An Experimental and Numerical Study of Added Mass and Damping for Side-by-Side Plates in Oscillating Flow

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Frøydis Solaas ◽  
Fredrik Mentzoni ◽  
Mia Abrahamsen-Prsic ◽  
Trygve Kristiansen
Keyword(s):  
Numerical Study ◽  
Vertical Direction ◽  
Added Mass ◽  
Mass Force ◽  
Force Estimation ◽  
Damping Force ◽  
Side Plate ◽  
Flow Solver ◽  
Damping Coefficients ◽  
Horizontal Side

Abstract Forced harmonic oscillations of nine configurations consisting of horizontal side-by-side plate elements are performed experimentally and numerically. The configurations are oscillated in vertical direction and represent generalized mudmats of subsea structures. The tests are performed for Keulegan–Carpenter (KC) numbers relevant for force estimation during lifting operations. Hydrodynamic added mass and damping coefficients are presented. The coefficients are found to be amplitude dependent for all tested configurations. The interaction effects between the plates increase with increasing amplitude and decreasing distance between the plates. For small oscillation amplitudes, compared with the gap between the plates, the plates behave approximately like individual plates. A study of the relation between the damping force and the added mass force for the tested structures illustrates the importance of applying representative damping coefficients in numerical analysis of marine operations. Numerical results are obtained using a potential flow solver (BEM) and a viscous flow solver (CFD). Low-KC added mass coefficients predicted with the BEM are in accordance with the experiments. There is acceptable agreement between the CFD and the experiments. Best agreement is obtained for small KC numbers. As the KC numbers increase, the differences are, in general, larger. This is possibly due to the CFD being based on the two-dimensional laminar flow.

An Experimental and Numerical Study of Added Mass and Damping for Side by Side Plates in Oscillating Flow

2019 ◽  
Author(s):  
Frøydis Solaas ◽  
Fredrik Mentzoni ◽  
Mia Abrahamsen-Prsic ◽  
Trygve Kristiansen
Keyword(s):  
Numerical Study ◽  
Vertical Direction ◽  
Added Mass ◽  
Mass Force ◽  
Force Estimation ◽  
Damping Force ◽  
Side Plate ◽  
Flow Solver ◽  
Damping Coefficients ◽  
Horizontal Side

Abstract Forced harmonic oscillations of seven configurations consisting of horizontal side by side plate elements are performed experimentally and numerically. The configurations are oscillated in vertical direction and represent generalized mudmats of subsea structures. The tests are performed for Keulegan-Carpenter (KC) numbers relevant for force estimation during lifting operations. Hydrodynamic added mass and damping coefficients are presented. The coefficients are found to be amplitude dependent for all configurations tested. The interaction effects between the plates increase with increasing amplitude and decreasing distance between the plates. For oscillation amplitudes small compared with the gap between the plates, the plates behave approximately like individual plates. A study of the relation between the damping force and the added mass force for the tested structures illustrates the importance of applying representative damping coefficients in numerical analysis of marine operations. Numerical results are obtained using a potential flow solver (BEM) and a viscous flow solver (CFD). Low-KC added mass coefficients predicted with the BEM are in accordance with the experiments. There is acceptable agreement between the CFD and the experiments. Best agreement is obtained for small KC numbers. For increasing KC numbers, the differences are, in general, larger. This is possibly due to the CFD being based on two-dimensional laminar flow.

scholarly journals Hydrodynamic Coefficients of Simplified Subsea Structures

2018 ◽  
Author(s):  
Fredrik Mentzoni ◽  
Mia Abrahamsen-Prsic ◽  
Trygve Kristiansen
Keyword(s):  
Cross Section ◽  
Significant Interaction ◽  
Hydrodynamic Interaction ◽  
Forced Oscillation ◽  
Large Range ◽  
Circular Cross Section ◽  
Added Mass ◽  
Hydrodynamic Coefficients ◽  
Force Estimation ◽  
Damping Coefficients

Simplified two-dimensional models, representing components of complex subsea structures, are experimentally investigated. Individual as well as combinations of components in different configurations are tested, in order to study the effect of hydrodynamic interaction. The components include porous plates and cylindrical pipes with circular cross-section. Hydrodynamic added mass and damping coefficients, relevant for force estimation during lifting operations, are presented. The coefficients are obtained based on forced oscillation tests for a large range of Keulegan–Carpenter (KC) numbers and forcing periods, and compared to numerical source panel results for the low KC limit, as well as recommendations given by DNV GL, where relevant. Coefficients for all configurations are found to be highly amplitude dependent. Significant interaction effects are found for the assembled structures, causing either reduced or increased total added mass and damping coefficients compared to the super-position of the coefficients for individual members.

