径向驱动式啮合电机结构设计与静态转矩分析

针对机器人系统对驱动电机的启动性能和空间适应性的要求,设计了一种径向驱动式啮合电机结构.该电机利用3个定子和1个转子间磁阻的变化将电能转化为机械能,驱动转子在十字滑块机构约束下绕定子轴线做圆周平动,进而直接带动摆线机构输出低速大扭矩.设计制作了一台物理样机,给出了该电机的控制方法,运用有限元方法分析了在不同转子位置角的...     

Representative static load models for transient stability analysis: development and examination

Load representation has a significant impact on power system analysis and control results. Currently, static load models are still popular in power industry for transient stability analysis. Dynamic load models are recommended in both industry and academia for possible improvement in analysis accuracy. The accuracy of using static (nonlinear) load models with suitably identified parameters for transient stability analysis is examined. Numerical studies conducted using on-line measurement data indicate that static load models, as compared with induction motor load models, are acceptable for modelling real power behaviours during disturbances and hence are adequate for transient stability analysis. Using multiple sets of on-line measurements, representative model parameters of five static nonlinear load models are derived and their performance in modelling dynamic behaviours of both real and reactive powers is compared. A method is presented to determine a representative set of parameters of static (nonlinear) load models for each loading condition     

Harmonics and voltage stability analysis in power systems including thyristor-controlled reactor

In this study, non-sinusoidal quantities and voltage stability, both known as power quality criteria, are examined together in detail. The widespread use of power electronics elements cause the existence of significant non-sinusoidal quantities in the system. These non-sinusoidal quantities can create serious harmonic distortions in transmission and distribution systems. In this paper, harmonic generation of a static VAR compensator with thyristor-controlled reactor and effects of the harmonics on steady-state voltage stability are examined for various operational conditions.     

An integrated approach to path analysis for weighted citation networks

Scientometrics - Profuse growth of scientometrics as a research field owes a discernible attribution to the introduction of citation networks and other scientograms. Centrality analysis, path...     

A stochastic programming approach to determine robust delivery profiles in area forwarding inbound logistics networks

One technique to coordinate the suppliers’ and the producers’ production plans in a supply chain is the use of delivery profiles, which provide fixed delivery frequencies for all suppliers. The selection of a delivery profile assignment has major effects on the cost efficiency and the robustness of a supply chain and thus should be performed carefully. In this work, we consider planning approaches to select delivery profiles for the case of area forwarding-based inbound logistics networks, which are commonly used in several industries to consolidate supplies in an early stage of transport. We present a two-stage stochastic mixed integer linear programming model to determine robust delivery profile assignments under uncertain and infrequent demands and complex tariff systems. The model is embedded into a solution framework consisting of scenario generation and reduction techniques, a decomposition approach, a genetic algorithm, and a standard MILP solver. On the basis of an industrial case study, we show that our approach is computationally feasible and that the planning solutions obtained by our model outperform both a deterministic approach and the planning methodology prevailing in industrial practice.     

Alternative approach for defining the particle population requirements for static image analysis based particle characterization methods

For image based particle characterisation approaches one of the most common discussion points is determining the number of particles required to have statistical confidence that the measurement is able to adequately describe the distribution of the sample. This topic becomes significantly more challenging when applied to the extraction of single component size distributions from multi-component samples.The aim of this work was to propose a means to accurately assess the particle number requirements using a method specific approach. The method applies a sub-sampling method to the original imaged dataset in order to provide an understanding of the impact of sub-sampling on the ability to accurately reproduce the original distribution.The method was applied to understand the particle number requirements for two batches of theophylline anhydrous with varied particle size distributions, using the input size distribution to guide the requirements for the subsequent multi-component samples of both materials.The results demonstrate the utility of the method to determine the appropriate number of particles required to recreate the size distributions. Whilst the minimum number of particles required to be sampled can be estimated, how those particles are sampled can also affect the validity of the measurement and must be taken into consideration.     

