A METHOD FOR CHARACTERIZING DUST DEFLAGRATION BEHAVIOR FOR APPLICATION TO VENT RELIEF DESIGN

ABSTRACT

The best available design data for vent relief of dust deflagrations are contained in the nomagraphs presented by NFPA and VDI. In order to utilize these data, experimental measurements must be made to characterize the dust in the enclosure to be protected. In the absence of a single standard test for such measurements, various test vessels of 20 liters or greater volume are in use following the demonstration that the 1.2 liter Hartmann apparatus yields data which are incompatible with the nomograph method. A 26-liter test facility is described and the effect of test variables detailed, showing how these test variables may be standardized. The overall philosophy of vent relief design is outlined and it is shown that various approximations exist at every stage of the design process, which is a compromise rather than a “worst case” solution.     

Dust explosion protection — a comparative study of selected methods for sizing explosion relief vents

Explosion relief vents are commonly used to discharge safely the combustion products of a dust explosion in items of powder handling plant. A problem associated with this method of explosion protection is the sizing of the vent area; this must be large enough to prevent explosion pressures from reaching damaging levels but not so large that the use of vents becomes impracticable. This report compares three common methods of estimating vent areas by applying explosibility data determined in the Hartmann bomb and the 20 litre sphere.     

树脂传递成型加工注射口位置的快速优化法

树脂传递成型加工工艺是一种先进复合材料加工的方法。虽然计算机数值模拟的研究已经取得了很大进步,但计算机数值模拟非常耗时间。本文中提出了一种树脂传递成型工艺注射口位置的快速优化方法。该法假设树脂首先注满离注射口近的节点,再根据溢料口的位置安排要求避免干点的出现这一点来决定溢料口位置;如果设计的溢料口数量比计算出来的必须的溢料口数量少,则会出现干点区。把干点区的面积作为罚函数加入目标函数中,目标函数的主体是从注射口到溢料口的距离。因此,笔者是在固定溢料口和注射口数量的前提下优化注射口的位置,获得注射口位置后,经过计算将获得溢料口位置。由于注射口位置是在离散的节点位置上,优化的变量是节点编号,所以优化方法采用功能很强的遗传算法来进行。针对五种模型进行了优化,优化的结果说明了本方法的可行性。     

ECONOMIC PRODUCTION QUOTAS FOR PULL MANUFACTURING SYSTEMS

We consider the problem of using “safety capacity” to ensure due date integrity in a pull manufacturing system and quantify the basic tradeoff between lost revenue opportunity and overtime costs. In this context, we address the question of when it is economically attractive to use “under capacity scheduling” and the problem of setting economic production quotas.

We develop four models for addressing the quota setting problem. The first three assume that quota shortfalls cannot be carried over to the next regular time production period. Models 1 and 3 assume that these shortages are made up on overtime and incur fixed or fixed plus variable costs. Model 2 does not use a capacity buffer and treats shortages as lost sales. Finally, Model 4 assumes that shortages can be backlogged to the next regular time production period at a cost. For this model, we compute both an optimal quota and an overtime “trigger,” which represents the minimum shortage for which overtime is used. We give computational results that illustrate and contrast the various models.     

Improved design of dust test chamber for uniform distribution of dust sedimentation rate

Soiling problems are always encountered for equipment installed in outdoor environments, such as headlamps of automobiles, air conditioners, solar collectors, and so on. How to prevent soiling problems on this equipment is one of the challenges for the design of their external layouts. Thus, evaluations of the dust sedimentation quantities on the surfaces of such equipment are necessary. Outdoor testing is usually straightforward but it takes a long time to experience various environmental parameters, such as dust-laden air, wind speed, wind direction, and so on. Indoor tests, performed in a dust test chamber, are instruments for controlling various environmental parameters independently. The conventional design for a dust test chamber is aimed at providing for a test under extreme environmental conditions. The uniformity of dust sedimentation rate within the chamber is not rigorously controlled. Nevertheless, some applications such as the effect of dust sedimentation on the glazing of solar collector require uniform distribution of dustfall in the test chamber for the indoor (laboratory) test. An improved design for a conventional dust test chamber is proposed. Performance tests done with the remodeled dust test chamber based on the improved design show that the normalized standard deviation of the dustfall concentration can be controlled within 2.41% ± 1.29%.     

