Three-dimensional Simulation Tool Research Articles

Design optimization of anti-splashing targets and simulation of droplet impact on it

Natural surfaces have micro and nanostructures that affect the splashing behavior of water droplets falling on them. Synthetic surfaces mimicking this natural phenomenon have been previously reported. The objective of our current work is to design such surfaces and fine-tune the fluid splashing behavior using three-dimensional simulation tools. We have designed and simulated splashing behavior on geometrically patterned micro scale surfaces using the volume of fluid method within the commercial software Ansys Fluent. Surfaces with microscale pillars of different heights, geometrical shapes, layouts as well as tip designs were simulated with the goal of minimizing fluid splash. We found that certain pillar models produce less splashes than others. We have further optimized array structures for fluid splashing diameter and velocity. Behavior at different falling angles and fluid types are also investigated in multi-pillar models. The results indicate that a non-uniform structured surface decreases the speed and energy of the falling droplet. We have reported here three finalized designed models that are 35%, 63.5%, and 69% effective in reducing velocity compared to a flat surface model.

Feasibility analysis of a direct injection H2 internal combustion engine: Numerical assessment and proof-of-concept

The present study is a proof-of-concept investigation of a lean hydrogen internal combustion engine aiming to understand and address its critical thermo-fluid dynamics aspects, by means of a multi-fidelity computational fluid dynamics approach. Starting from an existing gasoline engine, the influence of the most relevant parameters and components on performance and efficiency is investigated using both one- and three-dimensional simulation tools, with the goal of defining a comprehensive strategy for adapting the engine design to the new requirements imposed by the hydrogen fuel. In particular, the following parameters affecting the retrofit effectiveness are analyzed and modified by the authors: turbocharging system, injection strategy, compression ratio, valves timing and intake ports design. Promising performance are achieved with the final configuration, revealing that substantial improvements can be obtained through a dedicated design: the BMEP is consistently above 17 bar with a peak brake efficiency higher than 40%.

Optimization of Microchannels and Application of Basic Activation Functions of Deep Neural Network for Accuracy Analysis of Microfluidic Parameter Data.

The fabrication of microflow channels with high accuracy in terms of the optimization of the proposed designs, minimization of surface roughness, and flow control of microfluidic parameters is challenging when evaluating the performance of microfluidic systems. The use of conventional input devices, such as peristaltic pumps and digital pressure pumps, to evaluate the flow control of such parameters cannot confirm a wide range of data analysis with higher accuracy because of their operational drawbacks. In this study, we optimized the circular and rectangular-shaped microflow channels of a 100 μm microfluidic chip using a three-dimensional simulation tool, and analyzed concentration profiles of different regions of the microflow channels. Then, we applied a deep learning (DL) algorithm for the dense layers of the rectified linear unit (ReLU), Leaky ReLU, and Swish activation functions to train and test 1600 experimental and interpolation of data samples which obtained from the microfluidic chip. Moreover, using the same DL algorithm, we configured three models for each of these three functions by changing the internal middle layers of these models. As a result, we obtained a total of 9 average accuracy values of ReLU, Leaky ReLU, and Swish functions for a defined threshold value of using the trial-and-error method. We applied single-to-five-fold cross-validation technique of deep neural network to avoid overfitting and reduce noises from data-set to evaluate better average accuracy of data of microfluidic parameters.

Effects of initial conditions and transport on ram pressure, Mach number, and uniformity for plasma liner formation and implosion

Plasma jet driven magneto-inertial fusion involves the merging of high Mach number plasma jets in a spherically converging geometry to form an imploding plasma liner. A three-dimensional smooth particle hydrodynamic simulation tool was used to study the number of plasma jets, jet density, and implosion velocity on the effects of formation and subsequent implosion of a plasma liner. The effects of different transport physics are presented. Thermal radiation and two-temperature modeling were found to have the most significant impact on the ram pressure. Solid angle averaged ram pressure and Mach number degradation were of particular interest in this study. Higher jet numbers were found to result in higher peak ram pressure. A spherical harmonic analysis was conducted for each case, providing a quantitative measure of the non-uniformity of the liner during the implosion process and how non-uniformities are affected by the different parameters explored in this study.