Smart demand for improving short-term voltage control on distribution networks

Smart grids must involve active roles from end users in order to be truly smart. The energy consumption has to be done in a flexible and intelligent manner, in accordance with the current conditions of the power system. Moreover, with the advent of dispersed and renewable generation, increasing customer integration to aid power system performance is almost inevitable. This study introduces a new type of smart demand side technology, denoted demand as voltage controlled reserve (DVR), to improve short-term voltage control, where customers are expected to play a more dynamic role to improve voltage control. The technology can be provided by thermostatically controlled loads as well as other types of load. This technology is proven to be effective in case of distribution systems with a large composition of induction motors, where the voltage presents a slow recovery characteristic due to deceleration of the motors during faults. This study presents detailed models, discussion and simulation tests to demonstrate the technical viability and effectiveness of the DVR technology for short-term voltage control.     

Nonlinear stability analysis of FGM shallow arches under an arbitrary concentrated radial force

International Journal of Mechanics and Materials in Design - The nonlinear in-plane buckling behaviour of pinned-pinned shallow circular arches made of functionally graded material (FGM) is...     

Fleet sizing of automated guided vehicles: a linear programming approach based on closed queuing networks

We use multi-class closed queuing networks to model operations of automated guided vehicles in a manufacturing or distribution environment. We approximate the dynamics of the system using the first moment balance equations of the embedded stochastic chain representing the network under the steady-state conditions. These moments account for loaded and empty-travel times, as well as times when vehicles are being loaded/unloaded or waiting to be dispatched. We model the steady-state behaviour of the closed queuing network by a linear program whose optimal value is the estimate of the required fleet-size. The result of the analytical model is compared with those of the simulation studies for a set of numerical examples. The comparison shows that the analytical model provides a good estimate for the required number of vehicles.     

Non-iterative load-flow method as a tool for voltage stability studies

Here the use of a non-iterative (NI) method for load-flow solutions is investigated. The method, previously proposed in the literature, presents some advantages in comparison with the iterative approaches usually employed. There, because the Taylor expansion is used, the power flow Jacobian matrix is not updated along the process. Here, some improvements in the implementation are executed, and few control actions are incorporated into the formulation. The method is then applied for voltage stability studies, aiming to reduce the computational time associated with     

A GLOBAL/LOCAL approach to lengthwise cracked beams: static analysis

A simple model is developed for the calculation of stress intensity factors for a lengthwise cracked beam subjected to transverse loading. The simple model is based on a GLOBAL/LOCAL approach that separates the GLOBAL structural behavior from the LOCAL crack tip zone dominated by singular stresses. The GLOBAL model is that of a frame while the LOCAL model is based on a novel application of the J integral. The accuracy of this approach is assessed by comparing it to a fully two dimensional analysis of an elastic layer containing a lengthwise crack.     

Generation curtailment to manage voltage constraints in distribution networks

The issue of congestion management in distribution networks by considering a methodology for generation curtailment due to voltage constraints is addressed. The curtailment is based on the contribution of generators to the constraints as quantified by voltage-sensitivity factors. It has been shown that generation curtailment following a simple proportionality rule is not efficient and some alternatives, which give a more efficient outcome, have been proposed. Influence of network losses on the curtailment rules has also been shown. The considerations have been illustrated using two simple 11 kV networks     

An alternating optimization approach for mixed discrete non-linear programming

This article contributes to the development of the field of alternating optimization (AO) and general mixed discrete non-linear programming (MDNLP) by introducing a new decomposition algorithm (AO-MDNLP) based on the augmented Lagrangian multipliers method. In the proposed algorithm, an iterative solution strategy is proposed by transforming the constrained MDNLP problem into two unconstrained components or units; one solving for the discrete variables, and another for the continuous ones. Each unit focuses on minimizing a different set of variables while the other type is frozen. During optimizing each unit, the penalty parameters and multipliers are consecutively updated until the solution moves towards the feasible region. The two units take turns in evolving independently for a small number of cycles. The validity, robustness and effectiveness of the proposed algorithm are exemplified through some well known benchmark mixed discrete optimization problems.     