Reliability Based Design Optimization Using Design Explorer

Experimental design methods can be applied to engineering design activities to understand which variables affect the system under consideration, how these variables affect the system, and how to select variable settings that will give uniformly long life to the system. The objective of this paper is to demonstrate the use of Design and Analysis of Computer Experiment (DACE) methods (Sacks, J. et al., 1989) and design optimization via the Surrogate Management Framework (Booker, A. J. et al., 1999; Audet, C. et al., 2000) on reliability optimization problems. Reliabilities are calculated using the Probabilistic Structural Analysis Method (Palle Thoft–Christensen and Baker, 1982; Achintya Haldar and Sankaran Mahadevan, 2000), a method for estimation of reliabilities and reliability indices for a structural model given probability distributions for design variables and “environmental” variables such as loads. By maximizing reliability, or minimizing the probability of failure, we attempt to achieve a minimum cost design that is affected minimally by the variability in the design variables.     

The venting of dust explosions in a dust collector

Pressures generated by dust explosions in a commercial dust collector have been measured. The dust clouds were formed while the collector was operating under normal working conditions, i.e. dusts were dislodged from the filter elements inside the collector by pulsed reversed air jets. The vented explosion pressures measured under these conditions provide a realistic guide to the explosion pressures that the filter may have to withstand in practice. These pressures are low (2 kPa) when the explosion is vented through a vent close to the ignition source. If, however, the vent is remote from the ignition source and flame turbulence is generated, the rate of combustion is increased and the explosion pressures are higher (14 kPa). The vented explosion pressures encountered when the flame becomes turbulent are reasonably well predicted by the K_st nomograph approach. Pressures generated by highly turbulent explosions in a silo-shaped container have also been compared to the K_st homograph predictions. In these experiments, the pressures were always much higher than predicted.     

Process-oriented tolerancing for multi-station assembly systems

In multi-station manufacturing systems, the quality of final products is significantly affected by both product design as well as process variables. Historically, however, tolerance research has primarily focused on allocating tolerances based on the product design characteristics of each component. Currently, there are no analytical approaches to optimally allocate tolerances to integrate product and process variables in multi-station manufacturing processes at minimum costs. The concept of process-oriented tolerancing expands the current tolerancing practices, which bound errors related to product variables, to explicitly include process variables. The resulting methodology extends the concept of “part interchangeability” into “process interchangeability,” which is critical due to increasing requirements related to the selection of suppliers and benchmarking. The proposed methodology is based on the development and integration of three models: (i) the tolerance-variation relation; (ii) variation propagation; and (iii) process degradation. The tolerance-variation model is based on a pin-hole fixture mechanism in multi-station assembly processes. The variation propagation model utilizes a state space representation but uses a station index instead of a time index. Dynamic process effects such as tool wear are also incorporated into the framework of process-oriented tolerancing, which provides the capability to design tolerances for the whole life-cycle of a production system. The tolerances of process variables are optimally allocated through solving a nonlinear constrained optimization problem. An industry case study is used to illustrate the proposed approach.     

Design of a Closed Loop Computer Controlled System for Selective Area Laser Deposition. I. Laser Systems, Gasflow, and Substrate Temperature Control

A closed loop computer controlled system to implement selective area laser deposition (SALD) is described. The SALD process uses a laser beam that is moved relative to a substrate to control the region over which chemical vapor deposition occurs. Deposit shape control is achieved by controlling the laser beam path and power. The system combines a remote microwave plasma source with scanning laser induced chemical vapor deposition. Major design goals included computer control of process variables including reactor pressure, source gas flow rates, laser power and beam position, applied microwave power and tuning, and substrate bias temperature. Scanned shape data files are derived from industry standard “.STL” tessellated surface meshes. Control strategies for these process variables are described.     

Safety assessment of flame-arresting battery plugs

Hydrogen and oxygen produced by electrolysis during the charging of lead-acid batteries must be vented from the battery case. The accidental ignition of these gases can produce a flame which propagates back into the battery case causing an explosion. To minimise this risk, various flame-arresting vent plug designs have been marketed. To assess the performance of these, appropriate test equipment and procedures have been developed and are described in this paper. The concept of a danger zone to characterise the volume above the vent where the charge gases can be ignited is introduced. Typical results for the danger zone above an isolated hole are given.     

HPGe detectors for low-temperature nuclear orientation

Using the Low-Temperature Nuclear Orientation (LTNO) technique one can study various interesting properties of atomic nuclei and nuclear decay which can be deduced from the measurements of the angular distributions of charged particles emitted during the decay. However, the use of particle detectors working in conditions of LTNO devices (which are generally not available commercially) is a necessary precondition for the realization of these experiments.

