• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권4호
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• pp.1738-1756
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• 2020

To improve the accuracy and realism of the virtual surgical simulation system, this paper proposes an optimized mass-spring model with shape restoration ability based on volume conservation to simulate soft tissue deformation. The proposed method constructs a soft tissue surface model that adopts a new flexion spring for resisting bending and incorporates it into the mass-spring model (MSM) to restore the original shape. Then, we employ the particle swarm optimization algorithm to achieve the optimal solution of the model parameters. Besides, the volume conservation constraint is applied to the position-based dynamics (PBD) approach to maintain the volume of the deformable object for constructing the soft tissue volumetric model base on tetrahedrons. Finally, we built a simulation system on the PHANTOM OMNI force tactile interaction device to realize the deformation simulation of the virtual liver. Experimental results show that the proposed model has a good shape restoration ability and incompressibility, which can enhance the deformation accuracy and interactive realism.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1764-1773
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• 2018

A-PET is a quad-head PET scanner developed for use in small-animal imaging. The dimensions of its volumetric field of view (FOV) are $46.1{\times}46.1{\times}46.1mm^3$ and the gap between the detector modules has been minimized in order to provide a highly sensitive system. However, such a small FOV together with the quad-head geometry causes image quality degradation. The main factor related to image degradation for the quad-head PET is the mispositioning of events caused by the penetration effect in the detector. In this paper, we propose a precise method for modelling the system at the high spatial resolution of the A-PET using a LOR (line of response) based ML-EM (maximum likelihood expectation maximization) that allows for penetration effects. The proposed system model provides the detection probability of every possible ray-path via crystal sampling methods. For the ray-path sampling, the sub-LORs are defined by connecting the sampling points of the crystal pair. We incorporate the detection probability of each sub-LOR into the model by calculating the penetration effect. For comparison, we used a standard LOR-based model and a Monte Carlo-based modeling approach, and evaluated the reconstructed images using both the National Electrical Manufacturers Association NU 4-2008 standards and the Geant4 Application for Tomographic Emission simulation toolkit (GATE). An average full width at half maximum (FWHM) at different locations of 1.77 mm and 1.79 mm are obtained using the proposed system model and standard LOR system model, which does not include penetration effects, respectively. The standard deviation of the uniform region in the NEMA image quality phantom is 2.14% for the proposed method and 14.3% for the LOR system model, indicating that the proposed model out-performs the standard LOR-based model.

• 한국지반공학회논문집
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• 제22권10호
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• pp.173-181
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• 2006

본 논문에서는 정적 및 액상화와 같은 동적하중을 받는 흙의 거동해석을 위한 두 개의 활성면을 가진 구성모델을 제안하였다. 이 모델은 두 개의 활성면에 기초하고 있으며, 첫번째면은 회전하는 최대전단면을 나타내며 두 번째면은 고정된 수평면을 나타낸다. 이와 같은 두 개의 활성면을 이용하여 본 모델은 초기의 다른 응력상태하에 있는 시료의 직접단순전단시에 발생하는 주응력회전현상을 모델링할 수 있다. 제안된 모델은 초기의 응력비에 관계없이 평균유효응력이 동일할 경우에 유사한 거동을 보이는 흙의 실내실험결과를 묘사할 수 있다 그리고, 배수시 반복 직접단순전단으로 발생하는 흙의 거동 즉 제하시에 나타나는 체적감소 및 대변형에서 발생하는 체적팽창을 묘사할 수 있다. 비배수시의 흙의 정적 및 동적 거동은 배수거동에서 흙 골격사이에 존재하는 물의 구속력을 고려함으로써 해석하였다. 본 모델의 구성관계식은 응력-물의 상관관계를 동시에 묘사할 수 있는 FLAC을 이용하여 구현하였다. 배수 직접단순전단 시험을 이용한 Fraser River Sand의 실험결과를 이용하여 모델을 먼저 검증하였으며, 동일한 입력변수를 이용한 Fraser River Sand 비배수 거동의 예측치와 실험치를 비교하여 검증하였다.

