• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1148-1158
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• 2005

This work reports results of our study on the dynamic responses of the buried pipelines both along the axial and the transverse directions under various boundary end conditions. We have considered three cases, i.e., the free ends, the fixed ends, and the fixed-free ends. We have studied the seismic responses of the buried pipelines with the various boundary end conditions both along the axial and the transverse direction. We have considered three cases, i.e., the free ends, the fixed ends, and the fixed-free ends for the axial direction, and three more cases including the guided ends, the simply supported ends, and the supported-guided ends for the transverse direction. The buried pipelines are modeled as beams on elastic foundation while the seismic waves as a ground displacement in the form of a sinusoidal wave. The natural frequency and its mode, and the effect of parameters have been interpreted in terms of free vibration. The natural frequency varies most significantly by the soil stiffness and the length of the buried pipelines in the case of free vibration, which increases with increasing soil stiffness and decreases with increasing length of the buried pipeline. Such a behavior appears most prominently along the axial rather than the transverse direction of the buried pipelines. The resulting frequencies and the mode shapes obtained from the free vibration for the various boundary end conditions of the pipelines have been utilized to derive the mathematical formulae for the displacements and the strains along the axial direction, and the displacements and the bending strains along the transverse direction in case of the forced vibration. The negligibly small difference of 6.2% between our result and that of Ogawa et. al. (2001) for the axial strain with a one second period confirms the accuracy of our approach in this study.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.565-572
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• 2004

Numerical stability analysis of one-dimensional axial flow in solid rocket motors is performed based on the Euler equation coupled with an unsteady combustion equation of solid propellant. In order to check the numerical scheme, behavior of a standing wave in a closed tube is examined. A standing wave in solid rocket motor decays or grows depending on the total effect of propellant combustion, nozzle flow, and so on. The stability boundary of the fundamental mode standing wave is determined by changing one of the combustion parameters. In addition growth rates of the wave are calculated numerically in relatively low Mach number flow region for the motors with different port and nozzle throat diameters. The results obtained here agree well with the approximate solution. The same scheme is applied to a motor with shorter length and L＊-instability is observed.

• Journal of Power System Engineering
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• v.17 no.1
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• pp.36-41
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• 2013

A study of the possible axisymmetric modes that propagate at low frequencies in buried, water-filled pipes is presented. It is well known that for a vacuum-pipe-vacuum system the sole non-torsional axisymmetric mode that exists at low frequencies is the fundamental L(0,1) mode. When a pipe is filled with water and still surrounded by a vacuum it is also known that another mode then appears which at low frequencies is characterized by predominantly axial water-borne displacements. In addition to these modes. this paper explores two other, less well known axisymmetric modes whose exitence depends on the acoustic properties of the outer medium that surrounds a pipe. The predicted characteristics of these modes are presented and the likelihood of them propagating over any significant distance in a buried water pipe is discussed.

• Journal of Power System Engineering
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• v.10 no.1
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• pp.65-70
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• 2006

A study of the possible axisymmetric modes that propagate at low frequencies in buried, water-filled iron pipes is presented. It is well known that for a vacuum-pipe-vacuum system the sole non-torsional axisymmetric mode that exists at low frequencies is the fundamental L(0,1) mode. When a pipe is filled with water and still surrounded by a vacuum it is also known that another mode then appears which at low frequencies is characterized by predominantly axial water-borne displacements. In addition to these modes, this paper explores two other, less well known axisymmetric modes whose existence depends on the acoustic properties of the outer medium that surrounds a pipe. In this paper the predicted characteristics of these modes are presented.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.11
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• pp.538-543
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• 2006

A high-Power continuous-wave (CW) ten-vane double-strapped magnetron oscillator has been investigated using three-dimensional (3D) particle-in-cell (PIC) numerical simulation code, MAGIC3D. The resonant modes and their resonant frequencies of the ten-vane strapped magnetron resonator were obtained to show a large mode separation near the ${\pi}$-mode. An electron cloud formed in an anode-cathode gap, called an interaction space was confined well enough to result in no leakage current. Five spokes were clearly observed in the electron cloud, which definitely ensured the ${\pi}$-mode oscillation in the ten-vane magnetron. Numerical simulations predicted that the saturated microwave output power measured at the coaxial output port was 5.41 kW at the microwave frequency of 893 MHz, corresponding to a power conversion efficiency of 72.6% when the external axial magnetic field was 1150 gauss and the electron beam voltage and current were 6 kV and 1.25 A, respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1340-1347
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• 2006

