1,000 research outputs found
A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics
This paper presents a survey of ocean simulation and rendering methods in
computer graphics. To model and animate the ocean's surface, these methods
mainly rely on two main approaches: on the one hand, those which approximate
ocean dynamics with parametric, spectral or hybrid models and use empirical
laws from oceanographic research. We will see that this type of methods
essentially allows the simulation of ocean scenes in the deep water domain,
without breaking waves. On the other hand, physically-based methods use
Navier-Stokes Equations (NSE) to represent breaking waves and more generally
ocean surface near the shore. We also describe ocean rendering methods in
computer graphics, with a special interest in the simulation of phenomena such
as foam and spray, and light's interaction with the ocean surface
Functional requirements for the man-vehicle systems research facility
The NASA Ames Research Center proposed a man-vehicle systems research facility to support flight simulation studies which are needed for identifying and correcting the sources of human error associated with current and future air carrier operations. The organization of research facility is reviewed and functional requirements and related priorities for the facility are recommended based on a review of potentially critical operational scenarios. Requirements are included for the experimenter's simulation control and data acquisition functions, as well as for the visual field, motion, sound, computation, crew station, and intercommunications subsystems. The related issues of functional fidelity and level of simulation are addressed, and specific criteria for quantitative assessment of various aspects of fidelity are offered. Recommendations for facility integration, checkout, and staffing are included
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Bioengineering Analysis of Traumatic Brain Injury
Traumatic brain injury (TBI) is a serious health concern affecting over a million people in the UK. Brain shift and herniation, which are closely related to severe disability or death, are important signs of abnormally elevated intracranial pressure (ICP) or space-occupying intracranial mass after trauma.
This research aims to use medical image computing and biomechanical modelling techniques to characterise the specific deformation field of brain tissues under various TBI scenarios and strengthen the biomechanical understanding across the full spectrum of TBI.
Medical image computing provides the research with a solid clinical grounding. To better interpret the neuro-images, three computational tools have been developed, including a CT preprocessing pipeline, an automatic mid-sagittal plane detector and an automatic brain extractor. Using these tools, a novel concept of midplane shift (MPS) is developed to quantitatively evaluate the brain herniation condition across the mid-sagittal plane. In the meantime, a lesion heatmap is generated to quantify the asymmetric haematoma volumes across the mid-sagittal plane. The MPS heatmaps generated for 33 TBI patients with heterogeneous brain pathologies demonstrate highly similar shift patterns. Together with the lesion heatmap, a brain deformation mechanism has been presented: the brain will not deform randomly in response to trauma, instead, it will only deform in a regulated mechanism so that the deformation is directed and restricted to the soft ventricular region, thanks to the anatomic structures of the head such as the falx. The MPS heatmap, the lesion heatmap, together with the novel CT parameters derived from them, provide a rich abundance of information on intracranial brain herniation, for a more complete overview of TBI from medical images.
Biomechanical modelling, being one of the most important tools in trauma biomechanics, has been used to quantitatively simulate the brain shift and herniation condition caused by various intracranial lesions and increasing ICP. Preliminary finite element models reconstructed from the Virtual Human Project have demonstrated some limitations. To resolve the observed deficiencies, an advanced high-fidelity patient-specific FE brain model is constructed and explicitly assessed to optimise its injury simulation performance with the help of the developed medical image computing tools. During simulation, the patient-specific traumatic injuries have been reconstructed by imposing both the primary lesion and the secondary injury. The primary lesion simulation is achieved mechanically by ``indenting" a rigid lesion surface simulating the shape of the haematoma to the brain model. While the secondary swelling is modelled with a thermal-expansion-based method to simulate the bulging brain. Using this approach, the observed brain herniation can be decomposed into a deformation due to pure mass effect of space-occupying primary lesion and a shift as a result of secondary swelling. The head injuries of six different TBI patients have been reconstructed and simulated using the prescribed method. The realistic case study suggested that the subdural haematoma patients, as compared to the epidural haematoma patients, were exposed to more significant secondary swelling, which agrees well with the historical clinical findings. In addition to the realistic TBI case studies, an idealised traumatic lesion simulation is performed to investigate the role of lesion morphology and the lesion locations of onsets, in brain herniations during TBI. It is suggested by the idealised TBI cases that the brain is more sensitive to lesion that is more concentrated spatially, if lesion volumes and lesion locations were exactly the same. Moreover, in terms of lesion locations, lesions that strikes on the temporal region and the anterior region are more likely to lead to greater brain deformation, if other lesion morphologies were equal and no secondary swelling considered.
