基于功率跟踪控制策略的带式输送机动态设计方法

在带式输送机动态过程仿真的基础上 ,以多驱动带式输送机系统为对象 ,对可控多驱动系统进行动力学分析·采用基于功率跟踪的方法 ,在合理的启动曲线的基础上 ,将第一驱动按合理启动曲线启动 ,其他驱动顺次跟踪第一驱动功率的控制策略·基于有限元方法建立了系统的动力学方程 ,提出了可控启动过程的动态分析算法 ,开发了动态设计软件BCD 2 0 ,通过对实际系统的仿真 ,证明了算法和软件的正确性·

带式输送机停机动态过程的计算机仿真

研究了带式输送机停机过程的动态设计 ,通过分析提出了输送机停机过程的力学模型为两种 :第 1模型与启动过程的力学模型相同 ,第 2模型为具有固定端的振动模型·分析了制动力的传动机理 ;在综合各种停机方式的基础上给出了停机过程的分类 ,提出了控制速度停机、自由停机和制动停机的计算方式及其计算方法 ;开发了带式输送机动态分析软件BCD .2 0的停机计算部分 ;应用软件对停机过程进行仿真研究 ,对停机过程进行了分析 ;给出了停机过程的动态设计方法和拉紧装置行程的计算式 ;得出了不同的停机方式结束后输送带的张力分布是不同的结果·所提出的方法可用于大型带式输送机停机过程的合理设计 ,避免事故的发生

离散型封闭式传送带生产系统的研究——一种通用的分析方法

本文对离散型封闭式传送带生产系统给出了一种通用的分析方法.基于传送带参数和工作站的服务时间,研究了系统中各流量间的相互关系,建立了动态的和稳态的表达式,给出了系统的品质指标,并首次指出了系统中存在一种循环效应及其对系统容量的影响。最后用仿真方法检验了分析结果的正确性.

块体理论赤平投影解析法与关键块体滑落概率研究—以锦屏二级水电站皮带机隧道为例

Block theory is an effective method on stability analysis of fractured rigid rock mass. There are a lot of discontinuous planes developed in rock mass of Jinping II hydropower station conveyor tunnel, so the stability of conveyor tunnel is related with whether there are unstable blocks on excavation planes. This paper deals with the stability of conveyor tunnel with stereo-analytical method for block theory on the basis of detailed investigation of rock mass data, and makes judgements on the movable blocks sliding types which are induced by all rock discontinuous planes and every excavation plane of conveyor tunnel. A conclusion is obtained that the sliding type of blocks is mainly single sliding, and a relatively few sliding types of double-sided sliding and vertical block falling; Also, the obvious statistical distribution result on movable blocks in conveyor tunnel indicates that there are a bit more instability blocks in left wall, left and right arches than right wall. In this paper, the stochastic probability model is drawn into block theory to study the sliding probability of key block on the basis of detailed investigation of its rock mass data and the development of the discontinuous planes in rock mass of Jinping II hydropower station conveyor tunnel. And some following conclusions are obtained. The relationship between trace length and the probability of instability of key block is inverse ratio. The probability of 1-3m primary joints are relatively higher. Key block containing joints J2 is relatively stable and the reinforcement of the arch would be crucial in the conveyor tunnel. They are all useful to offer effective reinforcement design and have important engineering values.

Computational modelling of particle degradation in dilute phase pneumatic conveyors

The aim of this paper is to develop a mathematical model with the ability to predict particle degradation during dilute phase pneumatic conveying. A numerical procedure, based on a matrix representation of degradation processes, is presented to determine the particle impact degradation propensity from a small number of particle single impact tests carried out in a new designed laboratory scale degradation tester. A complete model of particle degradation during dilute phase pneumatic conveying is then described, where the calculation of degradation propensity is coupled with a flow model of the solids and gas phases in the pipeline. Numerical results are presented for degradation of granulated sugar in an industrial scale pneumatic conveyor.

Numerical predictions of particle degradation in industrial-scale pneumatic conveyors

This paper presents an Eulerian-based numerical model of particle degradation in dilute-phase pneumatic conveying systems including bends of different angles. The model shows reasonable agreement with detailed measurements from a pilot-sized pneumatic conveying system and a much larger scale pneumatic conveyor. The potential of the model to predict degradation in a large-scale conveying system from an industrial plant is demonstrated. The importance of the effect of the bend angle on the damage imparted to the particles is discussed.

Computational model for prediction of particle degradation during dilute-phase pneumatic conveying: modeling of dilute-phase pneumatic conveying

A complete model of particle impact degradation during dilute-phase pneumatic conveying is developed, which combines a degradation model, based on the experimental determination of breakage matrices, and a physical model of solids and gas flow in the pipeline. The solids flow in a straight pipe element is represented by a model consisting of two zones: a strand-type flow zone immediately downstream of a bend, followed by a fully suspended flow region after dispersion of the strand. The breakage matrices constructed from data on 90° angle single-impact tests are shown to give a good representation of the degradation occurring in a pipe bend of 90° angle. Numerical results are presented for degradation of granulated sugar in a large scale pneumatic conveyor.

Effect of bend orientation on life and puncture point location due to solid particle erosion of a high concentration flow in pneumatic conveyors

An investigation into predicting failure of pneumatic conveyor pipe bends due to hard solid particle impact erosion has been carried out on an industrial scale test rig. The bend puncture point locations may vary with many factors. However, bend orientation was suspected of being a main factor due to the biased particle distribution pattern of a high concentration flow. In this paper, puncture point locations have been studied with different pipe bend orientations and geometry (a solids loading ratio of 10 being used for the high concentration flow). Test results confirmed that the puncture point location is indeed most significantly influenced by the bend orientation (especially for a high concentration flow) due to the biased particle distribution and biased particle flux distribution.

