• 한국기계가공학회지
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• 제8권3호
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• pp.21-26
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• 2009

The finite element analysis of metal forming processes often fails because of severe mesh distortion at large deformation. As the concept of meshless methods, only nodal point data are used for modeling and solving. As the main feature of these methods, the domain of the problem is represented by a set of nodes, and a finite element mesh is unnecessary. This computational methods reduces time-consuming model generation and refinement effort. It provides a higher rate of convergence than the conventional finite element methods. The displacement shape functions are constructed by the reproducing kernel approximation that satisfies consistency conditions. In this research, A meshless method approach based on the reproducing kernel particle method (RKPM) is applied with metal forming analysis. Numerical examples are analyzed to verify the performance of meshless method for metal forming analysis.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 추계 학술대회논문집
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• pp.13-18
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• 1998

The practical use of the particle image velocimetry(PIV), a whole-field velocity measurement method, requires the use of fast, reliable, computer-based methods for tracking velocity vectors. The full search block matching, the most widely studied and applied technique both in area of PIV and Image Coding and Compression, is computationally costly. Many less expensive alternatives have been proposed mostly in the area of Image Coding and Compression. Among others, TSS, NTSS, HPM are introduced for the past PIV analysis, and found to be successful. But, these algorithms are based on small dynamic range, 7 pixels/frame in maximum displacement. To analyze the images with large displacement, Even and Odd field image separation and a simple version of multi-resolution hierarchical procedures are introduced in this paper. Comparison with other algorithms are summarized. A Results of application to the turbulent backward step flow shows the improvement of new algorithm.

• Geomechanics and Engineering
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• 제16권5호
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• pp.495-501
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• 2018

Geogrid application that has proved to be an effective and economic method of reinforcing particles, is widely used in geotechnical engineering. The discrete element method (DEM) has been used to investigate the micro mechanics of the geogrid deformation and also the interlocking mechanism that cannot be easily studies in laboratory tests. Two types of realistically shaped geogrid models with square and triangle apertures were developed using parallel bonds in PFC3D. The calibration test simulations have demonstrated that the precisely shaped triangular geogrid model is also able to reproduce the deformation and strength characteristics of geogrids. Moreover, the square and triangular geogrid models were also used in DEM pull-out test simulations with idealized shape particle models for validation. The simulation results have been shown to provide good predictions of pullout force as a function of displacement especially for the initial 30 mm displacement. For the granular material of size 40 mm, both the experimental and DEM results demonstrate that the triangular geogrid of size 75 mm outperforms the square geogrid of size 65 mm. Besides, the simulations have given valuable insight into the interaction between particle and geogrid and also revealed similar deformation behavior of geogrids during pullout. Therefore, the DEM provides a tool which enable to model other possible prototype geogrid and investigate their performance before manufacture.

• 한국수자원학회논문집
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• 제34권5호
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• pp.499-509
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• 2001

자연하천에서의 이송-확산 과정의 모의를 위하여 입자위치의 이산확률분포에 기초한 2차원 수송 모형을 개발하였다. 제안된 모형에서는 단위 시간간격동안 격자간의 질량이송을 예측하기 위하여 평균과 분산의 함수로 나타내어진 확률분포를 사용하였다. 개발된 모형은 유속, 확산계수, 단면적이 일정한 단순영역에 대하여 수치확산이 없는 해를 구하였고, 양의 확률을 만족시키는 안정조건이 성립한다면, 해석해와 다른 유한차분법과 비교하였을 때, 좋은 결과를 나타내었다. 본 모형의 현장적용성을 검토하기 위하여 캐나다에 위치한 Grand River를 대상을 얻은 수치실험 결과를 정상상태의 색소실험 결과와 비교하였다. 그 결과로서 본 모형은 자연하천에서의 2차원 이송-확산을 잘 모의할 수 있는 것으로 나타났다.

• 한국지반공학회논문집
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• 제25권12호
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• pp.119-130
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• 2009

흙의 변형을 측정하기 위해 적용되는 이미지 해석 기법으로는 Particle Image Velocimetry(PIV)와 Digital Image Correlation(DIC)가 있으며, 이 기법들이 더욱 널리 활용되기 위해서는 각 기법에 따라 다양한 조건에서 정밀도를 평가하는 연구가 필요하다. 본 연구에서는 이미지 해상도, 변위 및 변형 정도, 픽셀 집합의 크기 및 해석 기법의 다양한 요소를 고려하여 사질토의 변형을 관찰하기에 적합한 최적의 이미지 해석 기법을 제시하고자 한다. 개별요소법(DEM)을 이용하여 구성된 가상의 사질토 이미지를 활용하여 이미지 해석을 행하고 변위를 산정한 후, 개별 요소법의 변위와 비교하였다. 각 영향 요소들이 정확도에 미치는 영향을 분석하였고, 변위 및 변형 정도에 따라 최적의 이미지 해석조건을 제시할 수 있었다.

