Showing papers on "Added mass published in 2011"
TL;DR: In this paper, the effects of chordwise, spanwise, and isotropic flexibility on the force generation and propulsive efficiency of flapping wings are elucidated, and a relationship between the propulsive force and the maximum relative wing tip deformation parameter is established.
Abstract: Effects of chordwise, spanwise, and isotropic flexibility on the force generation and propulsive efficiency of flapping wings are elucidated. For a moving body immersed in viscous fluid, different types of forces, as a function of the Reynolds number, reduced frequency (k), and Strouhal number (St), acting on the moving body are identified based on a scaling argument. In particular, at the Reynolds number regime of O(10 3 - 10 4 ) and the reduced frequency of O(1), the added mass force, related to the acceleration of the wing, is important. Based on the order of magnitude and energy balance arguments, a relationship between the propulsive force and the maximum relative wing tip deformation parameter (γ) is established. The parameter depends on the density ratio, St, k, natural and flapping frequency ratio, and flapping amplitude. The lift generation, and the propulsive efficiency can be deduced by the same scaling procedures. It seems that the maximum propulsive force is obtained when flapping near the resonance, whereas the optimal propulsive efficiency is reached when flapping at about half of the natural frequency; both are supported by the reported studies. The established scaling relationships can offer direct guidance for MAV design and performance analysis.
243 citations
TL;DR: In this paper, a hydrodynamic model of perforated or slotted structures is proposed, in which the openings are infinitely small and numerous, and the wall thickness is assumed to be nil.
125 citations
01 Dec 2011
TL;DR: In this paper, the effects of chordwise, spanwise, and isotropic flexibility on the force generation and propulsive efficiency of flapping wings are elucidated, and a relationship between the propulsive force and the maximum relative wing tip deformation parameter is established.
Abstract: Effects of chordwise, spanwise, and isotropic flexibility on the force generation and propulsive efficiency of flapping wings are elucidated. For a moving body immersed in viscous fluid, different types of forces, as a function of the Reynolds number, reduced frequency (k), and Strouhal number (St), acting on the moving body are identified based on a scaling argument. In particular, at the Reynolds number regime of O(10 3 - 10 4 ) and the reduced frequency of O(1), the added mass force, related to the acceleration of the wing, is important. Based on the order of magnitude and energy balance arguments, a relationship between the propulsive force and the maximum relative wing tip deformation parameter (γ) is established. The parameter depends on the density ratio, St, k, natural and flapping frequency ratio, and flapping amplitude. The lift generation, and the propulsive efficiency can be deduced by the same scaling procedures. It seems that the maximum propulsive force is obtained when flapping near the resonance, whereas the optimal propulsive efficiency is reached when flapping at about half of the natural frequency; both are supported by the reported studies. The established scaling relationships can offer direct guidance for MAV design and performance analysis.
95 citations
TL;DR: In this paper, the impact of an elastic wedge-shaped body on a calm free-surface is modeled using a wet modal model, which is then transferred to a rigid-body model to predict the stress field on the fluid-structure interface.
83 citations
TL;DR: In this article, a nonlinear model was developed for a drillstring system in deviated well with axially moving motion and axial loading, using the perturbation techniques.
71 citations
TL;DR: The lattice Boltzmann method with the Bhatnagar–Gross–Krook linear collision operator is used to study the flow physics induced by a rigid lamina undergoing moderately large harmonic oscillations in a viscous fluid to compute the complex hydrodynamic function that describes the added mass and hydrod dynamic damping experienced by the lamina.
Abstract: In this paper, we use the lattice Boltzmann method with the Bhatnagar–Gross–Krook linear collision operator to study the flow physics induced by a rigid lamina undergoing moderately large harmonic oscillations in a viscous fluid. We propose a refill procedure for the hydrodynamic quantities in the lattice sites that are in the vicinity of the oscillating lamina. The numerically estimated flow field is used to compute the complex hydrodynamic function that describes the added mass and hydrodynamic damping experienced by the lamina. Results of the numerical simulations are validated against theoretical predictions for small amplitude vibrations and experimental and numerical findings for moderately large oscillations.
61 citations
TL;DR: In this article, a topology optimization approach is presented to maximize the modal damping ratio of the plate with constrained layer damping treatment, where damping material density and volume factor are considered as design variable and constraint respectively.
