• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.150-159
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• 2014

A simplified method for the calculation of buckling and vibrational characteristics of initially stressed rectangular plate and antisymmetric angle-ply laminated plates is presented in this paper using the natural frequencies under unloading state. The equation of motion of rectangular plate with two opposite edges simply supported is investigated on the basis of Rayleigh-Ritz method and Mindlin plate theory with effect of the curvature term. The relationships of the non-dimensional natural frequencies with initial stresses the coeffcients of critical buckling and the boundaries of the dynamic principal instability region can be characterized by the non-dimensional natureal frequencies under unloading state. Numerical examples are presented to verify the simplified equations and to illustrate potential applications of the analysis.

• Aerospace Engineering and Technology
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• v.3 no.1
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• pp.188-196
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• 2004

To optimize and limit the axial length of baffle in KSR-III engine, stability rating tests using pulse gun as one of artificial disturbance devices have been done. Decay time and other parameters for the evaluation of stabilization ability of engine to external perturbation have been analyzed to quantify stabilization capacity of engine, in other words, dynamic stability margin. If baffle does not cover flame zone enough which can be considered as collision region of injector, it wasn't be able to suppress external perturbation sufficiently. The limit of combustion stability margin of engine is assumed to be 50 mm length baffle.

• Structural Engineering and Mechanics
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• v.55 no.2
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• pp.435-459
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• 2015

Parametric resonance of shear deformable composite skew plates subjected to non-uniform (parabolic) and linearly varying periodic edge loading is studied for different boundary conditions. The skew plate structural model is based on higher order shear deformation theory (HSDT), which accurately predicts the numerical results for thick skew plate. The total energy functional is derived for the skew plates from total potential energy and kinetic energy of the plate. The strain energy which is the part of total potential energy contains membrane energy, bending energy, additional bending energy due to additional change in curvature and shear energy due to shear deformation, respectively. The total energy functional is solved using Rayleigh-Ritz method in conjunction with boundary characteristics orthonormal polynomials (BCOPs) functions. The orthonormal polynomials are generated for unit square domain using Gram-Schmidt orthogonalization process. Bolotin method is followed to obtain the boundaries of parametric resonance region with higher order approximation. These boundaries are traced by the periodic solution of Mathieu-Hill equations with period T and 2T. Effect of various parameters like skew angle, span-to-thickness ratio, aspect ratio, boundary conditions, static load factor on parametric resonance of skew plate have been investigated. The investigation also includes influence of different types of linearly varying loading and parabolically varying bi-axial loading.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.7
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• pp.574-579
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• 2016

Grid systems used in previous studies were determined to be valid only if the length between the perpendiculars in a model ship was in the range of 6-8 m, and the maximum dynamic trim angle was smaller than $1^{\circ}$. The application of the grid system to a small fishing boat can create numerical instability because the dynamic trim of small boats is generally larger than $3^{\circ}$, and their Froude numbers are in the range of 0.3-0.8. In the present study, resistances of a small fishing boat were stably obtained by reducing the length between the center of buoyancy and the inlet boundary of the numerical domain, and by refining grid cells vertically in a region that would be swept by a free surface. The effective power of the small fishing boat was predicted based on the ITTC-1978 two-dimensional analysis. By using the results of previous towing tank tests, the coefficient of quasi-propulsive efficiency and the brake horsepower at a design draft were calculated.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.1-11
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• 2020

In this study, a hot-firing test of a lab-scale gel rocket motor using liquid kerosene and gelled kerosene as fuel was performed in order to analyze the discrepancy of the static and dynamic pressure between the two fuels. The static pressure, characteristic velocity, and characteristic velocity efficiency of the liquid kerosene and gelled kerosene did not show any significant difference. However, in the case of dynamic pressure characteristics, the pressure oscillation amplitude in a specific high frequency region of the gelled kerosene demonstrated a significantly higher amplitude than liquid kerosene case. This is considered to be the effect of an intrinsic combustion mechanism of the gel propellant, and it can be postulated that this may act as a dominant factor influencing the high frequency combustion instability of the gel rocket motor.

• Journal of the Korean association of regional geographers
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• v.12 no.4
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• pp.475-495
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• 2006

This paper is to analyse a changing space of energy flows in Northeast Asia from geopolitical and geoeconomic perspectives that have been recently promoted for energy security of countries in this region. The research is based on an analytical framework in an integration of political ecology and political economy. Because of an ever-increasing input of energy resources for economic growth and of dramatically increasing price of crude oil and recent instability of oil market, South Korea, China and Japan have been deeply concerned with energy security and conducted very actively geopolitical strategies. And hence the space of energy flows in the region is now in a process of dynamic reconfiguration, in which the project for development of oil and natural gas fields in East Siberia and construction of pipelines to transport them can be seen as one of competitive issues among these countries. In spite of worrying about stagflation due to rapid increase of oil price, such geo-strategies for energy security and reconfiguration of space of energy flows seem to keep the accumulation of capital in this region continue with generation of huge privatized oil companies.