Planar HPGe detectors for detection of charged particles at “liquid helium” temperatures were developed and produced at NPI e . Relatively simple technology using vacuum evaporation and diffusion was employed. The performance of detectors at low temperatures was tested and their characteristics measured in a testing cryostat before using them in real experiments.

The HPGe detectors were extensively used in a whole range of LTNO experiments with various physical objectives — in offline (IKS Leuven) as well as online (CERN-ISOLDE, Louvain-la-Neuve — LISOL) experiments. In frame of the project “Meson-Exchange Enhancement of First-Forbidden Beta Transitions in the Lead Region”, the measurements of angular distribution of emitted β-particles allowed to determine experimentally the “meson-exchange currents” contribution to the β-decay. In the project “Isospin Mixing in NZ nuclei”, the isospin-forbidden β-transitions of the nuclei in region (A=50–100) were studied in order to obtain information on the isospin structure of the nuclear states. A new project looking for the possible presence of the tensor currents contribution to the β-decay is being prepared for the CERN-ISOLDE facility.     

OPTIMAL DEFINITION OF CLASS INTERVALS FOR FREQUENCY TABLES

Data sets are often analyzed in the form of collections of frequency tables (or percentiles derived from equivalent cumulative frequency distributions). Decisions concerning the number of intervals and interval width obviously affect the quality of the data in subsequent analysis. Relying on the basic concepts of information theory, a procedure is presented which evaluates the relative information content of a set of frequency data when subdivided in various manners. Maximum information is always preserved when “maximum entropy” histograms (with unequal class intervals) are used. Evaluation of several schemes of frequency table subdivision (phi-based arithmetic, log arithmetic, Z-score, log Z-score, maximum entropy) indicates that, surprisingly, collections of equal interval phi-based frequency tables contain the least information. Additionally, the concept of the relative entropy of a given collection of frequency tables is defined. The relative entropy is useful as a feature extractor wherein several collections of data with potentially similar information can be compared. An example of using the relative entropy as a feature extractor is given in shape analysis where the choice of which harmonic(s) represents the greatest shape differences need to be defined.     

岩石动态力学参数测试综述

岩石工程实践中,受动力荷载的作用现象比较普遍,例如工程爆破、自然地震及岩爆等。为了工程安全并兼顾经济效益的最大化,在这些工程问题的设计和施工中需要使用准确的岩石动态力学破坏强度及断裂韧度等力学性质。由于岩石动力测试较静态测试复杂得多,国际岩石力学学会岩石动力学专业委员会(ISRM-CRD)2012年才首次推出了岩石动态测试推荐方法,包括岩石动态压缩、动态拉伸及动态断裂方法。夏开文近几年在岩石动力实验室测量方面做了一系列工作,得到了国际同行广泛的认可,并执笔编写了ISRM动力测试推荐方法。夏开文作为新一届的国际岩石力学学会岩石动力学专业委员会(2011²015)主席,负责继续推动把更多切实有效的岩石动力测试方法建议为国际岩石力学学会(ISRM)推荐方法。在此背景下,我们结合多年来的研究工作,总结一些准确可靠的岩石动力学测试方法,希望能被应用到我国的工程爆破实践中,以期进一步提高我国工程爆破施工的高效性和安全性。     

Risk evaluation on the basis of pressure rate measured by automatic pressure tracking adiabatic calorimeter

An automatic pressure tracking adiabatic calorimeter (APTAC) had been employed to obtain the thermokinetic and the vapor pressure data during runaway reactions. The APTAC is an adiabatic calorimeter with a large-scale sample mass and low thermal inertia, and is an extremely useful tool for assessing thermal hazards of reactive chemicals. The data obtained by the APTAC are important information for the design of the safe industrial process. The thermodynamics parameters and the gas production were discussed on the basis of the experimental data of various concentrations and weights of di-tert-butyl peroxide (DTBP)/toluene solution for the purpose of investigating the properties of the APTAC data. The thermal decomposition of DTBP was studied on the basis of the temperature data and the pressure data obtained by the APTAC. The activation energy and the frequency factor of DTBP are nearly constant and the same as the literature values in the concentrations between 20 and 60 wt.%. The pressure rise due to gas production is important data for designing the relief vent of a reactor. The time history of the gas production was investigated with various weights and concentrations. The total gas production index, which had the vapor pressure correction, was 1.0 in the decomposition of DTBP.     

