Numerical Analysis of Steady Smoldering of Biomass Rods

Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensional(2D)steady model taking into account both char oxidation and pyrolysis was developed on the basis of a calculated propagation velocity according to empirical correlation.The model was validated against the smoldering experiment of biomass rods under natural conditions,and the maximum error was smaller than 31%.Parameter sensitivity analysis found that propagation velocity decreases significantly while oxidation area and pyrolysis zone increase significantly with the increasing diameter of rod fuel.

Radiative heat transfer analysis of a concave porous fin under the local thermal non-equilibrium condition:application of the clique polynomial method and physics-informed neural networks

The heat transfer through a concave permeable fin is analyzed by the local thermal non-equilibrium(LTNE)model.The governing dimensional temperature equations for the solid and fluid phases of the porous extended surface are modeled,and then are nondimensionalized by suitable dimensionless terms.Further,the obtained nondimensional equations are solved by the clique polynomial method(CPM).The effects of several dimensionless parameters on the fin's thermal profiles are shown by graphical illustrations.Additionally,the current study implements deep neural structures to solve physics-governed coupled equations,and the best-suited hyperparameters are attained by comparison with various network combinations.The results of the CPM and physicsinformed neural network(PINN)exhibit good agreement,signifying that both methods effectively solve the thermal modeling problem.

A new coupled map car-following model considering drivers' steady desired speed

Based on the pioneering work of Konishi et al., in consideration of the influence of drivers＇ steady desired speed ef/ect on the traffic flow, we develop a new coupled map car-following model in the real world. By use of the control theory, the stability condition of our model is derived. The validity of the present theoretical scheme is verified via numerical simulation, confirming the correctness of our theoretical analysis.

Existence for positive steady states of an eco-epidemiological model

An eco-epidemiological model with an epidemic in the predator and with a Holling type Ⅱ function is considered.A system with diffusion under the homogeneous Neumann boundary condition is studied.The existence for a positive solution of the corresponding steady state problem is mainly discussed.First,a prior estimates（positive upper and lower bounds） of the positive steady states of the reaction-diffusion system is given by the maximum principle and the Harnack inequation.Then,the non-existence of non-constant positive steady states by using the energy method is given.Finally,the existence of non-constant positive steady states is obtained by using the topological degree.

MOLECULAR MODELS AND FLOW CALCULATIONS Ⅱ.SIMULATION OF STEADY PLANAR FLOW

A multibead-rod model is used to replace the constitutive equation of continuum me- chanics in solving flow problems of steady-state planar flows of rigid-rodlike molecular suspensions.The governing equations then constitute a set of differential equations of the elliptic type,which is more ame- nable to numerical treatment than those of the mixed type.The conservation equations of the flow fields are solved by the boundary element method with linear boundary elements in physical space and the diffusion equation of the distribution function is solved separately by the Galerkin method in phase space. The solution to the flow problem is obtained when the convergence of the iteration procedure between the two spaces has been reached.Several numerical examples are shown and the interesting features of the present method are discussed in this paper.

Numerical Simulation for One Dimensional Steady Quasineutral Hybrid Model of Stationary Plasma Thruster

Based on the analysis of the physical mechanism of the Stationary Plasma Thruster （SPT）, an integral equation describing the ion density of the steady SPT and the ion velocity distribution function at an arbitrary axial position of the steady SPT channel are derived. The integral equation is equivalent to the Vlasov equation, but the former is simpler than the latter. A one dimensional steady quasineutral hybrid model is established. In this model, ions are described by the above integral equation, and neutrals and electrons are described by hydrodynamic equations. The transferred equivalency to the differential equation and the integral equation, together with other equations, are solved by an ordinary differential equation （ODE） solver in the Matlab. The numerical simulation results show that under various circumstances, the ion average velocity would be different and needs to be deduced separately.

