多孔质气体静压径向轴承的可压流动建模及数值求解

为研究可压流动下多孔质静压径向轴承的静特性,基于雷诺润滑方程、多孔质达西方程、气体压力-密度方程,建立了多孔质径向轴承的流动模型.提出了一种处理多孔质轴向端面压力边界条件的Laplace-Neumann虚拟节点法,结合有限差分法、松弛迭代法、压力-密度耦合迭代法对流动模型进行数值求解.分析了可压流动下轴承半径间隙和供给压力对静压特性的影响,并与不可压流动计算结果进行对比.结果表明:在同一最小膜厚下,随着半径间隙和供给压力的增大,可压流动与不可压流动的承载能力、质量流量和功耗均增大.可压流动下的承载能力在半径间隙0.01 mm和0.03 mm下小于不可压流动,在半径间隙0.05 mm下大于不可压.可压流动下的质量流量和功耗均大于不可压流动.本研究可为多孔质静压径向轴承的设计及快速计算提供参考.

涡轮动叶凹槽叶尖流动传热机理及建模研究进展

针对凹槽叶尖流动机理及组织方法,考虑冷却的凹槽叶尖气动与传热特征分析和凹槽叶尖泄漏流动的模化等相关工作的研究进展进行了简要总结。已有的研究表明:凹槽内部的流动对传热有明显的影响;凹槽内的冷却气与泄漏流动存在较强的相互作用,合理的凹槽形状和喷气孔位置可以有效提升叶尖的气动效率并降低热负荷;叶尖的加工和气动参数的不确定性会显著影响凹槽叶尖性能;通过对凹槽内流动结构进行模化,得到的考虑喷气的可压缩条件下的凹槽叶尖性能预测模型经过了实验和数值模拟的结果验证,可以有效评估凹槽叶尖性能,并为工程设计提供参考。

Method of Testing of Dynamic Forces on Digital Jet Elements

Method of testing for dynamic output forces from jet elements is studied, the handwidth is large in testing with this method. By establishing a model of the test system and simulating it, principles of how inherent features of the test system affect the dynamic force test are found out. Thus a theoretical foundation is given for the design and error modification to the actual test system.

Modeling and simulation of turbofan engine based on equilibrium manifold

Because the normal operation of the engine is located near the equilibrium manifold, the method of equilibrium mani fold nonlinear dynamic modeling is adopted for turbofan engine more than the local train modeling. The method studies the sys tem characteristics near the equilibrium manifold. The modeling method can be realized through dynamic and static twostep, and for the specific parameter modeling steps and algorithm are given. The output of the test data is compared with the model output through numerical simulation, to check the model with an additional set of test data. The simulation results show that the model has reached the requirements of engineering accuracy.

SDG-based Model Validation in Chemical Process Simulation

Signed direct graph (SDG) theory provides algorithms and methods that can be applied directly to chemical process modeling and analysis to validate simulation models, and is a basis for the development of a software environment that can automate the validation activity. This paper is concentrated on the pretreatment of the model validation. We use the validation scenarios and standard sequences generated by well-established SDG model to validate the trends fitted from the simulation model. The results are helpful to find potential problems, assess possible bugs in the simulation model and solve the problem effectively. A case study on a simulation model of boiler is presented to demonstrate the effectiveness of this method.

Physically based modeling and animation of tornado

Realistic modeling and rendering of dynamic tornado scene is recognized as a challenging task for researchers of computer graphics. In this paper a new physically based method for simulating and animating tornado scene is presented. We first propose a Two-Fluid model based on the physical theory of tornado, then we simulate the flow of tornado and its interaction with surrounding objects such as debris, etc. Taking the scattering and absorption of light by the participating media into account, the illumination effects of the tornado scene can be generated realistically. With the support of graphics hardware, various kinds of dynamic tornado scenes can be rendered at interactive rates.