• Atmosphere
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• v.26 no.2
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• pp.227-241
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• 2016

This study investigated the cause of the heavy snowfall that occurred in the East Coast of Korea from 6 February to 14 February 2014. The synoptic conditions were analyzed using blocking index, equivalent potential temperature, potential vorticity, maritime temperature difference, temperature advection, and ground convergence. During the case period, a large blocking pattern developed over the Western Pacific causing the flow to be stagnant, and there was a North-South oriented High-to-Low pressure system over the Korean Peninsula because of this arrangement. The case period was divided into three parts based on the synoptic forcing that was responsible for the heavy snowfall; detailed analyses were conducted for the first and last period. In the first period, a heavy snowfall occurred over the entire Korean Peninsula due to strong updrafts from baroclinic instability and a low pressure caused by potential vorticity located at the mid-troposphere. In the lower atmosphere, a North-South oriented High-to-Low pressure system over the Eastern Korea intensified the easterly airflow and created a convergence zone near the ground which strengthened the upslope effect of the Taebaek Mountain range with a cumulative fresh snowfall amount of 41 cm in the East Coast region. In the last period, the cold air nestled in the Maritime Province of Siberia and Manchuria strengthened much more than that in the first half and extended to the East Sea. The temperature difference between the 850 hPa air and the SST was large and convective clouds developed over the sea. The highest cumulative fresh snow amount of 39.7 cm was recorded in the coastal area during this period. During the entire period, vertically oriented equivalent potential temperature showed neutral stability layer that helped the cloud formation and development in the East Coast. The 2014 heavy snowfall case over the East Coast provinces of Korea were due to: 1) stagnation of the system by blocking pattern, 2) the dynamic effect of mid-level potential vorticity of 1.6 PVU, 3) the easterly air flow from North-South oriented High-to-Low pressure system, 4) the existence of vertically oriented neutral stable layer, and 5) the expansion of strong cold air into the East Sea which created a large temperature difference between the air and the ocean.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.8 no.2
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• pp.57-71
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• 2002

Cervical pain is a rapid increase that is owing to a flexion-extension whiplash injury, unappropriated posture, chronical repetition injury from abdominal position of head and neck, excessive repeating work, chronical deficiency of excercise. Because of that is bring about muscle unbalance, tightness of cervical extensor muscle, weakness of cervical deep flexor muscles, instability of cervical region and reduction of proprioceptive sensor. Recent the role of muscle is more emphasized for preservation of sine stabilization. And cognition of integrated muscular system, importance for the operation and relation is increased to maintain stability of the motor system and pertinent function. Therefore we are going to introduce the sling exercise and stabilization exercise method for advanced efficient of cervical and upper limb and for the muscle strengthening to importance cervical stabilization through neurological program as control the reaction of cervical stabilization. Sling exercise therapy(SET) concept consists of a system of diagnosis and treatment. The system of diagnosis involves testing the muscle's tolerance through progressive loading in open and close kinetic chains. The SET system contains elements such as relaxation, increasing the range of movement, traction, training the stabilizing musculature, sensory-motor exercises, training in open and close kinetic chains, dynamic training of the mobilizing musculature, cardiovascular exercise, group exercise, personal exercise at home Sensory-motor training is an essential element of the SET concept. The emphasis is on closed kinetic chain exercise on an unstable surface, there by achieving optimum stimulation of the sensory-motor apparatus.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.69-77
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• 2005

To optimize and limit the axial length of the baffle of the KSR-III engine, stability rating tests using pulse gun as one of artificial disturbance devices have been done. Generally a rocket engine can be considered to be dynamically stable if a certain imposed external perturbation or pressure oscillation in rocket combustion chamber could be suppressed within a short time period. Decay time and other parameters for the evaluation of stabilization ability of an engine to external perturbation have been analyzed to quantify stabilization capacity of engine, in other words, dynamic stability margin. Baffle not covering flame zone enough which can be considered as collision region of injector wasn't be able to suppress external perturbation sufficiently. The limit of combustion stability margin of engine is assumed to be 50 mm length baffle of the KSR-III engine.

• Journal of the Korean earth science society
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• v.40 no.6
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• pp.584-598
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• 2019

In this study, the effects of air-sea interactions on precipitation over the Seoul-Gyeonggi region of the Korean Peninsula from 28 to 30 August 2018, were analyzed using a Regional atmosphere-ocean Coupled Model (RCM). In the RCM, a WRF (Weather Research Forecasts) was used as the atmosphere model whereas ROMS (Regional Oceanic Modeling System) was used as the ocean model. In a Regional Single atmosphere Model (RSM), only the WRF model was used. In addition, the sea surface temperature data of ECMWF Reanalysis Interim was used as low boundary data. Compared with the observational data, the RCM considering the effect of air-sea interaction represented that the spatial correlations were 0.6 and 0.84, respectively, for the precipitation and the Yellow Sea surface temperature in the Seoul-Gyeonggi area, which was higher than the RSM. whereas the mean bias error (MBE) was -2.32 and -0.62, respectively, which was lower than the RSM. The air-sea interaction effect, analyzed by equivalent potential temperature, SST, dynamic convergence fields, induced the change of SST in the Yellow Sea. In addition, the changed SST caused the difference in thermal instability and kinematic convergence in the lower atmosphere. The thermal instability and convergence over the Seoul-Gyeonggi region induced upward motion, and consequently, the precipitation in the RCM was similar to the spatial distribution of the observed data compared to the precipitation in the RSM. Although various case studies and climatic analyses are needed to clearly understand the effects of complex air-sea interaction, this study results provide evidence for the importance of the air-sea interaction in predicting precipitation in the Seoul-Gyeonggi region.