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Showing papers on "Added mass published in 1993"


Journal ArticleDOI
TL;DR: The flight of a butterfly was observed in the take-off phase and was analyzed theoretically from aerodynamic and kinetic viewpoints and a vortex method, which was recently developed by the present authors, was used in this analysis.
Abstract: The flight of a butterfly, Pieris melete, was observed in the take-off phase and was analyzed theoretically from aerodynamic and kinetic viewpoints. A vortex method, which was recently developed by the present authors, was used in this analysis. During the downstroke, the butterfly generates mainly a vertical force. The acceleration of the butterfly9s body during the first half of the downstroke is especially large, and this acceleration is mainly caused by a large unsteady pressure drag acting on the wings. This large unsteady pressure drag is generated by the vortices shed into the flow from the outer edges of each wing of a pair; it is increased by the interference effect between a pair of wings when the opening angle is small. This force can be estimated by the previous quasi-steady analysis when the force coefficient is changed to 4. In addition to the unsteady pressure drag, an aerodynamic force due to added mass is generated and this is also increased by the interference effect between a pair of wings. During the upstroke the butterfly generates mainly a horizontal force. The change of direction of the forces during the down- and upstrokes is controlled by variation in the inclination of the stroke plane. The moment, which is created by the aerodynamic force acting on the wings and by abdominal motion, changes the thoracic angle, that is the inclination of the stroke plane.

97 citations


Journal ArticleDOI
TL;DR: In this article, an analytical solution to the velocity potential that governs the linear radiation problem is described, and a comparison with the available experimental data is made to determine the close form solutions for the added mass and damping coefficient of a large surfacepiercing and bottom-mounted vertical circular cylinder under-going horizontal oscillations in the surge (or sway) motion.

46 citations


Journal ArticleDOI
TL;DR: In this article, the Stokes resistance, added mass, and Basset force of spheroids were computed for finite-length, circular cross-section cylinders using a boundary integral formulation.
Abstract: The Stokes resistance, added mass, and Basset force are numerically computed for finite‐length, circular cross‐section cylinders using a boundary integral formulation. Numerical results are presented for cylinders translating parallel and perpendicular to their symmetry axes with length‐to‐width ratios in the range: 0.01≤a/b≤100. There is good agreement with the limited experimental and numerical results of previous studies and slender‐body theory. Simple, analytical formulas for the Stokes force, added mass, and Basset force of spheroids are contrasted with the numerical results for cylinders of the same aspect ratio. For some of these parameters, significant differences persist for disk‐ and rod‐shaped particles.

40 citations


Journal ArticleDOI
TL;DR: In this article, the effect of various combinations of clamped (C) and simply-supported (S) conditions along the edges of the plates on the natural frequencies is also presented.

28 citations



Journal ArticleDOI
TL;DR: In this paper, a mathematical model for dynamic stability and nonlinear parametric vibration of ideal cylindrical shells and cylinders with added mass is considered with regard to their geometrical nordinearity.

20 citations


Journal ArticleDOI
TL;DR: In this paper, the added mass coefficients for two and three-dimensional submerged bodies were calculated using a low-order panel code and the source and dipole strengths, and the panel surface area for each panel, were used to compute the integrals needed for added mass in all six degrees of motions.
Abstract: The added mass coefficients for two and three-dimensional submerged bodies were calculated using a low-order panel code. The source and dipole strengths, and the panel surface area for each panel, were used to compute the integrals needed for added mass in all six degrees of motions. Several applications of this method were used in comparing the results with the theoretical, when available, experimental or other numerical results. The method was found to be successful in predicting the added mass coefficients using relatively low numbers of panels.