Ultimately, the developed tools are expected to help clinicians better understand and predict the brain behaviour after the onset of TBI and during subsequent injury evolution.WD Armstrong Trus
On the Dependency of the Electromechanical Response of Rotary MEMS/NEMS on Their Embedded Flexure Hingesโ Geometry
This paper investigates how the electromechanical response of MEMS/NEMS devices changes when the geometrical characteristics of their embedded flexural hinges are modified. The research is dedicated particularly to MEMS/NEMS devices which are actuated by means of rotary comb-drives. The electromechanical behavior of a chosen rotary device is assessed by studying the rotation of the end effector, the motion of the comb-drive mobile fingers, the actuatorโs maximum operating voltage, and the stress sustained by the flexure when the flexureโs shape, length, and width change. The results are compared with the behavior of a standard revolute joint. Outcomes demonstrate that a linear flexible beam cannot perfectly replace the revolute joint as it induces a translation that strongly facilitates the pull-in phenomenon and significantly increases the risk of ruptures of the comb-drives. On the other hand, results show how curved beams provide a motion that better resembles the revolute motion, preserving the structural integrity of the device and avoiding the pull-in phenomenon. Finally, results also show that the end effector motion approaches most precisely the revolute motion when a fine tuning of the beamโs length and width is performed
Coupling an SPH-based solver with an FEA structural solver to simulate free surface flows interacting with flexible structures
This work proposes a two-way coupling between a Smoothed Particle Hydrodynamics (SPH) model-based named DualSPHysics and a Finite Element Analysis (FEA) method to solve fluidโstructure interaction (FSI). Aiming at having a computationally efficient solution via spatial adjustable resolutions for the two phases, the SPH-FEA coupling herein presented implements the EulerโBernoulli beam model, based on a simplified model that incorporates axial and flexural deformations, to introduce a solid solver in the DualSPHysics framework. This approach is particularly functional and very precise for slender beam elements undergoing large displacements, and large deformations can also be experienced by the structural elements due to the non-linear FEA implementation via a co-rotational formulation. In this two-way coupling, the structure is discretised in the SPH domain using boundary particles on which the forces exerted by fluid phases are computed. Such forces are passed over to the FEA structural solver that updates the beam shape and, finally, the particle positions are subsequently reshuffled to represent the deformed shape at each time step. The SPH-FEA coupling is validated against four reference cases, which prove the model to be as accurate as other approaches presented in literature.Ministerio de Ciencia e Innovaciรณn | Ref. PID2020-113245RB-I00Ministerio de Ciencia e Innovaciรณn | Ref. TED2021-129479A-I00Xunta de Galicia | Ref. ED431C 2021/44Xunta de Galicia | Ref. ED481A-2021/337Universidade de Vigo/CISU