Modeling and experimental studies of methyl methacrylate polymerization in a tubular reactor

In this study, rheological examination of the mixture of a tubular reactor in which methyl methacrylate was polymerized has been studied. The n(flow behavior index) value of Power Law Model of mixture contained in the reactor has been determined within the span of 0.3492 to 0.9889 by curve fitting. Employing these numerical data for velocity profile, the reactor has been modeled. Moreover, the functions of the reactor have been compared in the three modes of plug, mixed and laminar flow. The results obtained in this research indicate that the polymethyl methacrylate mixture contained in the reactor is pseudo-plastic. Moreover, as the conversion grows, the velocity profile starts as a parabolic profile and approaches the plug mode; although it never reaches the plug. The other conclusions borne in this study indicate that when the reactor's radius is decreased, the conversion rate grows. However, as decreasing the radius would also reduce the productions rate, this procedure is not economical. Finally, in this modeling, the amount of conversion is equal to 56.47% at the end and according to its laboratory proportion which is 55.88%, it has reached the conclusion that the modeling duly undertaken is applicable and valid.

Modeling of fluid-induced vibrations and identification of hydrodynamic forces on flow control valves

Dynamics and vibration of control valves under flow-induced vibration are analyzed. Hydrodynamic load characteristics and structural response under flow-induced vibration are mainly influenced by inertia, damping, elastic, geometric characteristics and hydraulic parameters. The purpose of this work is to investigate the dynamic behavior of control valves in the response to self-excited fluid flow. An analytical and numerical method is developed to simulate the dynamic and vibrational behavior of sliding dam valves, in response to flow excitation. In order to demonstrate the effectiveness of proposed model, the simulation results are validated with experimental ones. Finally, to achieve the optimal valve geometry, numerical results for various shapes of valves are compared. Rounded valve with the least amount of flow turbulence obtains lower fluctuations and vibration amplitude compared with the flat and steep valves. Simulation results demonstrate that with the optimal design requirements of valves, vibration amplitude can be reduced by an average to 30%.

A Dynamic Modeling For Cyclic Total Reflux Batch Distillation

Cyclic total reflux(CTR) batch distillation is a promising mode of the process but lacking of appropriate modeling for the period of filling the reflux drum.A new dynamic modeling method for the simulation of CTR batch distillation is proposed in this work,in which the changes in column holdup and liquid flow rate during the filling of the drum,and the consequent change in valid number of theoretical plates are considered.The effect of drum holdup on operation time is investigated and the optimal drum holdup is obtained from the simulation.The dynamic modeling is compared to the conventional modeling without consideration of change in liquid flow rate. The experimental result shows that the present modeling is more reliable and more accurate,especially for the column with large liquid holdup.

Modeling a magneto-rheological soft starter for use with belt conveyors

The theory of magnetic circuit design, the constitutive equations of a magneto-theological fluid, and the load properties of belt conveyors were used to design a magneto-rheological soft starter test-bed. The magnetic field distribution in the working gap was analyzed and the current-speed relationship was investigated. A mathematical model for the time response was deduced. The results show that a linear relationship between current and magnetic field is seen when the magnetic materials are not saturated and the magnetic field is uniform in the working section. The rotation speed of the driven shaft changes linearly with increasing time. The response is rapid and can be as short as milliseconds. This meets the starting requirements of belt conveyors.

Modeling and Numerical Simulation of Yield Viscoplastic Fluid Flow in Concentric and Eccentric Annuli

Numerical solution of yield viscoplastic fluid flow is hindered by the singularity inherent to the Herschel-Bulkley model. A finite difference method over the boundary-fitted orthogonal coordinate system is util- ized to investigate numerically the fully developed steady flow of non-Newtonian yield viscoplastic fluid through concentric and eccentric annuli. The fluid rheology is described with the Herschel-Bulkley model. The numerical simulation based on a continuous viscoplastic approach to the Herschel-Bulkley model is found in poor accordance with the experimental data on volumetric flow rate of a bentonite suspension. A strict mathematical model for Herschel-Bulkley fluid flow is established and the corresponding numerical procedures are proposed. However, only the case of flow of a Herschel-Bulkley fluid in a concentric annulus is resolved based on the presumed flow stnicture by using the common optimization technique. Possible flow structures in an eccentric afinulus are presumed, and further challenges in numerical simulation of the Herschel-Bulkley fluid flow are suggested.