• 한국지반신소재학회논문집
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• 제10권3호
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• pp.25-32
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• 2011

본 연구에서는 자동 흙-함수특성곡선 시험장치를 이용하여 새만금지역에서 채취한 준설토의 모관흡수력과 체적함수비를 측정하였다. 측정결과를 토대로 Van Genuchten(1980)의 방법을 이용하여 흙-함수특성곡선(SWCC)을 산정하였다. 동일한 유효포화도에서 건조과정의 모관흡수력은 습윤과정의 모관흡수력보다 크게 나타났다. Lu and Likos(2006)의 방법을 이용하여 모관흡수력에 따른 흡입응력을 산정하고, 흙-함수특성곡선(SWCC)의 불포화 관련계수를 토대로 흡입응력특성곡선(SSCC)을 예측하였다. 건조과정의 흡입응력은 유효포화도가 증가함에 따라 증가하다가 감소하지만 습윤과정의 흡입응력은 유효포화도가 증가함에 따라 지속적으로 감소한다. 또한 동일한 유효포화도에서 건조과정의 흡입응력은 습윤과정의 흡입응력보다 크게 나타났다. 한편 van Genuchten(1980)의 방법을 이용하여 투수계수함수(HCF)를 예측하였다. 체적함수비가 증가함에 따라 불포화 투수계수는 증가하며, 동일한 모관흡수력에서 건조과정의 투수계수가 습윤과정의 투수계수보다 크게 나타났다. 흙-함수특성곡선(SWCC)과 흡입응력특성곡선(SSCC)의 산정결과에 의하면 건조 및 습윤과정에서 흡입응력 혹은 모관흡수력에 대한 이력현상이 발생되었다. 이러한 이력현상은 흙입자 사이의 간극수로 인한 잉크병 효과에 의한 것이다.

• Korean Chemical Engineering Research
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• 제51권4호
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• pp.506-512
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• 2013

바이오매스 및 저등급 석탄인 갈탄은 잠재력이 큰 에너지원으로 이들을 가스화하여 합성가스를 얻으면 발전을 하거나 수송용 연료를 생산할 수 있다. 본 연구에서는 상압의 열천칭 반응기(thermobalance)에서 woodchip, 톱밥, 갈탄의 수증기 가스화반응의 kinetics를 조사하였다. 가스화 온도 $600{\sim}900^{\circ}C$, 수증기 분압 20~90 kPa 범위에서 수증기 가스화 반응을 수행하였다. 세 가지의 기체-고체 화학반응모델들이 가스화반응의 거동을 묘사하는 능력을 비교하였다. 이들 중에서 탄소전환율의 변화를 가장 잘 나타내는 modified volumetric model을 사용하여 가스화반응의 kinetic 정보를 도출하였다. Arrehenius plot으로부터 얻어진 시료들의 활성화에너지는 문헌상의 범위 내에서 얻어졌으며 톱밥 > woodchip > 갈탄의 순으로 나타났다. 각 시료에 대하여 수증기 분압에 대한 반응차수를 결정하였으며, 가스화공정 설계의 기초 데이터로서 겉보기 반응속도식을 제시하였다.

• 생물환경조절학회지
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• 제23권3호
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• pp.181-191
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• 2014

Modern commercial greenhouse requires the use of advanced climate control system to improve crop production and to reduce energy consumption. As an alternative to classical sensor-based control method, this paper introduces a model-based control method that consists of two models: the predictive model and the evaluation model. As a first step, this paper presents straightforward models to predict the effect of natural ventilation in a greenhouse according to meteorological factors, such as outdoor air temperature, soil temperature, solar radiation and mean wind speed, and structural factor, opening rate of roof ventilators. A multiple regression analysis was conducted to develop the predictive models on the basis of data obtained by computational fluid dynamics (CFD) simulations. The output of the models are air temperature drops due to ventilation at 9 sub-volumes in the greenhouse and individual volumetric ventilation rate through 6 roof ventilators, and showed a good agreement with the CFD-computed results. The resulting predictive models have an advantage of ensuring quick and reasonable predictions and thereby can be used as a part of a real-time model-based control system for a naturally ventilated greenhouse to predict the implications of alternative control operation.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권3호
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• pp.348-363
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• 2013