Abstract: Damping treatments have been extensively used as a powerful means to damp out structural resonant vibrations. Usually, damping materials are fully covered on the surface of plates. The drawbacks of this conventional treatment are also obvious due to an added mass and excess material consumption. Therefore, it is not always economical and effective from an optimization design view. In this paper, a topology optimization approach is presented to maximize the modal damping ratio of the plate with constrained layer damping treatment. The governing equation of motion of the plate is derived on the basis of energy approach. A finite element model to describe dynami c performances of the plate is developed and used along with an optimization algorithm in order to determine the optimal topologies of constrained layer damping layout on the plate. The damping of visco-elastic layer is modeled by the complex modulus formula. Considering the vibration and energy dissipation mode of the plate with constrained layer damping treatment, damping material density and volume factor are considered as design variable and constraint respectively. Meantime, the modal damping ratio of the plate is assigned as the objective funct ion in the topology optimization approach. The sensitivity of modal damping ratio to design variable is further derived and Method of Moving Asymptote (MMA) is adopted to search the optimized topologies of constrained layer damping layout on the plate. Numerical examples are used to demonstrate the effectiveness of the proposed topology optimization approach. The results show that vibration energy dissipation of the plates can be enhanced by the optimal constrained layer damping layout. This optimal technology can be further extended to vibration attenuation of sandwich cylindrical shells which constitute the major building block of many critical structures such as cabins of aircraft s, hulls of submarines and bodies of rockets and missiles as an invaluable design tool.
57 citations
TL;DR: In this article, the authors investigated the effect of submergence on the dynamic response of a submerged floating tunnel (SFT) due to moving load by evaluating the added mass of tunnel using two and three dimensional models.
47 citations
TL;DR: In this article, a MATLAB code was developed for numerical solutions to investigate the dynamic behavior of a beam carrying an accelerating mass, which is modelled as a moving finite element.
Abstract: In this study, the dynamic behaviour of a beam carrying accelerating mass is investigated. A MATLAB code was developed for numerical solutions. The accelerating moving mass that is travelling on the beam was modelled as a moving finite element in order to include inertial effects beside gravitation force of mass. Since the mass moves along the deflected curve of the beam, these effects are, respectively, the centripetal force, the inertia force, and the Coriolis force components of the moving mass. The effect of longitudinal force due to acceleration of the moving mass is also included. Dynamic response of the beam was obtained depending on the mass ratio (mass of the load / the mass of the beam) and the acceleration of the mass. Numerical results show the effectiveness of the method.
42 citations
TL;DR: In this paper, the added mass matrix is computed in a given geometrical and flow specifications for a specific propeller and its results are studied versus experimental results, which it's current numerical data.
Abstract: Added mass is an important and effective dynamic coefficient in accelerating, non uniform motion as a result of fluid accelerating around a body. It plays an important role, especially in vessel roll motion, control parameters as well as in analyzing the local and global vibration of a vessel and its parts like propellers and rudders. In this article, calculating the Added Mass Coefficient has been examined for a sphere, ellipsoid, marine propeller and hydrofoil; using numerical Boundary Element Method. Since an Ellipsoid and a sphere have simple geometric shapes and the Analytical values of their added mass coefficients are available, so that the results of added mass matrix are obtained and evaluated, using the boundary element method. Then the added mass matrix is computed in a given geometrical and flow specifications for a specific propeller and its results are studied versus experimental results, which it’s current numerical data. In comparison with other numerical methods has a good conformity with experimental results. The most important advantage of the method in determining the added mass matrix coefficients for the surface and underwater vessels and the marine propellers is extracting all the added mass coefficients with very good Accuracy, while in other numerical methods it is impossible to extract all the coefficients with the Desired Accuracy.
42 citations
TL;DR: In this paper, the fast multiple boundary element method (FMBEM) is applied to calculate the added mass coefficients of complicated 3D underwater bodies, such as spheroids and spheres.
TL;DR: In this paper, a simplified added-mass model was proposed, where the added mass of each vibration region is equivalent to the uniformly distributed air with a height of αml, where αm is the addedmass coefficient and l is the diameter of the inscribed circle of the corresponding vibration region.
