• Structural Engineering and Mechanics
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• v.69 no.5
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• pp.511-525
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• 2019

This paper presents an analytical study of wave propagation in simply supported graduated functional plates resting on a two-parameter elastic foundation (Pasternak model) using a new theory of high order shear strain. Unlike other higher order theories, the number of unknowns and governing equations of the present theory is only four unknown displacement functions, which is even lower than the theory of first order shear deformation (FSDT). Unlike other elements, the present work includes a new field of motion, which introduces indeterminate integral variables. The properties of the materials are assumed to be ordered in the thickness direction according to the two power law distributions in terms of volume fractions of the constituents. The wave propagation equations in FG plates are derived using the principle of virtual displacements. The analytical dispersion relation of the FG plate is obtained by solving an eigenvalue problem. Numerical examples selected from the literature are illustrated. A good agreement is obtained between the numerical results of the current theory and those of reference. A parametric study is presented to examine the effect of material gradation, thickness ratio and elastic foundation on the free vibration and phase velocity of the FG plate.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.667-679
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• 2020

As the LNG carrier operates in ice covered waters, it is key to ensure the overall safety, which is related to the coupling effect of ice-breaking process and internal liquid sloshing. This paper focuses on the sloshing simulation of the ice-breaking LNG carrier, and the numerical method is proposed using Circumferential Crack Method (CCM) and Volume of Vluid (VOF) with two main key factors (velocity νx and force Fx). The ship motion analysis is carried out by CCM when the ship navigates in the ice-covered waters with a constant propulsion power. The velocity νx is gained, which is the initial excitation condition for the calculation of internal sloshing force Fx. Then, the ship motion is modified based on iterative computations under the union action of ice-breaking force and liquid sloshing load. The sloshing simulation under the LNG tank is studied with the modified ship motion. Moreover, an ice-breaking LNG ship with three-leaf type tank is used for case study. The internal LNG sloshing is simulated with three different liquid heights, including free surface shape and sloshing pressure distribution at a given moment, pressure curves at monitoring points on the bulkhead. This present method is effective to solve the sloshing simulation during ice-breaking process, which could be a good reference for the design of the polar ice-breaking LNG carrier.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.3
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• pp.393-398
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• 2022

During the test operation period of the wind profiler prototype, radio frequency interference (RFI) contamination occurred in the spectrum. The reference of the RFI that removed the algorithm appearing in the wind profiler spectrum were investigated, and a new algorithm was developed to remove the RFI. First, it was filtered with a threshold value of 0.1 m/s of the spectral width, and the range of the number of gates with the same radial velocity was determined according to whether the beam was a vertical beam or an oblique beam. RFI contamination was removed through filtering and scanning of non-weather signals, and the continuity of wind vectors calculated from the improved spectral radial velocity was verified.

• Tribology and Lubricants
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• v.38 no.2
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• pp.63-69
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• 2022

In this research, the rotordynamic characteristics of the labyrinth seal with and without swirl brake were predicted using the computational fluid dynamic (CFD) model. Based on previous studies, a simple swirl brake consisting of square vanes without stagger angle is designed and placed in front of the seal inlet. The rotating frame of reference is utilized to consider the whirling motion of the rotor in the steady-state analysis since the whirling motion is transient behavior in nature. CFD analysis was performed in the range of -1 to 1 pre-swirl ratio for a given seal and swirl brake design and operating conditions. The CFD analysis result shows that the swirl brake effectively reduces the pre-swirl since the circumferential fluid velocity of labyrinth seal with swirl brake was lower than that without swirl brake. The cross-coupled stiffness coefficient, which is greatly affected by the circumferential fluid velocity, increased with an increasing pre-swirl ratio in a seal without a swirl brake but showed a low value in a seal with a swirl brake. The change in the damping coefficient was relatively small. The effective damping coefficient of the labyrinth seal with swirl brake was generally constant and showed a higher value than the labyrinth seal without swirl brake.

