Effect of process parameters on microstructure and properties of AM50A magnesium alloy parts formed by double control forming

Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting （DC） due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength （YS）, ultimate tensile strength （UTS） and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 ＆#176;C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 ＆#176;C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.

CONTROLLABILITY CANONICAL FORM FOR NONLINEAR CONTROL SYSTEMS

General nonlinear control systems are studied in this paper with the goal to transform them into the so-called controllability canonteal form via state transformation only. The conditions of transformability are given for both single input and multiple input cases. Besides, by an algebraic approach the procedure for constructing the state transformation is established. This paper is formulated in the framework of calculus rather than differential geometry approach.

NEW NORMAL FORMS FOR NONLINEAR SYSTEMS (Ⅱ)——CONTROLLABLE FORM

This paper proposes a sort of new normal forms consisting of observer form and controllable form for nonlinear systems. The conditions for transforming to these normal forms are given, respectively. These normal forms are used to treat the problems of observer design and linearization. The first part of this paper deals with the observer form, and the second the controllable form.

CONTROLLED HOT FORMING OF RETAINING RING OF GENERATOR

The relevant results of thermodynamics simulation test, recrystallization study and FEM numercal simulation are described. A method is also introduced that the controlled hot forming is carried out by adopting the program of expansion-extrusion compound forming.

Quality Control on Crimping of Large Diameter Welding Pipe

Crimping is used in production of large diameter submerged-arc welding pipes. Many researches are focused on crimping in certain manufacturing mode of welding pipe. The application scopes of research achievements become limited due to lack of uniformity in theoretical analysis. In order to propose a crimping prediction method in order to control forming quality, the theory model of crimping based on elastic-plastic mechanics is established. The main technical parameters are determined by theoretical analysis, including length of crimping, base radius of punch, terminal angle of punch, base radius of die, terminal angle of die and horizontal distance between punch and die. In addition, a method used to evaluate the forming quality is presented, which investigates the bending angle after springback, forming force, straight edge length and equivalent radius of curvature. In order to investigate the effects of technical parameters on forming quality, a two-dimensional finite element model is established by finite element software ABAQUS. The finite element model is verified in that its shapes error is less than 5% by comparable experiments, which shows that their geometric precision meets demand. The crimping characteristics is obtained, such as the distribution of stress and strain and the changes of forming force, and the relation curves of technical parameters on forming quality are given by simulation analysis. The sensitivity analysis indicates that the effects of length of crimping, technical parameters of punch on forming quality are significant. In particular, the data from simulation analysis are regressed by response surface method （RSM） to establish prediction model. The feasible technical parameters are obtained from the prediction model. This method presented provides a new thought used to design technical parameters of crimping forming and makes a basis for improving crimping forming quality.

Planar morphology and controlling factors of the gullies in the Yuanmou Dry-hot Valley based on field investigation

The plane form of a gully can provide a basis for evaluating the gully volume and erosion rate, acting process, and evolutionary stage. For describing the planar characteristics of a permanent gully and understanding their controlling factors, this study, utilizing a total station and GPS RTK, measured the shoulder lines and channel curves of 112 gullies in six sites of the Yuanmou Dry-hot Valley and then mapped them by Arc GIS software and calculated nine parameters. The results showed that the channel lengths range from 10.88 to 249.11 m; the widths range from 6.20 to 40.99 m; the perimeters range from 54.11 to 541.67 m; the gully areas range from 153.02 to 6,930.30 m2; the left-side areas range from 92.93 to 4,027.20 m2; and the right-side areas range from 63.65 to 3,539.77 m2. The slightly sinuous and straight gullies account for 73.21% of the total gullies; the quantity of the right skewed gullies is 8.93% greater than that of the left skewed ones based on the symmetry ratio; the shape ratios range from 1.12 to 1.40 and the morphology ratios from 0.038 to 1.294; the fractal dimension is 1.192. Gullies in different sites have diverse planar characteristics. Except for the symmetry index, which was close to a negatively skewed distribution, all of the other parameters had the characteristic of positively skewed distribution. The gully area is related to the length and width, but the gully length has a weak correlation with the width. The evolutionary stage, topographic conditions, strata, soil properties, and piping erosion played very important roles in the gully planar morphology. This study could provide useful information for controlling gully erosion and safeguarding human habitation and engineering buildings.

Hydroxy Propyl Methyl Cellulose： Different Aspects in Drug Delivery

Among the various research works going on nowadays, designing of controlled release dosage form is of great importance. For the development of suitable controlled release dosage form, a proper matrix needs to be formed from which the drug release generally occur by polymer swelling, polymer erosion, drug dissolution/diffusion mechanism. HPMC （hydroxy propyl methyl cellulose）, also known as hypromellose, is one of the best known cellulosic polymers used in the development of controlled released drug delivery. It is available in various grades. Cellulosic polymers are ingredients that contain units linked together which help to retain water. Due to its high water absorptive capacity, it acts as an excellent hydrophilic gel forming polymer. HPMC generally hydrates on the outer surface to form a gelatinous layer which is critical to prevent wetting and rapid drug release from the matrices. If the drug is sparingly soluble in the system, the release of drug from the system is slow and helps in formulation of controlled release dosage form. In the ophthalmic dosage form, HPMC is used as a matrix that swells and expands after absorbing water and expand the thickness of the tear film.

