Piston-Modal Resonance in a Box-Wall System

2019 ◽  
Author(s):  
Yu-xin Huang ◽  
Bao-lei Geng ◽  
Sheng-chao Jiang
Keyword(s):  
Wave Forces ◽  
Narrow Gap ◽  
Resonant Frequencies ◽  
Velocity Flow ◽  
Static Water ◽  
Horizontal Wave ◽  
The Difference ◽  
Wall System ◽  
Dynamic Wave ◽  
Modal Resonance

Abstract Hydrodynamic behavior of wave responses and wave forces induced by piston-modal resonance in the narrow gap formed by a ship section in front of a bottom mounted terminal is investigated based on the OpenFOAM® package. Numerical simulations suggested that the free surface piston-modal oscillations in the narrow gap have closely relationship with the vertical velocity along the gap bottom, implying the velocity flow around the gap bottom is able to affect the wave amplitude in the narrow gap, significantly. The horizontal wave forces can be decomposed into static water forces due to the difference of water level besides the box and the dynamic water forces due to the velocity flow. The amplitudes of static water forces are larger than that of horizontal wave forces, implying that the dynamic water forces can counteract part action of the static water forces. The dynamic wave forces approach to the maximal values at resonant frequencies, indicating that the extreme flow velocity around resonant frequency is useful for reducing the horizontal wave forces.

scholarly journals Determination of Force Coefficients for a Submerged Rigid Breakwater under the Action of Solitary Waves

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 315
Author(s):  
Francesco Aristodemo ◽  
Giuseppe Tripepi ◽  
Luana Gurnari ◽  
Pasquale Filianoti
Keyword(s):  
Solitary Waves ◽  
Pressure Sensors ◽  
Wave Forces ◽  
Wave Loads ◽  
Force Coefficients ◽  
Wave Flume ◽  
Physical Tests ◽  
The Difference ◽  
The University ◽  
Semi Empirical

We present an analysis related to the evaluation of Morison and transverse force coefficients in the case of a submerged square barrier subject to the action of solitary waves. To this purpose, two-dimensional experimental research was undertaken in the wave flume of the University of Calabria, in which a rigid square barrier was provided by a discrete battery of pressure sensors to determine the horizontal and vertical hydrodynamic forces. A total set of 18 laboratory tests was carried out by varying the motion law of a piston-type paddle. Owing to the low Keulegan–Carpenter numbers of the tests, the force regime of the physical tests was defined by the dominance of the inertia loads in the horizontal direction and of the lift loads in the vertical one. Through the use of the time series of wave forces and the undisturbed kinematics, drag, horizontal inertia, lift, and vertical inertia coefficients in the Morison and transverse semi-empirical schemes were calculated using time-domain approaches, adopting the WLS1 method for the minimization of the difference between the maximum forces and the linked phase shifts by comparing laboratory and calculated wave loads. Practical equations to calculate these coefficients as a function of the wave non-linearity were introduced. The obtained results highlighted the prevalence of the horizontal forces in comparison with the vertical ones which, however, prove to be fundamental for stability purposes of the barrier. An overall good agreement between the experimental forces and those calculated by the calibrated semi-empirical schemes was found, particularly for the positive horizontal and vertical loads. The analysis of the hydrodynamic coefficients showed a decreasing trend for the drag, horizontal inertia, and lift coefficients as a function of the wave non-linearity, while the vertical inertia coefficient underlined an initial increasing trend and a successive slight decreasing trend.

Second-order vertical and horizontal wave forces on a circular dock

1985 ◽  
Vol 12 (4) ◽  
pp. 341-361 ◽  
Author(s):  
Tarik Sabuncu ◽  
Ömer Gören
Keyword(s):  
Second Order ◽  
Wave Forces ◽  
Horizontal Wave

Low Frequency Wave Forces and Wave Induced Motions of a FPSO in Shallow Water

2007 ◽  
Author(s):  
Longfei Xiao ◽  
Jianmin Yang ◽  
Zhiqiang Hu
Keyword(s):  
Shallow Water ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Wave Force ◽  
Wave Forces ◽  
Frequency Wave ◽  
Wave Basin ◽  
The Difference ◽  
The One ◽  
Wave Induced

