Computational fluid dynamics simulation of formaldehyde emission characteristics and its experimental validation in environment chamber

We investigated the effect of supply air rate and temperature on formaldehyde emission characteristics in an environment chamber. A three-dimensional computational fluid dynamics （CFD） chamber model for simulating formaldehyde emission in twelve different cases was developed for obtaining formaldehyde concentration by the area-weighted average method. Laboratory experiments were conducted in an environment chamber to validate the simulation results of twelve different cases and the formaldehyde concentration was measured by continuous sampling. The results show that there was good agreement between the model prediction and the experimental values within 4.3% difference for each case. The CFD simulation results varied in the range from 0.21 mg/m3 to 0.94 mg/m3, and the measuring results in the range from 0.17 mg/m3 to 0.87 mg/m3. The variation trend of formaldehyde concentration with supply air rate and temperature variation for CFD simulation and experiment measuring was consistent. With the existence of steady formaldehyde emission sources, formaldehyde concentration generally increased with the increase of temperature, and it decreased with the increase of air supply rate. We also provided some reasonable suggestions to reduce formaldehyde concentration and to improve indoor air quality for newly decorated rooms.     

Numerical simulation of a gas pipeline network using computational fluid dynamics simulators

This article describes numerical simulation of gas pipeline network operation using high-accuracy computational fluid dynamics (CFD) simulators of the modes of gas mixture transmission through long, multi-line pipeline systems (CFD-simulator). The approach used in CFD-simulators for modeling gas mixture transmission through long, branched, multi-section pipelines is based on tailoring the full system of fluid dynamics equations to conditions of unsteady, non-isothermal processes of the gas mixture flow. Identification, in a CFD-simulator, of safe parameters for gas transmission through compressor stations amounts to finding the interior points of admissible sets described by systems of nonlinear algebraic equalities and inequalities. Such systems of equalities and inequalities comprise a formal statement of technological, design, operational and other constraints to which operation of the network equipment is subject. To illustrate the practicability of the method of numerical simulation of a gas transmission network, we compare computation results and gas flow parameters measured on-site at the gas transmission enter-prise.     

Computational fluid dynamics simulation of the wind flow over an airport terminal building

Turbulence in the wake generated by wind flow over buildings or obstacles may produce complex flow patterns in downstream areas. Examples include the recirculating flow and wind deficit areas behind an airport terminal building and their potential impacts on the aircraft landing on nearby runways. A computational fluid dynamics （CFD） simulation of the wind flow over an airport terminal building was performed in this study of the effect of the building wake on landing aircraft. Under normal meteorological conditions, the studied airport terminal building causes limited effects on landing aircraft because most of the aircraft have already landed before entering the turbulent wake region. By simulating the approach of a tropical cyclone, additional CFD sensitivity tests were performed to study the impacts of building wake under extreme meteorological conditions. It was found that, in a narrow range of prevalent wind directions with wind speeds larger than a certain threshold value, a substantial drop in wind speed （〉3.6 m/s） along the glide path of aircraft was observed in the building wake. Our CFD results also showed that under the most critical situation, a drop in wind speed as large as 6.4 m/s occurred right at the touchdown point of landing aircraft on the runway, an effect which may have a significant impact on aircraft operations. This study indicated that a comprehensive analysis of the potential impacts of building wake on aircraft operations should be carried out for airport terminals and associated buildings in airfields to ensure safe aviation operation under all meteorological conditions and to facilitate implementation of precautionary measures.     

Numerical simulation of a direct internal reforming solid oxide fuel cell using computational fluid dynamics method

A detailed mathematical model of a direct internal reforming solid oxide fuel cell （DIR-SOFC） incorporating with simulation of chemical and physical processes in the fuel cell is presented. The model is developed based on the reforming and electrochemical reaction mechanisms, mass and energy conservation, and heat transfer. A computational fluid dynamics （CFD） method is used for solving the complicated multiple partial differential equations （PDEs） to obtain the numerical approximations. The resulting distributions of chemical species concentrations, temperature and current density in a cross-flow DIR-SOFC are given and analyzed in detail. Further, the influence between distributions of chemical species concentrations, temperature and current density during the simulation is illustrated and discussed. The heat and mass transfer, and the kinetics of reforming and electrochemical reactions have significant effects on the parameter distributions within the cell. The results show the particular characteristics of the DIR-SOFC among fuel cells, and can aid in stack design and control.     

Numerical simulation of a direct internal reforming solid oxide fuel cell using computational fluid dynamics methodas

A detailed mathematical model of a direct internal reforming solid oxide fuel cell (DIR-SOFC) incorporating with simulation of chemical and physical processes in the fuel cell is presented. The model is developed based on the reforming and electrochemical reaction mechanisms, mass and energy conservation, and heat transfer. A computational fluid dynamics (CFD) method is used for solving the complicated multiple partial differential equations (PDEs) to obtain the numerical approximations.The resulting distributions of chemical species concentrations, temperature and current density in a cross-flow DIR-SOFC are given and analyzed in detail. Further, the influence between distributions of chemical species concentrations, temperature and current density during the simulation is illustrated and discussed. The heat and mass transfer, and the kinetics of reforming and electrochemical reactions have significant effects on the parameter distributions within the cell. The results show the particularchar acteristics of the DIR-SOFC among fuel cells, and can aid in stack design and control.     