Stress intensity factors for internal multiple cracks in thick-walled cylinders stressed by internal pressure using load relief factors

The concept of “load relief factor’ is used to determine in an approximate manner stress intensity factors for a multiply-cracked plane and an axisymmetric body. To demonstrate the validity of the method, which utilizes known available solutions, it is first shown to conservatively agree, within engineering accuracy, to that obtained from a more exact formulation. Stress intensity factors are then found for multiple-internal radial cracks in hollow cylinders of various wall ratios, stressed by internal pressure. Such a solution, although approximate and heretofore unavailable, will aid in ordnance design applications and serve as guidance until more rigorous analyses become available.     

A fracture model for surface flaws and certain types of weld defects in ductile materials

A model is proposed for prediction of fracture initiation from surface flaws, bands of slag inclusions and zones with low yield strength in thin-walled structures. The model applies to cases where the whole ligament or defect zone is plasticized. Application of the model to design cases requires information from stress and elongation measurements on tensile specimens cut perpendicular to defect regions of the actual type. Predictions by the model of critical stresses are compared to results from burst tests on pipes with surface flaws. The correlation is found to be good and existing deviations between experiment and theory can be given a rational explanation within the framework of the model. This suggests that bulging and out of plane loading effects which are not taken into account in the model are not significant in these problems. The model thus makes a “limit” analysis possible for “two-dimensional” structures containing defects of the types mentioned above.     

Probabilistic inversion for chicken processing lines

We discuss an application of probabilistic inversion techniques to a model of campylobacter transmission in chicken processing lines. Such techniques are indicated when we wish to quantify a model which is new and perhaps unfamiliar to the expert community. In this case there are no measurements for estimating model parameters, and experts are typically unable to give a considered judgment. In such cases, experts are asked to quantify their uncertainty regarding variables which can be predicted by the model. The experts’ distributions (after combination) are then pulled back onto the parameter space of the model, a process termed “probabilistic inversion”. This study illustrates two such techniques, iterative proportional fitting (IPF) and PARmeter fitting for uncertain models (PARFUM). In addition, we illustrate how expert judgement on predicted observable quantities in combination with probabilistic inversion may be used for model validation and/or model criticism.     

EXPERT SYSTEM FOR PRODUCT MANUFACTURABILITY AND COST EVALUATION

Product design is an important stage in the product development cycle. A large proportion of a product's cost is governed by product design. Every effort should be made to ensure a product is “rightly designed for manufacture” at the design stage in order to avoid unnecessary expenditure of time and money in production resulting from a need for redesign. An evaluation tool in the form of an expert system has been developed for product designers to assess manufacturability of product designs. This paper describes the mode of operation in the development of the expert system from which manufacturing information such as selection of processes and materials, and estimation of costs can be obtained. The system enables product designers to evaluate product design alternatives by comparing the analyzed results to come up with the optimum design which best satisfies the requirements. The developed system runs on the PC platform.     

On the uncertainties of decentralized controllers in a transfer production line

In this paper, an information theoretic approach is applied to analyze the performance of a decentralized control system. The control system plays the role of a correcting device which decreases the uncertainties associated with state variables of a production line by applying an appropriate “correcting signal” for each deviation from the target. In particular, a distributed feedback control policy is considered to govern a transfer production line, which consists of machines and buffers and processes a single part type in response to a stochastic demand. It is shown how the uncertainty of the demand propagates dynamically into the production system, causing uncertainties associated with buffer levels and machine production rates. The paper proposes upper estimates for these uncertainties as functions of the demand variance, parameters of the distributed controllers and some physical properties of the production line. The bounds are based on dynamic entropy measures of the system state and the control variables. Some practical implications into the area of decentralized controller design are proposed, an information-economical analysis is presented and a numerical study is performed.     

DESIGN GUIDELINES FOR CYCLONE IMPROVEMENT

ABSTRACT

There is a potential for improving cyclone separators by design and operating conditions. Secondary flow detrimental to dust separation can be avoided by proper gas inlets, dimensioning of body and swirl, or by use of a flow guide in the area of separation. Cyclone and bin are to be treated as one unit. Scavenging of the bin is most effective for high effiency. Cut sizes smaller than 1 μm can be realized with a cyclone separator unit consisting of a preseparator, a battery of small cyclones, and a scavenging cyclone with gas recirculation. Such arrangements are capable to cope with dust streaks and to make positive use of dust agglomeration. These principles are applicable also for big cyclone batteries as used behind rotary dryers for wood chips, etc.