Showing papers on "Added mass published in 2014"
TL;DR: In this article, a case study based on a cylindrical tank is introduced in order to investigate various aspects of dynamic buckling, including the secondary buckling occurring in the top part of the tank.
Abstract: SUMMARY
Buckling plays a fundamental role in the design of steel tanks because of the small thicknesses of the walls of this class of structures. The first part of the paper presents a review of this phenomenon for liquid-containing circular cylindrical steel tanks that are fully anchored at the base, considering the different buckling modes and especially the secondary buckling occurring in the top part of the tank.
A case study based on a cylindrical tank is then introduced in order to investigate various aspects of dynamic buckling. The finite element model of the case study tank is set-up using the added mass method for fluid modelling. The influence of pre-stress states caused by hydrostatic pressure and self-weight on the natural periods of the structure is first studied and it is found that this influence is very small as far as the global behaviour of the tanks is considered, while it is important for local, shell-type, vibration modes.
In the following, the efficiency and sufficiency of different ground motion intensity measures is analysed by means of cloud analysis with a set of 40 recorded accelerograms. In particular, the peak ground displacement has been found being the most efficient and sufficient intensity measure so far as the maximum relative displacement of the tank walls is concerned.
Finally, incremental nonlinear time-history analyses are performed considering the case study structure under recorded earthquake ground motions in order to identify the critical buckling loads and to derive fragility curves for the buckling limit state. Copyright © 2013 John Wiley & Sons, Ltd.
95 citations
TL;DR: In this paper, a simplified time-domain model for a fixed detached Oscillating Water Column (OWC) device is presented as a first step towards modeling a floating multi-chamber OWC device.
64 citations
TL;DR: It is shown that the second-order scheme is stable for any mass density ratio and hence is able to handle strong added-mass effects and second- order temporal accuracy is confirmed by numerical experiments on an elastic semi-circular cylinder problem.
57 citations
TL;DR: In this paper, the influence of the axial nearby rigid distance on the dynamic response of a submerged disk is evaluated when the radial gap is very small, and the effects of the fluid depth and fluid viscosity on the natural frequencies and damping ratio of the submerged disk are studied.
57 citations
TL;DR: This work reports experiments investigating jamming fronts in a floating layer of cornstarch suspension, which has a packing fraction close to jamming, which dynamically turns into a solid when impacted at a high speed.
Abstract: We report experiments investigating jamming fronts in a floating layer of cornstarch suspension. The suspension has a packing fraction close to jamming, which dynamically turns into a solid when impacted at a high speed. We show that the front propagates in both axial and transverse direction from the point of impact, with a constant ratio between the two directions of propagation of approximately 2. Inside the jammed solid, we observe an additional compression, which results from the increasing stress as the solid grows. During the initial growth of the jammed solid, we measure a force response that can be completely accounted for by added mass. Only once the jamming front reaches a boundary, the added mass cannot account for the measured force anymore. We do not, however, immediately see a strong force response as we would expect when compressing a jammed packing. Instead, we observe a delay in the force response on the pusher, which corresponds to the time it takes for the system to develop a close to uniform velocity gradient that spans the complete system.
51 citations
TL;DR: In this article, a simplified hydrodynamic pressure expression based on radiation theory is presented by introducing three dimensionless parameters including frequency ratio, wide depth ratio and relative height of bridge pier.
49 citations
TL;DR: In this paper, a dual-arm underwater vehicle-manipulator system (UVMS) is used for object manipulation in an underwater environment, where impacts due to contact are inevitable.
41 citations
TL;DR: In this article, the evolution of a flip-through event upon a vertical, deformable wall during shallow-water sloshing in a 2D tank is analyzed, with specific focus on the role of hydroelasticity.
