• Journal of the Society of Naval Architects of Korea
• /
• v.31 no.4
• /
• pp.73-81
• /
• 1994

The source and source/dipole distribution methods using 3-dimensional panel method have been widely used for ship motion analysis. When these methods are used, large errors in the predicted hydrodynamic coefficients are introduced around the irregular frequencies caused by the resonance of imaginary internal flow. Therefore, the irregular frequencies need to be removed for an accurate prediction of ship motion. This paper adopts 3-dimensional translating and oscillating Green function derived by Wu. The adaptive integration method, stretching transform and stationary phase method are used for the calculation of the calculation of Green function and the integral equation is derived by distributing the Green function n ship surface and inner free-surface. The condition of zero normal velocity, that is, wall condition on inner free-surface has been successfully used for the removal of irregular frequencies in oscillating problems. The calculations are carried out for series 60($C_B=0.7$) vessel and the results are compared with those of other theoretical analyses and experiment.

• The Journal of the Acoustical Society of Korea
• /
• v.29 no.2
• /
• pp.118-124
• /
• 2010

In this paper, design parameters of dynamic vibration absorber, which is used to reduce bending vibrations of a vehicle drive line, is optimized. For obtaining the correct dynamic response characteristics, a flexible-body drive line is made by applying the flexibility data extracted from vibration analysis of propeller shafts to the drive line dynamic model. Inner tube mass, rubber stiffness and rubber damping coefficient of the dynamic vibration absorber are taken as design parameters for optimization. To minimize the vertical acceleration of the drive line, a second-order regression equation of the objective function is generated by performing the central composite experimental design with 3 factors, 2 levels and 15 test runs. And the design parameters of the dynamic vibration absorber are determined by using optimization program. The vehicle model with optimized dynamic vibration absorber reduces the vertical acceleration peak of the drive line by 17.1 % in compared with the initial model.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.9
• /
• pp.51-62
• /
• 2016

Parametric studies for various site conditions by using 3d numerical model were carried out in order to estimate dynamic behavior of soil-pile-structure system in dry soil deposits. Proposed model was analyzed in time domain using FLAC3D which is commercial finite difference code to properly simulate nonlinear response of soil under strong earthquake. Mohr-Coulomb criterion was adopted as soil constitutive model. Soil nonlinearity was considered by adopting the hysteretic damping model, and an interface model which can simulate separation and slip between soil and pile was adopted. Simplified continuum modeling was used as boundary condition to reduce analysis time. Also, initial shear modulus and yield depth were appropriately determined for accurate simulation of system's nonlinear behavior. Parametric study was performed by varying weight of superstructure, pile length, pile head fixity, soil relative density with proposed numerical model. From the results of parametric study, it is identified that inertial force induced by superstructure is dominant on dynamic behavior of soil-pile-structure system and effect of kinematic force induced by soil movement was relatively small. Difference in dynamic behavior according to the pile length and pile head fixity was also numerically investigated.

• Progress in Medical Physics
• /
• v.11 no.2
• /
• pp.131-139
• /
• 2000

We designed high dose rate Ir-192 source which was prepared for substitute the Co-60 source in Ralstron unit (Simatsu, Japan) which is supplied for cervical cancer treatment. The source dimension is 1.5 mm in a diameter and 1.5mm thickness of cylinder and encapsulated with 3 mm diameter of stainless steel(SUS316L) to substituted for the Co-60 source size. The Ir-192 source was prepared the dose model for tissue dose computation through the experimental determination of apparent activity and applied the empirical tissue correction factors extended to 20cm distance. The tissue dose model was applied the 4.69 R/cm-mCi-hr gamma constant and the ratio of energy absorption coefficient of water to that of air showed 1.112 include filteration of the self-absorptions. In this experiments, we prepared the dose computation software to clinical usefulness.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.8 no.2
• /
• pp.27-33
• /
• 2004

Dynamic response analysis is conducted for a floating bridge subjected to multiple support earthquake excitation. The floating bridge used in this study is supported by discrete floating pontoons and horizontal pretension cables supported at both ends of the bridge. The bridge is modeled with finite elements and the hydrodynamic added mass and added damping due to the surrounding fluid around pontoons are obtained using boundary elements. During the analysis the concept of retardation function is utilized to consider the frequency dependency of the hydrodynamic coefficients. Multiple support excitation is introduced at both ends of the bridge and the time history response is compared to that of a simultaneous excitation. The results show that the multiple support excitation yields larger values in some responses. for example in cable tensions. than the sumultaneous excitation.