scholarly journals Time-Periodic Wave Loading on a Submerged Circular Cylinder in a Current

1986 ◽  
Vol 30 (03) ◽  
pp. 153-158
Author(s):  
John Grue
Keyword(s):  
Circular Cylinder ◽  
Fluid Layer ◽  
Periodic Wave ◽  
Added Mass ◽  
The Body ◽  
Source Distribution ◽  
Mass Force ◽  
Damping Force ◽  
Time Periodic ◽  
A Current

The time-periodic pressure loading, added mass, damping, and exciting forces on a horizontal submerged circular cylinder in a current are examined. The fluid layer is infinitely deep and the motion is two-dimensional. The boundary-value problem is solved by applying a source distribution along the contour of the body. The forces become finite for τ = Uσlg approaching 1/4 (where U is the speed of the current, σ the frequency, and g the acceleration due to gravity). The added-mass force becomes negative for τ close to 1//4. The damping force is very small for τ > 1/4. The exciting loading on the cylinder is larger for incoming waves traveling against the current than for incoming waves traveling with the current.

Numerical Study of HVAB Rotor Using a Mixed Mesh Flow Solver

2021 ◽  
Author(s):  
Sang Hyun Park ◽  
Jaeseong Han ◽  
Oh Joon Kwon
Keyword(s):  
Numerical Study ◽  
Flow Solver

scholarly journals Hydrodynamic Forces Exerting on an Oscillating Cylinder under Translational Motion in Water Covered by Compressed Ice

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 822
Author(s):  
Yury Stepanyants ◽  
Izolda Sturova
Keyword(s):  
Lift Force ◽  
Wave Motion ◽  
Translational Motion ◽  
Added Mass ◽  
Hydrodynamic Forces ◽  
Wave Resistance ◽  
Translational Velocity ◽  
Damping Coefficients ◽  
Incompressible Ideal Fluid ◽  
Theoretical Results

This paper presents the calculation of the hydrodynamic forces exerted on an oscillating circular cylinder when it moves perpendicular to its axis in infinitely deep water covered by compressed ice. The cylinder can oscillate both horizontally and vertically in the course of its translational motion. In the linear approximation, a solution is found for the steady wave motion generated by the cylinder within the hydrodynamic set of equations for the incompressible ideal fluid. It is shown that, depending on the rate of ice compression, both normal and anomalous dispersion can occur in the system. In the latter case, the group velocity can be opposite to the phase velocity in a certain range of wavenumbers. The dependences of the hydrodynamic loads exerted on the cylinder (the added mass, damping coefficients, wave resistance and lift force) on the translational velocity and frequency of oscillation were studied. It was shown that there is a possibility of the appearance of negative values for the damping coefficients at the relatively big cylinder velocity; then, the wave resistance decreases with the increase in cylinder velocity. The theoretical results were underpinned by the numerical calculations for the real parameters of ice and cylinder motion.

A Double Birkhoff Wake Oscillator for the Modeling of Vortex-Induced Vibration

2011 ◽  
Author(s):  
R. H. M. Ogink
Keyword(s):  
Free Vibration ◽  
Added Mass ◽  
Mass Force ◽  
Near Wake ◽  
Vibration Measurements ◽  
Vortex Induced Vibration ◽  
Fluid Forces ◽  
Wake Oscillator ◽  
Model Equations ◽  
Far Wake

A double Birkhoff wake oscillator for the modeling of vortex-induced vibration is presented in which the oscillating variables are assumed to be associated with the boundary layer/near wake and the far wake. The fluid forces are assumed to consist of a potential added mass force and a force due to vortex shedding. In the limit of vanishing incoming flow velocity, the model equations reduce to a form similar to the Morison equation. The results of the double wake oscillator have been compared with forced vibration measurements and free vibration measurements over a range of mass and damping ratios. The model is capable of describing the most important trends in both the forced and free vibration experiments. Specifically, the double wake oscillator is able to model both the upper and lower branch of free vibration.

