• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.1
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• pp.1-12
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• 2021

In the design of a tunnel boring machine (TBM), the excavation efficiency of the equipment depends on the design of the cutter head, which is directly in contact with the ground. Especially, the allocation of disc cutter is crucial issue. Disc cutters can be divided into center cutter zone, inner cutter zone and transition cutter zone depending on where they are placed. Many studies have been conducted to identify optimal cutting conditions for face cutters. However, research to determine the optimal cutting conditions for the transition cutter has been relatively incomplete. In this study, to identify the optimal cutting conditions for the transition cutter, numerical analysis using discrete element method was performed, and the specific energy curve according to the angle between the transition cutters was drawn to find out the optimum cutting conditions. The results show that the angle between the transition cutters showing minimum specific energy in the transition cutter zone is 9°. Transition cutter zone was divided into three sections according to the slope angle of the transition cutter. It is also found that, the greater the slope angle of the transition cutter. This finding shows good agreement with the present design of transition cutter zone.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.217-224
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• 2024

This paper proposes an efficient dimension reduction method (DRM) that considers the nonlinearity of the performance functions in reliability-based design optimization (RBDO). The dimension reduction method evaluates the reliability more accurately than the first-order reliability method (FORM) using integration quadrature points and weights. However, its efficiency is hindered as the number of quadrature points increases owing to the need for an additional evaluation of the performance function. In this study, we assessed the nonlinearity of the performance function in RBDO and proposed criteria for determining the number of quadrature points based on the degree of nonlinearity. This approach suggests adjusting the number of quadrature points during each iteration of the RBDO process while maintaining the accuracy of theDRM while improving the computational efficiency. The nonlinearity of the performance function was evaluated using the angle between the vectors used in the maximum probable target point (MPTP) search. Numerical tests were conducted to determine the appropriate number of quadrature points according to the degree of nonlinearity. Through a 2D numerical example, it is confirmed that the proposed method improves the efficiency while maintaining the accuracy of the dimension reduction method or Monte Carlo Simulation (MCS).

• Journal of the Korean GEO-environmental Society
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• v.25 no.4
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• pp.21-28
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• 2024

In this study, a polyhedral domain decomposition method for Smoothed Particle Hydrodynamics (SPH) analysis is introduced. SPH which is one of meshless methods is a numerical analysis method for fluid flow simulation. It can be useful for analyzing fluidic soil or fluid-structure interaction problems. SPH is a particle-based method, where increased particle count generally improves accuracy but diminishes numerical efficiency. To enhance numerical efficiency, parallel processing algorithms are commonly employed with the Cartesian coordinate-based domain decomposition method. However, for parallel analysis of complex geometric shapes or fluidic problems under dynamic boundary conditions, the Cartesian coordinate-based domain decomposition method may not be suitable. The introduced polyhedral domain decomposition technique offers advantages in enhancing parallel efficiency in such problems. It allows partitioning into various forms of 3D polyhedral elements to better fit the problem. Physical properties of SPH particles are calculated using information from neighboring particles within the smoothing length. Methods for sharing particle information physically separable at partitioning and sharing information at cross-points where parallel efficiency might diminish are presented. Through numerical analysis examples, the proposed method's parallel efficiency approached 95% for up to 12 cores. However, as the number of cores is increased, parallel efficiency is decreased due to increased information sharing among cores.

• Journal of Radiation Protection and Research
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• v.33 no.2
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• pp.61-65
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• 2008