STEADY-STATE SOLUTIONS FOR A ONE-DIMENSIONAL NONISENTROPIC HYDRODYNAMIC MODEL WITH NON-CONSTANT LATTICE TEMPERATURE

A one-dimensional stationary nonisentropic hydrodynamic model for semiconductor devices with non-constant lattice temperature is studied. This model consists of the equations for the electron density, the electron current density and electron temperature, coupled with the Poisson equation of the electrostatic potential in a bounded interval supplemented with proper boundary conditions. The existence and uniqueness of a strong subsonic steady-state solution with positive particle density and positive temperature is established. The proof is based on the fixed-point arguments, the Stampacchia truncation methods, and the basic energy estimates.

An Improved Three-Dimensional Non-Equilibrium Mixing Pool Model

This paper presents an improved three-dimensional non-equilibrium mixing pool model.It is a simplified form of the original model and is more practical for applications.The simulation re-sults show that the industrial scale distillation tray columns can be described closely by the improvedmodel.The effects of model parameters,such as the number of mixing pools,the point efficiencyand flow pattern,on separation are analyzed quantitatively.

Mass-Spring-Damper Model with Steady State Parameters for Predicting the Movement of Liquid Column and Temperature Oscillation in Loop Heat Pipe

In order to investigate the mechanism of the temperature oscillation in loop heat pipes,this paper investigated the movement of the phase interface as the changed input power by a mass-spring-damper model.The model was solved with MATLAB and was used to explain the high-frequency and low-amplitude temperature oscillation.Temperature variation with the input power from 20 W to 75 W was investigated based on a LHP prototype in a literature.The model agreed well with the experimental data in the literature.The simulation results suggested that the movement of the liquid column was caused by the fluctuation of pressure difference applied on the liquid column and the stiffness coefficients of the vapor springs increasing with the input power.According to parameter analyses,the temperature oscillation at the outlet of the condenser can be weakened by increasing the mass of the liquid column and keeping the temperature at the outlet of the condenser steady.

Numerical simulation of anode heat transfer of nitrogen arc utilizing two-temperature chemical non-equilibrium model

A detailed understanding of anode heat transfer is important for the optimization of arc processing technology.In this paper,a two-temperature chemical non-equilibrium model considering the collisionless space charge sheath is developed to investigate the anode heat transfer of nitrogen free-burning arc.The temperature,total heat flux and different heat flux components are analyzed in detail under different arc currents and anode materials.It is found that the arc current can affect the parameter distributions of anode region by changing plasma characteristics in arc column.As the arc current increases from 100 A to 200 A,the total anode heat flux increases,however,the maximum electron condensation heat flux decreases due to the arc expansion.The anode materials have a significant effect on the temperature and heat flux distributions in the anode region.The total heat flux on thoriated tungsten anode is lower than that on copper anode,while the maximum temperature is higher.The power transferred to thoriated tungsten anode,ranked in descending order,is heat flux from heavy-species,electron condensation heat,heat flux from electrons and ion recombination heat.However,the electron condensation heat makes the largest contribution for power transferred to copper anode.

Numerical investigation on the flow characteristics of a reverse-polarity plasma torch by two-temperature thermal non-equilibrium modelling

A two-temperature(2 T)thermal non-equilibrium model is developed to address the thermal nonequilibrium phenomenon that inevitably exists in the reverse-polarity plasma torch(RPT)and applied to numerically investigate the plasma flow characteristics inside and outside the RPT.Then,a detailed comparison of the results of the 2 T model with those of the local thermal equilibrium(LTE)model is presented.Furthermore,the temperature of the plasma jet generated by a RPT and the RPT’s voltage are experimentally measured to compare and validate the result obtained by different models.The differences of the measured excitation temperature and the arc voltage between the 2 T model and experimental measurement are less than 13%and 8%,respectively,in all operating cases,validating the effectiveness of the 2 T model.The LTE model overestimates the velocity and temperature distribution of the RPT and its plasma jet,showing that thermal non-equilibrium phenomena cannot be neglected in the numerical modelling of the RPT.Unlike other common hot cathode plasma torches,the thermal non-equilibrium phenomenon is found even in the arc core of the RPT,due to the strong cooling effect caused by the big gas flow rate.