TL;DR: In this article, a method to simultaneously determine the drag coefficient and added mass from a simple and economic experiment and a numerical identification procedure was presented, and the identification error was studied analytically and numerically for some experimental uncertainties.
Abstract: The drag coefficient and added mass (hydrodynamic mass) are the essential parameters for the dynamics analysis of submerged objects with mobility such as bio-mimicking fish robots or underwater vehicles. The shape dependence of these parameters makes them difficult to have good theoretical approximations and the parameters should be determined either numerically or experimentally. Different experiments have been proposed to obtain either the drag coefficient or added mass. This paper presents a new method to simultaneously determine the drag coefficient and added mass from a simple and economic experiment and a numerical identification procedure. An experiment was carried out to demonstrate the method and the identification error was studied analytically and numerically for some experimental uncertainties.
19 Dec 2011
TL;DR: In this paper, the authors investigate the applicability of a horizontal-axis wind turbine (HAWT) structural dynamics and unsteady aerodynamics analysis program (FAST and AeroDyn respectively) to modeling the forces on marine hydrokinetic (MHK) turbines.
Abstract: This paper describes a recent study to investigate the applicability of a horizontal-axis wind turbine (HAWT) structural dynamics and unsteady aerodynamics analysis program (FAST and AeroDyn respectively) to modeling the forces on marine hydrokinetic (MHK) turbines. This paper summarizes the added mass model that has been added to AeroDyn. The added mass model only includes flow acceleration perpendicular to the rotor disc, and ignores added mass forces caused by blade deflection. A model of the National Renewable Energy Laboratory's (NREL) Unsteady Aerodynamics Experiment (UAE) Phase VI wind turbine was analyzed using FAST and AeroDyn with sea water conditions and the new added mass model. The results of this analysis exhibited a 3.6% change in thrust for a rapid pitch case and a slight change in amplitude and phase of thrust for a case with 30° of yaw.
TL;DR: In this paper, the authors measured the unsteady forces on a sphere by observing the one-and two-dimensional trajectories of light spheres around the highest point of a moving sphere.
Abstract: When a ball moves through the air, the air exerts a force on the ball. For a sphere moving at constant velocity with respect to the air, this force is called the drag force and it has been well measured. If the sphere moves with a nonconstant velocity there are additional forces. These “unsteady” forces depend on the sphere’s acceleration and, in principle, also on higher derivatives of the motion. The force equal to a constant times the acceleration is called the “added mass” because it increases the effective inertia of the sphere moving through the fluid. We measure the unsteady forces on a sphere by observing the one- and two-dimensional projectile motion of light spheres around the highest point. The one-dimensional motion is well described by just the usual buoyant force and the added mass as calculated in the ideal fluid model. This measurement is an excellent experiment for introductory physics students. For spheres in two-dimensional projectile motion the downward vertical acceleration at the highest point increases with the horizontal velocity. This effect can be described by an additional force proportional to the speed times the acceleration.
TL;DR: In this paper, the effect of drag correlation and added mass force on the hydrodynamics of liquid-solid fluidization was investigated and it was shown that drag correlation has a significant effect on the simulation results and the correlation proposed by Beetstra et al. (2007) gives the best agreement with experimental data.
TL;DR: In this paper, Lee and Balachandar proposed analytically-based expressions for drag and lift coefficients for a spherical particle moving on a flat wall in a linear shear flow at finite Reynolds number.
TL;DR: In this article, a Vertical Planar Motion Mechanism (VPMM) test for the spheroid-type Unmanned Underwater Vehicle (UUV) was compared with a theoretical calculation and Computational Fluid Dynamics (CFD) analysis.
TL;DR: In this paper, the nonlinear coupled governing partial differential equations of vibrations by including the bending rotation of cross section, longitudinal and transverse displacements of an inclined pinned-pinned Timoshenko beam made of linear, homogenous and isotropic material with a constant cross section and finite length subjected to a traveling mass/force with constant velocity are derived.
