• Journal of Korean Society for Atmospheric Environment
• /
• v.20 no.1
• /
• pp.119-128
• /
• 2004

The nitrate concentrations in PM$_{2.5}$ and TSP measured at Gosan, Jeju Island, Korea, between March 1998 and February 2002, are discussed. Especially, the characteristics of high nitrate concentration days were analyzed. High nitrate concentration cases in PM$_{2.5}$ were highly correlated with anthropogenic species such as NH$_4$$^{[-10]}$ , and high nitrate concentration cases in TSP were highly correlated with crustal species such as nss-Ca$^{2+}$ and nss -Mg$^{2+}$ Backward trajectory analysis results show the cases of high correlation between nitrate and anthropogenic species occurred when the air parcels moved from China, and the cases of high correlation between nitrate and crustal species occurred when the air parcels moved from Mongolia. Also, high nitrate concentration cases occurred most often in spring (65%) when the air parcels moved from Mongolia and China.ina.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.19 no.5
• /
• pp.463-469
• /
• 2014

This paper proposes a maximum torque operation strategy for the direct torque control of a surface-mounted permanent-magnet synchronous motor (SPMSM). The proposed method analyzes the available operation region of the stator flux of the SPMSM under voltage and current constraints. Based on this analysis, the optimal stator flux trajectory that yields the maximum torque is obtained across the entire operation region, including constant torque and constant power regions. The proposed strategy is also applicable in the flux-weakening region II operation of the SPMSM, which has no speed limit. The validity of the proposed method is verified through experiments conducted on an 800 W SPMSM drive system.

• Asian Journal of Atmospheric Environment
• /
• v.4 no.1
• /
• pp.20-25
• /
• 2010

The gaseous $^{222}Rn$ concentration at the level of clouds was estimated by using the wet scavenging model of its decay products with the observed data of environmental radiation at the ground. And the origin of the $^{222}Rn$ was also discussed. The estimation was done for a precipitation event on Dec. 26-27, 2003, when a large increase of the radiation was observed in Tokai-mura in Ibaraki, Japan. From a backward trajectory analysis, the origin of $^{222}Rn$ atoms for that event was traced back to the northeastern part of China, and it was expected that the large amount of $^{222}Rn$ emitted in the northeastern part of China was transported to Tokai-mura by the Eurasian continental air mass.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.05a
• /
• pp.141-144
• /
• 2003

For the analysis of combustion instabilities of a liquid locket engine, a simple spray combustion model has been analyzed by the Euler-Lagrange method. Gas temperature, droplet trajectory, and droplet radius have been evaluated on 2-D axisymmetric coordinates. The Euler-Lagrange method has been shown to have a good tendency of gas temperature distribution as well as droplet trajectory and radius change.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.8
• /
• pp.942-950
• /
• 2011

Automation is important in modern agricultural environment, which demands the highest level of technology. In the paper an independent four-wheel steering driving platform is developed especially for horticulture in glass house farm. Mathematical modeling of the four wheel system is carried out for smooth movement. The relationships between steering angle, the turning radius, and escape trajectory are simulated using the dynamic analysis program. Optimal driving algorithm is sought through the performance evaluation.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.05a
• /
• pp.566-569
• /
• 2000

This hybrid position/force control for the dynamic walking of the biped robot is performed in this paper. After the biped robot was modeled with 14 degrees of freedom of the multibody dynamics, the equations of motion are constructed using velocity transformation technique. Then the inverse dynamic analysis is performed for determining the driving torques and the ground reaction forces. From this analysis, obtains the maximum ground contact force at the moment of contacting which act on the rear of the sole of swing leg and the distribution curve of the ground reaction. Because these maximum force and distribution type acts an important role to the stability of the whole dynamic walking, they are reduced and distributed smoothly by means of the trajectory of the modified ground reaction force. This new trajectory is used to the reference input for more stable dynamic walking of the whole walking region.

• Journal of applied mathematics & informatics
• /
• v.23 no.1_2
• /
• pp.243-256
• /
• 2007

This paper deals with determining the sufficient conditions of minimum for the class of problems in which the necessary conditions of optimum are satisfied in the strengthened form Legendre-Clebsch. To this paper, we shall use the sweep method which analysis the conditions of existence of the conjugated points on the optimal trajectory. The study we have done evaluates the command variation on the neighboring optimal trajectory. The sufficient conditions of minimum are obtained by imposing the positivity of the second variation. The results that this method offers are applied to the problem o the orbital rendez-vous for the linear case of the equations of movement.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.764-765
• /
• 2017

A trajectory analysis program was developed using a 3 DOF model to analyze KSLV-II performance with the reducing weight. The program estimates the injection performance on the SSO orbit, which is determined as payload weight for the orbit, with various vehicle structural ratios. The KSLV-II can transport 2.58 ton to the target orbit with a reduced structural ratio similar to the Angara rockets.

• International Journal of Highway Engineering
• /
• v.15 no.1
• /
• pp.65-73
• /
• 2013

PURPOSES: This paper presents the results of computer simulations of roadside safety barrier, called by safety roller guardrail, consisting of rotational roller, rotation control plate, post and subsidiary members. The rotation roller and rotation control plate are made by EVA(ethylene vinyl acetate), and PE(polyester), respectively. METHODS: The occupant risk analysis has been carried out under vehicle crash condition for high containment level of SB-4 for the purpose of local road. Simulations are performed with the finite element code LS/DYNA-3D. RESULTS: The numerical results obtained by LS/DYNA-3D software from the viewpoints of vehicle stability, vehicle trajectory, occupant risk, etc. CONCLUSIONS: It is noted that not only impact severity is drastically reduced but also vehicle trajectory is improved due to the characteristics of energy absorption and rotation pattern of EVA rollers connected by control plates.

• Journal of Korean Society of Water and Wastewater
• /
• v.16 no.6
• /
• pp.663-669
• /
• 2002

Electro-flotation (EF) has shown advantages, such as a high removal efficiency and easy control of bubble generation, over dissolved air flotation. However, the fundamental characteristics of the process have not been investigated in detail. According to recent modeling results from trajectory analysis, the size of the bubble is one of the most important factors that affect the efficiency of collision between bubble and particle. In this paper, the size characteristics of bubbles generated from EF under various conditions are measured using a new method for bubble size measurement, the Particle Counter Method (PCM). The size of the generated bubbles was found to be constant with respect to applied voltage but to vary with the electrode materials. These results and their implications are discussed.