Objective: To reduce urinary side effects in prostate cancer patients receiving radiation, patients were asked to drink certain amount of water to maintain bladder volume constant and the bladder volumes were measured weekly using ultrasound scanner. Materials and Methods: Twenty-six patients with prostate cancer who received radiation between December 2002 and August 2007 were enrolled in this study. Thirteen patients were enrolled in experimental group. These patients were asked to drink 450 cc of water, one hour prior to simulation, CT scan, and treatment. The other thirteen patients were given no information about bladder filing. Bladder, prostate, and rectum were contoured on CT and volumes were calculated. 3D conformal treatment planning was performed and effective volumes of bladder were calculated when a prescription dose of 70.2 Gy was delivered. For the patients in experimental group, bladder volumes were measured weekly using ultrasound scanner for 6-8 weeks and the bladder volume variations were analyzed. Results: Average bladder volumes and standard deviations obtained at CT scanning were $283.5{\pm}114.0\;cc$ (40%) and $181.2{\pm}120.1\;cc$ (66%) in experimental and control groups, respectively. Although it was not statistically significant, there was correlation between the bladder volumes measured from CT and ultrasound. The volumes measured using ultrasound scanner were 62% lower than the volumes using CT images on average. There was significant variations in volumes measured weekly for 6-8 weeks. It ranged between 33 - 75 %. Conclusion: Our results showed that it is possible to obtain larger bladder volume if they are asked to drink certain amount of water prior to CT scan. However, patients were unable to maintain constant bladder volumes over the 6-8 weeks of treatment period although they were asked to drink constant amount of water.

• Korean Journal of Environmental Biology
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• v.40 no.4
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• pp.413-422
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• 2022

Barnea manilensis is a bivalve which bores soft rocks, such as, limestone or mudstone in the low intertidal zone. They make burrows which have narrow entrances and wide interiors and live in these burrows for a lifetime. In this study, the morphology and the microstructure of the valve of rock-boring clam B. manilensis were observed using a stereoscopic microscope and FE-SEM, respectively. The chemical composition of specific part of the valve was assessed by energy dispersive X-ray spectroscopy (EDS) analysis. 3D modeling and structural dynamic analysis were used to simulate the boring behavior of B. manilensis. Microscopy results showed that the valve was asymmetric with plow-like spikes which were located on the anterior surface of the valve and were distributed in a specific direction. The anterior parts of the valve were thicker than the posterior parts. EDS results indicated that the valve mainly consisted of calcium carbonate, while metal elements, such as, Al, Si, Mn, Fe, and Mg were detected on the outer surface of the anterior spikes. It was assumed that the metal elements increased the strength of the valve, thus helping the B. manilensis to bore sediment. The simulation showed that spikes located on the anterior part of the valve received a load at all angles. It was suggested that the anterior part of the shell received the load while drilling rocks. The boring mechanism using the amorphous valve of B. manilensis is expected to be used as basic data to devise an efficient drilling mechanism.

• Radiation Oncology Journal
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• v.19 no.1
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• pp.66-73
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• 2001

Purpose : For the research of Boron Neutron Capture Therapy (BNCT), fast neutrons generated from the MC-50 cyclotron with maximum energy of 34.4 MeV in Korea Cancer Center Hospital were moderated by 70 cm paraffin and then the dose characteristics were investigated. Using these results, we hope to establish the protocol about dose measurement of epi-thermal neutron, to make a basis of dose characteristic of epi-thermal neutron emitted from nuclear reactor, and to find feasibility about accelerator-based BNCT. Method and Materials : For measuring the absorbed dose and dose distribution of fast neutron beams, we used Unidos 10005 (PTW, Germany) electrometer and IC-17 (Far West, USA), IC-18, ElC-1 ion chambers manufactured by A-150 plastic and used IC-l7M ion chamber manufactured by magnesium for gamma dose. There chambers were flushed with tissue equivalent gas and argon gas and then the flow rate was S co per minute. Using Monte Carlo N-Particle (MCNP) code, transport program in mixed field with neutron, photon, electron, two dimensional dose and energy fluence distribution was calculated and there results were compared with measured results. Results : The absorbed dose of fast neutron beams was $6.47\times10^{-3}$ cGy per 1 MU at the 4 cm depth of the water phantom, which is assumed to be effective depth for BNCT. The magnitude of gamma contamination intermingled with fast neutron beams was $65.2{\pm}0.9\%$ at the same depth. In the dose distribution according to the depth of water, the neutron dose decreased linearly and the gamma dose decreased exponentially as the depth was deepened. The factor expressed energy level, $D_{20}/D_{10}$, of the total dose was 0.718. Conclusion : Through the direct measurement using the two ion chambers, which is made different wall materials, and computer calculation of isodose distribution using MCNP simulation method, we have found the dose characteristics of low fluence fast neutron beams. If the power supply and the target material, which generate high voltage and current, will be developed and gamma contamination was reduced by lead or bismuth, we think, it may be possible to accelerator-based BNCT.

