• Journal of the Society of Naval Architects of Korea
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• v.55 no.3
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• pp.187-195
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• 2018

Ship's bottom slamming has been studied by many researchers for a very long time. But still some ships suffer structure damages caused by the bottom slamming impacts. This paper presents a practical computation method of the design impact pressure due to ship's bow bottom slamming. Large heave and pitch motions of a rigid hull ship are simulated by the nonlinear strip method in time domain and the relative colliding velocity between the bow bottom and the water surface is calculated using the simulated ship motions. The bottom slamming impact pressure is calculated as a product of the relative colliding velocity squared and the bottom slamming pressure coefficient that is obtained by modification of the SNAME pressure coefficients based on Ochi's slamming experiments. Not only the bottom slamming pressures but also the required bottom plate thicknesses are calculated and compared with those of the classification society rules. The comparisons show good agreements and it is confirmed that the present method is practically very useful for the bottom structure design against ship's bow bottom slamming impacts.

• Ocean Systems Engineering
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• v.12 no.4
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• pp.385-402
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• 2022

This paper deals with the study of hydrodynamic pressure in reservoir adjacent to the concrete gravity dam subjected to dynamic excitation. Widely famous finite element method is used to discretize the reservoir domain for modelling purpose. Pressure is considered as nodal variable following Eulerian approach. A suitable nonreflecting boundary condition is applied at truncated face of reservoir to make the infinite reservoir to finite one for saving the computational cost. Thorough studies have been done on generation of hydrodynamic pressure in reservoir with variation of different geometrical properties. Velocity profile and hydrodynamic pressure are observed due to harmonic excitation for variation of inclination angle of dam reservoir interface. Effect of bottom slope angle and inclined length of reservoir bottom on hydrodynamic pressure coefficient of reservoir are also observed. There is significant increase in hydrodynamic pressure and distinct changes in velocity profile of reservoir are noticeable for change in inclination angle of dam reservoir interface. Change of bottom slope and inclined length of reservoir bottom are also governing factor for variation of hydrodynamic pressure in reservoir subjected to dynamic excitation.

• Structural Engineering and Mechanics
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• v.69 no.5
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• pp.537-545
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• 2019

Stress analysis of bottom-hole rock has to be considered with much care to further understand rock fragmentation mechanism and high penetration rate. This original study establishes a fully coupled simulation model and explores the effects of overburden pressure, horizontal in-situ stresses, drilling mud pressure, pore pressure and temperature on the stress distribution in bottom-hole rock. The research finds that in air drilling, as the well depth increases, the more easily the bottom-hole rock is to be broken. Moreover, the mud pressure has a great effect on the bottom-hole rock. The bigger the mud pressure is, the more difficult to break the bottom-hole rock is. Furthermore, the maximum principal stress of the bottom-hole increases as the mud pressure, well depth and temperature difference increase. The bottom-hole rock can be divided into three main regions according to the stress state, namely a) three directions tensile area, b) two directions compression areas and c) three directions compression area, which are classified as a) easy, b) normal and c) hard, respectively, for the corresponding fragmentation degree of difficulty. The main contribution of this paper is that it presents for the first time a thorough study of the effect of related factors, including stress distribution and temperature, on the bottom-hole rock fracture rather than the well wall, using a thermo-poroelastoplasticity model.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1681-1688
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• 2019

In accordance with ASME Boiler and Pressure Vessel (B&PV) Code Sec.XI Appendix. G, a postulated crack is located at the beltline of a reactor pressure vessel because the neutron flux at the beltline is higher than elsewhere. This means that the distance between the core and the semi-spherical bottom head is longer than the distance between the core and the cylindrical beltline. However, several Small and Medium sized Reactors have bottom heads with diverse shapes, including dished or semi-elliptical shapes, to satisfy the requirement and performance. So, the aim of this paper is to evaluate the effect of crack location on Pressure-Temperature limit curve. To do this, two types of postulated crack location, such as beltline and semi-elliptical bottom head, were adopted to derive the Pressure-Temperature limit curve. Also, parametric studies for neutron flux, crack shape and so on were performed. As a result, core critical temperature of semi-elliptical bottom head is found to higher than that of beltline even when they have same values of thickness and neutron flux. This result will be useful to enhance the understanding of Pressure-Temperature limit curve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.10
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• pp.941-948
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• 2017

Recently, hydrogen energy has been in the spotlight as an alternative to diminishing fossil fuels and as a potential solution to environmental pollution. The development of hydrogen-fueled vehicles and the demands for improved fuel efficiencies have resulted in the need to increase the volume of the hydrogen pressure vessels. Pressure vessels having an elliptical bottom, as opposed to one that is hemispherical, allow for a greater capacity. However, there are insufficient studies on the feasibility of the forming process required for an elliptical bottom. In this study, the liner capacity is calculated according to the ratios of the major to the minor axes of the elliptical bottom part in a hydrogen pressure vessel. Structural safety is verified through finite element analyses, and the results are compared to the theoretical results. The feasibility of the proposed elliptical shape of the pressure vessel bottom, while filled to maximum capacity, is validated through forming analysis.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.3
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• pp.141-150
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• 1998

