstract: Shaking table tests of model blocks were conducted to study sliding behavior of a rigid body in the water during earthquakes. The accelerations and hydrodynamic pressures on the model block decreased instantaneously on set of sliding and remained the same levels during sliding. The static and dynamic coefficients of friction obtained from the vibration tests in consideration of the added mass of which inertia force corresponded to the hydrodynamic pressures on the model block were almost the same values as those measured by Euler's method. A method to estimate the displacements of the sliding block during earthquakes was presented. The displacement calculated from the horizontal and vertical base accelerations showed relatively good agreement to the measured value.
01 Jan 1985
TL;DR: In this paper, a singularity panel method based on Green's function integral equation is used to calculate the motion characteristics of ships and offshore structures, where the free surface and the body surface are discretized by source-sink and dipole type singularity panels.
Abstract: A singularity panel method based on Green's function integral equation is used to calculate the motion characteristics of ships and offshore structures. The free surface and the body surface are discretized by source-sink and dipole type singularity panels. This reduces the governing integral equation for the velocity potential to a system of algebraic equations which can easily be solved by a computer. The added mass and damping coefficients are computed by appropriate summations along the body surface. The approach is unique since it uses the free space Green's function instead of more complicated Green's function satisfying the free-surface boundary condition. The applications of the method are limited to linear, two-dimensional, incompressible free-surface problems. The extension to three-dimensional geometries is straightforward.
01 Jan 1985
TL;DR: PMMAを例にとり,粘弾性モデル定数の妥当性ならびに強制不規則振動の実験値
Abstract: PMMAを例にとり,粘弾性体モデルとして5要素線形固体モデルを導入し,それらの定数を両端自由のチモシェンコはりとしての自由振動ならびに有帯域ホワイトノイズ加振に対する不規則振動実験より求める2種類の定数決定法について研究した.さらに二つの方法により実験に定められた粘弾性モデル定数の妥当性ならびに一般的適合性を自由振動ならびに強制不規則振動の実験値と比較することにより検討した.
TL;DR: The following is a report on experimental results obtained for the added masses of cylinders and circular pipes which are limited in length.
Abstract: It is important to determine the added mass of objects to estimate the hydrodynamic force on floating fisheries banks. The following is a report on experimental results obtained for the added masses of cylinders and circular pipes which are limited in length. The apparatus used in this experiment is essentially a torsion pendulum which has been improved by the authors. The values of added masses are calculated from the difference between the periods of this pendulum in water and in air. By using a phosphore bronze plate to which strain gages were affixed for this pendulum, it was possible to pick up the torsion electrically and to put record into computer. In this way, the experiment was simplified and the treatment of the data was very efficient. Objects used in this experiment were cylinders varying in diameter and length and circular pipes varying in diameter, length, and thickness.We were able to determine the added masses of these objects.
Dissertation•
01 Jan 1985
TL;DR: This thesis describes the development of a number of numerical tools designed to study the non-linear free surface flow problems caused by slamming and the quantitative importance of the various physical parameters involved in slamming on the ship scale.
Abstract: The ability of ships and other marine vehicles to maintain forward speed in heavy weather is often limited by the phenomenon of slamming. The hydrodynamics of this impact problem are poorly understood in a quantative sense, though previous research has identified various physical mechanisms important to ship slamming. This thesis describes the development of a number of numerical tools designed to study the non-linear free surface flow problems caused by slamming. The research focused on two major areas of study. Firstly, a generalised simulation method for the solution of the mass and momentum conservation equations over a fluid domain bounded by a free surface and containing dynamic boundaries was developed. This technique was used to study the hydrodynamic impact of an arbitrary shaped body. A finite difference time marching solution to the continuity coupled Navier Stokes equations was employed as the basis of the simulation technique. A novel application of the well known source distribution method was used to model moving solid boundaries of arbitrary shape within the confines of the regular finite difference mesh. This particular aspect of the research allowed a marriage of traditional hydrodynamic theory and the more recent developments in computational fluid dynamics. The second area of study examined the behaviour of the compressible air layer formed between the free surface and an approaching bluff body. Again, the techniques of computational fluid dynamics were employed to solve the equations of mass and momentum conservation in the air layer and the associated free surface motions caused by the build up of pressure beneath the falling body. The thesis presents a number of computational examples in order to illustrate the development and final levels of accuracy achieved by the two classes of numerical algorithm mentioned above. Simulations of steady viscous free surface flow, wavemaker modelling, vehicle motions and added mass computations are employed to test the numerical algorithms. Results from hydrodynamic impact simulations are presented and compared with existing numerical and experimental data, for a range of hull shapes. The effects of air entrapment on impact geometry is discussed via a comparison of results obtained by the present method and data from both computations and experiment reported in the open literature. Conclusions concerning the quantitative importance of the various physical parameters involved in slamming on the ship scale are presented at the end of the thesis.
TL;DR: The numerical analysis procedure considering the fluid inertia effect was developed ion the previous report for solving the fluid-structure interactive vibration of a three dimensional structure with complicated configuration such as ship structure, offshore structure and so on as mentioned in this paper.
Abstract: The numerical analysis procedure considering the fluid inertia effect was developed ion the previous report for solving the fluid-structure interactive vibration of a three dimensional structure with complicated configuration such as ship structure, offshore structure and so on. This numerical approach was applied to the following dynamic problems with obtaining the good agreement with the theoretical or experimental results, leading to confirm the effectiveness and availability of this method. (a) Dynamic pressure and added mass of the double spheres containing fluid. (b) Dynamic characteristics of the uniform beam with finite length in water. (c) Vibration problems of actual ship structure.
TL;DR: In this paper, a numerical procedure for solving the fluid-structure interactive vibration of a three dimensional structure with complicated configuration such as ship structures, offshore structures and so on is presented.
Abstract: This paper presents the numerical procedure for solving the fluid-structure interactive vibration of a three dimensional structure with complicated configuration such as ship structures, offshore structures and so on. This numerical analysis procedure consists of the following three steps. (a) Experiment or finite element numerical code enables us to obtain the preliminary dynamic characteristics of the structure without fluid inertia effect or with lumped added mass approximating the fluid inertia effect. (b) Boundary element method determines the added mass matrix of fluid surrounding the structure whose surface has three dimensional and complicated configuration. (c) Model analysis technique combines the added mass matrix of fluid with the preliminary dynamic characteristics of the structure and leads to obtain the final results of fluid-structure interactive vibration. In the case of using the preliminary result with approximated lumped mass, lumped mass is to be subtracted from the added mass matrix of fluid.