Analysis of crack growth problems using the object-oriented program bemcracker2D
This paper presents an application of the boundary element method to the analysis of crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental data. The methodology consists of computing stress intensity factors (SIFs), the crack growth path and the estimation of fatigue life, via an incremental analysis of the crack extension, considering two independent boundary integral equations, the displacement and traction integral equations. Moreover, a special purpose educational program for simulating two-dimensional crack growth based on the dual boundary element method (DBEM), named BemCracker2D, written in C++ with a MATLAB graphic user interface, has been developed and used to verify the adopted methodology. The numerical results are compared with those of the finite element method (FEM) and correlated with experimental data of fatigue crack-growth tests for two-dimensional structural components under simple loading, aiming to demonstrate the accuracy and efficiency of the methodology adopted, as well as to evaluate the robustness of the BemCracker2D code
Analysis of crack growth problems using the object-oriented program bemcracker2D
This paper presents an application of the boundary element method to the analysis of crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental data. The methodology consists of computing stress intensity factors (SIFs), the crack growth path and the estimation of fatigue life, via an incremental analysis of the crack extension, considering two independent boundary integral equations, the displacement and traction integral equations. Moreover, a special purpose educational program for simulating two-dimensional crack growth based on the dual boundary element method (DBEM), named BemCracker2D, written in C++ with a MATLAB graphic user interface, has been developed and used to verify the adopted methodology. The numerical results are compared with those of the finite element method (FEM) and correlated with experimental data of fatigue crack-growth tests for two-dimensional structural components under simple loading, aiming to demonstrate the accuracy and efficiency of the methodology adopted, as well as to evaluate the robustness of the BemCracker2D code
The statistical modelling of production processes of biodegradable aliphatic aromatic co-polyester fibres used in the textile industry
