Showing papers on "Added mass published in 1995"

Efficient dynamic simulation of an underwater vehicle with a robotic manipulator

Abstract: In this paper, an efficient dynamic simulation algorithm is developed for an underwater robotic vehicle (URV) with a manipulator. It is based on previous work on efficient O(N) algorithms, where N is the number of links in the manipulator, and has been extended to include the effects of a mobile base (the URV body). In addition, the various hydrodynamic forces exerted on these systems in underwater environments are also incorporated into the simulation. The effects modeled in this work are added mass, viscous drag, fluid acceleration, and buoyancy forces. With efficient implementation of the resulting algorithm, the amount of computation with inclusion of the hydrodynamics is almost double that of the original algorithm for a six degree-of-freedom land-based manipulator with a mobile base. Nevertheless, the amount of computation still only grows linearly with the number of degrees of freedom in the manipulator. >

Mechanisms of removal of micron-sized particles by high-frequency ultrasonic waves

Abstract: In this paper, theories of particle removal by high-frequency ultrasonic waves are discussed and tested against recent experimental data. First, the principal adhesion forces such as van der Waals forces are briefly reviewed and the typical uncertainties in their size in particle-surface systems are assessed. The different ultrasound-induced forces-linear forces such as added mass, drag, lift, and Basset forces and nonlinear ones due to radiation pressure, and drag exerted by acoustic streaming-are discussed and their magnitudes are evaluated for typical cleaning operations. It is shown that high-frequency ultrasound can clean particles most effectively in media with properties like water because: (1) the wavelength can be made comparable to the particle radius to promote effective sound-particle interaction; (2) the viscous boundary layer is thin, minimizing particle "hide-out;" and (3) both the added mass and radiation pressure forces exceed typical adhesion forces at high frequencies. Based on these analyses, possible mechanisms of particle removal are discussed and interpreted in terms of experimental observations of particle cleaning. >

Liquid level sensors using thin walled cylinders vibrating in circumferential modes

Abstract: The development of a prototype liquid level sensor using a thin walled cylinder vibrating in a circumferential mode and thin film piezo-electric polymer transducers is presented. Vibration characteristics of the fluid loaded cylinder are analysed with a finite element model incorporating the 'added mass' concept. The model is shown to predict the prototype sensor performance. It is also demonstrated that a series of non-dimensional graphs of the modal characteristics of empty cylinders can be used to predict the performance of this family of level sensors and provide a valuable design tool in the selection of suitable cylinder dimensions.

On the heave radiation of a rectangular structure

Abstract: In this paper, an analytic solution to the heave radiation problem of a rectangular structure is presented. To solve the problem analytically, the nonhomogeneous boundary value problem is linearly decomposed into homogenous ones, which can be readily solved. To provide further comparisons to the analytic solution, a boundary element method is also presented to solve the problem. The analytic solution is compared with the result by Black et al. (1971), and the boundary element solution, and the comparisons show very good agreements. Upon examination of the analytic solution, it is shown that the solution satisfies the nonhomogeneous boundary condition in a sense of series convergence. Using the analytic solution, the generated waves, the added mass and the radiation damping coefficients, as well as the hydrodynamic effects of the submergence and the width of the structure, are investigated.

Effect of concentrated mass on stability of cantilevers under rocket thrust

Abstract: The paper describes the effect of an intermediate concentrated mass on the dynamic stability of cantilevered columns subjected to a rocket thrust. It is assumed that the rocket thrust is produced by the installation of a solid rocket motor at the tip end of the cantilevered columns having the intermediate mass. The rocket motor is assumed to be a rigid body having finite sizes but not a mass point. The importance of the magnitude and size of the intermediate mass is demonstrated by theory and experiment. The experimental results are compared with theoretical predictions made by taking into account the mass and size of the rocket motor as well as intermediate mass effect. The internal damping was neglected in the theoretical predictions. It is shown that theoretical stability predictions and experimental flutter limits agreed well.

