Three-dimensional Simulation Technique Research Articles

Novel three-dimensional simplified numerical simulation method of a compact precooler for hypersonic precooled air-breathing engine

The revolutionary thermal cycle of precooled air-breathing engines has led to the application of a compact tubular precooler. A novel three-dimensional simplified numerical simulation method for a compact tube precooler is proposed. The unique aspect of this method is the integration of low-dimensional design method of the precooler with three-dimensional simulation technique. The method includes a segmented model to discretize the precooler into sub-precoolers, with corresponding performance calculation programs for circumferential uniform and non-uniform airflows in the circumferential direction. The heat transfer and pressure drop are then simulated using a combination of the distributed heat source method and porous model. The developed method was verified with previous experiments, and showed good agreement. In addition, the flow and heat transfer characteristics of the precooler were investigated under both circumferential uniform and non-uniform inlet conditions. The results show that the radial total temperature distortion intensity at the outlet of the precooler is 0.087 and 0.073 under uniform and non-uniform inlet conditions, respectively. Additionally, the intensity of circumferential total temperature distortion increases from 0.004 under uniform inlet conditions to 0.029 under non-uniform inlet conditions. Overall, this method provides an accurate evaluation of the precooler during the engineering design phase.

Brownian Motion Simulation for Estimating Chloride Diffusivity of Cement Paste

Chloride ion diffusion properties are important factors that affect the durability of cementitious materials. Researchers have conducted much exploration in this field, both experimentally and theoretically. Numerical simulation techniques have been greatly improved as theoretical methods and testing techniques have been updated. Researchers have modeled cement particles mostly as circular shapes, simulated the diffusion of chloride ions, and derived chloride ion diffusion coefficients in two-dimensional models. In this paper, a three-dimensional random walk method based on Brownian motion is employed to evaluate the chloride ion diffusivity of cement paste with the use of numerical simulation techniques. Unlike previous simplified two-dimensional or three-dimensional models with restricted walks, this is a true three-dimensional simulation technique that can visually represent the cement hydration process and the diffusion behavior of chloride ions in cement paste. During the simulation, the cement particles were reduced to spheres, which were randomly distributed in a simulation cell with periodic boundary conditions. Brownian particles were then dropped into the cell and permanently captured if their initial position in the gel fell. Otherwise, a sphere tangential to the nearest cement particle was constructed, with the initial position as the center. Then, the Brownian particles randomly jumped to the surface of this sphere. The process was repeated to derive the average arrival time. In addition, the diffusion coefficient of chloride ions was deduced. The effectiveness of the method was also tentatively confirmed by the experimental data.

Assessment of lower third molar space: A comparative radiographic study.

The aim of this study was to assess lower third molar space using four different radiographic reconstructed Cone Beam Computed Tomography (CBCT) images: orthopantomogram, lateral cephalogram, multiplanar CBCT and a newly introduced three-dimensional (3D) simulation technique. The CBCT scans of 32 individuals (20.97 ± 2.152 years) with a total of 50 lower third molars were collected and analyzed. The ratio between the necessary space and available space for lower third molars was calculated on each radiographic reconstructed image. Repeated-measure analysis of variance followed by multiple comparison tests were used. The mean ratio was significantly smaller with cephalograms (0.611 ± 0.263), followed respectively by orthopantomograms (0.756 ± 0.221), multiplanar CBCT (0.789 ± 0.191) and 3D simulation technique (0.807 ± 0.193) (p < 0.001). The lowest mean difference was recorded between multiplanar CBCT and 3D simulation technique (0.017). Intraclass correlation coefficient was strong (>0.90) for all techniques except cephalograms. The assessment of the lower third molar space differs according to the adopted imaging technique. Three-dimensional simulation technique is a useful novel technology that allows an exploration of the crown in many different dimensions and orientations, giving more predictable results than the conventional methods.

Simulation and Visualization of Internal Heat and Mass Flow Distribution of SOFCs