Since the success of production processes in the textile industry depends on good planning and having a clear programme from the raw materials until the final product, the focus of this research is in the modelling of the production process of biodegradable aliphatic-aromatic co-polyester (AAC) fibres. The statistical modelling of the effects of the extrusion temperature profile and polymer grade on the properties of linear AAC as-spun fibres aims to find the better linear grade to be used. The investigation helped to establish a statistical method to optimize the extrusion temperature profile required for extrusion of AAC fibres. The effects of melt spinning conditions together with linear and branched grades of AACs on as-spun fibres were statistically modelled, programmed and evaluated. To identify the effect of the drawing process, the effect of multi stage hot and cold drawing process on AACs fibres has been statistically investigated and modelled. The additional effect gained from twisting the drawn fibres has been investigated in terms of process parameters interactions. Forecasting models have been set for optimizing and controlling the manufacturing of biodegradable AACs fibres. The novel statistical factorial method will help when taking the best experimental decision controlled by the design factors
Development of GPU-based SPH Framework for Hydrodynamic Interactions With Non-spherical Solid Debris
์ผ๋ณธ์ ํ์ฟ ์๋ง ์ฌ๊ณ ์ดํ ์์๋ก ์ค๋ ์ฌ๊ณ ์ ๋ํ ์ฐ๊ตฌ์ ํ์์ฑ๊ณผ ๋์ฒ ๋ฅ๋ ฅ ํ๋ณด์ ๋ํ ์ค์์ฑ์ด ์ ์ ์ฆ๊ฐํ๊ณ ์๋ค. ์ฌ๊ณ ์ ๋ฐ์ํ ์ ์๋ ๋
ธ์ฌ ์ฉ์ต๋ฌผ ๊ฑฐ๋์ ๋ํ ํ๊ฐ๋ ์ฉ์ต๋ฌผ-์ฝํฌ๋ฆฌํธ ์ํธ์์ฉ(MCCI, Molten Core Concrete Interaction)๊ณผ ์ฆ๊ธฐ ํญ๋ฐ๋ก๋ถํฐ์ ์์๋ก ๋
ธ์ฌ ๋๊ฐ์ฑ ๋ฐ ๊ฑด์ ์ฑ์ ๋ฐ๋ฅธ ์ฌ์๊ณ ์ธก๋ฉด์์ ๋งค์ฐ ์ค์ํ๋ค. ํนํ OPR 1000์ ๊ฒฝ์ฐ, ์ฌ์ ์ถฉ์ ์กฐ๊ฑด(Wet cavity condition)์ ๊ธฐ๋ณธ์ ์ธ ์์๋ก ์ธ๋ฒฝ ๋๊ฐ ๋์ ์ ๋ต์ผ๋ก ์ฑํํจ์ผ๋ก์จ ํต์ฐ๋ฃ-๋๊ฐ์ฌ ์ํธ์์ฉ(FCI, Fuel Coolant Interaction) ๋ฐ์์ด ํ์ฐ์ ์ผ๋ก ๋ฐ์ํ๋ ๊ฒ์ผ๋ก ์๋ ค์ ธ ์๋ค. [Jin, 2014] FCI ํ์์ ์์ ํํ์ ํต์ฐ๋ฃ ๊ณ ์ฒด ํํธ๋ฌผ๊ณผ ๋๊ฐ์ฌ์ ์ํธ์์ฉ๋ฟ๋ง ์๋๋ผ, ๋๊ฐ์ฌ ๋น๋ฑ ํ์ ๋ฑ๋ ํฌํจํ๋ ๋ค์ ์ฒด, ๋ค์ ํ์์ผ๋ก ๊ทธ ํ์์ด ๋งค์ฐ ๋ณต์กํ๋ค. ์ด ๊ณผ์ ์์ ์์๋ก ๊ฑด๋ฌผ ํ๋ถ์ ๊ณ ์ฒด ํํธ๋ฌผ์ด ํด์ ๋์ด ์ํด ์ธต์ด ํ์ฑ๋๊ณ , ๊ทธ ๋๊ฐ์ฑ์ ๋ฐ๋ผ ์ฌ๊ณ ์ ๋ค์ ์งํ ์ํฉ์ ์ํฅ์ ์ค ์ ์๋ค. ์ด๋ฌํ ๋น๊ตฌํ ๊ณ ์ฒด ํํธ๋ฌผ ๊ฑฐ๋์ ๋ํ ์ดํด๋ฅผ ์ํด ๊ฐ์ฒด ๊ฐ๋
์ ์ ์ฉํ ๊ณ ์ฒด ํด์ ์ฒด๊ณ๋ ์ข์ ์ ๊ทผ๋ฒ์ด ๋ ์ ์๋ค. ๋ฐ๋ผ์ ๋ณธ ์ฐ๊ตฌ์์๋ ์ ์ฒด์ ๊ณ ์ฒด ๊ฐ ์๋ ฅํ์ ์ํธ์์ฉ ํด์์ ์ํด ์
์์ ์ฒด๋์ญํ(SPH, Smoothed Particle Hydrodynamics) ๊ธฐ๋ฒ๊ณผ ๊ฐ์ฒด์ญํ(RBD, Rigid Body Dynamics) ๊ธฐ๋ฒ์ ์ฐ๊ณํ์ฌ ๋ผ๊ทธ๋์ง์ ํด์ ์ฒด๊ณ๋ฅผ ๊ตฌ์ถํ์๋ค.
์ํ์
์์ ์ฒด๋์ญํ ๊ธฐ๋ฒ์ ํด์ ์ ์ฒด๋ฅผ ์ ํ๊ฐ์ ์
์๋ก ํํํจ์ผ๋ก์จ ์ ๋์ ํด์ํ๋ ๋ผ๊ทธ๋์ง์ ํด์ ๊ธฐ๋ฒ ์ค ํ๋์ด๋ค. ๊ฐ๋ณ ์
์๋ค์ ์์ง์์ผ๋ก ์ ๋์ ํด์ํ๋ฏ๋ก ๋น์ ํ์ ๋๋ฅํญ์ ๋ํ ๊ณ์ฐ์ด ํ์ ์์ผ๋ฉฐ, ์
์๊ฐ ์ถ๊ฐ๋๊ฑฐ๋ ์ฌ๋ผ์ง์ง ์๋ ํ ํด์ ๊ณ์ ์ ์ฒด ์ง๋์ ์๋์ผ๋ก ๋ณด์กด๋๋ค. ์ด๋ฌํ ๋ผ๊ทธ๋์ง์ ๊ธฐ๋ฒ์ ํน์ฑ์ผ๋ก SPH ๋ฐฉ๋ฒ์ ์์ ํ๋ฉด ์ ๋, ๋ค์ ์ฒด ์ ๋, ๋ค์ ์ ๋, ํํ ๋ณํ๊ฐ ํฐ ์ ๋ ๋ฑ์ ๋ํด ํด์ ์ฅ์ ์ ๊ฐ๋๋ค. ๋ณธ ์ฐ๊ตฌ์์๋ SPH ๊ธฐ๋ฒ์ ์ ์ฉํ in-house SOPHIA ์ฝ๋๋ฅผ ์ฌ์ฉํ์ฌ ๋น์์ถ ๋ค์ ์ ๋ ํด์์ ์ํํ์์ผ๋ฉฐ, ๋ฒค์น๋งํฌ ๋ฐ์ดํฐ์์ ๋น๊ต์์ ์ข์ ๊ฒ์ฆ ํด์ ๊ฒฐ๊ณผ๋ฅผ ๋ณด์๋ค.
