Mo－算法的数值效率

Ｍｏ－算法的数值效率王大麒，李乔祥（中山大学数学系）ＴＨＥＮＵＭＥＲＩＣＡＬＶＡＬＵＥＥＦＦＩＣＩＥＮＣＹＯＦＭｏ－ＡＬＧＯＲＩＴＨＭ￥ＷａｎｇＤａ－ｑｉ；ＬｉＱｉａｏ－ｘｉａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｈｅｍａｔｉｃｓ，ＺｈｏｎｇｓｈａｎＵ...

信赖域子问题求解方法及其数值试验研究

信赖域算法是目前求解无约束优化问题的一种重要的数值计算方法,而信赖域子问题的求解则是实现信赖域算法的关键。阐述求解信赖域子问题的3种方法(不定折线法、Moré-Sorensen法以及截断共轭梯度法),利用国际上广泛采用的无约束优化测试函数包对以上3种方法进行大量的数值试验。结果表明截断共轭梯度法的数值计算效率在一定程度上优于其他两种方法,非单调的信赖域算法在一定程度上优于传统的单调算法。

哈尔滨第三发电厂600MW机组循环水泵改造叶轮优化设计

哈尔滨第三发电厂两台600MW机组现场测试及调研的结果表明,循环水泵机组运行效率低于原型泵设计。对机组进行了技术改造,并利用CFD技术对改造前后叶轮进行数值分析比较,结果表明,改造后循泵振动小、流量大,2a多无检修,确保了电厂发电机组安全可靠、经济的运行。

新型电子阻挡层结构对蓝光InGaN发光二极管性能的提高(英文)

分别对3种不种电子阻挡层的蓝光AlGaN LED进行数值模拟研究。3种阻挡层结构分别为传统Al-GaN电子阻挡层,AlGaN-GaN-AlGaN电子阻挡层和Al组分渐变的AlGaN-GaN-AlGaN电子阻挡层。此外对这对三种器件的活性区的载流子浓度、能带图、静电场和内量子效率进行比较和分析。研究结果表明,相较于传统AlGaN和AlGaN-GaN-AlGaN两种电子阻挡层的LED,具有Al组分渐变的AlGaN-GaN-AlGaN电子阻挡层结构的LED具有较高的空穴注入效率、较低的电子外溢现象和较小的静电场(活性区)。同时,具有Al组分渐变的AlGaN-GaN-AlGaN电子阻挡层结构的LED的efficiency droop现象也得到一定的缓解。

Effects of SPAD Decline Value of Mid-season Hybrid Rice Leaves after Full-heading Stage on Productivity of Rice Fertilized with Nitrogen

[Objective] The aim was to research relationship between SPAD decline index after full-heading stage （SDIFHS） and productivity of rice. fertilized with nitro- gen in order to provide theoretical and practical references for selection and breed- ing of rice varieties. [Method] From 2008 to 2010, 18 mid-season hybrid rice vari- eties were researched every year to explore relationship＇ between SDIFHS and pro- ductivity of rice fertilized with nitrogen. [Result] The productivity of rice fertilized with nitrogen was of extremely significant positive corretation with SDIFHS, because the higher SPAD decline index is, the higher LAI decline index and the transformation ratio of dry matter to spikes in overground plant would be. [Conclusion] The re- search established a new method to predict productivity of rice fertilized with nitro- gen based on SPAD decline index.

Multiple attenuation using λ–f domain high-resolution Radon transform

The parabolic Radon transform has been widely used in multiple attenuation. To further improve the accuracy and efficiency of the Radon transform, we developed the 2- fdomain high-resolution Radon transform based on the fast and modified parabolic Radon transform presented by Abbad. The introduction of a new variable 2 makes the transform operator frequency-independent. Thus, we need to calculate the transform operator and its inverse operator only once, which greatly improves the computational efficiency. Besides, because the primaries and multiples are distributed on straight lines with different slopes in the 2-fdomain, we can easily choose the filtering operator to suppress the multiples. At the same time, the proposed method offers the advantage of high-resolution Radon transform, which can greatly improve the precision of attenuating the multiples. Numerical experiments suggest that the multiples are well suppressed and the amplitude versus offset characteristics of the primaries are well maintained. Real data processing results further verify the effectiveness and feasibility of the method.

