Showing papers on "Added mass published in 1989"
TL;DR: In this article, the authors presented a model for the reaction of the air on a vibrating circular plate, showing that reaction to be equivalent to a virtual mass and radiation damping, to be added to the plate mass and the mechanical damping.
118 citations
TL;DR: In this paper, the authors compared models published in the two-phase flow literature for the added mass coefficient of a dilute bubbly dispersion and showed that the differences between the models are mainly due to the different ways in which the added masses are defined.
90 citations
TL;DR: In this article, a modified integral equation is obtained by the linear superposition of the classical Green equation and its normal derivative with respect to the field point, which removes the effects of all irregular frequencies in boundary-integral equations governing the interaction of regular waves with floating bodies of general geometry.
Abstract: The paper presents a method that removes the effects of all irregular frequencies in boundary-integral equations governing the interaction of regular waves with floating bodies of general geometry. A modified integral equation is obtained by the linear superposition of the classical Green equation and its normal derivative with respect to the field point.
71 citations
TL;DR: In this article, a simplified procedure is developed to evaluate the added hydrodynamic mass for towers of arbitrary cross section, having two axes of symmetry and dimensions varying along the height, and demonstrated that the added mass associated with surrounding (outside) water or inside water can be determined to a useful degree of accuracy without rigorous three-dimensional analysis of the two fluid domains.
Abstract: For the preliminary phase of design or safety evaluation of intake‐outlet towers, the hydrodynamic interaction effects can be most simply represented in earthquake response analysis by added hydrodynamic mass distributed over the height of the tower. A simplified procedure is developed to evaluate the added hydrodynamic mass for towers of arbitrary cross section, having two axes of symmetry and dimensions varying along the height. It is demonstrated that the added mass associated with surrounding (outside) water or inside water can be determined to a useful degree of accuracy without rigorous three‐dimensional analysis of the two fluid domains. Standard data are presented for convenient implementation of the simplified procedures developed in this paper.
61 citations
TL;DR: The dynamics of the above manipulators are formulated to evaluate the influence of the added mass tensor, the added inertia Tensor, and fluid drag, and the lift on each arm according to classical Newton-Euler mechanics.
Abstract: Recently, applications of articulated manipulators have increased to include extreme environments such as underwater and space. Simulation systems to support the design and control of industrial robots have been developed in many laboratories, and some high-speed calculation methods for inverse dynamics analysis of manipulators with series connections have been proposed. This paper deals with the dynamic simulation and modelling of underwater articulated manipulators. The dynamics of the above manipulators are formulated to evaluate the influence of the added mass tensor, the added inertia tensor, and fluid drag, and the lift on each arm according to classical Newton-Euler mechanics. Moreover, by generalizing this model, we can discuss the dynamics of a manipulator with dual arms and simulate some constrained motion of an end-effector. As an example of inverse dynamics analysis, the force and moment of a nine degrees of freedom (d.o.f.) manipulator with dual arms are analysed. As an example of direct dyna...
49 citations
TL;DR: In this article, the added masses of a single body, moving with six degrees of freedom, in terms of the system of hydrodynamic singularities which generate the irrotational flow about the body were further generalized for the case when another moving body is present.
Abstract: The Taylor formula expresses the added masses of a single body, moving with six degrees of freedom, in terms of the system of hydrodynamic singularities which generate the irrotational flow about the body. In this paper, the formula is further generalized for the case when another moving body is present. This work was stimulated by a study of the hydrodynamic interactions between an ice mass and a ground-based offshore structure. The results are applied to calculate the variation of the added masses as a rectangular cylinder approaches a circular one. A new simple relation between the added masses of a rectangle moving parallel to its longer or shorter side, and a more complete table of the added- mass coefficients for various thickness-length ratios than was previously available, is presented in an appendix.
23 citations
TL;DR: In this paper, the problem of wave radiation and diffraction by submerged spheroids is analyzed using linearized three-dimensional potential-flow theory, and the solution is obtained by expanding the velocity potential into a series of Legendre functions in a spheroidal coordinate system.