Abstract: In the first part of this paper, the nonlinear coupled governing partial differential equations of vibrations by including the bending rotation of cross section, longitudinal and transverse displacements of an inclined pinned–pinned Timoshenko beam made of linear, homogenous and isotropic material with a constant cross section and finite length subjected to a traveling mass/force with constant velocity are derived. To do this, the energy method (Hamilton’s principle) based on the large deflection theory in conjuncture with the von-Karman strain-displacement relations is used. These equations are solved using the Galerkin’s approach via numerical integration methods to obtain dynamic responses of the beam under act of a moving mass/force. In the second part, the nonlinear coupled vibrations of the beam traveled by an arbitrary number of successive moving masses/forces are investigated. To do a thorough study on the subject at hand, a parametric sensitivity analysis by taking into account the effects of the magnitude of the traveling mass or equivalent concentrated force, the velocity of the traveling mass/force, beam’s inclination angle, length of the beam, height of the beam and spacing between successive moving masses/forces are carried out. Furthermore, the dynamic magnification factor and normalized time histories of the mid-point of the beam are obtained for various load velocity ratios, and the results are illustrated and compared to the results obtained from traditional linear solution. The influence of the large deflections caused by a stretching effect due to the beam’s immovable end supports is captured. It is seen that the existence of quadratic–cubic nonlinear terms in the coupled governing PDEs of motion renders stiffening (hardening) behavior of the dynamic responses of the beam under the action of a moving mass/force.
TL;DR: In this article, a bulk flow model for groove oil seals operating eccentrically and its solution via the finite element method was introduced. But the authors did not consider the impact of the inner land groove depth on the performance of the oil seal.
Abstract: Oil seals in centrifugal compressors reduce leakage of the process gas into the support bearings and ambient. Under certain operating conditions of speed and pressure, oil seals lock, becoming a source of hydrodynamic instability due to excessively large cross coupled stiffness coefficients. It is a common practice to machine circumferential grooves, breaking the seal land, to isolate shear flow induced film pressures in contiguous lands, and hence reducing the seal cross coupled stiffnesses. Published tests results for oil seal rings shows that an inner land groove, shallow or deep, does not actually reduce the cross-stiffnesses as much as conventional models predict. In addition, the tested grooved oil seals evidenced large added mass coefficients; while predictive models, based on classical lubrication theory, neglect fluid inertia effects. This paper introduces a bulk-flow model for groove oil seals operating eccentrically and its solution via the finite element method. The analysis relies on an effective groove depth, different from the physical depth, which delimits the upper boundary for the squeeze film flow. Predictions of rotordynamic force coefficients are compared to published experimental force coefficients for a smooth land seal and a seal with a single inner groove with depth equaling 15 times the land clearance. The test data represent operation at 10 krpm and 70 bar supply pressure, and four journal eccentricity ratios (e/c = 0, 0.3, 0.5, 0.7). Predictions from the current model agree with the test data for operation at the lowest eccentricities (e/c = 0.3); discrepancies increasing at larger journal eccentricities. The new flow model is a significant improvement towards the accurate estimation of grooved seal cross-coupled stiffnesses and added mass coefficients; the later previously ignored or largely under predicted.Copyright © 2011 by ASME
TL;DR: In this article, the hydrodynamic force has been modeled with string of spheres and the effect of the damping and the added mass on the model has been analyzed, this force is applied to the dynamic equation so that the dynamic behavior of atomic force microscopy (AFM) cantilevers is studied in liquids by analyzing some important parameters such as added mass, internal and fluid damping.
Abstract: The dynamic behavior of atomic force microscopy (AFM) cantilevers in liquid is completely different from its behavior in air due to the applied hydrodynamic force. Exciting cantilever with frequencies close to resonance frequency and primary position alignment are two critical issues that should be considered in deriving frequency response function (FRF). In this paper, the hydrodynamic force has been modeled with string of spheres and the effect of the damping and the added mass on the model has been analyzed. Afterward, this force is applied to the dynamic equation so that the dynamic behavior of AFM cantilevers is studied in liquids by analyzing the effect of some important parameters such as added mass, internal, and fluid damping. By simulations of the dynamic equations for a silicon cantilever, FRF is determined in both air and liquid. In addition, the effects of two significant parameters of liquid mechanical properties (liquid viscosity and density) and geometrical parameters of cantilever on FRF are studied. The results for string of spheres model are compared with the other hydrodynamic model and the experimental data. When length/width ratio decreases, it is found that string of spheres model has a better agreement than the other hydrodynamic model with experimental data.
