• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.1
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• pp.77-84
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• 2023

In autonomous robots, obstacle avoidance is a key feature. Potential Field is the most widely used method in this field. Such method requires real-time calculation of the nearest point of the obstacle from the robot, which involves difficulty of reliably segmenting the obstacle region from the distance sensor data profile. In this paper, Active Min-Depth Filter is introduced to obtain the nearest point of each obstacle using real-time calculation but without segmentation. Through simulations on various sensor noise environments, the robustness of the Active Min-Depth Filter could be confirmed, and successful results were obtained by applying real-world moving robots.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2748-2755
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• 2024

This paper presents two new methods for variance reduction for shielding calculation in Monte Carlo radiation transport. One method is CADIS-NEE, which combines Consistent Adjoint Driven Importance Sampling (CADIS) and next-event estimator (NEE) methods to increase the calculation efficiency of tallies at points. The other is CADIS-deterministic transport (DXTRAN), which combines CADIS and DXTRAN to obtain higher performance than using CADIS and DXTRAN separately. The combination processes are derived and implemented in the hybrid Monte-Carlo-Deterministic particle-transport code NECP-MCX. Various problems are tested to demonstrate the effectiveness of the two methods. According to the results, the two combination methods have higher efficiency than using CADIS, NEE or DXTRAN separately. In a long-distance photon-transport problem, CADIS-NEE converges faster than NEE and the figure of merit (FOM) of CADIS-NEE is 75.6 times of NEE. In a labyrinthine problem, CADIS-DXTRAN's FOM surpasses that of DXTRAN and CADIS by a factor of 45.3 and 17.7, respectively. Therefore, it is advisable to employ these two novel methods selectively in appropriate scenarios to reduce variance.

• Journal of Korean Society of Forest Science
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• v.97 no.6
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• pp.611-616
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• 2008

The investigation was accomplished on the test area in Forest Practice Research Center in order to compare Point Grid method with Bufferring method in process of the calculation of the Actual Mean Skidding Distance with the GIS aided harvesting method. the investigation site amounted to 264.9 ha in area and 32.67 m in the road density, 306.1 m in road spacing. the Net Correction Factor (Kn) was 1.53 in both sides skidding. the theoretical mean skidding distance was 72.52 m. the shortest mean skidding distance amounted to 149.57 m with point grid method and 139.68 m with Buffering methode. skidding distance correction factor (Kr) was 2.15. actual mean skidding distance amounted to 251.51 m and factor of wood assortment skidding (Kg) was 3.29. when the tractor (Dongyang) and tower yader (Koller 303) are used on investigation site, the logging cost is calculated 11,808 Won with Tractor below 25% slope and 12,336 won with Tractor between 25~55% slope, 10,020 won with Tower Yarder more than 55% slope.

• Journal of Korean Society of Transportation
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• v.22 no.6
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• pp.101-108
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• 2004

The new transit fare in the Seoul Metropolitan is basically determined based on the distance-based fare system (DBFS). The total fare in DBFS consists of three parts- (1) basic fare, (2) transfer fare, and (3) extra fare. The fixed amount of basic fare for each mode is charged when a passenger gets on a mode, and it proceeds until traveling within basic travel distance. The transfer fare may be added when a passenger switches from the present mode to another. The extra fare is imposed if the total travel distance exceeds the basic travel distance, and after that, the longer distance the more extra fare based on the extra-fare-charging rule. This study proposes an algorithm for finding minimum fare route in DBFS. This study first exploits the link-label-based searching method to enable shortest path algorithms to implement without network expansion at junction nodes in inter-modal transit networks. Moreover, the link-expansion technique is adopted in order for each mode's travel to be treated like duplicated links, which have the same start and end nodes, but different link features. In this study, therefore, some notations associated with modes can be saved, thus the existing link-based shortest path algorithm is applicable without any loss of generality. For fare calculation as next steps, a mathematical formula is proposed to embrace fare-charging process using search process of two adjacent links illustrated from the origin. A shortest path algorithm for finding a minimum fare route is derived by converting the formula as a recursive form. The implementation process of the algorithm is evaluated through a simple network test.

• Journal of the Korean Institute of Landscape Architecture
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• v.47 no.1
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• pp.1-9
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• 2019

The objective of this study was to derive the served distance of the senior-friendly park considering physical changes, which were estimated through a comparison experiment at an actual target site. The time to walk 500m was examined because 500m is considered the served distance of a neighborhood park and as a standard set by the city. The mean walking time of the control group (younger than 65 years) was 536 seconds, while that of the treatment group (older than 65 years) was 889 seconds, which was approximately 1.7 times longer than the control group. The results of this study also showed that the walking time of females was longer than that of males when they were older than 65 years old. The walking velocities of the control group and the treatment groups were also calculated using the mean walking time. The weight estimated by a proportional formula was 0.6. When it was applied to 500m, which is the served distance of a neighborhood park, the served distance of the senior-friendly park was estimated as 300m. Lastly, the green service excluded area was quantified by applying the 300m, the served distance of a senior-friendly park, to the Jung-gu, Daegu, which had the highest elderly population in the Daegu Metropolitan City. The results of this calculation showed that the area served by a city park was $2,425,747m^2$ and the area excluded from the city park service was $4,627,700m^2$ for senior citizens. The results also showed that, in terms of the distributive equity, the administrative districts received unequal am ounts of urban green area services.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1276-1283
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• 2002

