• Advances in concrete construction
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• v.13 no.3
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• pp.223-231
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• 2022

The problem is formulated by applying the Kirchhoff's conception for shell theory. The longitudinal modal displacement functions are assessed by characteristic beam ones meet clamped-clamped end conditions applied at the shell edges. The fundamental natural frequency of rotating functionally graded cylindrical shells of different parameter versus ratios of length-to-diameter and height-to-diameter for a wide range has been reported and investigated through the study with fractions laws. The frequency first increases and gain maximum value with the increase of circumferential wave mode. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing height-to-radius ratio. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases. The trigonometric frequencies are lower than that of exponential and polynomial frequencies. Stability of a cylindrical shell depends highly on these aspects of material. More the shell material sustains a load due to physical situations, the more the shell is stable. Any predicted fatigue due to burden of vibrations is evaded by estimating their dynamical aspects.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.49-59
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• 2008

Hastelloy C-276, corrosion resistant alloy at high temperature, is used in chemical plant and power generation industry. In this study, process parameter of laser welding for welding property in Hastelloy C-276 using a continuous wave Nd:YAG laser was studied. As the result of experiment, laser welding did not show segregation or crack at heat affected zone compared to conventional GTWA welding. The melting zone showed cell dendritic structure along with welding line. In addition, planer front solidification is occurred from welding structure, and it was progressed to cellular solidification. Optimal process parameter for butt welding was 1.2kW and 2.0 m/min for laser power and welding speed, respectively. While heat input, output density, tensile stress, and longitudinal strain was $441.98{\times}103$ J/cm2, $29.553{\times}103$ W/cm2, 768 MPa, and 0.689, respectively. Lap welding of the same material showed greater discrepancy in tensile property during 1 line and 2 line welding. For 1 line welding, tensile stress was about 320 MPa, and 2 line showed slightly larger tensile stress. However, strain was decreased by 20%. From this result, lap welding of the same material, Hastelloy C-276, with 2 line welding is considered to be more effective process than 1 line welding with consideration of mechanical property.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.118-131
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• 1995

The shock fracture analysis for the structures of navy vessels subject to underwater explosions or of high speed vessels frequently subject to impact loads has been carried out in two steps such as the global or macro analysis and the fine or micro analysis. In the macro analysis, Doubly Asymptotic Approximation(DAA) has been applied. The three main failure modes of structure members subject to strong shock loading are late time fracture mode such as plastic large deformation mainly due to dynamic plastic buckling, and the early time fracture mode such as tensile tearing failure or transverse shear failure. In this paper, the tensile tearing failure mode is numerically analyzed for the micro analysis by calculating the dynamic stress intensity factor $K_I(t)$, which shows the relation between stress wave and crack propagation on the longitudinal stiffener of the model. Especially, in calculating this factor, the numerical caustic method developed from shadow optical method of caustic well known as experimental method is used. The fully submerged vessel is adopted for the macro analysis at first, of which the longitudinal stiffener, subject to early shock pressure time history calculated in macro analysis, is adopted for the micro analysis.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.2
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• pp.127-138
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• 1996

The strip method, unified theory and 3-D panel method are commonly used methods for the seakeeping analysis of high-speed vessels. The strip method which is basically 2-dimensional method is known to give incorrect hydrodynamic coefficients and motion responses for the cases of high speed and low frequency region. And the unified theory which uses two dimensional approach in inner domain and slender body theory in outer domain is very complicate in computational modelling. Though the 3-D panel method requires comparatively long computation time, it is believed that the method gives good results without any limitation in ship speed and range of frequency for computation. In the 3-D panel method the source singularity representing translating and pulsating Green function is used and Hoff's method is adopted for the numerical calculation of the Green function. The computation time can be reduced by using the symmetry relationship with respect to longitudinal axis. In this paper the strip method and the 3-D panel method are compared for the seakeeping analysis of a high-speed catamaran. The Compared items are the hydrodynamic coefficients, wave exciting forces, frequency response functions and short-term responses in irregular waves.

• Journal of the Korean Wood Science and Technology
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• v.18 no.3
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• pp.53-68
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• 1990

This research has been executed for maximization of lumber yield and more efficient use of small diameter logs. Sample logs from thinnings carne from densed artificial stands at the Kwangnung Experimental Forests situated in the central region of Korean peninsula. Species of sample logs were obtained to execute sawing and strength test for larch, and lumber strength test in full size for pitch pine and Korean pine. A survey on sawmills consuming domestic logs was carried out to know sawmill production, costs and utilization structure of lumber as a guide to business analysis. Results showed that sawing pattern from small logs less than 15cm in diameter was necessary to cut 9cm by 9cm square per one log in order to obtain high lumber recovery and provide for wide market needs. The total lumber yield of squares plus side boards was 56 percent to 58 percent from small logs and the yield for log sweep in 30 percent decreased by 24.5 percent in sawing production, compared to yield for straight logs. In sawing efficiency, production of lumber by twin band saw could be improved 238 percent higher than lumber of the same species produced by conventional sawmilling methods, and sawing accuracy with twin band saw was much higher at the lumber production than band saw. Lumber from the small larch logs has shown 70 knots per $m^2$ on its faces and also lumber showed lots of face checkings by air drying on the yard, compared to other species. MOR in bending of lumber in full size from small logs of larch was found ranging from 380kg/$cm^2$ to 460kg/$cm^2$, resulting in 40 percent less than the strength from clear small specimens. In lumber containing knots, cross grain, etc, longitudinal stress wave speed was delayed about 48 percent by defects in lumber from both larch and pitch pine logs. The surveyed sample sawmills consumed the domestic logs at the rate of 54 percent to 84 percent in the total timber consumption, showing high consumption at mills located in the mountains.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.14-22
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• 2001

This paper presents the results of hull form design and powering performance for a 2.500 ton class trimaran frigate. A series of resistance tests and numerical calculations have been conducted to figure out the influences of side-hull form and position on the resistance characteristics of the trimaran. And the propulsion test was conducted to investigate the propulsion efficiency of the trimaran, and the powering performance of the trimaran was compared with that of the similar mono-hull ships in full scale. From the research it was found that the longitudinal position of side-hull had a large influence on the resistance characteristics of the trimaran while the side-hull form and transverse position had a small influence on it. The trimaran showed favorable resistance performance when the side-hull was located near the stern of trimaran, which was resulted from the fact that the side-hull stem was located near the primary wave hollow generated by the main hul1. The powering performance of the trimaran was superior to that of the similar mono-hull ships above the middle speed range.