๊ฐ์ฒด์ญํ์ ์ธ๋ ฅ์ ์ํด ํํ๊ฐ ๋ณํ์ง ์๋ ๊ฐ์ฒด์ ๊ฐ๋
์ ์ด์ฉํ์ฌ ๊ณ ์ฒด์ ๋ณ์ง ์ด๋๊ณผ ํ์ ์ด๋์ ํด์ํ๋ ์ฐ๊ตฌ ๋ถ์ผ์ด๋ค. ๋ณธ ์ฐ๊ตฌ์์๋ ์ด์ฐ์์๋ฒ(DEM, Discrete Element Method) ๋ถ์ผ์์ ์ค๋ ์๊ฐ ๋์ ๋๋ฆฌ ์ฌ์ฉ๋๊ณ ๊ฒ์ฆ๋์๋ Hertz-Mindlin ์ถฉ๋ ๋ชจ๋ธ์ ์ ์ฉํ์ฌ ๊ฐ์ฒด ๊ฐ ์ถฉ๋ ํด์์ ๊ตฌํํ์๋ค. ๊ฐ์ฒด๋ ์ ํ๊ฐ์ ์
์๋ค๋ก ํํํ ์ ์์ผ๋ฉฐ, ๊ฐ์ฒด ๊ฐ ์ถฉ๋์ ๊ฐ ๊ฐ์ฒด๋ฅผ ๊ตฌ์ฑํ๊ณ ์๋ ์
์์์ ์์ ์ค์ฒฉ์ ๊ธฐ๋ฐ์ผ๋ก ๊ณ์ฐ๋๋ค. ๋ณธ ์ฐ๊ตฌ์์๋ ์
์๊ธฐ๋ฐ์ ๊ฐ์ฒด์ญํ ํด์ ์ฝ๋๋ฅผ ์ด์ฉํ์ฌ ๋จ์ผ ๊ฐ์ฒด ๋ฐ ๋ค์ค ๊ฐ์ฒด ์ถฉ๋์ ๋ํด ๊ฒ์ฆ ํด์์ ์ํํ์์ผ๋ฉฐ, ํด์ํด ๋ฐ ๋ฒค์น๋งํฌ ๋ฐ์ดํฐ ๊ฒฐ๊ณผ์ ์ ์ผ์นํจ์ ํ์ธํ์๋ค.
์์๋ ฅ ๋ถ์ผ์์ ๋ฐ์ํ ์ ์๋ ๋น๊ตฌํ ๊ณ ์ฒด์ ์ ์ฒด๊ฐ ์ํธ์์ฉ ํด์์ ์ํด ์์ ์ค๋ช
ํ SPH ๊ธฐ๋ฒ๊ณผ ๊ฐ์ฒด์ญํ ์ฐ๊ณ ํด์ ์ฝ๋๋ฅผ ๊ฐ๋ฐํ์๋ค. ๋ณธ ์ฐ๊ตฌ์์ ์ ์ฉํ ์์ ํด์ ๋ฐฉ์(Fully resolved approach)์ ์ ์ฒด-๊ณ ์ฒด์ ์์ด ๋ถ๋ฆฌ๋์ด ์๊ณ , ์ 1 ์๋ฆฌ๋ฅผ ๋ง์กฑํ๋ฏ๋ก ๊ณ ์ฒด์ ํ์์ ๋ฐ๋ฅธ ์๊ด์๊ณผ ํ๋ฉด ์ ๋ถ์ด ํ์ํ์ง ์๋ค๋ ์ฅ์ ์ด ์๋ค. ๋ํ ๊ณ ์ฒด ๊ฒฝ๊ณ๋ฉด์์์ ์ ํํ ์๋ ฅ ๊ณ์ฐ์ ์ํด ์ ์ฒด ์
์ ์ ๋ณด๋ฅผ ๊ธฐ๋ฐ์ผ๋ก ๋
ธ์ด๋ง ์๋ ฅ ๊ฒฝ๊ณ ์กฐ๊ฑด์ ์ ์ฉํ์๋ค. ๋ณธ ์ฐ๊ตฌ์์๋ ์ด๋ฌํ ํด์ ๋ฐฉ์์ ์ ์ฒด-๊ฐ์ฒด ์ฐ๊ณ ํด์ ์ฝ๋๋ฅผ ์ด์ฉํ์ฌ ๋น๊ตฌํ ๊ณ ์ฒด์ ์ ์ฒด์ ์๋ ฅํ์ ์ํธ์์ฉ์ ๋ํ ๊ฒ์ฆ ํด์์ ์ํํ์์ผ๋ฉฐ, ์ ํ๋ ์คํ๊ณผ์ ๋น๊ต์์ ์ข์ ๊ฒฐ๊ณผ๋ฅผ ๋ณด์๋ค.
