Simultaneous nitrification and denitrification in step feeding biological nitrogen removal process

The simultaneous nitrification and denitrification in step-feeding biological nitrogen removal process were investigated under different influent substrate concentrations and aeration flow rates. Biological occurrence of simultaneous nitrification and denitrification was verified in the aspect of nitrogen mass balance and alkalinity. The experimental results also showed that there was a distinct linear relationship between simultaneous nitrification and denitrification and DO concentration under the conditions of low and high aeration flow rate. In each experimental run the floc sizes of activated sludge were also measured and the results showed that simultaneous nitrification and denitrification could occur with very small size of floc.

Theoretical evaluation on nitrogen removal of step-feed anoxic/oxic activated sludge process

Evaluation on nitrogen removal of step-feed anoxic/oxic activated sludge process at the standpoint of reaction kinetics and process kinetics was conducted. Theoretical biological nitrogen removal efficiency was deduced based on the mass balance of nitrate in the last stage. The comparison of pre-denitrification process and step feed process in the aspects of nitrogen removal efficiency, volume of reactor and building investment was studied, and the results indicated that step-feed anoxic/oxic activated sludge process was superior to pre-denitrification process in these aspects.

Automatic control strategy for step feed anoxic/aerobic biological nitrogen removal process

Control of sludge age and mixed liquid suspended solids concentration in the activated sludge process is critical for ensuring effective wastewater treatment. A nonlinear dynamic model for a step-feed activated sludge process was developed in this study. The system is based on the control of the sludge age and mixed liquor suspended solids in the aerator of last stage by adjusting the sludge recycle and wastage flow rates respectively. The simulation results showed that the sludge age remained nearly constant at a value of 16 d in the variation of the influent characteristics. The mixed liquor suspended solids in the aerator of last stage were also maintained to a desired value of 2500 g/m3 by adjusting wastage flow rates.

A two-step transient liquid phase diffusion bonding process of T91 steels

In this study, a two-step heating process is introduced for transient liquid phase （ TLP） diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9／ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend＇s strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.

Effect of Cu content on microstructures and mechanical properties of ADI treated by twostep austempering process

The effect of Cu content on the microstructures and mechanical properties (yield strength, ultimate tensile strength, impact energy, fracture toughness) of austempering ductile iron (ADI) treated by two-step austempering process were investigated. High Cu content in nodular cast irons leads to a significant volume fraction of retained austenite in the iron after austempering treatment, but the carbon content of austenite decreases with the increasing of Cu content. Moreover, austenitic stability reaches its maximum when the Cu content is 1.4% and then drops rapidly with further increase of Cu. The ultimate tensile strength and yield strength of the ADI firstly increases and then decreases with increasing the Cu content. The elongation keeps constant at 6.5% as the Cu content increases from 0.2% to 1.4%, and then increases rapidly to 10.0% with further increase Cu content to 2.0%. Impact toughness is enhanced with Cu increasing at first, and reaches a maximum 122.9 J at 1.4% Cu, then decreases with the further increase of Cu. The fracture toughness of ADI shows a constant increase with the increase of Cu content. The influencing mechanism of Cu on austempered ductile iron (ADI) can be classified into two aspects. On the one hand, Cu dissolves into the matrix and functions as solid solution strengthening. On the other hand, Cu reduces solubility of C in austenite and contributes more stable retained austenite.

A Novel 2-D Signal Processing Scheme for Quasi-Random Step Frequency Signal

Due to the heavy congestion in HF bands, HF radars are restricted to operating within narrow frequency bands. To improve the system bandwidth and avoid heavy interference bands, a quasi-random step frequency signal with discontinuous bands is presented. A novel two-dimensional signal processing scheme for this signal is proposed on the basis of delicate signal analysis. Simulation results demonstrate that the scheme could successfully realize the resolutions by decoupling the range-Doppler ambiguity, and effectively suppress the maximal sidelobe. Moreover, the scheme is simple and has good numerical stability.

Defects of (Tb_(0.3)Dy_(0.7))Fe_(1.95) Alloys with "One-Step" Directional Solidification Process

The main types of defect in the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys with the 'one-step' directional solidification process were investigated. The effect of the dendrite, grain boundaries, twin boundaries, and REFe_3 precipitates on the magnetostrictive response of the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys was analyzed respectively. The experiment results demonstrate that the dendrite, twin boundaries, and REFe_3 precipitates can be avoided by modifying alloying ingredient, solidification parameters and annealing technique. The dendritic growth front often leads to dendrite sheet, rare earth-rich phase, and twin boundaries. The lower proportion of rare earth, or slow solidification rate, results in the occurrence of REFe_3 precipitatates. It is vital for diminishing the defects to control the undercooling of solid-liquid interface at (2.4～5.1)×10~4 K·s·cm^(-2) so that the crystal grows in cellular growth front.