基于高阶格式的高精度化学驱模拟

油藏数值模拟的精度取决于网格尺寸,网格越小,模拟结果的精度越高,结果越趋近于收敛。大尺寸网格往往伴随着严重的数值扩散现象。化学驱作为一种复杂的提高采收率过程,由于其复杂的机理(如乳液的相态变化),往往需要很小尺寸的网格以获得精确的模拟结果。本文重点探讨使用高阶格式来改进化学驱模拟的精度。首先对提高油藏数值模拟精度的主流方法进行了全面的分析,包括网格粗化方法、自适应网格加密方法和高阶格式方法。考虑到化学驱模拟的特点,本文选用高阶格式方法对化学驱模拟的精度进行改进提升。随后测试了一维、二维和三维矿场尺度的ASP三元复合驱模拟问题,结果发现模拟的精度高度依赖于所用的网格尺寸。为了获得接近收敛的结果,化学驱所需的网格尺寸远小于水驱模拟。一维化学驱中,网格越粗,表面活性剂分布越"平均化",最终采收率越低。使用二阶和三阶格式,一维、二维和三维矿场尺度三元复合驱模型测试的模拟精度均有大幅提升。使用较粗的网格及高精度格式,即可获得与细网格类似的精度。高精度格式为降低数值黏性、提高精度、降低模拟所需网格数和计算时间,提供了有效的解决办法。该方法也有助于大型油田化学驱的快速精确数值模拟、历史拟合、优化等技术的顺利实施。

Efficient Mass Transport and Electrochemistry Coupling Scheme for Reliable Multiphysics Modeling of Planar Solid Oxide Fuel Cell Stack

A multiphysics model for a production scale planar solid oxide fuel cell （SOFC） stack is important for the SOFC technology, but usually requires an unpractical amount of computing resource. The major cause for the huge computing resource requirement is identified as the need to solve the cathode O2 transport and the associated electrochemistry. To overcome the technical obstacle, an analytical model for solving the O2 transport and its coupling with the electrochemistry is derived. The analytical model is used to greatly reduce the numerical mesh complexity of a multiphysics model. Numerical test shows that the analytical approximation is highly accurate and stable. A multiphysics numerical modeling tool taking advantage of the analytical solution is then developed through Fluent@. The numerical efficiency and stability of this modeling tool are further demonstrated by simulating a 30- cell stack with a production scale cell size. Detailed information about the stack performance is revealed and briefly discussed. The multiphysics modeling tool can be used to guide the stack design and select the operating parameters.

Numerical Simulation of the Scalar Mixing Characteristics in Three-dimensional Microchannels

Based on the transport phenomena theory, the passive mixing of water and ethanol in different threedimensional microchannels is simulated numerically. The average variance of water volume fraction is used to index the mixing efficiency in the cases with different Reynolds number and different fabricated mixers. The results show that the efficiency of liquid mixing is progressively dependent on the convective transport as the Reynolds number increases. The efficiency of serpentine microchannel decreases with the increasing Reynolds number in the laminar regime. Altering the aspect ratio of channel inlet section has no significant effect on the mixing efficiency. Increasing the area of channel inlet section will cause the decrease of the mixing efficiency. The mixing in serpentine channels is the most efficient among three different mixers because of the existence of second flow introduced by its special structure.

Numerical Investigation on Mixing Efficiency and Exponential Fluid Stretching in Chaotic Mixing

The stretching and folding of fluid element during chaotic mixing field is studied using numerical method. The chaotic mixing process is caused by periodic secondary flow in a twisted curved pipe. Using the nonlinear discrete velocity field as the dynamical system, the present study connects the fluid particle's stretching along its trajectory in one period to a linearized time-varying variational equation. After numerical approximation of the variational equation, fluid stretching is calculated on the whole cross section. The stretching distribution shows an exponential fluid stretching and folding, which indicates an excellent mixing performance.