Dynamic response of buried pipelines both in the axial and the transverse directions on concrete pipe and steel pipe, FRP pipe were investigated through a free vibration analysis. End boundary conditions considered herein consist of free ends, fixed ends, and fixed-free ends in the axial and the transverse direction. Guided ends, simply supported ends, and supported-guided ends were added to the transverse direction. The buried pipeline was regarded as a beam on an elastic foundation and the ground displacement of sinusoidal wave was applied to it. Natural frequencies and mode shapes were determined according to end boundary conditions. In addition, the effects of parameters on the natural frequency were evaluated. The natural frequency is affected most significantly by the soil stiffness and the length of the buried pipelines. The natural frequency increases as the soil stiffness increases while it decreases as the length of the buried pipeline increases. Such behavior appears to be dominant in the axial direction rather than in the transverse direction of the buried pipelines.

• Structural Monitoring and Maintenance
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• v.4 no.2
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• pp.153-173
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• 2017

An improved method is presented to estimate the axial force of a bar member with vibrational measurements based on modified Timoshenko beam theory. Bending stiffness effects, rotational inertia, shear deformation, rotational inertia caused by shear deformation are all taken into account. Axial forces are estimated with certain natural frequency and corresponding mode shape, which are acquired from dynamic tests with five accelerometers. In the paper, modified Timoshenko beam theory is first presented with the inclusion of axial force and rotational inertia effects. Consistent mass and stiffness matrices for the modified Timoshenko beam theory are derived and then used in finite element simulations to investigate force identification accuracy under different boundary conditions and the influence of critical axial force ratio. The deformation coefficient which accounts for rotational inertia effects of the shearing deformation is discussed, and the relationship between the changing wave speed and the frequency is comprehensively examined to improve accuracy of the deformation coefficient. Finally, dynamic tests are conducted in our laboratory to identify progressive axial forces of a steel plate and a truss structure respectively. And the axial forces identified by the proposed method are in good agreement with the forces measured by FBG sensors and strain gauges. A significant advantage of this axial force identification method is that no assumption on boundary conditions is needed and excellent force identification accuracy can be achieved.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.1
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• pp.124-136
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• 2001

In this paper, we designed and manufactured the Ku-band circular waveguide antenna to do wireless communication with a ground radar as on-board antenna of missile. Using the MATLAB and the HFSS, we designed the circular polarizer which has a characteristic of circular polarization and broadband using the capacitive pin method, the feeder to feed coaxial line to circular waveguide, and a stopper to prevent a conductor material from being inserted. Then we simulated the designed antenna using the HFSS, obtained the gain and the radiation pattern. Because of a difficulty of manufacture, we established a manufacture process procedure. Antenna is manufactured with this procedure, test results of the manufactured antenna are the axial ratio of 1.37 ~ 1.72, the 3 ㏈ beamwidth of $72.23^{\circ}{\sim}78.54^{\circ},$ and the gain of 3.26 ~ 4.61 ㏈ within frequency band. We knew that these results are similar with simulation results. Also, we confirmed that the manufactured antenna is satisfied with requirement conditions through performance test, environmental test and flight test.

• Journal of Power System Engineering
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• v.20 no.4
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• pp.26-31
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• 2016

The implementation of chirplet transform to locate axially aligned defects in pipes has been investigated. The results are obtained from experiments performed on a carbon steel pipe using magnetostrictive sensors. Chirplet transform is applied to the reflected signal to separate the individual modes from dispersive and multimodal waveform. The separated modes are used to calculate reflection coefficients which would be used to characterize defects. It is found that the reflection from a defect consists of the wave pulses with gradually decaying amplitudes. Also the results show that the reflection coefficient initially increases with the crack length but finally reaches an oscillating regime.

• Journal of the Korean Society for Railway
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• v.4 no.3
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• pp.110-115
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• 2001

Recently, many engineers actively participate in research and development w.r.t the weight reduction and the safety increase of vehicle body structure to meet the requirement of fuel economy and regulations. However, vehicle design concept related with weight reduction and safety increase is reduced to the design conflict problem. In the paper, the axial and bending collapse test of aluminum extruded beams are performed and the collapse characteristics are investigated. The analysis method to verify the fracture characteristics of aluminum extruded beam is presented and discussed.