Wave response analysis of a flexible floating structure by be-fe combination method

Abstract: This paper deals with a large scale pontoon-type structure such as a floating airport To analyze the wave response of such a large scale structure, the effect of the structural flexibility on the fluid- structure interactions should be considered The proposed analytical method employs the boundary element method for evaluating hydrodynamic forces (wave excitation force, added mass force, and hydrodynamic damping force), and the finite element method for calculating wave response of the elastic floating body The experiments are performed for a 2D model structure made of polyurethane plate and having a length of 10m, width of 05m and a thickness of 76mm, 38mm and 19mm Some numerical examples for the 2D structure are presented and compared with experimental results

A Formulation for Mean Flow Effects on Sound Radiation from Rectangular Baffled Plates with Arbitrary Boundary Conditions

Abstract: A general formulation of the sound radiation from fluid-loaded rectangular baffled plates with arbitrary boundary conditions has been developed by Berry et al. (JASA, Vol. 90, No. 4, Pt. 2, 1991). In this paper, an extension of this formulation to inviscid, uniform subsonic flow is considered. The analysis is based on a variational formulation for the transverse vibrations of the plate and the use of the extended, to uniformly moving media, form of the Helmholtz integral equation. The formulation shows explicitly the effect of the flow in terms of added mass, and radiation resistance. Furthermore, it avoids the difficult problem of integration in the complex domain, typical of the wavenumber transform approaches to fluid-loading problems. Comparison of the acoustic radiation impedance with existing studies supports the validity of the approach. The details of the formulation and its numerical implementation is exposed and a discussion of the flow effects on the radiation impedance of a rectangular piston is presented. It is shown that subsonic mean flow increases the modal radiation resistance at low frequencies and affects added mass more strongly than it affects radiation resistance

Time-marching analysis of fluid-coupled systems with large added mass

Abstract: Time-marching stability analysis of fluid-structure interaction problems is considered in this paper. The Navier-Stokes equations and the equation of motion of the structure are integrated simultaneously in time in a coupled manner to assess structural dynamics and thereby the possibility for flutter and/or divergence. A method developed by the authors for the incompressible Navier-Stokes equations consists of combining a Runge-Kutta time integration for the structure with a three-point backward time discretization for the fluid. Problems have been encountered with that method, however, when the fluid-added mass is larger than the structural mass, leading to numerical instability in the integration scheme. A cure to remedy these difficulties is proposed in this paper. It consists of introducing estimates for the added mass, obtained, for example, from potential flow calculations, into the structural equation so as to cancel the fluid inertial forces. To illustrate the possibilities of the method, analysis of the free vibrations of two coaxial cylinders coupled by annular fluid is performed

Theoretical and experimental study of mass sensitivity of PSAW-APMs on ZX-LiNbO/sub 3/

Abstract: Acoustic plate mode (APM) devices have recently been used as sensing elements, both for the physical measurement of fluid properties and in biosensor applications. One of the primary interaction mechanisms in these devices is mass loading caused by the added mass bound to the layered crystal surface. However, the material properties of these thin composite layers are not well characterized or known as is required in order to accurately predict the sensor response. In the present work, perturbation theory is used to derive expressions for the sensitivity of the APM sensors to mass loading and viscoelastic stiffening. Mass sensitivity experiment was conducted on ZX-LiNbO/sub 3/ in a liquid environment to accurately reflect the sensitivity of an actual biosensor and the results are compared to theory. The measured data show a f/sup 2/ dependence for the mass sensitivity for APMs on ZX-LiNbO/sub 3/ in the measured frequency range, which indicates a SAW-like behavior. This behavior is due to the fact that the acoustic plate modes on ZX-LiNBO/sub 3/ are pseudo-SAW (PSAW) derived, and the acoustic energy is confined to the sensing surface. As a result, the APMs on ZX-LiNbO/sub 3/ are referred to as PSAW-APMs. Discussions are given in terms of the added mass which occurs in typical biosensor applications. >

Intermittency Route to Chaos of a Cantilevered Pipe Conveying Fluid With a Mass Defect at the Free End

Abstract: The nonlinear equations for planar motions of a vertical cantilevered pipe conveying fluid are modified to take into account a small lumped mass added at the free end. The resultant equations contain nonlinear inertial terms ; by discretizing the system first and inverting the inertia matrix, these terms are transferred into other matrices. In this paper, the dynamics of the system is examined when the added mass is negative (a mass defect), by means of numerical computations and by the software package AUTO. The system loses stability by a Hopf bifurcation, and the resultant limit cycle undergoes pitchfork and period-doubling bifurcations. Subsequently, as shown by the computation of Floquet multipliers, a type I intermittency route to chaos is followed-as illustrated further by a Lorenz return map, revealing the well-known normal form for this type of bifurcation. The period between turbulent bursts of nonperiodic oscillations is computed numerically, as well as Lyapunov exponents. Remarkable qualitative agreement, in both cases, is obtained with analytical results.