19 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented the results of investigations conducted to evaluate the added mass to represent fluid-structure interaction effects in vibration/dynamic analysis of floating bodies such as ship hulls.
Abstract: The paper presents the results of investigations conducted to evaluate the added mass to represent fluid-structure interaction effects in vibration/dynamic analysis of floating bodies such as ship hulls While the structural plating is idealized by 9-noded plate/shell finite elements, the fluid domain is modelled by 20-noded/21-noded 3-D finite elements in the investigations conducted A new 8-noded element has been developed to model the interface between the structure and the fluid An efficient computational methodology has been used for computation of added mass The finite element models are validated by comparing the results with those given by analytical solution for a submerged sphere The efficacy of the finite element model is demonstrated through convergence of the results obtained for a floating barge problem A better convergence rate and distribution of added mass in three orthogonal directions have been obtained

17 citations


Journal ArticleDOI
TL;DR: In this paper, a number of single spheres were attached to springs and oscillated in water-filled tubes of several diameters and lengths with various boundary conditions at the ends of the tubes.
Abstract: Rows of single spheres were attached to springs and oscillated in water‐filled tubes of several diameters and lengths with various boundary conditions at the ends of the tubes. Similar tests were performed using arrays of spheres in a closed‐end tube. The added mass coefficient was deduced from the measured natural frequency. Results for finite systems were systematically extrapolated to predict the coefficient for an infinite system. The results are closely described by adapting the spheres‐in‐tube potential flow theory of Cai and Wallis [Phys. Fluids A 4, 904 (1992)] and the image method applied to arrays by Wallis et al. [Chem. Eng. Commun. 118, 141 (1992)]. The coefficient of added mass is shown to depend on the external impedance of a fluid circuit to which the system is connected. Wallis’ [Multiphase Sci. Technol. 5, 239 (1989)] and Zuber’s [Chem. Eng. Sci. 19, 897 (1964)] coefficients are recovered as limiting cases.

15 citations


Journal ArticleDOI
TL;DR: In this paper, the deterministic and random vibration response analysis of a model which simulates a robotic arm has been presented, where the model is considered as a uniform, mass-loaded, hysteretically damped beam, the left end attached by both translational and rotational springs and the right end of which is free and carrying a heavy tip mass.

15 citations


Journal ArticleDOI
TL;DR: In this paper, the first and second-order heave and pitch motions of a freely floating toroidal body in unidirectional irregular seas are studied using a ring-source boundary integral equation method and a two-term Volterra statistical model.

Journal ArticleDOI
TL;DR: In this paper, the fundamental frequencies of rectangular plates carrying a mass mounted at various positions were determined using an energy method involving double trigonometric functions, and a finite element analysis was also presented for comparison.
Abstract: The present work is concerned with the determination of the fundamental frequencies of rectangular plates carrying a mass mounted at various positions. Although direct solution of the Navier and Levy methods is not generally practical, an energy method involving double trigonometric functions was developed to obtain approximate closed-form solutions. A finite element analysis is also presented for comparison. Extensive experimental investigation on the three plates through a shaker system was conducted to collect useful test data. Comparisons of experimental results with theoretical predictions of the finite element and energy methods are made. The results confirm that the frequency of the plate decreases as the weight of the component mass is increased, and the frequency increases as the mass moves away from the center of the plate. The work suggested that the tested plates can be approximately represented by plates with two opposite edges simply supported and the other two edges clamped (SCSC) boundary conditions. A set of comparisons also reveals that there is a need for improvement in the analytical methods for heavier masses.

Journal ArticleDOI
TL;DR: In this article, the authors developed and validated an optimization procedure to systematically place tuning masses along a rotor blade span to minimize vibratory loads, and applied the procedure to a one-sixth, Mach-scaled rotor blade model to place three masses and then again to place six masses.
Abstract: This article describes the development and validation of an optimization procedure to systematically place tuning masses along a rotor blade span to minimize vibratory loads. The masses and their corresponding locations are the design variables that are manipulated to reduce harmonics of hub shear for a four-bladed rotor system without adding a large mass penalty. The procedure incorporates a comprehensive helicopter analysis to calculate the airloads. Predicting changes in airloads due to changes in design variables is an important feature of this research. The procedure was applied to a one-sixth, Mach-scaled rotor blade model to place three masses and then again to place six masses. In both cases the added mass was able to achieve significant reductions in the hub shear. In addition, the procedure was applied to place a single mass of fixed value on a blade model to reduce the hub shear for three flight conditions. The analytical results were compared to experimental data from a wind-tunnel test performed in the Langley transonic dynamics tunnel (TDT). The correlation of the mass location was good and the trend of the mass location with respect to flight speed was predicted fairly well. However, it was noted that the analysis was not entirely successful at predicting the absolute magnitudes of the fixed-system loads.