Modeling of Ions Mobility in Plasma Like Concept and Transfer Processes in Electrolyte Solutions

Plasma like concept of ions in electrolyte solutions is accepted as a basis for development of equation mobility for transfer processes （viscosity, diffusion, thermal conductivity and electrical conductivity）. The examples of isomorphism of dissipative processes are given in the article. The integrated assessment equation of transfer properties is developed based on the ion-dipole, dipole-dipole and ion-ion interactions and the force of liquid dielectric resistance to oscillating solvated particles. It is shown that the estimated magnitude of viscosity, diffusion, electrical conductivity and thermal conductivity are comparable with the current knowledge and experimental values in a wide range of electrolyte concentrations.

New approach for modeling flow stress of aluminum alloy 6A10 considering temperature variation

The flow stress behavior of aluminum alloy 6A10 was studied by the hot compression tests at temperatures from 350℃ to 550 ℃ and strain rates from 0.1 s^-1 to 10 s^-1 with Gleeble-1500 thermo-mechanical simulator. The result demonstrates that the temperatures of specimen differ from initial ones affected by deformation conditions, and that the softening mechanism is dynamic recovery. A new approach was proposed to analyze the flow stress character directly from actual stress, strain, temperature and strain rate data, without performing any previous flow stress correction caused by temperature variation. Comparisons between the experimental and predicted results confirm that the established flow stress model can give reasonable estimation, indicating that the mentioned approach can be used in flow stress model analysis of the materials that undergo only dynamic recovery based on the data obtained under variable deformation temperature.

Inertisation options for BG method and optimisation using CFD modelling

Spontaneous combustion(sponcom) is one of the issues of concern with the blasting gallery(BG) method of coal mining and has the potential to cause fires, and impact on production and safety, greenhouse gas(GHG) emissions and huge costs involved in controlling the aftermath situations. Some of the research attempts made to prevent and control coal mine fires and spontaneous combustion in thick seams worked with bord and pillar mining methods are presented in this paper. In the study, computational fluid dynamics(CFD) modelling techniques were used to simulate and assess the effects of various mining methods, layouts, designs, and different operational and ventilation parameters on the flow of goaf gases in BG panels. A wide range of parametric studies were conducted to develop proactive strategies to control and prevent ingress of oxygen into the goaf area preventing spontaneous combustion and mine fires.

Modeling the Effects of Nutrient Dynamics and Surface Circulation on the Productivity of Hooghly Estuary

River estuarine environment plays a key role in the cycling of biological and chemical parameters and a significant region for the transaction of freshwater and seawater. In the present study, a first attempt has been made towards the development of a coupled three-dimensional hydrodynamic circulation model with four compartment （nitrate, phytoplankton, zooplankton and detritus） biogeochemical model in the Hooghly estuary （21 °36′-22° 16′1 and 87°42＇-88°15′E） to simulate the varying effect of plankton biomass with the heavy input of anthropogenic litter from industrial effluents of Haldia port which is effecting the chemical and biological processes that control the plankton dynamics in the estuary. In-situ observational data for physico-chemical and biological parameters are collected from Calcutta University during 2010 are assimilated using multiscale OA （objective analysis） for different seasons and incorporated in ROMS （Regional Ocean Modeling System） to develop a high resolution （0.5 km x 0.5 kin） biogeochemical model. Recent analysis on physico-chemical parameters of the estuary is done as it is one of the largest estuaries in India and is the habitat for vast biodiversity. Influence of high nitrate （above 34 μg/L） and phosphate （5.22 μg/L） is predominant whereas DO （dissolved oxygen） is low （4.07 mg/L） in the Haldi River mouth which is sliding the productivity （less than 1 mg/L） and also affects water quality.

Three-dimensional Computational Fluid Dynamics Modeling of Two-phase Flow in a Structured Packing Column

Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.

