INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE (ENGLISH)
Year:2004 | Volume:15 | Issue:2|Papers Count:16

Linear elastic fields may be effectively represented by either Papkovich [1] – Neuber [2] or Muskhelishvili's [3] complex variable representation. The converse is normally true for Muskhelishvili"s representation which employs the Airy's stress function, but not necessarily for Papkovich - Neuber representation. This' is to some extend due to the fact that the two - dimensional Papkovich- Neuber representation involves three independent harmonic functions, in contrast to the Muskhelishvili's complex representation which is in terms of only two independent harmonic functions. In this study such an inconsistency is discussed. In fact this note provides reconciliation between these two types of representation. An integral equation technique based upon biharmonic fields for our modified approach will be implemented.

Wavelet functions are developed to approximate the solution of the differential equations. Properties of wavelet function are first presented, the operational matrix of integration together with product operational matrix are utilized to reduce the computation of differential equations. The method is computationally attractive, and applications are demonstrated through an illustrative example.

Induced current and subsequent maximum heat generation in MF furnace occurs in liquid metal near to the contact surface with the refractory wall. In addition, due to non-uniformity of healing the cracks, corrosion of the refractory lining may become severe if appropriate precautions are not considered.In the present paper particle size distribution (PSD), cold crushing strength (CCS), and free iron content of two silica mixes, i.e. Iranian and imported ones, which are currently used in service, were studied. Results from postmortem analysis of both silica ramming mixes after 5 working days showed that the probable reason for the short life of the refractory lining can be attributed to non-uniformity of ramming and sintering as well as the healing profile and the amount of acid boric in the refractory silica mixes. The effects of each mentioned parameters have been discussed in this article.

Robust engineering (RE) which is also referred to as Taguchi Method, (TM), systematically evolved starting in the 1950s and aims at providing industries with a cost effective methodology for enhancing their competitive position in the global market. In this study, RE method has been used to improve the quality of oil pump housing production of Iranian diesel engine manufacturing (IDEM) company in which 134% improvement over the current condition has been achieved. It is interesting to mention that the above wonderful result has been obtained under vast conditions of production and operation environments, and increasing production capacity and not imposing any further investment in factors of production. This paper has been organized so to introduce RE method of optimization and IDEM company in sections 1 and 2, respectively. Design and conduction of experiment are given in section 3. Design analysis of obtained skewed data along with its comparison of another method of analysis is discussed in section 4. Finally, a practical comparison between current and improved conditions through a confirmation experiment is given in section 5.

Portland Cement is used frequently as the bonding agent for grouted rock bolts in geotechnical projects. The load bearing capacity of this type of reinforcement is depended on the strength properties of the cement grout. Amongst the most important parameters in this regard are the uniaxial compressive strength, cohesion and friction angle of the grout annulus which control the shear resistance of the bar to pull-out forces. To obtain these parameters, a number of uniaxial and triaxial compressive tests were carried out under controlled laboratory conditions.Special setup for the triaxial tests facilitated the calculation of spedmen's volumetric changes. Different confining pressures applied to the specimens covered the full range of cement grout mechanical behavior, i.e. elastic fragile to plastic ductile response. Strength and mechanical parameters, such as uniaxial and triaxial compression strength, cohesion and friction angle (C,f) as well as Young's Modulus and Poisson's ratio (E, v) were obtained from the test results.

Dynamic simulation of rotary cement kiln is a useful tool to study its behavior in different operating conditions. In this work a generalized cement kiln model, which is a highly non-linear distributed parameter system, was developed. Partial Differential Equations (PDE's) were discretized in spatial direction, applying Orthogonal Collocation (OC) technique. The model comprises differential equations as well as non-linear algebraic constraints. The NIMBUS dynamic simulation package (Newell and Cameron 1991) [1] was used to solve the resulting differential and algebraic equations (DAB's). The DAB's were solved simultaneously via sparse and dense numerical methods. Dynamic responses of the model to step changes in some manipulated variables were studied to predict open loop behavior of the system. The step changes include increase or decrease in gas and solid temperatures as well as solid and gas velocities. Sensitivity study indicated that the model successfully predicted qualitative behavior of an actual cement kiln.