Optimization study of a PEM fuel cell performance using 3D multi-phase computational fluid dynamics model

INTRODUCTION Water management is one of the critical opera-tion issues in proton exchange membrane (PEM) fuelcells. Spatially varying concentrations of water inboth vapour and liquid form are expected throughoutthe cell because of varying rates of production andtransport (Sui and Djilali, 2005). Devising betterwater management is therefore a key issue in PEMFCdesign, and this requires improved understanding ofthe parameters affecting water transport in the mem-brane. Proper thermal m…     

Wind suitability in site analysis of coastal concave terrains using computational fluid dynamics simulation: a case study in East Asia

The effect of wind environment is becoming increasingly important in analyzing and selecting sites for better natural ventilation of residential buildings, external comfort, and pollution dispersion. The main purpose of this study was to develop a set of methods for wind environment assessment in coastal concave terrains. This set of methods can be used to provide quantifiable indicators of preferable wind conditions and help site analysis. Firstly, a total of 20 types of coastal bays with concave terrains in East Asia were characterized to find ideal locations. The selected areas were divided into five categories according to the main terrain features. Then a sample database for the concave terrains was compiled for modelling comparisons. Secondly, a number of key wind variables were identified. Computational fluid dynamics (CFD) models of the typical coastal concave terrains identified as a result of the study were created, and the local wind environments were simulated with input from geographic information system (GIS) and statistic package for social science (SPSS) analysis. A measure of wind suitability was proposed that takes wind velocity and wind direction into account using GIS. Finally, SPSS was used to find the relationship between wind suitability and key terrain factors. The results showed that wind suitability was significantly associated with terrain factors, especially altitude. The results suggest that residential building sites should be selected such that their bay openings face the direction of the prevailing wind and that the opposite direction should be avoided.     

A study of airfoil parameterization,modeling, and optimization based on the computational fluid dynamics method

An excellent airfoil with a high lift-to-drag ratio may decrease oil consumption and enhance the voyage. Based on NACA 0012, an improved airfoil is explored in this paper. The class/shape function transformation has been proved to be a good method for airfoil parameterization, and in this paper it is modified to improve imitation accuracy. The computational fluid dynamics method is applied to obtain numerically the aerodynamic parameters of the parameterized airfoil, and the result is proved credible by comparison with available experimental data in the open literature. A polynomial-based response surface model and the uniform Latin hypercube sampling method are employed to decrease computational cost. Finally, the nonlinear programming by quadratic Lagrangian method is utilized to modify the multi-island genetic algorithm, which has an improved optimization effect than the method used on its own. The obtained result shows that the modified class/shape function transformation method produces a better imitation of an airfoil in the nose and tail regions than the original method, and that it will satisfy the tolerance zone of the model in a wind tunnel. The response surface model based on the uniform Latin hypercube sampling method gives an accurate prediction of the lift-to-drag ratio with changes in the design variables. The numerical result of the flow around the airfoil shows reasonable agreement with the experimental data graphically and quantitatively. Ultimately, an airfoil with better capacity than the original one is acquired using the multi-island genetic algorithm based nonlinear programming by quadratic Lagrangian optimization method. The pressure contours and lift-to-drag ratio along with the attack angle have been compared with those of the original airfoil, and the results demonstrate the strength of the optimized airfoil. The process for exploring an improved airfoil through parameterization to optimization is worth referencing in future work.     

航空虚拟仿真实验平台构建及教学实施

阐述了航空虚拟仿真实验平台的构建层次、实验教学内容和实验教学阶段安排,探讨了实验平台管理运行机制和相关保障措施。该实验平台立足海军初级飞行学员和地勤学员的人才培养,在满足飞行技术和空中对抗战术模拟训练和仿真实验需求的同时,也为飞行控制系统原理、飞行原理、航空雷达和通信导航原理等专业课程教学提供了实践教学保障。该平台具有开放性、趣味性和竞技性,可优化学员的专业知识。     

风力发电电动变桨距载荷模拟及控制策略仿真实验平台开发

根据新能源专业技术人员的培养目标,采用模拟仿真的方法,开发变桨距动态仿真实验装置,旨在通过实验,让学生掌握变桨距技术和原理。设计了一套模拟风力发电变桨执行机构及实现变桨距控制原理的实验平台,为教师和学生提供一个教学实验装置,也方便专业人士研究独立变桨距控制技术。     

基于Authorware的灰鸽子木马实验仿真软件的设计与实现

不论是网络安全的教学,还是网络安全实验,都会遇到硬件配置不足的问题。构建能够摆脱计算机硬件环境约束的实验方法,将在很大程度上推进网络安全实验的突破与创新,而且可以提高实验结果的可重复性。本文以灰鸽子木马入侵实验为例,介绍了基于Authorware的灰鸽子木马实验仿真软件的设计思路、软件实现及其使用效果,并重点描述了交互技术在Authorware中的应用。     

室内风速模拟的一种数值方法

在风力发电技术的研究中,进行室内试验是最有效率的方法,这样就必须模拟实际风场的风,而自然风具有不确定性,难于精准的构造模型.运用非平稳随机过程的方法,建立基于观测数据的非平稳随机过程的数学模型,运用这个模型和康平风场实际观测数据,进行了风速样本模拟.结果表明,采用本方法只需利用少量的风速观测数据就可以很好的模拟自然风.     