์ ๋ ํด์์ ์ํด ๋ณธ ์ฐ๊ตฌ์ ์ ์ฉํ SPH ๋ฐฉ๋ฒ์์๋ ์์๋ค์ด ๋งค์ฐ ์ ํ์ ์ด๊ณ ์ธ์ฐ์ (Explicit)์ผ๋ก ๊ณ์ฐ์ ์ํํ๊ธฐ ๋๋ฌธ์ ๊ฐ ์
์์ ๋ํ ๊ณ์ฐ์ด ๋
๋ฆฝ์ ์ผ๋ก ์ํ๋์ด๋ ๋ฌธ์ ๊ฐ ์๋ค. ๋ฐ๋ผ์ SPH ๋ฐฉ๋ฒ์ ๊ณ์ฐ ๋ณ๋ ฌํ์ ์ต์ ํ๋ ๋ฐฉ๋ฒ์ผ๋ก ์ ์๋ ค์ ธ ์์ผ๋ฉฐ, ๋๊ท๋ชจ ๊ณ ํด์๋ ํด์์ ์ํด ์ด๋ ํ์์ ์ด๋ค. ๋ํ ์
์ ๊ธฐ๋ฐ์ ๊ฐ์ฒด ๊ณ์ฐ์ ์ํด์๋ ํจ์จ์ ์ธ ๊ณ์ฐ ์๊ณ ๋ฆฌ์ฆ์ด ํ์ํ๋ค. ๋ฐ๋ผ์ ๋ณธ ์ฐ๊ตฌ์์๋ ๋๊ท๋ชจ ๊ณ์ฐ๊ณผ ๋์ ์ฐ์ฐ ํจ์จ์ฑ์ ์ํด ๊ทธ๋ํฝ์ฒ๋ฆฌ์ฅ์น(GPU, Graphic Processing Unit)๋ฅผ ์ด์ฉํ์ฌ ๊ณ์ฐ ๋ณ๋ ฌํ๋ฅผ ์ํํ์์ผ๋ฉฐ, ์ด๋ฅผ ์ด์ฉํ ๋ค์ค ๊ณ ์ฒด์ ์ ์ฒด์ ์ํธ์์ฉ ํด์์์ ์ข์ ๊ณ์ฐ ์ฑ๋ฅ์ ํ์ธํ์๋ค.
๋ณธ ์ฐ๊ตฌ์์ ์ํํ ๋น๊ตฌํ ๊ณ ์ฒด์ ์ ์ฒด์ ์๋ ฅํ์ ์ํธ์์ฉ์ ์ํ GPU ๊ธฐ๋ฐ์ SPH ํด์ ์ฝ๋ ๊ฐ๋ฐ ์ฐ๊ตฌ๋ฅผ ํตํด ์์๋ก ์ค๋์ฌ๊ณ ์ ๋ฐ์ํ ์ ์๋ ๋๊ฐ์ฌ์ ํต์ฐ๋ฃ ๊ณ ์ฒด ํํธ๋ฌผ์ ์๋ ฅํ์ ์ํธ์์ฉ ๋ฟ๋ง ์๋๋ผ, ๊ณ ์ฒด ํํธ๋ฌผ ๊ฐ ์ญํ์ ์ํธ์์ฉ์ ๋ํด ํจ์จ์ ์ธ ํด์ ์ฒด๊ณ๋ฅผ ๊ฐ๋ฐํ์๋ค. ์ด๋ฅผ ํตํด ์ต์ ๊ณต๋(wet cavity)์์ ๋ฐ์ํ๋ ํต์ฐ๋ฃ ๊ณ ์ฒด ํํธ๋ฌผ์ ํด์ ์์ฉ, ์ฐ๋๋ฏธ ์ฌ๊ณ ๋ก ์ธํ ํด์ ๊ตฌ์กฐ๋ฌผ์ ์๋ ฅํ์ ์ํธ์์ฉ, ๊ทธ๋ฆฌ๊ณ ์นจ์ ์ฌ๊ณ ์ ์์๋ก ๊ฑด๋ฌผ ๋ด ๋ถ์ ๋ฌผ์ ๊ฑฐ๋ ๋ฑ ์์๋ ฅ ๋ถ์ผ์์ ๋ฐ์ํ ์ ์๋ ๋ค์ํ ๊ณ ์ฒด-์ ์ฒด์ ์๋ ฅํ์ ์ํธ์์ฉ์ ๋ํ ํด์์ ์ฐ๊ตฌ์ ์ ์ฉํ๊ณ ๊ธฐ์ฌํ ์ ์์ ๊ฒ์ผ๋ก ๊ธฐ๋ํ๋ค.Since the Fukushima accident, the necessity for researches on severe accidents and the importance of securing the ability to cope with the accidents have been increasing. The evaluation of the molten core behavior that may occur during the accident is very important in terms of re-criticality according to the coolability and integrity of the reactor core from the MCCI (Molten Core Concrete Interaction) and steam explosion. In the case of OPR 1000, especially, FCI (Fuel Coolant Interaction) is known to occur unconditionally because the wet cavity condition has been adopted as a basic strategy for ex-vessel cooling. [Jin, 2014] FCI is a highly complicated phenomenon, which includes multi-fluid, multi-phase interaction between the arbitrary shape of solid debris and coolant as well as coolant boiling. In this process, the debris bed is formed at the bottom of the containment, and its coolability influences the next phase of the accident. For the understanding on the solid debris behavior, a solid system with a rigid body can be a good approach for the non-spherical solid debris analysis. Therefore, in this study, Smoothed Particle Hydrodynamics (SPH) method and Rigid Body Dynamics (RBD) are coupled in a fully Lagrangian manner for the hydrodynamic interactions between fluid and solid.