Abstract: The evolution of a flip-through event [6] upon a vertical, deformable wall during shallow-water sloshing in a 2D tank is analyzed, with specific focus on the role of hydroelasticity. An aluminium plate, whose dimensions are Froude-scaled in order to reproduce the first wet natural frequency associated with the typical structural panel of a Mark III containment system, is used. (Mark III Containment System is a membrane-type tank used in the Liquefied Natural Gas (LNG) carrier to contain the LNG. A typical structural panel is composed by two metallic membranes and two independent thermal insulation layers. The first membrane contains the LNG, the second one ensures redundancy in case of leakage.) Such a system is clamped to a fully rigid vertical wall of the tank at the vertical ends while being kept free on its lateral sides. Hence, in a 2D flow approximation the system can be suitably modelled, as a double-clamped Euler beam, with the Euler beam theory. The hydroelastic effects are assessed by cross-analyzing the experimental data based both on the images recorded by a fast camera, and on the strain measurements along the deformable panel and on the pressure measurements on the rigid wall below the elastic plate. The same experiments are also carried out by substituting the deformable plate with a fully stiff panel. The pressure transducers are mounted at the same positions of the strain gauges used for the deformable plate. The comparison between the results of rigid and elastic case allows to better define the role of hydroelasticity. The analysis has identified three different regimes characterizing the hydroelastic evolution: a quasi-static deformation of the beam (regime I) precedes a strongly hydroelastic behavior (regime II), for which the added mass effects are relevant; finally, the free-vibration phase (regime III) occurs. A hybrid method, combining numerical modelling and experimental data from the tests with fully rigid plate is proposed to examine the hydroelastic effects. Within this approach, the measurements provide the experimental loads acting on the rigid plate, while the numerical solution enables a more detailed analysis, by giving additional information not available from the experimental tests. More in detail, an Euler beam equation is used to model numerically the plate with the added-mass contribution estimated in time. In this way the resulting hybrid method accounts for the variation of the added mass associated with the instantaneous wetted length of the beam, estimated from the experimental images. Moreover, the forcing hydrodynamic load is prescribed by using the experimental pressure distribution measured in the rigid case. The experimental data for the elastic beam are compared with the numerical results of the hybrid model and with those of the standard methods used at the design stage. The comparison against the experimental data shows an overall satisfactory prediction of the hybrid model. The maximum peak pressure predicted by the standard methods agrees with the result of the hybrid model only when the added mass effect is considered. However, the standard methods are not able to properly estimate the temporal evolution of the plate deformation.
38 citations
TL;DR: In this paper, a simplified analytical fluid-structure interaction (FSI) model is derived to expose the role of each of the fluid and beam properties effecting the energy transfer process.
38 citations
TL;DR: In this paper, a force balance model was developed to predict the terminal velocity of a sub-millimetric bubble as its rises in water under buoyancy, which is capable of giving quantitative agreement with measured trajectories and observed collisions and rebounds against a solid surface as well as the spatiotemporal evolution of the thin film during collision as measured by interferometry.
Abstract: A force balance model has been developed to predict the terminal velocity of a sub-millimetric bubble as its rises in water under buoyancy. The dynamics of repeated collisions and rebounds of the bubble against a horizontal solid surface is modeled quantitatively by including forces due to buoyancy, added mass, drag, and hydrodynamic lubrication—the last arises from the drainage of water trapped in the thin film between the solid surface and the surface of the deformable bubble. The result is a self-contained, parameter-free model that is capable of giving quantitative agreement with measured trajectories and observed collisions and rebounds against a solid surface as well as the spatio-temporal evolution of the thin film during collision as measured by interferometry.
36 citations
TL;DR: Numerical modeling and testing of a complex-shaped remotely-operated vehicle (ROV) are shown and the proposed method is able to determine most of the hydrodynamic added mass coefficients of the open frame ROV.