Task-and-role-based access-control model for computational grid

Access control in a grid environment is a challenging issue because the heterogeneous nature and independent administration of geographically dispersed resources in grid require access control to use fine-grained policies. We established a task-and-role-based access-control model for computational grid (CG-TRBAC model), integrating the concepts of role-based access control (RBAC) and task-based access control (TBAC). In this model, condition restrictions are defined and concepts specifically tailored to Workflow Management System are simplified or omitted so that role assignment and security administration fit computational grid better than traditional models; permissions are mutable with the task status and system variables, and can be dynamically controlled. The CG-TRBAC model is proved flexible and extendible. It can implement different control policies. It embodies the security principle of least privilege and executes active dynamic authorization. A task attribute can be extended to satisfy different requirements in a real grid system.     

Measuring in-service teacher self-efficacy for teaching computational thinking: development and validation of the T-STEM CT

Education and Information Technologies - Despite a growing recognition that K-12 teachers should be prepared to teach students computational thinking (CT) skills across disciplines, there is a lack...     

Biological pacemaker: from biological experiments to computational simulation

Pacemaking dysfunction has become a significant disease that may contribute to heart rhythm disorders, syncope, and even death. Up to now, the best way to treat it is to implant electronic pacemakers. However, these have many disadvantages such as limited battery life, infection, and fixed pacing rate. There is an urgent need for a biological pacemaker (bio-pacemaker). This is expected to replace electronic devices because of its low risk of complications and the ability to respond to emotion. Here we survey the contemporary development of the bio-pacemaker by both experimental and computational approaches. The former mainly includes gene therapy and cell therapy, whilst the latter involves the use of multi-scale computer models of the heart, ranging from the single cell to the tissue slice. Up to now, a bio-pacemaker has been successfully applied in big mammals, but it still has a long way from clinical uses for the treatment of human heart diseases. It is hoped that the use of the computational model of a bio-pacemaker may accelerate this process. Finally, we propose potential research directions for generating a bio-pacemaker based on cardiac computational modeling.

     

A derived grid-based model for simulation of pedestrian flow

We present a derived grid-based model for the simulation of pedestrian flow. Interactions among pedestrians are considered as the result of forces within a certain neighbourhood. Unlike the social force model, the forces here, as in Newtonian physics, are proportional to the inverse of the square of the distance. Despite the notion ofneighbourhood and the underlying grid, this model differs from the existing cellular automaton （CA） models in that the pedestrians are treated as individuals. Bresenham＇s algorithm for line rastering is applied in the step calculation.     

Thermal optimization of a totally enclosed forced ventilated permanentmagnet traction motor using lumped parameter and partial computational fluid dynamics modeling

In this study, we present a thermal optimization method using the overall lumped parameter (LP) and partial computational fluid dynamics (CFD) modeling for a 600-kW permanent magnet traction motor developed for high-speed trains. The motor is totally enclosed forced ventilated to achieve high power density, high efficiency, and low maintenance requirements. Considering the electro-magnetic performance, bogie space, and thermal capacity, we propose a ventilation structure with zigzag plates in sector cross-section. We focus particularly on the ventilation channels and propose an overall LP model for thermal optimization, in which the full consideration of the influence of turbulent flow is given by using a partial CFD model. Given the specific critical parameters from the optimization results, we present a complete 3D CFD model of the whole motor to obtain an accurate temperature distribution and the maximum temperature rises in local points. The benefit of zigzag plates is studied extensively using both the LP and the complete CFD models and the results are verified by equivalent thermal experiments under rated operations. Experimental results indicate that the ventilation structure fulfills the normal operational demands of high-speed trains by improving thermal performance by more than 15%. Additionally, we propose an engineering method to estimate iron loss constraint with the complete CFD model to guide the control system design.     

A derives grid-based model for simulation of pedestrian flow

We present a derived grid-based model for the simulation of pedestrian flow. Interactions among pedestrians are considered as the result of forces within a certain neighbourhood. Unlike the social force model, the forces here, as in Newtonian physics, are proportional to the inverse of the square of the distance. Despite the notion of neighbourhood and the underlying grid, this model differs from the existing cellular automaton (CA) models in that the pedestrians are treated as individuals. Bresenham's algorithm for line rastering is applied in the step calculation.