Smoothed Particle Hydrodynamics (SPH) is one of the Lagrangian-based analysis methods which represents the fluid flow as a finite number of particles. Since the flow is analyzed by the motion of individual particles, there is no need to calculate the nonlinear convective term, and the total mass of the system is automatically conserved as long as particles are not added or removed. Through these Lagrangian nature, it is well known that the SPH method is effective for the free surface flow, multi-fluid and multi-phase flow, and highly deformable flow. In this study, the incompressible multi-phase flow analysis has been performed using the in-house SPH code, SOPHIA code, and V&V simulation results showed good agreement with the benchmark data.
Rigid Body Dynamics (RBD) is a research field that analyses the translation and rotation of a solid body by using the concept that a rigid body doesnโt change its shape by external forces. In this study, the collision calculation between rigid bodies is implemented by applying the Hertz-Mindlin contact force model commonly used and verified for a long time in the Discrete Element Method (DEM) field. A rigid body can be expressed as a group of finite particles, and the contact forces between solid bodies are calculated based on the small overlap of the particle pairs. Using the particle-based RBD analysis code implemented in this study, V&V simulations on single- and multi- rigid body collisions have been performed and showed good agreement with the analytical solution and the benchmark data.
To analyze the hydrodynamic interactions between non-spherical solids and fluids that can occur in the nuclear field, the integrated code has been developed by coupling RBD with SPH code. Since a fully resolved approach adopted in this study as a phase coupling method satisfies the 1st principle and the fluid-solid phase is entirely separated from each other, there is no need for the surface integral and empirical correlations depending on the solid geometry. In addition, the Neumann pressure boundary condition is implemented for accurate pressure estimation at the solid interface using the fluid particle properties. By applying the resolved SPH-RBD coupled code, V&V simulations were carried out on the hydrodynamic interactions of non-spherical solid-fluid and showed good agreement with the experimental data.
In the SPH method, since the numerical expression are highly linear and the calculations are performed explicitly, there is no problem even if the calculations for each particle are performed independently. Therefore, the SPH is well known as an optimized method for parallelization, and it is essential for large scale high-resolution simulations. In addition, an efficient computational algorithm is required for particle-based rigid body calculation. In this study, therefore, the parallelization was performed using a Graphical Processing Unit (GPU) for large-scale calculations and high computational efficiency, and it showed a good performance in analyzing the interactions of a large number of solids and fluids particles.
