• Journal of Ocean Engineering and Technology
• /
• v.25 no.1
• /
• pp.1-7
• /
• 2011

The radiation of water waves by a heaving truncated circular cylinder with damping plate is solved in the frame of the three-dimensional linear potential theory. The damping plate has a distinct advantage in reducing the motion response of a floating circular cylinder by increasing the added mass and the damping coefficient. Using the matched eigenfunction expansion method, the characteristics of hydrodynamic added mass and the damping coefficient are investigated with various system parameters, such as the radius and submergence depth of the damping plate. It is found that both added mass and the damping coefficient are significantly increased due to the arranged features of the larger damping plate with shallow submergence, which are positive factors as a motion reduction device of the floating offshore platform. Also the numerical results for an oscillating submerged disk show that the added mass is negative and that the damping coefficient has a peak value at resonant frequency when submergence depth is sufficiently small.

• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.2 s.140
• /
• pp.124-128
• /
• 2005

This paper describes motion stability of a spar platform with and without a damping plate in regular waves. The heave and pitch motion equation is derived in terms of Mathieu equation and the stability diagram is obtained. It is shown that the spar platform with damping plate has smaller unstable region than that without damping plate in the stability diagram. Model tests are carried out to verify the mathematical analysis. Under the condition that the pitch natural period is approximately double the heave natural period and the heave motion is amplified at heave resonance, unstable pitch motions are evoked. However the unstable motion is stabilized in cases of spar platform with damping plate. Therefore the damping plate is an effective device to stabilize the motion of spar platform.

• Journal of KSNVE
• /
• v.5 no.4
• /
• pp.493-501
• /
• 1995

Optimum design of a viscoelastic damping layer which is unconstrainedly cohered on a steel plate is discussed from the viewpoint of the modal loss factor. Themodal loss factor is analyzed by using the energy method to the base steel plate and cohered damping layer. Optimum distributions of the viscoelastic damping layer for modes are obtained by sequentially changing the position of a piece of damping layer to another position which contributes to maximizing the modal loss factors. Analytical procedure performed by using this method simulated for 3 fundamental modes of an edge-fixed plate. Simulated results indicate that the modal loss factor ratios can be increase by as much as 210%, or more, by optimizing the thickness distribution of the damping layer to two times of the initial condition which is entirely covered. Optimum configurations for the modes are revealed by positions where added damping treatments become most effective. The calculated results by this method are validated by comparison with the experimental results and the calculated results obtained by the Ross-Ungar-Kerwin's model in the case of the layer is uniformly treated over the steel plate.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.12 no.5
• /
• pp.317-322
• /
• 2002

A solution procedure of vibration and radiated noise of the plate covered with damping material has been studied. To predict the vibration level and the radiated noise level of the plate covered with damping material, FEM and BEM have been utilized, respectively. A property of damping material has been measured by using a composite beam. Two different kinds of measuring procedure for the composite beam have been introduced by comparing its characteristics. The numerical prediction of vibration level of the Plate covered with damping material has been proved with experimental data.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.7 s.112
• /
• pp.690-696
• /
• 2006

Thickness of damping layer in sandwich plate needs to be optimized in order to make modal loss factor of the sandwich plate maximum. Since previous studies were interested in noise reductions over high frequency range, the modal properties were derived based on simply supported boundaries. This conventional formula is approximately applicable to other boundary conditions over high frequency range only. The purpose of this study is to propose a method to determine optimum damping layer thickness of sandwich plate for maximum modal damping in low frequency range when the boundary condition is not a simple support. The conventional RKU equation based on simply supported boundary is modified to reflect other boundary conditions and the modified RKU equation is subsequently applied to determine the optimum damping layer thickness for arbitrary conditions. In order to reflect frequency-dependent characteristics of elastic modulus of the damping layer, an iteration method is proposed in determining the modal properties. Test results on sandwich plates for optimum damping layer thickness are compared with predictions by the proposed method and conventional method.