A new semi-empirical spectrum model for complex steady shear viscosity of complex fluids

A semi-empirical spectrum model is proposed to describe the experimental data of the steady shear properties of a Shengli waxy crude oil near its gel point, where sophisticated structural effects become apparent due to the existence of waxy crystals in the crude oil. The model, consisting of a time spectrum, can well fit the steady shear viscosities of the waxy crude oil over the whole experimental shear rate region from 10-4 to 102 s- 1. Two other experiments on complex fluids reported recently in the literature are also well described by this model demonstrating the applicability and accuracy of the model.

Steady polarization process modelling of noble metal-electrolyte cermet composite electrode

Cermet composites containing mixture of noble metal phase and electrolyte phase are the state-of-the-art electrode materials used for electrochemical sensor and solid oxide fuel cell(SOFC). A steady polarization model was developed. The model was based on electronic and ionic transfer process together with the electrochemical reaction regardless of mass transport in the electrode. The modelling results can help to understand the electrochemistry of cermet composite electrode.

Performance of a quasi-steady model for hovering hummingbirds

A quasi-steady model describing aerodynamics of hovering Ruby-throated hummingbirds is presented to study extent of the low-order model in representing the flow physics of the bird and also to separately quantify the forces from the translational, rotational, and acceleration effects. Realistic wing kinematics are adopted and the model is calibrated against computational fluid dynamics （CFD） simulations of a cor- responding revolving-wing model. The results show that the quasi-steady model is able to predict overall lift production reasonably well but fails to capture detailed force oscillations. The downstroke-upstroke asymmetry is consistent with that in the previous CFD study. Further analysis shows that significant ro- tational force is nroduced during mid-stroke rather than win~ reversal.

Steady thermal hydraulic characteristics of nuclear steam generators based on the drift flux code model

To investigate the steady thermal hydraulic characteristics of U-tube steam generator(SG), a 1D simulation code based on the four-equation drift flux model is developed. The U-tube channels presumably consist mainly of the primary channel, secondary channel, and tube wall. In the sub-cooling regions of the primary and secondary channels, flow is simulated using the single-phase flow model, whereas that in the boiling regions of the secondary channels is simulated using the four-equation drift flux model. The first-order equations of upwind difference are derived based on the staggered grid. Steady-state thermal hydraulic parameters are obtained with a cross-iteration scheme of heat balance and natural circulation requirement. The developed code is applied to analyze the SG behavior of the Qinshan I Nuclear Power Plant under 100%, 75%, 50%, 30%, and 15% power conditions. Analysis results are then compared with the simulation results obtained using RELAP5.

Three-Temperature Model Applied to Thermochemical Non-Equilibrium Reentry Flows in 2D—Seven Species

In this work, a study involving the fully coupled Euler and Navier-Stokes reactive equations is performed. These equations, in conservative and finite volume contexts, employing structured spatial discretization, on a condition of thermochemical non-equilibrium, are analyzed. High-order studies are accomplished using the Spectral method of Streett, Zang, and Hussaini. The high enthalpy hypersonic flows around a circumference, around a reentry capsule, along a blunt body, and along a double ellipse in two-dimensions are simulated. The Van Leer, Liou and Steffen Jr., and Steger and Warming flux vector splitting algorithms are applied to execute the numerical experiments. Three temperatures, which are the translational-rotational temperature, the vibrational temperature, and the electron temperature, are used to accomplish the numerical comparisons. Excellent results were obtained with minimum errors inferior to 6.0%. The key contribution of this work is the correct implementation of a three temperature model coupled with the implementation of three algorithms to perform the numerical simulations, as well the description of energy exchange mechanisms to perform more realistic simulations.