Model tests were performed to examine the mechanical behavior of steel circular caisson by horizontal load. It was generally found that displacements and bottom pressure of the caisson model were increased rapidly at the local plastic load. The maximum displacement was measured at the loading point, whereas the less displacement was measured at the upper part of the caisson model. The bottom pressure was getting higher, as it was nearer the loading side. Furthermore, the increase ratio of the bottom pressure was higher as the load was increased.

• Journal of Korean Port Research
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• v.6 no.2
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• pp.43-64
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• 1992

This study discusses the interacting with deep water waves approaching from deep water based on the linear wave theory and steep sloping sea bottom floor by the numerical procedure. The results of particular interest are particle velocity and acceleration in x, y, z direction wave height amplification factor reflection coefficient and dimensionless pressure distribution on the steep sloping bottom with respect to the various incident wave angle. The wave loads relative to various bottom slopes, incident wave angles and wave periods on submerged breakwater and pipe are represented in comparison with mild sloping bottom the wave load parameters on the steep sloping bottom seemed to be influenced by variation of incident wave angle. In general the particle velocities and accelerations in x, y, z directions on the steep sloping bottom represented larger value or about two than those on the mild sloping bottom according to incident wave angle. However, the wave height amplification factors did not show distinct difference, but the slight variation with respect to the various incident angle showed on mild sloping bottom. The reflection coefficient increased with respect to increase of the incident angle on the steep sloping bottom the results also indicate that the very steep sloping beach produces a rather substantial amount of reflection as we expected. No significant variation of wave pressure was shown on the steep sloping bottom but it represented a certain amount of variation on the mild sloping bottom according to the various incident wave angle. The analysis at the OTEC site also showed similar results.

• Journal of Industrial Technology
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• v.22 no.B
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• pp.27-34
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• 2002

3-D numerical studies are performed to investigate the effect of the air dam height and approaching air velocities on the pressure distribution of notchback road vehicle. For this purpose, the models of test vehicle with four different air dam heights are introduced and PHOENICS, a commercial CFD code, is used to simulate the flow phenomena and to estimate the values of pressure coefficients along the surface of vehicle. The standard $k-{\varepsilon}$ model is adopted for the simulation of turbulence. The numerical results show that the height variation of air dam makes almost no influence on the distribution of the value of pressure coefficient along upper and rear surface but makes strong effects on the bottom surface. That is, the value of pressure coefficient becomes smaller as the height is increased along the bottom surface. Approaching air velocity makes no differences on pressure coefficients. Through the analysis of pressure coefficient on the vehicle surface, one tries to assess aerodynamic drag and lift of vehicle. The pressure distribution on the bottom surface affects more on lift than the pressure distribution on the upper surface of the vehicle does. The increase of air dam height makes positive effects on the lift decrease but no effects on drag reduction.

• Smart Structures and Systems
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• v.28 no.6
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• pp.839-853
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• 2021

In this paper, a novel multimode liquid metal-based pressure sensor is developed. The main body of the sensor is composed of polydimethylsiloxane (PDMS) elastomer. The structure of the sensor looks like a sandwich, in which the upper structure contains a cylindrical cavity, and the bottom structure contains a spiral microchannel, and the middle partition layer separates the upper and the bottom structures. Then, the liquid metal is injected into the top cavity and the bottom microchannel. Based on linear elastic fracture mechanics, the deformation of the microchannel cross-section is theoretically analyzed. The changes of resistance, capacitance, and inductance of the microchannel under pressure are deduced, and the corresponding theoretical models are established. The theoretical values of the pressure sensor are in good agreement with experimental data, implying that the developed theoretical model can explain the performance of the sensor well.

• Journal of the Korean Institute of Gas
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• v.8 no.2 s.23
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• pp.35-41
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• 2004

This paper presents the stress and deformation characteristics of $9\%$ nickel based inner tank bottom plate in full containment LNG storage tank. When a . maximum hydrostatic pressure applies the bottom plate of inner tank, the maximum = f stress and displacement distributions of the bottom plate have been analyzed as ' functions of inclined angle of the bottom plate, and the thickness and length of the annular plate between the shell plate and bottom one. The calculated results indicate that the taper of the bottom plate is recommended by 100${\~}$200 : 1 for $140,000m^3$ storage capacity of the inner tank. The results recommend that the thickness of the annular plate is around 20mm and the length is greater than 3m for a maximum hydrostatic pressure of $140,000m^3$ tank capacity.