Showing papers on "Added mass published in 2021"

Illuminating the complex role of the added mass during vortex induced vibration

Abstract: The role of the added mass coefficient in vortex induced vibration (VIV) of the bluff body is complex and elusive. It is certain that decoding the relationship between the added mass and the vibration pattern will benefit the prediction and prevention of VIV. We present a study on VIV of a long flexible cylinder and forced vibration of a rigid cylinder, in a combination of experimental optical measurements and high-fidelity numerical simulation. We focus on uniform flow over a uniform cylinder at a fixed Reynolds number, Red = 900, but systematically varied the motion amplitude in the in-line ( Axd) and cross-flow direction ( Ayd), as well as the phase angle (θ) between the motions. We show that θ∈[π2,3π2] is associated with negative added mass coefficients in the cross-flow direction (Cmy < 0), and there is a strong correlation between the vortex shedding mode of “2P” or “P+S” and Cmy < 0.

Influence of the Drag Force on the Average Absorbed Power of Heaving Wave Energy Converters Using Smoothed Particle Hydrodynamics

Abstract: In this paper, we investigated how the added mass, the hydrodynamic damping and the drag coefficient of a Wave Energy Converter (WEC) can be calculated using DualSPHysics DualSPHysics is a software application that applies the Smoothed Particle Hydrodynamics (SPH) method, a Lagrangian meshless method used in a growing range of applications within the field of Computational Fluid Dynamics (CFD) Furthermore, the effect of the drag force on the WEC’s motion and average absorbed power is analyzed Particularly under controlled conditions and in the resonance region, the drag force becomes significant and can greatly reduce the average absorbed power of a heaving point absorber Once the drag coefficient has been determined, it is used in a modified equation of motion in the frequency domain, taking into account the effect of the drag force Three different methods were compared for the calculation of the average absorbed power: linear potential flow theory, linear potential flow theory modified to take the drag force into account and DualSPHysics This comparison showed the considerable effect of the drag force in the resonance region Calculations of the drag coefficient were carried out for three point absorber WECs: one spherical WEC and two cylindrical WECs Simulations in regular waves were performed for one cylindrical WEC with two different power take-off (PTO) systems: a linear damping and a Coulomb damping PTO system The Coulomb damping PTO system was added in the numerical coupling between DualSPHysics and Project Chrono Furthermore, we considered the optimal PTO system damping coefficient taking the effect of the drag force into account

A hybrid model for simulation of fluid–structure interaction in water entry problems

Abstract: A hydroelastic hybrid model is developed to simulate the fluid–structure interaction in water entry problems using the partitioned approach. The interactions between a flat plate and the water are modeled by a hydroelastic model using explicit and implicit couplings. Both couplings are unstable due to numerical instability associated with the fluid added mass. To overcome the instability, an extended Wagner’s model is combined with the hydroelastic model, and a hybrid model is developed. The extended Wagner’s model is the extension of the classical Wagner’s model that is used to estimate the fluid inertial, damping, and restoring forces of a flexible plate within the potential flow theory. The fluid flow is described by the unsteady Reynolds averaged Navier–Stokes equations in the hydroelastic model and hybrid model. The longitudinal bending of the plate is approximated by the strips in all models. The hybrid model is verified and validated by comparing the available computational and semi-analytical results of the vertical and oblique water entries for the plate with different boundary conditions. The results show that the hybrid model is stable, accurate, and simple to implement. This two-dimensional model can be generalized to the third dimension and applied for more complex structures.

Nonlinear dynamics of inertial particles in the ocean: from drifters and floats to marine debris and Sargassum

Abstract: Buoyant, finite-size, or inertial particle motion is fundamentally unlike neutrally buoyant, infinitesimally small, or Lagrangian particle motion. The de-jure fluid mechanics framework for the description of inertial particle dynamics is provided by the Maxey–Riley equation. Derived from first principles—a result of over a century of research since the pioneering work by Sir George Stokes—the Maxey–Riley equation is a Newton-type law with several forces including (mainly) flow, added mass, shear-induced lift, and drag forces. In this paper, we present an overview of recent efforts to transfer the Maxey–Riley framework to oceanography. These involved: (1) including the Coriolis force, which was found to explain behavior of submerged floats near mesoscale eddies; (2) accounting for the combined effects of ocean current and wind drag on inertial particles floating at the air–sea interface, which helped understand the formation of great garbage patches and the role of anticyclonic eddies as plastic debris traps; and (3) incorporating elastic forces, which are needed to simulate the drift of pelagic Sargassum. Insight into the nonlinear dynamics of inertial particles in every case was possible to be achieved by investigating long-time asymptotic behavior in the various Maxey–Riley equation forms, which represent singular perturbation problems involving slow and fast variables.