• Journal of the Society of Naval Architects of Korea
• /
• v.38 no.3
• /
• pp.47-53
• /
• 2001

When a ship advancing in waves is subjected to impact forces or irregular forces, the motion analyses for ship are convenient for being calculated in the time domain. The added mass, wave damping coefficients, wave exciting forces and mean drift forces are calculated by 3-Dimensional panel method used the translating pulsating Green function in the frequency domain and the motion equations which are considered by the memory effect due to waves are numerically solved by using the Newmark-$\beta$ method in the time domain. The motion analyses are carried out for a Series 60($C_B=0.7$) moving in irregular waves. The items of calculation are 6-degree motions, accelerations at the fore and after position, numbers of deck wetness and numbers of exposure at ship-bottom, etc. Moreover, the thrust addition in waves is examined by considering the time mean drift forces in the motion equations of time domain.

• Journal of the Society of Naval Architects of Korea
• /
• v.38 no.3
• /
• pp.41-46
• /
• 2001

The very large vessels like VLCC and container ship have been built recently and those vessels have smaller structural strength in comparison with the other convectional skips. As a result the fatigue destruction of upper deck occurs a frequently due to the springing phenomenon at the encountering frequencies. In this study, the hydrodynamic loads are calculated by three-dimensional source distribution method with the translating and pulsating Green function. A ship is longitudinally divided into 23 sections and the added mass, damping and hydrodynamic force of each section is calculated. focusing only on the vertical motion. Stiffness matrix is calculated by the Euler beam theory. The calculation is carried out for Esso Osaka.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.6
• /
• pp.90-94
• /
• 2021

With the increased interest on quiescent place for residential place, the noise generation from facilities needs to be minimized. One important noise source include sounds from operation of elevators. The elevator operates between floors and generates significantly annoying sounds to the nearby living spaces. It is recognized as the significant contributor inducing noise annoyance to residents. Elevator is supported to the building structure at several locations for movements between floors. In this study, the vibration reduction by use of polymer concrete on the support location was demonstrated. By measuring and comparing the vibration generation when supported on cement and polymer concrete, the noise reduction performance was evaluated. The polymer concrete was made in the form of being inserted into the wall that imitates the hoistway. The impact vibration was induced to the bracket and vibration transfer magnitude was measured. The damping ratio was evaluated through normalization and curve fitting of transient response, and comparison was performed for each resin mixing ratio. By use of polymer concrete, it was possible to reduce the vibration generation in an effect manner without sacrifice on the structural rigidity.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.17 no.3
• /
• pp.138-148
• /
• 2005

Dynamic response of floating structures such as floating body and floating bridges subject to wave load is to be calculated in frequency domain. Added mass coefficient, damping coefficient and wave exciting force are obtained numerically from frequency domain formulation of linear potential theory and boundary element method for a floating body which is partially submerged into water and subjected to wave force. Next, the equation of motion for the dynamic behavior of a floating structure which is supported by the floating bodies and modeled with finite elements is written in frequency domain. hker a hemisphere is analyzed and compared with the published references as examples of floating bodies, the hydrodynamic coefficients for a pontoon type floating body which supports a floating bridge are determined. The dynamic response of the floating bridge subject to design wave load can be solved using the coefficients obtained for the pontoons and the results are plotted in the frequency domain. It can be seen from the example analysis that although the peak frequency of the incoming wave spectrum is near the natural frequency of the bridge, the response of the bridge is not amplified due to the effect that the peak frequency of wave exciting force is away from the natural frequency of the bridge.