Simulation of nonlinear waves and forces due to transient and steady motion of submerged sphere

Abstract: This paper presents a time domain simulation of fully nonlinear waves and nonlinear hydrodynamic forces that are generated by a submerged sphere in a transient and steady motion near the free surface. A higher-order boundary element method previously developed in the frequency domain was further developed to solve the boundary integral equation in the time domain. The multiple node technique was applied on elements in the neighbourhood of the edges and corners of the truncated rectangular numerical wave tank. Orlanski's open boundary condition was modified in association with the boundary element method to satisfy the radiation conditions at the upstream and downstream boundary. The initial force variation provides the impacting hydrodynamic force (added mass) and the near-steady forces give the averaged steady nonlinear hydrodynamic forces. The nonlinear stern wave appears to be steep and asymmetric and its progressing speed is faster than that of the linear one.

On the Importance of the Basset History Term on the Particle Motion Induced by a Plane Shock Wave

Abstract: The influence of the various forces in the particle momentum equation (i.e. drag force, added mass, Basset history force, and the force due to an external pressure gradient) on the shock wave propagation through a gas-particle mixture were evaluated by one-dimensional numerical analysis. The temporal evolution of the different forces at various locations in the low pressure section of the shock tube were evaluated for different particle response times and initial shock strengths. Furthermore, an effective drag coefficient which includes the influence of all forces affecting the particle motion was determined and compared to the standard drag curve and existing experimental data.

Experimental Determination of the Added Inertia and Damping of Planing Boats in Roll.

Abstract: : This is the third of four reports on research designed to obtain basic hydrodynamic information about planing hulls through the use of captive models tests. The information is to be used for the general study of dynamic stability while underway, course keeping, turning and maneuvering, etc. The models tested were of idealized patrol boats having an LBP of 100 ft., a beam of 20 ft., and a displacement of 100 long tons. The models had prismatic hull forms with 10, 20, and 30 degrees of deadrise. The report presents the results of free oscillation tests on two unappended prismatic hulls of 10 and 20 degrees of deadrise. The tests were conducted at a beam loading coefficient of 0.4375, at three speeds Ov = 1.5, 3.0, and 4.0, three trim angles 0, 3, AND 6 DEGREES, and at yaw angles of 0,10, and 15 degrees. Roll extinction records were taken with three different spring stiffnesses, first at rest in air and then underway in water, at each test condition. The roll period and logarithmic decrement were determined from these records and tabulated. The added mass moment of inertia and damping in roll were deduced from these data assuming a linear damped harmonic oscillator. Empirical expressions for the inertia and damping are presented and compared with the data. These expressions are used to predict the rolling characteristics of a prototype 100 ft. boat.

High frequency flow-structural interaction in dense subsonic fluids

Abstract: Prediction of the detailed dynamic behavior in rocket propellant feed systems and engines and other such high-energy fluid systems requires precise analysis to assure structural performance. Designs sometimes require placement of bluff bodies in a flow passage. Additionally, there are flexibilities in ducts, liners, and piping systems. A design handbook and interactive data base have been developed for assessing flow/structural interactions to be used as a tool in design and development, to evaluate applicable geometries before problems develop, or to eliminate or minimize problems with existing hardware. This is a compilation of analytical/empirical data and techniques to evaluate detailed dynamic characteristics of both the fluid and structures. These techniques have direct applicability to rocket engine internal flow passages, hot gas drive systems, and vehicle propellant feed systems. Organization of the handbook is by basic geometries for estimating Strouhal numbers, added mass effects, mode shapes for various end constraints, critical onset flow conditions, and possible structural response amplitudes. Emphasis is on dense fluids and high structural loading potential for fatigue at low subsonic flow speeds where high-frequency excitations are possible. Avoidance and corrective measure illustrations are presented together with analytical curve fits for predictions compiled from a comprehensive data base.

Added Mass of High-Altitude Balloons

Abstract: Acoustic theory is used to find the added mass for several rigid, immersed bodies. The classical cases of a thin circular disk and a sphere are used to determine the mesh fineness required for engineering accuracy. A family of five Smalley-shaped balloons (zero circumferential stress in the film) is then considered, at different inflation ratios. Acoustical boundary elements are used. The fluid is assumed incompressible and, therefore, the added masses are identical in spirit with those from hydrodynamics. Although not important for this study, compressibility effects can be included for other bodies, if needed. Both vertical and horizontal accelerations are considered. Results show that the pear-shaped balloons behave in an intermediate way between spheres and cylinders, as expected. Such accurate values for added mass will allow better simulation of balloon flight, particularly for dynamic motion resulting from ballast or pay load drop. A major feature of this article is to demonstrate the feasibility of calculating added masses for arbitrarily shaped bodies using acoustics. The authors feel this approach will become a standard working tool for studies of immersed bodies such as balloons, parachutes, and submarines because of the ease of computation. The method uses commercial finite element preprocessors for building the model, calculation of enclosed volumes, and transferring rigid body information to the acoustic computer program.

