• Journal of Advanced Research in Ocean Engineering
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• v.4 no.4
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• pp.204-216
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• 2018

A ship repeatedly face free surface under rough sea conditions owing to relative motion with wave encounter. The impact pressure is transferred to the hull structure and causes structural damage. In this study, the bow flare slamming load of a container ship is estimated using computations fluid dynamics (CFD) and prescript formula according to various classifications. It is found that the bow flare slamming load calculated by the formulas of the common structural rule and ABS tends to be similar to the CFD results.

• Geomechanics and Engineering
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• v.23 no.2
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• pp.115-125
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• 2020

This study aims to explore practical and useful equations for rapid evaluation of uniaxial compressive strength of concrete (UCS-C) during the preliminary design stage of aggregate selection. For this purpose, aggregates which were produced from eight different intact rocks were used in the production of concretes. Laboratory experiments involved the tests for uniaxial compressive strength (UCS-R), point load index (PLI-R), P wave velocity (UPV-R), apparent porosity (n-R), unit weight (UW-R) and aggregate impact value (AIV-R) of the rock samples. UCS-C, point load index (PLI-C) and P wave velocity (UPV-C) of concrete samples were also determined. Relationships between UCS-R-rock parameters and UCS-C-concrete parameters were developed by regression analyses. In the simple regression analyses, PLI-C, UPV-C, UCS-R, PLI-R, and UPV-R were found to be statistically significant independent variables to estimate the UCS-C. However, higher coefficients of determination (R²=0.97-1.0) were obtained by multiple regression analyses. The results of simple regression analysis were also compared to the limited number of previous studies. The strength conversion factor (k) values were found to be 14.3 and 14.7 for concrete and rock samples, respectively. It is concluded that the UCS-C can roughly be estimated from derived equations only for the specified rock types.

• Structural Engineering and Mechanics
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• v.50 no.4
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• pp.471-486
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• 2014

The number of explosive attacks on civilian structures has recently increased. Protection of structure subjected to blast load remains quite sophisticated to predict. The use of the pyramid cover system (PCS) to strengthen sandwich structures against a blast terror has great interests from engineering experts in structural retrofitting. The sandwich steel structure performance under the impact of blast wave effect is highlighted. A 3-D numerical model is proposed to study the PCS layer to strengthen sandwich steel structures using finite element analysis (FEA). Hexagonal core sandwich (XCS) steel panels are used to study structural retrofitting using the PCS layer. Field blast test is conducted. The study presents a comparison between the results obtained by both the field blast test and the FEA to validate the accuracy of the 3-D finite element model. The effects are expressed in terms of displacement-time history of the sandwich steel panels and pressure-time history effect on the sandwich steel panels as the explosive wave propagates. The results obtained by the field blast test have a good agreement with those obtained by the numerical model. The PCS layer improves the sandwich steel panel performance under impact of detonating different TNT explosive charges.

• Ocean Systems Engineering
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• v.1 no.1
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• pp.31-57
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• 2011

Impact pressure due to sloshing is of great concern for the ship owners, designers and builders of the LNG carriers regarding the safety of LNG containment system and hull structure. Sloshing of LNG in partially filled tank has been an active area of research with numerous experimental and numerical investigations over the past decade. In order to accurately predict the sloshing impact load, a new numerical method was developed for accurate resolution of violent sloshing flow inside a three-dimensional LNG tank including wave breaking, jet formation, gas entrapping and liquid-gas interaction. The sloshing flow inside a membrane-type LNG tank is simulated numerically using the Finite-Analytic Navier-Stokes (FANS) method. The governing equations for two-phase air and water flows are formulated in curvilinear coordinate system and discretized using the finite-analytic method on a non-staggered grid. Simulations were performed for LNG tank in transverse and longitudinal motions including horizontal, vertical, and rotational motions. The predicted impact pressures were compared with the corresponding experimental data. The validation results clearly illustrate the capability of the present two-phase FANS method for accurate prediction of impact pressure in sloshing LNG tank including violent free surface motion, three-dimensional instability and air trapping effects.

• Steel and Composite Structures
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• v.47 no.2
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• pp.297-313
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• 2023

This study aims to extend the application of the spectral element method (SEM) to wave propagation and free vibration analysis of functionally graded (FG) plates integrated with thin piezoelectric layers, plates with tapered thickness and structure on elastic foundations. Also, the dynamic response of the smart FG plate under impact and moving loads is presented. In this paper, the dynamic stiffness matrix of the smart rectangular FG plate is determined by using the exact dynamic shape functions based on Mindlin plate assumptions. The low computational time and results' independence with the number of elements are two significant features of the SEM. Also, to prove the accuracy and efficiency of the SEM, results are compared with Abaqus simulations and those reported in references. Furthermore, the effects of boundary conditions, power-law index, piezoelectric layers thickness, and type of loading on the results are studied.