• Journal of Auto-vehicle Safety Association
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• v.16 no.1
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• pp.6-11
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• 2024

This paper presents a motion planning algorithm of autonomous racing vehicles for mimicking the characteristics of a human driver. Time optimal maneuver of a race car has been actively studied as a major research area over the past decades. Although the time optimization problem yields a single time series solution of minimum time maneuver inputs for the vehicle, human drivers achieve similar lap times while taking various racing lines and velocity profiles. In order to model the characteristics of a specific driver and reproduce the motion, a stochastic motion planning framework based on kernelized motion primitive is introduced. The proposed framework imitates the behavior of the generated reference motion, which is based on a small number of human demonstration laps along the racetrack using Gaussian mixture model and Gaussian mixture regression. The mean and covariance of the racing line and velocity profile mimicking the driver are obtained by accumulating the outputs tested at equidistantly sampled input points. The results confirmed that the obtained lateral and longitudinal motion simulates the driver's driving characteristics, which are feasible for actual vehicle test environments.

• Fire Science and Engineering
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• v.31 no.1
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• pp.50-57
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• 2017

The present article discusses the response characteristics of smoke detector chamber due to dust and wind velocity. Although situations have improved in terms of early sensing of fires as the smoke detectors are applied indoors, studies tend to place insufficient focus on the side effects and malfunction that can be caused by diversified life dust produced indoors and environmental requirements, etc. Therefore, in the present study, 4 types of photoelectric smoke detectors with different forms and structures of smoke chamber were selected as the experimental objects, and dust test was conducted with fly ash, talcum powder and fiber dust as experiment samples to study indoor applicability of the smoke detectors in terms of their response to diversified dust and wind velocity. Also, to observe response characteristics due to pollution level inside the smoke chamber, wind velocity for dust test were set additionally at 0.25 m/s, 0.5 m/s, and 1.0 m/s. Based to the experimental results, fly ash, talcum powder, and fiber dust (black hair powder) were found to be suitable at the dust test reference wind velocity conditions of 0.25 m/s for both operation test and non-operation test after dust application. On the other hand, under the harsh wind velocity conditions of 0.5 m/s and 1.0 m/s, malfunction of unwanted alarm was observed in non-operation tests in the case of fly ash and talcum powder, and non-operation was confirmed to occur in the case of fiber dust as the alarm failed to operate normally in operation tests.

• Journal of Conservation Science
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• v.34 no.2
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• pp.97-106
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• 2018

The lime-soil mixture on barrier (LSMB) tomb is a representative type of tomb from the Joseon Dynasty. It is an important reference for understanding the society and funeral culture of that time. The LSMB excavated at the Gungri site were classified with manufacturing type. The ultrasonic velocity and rebound hardness method were used to estimate the physical properties of the LSMB. The strength values on the tomb of layered wall were different depend on measuring method. The compressive strengths of the tomb with layered wall, which is calculated by ultrasonic velocity and rebound hardness ranged from 4.0 to 355 (mean 43.6) $kgf/cm^2$ and 18.8 to 538 (mean 245.2) $kgf/cm^2$ ranges. The damage to the tomb with integrated wall during excavation and removal of the corpse could be a reason for the difference in results obtained using ultrasonic velocity method. Compressive strengths of tombs with integrated wall, which is calculated by ultrasonic velocity and rebound hardness ranged from 5.7 to 793 (mean 281.6) $kgf/cm^2$ and 4.5 to 550.5 (mean 172.4) $kgf/cm^2$ values. Physical properties on the tombs of integrated wall had different in compressive strength value but showed similar tendency. Thus, evaluation of the physical properties has shown that measuring ultrasonic velocity and rebound hardness methods are more effective in the LSMB with integrated walls. Further, the strength values obtained through the rebound hardness method are more constant than those obtained through the ultrasonic method due to the small detection area required by the former.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.11 no.2
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• pp.62-70
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• 2005