Through the researches on the development of a GPU-based SPH framework for the hydrodynamic interaction of non-spherical solids and fluids in this study, an efficient analysis system has been developed for not only the hydrodynamic interaction of solid corium debris with coolant but also the mechanical interaction between solid debris which can occur at the severe accidents in the nuclear reactor. By using this, it is expected that the integrated code will contribute to analytical researches on various accident scenarios that may occur in the nuclear field such as solid fuel debris sedimentation in the wet cavity, hydrodynamic interactions with coastal structures caused by the Tsunami, and the behavior of floating objects in the reactor building at the flooding accident, etc.Chapter 1 Introduction 1
1.1 Background and Motivation 1
1.2 Previous Studies 3
1.2.1 Numerical Studies on FCI Premixing Jet Breakup 3
1.2.2 Numerical Studies on Fluid-Solid Coupling with RBD 4
1.3 Objectives and Scope 5
Chapter 2 Smoothed Particle Hydrodynamics (SPH) 9
2.1 SPH Overview 9
2.1.1 Basic Concept of SPH 9
2.1.2 SPH Particle Approximation 10
2.1.3 SPH Kernel Function 12
2.1.4 SPH Governing Equations 13
2.2 SPH Multi-phase Models 16
2.2.1 Normalized Density Approach 16
2.2.2 Treatments for Multi-phase Flow 17
2.2.3 Surface Tension Force Model 18
2.3 SPH Code Implementation 20
2.3.1 Nearest Neighbor Particle Search (NNPS) 20
2.3.2 Algorithm of SPH Code 21
2.3.3 Time Integration 21
2.3.4 GPU Parallelization 22
Chapter 3 Rigid Body Dynamics (RBD) 30
3.1 RBD Overview 30
3.2 Collision Models of Rigid Body 31
3.2.1 Monaghan Boundary Force (MBF) Model 31
3.2.2 Ideal Plastic Collision Model 33
3.2.3 Impulse-based Boundary Force (IBF) Model 35
3.2.4 Penalty-based Contact Model 37
3.2.5 Determination of Collision Model 40
3.3 Algorithm of RBD 41
3.3.1 Calculation of Rigid Body Information 41
3.3.2 Contact Detection 42
3.3.3 Contact Normal Calculation 42
3.3.4 Contact Force Calculation 45
3.3.5 Summation of Rigid Body Particles 46
3.3.6 Time Integration 47
3.4 GPU Parallelization 48
3.4.1 Algorithm 1: Atomic Operation 49
3.4.2 Algorithm 2: Sorting 50
3.5 Code V&V Simulations 51
3.5.1 Conservation of Momentum & Angular Momentum 51
3.5.2 Conservation of Kinetic Energy in Elastic Collision 52
3.5.3 Bouncing Block 53
3.5.4 Sliding Block on a Slope 55
3.5.5 Collapse of Stacked Multi-body 57
Chapter 4 Two-way Coupling of SPH-RBD 75
4.1 Resolved Approach 75
4.2 Governing Equations 75
4.2.1 Solid Phase 75
4.2.2 Fluid Phase 78
4.3 Algorithm of SPH-RBD Code 78
4.4 Code V&V Simulations 81
4.4.1 Karman Vortex Problem 81
4.4.2 Water Entry 84
4.4.3 Sinking & Rotating Body 85
4.4.4 Floating & Falling Body 85
4.4.5 Collapse of Stacked Multi-body with Fluid 87
4.4.6 Code Application to Non-spherical Debris Sedimentation 89
Chapter 5 Conclusion 110
5.1 Summary 110
5.2 Recommendations 112
Nomenclature 114
Bibliography 117
๊ตญ๋ฌธ ์ด๋ก 127๋ฐ
Handbook of Mathematical Geosciences
This Open Access handbook published at the IAMG's 50th anniversary, presents a compilation of invited path-breaking research contributions by award-winning geoscientists who have been instrumental in shaping the IAMG. It contains 45 chapters that are categorized broadly into five parts (i) theory, (ii) general applications, (iii) exploration and resource estimation, (iv) reviews, and (v) reminiscences covering related topics like mathematical geosciences, mathematical morphology, geostatistics, fractals and multifractals, spatial statistics, multipoint geostatistics, compositional data analysis, informatics, geocomputation, numerical methods, and chaos theory in the geosciences
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