Modelling of heat transfer for progressive freeze concentration process by spiral finned crystallizer

This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration(PFC) system, which simplifies the setup of the conventional system. After the crystallizer has been designed, the research experiments have been conducted and evaluated through a thorough analysis of its performance by developing a mathematical model that can be used to predict the productivity of ice crystal at a range of coolant temperature. The model is developed based on the basic heat transfer equation, and by considering the solution's and the coolant's convective heat transfer coefficient(h) under the forced flow condition.The model's accuracy is verified by making comparison between the ice crystal mass' experimental value and the values predicted by the model. Consequently, the study found that the model helps in enhancing the PFC system.

Potentials of Cellular Vortex Element Modeling of Fluid Flow in Confined 2D Aquifer

Numerical methods such as finite difference, finite volume, finite element or hybrid methods have been globally used to successfully study fluid flow in porous stratum of which aquifers are typical examples. Those methods involve mathematical expressions which increases computation time with requirement of specific human expertise. In this paper, numerical models for single phase flow in 1D and 2D using the conservation of mass principles, Darcy＇s flow equation, equation of state, continuity equation and the STB/CFB （stock tank barrel/cubic feet barrel） balance were developed. The models were then recast into pressure vorticity equations using convectional algorithms. Derived equations were used to formulate transport equations which resemble the conventional vorticity transport equation. Formulated numerical models were used to investigate the daily instantaneous aquifer pressure drawdowns and pressure heads for 365 days. The developed equations were subsequently solved using cellular vortex element technique. The developed computer program was used to investigate confined aquifer of dimensions 10× 10 × 75 m with single vertex image. For the aquifer rate of 0.5 m3/s, 0.1 m3/s, 0.15 m3/s, 0.2 m3/s, 0.25 m3/s, 1.0 m3/s, 2.0 m3/s, 2.5 m3/s, 3.0 m3/s, 4.0 m3/s, the respective average head drawdowns and heads were, 1.127 ±0.0141 m, 1.317 ±0.0104 m, 1.412± 0.0041 m, 1.427 ± 0.116 m,1.527 ± 0.0141 m, 2.107 ± 0.0171 m, 2.197 ±0.0191 m, 3.007±0.0171 m, 3.127 ± 0.0041 m, 3.626 ± 0.0121 m, and 25 kN/m2, 35 kN/m2, 33 kN/m2, 5 kN/m2, 6 kN/m2, 11 kN/m2, 25 kN/m2, 42 kN/m2, 50 kN/m2, 62 kN/m2, respectively. Cellular vortex technique with relative little mathematics has been established to have recorded successes in numerical modeling of fluid flow in aquifer simulation.

Kinetic Adsorption of CO2/CH4 Mixture Using 13X Zeolite： Modeling and Simulation

In this work, the separation of carbon dioxide （CO2） from （PSA） column was modeled and simulated. The adsorption kinetics the methane （CH4） using fixed bed Pressure Swing Adsorption on the 13X zeolite adsorbent was described by Linear Driving Force （LDF） model. Simulation of adsorption phenomena inside the fixed bed was implemented using Computational Fluid Dynamic （CFD） method, based on porous media concept, and the mass transfer coefficients for gas components （COz and CH4） were developed using User Defined Scalars （UDS）. The model was validated by comparing with the experimental data, which were collected based on a varied set of laboratory conditions. The prediction of the adsorption isotherm （uptake curve） and methane recovery using the simulation results exhibited a reasonable agreement with the experimental data. Moreover, the effects of feed flow rate and bed concentration evolution were investigated. The current results suggested that CFD approach is capable to predicate the hydrodynamics and adsorption phenomena in the fixed bed adsorption column.

Study on Modeling for a New FCC Technique——MIP Riser Reactor

This research work developed a model for the MIP riser reactor using the data collected from an industrial MIP unit.Based on analysis of flow patterns in the reactor,three models were established and a comparison was made on each other.The results indicated that Model Ⅲ,which was assumed a plug flow in the first reaction zone and a gas plug flow and a continuously stirred catalyst flow in the second reaction zone,was the best.The results of this research could offer an information and guidance for optimization and development of MIP unit.