Enhancing the usability of numerical models with case-based reasoning

Numerical models are important tools used in engineering fields to predict the behaviour and the impact of physical elements. There may be advantages to be gained by combining Case-Based Reasoning (CBR) techniques with numerical models. This paper considers how CBR can be used as a flexible query engine to improve the usability of numerical models. Particularly they can help to solve inverse and mixed problems, and to solve constraint problems. We discuss this idea with reference to the illustrative example of a pneumatic conveyor problem. The paper describes example problems faced by design engineers in this context and the issues that need to be considered in this approach. Solution of these problems require methods to handle constraints in both the retrieval phase and the adaptation phase of a typical CBR cycle. We show approaches to the solution of these problesm via a CBR tool.

Application of simulation technologies in the analysis of granular material behaviour during transport and storage

Problems in the preservation of the quality of granular material products are complex and arise from a series of sources during transport and storage. In either designing a new plant or, more likely, analysing problems that give rise to product quality degradation in existing operations, practical measurement and simulation tools and technologies are required to support the process engineer. These technologies are required to help in both identifying the source of such problems and then designing them out. As part of a major research programme on quality in particulate manufacturing computational models have been developed for segregation in silos, degradation in pneumatic conveyors, and the development of caking during storage, which use where possible, micro-mechanical relationships to characterize the behaviour of granular materials. The objective of the work presented here is to demonstrate the use of these computational models of unit processes involved in the analysis of large-scale processes involving the handling of granular materials. This paper presents a set of simulations of a complete large-scale granular materials handling operation, involving the discharge of the materials from a silo, its transport through a dilute-phase pneumatic conveyor, and the material storage in a big bag under varying environmental temperature and humidity conditions. Conclusions are drawn on the capability of the computational models to represent key granular processes, including particle size segregation, degradation, and moisture migration caking.

Velocity measurement of pneumatically conveyed solids using electrodynamic sensors

Theoretical and experimental studies of cross correlation techniques applied to non-restrictive velocity measurement of pneumatically conveyed solids using ring-shaped electrodynamic flow sensors are presented. In-depth studies of the electrodynamic sensing mechanism, and also of the spatial sensitivity and spatial filtering properties of the sensor are included, together with their relationships to measurement accuracy and the effects of solids' velocity profiles. The experimental evaluation of a 53 mm bore sensing head is described, including trials using a calibrated pneumatic conveyor circulating pulverized fuel and cement. Comparisons of test results with the mathematical models of the sensor are used to identify important aspects of the instrument design. Off-line test results obtained using gravity-fed solids flow show that the system repeatability is within +/-0.5% over the velocity range of 2-4 m s(-1) for volumetric concentrations of solids no greater than 0.2%. Results obtained in the pilot-plant trials demonstrate that the system is capable of achieving repeatability better than +/-2% and linearity within +/-2% over the velocity range 20-40 m s(-1) for volumetric concentrations of solids in the range 0.01-0.44%.

A machine vision approach to the grading of crushed aggregate

The grading of crushed aggregate is carried out usually by sieving. We describe a new image-based approach to the automatic grading of such materials. The operational problem addressed is where the camera is located directly over a conveyor belt. Our approach characterizes the information content of each image, taking into account relative variation in the pixel data, and resolution scale. In feature space, we find very good class separation using a multidimensional linear classifier. The innovation in this work includes (i) introducing an effective image-based approach into this application area, and (ii) our supervised classification using wavelet entropy-based features.

Superimposed vibration confers no additional benefit compared with resistance training alone

Eighteen participants (22-43 years) were randomly allocated to one of two groups: resistance training combined with vibration (VIB; five males, four females) or resistance training alone (CON; five males, four females). Each participant trained three sessions per week (three sets of 10 seated calf raises against a load, which was increased progressively from 75% of one repetition maximum (1RM) to 90% 1RM for 4 weeks. For the VIB group, a vibratory stimulus (30 Hz, 2.5 mm amplitude) was applied to the soles of the feet by a vibration platform. The two groups did not differ significantly with respect to the total amount of work performed during training. Both groups showed a significant increase in maximum voluntary contraction and 1RM (P

Soil conditioning for EPBMs

Nowadays, the Earth Pressure Balanced (EPB) shields are used more and more caused by both the mechanical development of the machines and the more effective use of additives such as foams and polymers. These additives are used to condition spoil in the screw conveyor. A crucial component of EPB tunnelling applications is ground conditioning. Thus, in order to permit quantitative measurements of the conditioned ground behavior, it is necessary to develop and use a test able to simulate the extraction of earth from the chamber with a screw conveyor. This reliable test procedure can provide quantitative parameters that can really describe the conditioned soil behavior.

Laboratory tests for EPB tunnelling soil conditioning

The screw conveyor system plays a fundamental role during the EPB tunnelling operations for the tunnel face pressure control. On the other hand, the use of additives such chemical foams is even more applied in order to extend the EPB technology to the cohesionless soils. Despite the extensive use of the EPB technique in urban environment, little knowledge exists in the understanding of the behavior of such conditioned soil during the excavation operations. At the Turin University of Technology the Tunnelling and Underground Space Centre, in the mainframe of a wider research on soil conditioning, has developed an experimental apparatus that simulates the extraction phase with screw conveyor from a pressurized tank. In this paper the apparatus is presented and the results of a first series of tests carried out on sand are discussed. © 2007 Taylor & Francis Group.