Abstract: In this paper, numerical modeling and testing of a complex-shaped remotely-operated vehicle (ROV) are shown. The paper emphasizes on systematic modeling of hydrodynamic added mass using computational fluid dynamic software WAMIT^(TM) on the open frame ROV that is not commonly applied in practice. From initial design and prototype testing, a small-scale test using a free-decaying experiment is used to verify the theoretical models obtained from WAMIT^(TM). Simulation results have shown to coincide with the some of the experimental tests. The proposed method is therefore able to determine most of the hydrodynamic added mass coefficients of the open frame ROV.
TL;DR: In this paper, a review and theoretical study of the added-mass and aeroelastic instability exhibited by a linear elastic plate immersed in a mean flow is presented, and a formulation for predicting the critical velocity for the onset of flapping instability is presented.
Abstract: This work presents a review and theoretical study of the added-mass and aeroelastic instability exhibited by a linear elastic plate immersed in a mean flow. We first present a combined added-mass result for the model problem with a mean incompressible and compressible flow interacting with an elastic plate. Using the Euler–Bernoulli model for the plate and a 2D viscous potential flow model, a generalized closed-form expression of added-mass force has been derived for a flexible plate oscillating in fluid. A new compressibility correction factor is introduced in the incompressible added-mass force to account for the compressibility effects. We present a formulation for predicting the critical velocity for the onset of flapping instability. Our proposed new formulation considers tension effects explicitly due to viscous shear stress along the fluid-structure interface. In general, the tension effects are stabilizing in nature and become critical in problems involving low mass ratios. We further study the effects of the mass ratio and channel height on the aeroelastic instability using the linear stability analysis. It is observed that the proximity of the wall parallel to the plate affects the growth rate of the instability, however, these effects are less significant in comparison to the mass ratio or the tension effects in defining the instability. Finally, we conclude this paper with the validation of the theoretical results with experimental data presented in the literature.
TL;DR: Novel metabolic rate prediction equations for walking while carrying loads at the ankle, knees and back were developed based on experiments where subjects walked on a treadmill at 4, 5 or 6km/h bearing different amounts of added mass, and are 7-69% more accurate.
TL;DR: In this article, an innovative concept is introduced for reducing the displacement response of tower type fixed offshore platforms to wave loads, which is based on utilizing a Hydrodynamic Buoyant Mass Damper (HBMD), which employs damper's buoyancy and inertia forces, along with hydrodynamic damping effects, to reduce the platform displacement response.
TL;DR: In this article, the authors examined the dependence of the walker mass and momentum on its velocity and proposed a hydrodynamic boost factor for the walkers, which provides a new rationale for anomalous orbital radii reported in recent studies.
Abstract: It has recently been demonstrated that droplets walking on a vibrating fluid bath exhibit several features previously thought to be peculiar to the microscopic realm. The walker, consisting of a droplet plus its guiding wavefield, is a spatially extended object. We here examine the dependence of the walker mass and momentum on its velocity. Doing so indicates that, when the walker’s time scale of acceleration is long relative to the wave decay time, its dynamics may be described in terms of the mechanics of a particle with a speed-dependent mass and a nonlinear drag force that drives it towards a fixed speed. Drawing an analogy with relativistic mechanics, we define a hydrodynamic boost factor for the walkers. This perspective provides a new rationale for the anomalous orbital radii reported in recent studies.
TL;DR: In this article, an analytical solution for a water wave radiation problem by a submerged vertical cylinder in finite water depth was developed based on the methods of variable separation and matching eigenfunction expansions for velocity potential and validated by comparison with results from the higher order boundary element method and convergent examinations on the number of expansion models.
Abstract: Based on the methods of variable separation and matching eigenfunction expansions for velocity potential, analytical solutions are developed for a water wave radiation problem by a submerged vertical cylinder in finite water depth. They are validated by comparison with results from the higher order boundary element method and convergent examinations on the number of expansion models. Numerical analysis is carried out to investigate the influence submerged depth, cylinder length, and water depth on added mass and radiation damping. When the submerged depth is large, the added mass approaches a stable value, and radiation damping tends to zero. At high frequency range, the heave and pitch of the added mass of the submerged cylinder is about twice that of the floating cylinder. The influence of cylinder length for hydrodynamic coefficients is quite complex and shows the various properties at different frequency ranges. Added mass can be increased with the decrease of water depth, whereas the effect o...