Recently, HSDI (High Speed Direct Injection) diesel engine has been spotlighted as a next generation engine because it has a good potential for high thermal efficiency and fuel economy. This study was carried out to investigate the in-cylinder flow characteristics generated in a 4-valve small diesel cylinder head with a tangential and helical intake port. The flow characteristics such as coefficient of flow rate(Cf), swirl ratio (Rs), and mass flow rate (ms) were measured in the steady flow test rig using the impulse swirl meter and the analysis of in-cylinder flow field was conducted by experiment using the PIV and calculation using the commercial CFD code. As the results from steady flow test indicate, the mass flow rate of the cylinder head with a short distance between the two intake ports is increased over 13% than that of the other head. However, the non-dimensional swirl ratio is decreased approximately 15%. From in-cylinder flow characteristics obtained by PIV and CFD calculation, we found that the swirl center was eccentric from the cylinder center and the velocity distribution became uniform near the TDC. In addition, the results of the calculation are good agreement with the experimental results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.10
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• pp.999-1004
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• 2011

In this paper, calculation method of mutual inductance for two circular coils which are widely used in wireless power transfer system and analysis results using the method are proposed. Two circular coils are arranged in a perpendicular way. For calculation of the mutual inductance, an Rx coil placed perpendicularly with the other coil is uniformly subdivided into many unit cells and both magnetic flux density linked with the Rx coil at each unit cell and the total magnetic flux density of the Rx coil are obtained. Two circular coils are considered as a filamentary coil and uniform current density on each coil is assumed. For verification, helical and spiral coils are fabricated. As a result of measurement in 50 cm to 100 cm distance, theoretical mutual inductance is almost agreed with measured one.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.2
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• pp.27-38
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• 1997

This paper is concerned with the calculation of the wave resistance for SWATH ships based on a low order Rankine source panel method. Two types of free surface boundary conditions, Dawson type (double model approximation) and Kelvin type (free stream approximation) are used. For the free surface boundary calculation, an analytic differentiation is employed instead of implementing a finite difference scheme. Then, the radiation condition is satisfied by, so called, the panel shift method. The numerical results using the above two methods are compared with those using the thin ship/modified slender body approximation and also with the experimental results. The SWATH models considered are a single strut SWATH and a twin strut SWATH together with the variations of two demihull separation distance. In order to prove the validity of the program developed, the numerical calculations for a Wigley mono hull and Wigley twin hulls are compared with the available experimental results.

• Progress in Medical Physics
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• v.10 no.1
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• pp.55-62
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• 1999

In an effort to study the characteristics of x-rays utilized in radiation therapy, we calculated the energy distribution and the mean energy of x-rays generated from a tungsten target bombarded by 6, 10, and 15 MeV electron beams, using a Monte Carlo technique. The average photon energies calculated as a function of the beam radius lied in 1.4 ∼ 1.6, 2.1 ∼ 2.5 and 2.8 ∼ 3.3 MeV ranges for 4, 10, and 15 MV electron beams, respectively, which turned out to have no strong dependence on the radius. Using the energy distributions of 6,10, and 15 MV x-rays obtained for the target distance of 100 cm, percentage depth doses were determined using Monte Carlo calculations. For the case 10 MV, a comparison was made between our calculation and measurement performed by others. The calculated percentage depth dose appeared somewhat smaller than the measured one except in the surface region. We conclude that this is due to the fact that the beam hardening effect resulting from the flattening filter was not properly allowed for in our Monte Carlo calculations.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.20 no.2
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• pp.111-118
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• 2002

These days, surveying instruments are developing rapidly and the precision is improving continuously. The building of three dimensional terrains of high precision are possible and the calculation of the areas or the volumes have high precision due to the development of the technique of the spatial information system using computer. But actually, in construction site they calculate two-dimensional area using the traditional method, plate table surveying, planimeter, and then get three-dimensional area through multiplying two-dimensional area by the slope correction factor. In this study, we show the defect and inefficiency of the calculation of area by the traditional methods and survey the area with Electric Distance Measurement and GPS instrument. With this data, we made the three dimensional terrain model and calculated two-dimensional area, three-dimensional area. After that, we compared areas that calculated by algorithm of triangulated irregular network and analysis of grid method with standard area that calculated by the traditional method. Finally, this paper suggested more effective and precious method in calculating three-dimensional area.