Measured Static and Rotordynamic Coefficient Results for a Rocker-Pivot, Tilting-Pad Bearing With 50 and 60% Offsets

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Chris D. Kulhanek ◽  
Dara W. Childs
Keyword(s):  
Dynamic Stiffness ◽  
Mass Matrix ◽  
Excitation Frequency ◽  
Quadratic Function ◽  
Added Mass ◽  
Damping Coefficients ◽  
Stiffness Coefficients ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Direct Stiffness

Static and rotordynamic coefficients are measured for a rocker-pivot, tilting-pad journal bearing (TPJB) with 50 and 60% offset pads in a load-between-pad (LBP) configuration. The bearing uses leading-edge-groove direct lubrication and has the following characteristics: 5-pads, 101.6 mm (4.0 in) nominal diameter,0.0814 -0.0837 mm (0.0032–0.0033 in) radial bearing clearance, 0.25 to 0.27 preload, and 60.325 mm (2.375 in) axial pad length. Tests were performed on a floating bearing test rig with unit loads from 0 to 3101 kPa (450 psi) and speeds from 7 to 16 krpm. Dynamic tests were conducted over a range of frequencies (20 to 320 Hz) to obtain complex dynamic stiffness coefficients as functions of excitation frequency. For most test conditions, the real dynamic stiffness functions were well fitted with a quadratic function with respect to frequency. This curve fit allowed for the stiffness frequency dependency to be captured by including an added mass matrix [M] to a conventional [K][C] model, yielding a frequency independent [K][C][M] model. The imaginary dynamic stiffness coefficients increased linearly with frequency, producing frequency-independent direct damping coefficients. Direct stiffness coefficients were larger for the 60% offset bearing at light unit loads. At high loads, the 50% offset configuration had a larger stiffness in the loaded direction, while the unloaded direct stiffness was approximately the same for both pivot offsets. Cross-coupled stiffness coefficients were positive and significantly smaller than direct stiffness coefficients. Negative direct added-mass coefficients were obtained for both offsets, especially in the unloaded direction. Cross-coupled added-mass coefficients are generally positive and of the same sign. Direct damping coefficients were mostly independent of load and speed, showing no appreciable difference between pivot offsets. Cross-coupled damping coefficients had the same sign and were much smaller than direct coefficients. Measured static eccentricities suggested cross coupling stiffness exists for both pivot offsets, agreeing with dynamic measurements. Static stiffness measurements showed good agreement with the loaded, direct dynamic stiffness coefficients.

An Investigation to Added Mass Force on the Wing of Insect Inspired from a Rigid Sphere Model

2012 ◽  
Vol 476-478 ◽  
pp. 2485-2488
Author(s):  
Mei Jun Hu ◽  
Xing Yao Yan ◽  
Jin Yao Yan
Keyword(s):  
Insect Flight ◽  
Aerodynamic Force ◽  
Mass Effect ◽  
Added Mass ◽  
Rigid Sphere ◽  
Force Model ◽  
Mass Force ◽  
Real Time Control ◽  
Wing Model ◽  
Force Peak

There is a force peak at the beginning of each stroke during the insect flight, this force peak contributes a lot to the total aerodynamic force. To build a man made insect inspired man-made micro aero vehicle, this force need to be considered in the aero force model, and this model should as simple as possible in order to be used in feedback real-time control. Here we presented a simplified model to take the medium added mass effect of the wing into account. Simulated results show a high force peak at the beginning of each stroke and are quite similar to the measured forces on the physical wing model which were carried out by Dickinson et.al.

On the unsteady inviscid force on cylinders and spheres in subcritical compressible flow

2008 ◽  
Vol 366 (1873) ◽  
pp. 2161-2175 ◽  
Author(s):  
M Parmar ◽  
A Haselbacher ◽  
S Balachandar
Keyword(s):  
Mach Number ◽  
Compressible Flow ◽  
Propagation Speed ◽  
Added Mass ◽  
The Body ◽  
Mass Force ◽  
Unsteady Force ◽  
Mass Coefficient ◽  
Added Mass Coefficient ◽  
Cylinders And Spheres

The unsteady inviscid force on cylinders and spheres in subcritical compressible flow is investigated. In the limit of incompressible flow, the unsteady inviscid force on a cylinder or sphere is the so-called added-mass force that is proportional to the product of the mass displaced by the body and the instantaneous acceleration. In compressible flow, the finite acoustic propagation speed means that the unsteady inviscid force arising from an instantaneously applied constant acceleration develops gradually and reaches steady values only for non-dimensional times c ∞ t / R ≳10, where c ∞ is the freestream speed of sound and R is the radius of the cylinder or sphere. In this limit, an effective added-mass coefficient may be defined. The main conclusion of our study is that the freestream Mach number has a pronounced effect on both the peak value of the unsteady force and the effective added-mass coefficient. At a freestream Mach number of 0.5, the effective added-mass coefficient is about twice as large as the incompressible value for the sphere. Coupled with an impulsive acceleration, the unsteady inviscid force in compressible flow can be more than four times larger than that predicted from incompressible theory. Furthermore, the effect of the ratio of specific heats on the unsteady force becomes more pronounced as the Mach number increases.

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