Numerical study of effect of front cavity on hydrogen/air premixed combustion in a micro-combustion chamber

The micro-combustion chamber is the key component for micro-TPV systems. To improve the combustor wall temperature level and its uniformity and efficiency, an improved flat micro-combustor with a front cavity is built, and the combustion performance of the original and improved combustors of premixed H2/air flames under various inlet velocities and equivalence ratios is numerically investigated. The effects of the front cavity height and length on the outer wall temperature and efficiency are also discussed. The front cavity significantly improves the average outer wall temperature, outer wall temperature uniformity, and combustion efficiency of the micro-combustor, increases the area of the high temperature zone, and enhances the heat transfer between the burned blends and inner walls. The micro-combustor with the front cavity length of 2.0 mm and height of 0.5 mm is suitable for micro-TPV system application due to the relatively high outer wall temperature, combustion efficiency, and the most uniform outer wall temperature.

Combustion characteristics of supersonic strut-cavity combustor under plasma jet-assisted combustion

Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method,but currently it is mostly combined with the traditional wall fuel injection method,while the application combined with the central fuel injection method is less.In order to expand the combustion range,the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge.The effects of total pressure of strut fuel injection,total pressure of cavity fuel injection,total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain.The combustion field structure,wall pressure distribution,combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed.The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure.However,the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range.The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5−2.0 MPa,but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased.With the increased total injection pressure of the plasma jet,the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved.When the total pressure of the plasma jet is 1.25 MPa,the combustion efficiency reaches a maximum of 82.1%.The combustion-assisted effect of different plasma jet media is significantly different.When the medium of the plasma jet is O2,the combustion-assisted effect on the combustor is most significant.

Droplets Turbulence Effect of Gas-Water Separator with Corrugated Plates

Droplet turbulence effect on gas-water separator with corrugated plates is explored using the Eulerian-Lagrangian two-way coupled multiphase approach of FLUENT. It is concluded that the inertial force is dominant in separating large droplets, while droplet turbulence dispersion plays a decisive role in separating fine droplets. Good agreement exists between calculations and air-water experiments. The numerical method developed provides a rea-sonable description of the droplet trajectories and separating efficiency, and it can be applied to predicting the performance of gas-water separator with corrugated plates.

Collision performance of bitubular tubes with diaphragms

A numerical study of bitubular tubes with diaphragms compared with single and bitubular tubes subjected to dynamic axial impact force was presented. At first, the energy absorption response of the composite structure under axial loading was analyzed by finite element simulation. The results show that the efficiency of energy absorption can be improved by introducing diaphragms to the double-walled columns. Then, the effect of the amount and location of diaphragms, the shape and the size of the inner tubes, and the thickness of the composite structures were also studied numerically. The collision performance of the composite structure is affected by the deformation of diaphragms, as well as the interaction of outer and inner tube. The non-uniform distribution of diaphragms can improve the energy absorption efficiency of structures for a constant number of diaphragms. The specific energy absorption of the hexagonal inner tube is the highest, followed by the circular, octagonal and square ones.

Numerical simulation and model of control-efficiency of thermal crown of work rolls in cold rolling

Aiming at accuracy control of the thermal crown of work rolls in cold rolling,new parameters such as regulation domain and control-efficiency factors were proposed and a numerical analysis model of the thermal crown of work rolls was established using finite difference method to study roll's thermal deformation.Based on simulation results,the influences of control-efficiency factors on thermal crown are presented and the thermal crown of work rolls is analyzed after taking sub-cooling of sprinkling beam into consideration.It has been found that the control-efficiency factor of any position on the roll's surface is linear function of the temperature and the control ability of water temperature is stronger than other control parameters.In addition,the verification of the model has been carried out based on the producing technology data in some factories and the numerical simulation results coincide well with the experimental data.Therefore,this work has important value for on-line control of roll's crown in cold rolling.

Parametric Study of Two-Body Floating-Point Wave Absorber

In this paper, we present a comprehensive numerical simulation of a point wave absorber in deep water. Analyses are performed in both the frequency and time domains. The converter is a two-body floating-point absorber （FPA） with one degree of freedom in the heave direction. Its two parts are connected by a linear mass-spring-damper system. The commercial ANSYS-AQWA software used in this study performs well in considering validations. The velocity potential is obtained by assuming incompressible and irrotational flow. As such, we investigated the effects of wave characteristics on energy conversion and device efficiency, including wave height and wave period, as well as the device diameter, draft, geometry, and damping coefficient. To validate the model, we compared our numerical results with those from similar experiments. Our study results can clearly help to maximize the converter＇s efficiency when considering specific conditions.