Abstract: The problem of wave radiation and diffraction by submerged spheroids is analyzed using linearized three-dimensional potential-flow theory. The solution is obtained by expanding the velocity potential into a series of Legendre functions in a spheroidal coordinate system. Tabulated and graphical results are provided for added mass and damping coefficients of various spheroids undergoing motions in six degrees of freedom. Graphs are also provided for exciting forces and moments corresponding to a range of incoming wave angles.
22 citations
Patent•
20 Jun 1989
TL;DR: In this article, the authors propose to prevent an excessive force from being exerted on machineries, when the vibration in a main vibration system is fed back to the control device for an active system dynamic vibration reducer, by reducing the feedback gain in response to the increase in amplitude of an added mass.
Abstract: PURPOSE: To prevent an excessive force from being exerted on machineries, when the vibration in a main vibration system is fed back to the control device for an active system dynamic vibration reducer, by reducing the feedback gain in response to the increase in amplitude of an added mass. CONSTITUTION: After detected by an acceleration sensor 14, the vibration of a main vibration system 10 is fed back to a damping controller 18, and a control signal is output, via a multiplier 40 and a displacement controller 20, to a servo valve 22, a hydraulic cylinder 24, and an auxiliary vibration system (added mass) 12 constituting an active system dynamic vibration reducer, so as to damp the vibration. In this case, the amplitude of the added mass 12 is detected by a displacement sensor 26, and a given value C1 is subtracted from the absolute value of the amplitude calculated by a computing element 28, and further thereto a given value C2 is added via a limiter 32, and a smoothing circuit 34, and the feedback gain in the multiplier 40 is decreased by a reciprocal computing element 38 in response to the increase in amplitude of the added mass 12. Thus, an excessive force can be prevented from being exerted on machineries, and even if the vibration increases, operation can be continued. COPYRIGHT: (C)1991,JPO&Japio
8 citations
TL;DR: In this experiment, the fluid force was measured on simplified models of aquaculture net cage in steady flow and wave and the drag coefficient and mass coefficient were calculated and the ratio of the drag force to the maximum wave force became small as the wave height-length ratio increased.
Abstract: In this experiment, we measured the fluid force on simplified models of aquaculture net cage in steady flow and wave. Then we calculated the drag coefficient and added mass coefficient from the measured fluid force. The main results are as follows:The added mass coefficient of models in wave was 12. The ratio of the drag force to the maximum wave force became small as the wave height-length ratio increased. However, the ratio of the mass force to the maximum wave force became large as the wave heightlength ratio increased. Therefore, we cannot disregard the mass force and consider only the drag force, when we calculate the fluid force acting on aquaculture net cage in wave.
6 citations
TL;DR: In this experiment, the wave force action on plane nets was measured in a wave tank, and the drag and added mass coefficients were obtained.
Abstract: The drag force action on plane nets of steady current flow has been investigated both analytically and experimentally by many researchers. Although wave force is a very important factor that should be considered in designing aquaculture net cage in the marine environment, there are few studies on the wave force action on plane nets. Moreover, many problems still remain unsolved regarding wave force action. In this experiment, the wave force action on plane nets was measured in a wave tank, and the drag and added mass coefficients were obtained. The main results are as follows: 1) The drag coefficient obained from the wave force and from the drag force under the steady flow were similar. The drag coefficient could be expressed as a founction of the Reynold's number (Rn).2) When the Kenlegan Carpenter, KC number was larger than 35, the horizontal added mass coefficient was about 6, and vertical one about 2.
5 citations
TL;DR: In this article, it was shown that the exciting force coefficients, the added mass and radiation damping matrices, and the far-field wave amplitude can all be written as stationary values of well-defined functionals.