• Progress in Medical Physics
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• v.22 no.4
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• pp.190-197
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• 2011

Currently, the dose distribution calculation used by commercial treatment planning systems (TPSs) for high-dose rate (HDR) brachytherapy is derived from point and line source approximation method recommended by AAPM Task Group 43 (TG-43). However, the study of Monte Carlo (MC) simulation is required in order to assess the accuracy of dose calculation around three-dimensional Ir-192 source. In this study, geometry factor was calculated using segmented sources integration method by dividing microSelectron HDR Ir-192 source into smaller parts. The Monte Carlo code (MCNPX 2.5.0) was used to calculate the dose rate $\dot{D}(r,\theta)$ at a point ($r,\theta$) away from a HDR Ir-192 source in spherical water phantom with 30 cm diameter. Finally, anisotropy function and radial dose function were calculated from obtained results. The obtained geometry factor was compared with that calculated from line source approximation. Similarly, obtained anisotropy function and radial dose function were compared with those derived from MCPT results by Williamson. The geometry factor calculated from segmented sources integration method and line source approximation was within 0.2% for $r{\geq}0.5$ cm and 1.33% for r=0.1 cm, respectively. The relative-root mean square error (R-RMSE) of anisotropy function obtained by this study and Williamson was 2.33% for r=0.25 cm and within 1% for r>0.5 cm, respectively. The R-RMSE of radial dose function was 0.46% at radial distance from 0.1 to 14.0 cm. The geometry factor acquired from segmented sources integration method and line source approximation was in good agreement for $r{\geq}0.1$ cm. However, application of segmented sources integration method seems to be valid, since this method using three-dimensional Ir-192 source provides more realistic geometry factor. The anisotropy function and radial dose function estimated from MCNPX in this study and MCPT by Williamson are in good agreement within uncertainty of Monte Carlo codes except at radial distance of r=0.25 cm. It is expected that Monte Carlo code used in this study could be applied to other sources utilized for brachytherapy.

• Korean Journal of Agricultural Science
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• v.12 no.1
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• pp.118-127
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• 1985

The grain temperature is a crucial factor determining the deterioration rate of stored grain. Therefore, it is used to be predicted in order to evaluate the various stored methods rapidly and inexpensively. In this study, a mathematical model was developed to simulate the temperatures of grain stored in a cylinderical bin. It was formulated for the two dimensional heat transfer by the finite difference method. Then, it was verified statistically using the actual test deta and the predicted. The changes of grain temperature were analyed using the simulated data of one year for a safe stoarge and the following results were obtained: 1. Simulation model developed by the finite difference method was validated with the actual and the predicted grain temperatures and it's result showed that it could predict the grain temperature of storage bin reasonably well. 2. Grain temperature near the wall of storage bin were changed with $6-7^{\circ}C$ higher then average atmospheric temperature from June to September. Therefore, the parts of stored grain near the wall is supposed to be deteriorated fast. 3. When the dimension of bin diameter is about the same as the bed height, the changes of grain temperature of radial direction was higher than the verticals. 4. The predicted temperature showed that the grain temperature of which were from the end of April to mid October were higher than the safe storage limit at Yusung, Korea.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.1
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• pp.27-35
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• 2017

Purpose: On the left side, breast cancer patients have more side effects than those on the right side because of unnecessary doses in normal organs such as heart and lung. DIBH is performed to reduce this. To evaluate the dose of peripheral organs in the left breast cancer including supraclavicular lymph nodes and internal mammary lymph nodes according to the treatment planning method of Conventional Radiation Therapy, Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy. Materials and Methods: We performed CT-simulation using free breathing and deep inspiration breath-hold technique for 8 patients including left supraclavicular lymph nodes and internal mammary lymph nodes. Based on the acquired CT images, the contour of the body is drawn and the convention is performed so that $95%{\leftarrow}PTV$, $Dmax{\leftarrow}110%$. Conventional Radiation Therapy used a one portal technique on the supraclavicular lymph node and used a field in field technique tangential beam on the breast. Intensity Modulated Radiation Therapy was composed of 7 static fields. Volumetric Modulated Arc Therapy was planned using 2 ARC with a turning radius of $290^{\circ}$ to $179^{\circ}$. The peripheral normal organs dose was analyzed by referring to the dose volume of Eclipse. Results: By applying the deep inspiration breath-hold technique, the mean interval between the heart and chest wall increased $1.6{\pm}0.6cm$. The mean dose of lung was $19.2{\pm}1.0Gy$, which was the smallest value in Intensity Modulated Radiation Therapy. The V30 (%) of the heart was $2.0{\pm}1.9$, which was the smallest value in Intensity Modulated Radiation Therapy. In the left anterior descending coronary artery, the dose was $25.4{\pm}5.4Gy$, which was the smallest in Intensity Modulated Radiation Therapy. The maximum dose value of the Right breast was $29.7{\pm}4.3Gy$ at Intensity Modulated Radiation Therapy. Conclusion: When comparing the values of surrounding normal organs, Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy were applicable values for treatment. Among them, Intensity Modulated Radiation Therapy is considered to be a suitable treatment planning method.