Stochastic dynamic programming model for optimal resource allocation in vehicular ad hoc networks

Vehicular ad hoc network (VANET) is an emerging trend where vehicles communicate with each other and possibly with a roadside unit to assist various applications like monitoring, managing and optimizing the transportation system. Collaboration among vehicles is significant in VANET. Resource constraint is one of the great challenges of VANETs. Because of the absence of centralized management, there is pitfall in optimal resource allocation, which leads to ineffective routing. Effective reliable routing is quite essential to achieve intelligent transportation. Stochastic dynamic programming is currently employed as a tool to analyse, develop and solve network resource constraint and allocation issues of resources in VANET. We have considered this work as a geographical-angular-zone-based two-phase dynamic resource allocation problem with a homogeneous resource class. This work uses a stochastic dynamic programming algorithm based on relaxed approximation to generate optimal resource allocation strategies over time in response to past task completion status history. The second phase resource allocation uses the observed outcome of the first phase task completion to provide optimal viability in resulting decisions. The proposed work will be further extended for the scenario that deals with heterogeneous resource class. Simulation results show that the proposed scheme works significantly well for the problems with identical resources.     

An investigation of the static stability in self-piloting drilling

A comprehensive analysis of the static stability in self-piloting drilling is made in order to define the optimal location 7lpar;based upon the criteria of the equal pad normal reactions and equal stability coefficients) of the drill's supporting pads (relative to the drill's cutters). The optimal location is achieved under unsyrnmetrical location of the supporting pad relative to direction of the resultant cutting force in a plain perpendicular to the drill axis. Significant attention is paid to the drill entrance stability and three methods to reduce the bell mouth (the increase of the bore diameter and worse surface finish at the entrance) are introduced. By the detailed consideration of the drill static force system in the plain which contains the drill axis and vectors of the radial and tangential forces, a new design concept is proposed. The essence of this concept is to design the self-piloting drills with minimum offsets of the pad faces relative to the bottom of the hole being drilled. The experimental study of the newly designed drill shows that the use of the proposed design concept provides better hole quality, reduction of the bell mouth (diameter error and length), and reduction of the drill sensitivity to the value of the clearance between tool and pilot bush.     

A BEM approach to static and dynamic analysis of plates with internal supports

A boundary element approach is developed for the static and dynamic analysis of Kirchhoff's plates of arbitrary shape which, in addition to the boundary supports, are also supported inside the domain on isolated points (columns), lines (walls) or regions (patches). All kinds of boundary conditions are treated. The supports inside the domain of the plate may yield elastically. The method uses the Green's function for the static problem without the internal supports to establish an integral representation for the solution which involves the unknown internal reactions and inertia forces within the integrand of the domain integrals. The Green's function is established numerically using BEM. Subsequently, using an effective Gauss integration for the domain integrals and a BEM technique for line integrals a system of simultaneous, in general, nonlinear algebraic equations is obtained which is solved numerically. Several examples for both the static and dynamic problem are presented to illustrate the efficiency and the accuracy of the proposed method.     

A method for computing minimum voltage stability margins of power systems

A new and fast method for computing the minimum voltage stability margin (VSM) of power systems is presented. The computation of the VSM is required for power systems planning and operation. Usually, it is assumed that loads increase along a predefined direction (e.g. with constant power factor, followed by a proportional MW generation increase) up to the system's maximum loading point is reached. Situations may occur where variations from the predefined load increase direction, for example an unexpected load increase at some bus or area may result in smaller VSM, taking the system to an insecure state. The computation of the minimum VSM (mVSM) allows forecasting the load increase worst scenario. The information regarding the mVSM and the corresponding load increase direction for which it occurs, along with the usual VSM, allows operators to take measures like preventive control actions to move the system to securer operating points. Simulation results for IEEE test systems and for realistic systems are shown. Also, the proposed method is compared with other methods found in the literature.