Grid Forming Converters in Renewable Energy Sources Dominated Power Grid:Control Strategy,Stability,Application,and Challenges

The renewable energy sources(RESs)dominated power grid is an envisaged infrastructure of the future power system,where the commonly used grid following(GFL)control for grid-tied converters suffers from lacking grid support capability,low stability,etc.Recently,emerging grid forming(GFM)control methods have been proposed to improve the dynamic performance and stability of grid-tied converters.This paper reviews existing GFM control methods for the grid-tied converters and compares them in terms of control structure,grid support capability,fault current limiting,and stability.Considering the impact of fault current limiting strategies,a comprehensive transient stability analysis is provided.In addition,this paper explores the typical applications of GFM converters,such as AC microgrid and offshore wind farm high-voltage direct current(OWF-HVDC)integration systems.Finally,the challenges to the GFM converters in future applications are discussed.

Simulation of construction shape-forming process of cable domes

A cable dome has no stiffness or load carrying capacity unless it has been prestressed.Analyses of cable domes are based on successful prestressing designs,making force finding analysis very important.A new force finding method named the imbal-ance force iterative method is proposed,which can overcome some limitations of the integrity feasible prestressing method.For instance,even if groups are assigned by mistake,the pretension distribution that satisfies the known geometry form can also be found.This method possess good stability and calculation efficiency,and a case study indicates that it is applicable to the force finding of large and complicated cable domes.On the other hand,form finding analysis of cable domes is also a key engineering problem.However,rigid displacement occurs in this process,which makes the analysis more complex.In this pa-per,the dynamic relaxation method was selected,and the problem of rigid displacement was therefore effectively solved.The method includes two steps:first,the stretching cables are released,and secondly,an axial force is imposed on the two ends of each released cable.This method is convenient in its calculation and clear in its conception.A case study indicates that the method is suitable for the simulation of the construction process of various cable domes and cable-strut tension structures.Moreover,a form finding experiment was conducted on a model of a cable dome with a diameter of 4.8 m by tensing diagonal cables.The behavior of the model in the form finding process was investigated.The experimental results indicate that the ini-tial lengths of members and prestress loss are key issues in cable domes design.The results also prove that the methods of form finding and force finding proposed in this paper are reliable and effective.

ADRC in output and error form:connection,equivalence,performance

In this work,we investigate two specific linear ADRC structures,namely output-and error-based.The former is considered a“standard”version of ADRC,a title obtained primarily thanks to its simplicity and effectiveness,which have spurred its adoption across multiple industries.The latter is found to be especially appealing to practitioners as its feedback error-driven structure bares similarities to conventional control solutions,like PI and PID.In this paper,we describe newly found connections between the two considered ADRC structures,which allowed us to formally establish conditions for their equivalence.Furthermore,the conducted comprehensive performance comparison between output-and error-based ADRCs has facilitated the identification of specific modules within them,which can now be conveniently used as building blocks,thus aiding the control designers in customizing ADRC-based solutions and making them most suitable for their applications.

ABSOLUTE OBSERVABILITIES OF NONLINEAR CONTROL SYSTEMS AND THEIR NORMAL FORMS

In this paper the concept of absolute observability of nonlinear control systems is advanced.Different from the linear time-invariant version, there are different definitions of absolute observability for nonlinear control systems.Two algorithms for maximal absolutely observable subsystems are given.Correspondingly,there are two relevant normal forms.The relations with the largest controlled invariant distribution contained in kerdh,zero dynamics etc.,are discussed from the view point of maximal absolute observabilities.

NEW DELAY-DEPENDENT STABILITY CRITERIA AND ROBUST CONTROL OF NONLINEAR TIME-DELAY SYSTEMS

This paper investigates the stability analysis and H_∞ control for a class of nonlinear timedelay systems,and proposes a number of new results.Firstly,an equivalent form is given for this class of systems by means of coordinate transformation and orthogonal decomposition of vector fields.Then,based on the equivalent form,some delay-dependent results are derived for the stability analysis of the systems by constructing a novel Lyapunov functional.Thirdly,the authors use the equivalent form and the obtained stability results to investigate the H_∞ control problem for a class of nonhnear time-delay control systems,and present a control design procedure.Finally,an illustrative example is given to show the effectiveness of the results obtained in this paper.It is shown that the main results of this paper are easier to check than some existing ones,and have less conservatism.

Tuning and implementation variants of discrete-time ADRC

Practical implementations of active disturbance rejection control(ADRC)will almost always take place in discretized form.Since applications may have quite different needs regarding their discrete-time controllers,this article summarizes and extends the available set of ADRC implementations to provide a suitable variant for as many as possible use cases.In doing so,the gap between quasi-continuous and discrete-time controller tuning is closed for applications with low sampling frequencies.The main contribution of this article is the derivation of three different discrete-time implementations of error-based ADRC.It is shown that these are almost one-to-one counterparts of existing output-based implementations,to the point where transfer functions and coefficients can be reused in unaltered form.In this way,error-based implementations become firmly rooted in the established landscape of discrete-time ADRC.Furthermore,it becomes possible to equip error-based variants with windup protection abilities known from output-based ADRC.