TL;DR: In this article, the influence of the boundary conditions on the added mass of a NACA0009 cantilever hydrofoil has been numerically and experimentally investigated, and the results are in reasonable good agreement with experimental data.
TL;DR: In this paper, a phenomenological model and analytical-numerical approach to systematically characterize variable hydrodynamic coefficients and maximum achievable responses in two-dimensional vortex-induced vibrations with dual two-to-one resonances are presented.
Abstract: A phenomenological model and analytical-numerical approach to systematically characterize variable hydrodynamic coefficients and maximum achievable responses in two-dimensional vortex-induced vibrations with dual two-to-one resonances are presented. The model is based on double Duffing and van der Pol oscillators which simulate a flexibly-mounted circular cylinder subjected to uniform flow and oscillating in simultaneous cross-flow/in-line directions. Depending on system quadratic and cubic nonlinearities, amplitudes, oscillation frequencies and phase relationships, analytical closed-form expressions are derived to parametrically evaluate key hydrodynamic coefficients governing the fluid excitation, inertia and added mass force components, as well as maximum dual-resonant responses. The amplification of the mean drag is ascertained. Qualitative validations of numerical predictions with experimental comparisons are discussed. Parametric investigations are performed to highlight the important effects of system nonlinearities, mass, damping and natural frequency ratios.
TL;DR: In this article, the hydrodynamic characteristics of a heave plate under steady current conditions using three-dimensional direct numerical simulations were investigated, and the influences of three parameters, the Keulegan-Carpenter number (KC), the reduced current velocity (Vr), and the aspect ratio of the disk, on the flow structures, the current drag force, the added mass and the damping of the heave plates were examined both qualitatively and quantitatively.
TL;DR: In this paper, a time-domain higher-order boundary element method for seakeeping analyses in the framework of linear potential theory is proposed, in which an artificial damping beach is installed at an outer portion of the free surface except the downstream side for satisfying the radiation condition.
Abstract: A time-domain higher-order boundary element method for seakeeping analyses in the framework of linear potential theory is newly developed. Ship waves generated by two modified Wigley models advancing at a constant forward speed in calm water or incident waves and the resultant radiation and diffraction forces are computed to validate this code. A rectangular computational domain moving with the same forward speed as the ship is introduced, in which an artificial damping beach is installed at an outer portion of the free surface except the downstream side for satisfying the radiation condition. The velocity potential on the ship hull and the normal velocity on the free surface are calculated directly by solving the boundary integral equation. An explicit time-marching scheme is employed for updating both kinematic and dynamic free-surface boundary conditions, with an embedding of a second-order upwind difference scheme for the derivative in the x-direction to stabilize the calculation. Extensive results including the exciting forces, added mass and damping coefficients, wave profiles, and wave patterns for blunt Wigley and slender Wigley hulls with forward speed are presented to validate the efficiency of the proposed 3D time-domain approach. The corresponding physical tests of the radiation and diffraction problems in a towing tank are also carried out. Computed numerical results show good agreement with the corresponding experimental data and other numerical solutions.
TL;DR: Durand et al. as discussed by the authors used numerical simulations to model gennakers, in order to predict both propulsive force and sail dynamic stability, using a finite element structural analysis program dedicated to sails and rig simulations coupled with an unsteady Reynolds averaged Navier-Stokes equations (URANSE) solver.
TL;DR: In this paper, the fluid dynamics induced by a rigid lamina undergoing harmonic oscillations in a non-Newtonian calm fluid is investigated and the effect of the non-newtonian feature is highlighted by investigating the fluid forces acting on a harmonically oscillating lamina for different values of the Reynolds number.