Steady-State Modeling of Heat Transfer on the Recovery System of Condensing Boiler

The increase of energy production is very important nowadays. It is necessary to improve the performance and efficiency of heat production facilities. The objective is to reduce pollutant emissions and regulate investment costs. One of the solutions is to control fuel and electricity consumption. This article develops a new model of simulation heat diffusion on the recovery system of condensing boiler. The method is based on the first and second thermodynamic systems. The Numerical discrete Model (NDM) was applied using MATLAB to simulate different characteristics of heat transfer in the recovery system. The result shows that the recovery unit can absorb the following temperatures;the range from 88°C to 90.7°C when the length of the tube is between respectively 110 and 111 m. the energy efficiency was between 0.55 and 0.57 which allowed confirming the model. This new model has some advantages such as;the use of an instantaneous calculation time. The heat recovered by the water tank can also serve as preheating different systems. One part of the heat recovered will be accumulated to be used as domestic hot water.

基于Y-MMC的柔性低频输电控制策略

采用传统矢量控制的Y型模块化多电平换流器(Y-MMC),存在控制结构复杂、参数整定困难等缺点。针对上述问题,采用模型预测控制方法对Y-MMC进行控制器设计,提出一种适用于柔性低频输电的分层协调控制策略。建立各桥臂开关状态组合下的预测模型,实现内环电流控制和电容电压均衡控制。采用分层优化思想建立直流电容电压跟踪、交流电流跟踪和开关频率优化的逐级评估系统。结合稳态逆模型和比例积分控制实现了功率换流站的功率控制和电压频率换流站的低频电压控制。通过MATLAB/Simulink对双端低频输电系统进行仿真,结果验证了所提控制方案在多种工况下的正确性和有效性。相较于传统的矢量控制,该策略简化了控制器设计,加快了响应速度。

面向数字孪生模型应用的油浸式变压器绕组温度POD-RBFLP降阶计算方法

了解油浸式电力变压器绕组的温度情况是保证其运行稳定性的关键,也是当前针对油浸式变压器数字孪生分析的必然需求。为了快速地获得变压器绕组的稳态温度,该文提出一种基于本征正交分解(proper orthogonal decomposition,POD)和包含线性多项式的径向基函数响应面法(radial basis function response surface method including linear polynomial,RBFLP)的降阶计算模型。首先,讨论POD方法的降阶特性,并设计一种基于留一法交叉验证的自适应获得快照矩阵方法,以提高计算精度及效率;其次,采用响应面方法建立POD模态系数与绕组工况的相关关系,旨在实现通过绕组工况快速获得POD模态系数,从而跳过对降阶模型的复杂非线性计算,进而高效重构绕组温度场。相关算例表明,该方法具有较好的计算精度和效率,在50组测试工况下,与全阶计算相比,误差不超过2.5 K,且总计算时间仅为1.45 s;最后,基于110 kV变压器绕组搭建温升试验平台,试验结果表明,降阶计算结果相较于试验结果,平均计算误差不超过2 K,且单步计算时间仅为0.03 s,相较于同等规模的全阶计算,计算效率有较大幅度地提升。

基于稳态响应规律的双线性滞回模型等效参数研究

为了研究等效线性化方法的位移估算精度,以双线性滞回模型为分析模型,分析了非线性单自由度体系的自由振动过程,指出采用割线刚度法(R-H法)计算的等效参数与实际结果偏差较大,进而提出了一种简谐力作用下的等效参数计算方法。考虑了简谐激励的激励周期以及结构振动的位移峰值对计算结果的影响,通过数值分析对不同参数对应下的非线性体系进行等效线性化分析,验证了所提出的等效参数计算方法的有效性与准确性。结果表明,采用R-H法计算的等效刚度偏大,而改进方法能够合理估算非线性时程位移结果,其计算精度优于R-H法。