• Journal of the Korean Society of Marine Environment & Safety
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• v.11 no.2 s.23
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• pp.77-82
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• 2005

Previously sailing yachts or leisure yachts were mainly made from FRP(Fiber glass reinforced plastic) in the small shipbuilding, but recently there is a trend to replace it for steel or aluminum to substitute FRP for environmental friendly materials. Although It have to need a many checked item in case of hull girder strength and transverse strength normally evaluate base on calculation of class guideline so called direct calculation method. Otherwise. this method of initial structural design considered enough for safety margin on the structure. But, case of small craft must consider for evaluating local strength through rational method. In this paper, check the bow structure members for satisfying results base on allowable stress criterion of damaged bow structure by dynamic load due to slamming and bottom impact load due to pitching motion through finite element analysis. and investigate engine bed structure considering engine weight load and transverse wave load.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.6
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• pp.151-158
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• 2007

The static and dynamic behaviour of VGT and EGR systems has a significant impact on overall engine performance, fuel economy and exhaust emissions. This is because they define the state and composition of the air charge entering the engine. This work focused on the effect of the aperture ratio of VGT and EGR on the emission and flow characteristics under partial loads conditions. The investigation carried out using 2 liter PCCI 4 cylinder diesel engine with VGT and EGR. The result of this study shows that smoke increases with increasing EGR rate and NOx decreases with increasing EGR rate. It was also found that the residual gas contents greatly impact on soot emission under partial load condition. Finally, it can be concluded that VGT and EGR aperture ratio can greatly impact not only on soot and NOx but also air charging.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1557-1564
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• 2000

When the half infinite crack in the orthotropic material strip with a large anisotropic ratio(E11>>E22) propagates with constant velocity, dynamic stress component $\sigma$y occurre d along the $\chi$ axis is derived by using the Fourier transformation and Wiener-Hopf technique, and the dynamic stress intensity factor is derived. The dynamic stress intensity factor depends on a crack velocity, mechanical properties and specimen hight. The normalized dynamic stress intensity factors approach the maximum values when normalized time(=Cs/a) is about 2. They have the constant values when the normalized time is greater than or equal to about 2, and decrease with increasing a/h(h: specimen hight, a: crack length) and the normalized crack propagation velocity( = c/Cs, Cs: shear wave velocity, c: crack propagation velocity).

• Journal of Advanced Research in Ocean Engineering
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• v.4 no.4
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• pp.195-203
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• 2018

The wave impact on ships could cause local damage to the ship's hull, which has been a concerning issue during the ship design process. In recent years, local structural damages of ships caused by slamming loads have been reported by accident; therefore, it is necessary to study the local slamming pressure loads and structural response assessment. In the present study, slamming loads around the ship's bow region in the presence of regular wave have been simulated by RANS equations discretized with a cell-centered finite volume method (FVM) in conjunction with the $k-{\Box}$ turbulence model. The dynamic structural response has been calculated using an explicit FE method. By adding the slamming pressure load of each time step to the finite element model, establishing the reasonable boundary conditions, and considering the material strain-rate effects, the dynamic response prediction of the bow flare structure has been achieved. The results and insights of this study will be helpful to design a container ship that is resistant enough to withstand bow flare slamming loads.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.752-763
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• 2000

The stress field around the dynamically propagating interface crack tip under a remote mixed mode loading condition has been studied with the aid of dynamic photoelastic method. The variation of stress field around the dynamic interface crack tip is photographed by using the Cranz-Shardin type camera having $10^6$ fps rate. The dynamically propagating crack velocities and the shapes of isochromatic fringe loops are characterized for varying mixed load conditions in double cantilever beam (DCB) specimens. The dynamic interface crack tip complex stress intensity factors, $K_1\;and\;K_2$, determined by a hybrid-experimental method are found to increase as the load mixture ratio of y/x (vertical/horizontal) values. Furthermore, it is found that the dynamically propagating interface crack velocities are highly dependent upon the varying mixed mode loading conditions and that the velocities are significantly small compared to those under the mode I impact loading conditions obtained by Shukla (Singh & Shukla, 1996a, b) and Rosakis (Rosakis et al., 1998) in the USA.