01 Jan 2014
TL;DR: A rational treatment of the relations of balance for mechanical systems with a time-variable mass and other non-classical supplies is given in this article, where the authors consider systems with mass explicitly dependent on position.
Abstract: A rational treatment of the relations of balance for mechanical systems with a time-variable mass and other non-classical supplies. - Systems with mass explicitly dependent on position. - Dynamics of the mass variable body. - Mechanics of multi-component media with exchange of mass and non-classical supplies. - Modeling of fluid-structure interaction: effects of added mass, damping and stiffness. - Dynamics and stability of engineering systems with moving continua.
TL;DR: In this paper, a two-way coupled Euler-Euler model is presented to simulate the dilute suspension of fine particles, which is a three-dimensional numerical model that is capable of replicating detailed features of particle-laden turbulent flow.
TL;DR: In this article, the authors used a fluid film flow model to predict the forced response of tilting pad journal bearings (TPJBs) under a load-between-pad (LBP) configuration.
Abstract: The accurate prediction of the forced performance of tilting pad journal bearings (TPJB) relies on coupling a fluid film model that includes thermal energy transport, and on occasion fluid inertia, to the structural stiffness of the pads’ pivots and the thermomechanical deformation of the pads’ surfaces. Often enough, the flexibility of both pads and pivots is ignored prior to the bearing actual operation; practice dictating that force coefficients, damping in particular, decrease dramatically due to pivot flexibility. Even in carefully conducted experiments, components’ flexibilities are invoked to explain dramatic differences between measurements and predictions. A multiple-year test program at TAMU has demonstrated the dynamic forced response of TPJBs can be modeled accurately with matrices of constant stiffness K, damping C, and added mass M coefficients. The K-C-M model, representing frequency independent force coefficients, is satisfactory for excitation frequencies less or equal to the shaft synchronous speed. However, as shown by the authors in Ref. [1], pivot flexibility reduces the applicability of the simple constant parameter model to much lower excitation frequencies. Presently, a fluid film flow model predicts the journal eccentricity and force coefficients of a five-pad rocker-back TPJB tested at TAMU under a load-between-pad (LBP) configuration. The predictions agree well with the test results provided the model uses actual hot bearing clearances and an empirical characterization of the pivot stiffness. A study follows to determine the effects of pad preload, Display Formular¯p = 0.0, 0.27 (test article) and 0.50, as well as the load orientation, LBP and load-on-pad (LOP), on bearing performance with an emphasis on ascertaining the configuration with most damping and stiffness, largest film thickness, and the least drag friction. In the study, a rigid pivot and two flexible pivots are considered throughout. Further examples present the effective contribution of the pads’ mass and mass moment of inertia and film fluid inertia on the bearing force coefficients. To advance results of general character, predictions are shown versus Sommerfeld number (S), a design parameter proportional to shaft speed and decreasing with applied load. Both LBP and LOP configurations show similar performance characteristics; the journal eccentricity increasing with pivot flexibility. For LBP and LOP bearings with 0.27 preload, pivot flexibility decreases dramatically the bearing damping coefficients, in particular at the low end of S, i.e., large loads. The model and predictions aid to better design TPJBs supporting large specific loads.© 2014 ASME
TL;DR: In this article, an experimental study is combined with numerical modelling to investigate new ways to reduce cross-flow vibrations of hydraulic gates with underflow, which is known to play a key role in most excitation mechanisms.
TL;DR: In this paper, both modal and non-modal linear stability analysis of a channel flow with spherical and solid particles is presented, where the particles are assumed to have a density ratio of order one and a modified Reynolds number is defined to account for the volume and mass of the particles.
