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.

scholarly journals ON THE HYDRODYNAMIC FORCES OF TWIN-HULL VESSELS

1970 ◽  
Vol 1 (12) ◽  
pp. 103
Author(s):  
Shen Wang
Keyword(s):  
Oscillation Frequency ◽  
Three Dimensional ◽  
Vertical Motion ◽  
Added Mass ◽  
Hydrodynamic Forces ◽  
Theory Approach ◽  
Damping Coefficients ◽  
Damping Characteristics ◽  
Spacing Ratio ◽  
Strip Theory

The added mass and damping coefficients for semi- and fully submerged twin cylinders in vertical motion are determined as functions of the oscillation frequency, the cylinder spacing ratio, and the cylinder submergence ratio It has been found that resonance may occur in particular combinations of cylinder spacing and oscillation frequency at which the hydrodynamic mertial and damping characteristics deviate from the trend curves for the case of a single cylinder Justification of using the two-dimensional results to calculate motions of three dimensional twin-hull vessels is discussed It is suggested that, by means of strip theory approach, these results can be used to estimate the hydrodynamic forces for catamaran type vessels in pitch and heave motions.

An Experimental Study on the Effect of Submergence on a Vertically Oscillating Hydrofoil at Zero Translational Velocity

2012 ◽  
Vol 226-228 ◽  
pp. 459-465
Author(s):  
Rajan Fernandez ◽  
Keith Alexander
Keyword(s):  
Experimental Study ◽  
Free Surface ◽  
Flat Plate ◽  
Finite Thickness ◽  
Added Mass ◽  
Hydrodynamic Forces ◽  
Experimental Results ◽  
Translational Velocity ◽  
Oscillating Foil ◽  
Spanwise Flow

This paper presents experimental results for the hydrodynamic forces on several different bodies oscillating in the vicinity of the free surface. Firstly, results for two horizontally symmetric bodies, a flat plate of finite thickness and a cylinder, are presented. Results show that these two different shaped bodies react in different ways with the free surface and are likely to have different added mass associated with them. Secondly, results for two thrusting bodies, a NACA0012 symmetrical foil and a NACA4415 cambered foil, show that the free surface amplifies the thrust produced by a vertically oscillating foil. Results showing the effects of spanwise flow are also presented and indicate spanwise flow is negligible at zero translational velocity and so the use of endplates of the foils was unnecessary. The conclusion of these experiments is that a submergence of 5 chord lengths is sufficient for the horizontal and vertical forces on the vertically oscillating objects to be unaffected by the free surface.

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.

On the Radiation and Diffraction of Surface Waves by Submerged Spheroids

1989 ◽  
Vol 33 (02) ◽  
pp. 84-92
Author(s):  
G. X. Wu ◽  
R. Eatock Taylor
Keyword(s):  
Degrees Of Freedom ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Added Mass ◽  
Wave Radiation ◽  
Legendre Functions ◽  
Incoming Wave ◽  
Six Degrees Of Freedom ◽  
Damping Coefficients ◽  
Exciting Forces

The problem of wave radiation and diffraction by submerged spheroids is analyzed using linearized three-dimensional potential-flow theory. The solution is obtained by expanding the velocity potential into a series of Legendre functions in a spheroidal coordinate system. Tabulated and graphical results are provided for added mass and damping coefficients of various spheroids undergoing motions in six degrees of freedom. Graphs are also provided for exciting forces and moments corresponding to a range of incoming wave angles.

Ship Motions in Shallow Water

1970 ◽  
Vol 14 (04) ◽  
pp. 317-328 ◽  
Author(s):  
E. O. Tuck
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Incident Wave ◽  
Degrees Of Freedom ◽  
Added Mass ◽  
Exciting Force ◽  
Ship Motions ◽  
Wave System ◽  
Six Degrees Of Freedom ◽  
Damping Coefficients

The problem discussed concerns small motions of a ship, in all six degrees of freedom, but at zero speed of advance, due to an incident wave system in shallow water of depth comparable with the ship's draft. The problem is completely formulated for an arbitrary ship, and is partially solved for the case when the ship is slender and the wavelength much greater than the water depth. Sample numerical computations of heave, pitch, and sway added mass and damping coefficients and the sway exciting force are presented.