Numerical assessment of spacing–burden ratio to effective utilization of explosive energy

The spacing–burden(S/B) ratio plays significant role on rock fragmentation and proper utilization of explosive energy to minimize the undesirable damage.Low S/B ratio generates fine fragments due to pressure rings coalescence of two blast holes,whereas boulder generations were observed above optimum S/B ratio.Both conditions are not acceptable because of wastage of explosive energy.Therefore,to resolve this issue,a numerical model study was conducted to optimize the S/B ratio and to envisage its effect on rock fragmentation based on utilization of explosive energy.Finite element simulation tool was used to see the extent of two blast hole influence area variation with varying S/B ratio.The better results were obtained at S/B ratio of 1:2 with optimum utilization of peak explosive energy.The performance was observed based on peak kinetic energy,peak pressure,radial and hoop stresses on centre of the two blast holes,where pressure rings coalescence.

Numerical Simulation and Experimental Study on the Performance of Gas/liquid Spiral Separator

The gas/liquid spiral separator, a key component in the compressed air system, was used to remove liquid and oil from gas stream by centrifugal and gravitational forces. To optimize the design of the separator,the relationship between the performance and structural parameters of separators is studied. Computational fluid dynamics (CFD) method is employed to simulate the flow fields and calculate the pressure drop and separation efficiency of air-liquid spiral separators with different structural parameters. The RSM (Reynolds stress model)turbulence model is used to analyze the highly swirling flow fields while the stochastic trajectory model is used to simulate the traces of liquid droplets in the flow field. A simplified calculation formula of pressure drop in spiral structures is obtained by modifying Darcy's equation and verified by experiment.

Optimizing the drilled well patterns for CBM recovery via numerical simulations and data envelopment analysis

Coalbed methane(CBM) commercial development requires choosing the arrangement of the wells.This should be done by considering the corresponding input-output(investment-profit) efficiencies.Simulations were obtained from the computer modeling group(CMG) given the reservoir conditions of the Panzhuang block in the southern part of the Qinshui Basin.This is a demonstration region for CBM development located in Shanxi province of northern China.The sensitivity of gas production from a single vertical well to the primary reservoir parameters was estimated first.Then multi-well gas production from three different well patterns was simulated to estimate the most appropriate well spacing.Combining the investment requirements then gave investment-profit efficiencies for these well patterns.A data envelopment analysis(DEA) model was used to optimize the efficiency.The results show that the permeability,the reservoir pressure,and the gas content have an evident impact on single well gas production.The desorption time has little or no affect on production.The equilateral triangular well pattern(ETWP) in a 400 m well spacing is,for multi-well development,the optimal pattern.It has a better input-output ratio,a longer stable yield time,and provides for greater CBM recovery than does either the rectangular well pattern(RWP) or the five point well pattern(FPWP).

Thermal performance of a single U-tube ground heat exchanger:A parametric study

In this research,the thermal performance of a single U-tube vertical ground heat exchanger is evaluated numerically as a function of the most influential flow parameters,namely,the soil porosity,volumetric heat capacity,and thermal conductivity of the backfill material,inlet volume flow rate,and inlet fluid temperature.The results are discussed in terms of the variations of the heat exchange rate,the effective thermal resistance,and the effectiveness of the ground heat exchanger.They show that the inlet volume flow rate,inlet fluid temperature,and backfill material thermal conductivity have significant effects on the thermal performance of the ground heat exchanger,such that by decreasing the inlet volume flow rate and increasing the backfill material thermal conductivity and inlet fluid temperature,the outlet fluid temperature decreases considerably.On the contrary,the soil porosity and backfill material volumetric heat capacity have negligible effects on the studied ground heat exchanger’s thermal performance.The lowest inlet fluid temperature reaches a the maximum effective thermal resistance of borehole and soil,and consequently the minimum heat transfer rate and effectiveness.Also,multilinear regression analyses are performed to determine the most feasible models able to predict the thermal properties of the single U-tube ground heat exchanger.