Abstract: Both modal and non-modal linear stability analysis of a channel flow laden with particles is presented. The particles are assumed spherical and solid and their presence modelled using two-way coupling, with Stokes drag, added mass and fluid acceleration as coupling terms. When the particles considered have a density ratio of order one, all three terms become important. To account for the volume and mass of the particles, a modified Reynolds number is defined. Particles lighter than the fluid decrease the critical Reynolds number for modal stability, whereas heavier particles may increase the critical Reynolds number. Most effect is found when the Stokes number defined with the instability time scale is of order one. Non-modal analysis shows that the generation of streamwise streaks is the most dominant disturbance-growth mechanism also in flows laden with particles: the transient growth of the total system is enhanced proportionally to the particle mass fraction, as observed previously in flows laden with heavy particles. When studying the fluid disturbance energy alone, the optimal growth hardly changes. We also show that the Basset history force has a negligible effect on stability. The inclusion of the extra interaction terms does not show any large modifications of the subcritical instabilities in wall-bounded shear flows.
TL;DR: In this paper, a thin rigid lamina oscillating in an otherwise quiescent viscous fluid is used to extract the flow kinematics, which is, in turn, utilized to reconstruct the pressure distribution around the lamina through the integration of Navier-Stokes equations.
Abstract: In this paper, we study the flow physics produced by a thin rigid lamina oscillating in an otherwise quiescent viscous fluid. Particle image velocimetry (PIV) is used to extract the flow kinematics, which is, in turn, utilized to reconstruct the pressure distribution around the lamina through the integration of Navier-Stokes equations. The hydrodynamic loading experienced by the lamina is ultimately estimated from PIV data to investigate added mass and fluid damping phenomena. Experiments are conducted for varying Reynolds and Keulegan-Carpenter numbers to elucidate the relative weight of inertial, convective, and viscous phenomena on the resulting flow physics. In agreement with prior numerical studies, experimental results demonstrate that increasing the Reynolds and the Keulegan-Carpenter numbers results into the formation of coherent structures that are shed at the edges of the lamina and advected by the flow. This phenomenon is associated with nonlinearities in the hydrodynamic loading, whereby fluid...
TL;DR: Considering the effect of bubble-emulsion structures in bubbling fluidized beds, a bubble-structure-dependent drag coefficient model is developed in this paper, where acceleration in the bubble and emulsion phases are incorporated into the solution of the drag coefficient.
Abstract: Considering the effect of bubble-emulsion structures in bubbling fluidized beds, a bubble-structure-dependent drag coefficient model is developed. Accelerations in the bubble and emulsion phases are incorporated into the solution of the drag coefficient. Meanwhile, the influence of solid pressure and bubble-induced added mass force is also taken into account. In combination with the two-fluid model, flow behaviors in two-dimensional and three-dimensional bubbling fluidized beds are simulated. The predictions by the present model with consideration of bubble effects are in more reasonable agreement with the experimental results compared to the Gidaspow drag model. It is shown that the present model obtains a zonal distribution of the drag coefficient with solid concentration, which reveals that the drag coefficient not only depends on the local solid concentration but also is greatly influenced by the local velocities.
01 Dec 2014
TL;DR: This paper presents a control-oriented model of a neutrally buoyant underwater snake robot that is exposed to a constant irrotational current and describes the qualitative behaviour of the robot by a simplified kinematic approach, thus neglecting some of the non-linear effects that do not significantly contribute to the overall behaviour.
Abstract: In this paper we consider swimming underwater snake robots that are fully immersed in water and moving in a virtual horizontal plane. The main objective of the paper is to develop a model that is well suited for control design and stability analysis for swimming snake robots. The proposed model is notably less complex than the existing models, while significant parameters such as added mass effects, linear drag forces, torques due to the added mass and linear drag forces, are all taken into account in the modeling. An extensive analysis of a previously proposed complex model of underwater snake robots ([1]) is presented, and from this analysis a set of essential properties that characterize the overall motion of underwater snake robots is derived. The proposed control-oriented modeling approach captures these essential properties, resulting in a less complex model that is well suited for control design, and at the same time has the same essential properties as the complex model. A qualitative validation of this is given by simulations that present a comparison of representative parameters of the complex and the control-oriented models for lateral undulation and eel-like motion.