Introduction In recent years, electrochemical energy conversion technologies receive much attention, as a very high power-generation efficiency beyond 70 to 80% using SOFCs may be possible (1). Although it is important to understand the phenomena in SOFC stacks for highly efficient power generation, it is rather difficult to measure the distribution of internal power generation characteristics experimentally. Here, the performance visualization and prediction by simulation techniques are useful. Exchange current density is an important phenomenological parameter in simulating electrochemical performance (2-3). The exchange current density, expressing the electrode performance quantitatively, is a physical value which depends on gas composition, operating temperature, cell electrode materials, and cell structure. Whilst it is therefore essential to take into account these effects in the numerical calculation, there are not many consistent studies fairly comparing experimental and numerical results.Here in this study, the cell performance is experimentally measured using planar cells composed of typical materials under humidified hydrogen fuel supply. In parallel, the cell performance is also numerically simulated using the exchange current density values. Both results are then compared each other. The aim of this study is to develop three-dimensional simulation technique for visualizing the internal distribution in solid oxide fuel cells, by comparing experimental results with numerical results. Experimental and calculation conditions Electrolyte-supported 50 mm × 50 mm size planar cells with ScSZ electrolyte (ScSZ: 10 mol% Sc2O3–1 mol% CeO2–89 mol% ZrO2) were used to measure the actual cell performance. NiO-ScSZ cermet and (La0.8Sr0.2)0.98MnO3-ScSZ (LSM-ScSZ) composite were used as the anode and the cathode, respectively. Electrode layers with the electrode area of 40 mm×40 mm (16 cm2) were prepared via screen printing technique. In this study, I-V characteristics were measured as a function of fuel utilization (Uf) at the outlet by varying the inlet flow rate of humidified hydrogen fuel supplied to the anode under a given current value. In the simulation, a three-dimensional actual-shape CAD model with cross-flow channels was constructed, using numerical simulation software COMSOL Multiphysics (Ver. 5.2). Cell performance simulation was performed at the operating temperature of 1073 K for 3%-humidified hydrogen fuels. The phenomenological equation describing exchange current density was applied which has been determined for the cells using the same materials and the same preparation conditions. Results and discussion The comparison between experimental and calculated results for various flow rates is shown in Figure 1. The current density value in the simulation is the average current density for the geometric electrode area. The experimental results showed that the OCV decreased as the inlet flow rate decreased. While the experimental value and the simulation result are slightly different due to a difference in the OCV, the slopes of these I-V characteristics are identical in all these cases. These results indicate that this numerical model can simulate I-V characteristics experimentally obtained for the SOFC planar cells under any local conditions.The current density distribution at the electrode/electrolyte interface, at the inlet flow rate for Uf =10% and at the in-plane average current density of 0.2 A cm-2, is shown in Figure 2. The current density distribution exhibited a maximum value near the fuel inlet. The current density gradually decreased towards the fuel outlet. These results indicate that the concentration distribution of hydrogen affects the current density distribution. These results suggest that the electrochemical reaction tends to occur mainly near the anode inlet for humidified hydrogen fuels. Hydrogen is consumed along with the gas flow from the inlet to the outlet, leading to a decrease in current density. Various simulation and visualization results will be reported and discussed. References Y. Matsuzaki, Y. Tachikawa, T. Somekawa, T. Hatae, H. Matsumoto, S. Taniguchi, and K. Sasaki, Sci. Rep., 5, 12640 (2015).T. Hosoi, T. Yonekura, K. Sunada, and K. Sasaki, J. Electrochem. Soc., 162 (1), F136-F152 (2015).T. Yonekura, Y. Tachikawa, T. Yoshizumi, Y. Shiratori, K. Ito, and K. Sasaki, ECS Trans., 35 (1), 1007-1014 (2011). Acknowledgment This study is partially supported by the Center of Innovation (COI) program (JPMJCE1318) of the Japan Science and Technology Agency. Figure 1

Early Time Modifications to the Buoyancy-Drag Model for Richtmyer–Meshkov Mixing

Abstract The Buoyancy-Drag model is a simple model, based on ordinary differential equations, for estimating the growth in the width of a turbulent mixing zone at an interface between fluids of different densities due to Richtmyer–Meshkov and Rayleigh–Taylor instabilities. The model is calibrated to give the required self-similar behavior for mixing in simple situations. However, the early stages of the mixing process are very dependent on the initial conditions and modifications to the Buoyancy-Drag model are then needed to obtain correct results. In a recent paper, Thornber et al. (2017, “Late-Time Growth Rate, Mixing, and Anisotropy in the Multimode Narrowband Richtmyer–Meshkov Instability: The θ-Group Collaboration,” Phys. Fluids, 29, p. 105107), a range of three-dimensional simulation techniques was used to calculate the evolution of the mixing zone integral width due to single-shock Richtmyer–Meshkov mixing from narrowband initial random perturbations. Further analysis of the results of these simulations gives greater insight into the transition from the initial linear behavior to late-time self-similar mixing and provides a way of modifying the Buoyancy-Drag model to treat the initial conditions accurately. Higher-resolution simulations are used to calculate the early time behavior more accurately and compare with a multimode model based on the impulsive linear theory. The analysis of the iLES data also gives a new method for estimating the growth exponent, θ (mixing zone width ∼ tθ), which is suitable for simulations which do not fully reach the self-similar state. The estimates of θ are consistent with the theoretical model of Elbaz and Shvarts (2018, “Modal Model Mean Field Self-Similar Solutions to the Asymptotic Evolution of Rayleigh-Taylor and Richtmyer-Meshkov Instabilities and Its Dependence on the Initial Conditions,” Phys. Plasmas, 25, p. 062126).