Journal ArticleDOI
Lee In1, Lee Jung-Jin1
TL;DR: In this article, the effect of tip mass, engine, sweep angle, fiber orientation and aspect ratio of a composite wing, which is composed of graphite/epoxy laminate with a symmetric stacking sequence, on vibration characteristics was analyzed.

Journal ArticleDOI
TL;DR: In this article, a boundary integral method based on variable transformations is developed to evaluate integrations over steep peaks of the cylindrical surface of a sphere conveyed by a uniform flow around a fixed circular cylinder in an inviscid fluid.
Abstract: Hydrodynamic interactions between a three-dimensional body of revolution and an infinitely long circular cylinder in an inviscid fluid are studies numerically by the boundary-integral method. The added-mass coefficients and their derivatives are computed in terms of the solutions of four integral equations of the second kind. A numerical technique based on variable transformations is developed to evaluate integrations over steep peaks. Integrations over the cylindrical surface are properly computed by mapping the infinite region onto a finite region and regularizing the ill-behaved kernels with sharp peaks. The discrete added masses and their derivatives are fitted by the least-squares approximation on the basis of Legendre polynomials. As a practical example, the moving trajectories of a sphere conveyed by a uniform flow around a fixed circular cylinder are computed and presented.

Journal ArticleDOI
TL;DR: In this article, an energy method based on the Rayleigh's approach has been developed to obtain approximate closed-form solutions for determining the fundamental frequencies of a simply supported-clamped (SCSC) plate carrying a concentrated mass.
Abstract: The present work is concerned with the determination of the fundamental frequencies of a simply supported-clamped-simply supported-clamped (SCSC) plate carrying a concentrated mass. An energy method based on the Rayleigh’s approach has been developed to obtain approximate closed-form solutions. A finite element analysis is also presented for comparison. Extensive experimental investigation through a shaker system was conducted to collect useful test data. The comparison of experimental results with theoretical predictions of the energy method shows favorable correlations. In the parametric study, the effect of various sizes of the concentrated mass, and the effect of the variation in the plate geometry and material properties on the fundamental frequencies of the plate are presented.

Journal ArticleDOI
TL;DR: In this paper, a generalization of a computational method for the linearized potential flow, previously applied to a two-step vertical cylinder, is presented for the study of hydrodynamic forces on a cylinder with a large number of steps.

Journal ArticleDOI
TL;DR: In this paper, a simple series of single term polynomials is used for the assumed mode in place of the beam functions, and the effect of tip mass is examined using numerical simulations for various prescribed axial motions of a beam.

Proceedings ArticleDOI
01 Apr 1993
TL;DR: In this paper, the authors compare a typical fluid film bearing transfer function with a typical magnetic bearing transfer functions (PID controller) to illustrate the differences and explain how equivalent coefficients are defined for magnetic bearings.
Abstract: Conventional eigenvalue analysis techniques for rotating machines use a linearized force coefficient bearing model that fits experimental data for fluid film bearings and seals. In this model, real and constant stiffness, damping, and added mass coefficients define the frequency dependence of the fluid film bearing force/displacement transfer function. This model can not adequately represent the more complicated frequency dependence of a magnetic bearing transfer function. Therefore, application of standard eigenvalue techniques to magnetic bearing supported rotors requires equivalent coefficients that are frequency dependent. In this paper, a typical fluid film bearing transfer function is compared to a typical magnetic bearing transfer function (PID controller) to illustrate the differences and explain how eqivalent coefficients are defined for magnetic bearings. The iterative procedure required to use the equivalent coefficients in standard rotordynamic eigenvalue analysis programs is discussed. Iteration can be eliminated by modifying a conventional eigenvalue analysis program to include the electromechanical equations of the magnetic bearing controller, an approach that provides a direct description of the frequency dependence of the magnetic bearing transfer function. The controller model applied by Chen and the more general approach applied by Maslen are discussed.