Size-dependent vibration and dynamic stability of AFG microbeams immersed in fluid

Abstract: This paper analyzes the size-dependent vibration and dynamic stability for axially functionally graded (AFG) microbeams immersed in fluid. We consider rectangular and circular cross-section shapes of AFG microbeams. The modified couple stress theory (MCST) is employed to characterize the size dependency of microbeams. The Mori-Tanaka method provides the formulations of material properties with axially continuous gradual variation. The fluid effect on the microbeam is simulated as the added mass. According to the variational principle, we can obtain the governing equations and the boundary conditions of the free vibration and dynamic stability problems. The natural frequency and critical excitation frequency are solved by the differential quadrature (DQ) method and iterative method. Numerical examples present the response of the natural frequency, critical buckling load and critical excitation frequency on the fluid depth, size parameter, fluid density and cross-section shape.

Nanoflows induced by MEMS and NEMS: Limits of two-dimensional models

Abstract: The mechanical oscillations of a miniaturized resonator generate viscous oscillatory nanoflows in the surrounding fluid As a result, the fluid presents an effective added mass and damping to the resonator, which is commonly predicted by a two-dimensional flow model Here, the limitations to the two-dimensional model are examined when a substrate and axial flow are present Results from experiments and three-dimensional finite element models are presented to illustrate where and why the two-dimensional flow models break down

Nonlinear analysis and effectiveness of weakly coupled microbeams for mass sensing applications

Abstract: In this work, we develop a general model of a mass sensor made of N weakly mechanically coupled microbeams subject to electric actuation. The developed model is verified by comparing the simulated pull-in voltages, natural frequencies, and frequency response of a two-weakly coupled beam system against their experimental counterparts reported in the literature. The sensitivity of the mass sensor in terms of frequency shift is observed to significantly increase when enlarging the size of the beams array. The simulation results reveal a clear transformation of the frequency response from a nearly linear to nonlinear behavior as result of the deposition of a small mass on the coupled system. As such, we show the potential use of bifurcations that result in an abrupt jump to a large-amplitude motion for sensing purposes. Furthermore, by exploiting the mode localization effect, the nonlinear response can be triggered on one of the beams when an added masses is introduced, allowing for an amplitude-based mass detection mechanism of the device. The proposed sensing method has the possibility to operate in bifurcation mode for mass threshold detection that can be tuned using the AC actuation or in continuous mode based on extracting the added mass from the amplitude of the sensing beam’s oscillations.

Added-mass force on elliptic airfoils

Abstract: Herein, exact algebraic expressions for the non-circulatory (added-mass) forces on elliptic airfoils are derived for any two-dimensional motion – including simultaneous rectilinear acceleration and rotation – embedded in a steady free-stream flow. Despite the lengthy history of the added-mass concept and its widespread application to cylinders of various cross-sections, such closed-form expressions for elliptic cylinders, in terms of kinematic and geometric parameters alone, have remained absent from the literature until now. Inspection of the derived equations reveals that for pure pitching about a point on the chord-line, increasing thickness always decreases the added-mass force magnitude. For any given motion of the chord-line, the difference in force between thick and thin airfoils is proportional to the square of the thickness, although this difference may be positive or negative for the general three-degree-of-freedom case. In the special case of zero thickness and small pitch angles, Theodorsen's added-mass lift force on rigid thin airfoils is recovered; for large pitch angles, an exact generalization of Theodorsen's expression, applicable to the chord-normal direction, is given.

