• Journal of the Society of Naval Architects of Korea
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• v.55 no.4
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• pp.341-349
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• 2018

Recently, it has been reported that the whipping response, which is the elastic phenomenon of the ship, may be one of the causes of the ship accident. Unfortunately, the commonly used methodology for evaluating the whipping effect effectively has not been developed yet. In this study, we developed a procedure to estimate the whipping effect of hull in actual design stage. Fluid-structure interaction analysis was performed for a dominant short term sea state to obtain the time series data of vertical wave bending moment including the whipping response by slamming. In order to estimate the whipping effect by using the time series, some signal processing and statistical techniques such as low pass filtering, Weibull fitting and so on, were applied. the hydro-elasticity analysis was performed on container ships of various sizes to evaluate the whipping effect. The parameters that can affect the response of the hull vibration was selected and the effect of these parameters on whipping was analyzed.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.306-320
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• 2010

Modern ultra-large container carriers can be exposed to the unprecedented springing excitation from ocean waves due to their relatively low torsional rigidity. Large deck opening on the deck of container carriers tends to cause warping distortion of hull structure under wave-induced excitation, eventually leading to the higher chance of resonance vibration between its torsional response and incoming waves. To handle this problem, a higher-order B-spline Rankine panel method and Vlasov-beam FE model was directly coupled in the time domain, and the coupled equation was solved by using an implicit iterative method. In order to capture the complicated behavior of thin-walled open section girder, a sophisticated beam-based finite element model was developed, which takes into account warping distortion and shear-on-wall effect. Then, the developed beam model was directly coupled with the time-domain Rankine panel method for hydrodynamic problem by using the fixed-point iteration method. The developed computational scheme was validated through the comparison with the frequency-domain solution on the container carrier model in linear springing regime.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.26-32
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• 2001

In this paper, elastic responses of a floating structure in waves with a breakwater are presented. The method of source-dipole distribution is used to analyze the velocity potentials for the fluid region. The deflections of structure are expanded approximately in terms of natural mode functions of free-free beam. The model for present calculation is a floating plate with an length of 1000m and the hydroelastic responses for a floating structure with a straight breakwater are shown. The effects of distance between breakwater and structure, bending rigidity and relative length of regular waves are examined.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.6
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• pp.348-357
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• 2021

In this paper, the generalized hydrodynamic force and response of a flexible body are calculated at different reference coordinate systems. We generalize the equation of motion for a flexible body by using the conservation of momentum (Mei et al., 2005). To obtain the equations in the generalized mode, two different reference coordinates are adopted. The first is the body-fixed coordinate system by a rigid body motion. The other is the inertial coordinate system which has been adopted for the analysis. Using the perturbation scheme in the weakly-nonlinear assumption, the equations of motion are expanded up to second-order quantities and several second-order forces are obtained. Numerical tests are conducted for the flexible barge model in head waves and the vertical bending is only considered in the hydroelastic responses. The results show that the linear response does not have the difference between the two formulations. On the other hand, second-order quantities have different values for which the rigid body motion is relatively large. However, the total summation of second-order quantities has not shown a large difference at each reference coordinate system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.14-22
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• 2016

Because fuses have many parts, human error can occur during visual inspections. This paper proposes an automatic ammunition test algorithm for preventing human error during an inspection. The automatic ammunition test algorithm consists of the following three steps. First, the image input and preprocessing step is where an inspection image is rotated using an image rotation algorithm and the image is converted to a binary image. Second, the inspection step of arming determines if the ammunition is armed using Masked Template Matching algorithm, etc. Third, the inspection step of the parts determines if the parts are omitted using an image searching algorithm, etc. The arming or parts omission of the fuse are detected efficiently using the ammunition automatic test algorithm. The ammunition automatic test algorithm is expected to help improve the safety and reliability of 40 mm grenade fuse.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.4
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• pp.182-193
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• 1997

The interaction of monochromatic incident waves with a horizontal flexible membrane is investigated in the context of two-dimensional linear hydro-elastic theory. First, analytic diffraction and radiation solutions for a submerged impermeable horizontal membrane are obtained. Second, the theoretical prediction was compared with a series of experiments conducted in a two-dimensional wave tank at Texas A & M University. The measured reflection and transmission coefficients reasonably follow the trend of predicted values. Using the developed computer program, the performance of surface-mounted or submerged horizontal membrane wave barriers is tested with various system parameters and wave characteristics. It is found that the properly designed horizontal flexible membrane can be an effective wave barrier.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.3
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• pp.213-217
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• 2007

Pontoon type very large floating structure has been considered and actively studied as one of the most important ocean space utilization. The hydroelastic displacement of the pontoon type floating structure in waves is the largest at its weather side. The purpose of this study is to investigate the characteristics and effects of the submerged horizontal plate which is developed to reduce the wave exciting forces acting on the pontoon type floating structure using numerical analysis. The numerical method based on the finite difference method has been adopted and compared with the experimental data to confirm the reliability of it. We have performed the numerical computation of wave exciting forces acting on the pontoon type floating structure with/without submerged plate and discuss the results of simulation.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.644-653
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• 2005

In general the loads due to ocean wave are considered as main design parameters governing the global structural safety of VLFS (Very Large Floating Structure). In order to predict design wave loads accurately, hydro-elastic analysis must be conducted considering the initial global flexural rigidity of VLFS. However, in order to determine the structural scantling of major members (deck, bottom, side panels and longitudinal / transverse BHD etc.), static load and design wave loads must be given as explicit form generally. Therefore in order to determine a proper structural arrangement and scantlings of VLFS at initial design stage, both calculations of structural scantling and hydro-elastic analysis for wave conditions must be conducted iteratively and the convergence of their results must be checked. On this paper, based on the case design of a 500×300 m size's floating marina resort, the details of structural design technique using hydro-elastic analysis are explained and discussed. At first, the environmental conditions and the system requirements of the design of marina resort are described. The scantling formulas for the major members of pontoon type VLFS are proposed from the local and global design points of view. Considering the design wave loads as well as static design loads, the structural safety is checked iteratively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.130-135
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• 2019

This study performed the quality improvement of a red dot sight for a 40 mm grenade launcher through parallax reduction. The red dot sight cited in this study is currently in mass production for military use as a non-weapon system. While the red dot sight's parallax currently meets requirements, slightly greater error was observed on the outside of effective optical area of the reflection lens compared to other sights. Parallax is easily affected by eye movement, which can result in aiming error. To improve the red dot sight's quality, this study analyzed why parallax is observed in the effective optical area of the reflection lens and how to reduce it. As a result, the red dot sight demonstrated lower parallax error using the new optical system design with an increased reflection lens thickness and modified components configuration related to the reflection lens assembly. Parallax was calculated and simulated by using a particular program to verify that it decreased. This improvement for the 40 mm. grenade launcher red dot sight more than satisfies requirements, offers advanced capabilities for users, and as a result, successful operation carryout.

• Journal of the Korean Society for Marine Environment & Energy
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• v.1 no.2
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• pp.27-39
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• 1998

The interaction of monochromatic incident waves with a horizontal flexible membrane is investigated in the context of two-dimensional linear hydro-elastic theory. First, analytic diffraction and radiation solutions for a submerged impermeable horizontal membrane are obtained. Second, the theoretical prediction was compared with a series of experiments conducted in a two-dimensional wave tank at Texas A&M University. The measured reflection and transmission coefficients reasonably follow the trend of predicted values. Using the developed computer program, the performance of surface-mounted or submerged horizontal membrane wave barriers is tested with various system parameters and wave characteristics. It is found that the properly designed horizontal flexible membrane can be an effective wave barrier.