• 대한전자공학회논문지
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• 제27권4호
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• pp.534-540
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• 1990

In this paper the characteristics of submicron gate GaAs MESFET's have been studied using a particle model which takes into account the hot-electron transport phenomena, i.e., the velocity overshoot. \ulcornervalley(<000> direction), L valley (<111>direction), X valley (<100>direction) as the GaAs conduction energy band and optical phonon, acoustic phonon, equivalent intervalley, nonequivalent intervalley scattering as the scattering models, have been considered in this simulation. And the GaAs material and the device simulation have been done by determination of the free flight time, scattering mechanism and scattering angle according to Monte-Carlo algorithm which makes use of a particle model. As a result of the particle simulation, firstly the electron distribution, the potential energy distribution and the situation of electron displacement in 0.6 \ulcorner gate length device have been obtained. Secondly, the cutoff frequency, obtained by this method, is k47GHz which is in good agreement with the calculated result of theory. And the current-voltage characteristics curve which takes account of the buffer layer effect has been obtained. Lastly it has been verified that parasitic current at the buffer layer can be analyzed using channel depth modulation.

• 비파괴검사학회지
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• 제12권4호
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• pp.9-17
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• 1993

Three types of piezoelectric sensors to detect acoustic emission signals were developed and characterized. Epicentral displacement and velocity of a plate to have infinite boundary were calculated by convolution between a Green's function and a simulated source time function to show parabolic rising characteristic. The sensor calibration system set up was composed of a steel plate, a glass capillary, an indentor and a load cell indicator The transient elastic signals were detected by the sensors. The results were compared with the theoretical results and Fast Fourier Transformed. As the results, the sensor fabricated using a disk shape of a piezoelectric PZT element showed resonant characteristics. The sensors fabricated using a conical shape PZT element and a PVDF polymer film showed the wide band characteristics for particle displacement and velocity, respectively. The calculated results showed good agreements with the transient responses in the cases of the wide band sensors and it was confirmed that the simulated source time function had been properly assumed.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2011년도 한국우주과학회보 제20권1호
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• pp.28.1-28.1
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• 2011

Radiation-induced displacement damage which has caused the increase of the dark current in the focal plane adopted in the Ozone Monitoring Instrument (OMI) was studied in regards of the primary protons and the secondaries generated by the protons in the orbit. By using the Monte Carlo N-Particle Transport Code System (MCNPX) version 2.4.0 along with the Stopping and Range of Ions in Matter version 2010 (SRIM2010), effects of the primary protons as well as secondary particles including neutron, electron, and photon were investigated. After their doses and fluxes that reached onto the charge-coupled device (CCD) were examined, displacement damage induced by major sources was presented.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2975-2981
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• 2020

Radiation damage is one of the aging important causes in nuclear reactors. Radiation damage causes changes in material properties. In this study, this effect has been evaluated and analyzed on the clad of the Tehran research reactor (TRR). A grade 6061 aluminum is used as a clad in the TRR. The MCNPX code is used to designate the most sensitive location of the reactor and calculate neutron flux distribution. Then, a software using FORTRAN language programming is developed to process the particle track (PTRAC) output file of the MCNPX code. The SRIM code is used here to calculate the rate of displacement per atom. Moreover, the SPECOMP and SPECTER codes are also applied to estimate the displacement rate and compared with the results attained using the SRIM code. The rate of displacement per atom by the SPECTER and SRIM codes have been obtained 2.54 × 10^-7 dpa/s and 2.44 × 10^-7 dpa/s (QD method), respectively. Also, the mechanical properties have been evaluated using the RCC-MRx code and have been compared with experimental results. Finally, the change in the matter specification has been analyzed as a function of time.

• 화약ㆍ발파
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• 제17권1호
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• pp.27-55
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• 1999

The excavation works for deep foundation in urban areas have recently increased complaints of blasting vibration and settlement of ground level. Foundation must be excavated approximately up to 24-28m depths from the surface. The roads and subway line pass through the excavation area. The Dae-chung station is also located at the nearest distance 5-35m from the working site. To protect subway station and adjacient some structures from blasting and settlement, the level of ground vibration, displacements and stress were monitored and analyzed. The results can be summarized as follows ; 1. An empirical particle velocity equation were obtained by test blasts at Nassan Missi 860 Office tel construction site. $V{\;}={\;}K(D/\sqrt{W})^{-n}$, where the values for n and k are estimated tobe 0.371 and 1.551. From this ground vibration equation, the max. charge weight per delay time against distance from blasting point is calculated. Detailed blasting method is also presented. 2. To measure the horizontal displacement in directions perpendicular to the borehole axis, 6 inclinometers installed around working sites. The displacement at the begining was comparatively high because the installation of struts was delayed, but after its installation the values showed a stable trend. Among them, the displacement by 3 inclinometers installed on a temporary parking area showed comparatively high values, for example, the displacement measured at hole No. IC-l recoded the max. 47.04mm for 6 months and at hole No. IC-2 recorded the max. 57.33mm for 7 months. So, all of these data was estimated below a safe standard value 103mm. 3. Seven strain gauge meter was installed of measure the magnitude and change of stress acted on structs. The measured value of maximum stress was $-465{\;}kgf/\textrm{cm}^2,{\;}-338.4{\;}kgf/\textrm{cm}^2,{\;}302.3{\;}kgf/\textrm{cm}^2$ respectively. In compareto the allowable stress level of steel, they are estimated to be safe.