Damage risk assessment in historic buildings using equivalent wall-parts

Damage risks in historic buildings are often connected to moisture level, in turn related to temperature. Hence, when damage risk is being assessed, the risk at the points in the geometry of the building where the heat flow is the largest, for instance by the thermal bridges, is of crucial interest. In practice, such assessments may often be based on simulated average conditions of the room air, instead being made for the risk-prone points where the damages are most likely to occur. The reason is that the whole-building simulation tools are generally one-dimensional in their calculations, and unable to deal with the multi-dimensional heat flows at the thermal bridges. Hence the actual damage risk remains unknown, and may be under-estimated to an extent that is impossible to evaluate, without further investigations. Subsequent investigations can be performed for assumed risk-prone points, using two- or three-dimensional simulation tools, but in order to know what points that needs to be scrutinized it would be of value to get a first risk assessment directly in the whole building simulation process. In this article a method, based on the use of equivalent wall-parts, mimicking the performance of the most extreme points of the thermal bridges, is presented. It is displayed how the use of the wall-parts may provide an overview of the risk levels already in the whole-building simulation.

3D Modelling for Solar Erythemal UV Protection Provided by Human Hair

The head is one of the most sun-exposed anatomical zones and its ultraviolet (UV) exposure is often underestimated. The goal of this research is to quantify the solar erythemal UV protection provided by human hair for different orientations and Solar Zenith Angles (SZA). For this purpose, a three-dimensional (3D) numeric simulation tool called SimUVEx was used to forecast the distribution of UV exposure based on geometric information and solar irradiance. The relative UV dose reduction was expressed in terms of predictive protection factor (PPF). Results showed that the effectiveness of the protection depends strongly on the orientation of the head and on the tilt of the hairs. As the SZA increases, the PPF also increases. PPFs provided by hair with a certain degree of order (parallel alignment) were generally higher by a range of about 10%–30% than the ones provided by random arrangements. A significant exposure to the scalp through the hair, even for an average hair density, was found. It confirms that hair is an important natural sunscreen in reducing transmission of UV radiation and must be considered in the prevention messages of skin cancer on the scalp, particularly in people with alopecia.

Aero-structural optimization and analysis of a camber-morphing flying wing: Structural and wind tunnel testing

This article presents the design, optimization and performance assessment of a novel structure-actuation morphing concept for a flying wing, enabling the flight control for straight flight and around the pitch and roll axes. The applied camber-morphing concept utilizes an optimized selectively compliant internal structure, combined with electromechanical actuators to achieve a trailing edge deflection. These deflections lead to variations of the local and global lift, permitting to control the flight of the aircraft. The aero-structural behaviour of the wing is analysed using a coupled three-dimensional aerodynamic and structural simulation tool. An optimization of the planform, aerodynamic shape, internal structure and actuation parameters is performed to attain a longitudinally stable and aerodynamically efficient flying wing. The drag increment caused by morphing is minimized through the numerical optimization, resulting in high aerodynamic efficiency across a range of flight speeds. The stiffness and morphing capabilities of the manufactured wing are characterized experimentally and are compared with the numerical predictions, and the aerodynamic and aeroelastic behaviour of the wing is investigated through wind tunnel tests. The test results indicate the ability of the flying wing to achieve sufficient variations in lift, roll and pitch to control the flight completely through camber morphing.

Effect of Self-Heating on the Electrical Characteristics of Strained Si FinFETs.