Journal Article
TL;DR: In this article, the authors developed a rapid but rigorous tool to help acoustics engineers understand and predict the vibro-acoustic behavior of a constrained-layer damping of a plate.
Abstract: The authors develop a rapid but rigorous tool to help acoustics engineers understand and predict the vibro-acoustic behavior of a constrained-layer damping of a plate. A rectangular four layered simply supported baffled plate is considered. In addition, the plate is assumed to be semi-complex in the sense that it can support added masses, stiffeners and several types of excitation (i.e. point, line, surface forces and moment). The problem is formulated using a variational approach and solved by the Rayleigh-Ritz method. The modeling of the stiffeners is based on an equivalent orthotropic layer. Since the plate is assumed to radiate in air, added mass due to fluid loading is ignored. However, possible cross modal coupling due to stiffening or the type of the excitation is accounted for. This is done using a novel method for evaluating the radiation impedance matrix based on multipoles expansions of Green's kernel. The numerical evaluation of the radiated power is done easily from the radiation impedance matrix

Journal ArticleDOI
W. G. Sim, Y. C. Cho1
TL;DR: In this article, a newly developed spectral collocation method for the study of the unsteady annular flow between two eccentric cylinders is presented, which is validated by comparison with the available analytical solutions.
Abstract: This paper presents a newly developed spectral collocation method for the study of the unsteady annular flow between two eccentric cylinders. In order to predict the stability of a system in a confined flow, the formulae and results of added mass and fluid damping are provided in the present paper when a cylinder undergoes oscillatory motion in the plane of symmetry and normal to the plane of symmetry in an eccentric annulus. The potential flow theory has been developed to obtain the added mass for incompressible, inviscid and irrotational fluid. For the viscous fluid, the added mass and the viscous damping are presented. This method is validated by comparison with the available analytical solutions obtained for the unsteady potential flow in the eccentric annular space. Excellent agreement was found between the solutions obtained with the present spectral method and the available analytical solutions. In the present study, the viscous effect on the added mass can be evaluated, comparing the results obtained by potential flow theory with those obtained by the viscous flow theory, and viscous damping is investigated.

Journal ArticleDOI
TL;DR: In this paper, an analysis procedure is presented which determines the rotordynamic stiffness, damping, and added mass coefficients for circumferentially-grooved annular seals with turbulent incompressible flow.
Abstract: An analysis procedure is presented which determines the rotordynamic stiffness, damping, and added mass coefficients for circumferentially-grooved annular seals with turbulent incompressible flow. Hirs' turbulent lubrication theory is used as the basis for the governing equations. Friction factors in the groove are based on theory for a turbulent shear layer and an entrance loss model is applied at the inlet and land regions of the seal. The governing equations are expanded into zeroth and first order equations for small rotor displacements about a centered position. The zeroth order solution determines the velocity distribution and seal leakage. The first order solution determines the dynamic pressure distribution which is integrated to yield the fluid force reactions. Comparison to published experimental results shows moderate quantitative agreement and good qualitative agreement with seal test data. Presented at the 47th Annual Meeting In Philadelphia, Pennsylvania May 4–7, 1992

Journal ArticleDOI
TL;DR: In this article, a review of the interactions of various cylindrical arrangements in heave and surge motions is presented, which can be used to estimate the induced side forces due to relative motions between floating structures.

Proceedings ArticleDOI
25 Oct 1993
TL;DR: In this article, the authors describe a general formulation allowing for the analysis of the vibroacoustic behavior of a baffled plate, acoustically or mechanically excited, immersed in a mean flow on one side and coupled to a rectangular hard-walled cavity on the other side.
Abstract: This paper describes a general formulation allowing for the analysis of the vibroacoustic behavior of a baffled plate, acoustically or mechanically excited, immersed in a mean flow on one side and coupled to a rectangular hard-walled cavity on the other side. The analysis i s based on a finite element method for the plate vibrations. Fluid loading on each side of the plate is taken into account through an impedance matrices approach. The plate-cavity impedance matrix is calculated using a boundary element method. The amount of computation is decreased by using a two indices Green's function inside the cavity. The external impedance matrix accounting for mean flow, is calculated using an extended form of Kirchoffs integral equation and a boundary element method. A detailed discussion of mean flow effects on the different vibroacoustic indicators (mean square plate velocity, acoustic radiated power and radiation efficiency of the plate inside the cavity) is presented. Coupling mechanisms are explained in terms of added mass, stiffness and damping. Important changes occur in the vibroacoustic indicators as the Mach number increases. It is seen that the mean flow effects tend to oppose cavity effects especially at low frequencies.