The low frequency (LF) response of a soft yoke moored 160kDWT FPSO in shallow water is investigated by conducting frequency domain computations and wave basin model tests. An incident wave with Hs = 4.1m and Tp = 8.9s is applied. An obvious LF part appears in the measured wave spectrum at water depth of 16.7m. As a result, the 1st order LF wave force exists and is much larger than the 2nd one. The difference of the spectrums is about one hundred times. The LF wave drift force increases enormously. Consequently, much larger resonant surge response is induced. The LF surge amplitude at h = 16.7m is about 7 times the one at h = 29.0m and 9 times the one in deep water, although the 2nd order response changes a little. Therefore, in very shallow water, LF part of incident waves should be taken into account carefully and LF wave forces and wave induced motions will be very serious.

scholarly journals Horizontal Forces Due to Waves Acting on Large Vertical Cylinders in Deep Water

1972 ◽  
Vol 94 (4) ◽  
pp. 862-866
Author(s):  
E. R. Johnson
Keyword(s):  
Deep Water ◽  
Large Diameter ◽  
Wave Force ◽  
Circular Cylinders ◽  
Wave Forces ◽  
Typical Application ◽  
Model Studies ◽  
Horizontal Wave ◽  
Horizontal Wave Force ◽  
Vertical Cylinders

The special case of horizontal wave forces on large vertical cylinders in deep water is considered. The typical application for such a case is the calculation of horizontal forces on column stabilized floating ocean platforms. Existing literature discussing horizontal wave forces on cylinders does not generally agree on how to predict these forces. Since for large diameter cylinders in deep water the maximum force is completely inertial, the problem of deriving a solution is considerably simplified. In this study, an expression for the maximum horizontal wave force on large diameter circular cylinders mounted vertically in deep water has been analytically derived. Experimental model studies were also conducted and the resulting measured forces were within 20 percent of predicted forces. An example of how to predict horizontal wave forces using the methods of this report is given.

scholarly journals HYDRODYNAMIC PERFORMANCE OF A FREE SURFACE SEMICIRCULAR PERFORATED BREAKWATER

2011 ◽  
Vol 1 (32) ◽  
pp. 20 ◽  
Author(s):  
Hee Min Teh ◽  
Vengatesan Venugopal ◽  
Tom Bruce
Keyword(s):  
Free Surface ◽  
Wave Attenuation ◽  
Hydrodynamic Performance ◽  
Wave Transformation ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Irregular Wave ◽  
Energy Dissipater ◽  
Horizontal Wave ◽  
Perforated Breakwater

The increasing importance of the sustainability challenge in coastal engineering has led to the development of free surface breakwaters of various configurations. In this study, the hydrodynamic characteristics of a perforated semicircular free surface breakwater (SCB) are investigated for irregular wave conditions. The hydrodynamic performance of the breakwater is evaluated in the form of transmission, reflection and energy dissipation coefficients, which are then presented as a function of the relative submergence depth (D/d) and the relative breakwater width (B/Lp), where D = the depth of immersion, d = the water depth, B = the breakwater width and Lp = the wavelength corresponding to the peak wave period. It is found that the wave attenuation ability of the SCB model improves with the increase of D/d and B/Lp. The SCB performs better as an energy dissipater than as a wave reflector. Based on the analysis of measured data, some empirical equations are proposed to predict the performance of the breakwater under varying submergence depths. The behaviour of wave transformation around and within the breakwater’s chamber is discussed. Also, the measured horizontal wave forces acting on the SCB are reported.

scholarly journals Effect of Waves on the Behavior of Emergent Buoyantly Rising Submarines Using CFD

2020 ◽  
Vol 10 (23) ◽  
pp. 8403
Author(s):  
Qinglong Chen ◽  
Hongwei Li ◽  
Shudi Zhang ◽  
Jian Wang ◽  
Yongjie Pang ◽  
...  
Keyword(s):  
Water Surface ◽  
Roll Angle ◽  
Head Wave ◽  
Longitudinal Motion ◽  
Wave Direction ◽  
Initial Angle ◽  
Slight Effect ◽  
Bow Wave ◽  
Static Water ◽  
The Difference