Optimization of Biodiesel Production from Waste Vegetable Oil Assisted by Co-Solvent and Microwave Using a Two-Step Process

The two-step catalyzing process for biodiesel production from waste vegetable oil was assisted by both co-solvent and microwave irradiation. Central composite design (CCD) was employed to optimize the reaction conditions. Optimal reaction conditions of the first step were alcohol to oil molar ratio of 9:1, catalyst (H2SO4) amount 1 wt%, reaction temperature 333 K, and reaction time 7.5 minutes;while for the second step, optimal reaction conditions were alcohol to oil molar ratio 12:1, catalyst (NaOH) amount 1 wt%, reaction temperature 333 K, and reaction time 2.0 minutes. The total reaction time was 9.5 min and the conversion rate of fatty acid methyl esters (FAMEs) achieved was 97.4%. The total reaction time was shorter than previous studies. Therefore, the co-solvent and microwave assisted two-step catalyzing process has a potential application in producing biodiesel from waste vegetable oil.

Non-Equilibrium Grain-Boundary Segregation of Phosphorus And the Effective Time in Step Cooling Process

The non-equilibrium grain-boundary segregation of phosphorus in step cooling process in an industrial steel, 12CrlMoV, is studied based on the effective-time-method and compared with that in isothermal holding process. The non-equilibrium grain-boundary segregation concentration of phosphorus was measured with Auger Electron Spectroscopy (AES) and calculated based on the kinetic equations of non-equilibrium grain-boundary segregation. Results show that the calculated result is in good accordance with the experimental observation.

Influence of a multi-step process on the thickness reduction error of sheet metal in a flexible rolling process

Flexible rolling is a forming process based on thickness reduction, and the precision of thickness reduction is the key factor affecting bending deformation. The major purpose of the present work is to solve the problem of bending deformation error caused by insufficient thickness reduction. Under the condition of different rolling reductions with the same sheet thickness and the same thickness reduction with different sheet thicknesses, the thickness reduction error of sheet metal is analyzed. In addition, the bending deformation of sheet metal under the same conditions is discussed and the influence of the multi-step forming process on the thickness reduction error is studied. The results show that, under the condition of the same sheet thickness, the thickness reduction error increases with increasing rolling reduction because of an increase in work hardening. As rolling reduction increases, the longitudinal bending deformation decreases because of the decrease of the maximum thickness difference. Under the condition with the same thickness reduction, the thickness reduction error increases because of the decrease of the rolling force with increasing sheet thickness. As the sheet thickness increases, the longitudinal bending deformation increases because of the increase in the maximum thickness difference. A larger bending deformation is divided into a number of small bending deformations in a multi-step forming process, avoiding a sharp increase in the degree of work hardening; the thickness reduction error is effectively reduced in the multi-step forming process. Numerical simulation results agree with the results of the forming experiments.

Corrosion resistance of 2195 aluminum alloy treated by multi-step-heating-rate controlled process

2195 aluminum-lithium alloy was widely applied in the aviation and aerospace industry, but it is highly susceptible to pitting and intergranular corrosion undergoing sever corrosive circumstance and moisture atmosphere. To solve this problem and consequently to prolong its service life, a multi-step-heating-rate(MSRC) process was carried out. Investigations were carried out to find the effect of the MSRC process on the alloys corrosion resistance. It is found that the MSRC process is more favorable for the uniform phase precipitation by comparing the corrosion resistance of samples treated by traditional heat treatments. The potential difference between phases can be reduced and intergranular corrosion is able to be prohibited efficiently. Besides, the rare earth infiltration is beneficial to improving the corrosion resistance. As heating time increases, the corrosion resistance declines gradually, samples treated by artificial aging and solid solution also exhibit a better corrosion resistance.

面向STEP-NC控制器的数控加工工艺规划模型

STEP -NC是欧美提出的一种用以取代ISO 6983的新数控接口标准 (ISO1 4649)。分析了STEP -NC数据模型及其对数控系统的影响 ,基于STEP -NC的基本思想将数控加工中的工艺规划划分为离线规划、在线规划和实时规划 ,重点研究了基于STEP -NC控制器的在线规划问题。为了避免过多地占用加工时间 ,提出了按工步级规划→特征级规划→零件级规划的在线规划模式 ,并据此分别给出了工步级铣削用量的优化模型、特征级工艺路线的筛选方法以及基于启发式算法的工步排序方法。

XML及STEP标准在流程工业信息集成中的应用研究

流程工业中数据结构复杂,数据之间关系多种多样,如何对这些数据实现标准化处理是一件很困难的事。以前人们采用的方法多为各种零散的方法,或者是借助于制造行业发展起来的STEP来实现,但是STEP主要是用在表述结构化数据的,而对于非结构化数据以及半结构化数据的描述存在很大困难。因此,文中提出用XML来表述流程工业的非结构化数据和半结构化数据,采用XML与STEP标准结合的方式,实现对流程工业数据的集中处理,以便让那些建立在其上的其他信息处理过程中应用。文末给出了XML与STEP相结合所描述的一个典型过程工业信息集成应用案例。