Abstract: It is shown that the linear and nonlinear exciting force coefficients, the added mass and radiation damping matrices, and the far-field wave amplitude (reflection and transmission coefficients in the two-dimensional case) can all be written as stationary values of well-defined functionals. As a consequence these quantities can be accurately determined with relatively crude approximations for the diffraction and radiation potentials. Numerical experiments confirm this feature: by inverting a 4 × 4 real symmetric matrix the results obtained by Vugts (1968), who computed the added mass and radiation damping matrices for several different geometries, were recovered over the whole range of frequencies.
01 Jan 1989
TL;DR: In this paper, the effects of ice covering the water surface upon the characteristics of added mass for an axisymmetric structure are investigated theoretically, and the theory to describe fluid motion due to oscillation of the structure is based on the linear potential theory with consideration of fluid compressibility.
Abstract: The effects of ice covering the water surface upon the characteristics of added mass for an axisymmetric structure are investigated theoretically. The theory to describe fluid motion due to oscillation of the structure is based on the linear potential theory with consideration of fluid compressibility. The problem to determine hydrodynamic forces on the structure is consequently formulated as a boundary value problem for the radiation potential in a compressible fluid. An extended eigenfunction expansion method is employed to solve the boundary value problem. Numerical results are presented to show the coupling effects of fluid compressibility and ice cover upon the characteristics of added mass.
01 Jan 1989
TL;DR: Theoretical, numerical and experimental tools are combined to derive the hydrodynamic properties of the ROSEAU stabiliser in this article, which is modelled as a porous or slotted circular cylinder.
Abstract: Theoretical, numerical and experimental tools are combined to derive the hydrodynamic properties of the ROSEAU stabiliser. In the theoretical approach it is modelled as a porous or slotted circular cylinder. Potential flow is assumed inside and outside while a quadratic discharge law is applied on the slots. Numerical results are compared to experimental ones and good agreements are obtained. The most striking results are that added mass and damping coefficients depend, to a large extent, on the motion amplitude, and that the damping is quite large, This last feature reduces the risk of low-frequency resonance under wind or wave excitation.
TL;DR: In this article, numerical results for the problem of two-dimensional incompressible viscous flow over a solid body which is undergoing specified harmonic oscillations in the direction of flow are presented.
18 Apr 1989
TL;DR: In this article, a method of analysis of the nonproportionally damped motions of fixed offshore structures in waves is presented, where the damping considered is that due only to radiation, and is assumed to be linear.
Abstract: A method of analysis of the nonproportionally damped motions of fixed offshore structures in waves is presented. The damping considered is that due only to radiation, and is assumed to be linear. Since both the radiation damping and the added mass are frequency dependent, the damping is, by nature, nonproportional. Hence, the standard normal‐mode analysis cannot be used. To isolate the modes, the matrix equation of motion of the assumed lumped‐mass system is first transformed into a first‐order equation. The complex eigenvectors and eigenvalues for the underdamped system are then obtained through matrix iteration, The displacement of each mass is obtained in deterministic seas. One of the most important results of this analysis is the demonstration of the ability of the technique to predict the movement of the nodal points over time. That is, the nodal points move up and down the centerline of the structure over each period. This means that the analyst can predict the positions of maximum stresses and str...
TL;DR: In this paper, an experimental study on dynamic fluid reaction force and moment generated in axially long annular clearance between the rotor and stator of a submerged motor pump or in the balance piston of a turbo pump is presented.
Abstract: This paper describes the experimental study on dynamic fluid reaction force and moment generated in axially long annular clearance between the rotor and stator of a submerged motor pump or in the balance piston of a turbo pump. For measuring the dynamic fluid force, a test rig was made for having spin and whirl motion of the rotor. In the test, the rotor and the stator were set in concentric conditions and pressure fluctuation, fluid reaction force and flow rate were measured under the basic parameters of rotational speeds and pressure drop across the long seal. In measurement, the moment was obtained from dynamic fluid force and instability threshold (limit) of fluid force was determined. In addition, dynamic fluid force was expressed in terms of the stiffness coefficient, damping coefficient and added mass. It was recognized that moment stiffness coefficient and direct-moement damping coefficient increase with axial flow velocity.