The Free Vibration Behaviour of Ring Stiffened Cylinders - A Critical Review of the Unclassified Literature.

Abstract: : The free vibration characteristics of a submarine hull have an important influence on the noise signature. A submarine hull, or portion of one, can frequently be idealised as a ring stiffened cylinder subjected to external loading from the surrounding water, for the purposes of vibration analysis. The modal behaviour of ring stiffened cylinders is reviewed, including the effect of external pressure loading and added mass effects from surrounding fluid. The existing unclassified literature is inadequate in its coverage of the problem and these shortcomings are discussed, in order to identify the requirements for further work in order to be able to satisfactorily analyse a submarine hull structure.

Study on Vibration Characteristics of Stiffened Plates in Contact with Water by Use of Energy Method (1st Report)

Abstract: The dynamic characteristics of stiffened rectangular plates in contact with water are studied. Numerical analysis is performed by use of an energy method where vibration modes of the stiffened plate and fluid velocity potential are developed using harmonic wave series. Interaction of added mass of water adjoining stiffened plates are investigated.

Comparing the SFAV-based two-fluid model with virtual-mass models

Abstract: Several forms of virtual masses for two-phase flow models, used e.g., in the thermal-hydraulic codes TRAC-PF1, RELAP5/MOD2 and CATHARE, are compared against a new approach called «Separation of two-phase Flow According to Velocity» or SFAV that is suggested to replace the need of the virtual mass concept. The approach involves six conservation equations for the mass, momentum, and energy of two fluids as the conventional model. Only the momentum equations differ: the total flow is separated into two velocity fields and conservation equations are derived over their domains. The resulting SFAV-based six-equation model is hyperbolic over the whole range of void fractions from zero to unity and generally in any flow conditions, which means the introduction of the SFAV-formalism into the model has a remarkable, positive effect on the stability of the system. The effect is known to be of the same order as that achieved with the common virtual mass terms. In addition, the general purpose model, as SFAV, can be more suitably applied to large systems simulation, e.g., the safety analyses of water-cooled reactors, than the narrow range special purpose models

Experimental Determination of the Added Inertia and Damping of a 30 Degree Deadrise Planing Boat in Roll.

Abstract: : This is the fourth of four reports on research designed to obtain basic hydrodynamic information about planing hulls through the use of captive models tests. The information is to be used for the general study of dynamic stability while underway, course keeping, turning and maneuvering, etc. The models tested were of idealized patrol boats having an LBP of 100 ft., a beam of 20 ft., and a displacement of 100 long tons. The models had prismatic hull forms with 10, 20, and 30 degrees of deadrise. The report presents the results of free oscillation tests on an unappended prismatic hull with 30 degrees of deadrise. The tests were conducted at a beam loading coefficient of 0.4375, at three speeds Cv = 1.5, 3.0, and 4.0, three trim angles 0, 3, AND 6 DEGREES, and at yaw angles of 0,10, and 15 degrees. Roll extinction records were taken with four different spring stiffnesses, first at rest in air and then underway in water, at each test condition. The roll period and logarithmic decrement were determined from these records and tabulated. The added mass moment of inertia and damping in roll were deduced from these data assuming a linear damped harmonic oscillator. Empirical expressions for the inertia and damping are presented and compared with the data. These expressions are used to predict the rolling characteristics of a prototype 100 ft. boat.

副質量を有する建物制振用マスダンパに関する研究 : 第1報,応答解析による制振性能の予備的検討

Abstract: A new type of multi-tuned mass damper, which is designed to function well during both weak earthquake/wind and destructive earthquakes, has been investigated. This system uses impact forces from the primary mass and the added mass to reduce the displacement of the primary mass. From the results, it is confirmed that the performance of vibration control is about the same as that of optimally tuned mass dampers, although the displacement of the primary mass is markedly reduced to about half that generated by the TMD. In the practical design of vibration attenuation systems such as TMD or AMD, the stroke of the damper is one of essential problems to be considered to satisfy the seismic requirements for destructive earthquakes. This paper presents one of the "break-through-techniques" for such problem. In addition, using an actuator to control the added mass, it is confirmed that a smaller capacity of the actuator is required to obtain the same performance as that of the optimally controlled AMD.