TL;DR: In this paper, the authors used axially symmetrically distributed damping to predict the phase shift in a straight, vibrating, non-fluid-conveying pipe and found that axial asymmetry in the axial distribution of damping will induce zero shifts similar to the phase shifts due to fluid flow.
TL;DR: In this article, the authors studied the dynamic behavior generated by the instability of the vibration of a loaded mass, uniformly moving along an Euler-Bernoulli beam on a viscoelastic foundation, induced by the anomalous Doppler waves excited in the beam.
Patent•
10 Feb 2011
TL;DR: A floating vessel is equipped with perforated plates which exhibit both an added-mass effect and a damping effect as mentioned in this paper, and the porosity is in the range of about 5% to about 15% of total plate area.
Abstract: A floating vessel is equipped with perforated plates which exhibit both an added-mass effect and a damping effect. The addition of porosity to an added mass plate phase-shifts the added mass force so that it becomes at least partially a damping force which does not depend on large velocities to develop a large damping force. Preferred porosity is in the range of about 5% to about 15% of total plate area. A semi-submersible vessel may have damper plates fitted between its surface-piercing columns, within a support grid in the area between the pontoons and/or extending from the sides of its pontoons. A truss spar offshore platform may have damper plates installed within its truss structure intermediate its hull and ballast tank. Drill ships and similar vessels may be equipped with damper plates extending from the sides of their hulls to reduce both heave and roll.
16 Sep 2011
TL;DR: In this article, the influence of the gas volume fraction on the dynamic characteristics of a textured annular seal was analyzed and it was shown that variations of the volume fraction between 1% and 0.1% can lead to frequency dependent stiffness, damping and added mass coefficients.
Abstract: For some applications it must be considered that the flow in the annular seal contains a mixture of liquid and gas. The multiphase character of the flow is described by the volume fraction of gas (usually air) contained in the liquid under the form of bubbles. The fluid is then a homogenous mixture of air and liquid all thru the annular seal. Its local gas volume fraction depends on the pressure field and is calculated by using a simplified form of the Rayleigh-Plesset equation. The influence of such of a multiphase (bubbly) flow on the dynamic characteristics of a straight annular seal is minimal because the volume of the fluid is reduced. The situation is quite different for textured annular (damper) seals provided with equally spaced deep cavities intended to increase the damping capabilities and to reduce the leakage flow rate. As a by-product, the volume of the fluid in the seal increases drastically and the compressibility effects stemming from the bubbly nature of the flow are largely increased even for a low gas volume fraction. The present work depicts the influence of the gas volume fraction on the dynamic characteristics of a textured annular seal. It is shown that variations of the gas volume fraction between 1% and 0.1% can lead to frequency dependent stiffness, damping and added mass coefficients.
DOI•
01 Jan 2011
TL;DR: In this paper, a movable highly instrumented block, simulating an "artificial rock block" founded in a fissured rock mass with one degree of freedom (along the vertical axis), has been modified to study the complex interaction between pressures fluctuations acting inside a cylindrical plunge pool and inside a 3-dimensional fissure.
Abstract: High-velocity plunging jets, issuing from ood release structures of dams, may result in scouring of the rocky riverbed and even endanger the foundation of the dams. Assessment of the scour extent is essential to ensure the safety of the dam and appurtenant structures as well as to guarantee the stability of its abutments. The existing near-prototype scaled experimental facility developed at the Laboratory of Hydraulic Constructions (LCH) of the Ecole Polytechnique Federale de Lausanne (EPFL) has been modified to study the complex interaction between pressures fluctuations acting inside a cylindrical plunge pool and inside a full interconnected 3-dimensional fissure. The present facility allows to simulate near-prototype jets in terms of velocity, turbulence and aeration. A movable highly instrumented block, simulating an "artificial rock block" founded in a fissured rock mass with one degree of freedom (along the vertical axis), has been inserted in the existing facility. The block and the measured box (new set-up), simulating the fissured rock mass, represent a sophisticated installation allowing to perform several measurements simultaneously. The block, having a cubic shape of 200 mm side and a density similar to in-situ rocks, is equipped with pressure, displacement and acceleration transducers. It is embedded in an artificially created surrounding rock mass equipped as well by pressure transducers. Between the block and the measurement box a 3-dimensional fissure of 1 mm thickness has also been created. The plunge pool and the new experimental set-up have been impacted by high-velocity jets to generate different loading conditions (core, transition or developed jets impacts). The