TL;DR: In this article, the authors present flow-induced vibration characteristics which were obtained in a model gate test, and the results of these experiments, taken as a whole, suggest that the flow induced vibration characteristics of the long span gates are well predicted by the dimensionless parameters, such as the reduced gate opening height and the reduced velocity.
Abstract: Submerged long span gates which dam a wide river undergo violent streamwise vibrations caused by vortex shedding beneath the gate. This study presents flow-induced vibration characteristics which were obtained in a model gate test. From the measured vibration frequencies and damping ratios in air and water, respectively, the level of fluid excitation and the added mass for small amplitude gate vibrations were calculated and reduced to a dimensionless form, and thus the vibration onset criteria were obtained. In addition to the average value of the maximum amplitude of gate vibration, was measured. The results of these experiments, taken as a whole, suggest that the flow-induced vibration characteristics of the long-span gates are well predicted by the dimensionless parameters, such as the reduced gate opening height and the reduced velocity.
TL;DR: In this article, a method is proposed to calculate the interaction between an oscillating body and the water surrounding it for low values of the Keulegan-Carpenter number and in laminar flow conditions.
Abstract: A method is proposed to calculate the interaction between an oscillating body and the water surrounding it for low values of the Keulegan-Carpenter number and in laminar flow conditions. Rather than dividing the viscous forces originated by the unsteady motion into an added mass inertia force and a frictional, energy dissipating, component, the interaction is here evaluated through a “Basset term” style convolution integral of the expression of the force calculated for impulsively started flow. A numerical procedure is employed to show that, for simple motions, the method herein proposed yields solutions similar to those obtainable by the classical approach. It can also deal efficiently with problems involving complex forcing actions or very short impulses, where the traditional approach fails to provide satisfactory results. The applicability of this technique is limited to purely laminar flows, thus including most of the problems related to the hydrodynamic damping of vibrating structures and excluding the whole domain of wave inducted forces.
TL;DR: In this article, a Modified Approximate Method extended to the time domain problem is presented and compared with the experimental results and they are found to be in good agreement with the calculated results.
Abstract: Dynamic tensions of mooring lines may be ignored in the estimation of wave frequency motions of a floating structure, but for slow drift oscillations hydrodynamic forces acting on mooring lines are important, because drag forces acting on mooring lines act as the damping force and have a great effect on the slow drift oscillation. When dynamic tension of mooring lines are calculated in full consideration of added mass forces and drag forces acting on mooring lines, a numerical calculation such as Lumped Mass Method is usually used. The numerical calculation needs prohibitively long computer time and it is not practical in the early stage of the design of a floating structure. The authors have developed an Approximate Method for calculating the dynamic tension taking the added mass force and drag force into consideration. The method has a short computation time and the accuracy has been confirmed by comparing calculated results with experiments. In this paper a Modified Approximate Method extended to the time domain problem is presented. The calculated results are compared with the experimental ones and they are found to be in good agreement.
TL;DR: In this paper, the authors compared time domain simulations of slow drift motion with model experiments in wave basin and found that the importance of each slow motion hydrodynamic forces on the slow drift oscillation in irregular waves of a moored floating vessel depends on a type of vessel.
Abstract: Time domain simulations of slow drift motion are compared with model experiments in wave basin. The simulations include various slow motion hydrodynamic forces such as drag coefficient depending on Kc number, time varying wave drift damping, added mass change due to waves etc. as well as second order wave excitation. Most of them are given by slow motion forced oscillation tests in regular waves. The simulation and the model experiments are carried out for two types of floating structures moored in bi-chromatic or irregular waves.They show excellent agreement with the experiments. It is clarified that importance of each slow motion hydrodynamic forces on the slow drift oscillation in irregular waves of a moored floating vessel depends on a type of vessel. Wave drift damping affects significantly the tuned motion amplitude of not only a barge but also a semi-submersible. Added mass change due to waves affects the tuned frequency only for a semi-submersible.