Self-heating effect (SHE) on the electrical characteristics of fin field-effect transistors (FinFETs) model with a strained Si channel was investigated by using a three-dimensional simulation tool. Strain was applied from 0.1 to 2.0 GPa by changing Si mole fraction of the Si1-xGex. Simulation results showed that the drain current of the strained Si FinFETs increased with increasing applied strain from 0.5 to 2.0 GPa. The drain current of the FinFETs under strain of 2.0 GPa increased up to 20.59 μA. While the drain current of the FinFETs without a SHE increased with increasing strain, the increase of the drain current generating from the strain interrupted the applications for the practical device operation due to a large SHE. The drain current decreased due to the increased scattering resulting from the increased device temperature with an increase in the SHE.

3D Virtual Simulation approach in Brazilian Vocational Education for Computers Network Adapted to Student Knowledge

This paper presents an experiment with real users in a realistic three-dimensional simulation tool manufacture and installation of computer networks. The study highlights the use of virtual simulators for vocational education applied technology courses, with the main focus on the upper reaches of Technology Analysis and Systems Development. The tests were performed microarray in vitro to determine the usability and functionality of the system, and behavioral tests to determine which system use ratio and the effectiveness of learning. The results showed that the use of simulators is relevant to the determination of the content and can reduce deployment costs and maintenance of a physical laboratory without prejudice to the teaching practice. An evaluation was carried out with students in class paired (with and without simulation). It follows that is propaedeutic use a simulation tool for the professional education of a higher level, virtual laboratories can provide a balanced sense of knowledge and low operating cost practice in addition to increasing the motivation of students

A micro-climatic study on cooling effect of an urban park in a hot and humid climate

The cooling effect of a 4.5ha urban forest park located in a dense city center area in a hot and humid climate was investigated with the three-dimensional microclimate simulation tool ENVI-met v3.1. Dynamic predictions are firstly performed with different wind directions (northerly, southerly, easterly and westerly) for a typical summer day. Then the meteorological data were averaged to eliminate the effect of wind direction, considering equal probability for each wind direction. Overall, when wind speed is 1.5m/s, park cool island (PCI) intensity is about 2°C and the PCI center is offset from the park center if a preponderant prevailing wind direction exists. After eliminating the influence of wind direction by considering equal probability for each wind direction, PCI intensity is about 0.8°C and the PCI center is near to the park center. A higher wind speed would lead to a lower PCI intensity and a smaller area of influence. Compared to air temperature, the spatial distributions of mean radiant temperature and relative humidity are not significantly affected by a preponderant prevailing wind direction. And mean radiant temperature was found to be about 30°C lower in shaded areas of the park.

Development of a Computational Tool to Simulate Foil Bearings for Supercritical CO2 Cycles

The foil bearing is an enabling technology for turbomachinery systems, which has the potential to enable cost efficient supercritical CO2 cycles. The direct use of the cycle's working fluid within the bearings results in an oil-free and compact turbomachinery system; however, these bearings will significantly influence the performance of the whole cycle and must be carefully studied. Moreover, using CO2 as the operating fluid for a foil bearing creates new modeling challenges. These include highly turbulent flow within the film, non-negligible inertia forces, high windage losses, and nonideal gas behavior. Since the flow phenomena within foil bearings is complex, involving coupled fluid flow and structural deformation, use of the conventional Reynolds equation to predict the performance of foil bearings might not be adequate. To address these modeling issues, a three-dimensional flow and structure simulation tool has been developed to better predict the performance of foil bearings for the supercritical CO2 cycle. In this study, the gas dynamics code, eilmer, has been extended for multiphysics simulation by implementing a moving grid framework, in order to study the elastohydrodynamic performance of foil bearings. The code was then validated for representative laminar and turbulent flow cases, and good agreement was found between the new code and analytical solutions or experiment results. A separate finite difference code based on the Kirchoff plate equation for the circular thin plate was developed in Python to solve the structural deformation within foil thrust bearings, and verified with the finite element analysis from ansys. The fluid-structure coupling algorithm was then proposed and validated against experimental results of a foil thrust bearing that used air as operating fluid. Finally, the new computational tool set is applied to the modeling of foil thrust bearings with CO2 as the operating fluid.