Dissertation
01 Jan 1993
TL;DR: In this article, the effect of the forward speed effect on the body boundary conditions of a rigidly connected two-rigid cylinders in waves is investigated. But the results in this paper are limited to the case of a single circular cylinder.
Abstract: This thesis is in two volumes and the second one contains the Figures. Dynamic motion responses of twin hulled offshore structures, such as semi- submersible drilling rigs, are of more concern to designers of offshore structures than those of ships, since it is not easy for such offshore structures to move away from stormy weather. These structures should operate stably around their fixed positions and, from the viewpoint of practical design and construction, they should be well designed to withstand severe wave excitation forces in general. A lot of the twin hulled offshore structures designed for developing the ocean resources are of two submerged long body configuration. Their behaviour in waves with crests parallel to the long bo4y axis are studied by considering the motion dynamics of two rigidly connected submerged cylinders in waves and the two dimensional radiation and diffraction problems are investigated with the forward speed effect (equivalent current effect). Under a linear assumption of the boundary value problem, the numerical solution is obtained exactly by solving the integral equation for the velocity potential on the body surface. Chapter One surveys the history of this research work on motion dynamics of floating offshore structures in waves. The new developing theories for predicting radiation forces and wave excitation forces to improve numerical accuracy and computational efficiency are reviewed and a preliminary study on the hydrodynamic behaviour of floating offshore structures in waves is performed. The practical prediction of the Froude Krylov forces acting on floating buoys and twin hulled vehicles in waves is also carried out. The engineering application of the hydrodynamic behaviour of the floating buoys with the mooring systems in waves is reviewed and extended to twin hulled offshore vehicles. In Chapter Two the complete boundary value problem is theoretically formulated for the velocity potential, which describes the unsteady flow around a submerged long cylinder advancing with a constant forward speed and with wave crests parallel to the long body axis. The theoretical terms due to the forward speed effect are included in the body boundary conditions. The effect of non-uniformity of the steady flow induced by the forward speed in the neighbourhood of the submerged structure is especially considered In Chapter Three the mathematical formulation of the Green function for this hydrodynamic problem is described theoretically and its derivatives are worked out for the solutions of the velocity potential over the body boundary contours in the integral equations. The mathematical manipulation of the Green function which makes the numerical computations more convenient is achieved. In Chapter Four comprehensive derivation of analytical expressions for the radiation and wave excitation forces acting on the submerged structure is described in detail. These forces are of first order with respect to the motion responses and wave amplitudes. Due to forward speed effect there is a contribution from the hydrodynamic restoring force terms proportion to the body displacement. The theoretical relation between the work done by the damping force and the energy transportation of the generated waves by the body motions is mathematically derived and is applied to confirm the accuracy of numerical computations. Based on such radiation forces and wave excitation forces, the motion equations of the dynamic responses of the submerged structure translating at a constant forward speed (equivalent current speed) in waves, but left to oscillate freely, are systematically formulated. In Chapter Five the theoretical formulation of the m-vector contribution due to the effects of the forward speed and the interaction between two submerged hulls is derived by the image method. The mathematical expression of the m-vector contribution for the single submerged circular or elliptical cylinder is also described. The predicted results in the hydrodynamic aspects with the m-vector contribution are compared with and without taking the m-vector contributions into consideration. The parametric studies are performed on the hydrodynamic characteristics such as the added mass and damping coefficients and the real and imaginary part of the Kochin functions, with and without the m-vector contributions for different submerged depths, Froude number, separation distance and inclinations. In Chapter Six the mathematical formulation of the restoring forces due to the forward speed effect for the submerged single and twin circular cylinder cases is derived in detail and the numerical results of the submerged two circular cylinder case is confirmed by the analytical solution of the submerged single circular cylinder case. The dynamic motion responses of an inclined offshore twin hulled structure with and without restoring forces due to the forward speed effect in head and following waves are extensively investigated. The results of a parametric study of the dynamic motion responses of a twin hulled offshore structure for different submerged depths, Froude numbers (equivalent current effect), separation distances and inclinations in head and following waves are studied and discussed. Moreover, the dynamic motion behaviour of twin hulled marine vehicles in the low frequency region at resonance is also investigated. (Abstract shortened by ProQuest.).