基于STEP的零件加工工艺计划模型

为了满足ＣＩＭＳ环境下工艺设计系统与其它系统集成的需要，建立标准工艺计划模型具有十分重要的意义。本文描述了一个基于ＳＴＥＰ的零件加工工艺计划模型，介绍了建立这一模型的关键技术，给出了参照ＳＴＥＰ建立工艺计划模型的方法。

基于STEP的面向对象工艺计划信息模型

工艺计划信息的表达方式直接影响ＣＡＰＰ系统与ＣＩＭ环境下其它分系统之间的信息交换。本文在分析工艺计划信息模型研究现状的基础上，从应用需求出发，提出了将实用性与通用性相结合的工艺计划信息建模策略。基于该策略，提出了面向对象的分层工艺计划信息表达方式，并建立了相应的ＥＸＰＲＥＳＳ模型。最后介绍了ＥＸＰＲＥＳＳ模型向底层实现机制转换的两种方式。

基于STEP-NC智能数控系统的研究

论述了基于STEP-NC智能数控系统的工艺流程,提出一种基于多智能体STEP-NC智能数控系统的体系结构,整个系统由解释Agent、工艺规划Agent、监控Agent和决策Agent等12个不同功能的Agent组成,各Agent之间相互协作,共同实现STEP-NC智能数控系统的各种功能。以系统中的两个核心模块——解释Agent和工艺规划Agent为例,阐述了其实现的具体方法。给出了开发完成的原型系统部分功能模块。提出的构建智能型STEP-NC数控系统的策略和方法,对深入研究基于STEP-NC智能数控系统具有一定参考作用。

面向STEP-NC的特征CAD/CAPP系统

将特征建模技术与STEP及STEP-NC标准相结合,为实现CAD/CAPP/CAM及CNC的集成,探索了一条有效的途径。建立基于STEP AP224的特征模型,它包含工艺设计所需要的产品管理、材料、精度等信息。另外,将特征与加工方法链相对应,并建立相应的数据库,同时讨论了工步排序的若干规则。在Pro/ENGINEER软件平台上,实现了CAD/CAPP/CAM高层次的集成。以三轴数控加工的棱柱体零件为例,阐述了工步的产生以及排序,最终生成符合STEP-NC标准的加工文件。

面向STEP-NC基于混合式遗传算法的工艺路线优化

为适应STEP-NC技术的发展需求,解决基于STEP-NC非线性工艺路线优化问题,在深入分析STEP-NC基于加工特征的数据模型基础上,探讨了工艺路线优化中存在的问题及其相关约束,提出采用基于操作优先图的智能搜索与遗传算法相结合的混合式算法。首先考虑加工操作排序中的强制性约束,采用基于操作优先图的智能搜索算法,获取多个可行的加工操作顺序,并将其作为遗传算法的初始化种群;然后综合考虑机床选择、刀具选择和刀具运动方向选择,以加工成本最低为目标函数,根据优化约束条件,通过遗传算法的复制、交叉和变异等操作实现有效工艺路线的优化决策,得到满足车间要求的最优或接近最优的工艺路线。通过实例,验证了该算法在面向STEP-NC加工特征的零件工艺路线优化上的可行性和有效性。

面向STEP-NC基于加工特征规则聚类的零件装夹规划

针对零件工艺规划过程中的装夹规划问题,提出一种面向STEP-NC加工特征的启发式聚类装夹规划求解方法。在分析STEP-NC数据模型和加工单元的基础上,建立了零件装夹规划的数学模型,基于加工特征制造优先级规则对加工单元进行聚类分组,形成零件的装夹方案集;随后通过专家打分和评定策略对这些装夹方案集进行排序,生成符合零件装夹要求的装夹规划方案。装夹规划考虑了零件的具体形状及其稳定性等多种约束条件,确定零件每一个加工单元的定位面和装夹面,较好地体现了零件实际加工过程中的装夹情况。基于Solid-works三维计算机辅助设计平台实现了零件装夹规划的生成,通过实例对所提算法进行了验证。

基于STEP-NC的工艺过程设计与优化技术研究

为了简化工艺决策过程的复杂性和实现工艺决策过程的模型化和算法化,在深入分析STEP-NC数据模型的基础上,针对数控工艺的特点,提出了元加工操作及制造特征加工链等概念,建立了支持非线性工艺设计的分步工艺决策过程;进而提出了基于排列和辅助时间的加工工步排序和优化的方法,实现了加工工步排序和优化过程的统一处理,使CAPP系统能够提供多个可选的工艺方案。通过一个基于STEP-NC的CAPP原型系统的实现及实例零件的工艺过程设计表明,所提出的工艺决策过程和优化方法是简单有效的。