Effect of the Si nanowire’s diameter and doping profile on the electrical characteristics of gate-all-around twin Si-nanowire field-effect transistors

The effect of the Si nanowire’s diameter and doping profile on the electrical characteristics of gate-all-around twin Si-nanowire field-effect transistors (TSNWFETs) was simulated by using the three-dimensional technology computer-aided design simulation tools of Sentaurus and taking into account quantum effects. While the switching and the short-channel immunity characteristics were improved with decreasing nanowire diameter, the threshold voltage and the total on-current for the TSNWFETs decreased, resulting in a deterioration of device performances. The swing characteristics for the TSNWFETs maintained almost the same behaviors regardless of the boron concentration variation in the nanowire. Gate-induced drain leakage (GIDL) of the TSNWFETs appeared at a high drain voltage, and the GIDL current increased with increasing boron concentration in the Si nanowires. The electrical characteristics of the TSNWFETs were improved by optimizing the diameter and the doping concentration of the Si nanowire to lower the GIDL and the off-state leakage current.

Impact of Combination of EGR, SCR, and DPF Technologies for the Low-Emission Rail Diesel Engines

The EU emission standards for new rail diesel engines are becoming more stringent: stage IV emission targets have just come into effect, while stage V is in under considerations. Both exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) technologies can be used to reduce nitric oxide (NOx) emissions, while the PM emission control requires a diesel particulate filter (DPF). The use of SCR requires on-board storage of urea, while the use of DPF needs to take into account its impact on engine efficiency performance. Both of these technologies require specific studies when applied to the rail engines; in particular, it becomes necessary to evaluate the engine performance trade-offs in order to evaluate how these technologies can be utilized efficiently in rail applications in order to meet current and future emission standards. The present study assesses the application of these technologies in diesel railcars on a quantitative basis using one- and three-dimensional numerical simulation tools. In particular, the study considers a 560-kW railcar engine with the use of different technology combinations for NOx reduction: SCR or EGR + DPF, and EGR + DPF + SCR. The NOx and PM emission performances are evaluated over the C1 homologation cycle and, in the case of the DPF, over an approximated railcar driving cycle as well. Several BSNOx targets were considered: 2 g/kWh, 1 g/kWh, and 0.4 g/kWh. Simulation results indicate that EGR + DPF + SCR-based solution is necessary to achieve stage IV emission limits for the 560-kW engine. On the other hand, SCR-based solutions have the potential to go beyond the stage IV NOx limit through scaling up the size of the SCR device and the on-board urea storage.

Analysis of eddy currents induced by transverse and longitudinal gradient coils in different tungsten collimators geometries for SPECT/MRI integration.

We investigated the temporal variation of the induced magnetic field due to the transverse and the longitudinal gradient coils in tungsten collimators arranged in hexagonal and pentagonal geometries with and without gaps between the collimators. We modeled x-, y-, and z-gradient coils and different arrangements of single-photon emission computed tomography (SPECT) collimators using FEKO, a three-dimensional electromagnetic simulation tool. A time analysis approach was used to generate the pulsed magnetic field gradient. The approach was validated with measurements using a 7T MRI scanner. Simulations showed an induced magnetic field representing 4.66% and 0.87% of the applied gradient field (gradient strength = 500 mT/m) for longitudinal and transverse gradient coils, respectively. These values can be reduced by 75% by adding gaps between the collimators for the pentagonal arrangement, bringing the maximum induced magnetic field to less than 2% of the applied gradient for all of the gradient coils. Characterization of the maximum induced magnetic field shows that by adding gaps between the collimators for an integrated SPECT/MRI system, eddy currents can be corrected by the MRI system to avoid artifact. The numerical model was validated and was proposed as a tool for studying the effect of a SPECT collimator within the MRI gradient coils.