Emergent buoyantly rising submarines encounter excess roll problems, partially owing to waves that significantly affect their behavior. This study predicts the behavior of a submarine, including when it rises in static water, beam sea, head wave, following wave, 30∘ bow wave, 60∘ bow wave, 30∘ quartering wave, and 60∘ quartering wave, using the computational fluid dynamics method. The beam sea has a slight effect on pitch prior to the submarine rising to the water surface, but the maximum roll angle in the beam sea is 4.43 times that in static water. After a submarine submerges in water, the pitching oscillation does not decay quickly owing to the yaw angle. The head wave and the following wave have a continuous significant effect on the pitch; the submarine sail remains under the water surface after it submerges from the highest position. The head wave and the following wave have a slight effect on the roll and yaw before the submarine rises to the water surface; however, the roll angle suddenly increases after the submarine submerges from the highest position. As the initial angle between the submarine centerline and wave direction increases, the effect of waves on the longitudinal motion decreases. The amplitude of the pitching oscillation decreases with an increase in the initial angle between the submarine centerline and wave direction, and the waterline when the submarine oscillates on the water surface decreases. The difference in the maximum roll angle between when a submarine rises in an oblique wave and when it rises in beam sea is below 6.3∘. Submarines should try to avoid rising in a head wave and the following wave.

scholarly journals Comparison of Analysis and Experiment for Gearbox Noise

1992 ◽  
Author(s):  
Fred B. Oswald ◽  
A. F. Seybert ◽  
T. W. Wu ◽  
William Atherton
Keyword(s):  
Narrow Band ◽  
Power Level ◽  
Experimental Results ◽  
Sound Power ◽  
Spur Gears ◽  
Contact Ratio ◽  
Acoustic Intensity ◽  
Resonant Frequencies ◽  
Gear Noise ◽  
The Difference

Abstract Low-contact-ratio spur gears were tested in the NASA gear-noise rig to study the noise radiated from the top of the gearbox. Experimental results were compared with a NASA acoustics code to validate the code for predicting transmission noise. The analytical code is based on the boundary element method (BEM) which models the gearbox top as a plate in an infinite baffle. Narrow-band vibration spectra measured at 63 nodes on the gearbox top were used to produce input data for the BEM model. The BEM code predicted the total sound power based on this measured vibration. The measured sound power was obtained from an acoustic intensity scan taken near the surface of the gearbox at the same 63 nodes used for vibration measurements. Analytical and experimental results were compared at four different speeds for sound power at each of the narrow-band frequencies over the range of 400 to 3200 Hz. Results are also compared for the sound power level at meshing frequency plus three sideband pairs and at selected gearbox resonant frequencies. The difference between predicted and measured sound power is typically less than 3 dB with the predicted value generally less than the measured value.

Theoretical and Experimental Analysis of Coupled Vibration of a Microcantilever Array

1999 ◽  
Author(s):  
Hiroshi Hosaka ◽  
Kiyoshi Itao
Keyword(s):  
High Speed ◽  
Damping Ratio ◽  
Beam Equation ◽  
Coupled Vibration ◽  
Vibrational Coupling ◽  
Resonant Frequencies ◽  
Micro Actuator ◽  
Actuator Arrays ◽  
The Difference ◽  
Actual Size

Abstract The coupled vibration of microcantilevers, which is induced by airflow, is analyzed in the present study in order to develop high-speed information and sensing devices that use micro-actuator arrays. Simple formulas that give the vibrational coupling amplitude and damping ratio are derived by replacing the cantilevers with a string of spheres, solving Stokes equation, then combining it with an ordinary beam equation. Using these formulas, the coupling amplitude is seen to increase as the beam size, beam gap, internal friction, and the difference in the resonant frequencies of the beams all decrease; the damping ratio is seen to increase as the beam becomes smaller. The validity of the theory advanced here is verified with actual size and enlarged model experiments.

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