• Journal of Ocean Engineering and Technology
• /
• v.27 no.4
• /
• pp.76-82
• /
• 2013

Motion reduction of an offshore structure at resonant frequency is essential for avoiding critical damage to the topside and mooring system. A damping plate has a distinct advantage in reducing the motion of a floating structure by increasing the added mass and the damping coefficient. In this study, the heave motion responses of a circular cylinder with an impermeable and a permeable damping plate attached at the bottom of the cylinder were investigated thru a model test. The viscous damping coefficients for various combinations of porosity were obtained from a free-decay test by determining the ratio between any pair of successive amplitudes. Maximum energy dissipation occurred at a porous plate with a porosity P = 0.1008. Experimental results for regular and irregular waves were compared with an analytical solution by Cho (2011). The measured heave RAO and spectrum reasonably followed the trends of the predicted values. A significant motion reduction at resonant frequency was pronounced and the heaving-motion energy calculated by the integration of the area under the heave motion spectrum was reduced by more than 75% by the damping plate. However, additional energy dissipation by eddies of strong vorticity and flow separation inside a porous damping plate was not found in the present experiments.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.17 no.1 s.118
• /
• pp.55-64
• /
• 2007

In the built-up structure consisting of a stiff beam and a flexible plate, Grice showed that the plate behaves as an energy absorber in narrow frequency bands(called plate blocking effect). This paper deals with such beam-plate coupled structures, where the plate is an energy absorber and the excited beam is an energy path. It is found that such energy dissipation can occur in the relatively broad bands, if different stiffnesses are used in the rectangular plate. It was experimentally verified by Heckl that the energies in terms of one-third octave band averages transferred to the plate(or dissipated in the plate) increase for increased plate damping. This Paper, however, shows that the energy absorption suddenly reduces at the certain narrow frequency bands where the plate damping effect upon the coupled beam is maximum. Also, in order to minimize energy transfer through the beam in terms of one-third octave band averages, it is advantageous to increase the plate damping closer to the excitation point All these results are based on the wane method.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.19 no.5
• /
• pp.530-536
• /
• 2009

In this paper, the power flow analysis(PFA) has been used to analyze the vibration of a plate covered with a damping sheet. Experiments have been performed to measure the loss factor and frequency response functions of the plate covered with the damping sheet. The data for the loss factor has been used as the input data to predict the vibration of the coupled plates with PFA. The comparison between the experimental results and the predicted PFA results for the frequency response functions has been performed. It showed that PFA can be effectively used to predict structural vibration of a plate covered with a damping sheet in medium-to-high frequency range.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11a
• /
• pp.341-348
• /
• 2001

In this study, nonlinear vibration analysis of the cylindrical orthotropic porous thin plate under V-shaped tension distribution with wire impact damping is considered. We make dynamic model of the plate under the tension using commercial FEM code and reduce the number of its degrees of freedom using dynamic condensation. The dynamic model of wire is obtained as lumped mass model from string equation. And then we analyze the nonlinear vibration of the plate including the impact phenomenon between the plate and the wire using the reduced mass and stiffness matrices of the plate and lumped model of the wire. The contact phenomenon between them can be described by impact contact elements composed of contact stiffness coefficients from Hertzian contact theory and contact damping coefficients from restitution coefficient between them. And we discussed the results of nonlinear vibration analysis for variations of their design parameters.

• Steel and Composite Structures
• /
• v.19 no.5
• /
• pp.1321-1331
• /
• 2015

A square steel sandwich plate with lattice corrugated core is explored for damping improvement. A range of damping materials are filled inside the openings provided by the corrugated core, or are applied on the surfaces of the facesheets. The dynamic properties such as natural frequency and damping factor are experimentally measured for the sandwich plate with each filling solution. The relative performance of each insertion is compared in terms of damping capacity and added mass.