On the role of added mass and vorticity release for self-propelled aquatic locomotion

Abstract: Aquatic locomotion of a deformable body from rest up to its asymptotic speed is given by the unsteady motion which is produced by a series of periodic reactions dictated by the body configuration and by the style of swimming. The added mass plays a crucial role, not only for the initial burst, but also along each manoeuvre, to accelerate the surrounding fluid for generating the kinetic energy and to enable vortex shedding in the wake. The estimate of these physical aspects has been largely considered in most theoretical models, but not sufficiently deepened in many experimental and numerical investigations. As a motivation, while the vortical structures are easily detectable from the flow field, the added mass, on the contrary, is usually embedded in the overall forcing terms. By the present impulse formulation, we are able to separate and to emphasize the role of the added mass and vorticity release to evaluate in a neat way their specific contributions. The precise identification of the added mass is also instrumental for a well-posed numerical problem and for easily readable results. As a further point, the asymptotic speed is found to be guided either by the phase velocity of the prescribed undulation and by the unavoidable recoil motion induced by the self-propelled swimming. The numerical results reported in the present paper concern simplified cases of non-diffusing vorticity and two-dimensional flow.

The One-Way FSI Method Based on RANS-FEM for the Open Water Test of a Marine Propeller at the Different Loading Conditions

Abstract: This paper aims to assess a new fluid–structure interaction (FSI) coupling approach for the vp1304 propeller to predict pressure and stress distributions with a low-cost and high-precision approach with the ability of repeatability for the number of different structural sets involved, other materials, or layup methods. An outline of the present coupling approach is based on an open-access software (OpenFOAM) as a fluid solver, and Abaqus used to evaluate and predict the blade’s deformation and strength in dry condition mode, which means the added mass effects due to propeller blades vibration is neglected. Wherein the imposed pressures on the blade surfaces are extracted for all time-steps. Then, these pressures are transferred to the structural solver as a load condition. Although this coupling approach was verified formerly (wedge impact), for the case in-hand, a further verification case, open water test, was performed to evaluate the hydrodynamic part of the solution with an e = 7.5% average error. A key factor for the current coupling approach is the rotational rate interrelated between two solution domains, which should be carefully applied in each time-step. Finally, the propeller strength assessment was performed by considering the blades’ stress and strain for different load conditions.

Flow-excited membrane instability at moderate Reynolds numbers

Abstract: In this paper, we study the fluid–structure interaction of a three-dimensional (3-D) flexible membrane immersed in an unsteady separated flow at moderate Reynolds numbers. We employ a body-conforming variational fluid–structure interaction solver based on the recently developed partitioned iterative scheme for the coupling of turbulent fluid flow with nonlinear structural dynamics. Of particular interest is to understand the flow-excited instability of a 3-D flexible membrane as a function of the non-dimensional mass ratio ( and larger flexibility. Based on the global aeroelastic mode analysis, we observe a frequency lock-in phenomenon between the vortex-shedding frequency and the membrane vibration frequency causing self-sustained vibrations in the dynamic balance state. To characterize the origin of the frequency lock-in, we propose an approximate analytical formula for the nonlinear natural frequency by considering the added mass effect and employing a large deflection theory for a simply supported rectangular membrane. Through our systematic high-fidelity numerical investigation, we find that the onset of the membrane vibration and the mode transition has a direct dependence on the frequency lock-in between the natural frequency of the tensioned membrane and the vortex-shedding frequency or its harmonics. These findings on the fluid-elastic instability of membranes have implications for the design and development of control strategies for membrane wing-based unmanned systems and drones.

Scaling laws for the propulsive performance of a purely pitching foil in ground effect

Abstract: Scaling laws for the thrust production and power consumption of a purely pitching hydrofoil in ground effect are presented. For the first time, ground-effect scaling laws based on physical insights capture the propulsive performance over a wide range of biologically relevant Strouhal numbers, dimensionless amplitudes and dimensionless ground distances. This is achieved by advancing previous scaling laws (Moored & Quinn (AIAA J., 2018, pp. 1–15)) with physics-driven modifications to the added mass and circulatory forces to account for ground distance variations. The key physics introduced are the increase in the added mass of a foil near the ground and the reduction in the influence of a wake-vortex system due to the influence of its image system. The scaling laws are found to be in good agreement with new inviscid simulations and viscous experiments, and can be used to accelerate the design of bio-inspired hydrofoils that oscillate near a ground plane or two out-of-phase foils in a side-by-side arrangement.