The use of I-Core sandwich panel has increased in cruise ship deck structure since it can provide similar bending strength with conventional stiffened plate while keeping lighter weight and lower web height. However, due to its thin plate thickness, i.e. about 4~6 mm at most, it is assembled by high power $CO_2$ laser welding to minimize the welding deformation. This research proposes a volumetric heat source model for T-joint of the I-Core sandwich panel and a method to use shell element model for a thermal elasto-plastic analysis to predict welding deformation. This paper, Part I, focuses on the heat source model. A circular cone type heat source model is newly suggested in heat transfer analysis to realize similar melting zone with that observed in experiment. An additional suggestion is made to consider negative defocus, which is commonly applied in T-joint laser welding since it can provide deeper penetration than zero defocus. The proposed heat source is also verified through 3D thermal elasto-plastic analysis to compare welding deformation with experimental results. A parametric study for different welding speeds, defocus values, and welding powers is performed to investigate the effect on the melting zone and welding deformation. In Part II, focuses on the proposed method to employ shell element model to predict welding deformation in thermal elasto-plastic analysis instead of solid element model.

• Nuclear Engineering and Technology
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• 제25권1호
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• pp.154-165
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• 1993

연속시간 마코프프로세스를 이용한 한 통계적 방법에 의한 일차원 지하 핵종이동 모델이 제시되었다. 지하매질은 보편적으로 지하수속도, 분산계수 또는 지연계수 등 물리화학적 변수 등의 비균질성을 보여 일반적인 결정론적 이류분산모델로는 잘 기술되지 않는다. 통계적 모델에서의 최종결과는 시간에 따른 함수로서의 기대값과 그 기대값의 분산도를 보여주는 분산치다. 매질이 균질하다고 생각될 정도로 나뉘어진 구획에 대한 핵종의 농도 분포를 구하여 결정론적인 해석해에 의한 농도분포와 비교하여 비균질 매질, 또는 현저하게 구분되는 다층매질의 경우에 대해서 유용 할 것이라는 결론을 얻었다. 매질을 나눈 구획수가 수치적 분산에 민감한 것으로 나타났지만 해석적 모델에 의해 분산계수가 보정될 수 있었다.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.579-588
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• 2024

The present paper investigates the curvature ductility of confined reinforced concrete (RC) beams with normal (NSC) and high strength concrete (HSC). For the purpose of predicting the curvature ductility factor, an analytical model was developed based on the equilibrium of internal forces of confined concrete and reinforcement. In this context, the curvatures were calculated at first yielding of tension reinforcement and at ultimate when the confined concrete strain reaches the ultimate value. To best simulate the situation of confined RC beams in flexure, a modified version of an ancient confined concrete model was adopted for this study. In order to show the accuracy of the proposed model, an experimental database was collected from the literature. The statistical comparison between experimental and predicted results showed that the proposed model has a good performance. Then, the data generated from the validated theoretical model were used to train the artificial neural network (ANN) prediction model. The R² values for theoretical and experimental results are equal to 0.98 and 0.95, respectively which proves the high performance of the ANN model. Finally, a parametric study was implemented to analyze the effect of different parameters on the curvature ductility factor using theoretical and ANN models. The results are similar to those extracted from experiments, where the concrete strength, the compression reinforcement ratio, the yield strength, and the volumetric ratio of transverse reinforcement have a positive effect. In contrast, the ratio and the yield strength of tension reinforcement have a negative effect.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1991년도 추계학술발표회 논문집 지반공학에서의 컴퓨터 활용 COMPUTER UTILIZATION IN GEOTECHNICAL ENGINEERING
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• pp.255-270
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• 1991

In recent years. finite element methods have been used with increasing effectiveness in analysis of displacements and stresses within soil masses. However, one of the weakest links in the analytical representations used in these methods is the models of the material behaviour. Herein is discribed a modification to the finite element methods that allows solution problems with realistic stress-strain relation for soils. A finite element program for the precision prediction of the stress distribution within foundation has been developed using the elasto-plastic Work-Hardening model. The developed program is verified by comparing the results of this study with the tested results for Sacramento river sand. The main results obtained from the numerical examples are as follows: The vertical total stress increments are insensitive to drainage and constitutive equation of materials. The horizontal total stress increments are considerably affected by the drainage and constitutive equation of materials. The maximum shear stresses are affected by the drainage only in elasto-ptastic meterirals. The excess pore water pressures and the volumetric strains not only are considerably affected by the constitutive equation of materials. but also have almost similar distribution.