purpose of the research project is to study the behavior of a single rock block separated from its surroundings by a 3-dimensional fissure and impacted by a high-velocity impinging water jet subjected to a natural aeration. Pressure fluctuations (pressure field) and block responses (displacements and accelerations) are recorded simultaneously for several jet impacts positions on the block upper face (at the plunge pool bottom level), for different water depths (Y/D ratio between 0 and 9.7) and near prototype jet velocities (2.5 - 27.0 m/s). The influence of the jet solicitations (symmetrical or asymmetrical jet impacts related to the block center) have been analyzed for several parameters: pressure field surrounding the block, dynamic block impulsion, natural and passive air entrainment, fissure geometries, block degree of freedom and block rotations in the fissured rock mass. The main conclusions coming from these analyses display interesting results. The pressure field acting on the block upper face follows the distribution found in literature (exponential distribution) whereas the pressures acting inside the 3-dimensional fissure are quite constant. The extreme pressures (positive and negative values) are attenuated inside the fissure. No transient phenomena have been observed inside the fissure. For the first time, the computation of the dynamic block impulsion has shown the relevance of the added mass and its different behavior whether the block is loaded by a symmetrical or an asymmetrical jet impact. When a body immerged in a fluid is subjected to accelerations, the surrounding fluid must accelerate as well. The inertia of the entrained fluid is the added mass. It influences the amplitudes of the vertical displacements. The added mass values obtained experimentally using the LCH facility are different from the literature values determined for different test conditions (a body moving in a quiet fluid and laterally confined). The highly instrumented block is strongly confined in the measurement box: it is surrounded on five of its six faces by the measurement box with a distance of 1 mm and it is directly loaded by high-velocity jets on its free surface. These conditions may explain this difference between observed and literature values. Theoretical block uplift shows good similitude with the measured uplift when the added mass is integrated in the computation of the dynamic block impulsion. Only the amplitude of the vertical displacements could not be always simulated exactly by the theoretical uplift, but the vertical fluctuations could be well reproduced. The maximum uplift was observed for a jet impacting on a corner of the block (∼160 mm for a block side of 200 mm). The air entrainment generated by a suction-based passive aeration system, together with the natural jet aeration, seems influence the extreme pressures (maximum and minimum) but not the block responses (displacements) related to a jet only naturally aerated. The influence of the air entrainment needed a more accurate investigation. To define the geometry of the fissure surrounding the block and to limit the block degrees of freedom to one, two type of lateral guides, fixed on the block lateral faces, have been tested. If the block is loaded symmetrically no differences have been observed, whereas for an asymmetrical jet impact for the same jet impact but on another block side some differences in the block responses (displacements) have been observed. The degree of freedom of the block influences strongly the pressure field generated inside the 3-dimensional fissure. When the block is fixed inside the measurement box, the pressures increase the hydrodynamic loading generating the propagation of the fissure networks in the rock mass. This pressure increase may reach some Bars of difference between the block free to move or fixed. The largest differences have been observed for a jet impacting on a corner of the block.
31 Oct 2011
TL;DR: In this paper, a forced rolling body is analyzed with MARIN in-house CFD code ReFRESCO, and the results for the flow computed around a 2D rolling hull section are presented.
Abstract: In this paper, the flow around a forced rolling body is analyzed with MARIN in-house CFD code ReFRESCO. The objective is to assess if the code can correctly predict the added mass and damping coefficients of a rolling vessel. After a description of code and numerical methods, the results for the flow computed around a 2D rolling hull section are presented. Sharp and rounded bilges are investigated for three roll amplitudes and three roll periods. The influence of grid and time discretisation and iterative errors are analyzed. The CFD results with Re-FRESCO are compared to experiments and to results obtained with the commercial CFD package CFX. The results shown here indicate that ReFRESCO is capable of accurately predicting the added mass and damping coefficients. However, it is also shown that fine grids and time-steps are required to obtain a grid and time-step converged solution.Copyright © 2011 by ASME
TL;DR: In this article, a numerical analysis of a steel catenary riser under random sea loads is presented, which is based on a simulation technique which duly considers the various nonlinear effects such as relative velocity squared drag force, variable added mass due to variable submergence and nonlinearity due to large excursions.