Vortex shedding and evolution induced by a solitary wave propagating over a submerged cylindrical structure

The shedding and evolution of the vortical structures generated by a solitary wave propagating over a submerged cylindrical structure are investigated experimentally and numerically. The cylindrical structure consists of two concentric cylinders and represents a simplified model for an offshore submerged intake structure typically used in coastal power plants. Flow visualization by dye injection is used to identify the dominant vortical structures near the structure. The flow visualization results show an unexpected flow reversal that causes shedding of secondary vortical structures. The experimental results are used to check a three-dimensional volume of fluid-large eddy simulation (VOF-LES) numerical model. The VOF-LES model is then used to further study the flow structure. A total of six dominant vortical structures generated by the wave motion are identified, followed by two more generated by the flow reversal. In summary, this paper provides the vorticity evolution for a complex fluid–structure interaction problem and a three-dimensional numerical simulation tool has also been validated, which can be extended to study more complex geometries and wave conditions.

Numerical analysis of Al vapour effects in gas metal arc welding of Al alloys

Using an in-house three-dimensional (GMAW) process simulation tool, the effects of Al vapour in the arc welding of aluminium alloys for various welding currents have been studied. The mathematical model, which takes into account the effects of metal vapour, is described. A bead-on-Al-plate problem is then modelled, with and without consideration of the Al vapour for various welding currents. The effects of the Al vapour on the energy flow of the system and the resulting weld profile are examined. The calculated plasma temperatures are compared with measured temperatures. The change of heat input to the workpiece due to the presence of Al vapour is examined. Finally, the calculated weld profiles with and without consideration of Al vapour are compared with actual weld profiles. It is found that the presence of Al vapour reduces the arc temperature and the weld depth significantly.

Toward Two-Dimensional Simulations of Hysteresis Losses in Partially Coupled Superconducting Wires

When designing superconducting magnets, it is of ample importance to be able to reliably simulate the electromagnetic behavior of the superconducting wires comprising the magnet. The filaments of the wires in the magnets are often twisted to minimize the coupling between the filaments in applied fields. In twisted superconductors, the filaments can be coupled, uncoupled or partially coupled. Typically, the partially coupled wires have been simulated using three-dimensional (3D) simulation tools. Even though they produce accurate results, the problems arising from 3D formulations can be computationally very heavy. In this paper, we present a two-dimensional (2D) approach to model coupled, partially coupled, and uncoupled superconducting wires using the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$H$</tex></formula> -formulation of the eddy current model. Furthermore, we use 3D simulations to benchmark our 2D simulations.

Comparison of simulations with PHITS and HIBRAC with experimental data in the context of particle therapy monitoring

Therapeutic irradiation with protons and ions is advantageous over radiotherapy with photons due to its favorable dose deposition. Additionally, ion beams provide a higher relative biological effectiveness than photons. For this reason, an improved treatment of deep-seated tumors is achieved and normal tissue is spared. However, small deviations from the treatment plan can have a large impact on the dose distribution. Therefore, a monitoring is required to assure the quality of the treatment. Particle therapy positron emission tomography (PT-PET) is the only clinically proven method which provides a non-invasive monitoring of dose delivery. It makes use of the β+-activity produced by nuclear fragmentation during irradiation. In order to evaluate these PT-PET measurements, simulations of the β+-activity are necessary. Therefore, it is essential to know the yields of the β+-emitting nuclides at every position of the beam path as exact as possible. We evaluated the three-dimensional Monte-Carlo simulation tool PHITS (version 2.30) [ 1] and the 1D deterministic simulation tool HIBRAC [ 2] with respect to the production of β+-emitting nuclides. The yields of the most important β+-emitting nuclides for carbon, lithium, helium and proton beams have been calculated. The results were then compared with experimental data obtained at GSI Helmholtzzentrum für Schwerionenforschung Darmstadt, Germany. GEANT4 simulations provide an additional benchmark [ 3]. For PHITS, the impact of different nuclear reaction models, total cross-section models and evaporation models on the β+-emitter production has been studied. In general, PHITS underestimates the yields of positron-emitters and cannot compete with GEANT4 so far. The β+-emitters calculated with an extended HIBRAC code were in good agreement with the experimental data for carbon and proton beams and comparable to the GEANT4 results, see [ 4] and Fig. 1. Considering the simulation results and its speed compared with three-dimensional Monte-Carlo tools, HIBRAC is a good candidate for the implementation in clinical routine PT-PET. Fig 1.Depth-dependent yields of the production of 11C and 15O during proton irradiation of a PMMA target with 140 MeV [ 4].