An Analysis of Heave Added Mass and Damping of a Surface-Effect Ship

1981 ◽  
Vol 25 (01) ◽  
pp. 44-61
Author(s):  
C. H. Kim ◽  
S. Tsakonas
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Surface Effect ◽  
Practical Method ◽  
Added Mass ◽  
Damping Coefficients ◽  
Calm Water ◽  
Surface Effect Ship ◽  
Long Time ◽  
Computational Procedures

The analysis presents a practical method for evaluating the added-mass and damping coefficients of a heaving surface-effect ship in uniform translation. The theoretical added-mass and damping coefficients and the heave response show fair agreement with the corresponding experimental values. Comparisons of the coupled aero-hydrodynamic and uncoupled analytical results with the experimental data prove that the uncoupled theory, dominant for a long time, that neglects the free-surface effects is an oversimplified procedure. The analysis also provides means of estimating the wave elevation of the free surface, the escape area at the stern and the volume which are induced by a heaving surface-effect ship in uniform translation in otherwise calm water. Computational procedures have been programmed in the FORTRAN IV language and adapted to the PDP-10 high-speed digital computer.

Hydrodynamic Forces on a Cylinder With a Flexible Splitter Plate Near the Free Surface

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
S. Satheesh ◽  
H. R. Díaz-Ojeda ◽  
L. M. González ◽  
F. J. Huera-Huarte
Keyword(s):  
Free Surface ◽  
Drag Reduction ◽  
Lift Force ◽  
Cross Flow ◽  
Hydrodynamic Forces ◽  
Splitter Plate ◽  
Rigid Cylinder ◽  
Splitter Plates ◽  
Cylinder Diameter

Abstract Experiments were conducted on two splitter plates of different structural rigidities, attached to a rigid cylinder and exposed to cross-flow at different submergence depths in order to study the influence of free surface. It was found that the presence of flexible splitter plate results in drag reduction at all submergence depths when compared with a plain cylinder, with the reduction being dependent on the rigidity of the splitter plate. The lift force was also found to increase abruptly at low depths for the cases involving splitter plates. The results from the analyses of tip kinematics on flexible splitter plate indicated that it performs vertical oscillations symmetrically about its mounting position at high submergence depths but is displaced in one direction up to an order of cylinder diameter and undergoes minimal oscillations when located near the free surface.

scholarly journals Surge motion on a floating cylinder in water of finite depth

2003 ◽  
Vol 2003 (57) ◽  
pp. 3643-3656 ◽  
Author(s):  
Dambaru D. Bhatta
Keyword(s):  
Velocity Potential ◽  
Separation Of Variables ◽  
Finite Depth ◽  
Added Mass ◽  
Computational Results ◽  
Complex Matrix ◽  
Interior Region ◽  
Exterior Region ◽  
Damping Coefficients ◽  
Calm Water

We derived added mass and damping coefficients of a vertical floating circular cylinder due to surge motion in calm water of finite depth. This is done by deriving the velocity potential for the cylinder by considering two regions, namely, interior region and exterior region. The velocity potentials for these two regions are obtained by the method of separation of variables. The continuity of the solutions has been maintained at the imaginary interface of these regions by matching the functions and gradients of each solution. The complex matrix equation is numerically solved to determine the unknown coefficients. Some computational results are presented for different depth-to-radius and draft-to-radius ratios.

Influence of Multiphysical Effects on the Dynamics of High Speed Minirotors—Part I: Theory

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Emre Dikmen ◽  
Peter J. M. van der Hoogt ◽  
André de Boer ◽  
Ronald G. K. M. Aarts
Keyword(s):  
Temperature Increase ◽  
High Speed ◽  
Heat Dissipation ◽  
Rotation Speed ◽  
Beam Theory ◽  
Added Mass ◽  
Air Gap ◽  
Finite Element Models ◽  
Surrounding Fluid ◽  
Theoretical Results

In this study, a modeling approach has been developed to take multiphysical effects into account in the prediction of the rotordynamic behavior of high speed minirotating machinery with a moderate flow confinement. The temperature increase in the confinement and the flow induced forces resulting from the surrounding fluid have been studied and these models are combined with the structural finite element models for determining the rotordynamic behavior. The structure has been analyzed via finite elements based on Timoshenko beam theory. Flow induced forces are implemented to the structure as added mass-stiffness-damping at each node representing the structure in the fluid confinement. A thermal model based on thermal networks in steady-state has been developed. This model is used to calculate the heat dissipation resulting from air friction and temperature increase in the air gap as a function of rotation speed. At each rotation speed, the temperature in the air gap between the rotor and stationary casing is calculated and air properties, which are used for the calculation of flow induced forces are updated. In this way, thermal and fluid effects in medium gap confinements are coupled with the rotordynamic model and their effects on stability, critical speeds, and vibration response are investigated. The experimental results are reported and compared with the theoretical results in an accompanying paper (Part II).

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