The Interaction of Ile-Phe Dipeptide with Phosphatidylinositide 3-Kinase (PI3K): Molecular Dynamics and Molecular Docking Studies

Self-assembly of phenylalanine creates Phe fibers which is the characteristic fiber model found in amyloid fibrils linked with various neurodegenerative diseases. L-Isoleucyl-L-Phenylalanine (Ile-Phe) dipeptide is composed of isoleucine and phenylalanine amino acids, having fibrillary structure similar to nanotube forms of the core recognition motif of Alzheimer's β-amyloid polypeptide. The integrated coordination of neuronal responses via the PI3-K / Akt pathway has a significant functional impact on Alzheimer's disease. Exposure to Aβ in neuronal cultures leads to deterioration of PI3-K, Akt and mTOR signaling, which may cause cognitive loss during disease. Modulation of PI3-K, Akt and mTOR signal activity need aim to reduce or eliminate the accumulation of potential neurotoxins. The therapeutic approaches aimed to normalize neuronal responses on these pathways or activation of PI3-kinase have a protective effect against cognitive decline in animal models of Alzheimer disease. This study aims to determine the interaction of PI3-kinase with Ile-Phe dipeptide having amyloid fibril structure by three-dimensional simulation techniques such as molecular dynamics (with the GROMACS program) and molecular docking techniques (Schrodinger Software program).

Morphological Changes of Collagen Fibers in Myocardium of Rats under Different Exercise Loads Based on Three-Dimensional Simulation Technique.

In order to improve the visual analysis ability of the morphological changes of rat liulimyocardial collagen fibers under different exercise loads, a method of extracting the morphological changes of collagen fibers in rat myocardium under different exercise loads based on three-dimensional simulation technique is proposed. The three-dimensional morphological characteristics of the collagen fibers in the original rat myocardium are made by CT scanning technique. Like information collection, a gradient decomposition method is used to filter the three-dimensional morphological features of rat myocardial collagen fibers. The edge contour features of the three-dimensional morphological features of rat myocardial collagen fibers under different motion loads are extracted. The threshold segmentation method is used to carry out the rat myocardial glue under different exercise loads. The segmentation of the regional pixel feature block of the three-dimensional morphological features of the original fiber is segmented into a block vector with high resolution, and the regional reconstruction of the three-dimensional morphological features of the rat myocardial collagen fibers under different motion loads is carried out to realize the high resolution identification and classification of the 3D morphological features of the rat myocardial collagen fibers. The simulation results show that the three-dimensional simulation of the morphological changes of rat myocardial collagen fibers under different exercise loads is better, and the accuracy of feature extraction is higher.

Comparison between two-dimensional and three-dimensional computational fluid dynamics techniques for two straight-bladed vertical-axis wind turbines in inline arrangement

This study is dedicated to drawing a comparison between two- and three-dimensional approach capabilities for the simulation of two similar rotors placed in three inline (or tandem) arrangements. This arrangement is generally recognized as the worst-case scenario for the downwind rotor considering the vortices and disorders produced by the upwind rotor. The rotor in question with the diameter of 2.5 m is made up of three NACA0015 blades with the chord length and span size equal to 0.4 and 3 m, respectively. Based on the authors’ previous works, the [Formula: see text] shear stress transport model was selected for this comparative study. According to the results, there is an appreciable deviation in the aerodynamic performance of the upwind rotor predicted by the two-dimensional and three-dimensional simulation techniques. There is no tangible difference between the two-dimensional and three-dimensional results in terms of the averaged power output for the downwind rotor. However, the study of flow field employing different means like vortex structures, axial velocity, and even torque variation indicates that the two-dimensional approach is unable to achieve realistic and reliable output data. The introduced “pillar effect” regarding the dimensional limitations of the two-dimensional approach, which affects the vorticity shape and its dissipation, is plausible evidence for this discrepancy.

Structural optimization of the air-blast atomizer based on three-dimensional simulation techniques

The experience gained in structural modifying the low-pressure drop gas turbine engine fuel atomizer with two air nozzles is presented. The volume of fluid (VOF) approach is used for analyzing the two-phase flows to describe the numerical analysis of atomization quality. The base design and the design based on numerical analysis are compared by using a full-scale experiment.