• Radiation Oncology Journal
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• v.28 no.3
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• pp.155-165
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• 2010

Purpose: In order to evaluate the positional uncertainty of internal organs during radiation therapy for treatment of liver cancer, we measured differences in inter- and intra-fractional variation of the tumor position and tidal amplitude using 4-dimentional computed radiograph (DCT) images and gated orthogonal setup kilovolt (KV) images taken on every treatment using the on board imaging (OBI) and real time position management (RPM) system. Materials and Methods: Twenty consecutive patients who underwent 3-dimensional (3D) conformal radiation therapy for treatment of liver cancer participated in this study. All patients received a 4DCT simulation with an RT16 scanner and an RPM system. Lipiodol, which was updated near the target volume after transarterial chemoembolization or diaphragm was chosen as a surrogate for the evaluation of the position difference of internal organs. Two reference orthogonal (anterior and lateral) digital reconstructed radiograph (DRR) images were generated using CT image sets of 0% and 50% into the respiratory phases. The maximum tidal amplitude of the surrogate was measured from 3D conformal treatment planning. After setting the patient up with laser markings on the skin, orthogonal gated setup images at 50% into the respiratory phase were acquired at each treatment session with OBI and registered on reference DRR images by setting each beam center. Online inter-fractional variation was determined with the surrogate. After adjusting the patient setup error, orthogonal setup images at 0% and 50% into the respiratory phases were obtained and tidal amplitude of the surrogate was measured. Measured tidal amplitude was compared with data from 4DCT. For evaluation of intra-fractional variation, an orthogonal gated setup image at 50% into the respiratory phase was promptly acquired after treatment and compared with the same image taken just before treatment. In addition, a statistical analysis for the quantitative evaluation was performed. Results: Medians of inter-fractional variation for twenty patients were 0.00 cm (range, -0.50 to 0.90 cm), 0.00 cm (range, -2.40 to 1.60 cm), and 0.00 cm (range, -1.10 to 0.50 cm) in the X (transaxial), Y (superior-inferior), and Z (anterior-posterior) directions, respectively. Significant inter-fractional variations over 0.5 cm were observed in four patients. Min addition, the median tidal amplitude differences between 4DCTs and the gated orthogonal setup images were -0.05 cm (range, -0.83 to 0.60 cm), -0.15 cm (range, -2.58 to 1.18 cm), and -0.02 cm (range, -1.37 to 0.59 cm) in the X, Y, and Z directions, respectively. Large differences of over 1 cm were detected in 3 patients in the Y direction, while differences of more than 0.5 but less than 1 cm were observed in 5 patients in Y and Z directions. Median intra-fractional variation was 0.00 cm (range, -0.30 to 0.40 cm), -0.03 cm (range, -1.14 to 0.50 cm), 0.05 cm (range, -0.30 to 0.50 cm) in the X, Y, and Z directions, respectively. Significant intra-fractional variation of over 1 cm was observed in 2 patients in Y direction. Conclusion: Gated setup images provided a clear image quality for the detection of organ motion without a motion artifact. Significant intra- and inter-fractional variation and tidal amplitude differences between 4DCT and gated setup images were detected in some patients during the radiation treatment period, and therefore, should be considered when setting up the target margin. Monitoring of positional uncertainty and its adaptive feedback system can enhance the accuracy of treatments.