CFD를 활용한 수소-천연가스 혼합연료에 대한 피해영향 분석

본 연구는 3차원 위험성평가 시뮬레이션 툴(FLACS)을 활용하여 연료의 종류에 따른 위험성을 비교 평가하였다. 일반적인 고압가스 충전소 레이아웃을 활용하여 연료를 CNG, 수소, 30%HCNG로 하였을 경우 충전소에서 가스누출에 의한 화재 폭발 상황을 모사하여 피해영향을 비교 분석하였다. 그리고 가스별 누출제트에 의한 피해영향을 평가하였다. 동일한 조건에서 수소, CNG, HCNG가 누출되어 화재폭발이 발생할 경우 수소는 최대과압이 30kPa, HCNG는 3.5kPa 그리고 CNG는 0.4kPa의 과압이 측정되었다. HCNG의 과압이 CNG에 비해 7.75배 높게 측정되었으나, 수소에 비해서는 11.7%에 불과했다. 화염 전파에 있어서 수소는 매우 빠른 화염전파 특성을 가지는 반면 HCNG와 CNG는 수소에 비해 전파속도 및 전파거리에서 비교적 안전한 경향을 보였다. 제트화염에 의한 화염경계거리는 수소가 5.5m, CNG가 3.4m이고 HCNG는 CNG보다 약간 확장된 3.9m로 예측되었다. This study evaluated comparison of the risk according to the type of fuel by three-dimensional simulation tool(FLACS). The consequence analysis of fire explosion and jet-fire was carried out in the layout of a typical high-pressure gas filling stations using CNG, hydrogen and 30%HCNG. Under the same conditions, hydrogen had a 30kPa maximum overpressure, CNG had a 0.4kPa and HCNG had a 3.5kPa. HCNG overpressure was 7.75 times higher than the CNG measurement, but HCNG overpressure was only 11.7% compared to hydrogen. In case of flame propagation, hydrogen had a very fast propagation characteristics. On the other hand, CNG and HCNG flame propagation velocity and distance tended to be relatively safe in comparison to hydrogen. The estimated flame boundary distance by jet-fire of hydrogen was a 5.5m, CNG was a 3.4m and HCNG was a 3.9m.

Best-Estimate Predictions and Model Calibration for Reactor Thermal Hydraulics

This work applies a recently developed best-estimate data assimilation and model calibration methodology to the three-dimensional reactor thermal-hydraulics simulation and design tool FLICA4. The experimental information used for calibrating FLICA4 parameters stems from the international Organisation for Economic Co-operation and Development/Nuclear Regulatory Commission boiling water reactor full-size fine-mesh bundle tests (BFBT) benchmarks, which were designed by the Nuclear Power Engineering Corporation of Japan for enabling systematic validation of simulation tools using full-scale experimental data. The following specific BFBT experiments have been used in this work for calibrating parameters and boundary conditions for FLICA4: (a) axial void fraction distributions and (b) transversal void fraction distributions. The resulting uncertainties for the predicted parameters and distributions of pressure drops and void fractions are shown to be smaller than the a priori experimental and computed uncertainties, thus demonstrating the successful calibration of a large-scale reactor core thermal-hydraulics code using the BFBT benchmark-grade experiments.