Two-wave behavior under various conditions of transition area from cancellous bone to cortical bone

The two-wave phenomenon, the wave separation of a single ultrasonic pulse in cancellous bone, is expected to be a useful tool for the diagnosis of osteoporosis. However, because actual bone has a complicated structure, precise studies on the effect of transition conditions between cortical and cancellous parts are required. This study investigated how the transition condition influenced the two-wave generation using three-dimensional X-ray CT images of an equine radius and a three-dimensional simulation technique. As a result, any changes in the boundary between cortical part and trabecular part, which gives the actual complex structure of bone, did not eliminate the generation of either the primary wave or the secondary wave at least in the condition of clear trabecular alignment. The results led us to the possibility of using the two-wave phenomenon in a diagnostic system for osteoporosis in cases of a complex boundary.

Three-Dimensional Plasma Etching Simulation using Advanced Ray Tracing and Level Set Techniques

We present three-dimensional simulation techniques for plasma etching processes. Models based on Langmuir-type adsorption and on ballistic particle transport at feature scale can be efficiently solved in three dimensions. Surface coverages are self-consistently calculated. The local sputter rates of ions and the fluxes of neutrals are computed using modern ray tracing algorithms. In this way angle and energy dependent sputter yields or specular reflections of ions can be incorporated in a natural manner. For the time evolution of the surface we apply a recently developed fast multi-level-set framework. Our simulation techniques are demonstrated using a SF6/O2 plasma etching process model.

Radiation therapy after breast-conserving surgery

The authors critically reviewed previous articles concerning the significance of breast irradiation following breast-conserving surgery in terms of the following subject items: indications for breast-conserving therapy, the significance and complications of breast irradiation, the timing of the start of breast irradiation, the significance of boost irradiation, the potential improvement of survival with systemic therapy plus breast irradiation, the significance of axillary dissection, indications and the significance of regional nodal irradiation, accelerated hypofractionated radiotherapy, omission of breast irradiation in low-risk patients, and future directions. In addition, our previously reported results of breast irradiation following breast-conserving surgery at the Keio University Hospital are outlined. Our newly developed tangential irradiation technique directed to the axilla and a recently introduced three-dimensional simulation technique for radiotherapy treatment planning are also presented.

CFD Simulation of Stratified Combustion Process in a Direct Injection Spark Ignition Engine

A three-dimensional simulation technique for the stratified combustion process in direct injection gasoline engines is developed. The effects of a widely distributed mixture equivalence ratio and a large amount of EGR on laminar flame speed are briefly modeled taking into account only the temperature of the unburned mixture and the flame temperature. The suggested laminar flame speed model is incorporated into a CFD code in combination with the coherent flame model. In burned gas, chemical equilibrium depending on the local equivalence ratio is assumed so that the post flame reaction upon mixing rich burned gas and lean burned gas or fresh air can be simply modeled as a change of the equilibrium. The calculated flame propagation process, heat release rate and exhaust emissions are confirmed by the results of measurements including the LIF technique. The good agreements obtained under various conditions indicate the applicability of this method.

Ion beam extraction and transport for high-field electron cyclotron resonance ion sources (abstract)

The next-generation, very high magnetic-field electron cyclotron resonance (ECR) ion sources, like VENUS, SERSE, or PHOENIX, strive for substantially (a factor of 10) higher extracted heavy ion beam intensities than currently achievable. Such high-intensity ion beams present significant challenges for the design and simulation of an ECR extraction and low-energy ion beam transport system. Extraction and beam formation take place in a strong (up to 3 T) axial magnetic field, which leads to significantly different focusing properties for the different ion masses and charge states of the extracted beam. Typically, beam simulations must take into account the contributions of up to 50 different charge states and ion masses. Space charge effects must be correctly included since the extraction and mass analyzing system have to be designed for a proton-equivalent current of ∼25 mA at 30 kV extraction voltage. The article discusses state of the art two-dimensional and three-dimensional simulation techniques for such ion beam extraction and transport systems. Furthermore, the main contributions to the ion beam emittance are discussed: (1) The induced beam rotation due to the strong axial magnetic field, (2) the concentration of high charge state ions at the source center axis, and (3) the ion beam temperature. A novel large-gap analyzing magnet design is described which allows efficient correction of higher-order aberrations for high-intensity heavy ion beams. Such a magnet limits emittance blow up, and is necessary if the analyzed beam has to be further transported or accelerated, e.g., in a radio frequency quadrupole.

CFD Simulation for Stratified Combustion Process in a Direct Injection Gasoline Engine.

A three-dimensional simulation technique for stratified combustion process in direct injection gasoline engines is developed. The laminar flame speed for wide range of mixture equivalence ratio and EGR condition is modeled taking into account the reference temperature Intermediate between unburned and flame temperature for chemical reaction. This new laminar flame speed model and the coherent flame model are incorporated into a CFD code. The calculated flame propagation process, heat release rate and exhaust emissions are validated by measurements including LIF technique. The good agreement obtained for various operating conditions shows the availability of this method.