The determination of peripheral nerve conduction velocity is an important part to electrodiagnosis. Its value as neurophysiologic investigative procedure has been known for many years but normal value of median and ulnar motor nerve was poorly reported in Korea. To evaluate of median and ulnar motor nerve terminal latency, amplitude of CMAP(compound muscle action potential), conduction velocity and F-wave latency for obtain clinically useful reference value. 71 normal volunteers(age, 19-65 years; 142 hands) examined who has no history of peripheral neuropathy, diabetic mellitus, chronic renal failure, endocrine disorders, anti-cancer medicine, anti-tubercle medicine, alcoholism, trauma, radiculopathy. Nicolet Viking II was use for detected terminal latency, amplitude of CMAP, conduction velocity and F-wave latency of median and ulnar motor nerve. Data analysis was performed using SPSS. Descriptive analysis was used for obtain mean and standard deviation, independent t-test was used to compare between Rt and Lt side also compare between different in genders. The results are summarized as follows: 1. Median motor nerve terminal latency was right 3.00ms, left 2.99ms and there was no significantly differences between right and left side and genders. 2. Median motor nerve amplitude of CMAP was right 17.26mV, left 1750mV and there was no significantly differences between right and left side and genders. 3. Median motor nerve conduction velocity was right 57.89m/sec, left 58.03m/sec and there was no significantly differences between right and left side and genders. 4. Median motor nerve F-wave latency was right 25.74ms, left 25.59ms and there was significantly differences between genders. 5. Ulnar motor nerve terminal latency was right 2.38ms, left 2.45ms and there was significantly differences between right and left side. 6. Ulnar motor nerve amplitude of CMAP was right 15.99mV, left 16.02mV and there was no significantly differences between right and left side and genders. 7. Ulnar motor nerve conduction velocity was right 60.35m/sec, left 59.73m/sec and there was no significantly differences between right and left side and genders. 8. Ulnar motor nerve F-wave latency was right 25.53ms, left 25.57ms and there was significantly differences between genders.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.11 no.2
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• pp.13-18
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• 2005

The ulnar nerve extends down the arm, across the elbow, and into the hand. It provides sensation to the little and ring fingers and activates many of the small muscles in the hand. The determination of peripheral nerve conduction velocity is an important part of ulnar nerve evaluation. The electrodiagnostic value as neurophysiologic investigative procedure has been known for many years but normal value of digital nerve was not reported in Korea. The purpose of this investigation was to measure the digital nerve conduction velocity of ulnar nerve for obtain clinically useful reference value and compare difference in each fingers and then compare with the other countries. 71 normal Korean volunteers (age, 19-65 years; 142 hands) examined who has no history of peripheral neuropathy, diabetic mellitus, chronic renal failure, endocrine disorders, anti-cancer medicine, anti-tubercle medicine, alcoholism, trauma, radiculopathy. Nicolet Viking II (EMG machine) was use for detected conduction velocity and amplitude of digital nerves in ulnar nerve. Data analysis was performed using SPSS. Descriptive analysis was used for obtain mean and standard deviation and independent t-test was used to compare with ring and little finger. Conduction velocity of the right ring finger was 57.44m/sec and little finger was 55.32msec. The left ring finger was 55.55msec and little finger was 54.11msec. Amplitude of the right ring finger was $30.28{\mu}V$ and little finger was $48.36{\mu}V$. The left ring finger was $30.67{\mu}V$ and little finger was $52.76{\mu}V$. There were significantly difference between ring and little in amplitude (p<.05) but there were no statistically difference between conduction velocity of ring and little finger (p>.05). The amplitude of little finger are greater than ring finger. The present results revealed that electodiagnosis can easily perform in little finger for digital nerve of ulnar nerve study.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.201-204
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• 2008

The mobile robot is known as a nonlinear system with constraints. The general tracking controller for the mobile platform has been divided into the kinematic and the dynamic controller. The reason of dividing controller is the constraints. We can get some information through some numerical experiments. When the reference linear and angular velocity were given, the stability of mobile robot without the kinematic controller depend on the start point of reference cart. Therefore this paper composed of two controller for solving tracking problem. The main controller is the dynamic controller which used generally such as the PID controller. And this paper adopts the auxiliary controller in order to compensate the difference of initial point between the reference cart and a mobile robot. Finally, the numerical experiment is performed in order to show the validity of our method.