Journal ArticleDOI
TL;DR: In this paper, added masses for a predominant mode in base excitation of multiple hexagonal-bar systems were investigated and the results showed that the actual added mass for the predominant mode are smaller than those determined by conventional analyses with the assumption of a two-dimensional fluid region because of axial pressure distribution.
Abstract: Fluid forces reacting to structures, which are usually modeled as added mass, should be taken into consideration in response analyses of structures immersed in liquid. In this study, added masses for a predominant mode in base excitation of multiple-hexagonal-bar systems were investigated. Shaking table experiments were conducted with models consisting of up to 127 hexagonal bars, which have relatively small aspect ratios. The results showed that the actual added masses for the predominant mode are smaller than those determined by conventional analyses with the assumption of a two-dimensional fluid region because of axial pressure distribution. A formula was proposed to evaluate the added mass with the three-dimensional effect, using a simplified analysis model. Another formula was also proposed to calculate the participation factor. Both formulas were verified by making a comparison between analytical and experimental results.

Journal ArticleDOI
W. G. Sim, Y. C. Cho1
TL;DR: In this article, a collocation finite-difference method for concentric configurations is used to estimate the unsteady fluid-dynamic forces generated by a flexural motion in axial (laminar) flow.
Abstract: The unsteady fluid-dynamic forces, generated by a flexural motion in axial (laminar) flow, have been formulated based on a collocation finite-difference method for concentric configurations, in connection with the flow-induced vibration problem. Based on the numerical method, the governing equations of the unsteady flow, obtained from the appropriate Navier-Stokes and continuity equations, redcuced to a system of algebraic equations leading to a block-tridiagonal system. To obtain a solution of the system, the LU decomposition method is used considering the factorization scheme. This numerical method is capable of taking fully into account unsteady viscous effects and of predicting viscous forces rigorously rather than approximately, in contrast with existing theories. In order to validate the numerical approach, semi-analytical approaches have been developed for estimating the fluid-dynamic forces. The numerical results are compared to the analytical results and good agreement was found. The contribution of unsteady viscous damping forces to the overall unsteady forces is significant for low values of the oscillatory Reynolds number, expecially in very narrow annuli.

Patent
07 Sep 1993
TL;DR: In this article, a damper is fixed in contact with a frame base through the narrowest possible seat part 105 and fitted to a place where the amplitude becomes largest in the case of the frame base 1 vibrating so as to let added mass converge, thus absorbing kinetic energy caused by vibration efficiently to damp the vibration effectively.
Abstract: PURPOSE:To display sufficient damping effect stably by fitting a damper, made of relatively large density material, to the specified place of the frame of equipment with vibration generating source so as to apply large mass in the concentrated state. CONSTITUTION:A damper 101 is manufactured of large density material such as brass, and the outer diameter d1 of a seat part 105 is to be smaller than the outer diameter d2 of a damper body 102. The damper 101 is fixed in contact with a frame base 1 through the narrowest possible seat part 105 and fitted to a place where the amplitude becomes largest in the case of the frame base 1 vibrating so as to let added mass converge, thus absorbing kinetic energy caused by vibration efficiently to damp the vibration effectively. The generation of noise can be thereby suppressed effectively.

Journal ArticleDOI
TL;DR: In this article, a semi-empirical procedure for the evaluation of sea loads on large buoyant cargos during ocean transport by heavy lift ships is presented, which predicts kinematics of the cargo and waves, the occurrence of coupling between waves and cargo, and the coupling forces in time domain.

01 Jan 1993
TL;DR: In this paper, a numerical procedure utilizing the finite element method for the calculation of hydrodynamic coefficients, such as added mass and wave damping as well as wave exciting force, wave drift force, and associated motion response for floating structures in water of finite depth over a moderately sloped seabed was described.
Abstract: This paper describes a numerical procedure utilizing the finite element method for the calculation of hydrodynamic coefficients, such as added mass and wave damping as well as wave exciting force, wave drift force, and associated motion response for floating structures in water of finite depth over a moderately sloped seabed. The combined refraction-diffraction-radiation problem is solved by using a finite element method based on a variational formulation within the context of linear potential theory. Numerical results indicating the influence of the sea bottom slope on the hydrodynamic characteristics of a floating vertical circular cylinder an a lay barge type vessel are presented. For the case of a flat sea bottom, the results are compared with solutions from a boundary integral method and experimental data.