The single-period problem (SPP), also known as the newsboy or news-vendor problem, is to find the order quantity which maximizes the expected profit or minimizes the expected cost in a single period probabilistic demand framework. This paper considers SPP with initial inventory at the beginning of the period as a stochastic variable. The proposed model applies when the order quantity has to be decided before the period. At the decision time, the inventory level is known, but the inventory level may be decreased due to various factors before the period.Consequently the inventory level will be a stochastic variable at the beginning of the period we present a method to determine the optimal order quantity for the proposed model. The presented model can be used in the sudden obsolescence case.This model has been extended to multi product with budget constraint. A method is derived to determine optimal order quantities with budget constraint using lagrange multipliers.

Consider a two - echelon repairable inventory system consisting of a central depot and multiple stocking centers. There are two kinds of defectives, both of them must be repaired at central depot. The difference between these kinds of defectives is related to their depot replenishment lead times. The centers provide parts replacement service to customers and the depot fills each kind of center replenishment orders on a FCFS (First Come First for Service) basis defective parts that are received by centers are passed to the depot for repair and depot inventory replenishment. For this system, existing models (for example, METRIC model) usually assume that there is only one kind of defective, and they also assume that the depot replenishment lead times (DRLTs) are i.i.d, which however, does not fit well into the service part logistics system, that motivated this research. Because the DRLTs consist of the sum of repair times, defective return times and transportation times, they are different across stocking centers, which are located globally. We study the impact of such center - dependent DRLTs on system performance. We show that for such systems, using the i.i.d DRLT assumption introduces errors in estimating system performance.

Using mass concrete in the thick structures can considerably increase the maximum temperature due to the cement hydration. In order to assess the risk of thermal cracking due to restrained thermal volume changes, it is necessary to analyze the temperature profile of the concrete body for the intended construction plan. In order to predict the temperature field, a numerical model is developed and utilized to solve the diffusive equation which is coupled to the concrete heat generation equation. The considerable effect of temperature on rate of heat generation of concrete is taken into account by using the maturity concept and derivation of equivalent age for various points in concrete. The accuracy of the developed computer model is assessed by comparison of the results with available experimental measurements of heat generation and transfer in a concrete block.

Many production planners try to design a program to maximize the profitability and meet customers' satisfaction. However, there is always a concern on the performance of the scheduled production planning. This paper presents a practical and efficient method to measure the performance of a production plan. The method ranks the performance of a production plan based on the Master Production Schedule (MPS). We explain that the algorithm can be effectively used to compare the performance of a production plan in different time schedules in order to detect improvement on performance. The implementation of the method is demonstrated by an example to explain that the burden of the computation is inexpensive.

Numerous methods have been developed to solve the motion planning problem, such as Potential Fields and Voronoi Diagrams. In order to benefit from the superiorities of these two methods and compensate their weaknesses, we propose an integrated model for path planning. In this paper, after building the environment's Generalized Voronoi diagram, we introduce the Pruned Generalized Voronoi Diagram. Then a potential function is assigned to it and incorporated into the Potential Field model. Finally, a steepest descent, mildest ascent bidirectional search technique is used for path planning. This enables us to overcome the famous local minima problem in Potential Fields. The algorithm performs satisfactorily in complicated problems, especially mazes.

Feyzi-Riazi equation of state [1] (FR-EOS) is modified in this paper. FR equation of state which is a modification of Peng-Robinson equation of state [2] (PR-EOS) predicts the volume of both liquid and vapor phases of nonpolar compounds accurately. But it fails in the prediction of the behavior of polar compounds.In addition to the reduced dipole moment the proposed equation requires critical temperature, critical pressure and acentric factor as the input parameters. The proposed equation of state estimates the specific volume of polar liquids and hydrogen-bonded fluids with greater accuracy while maintaining the ability of the FR-EOS in predicting vapor pressure and critical compressibility factor of pure compounds and mixtures.

In this study preliminary laboratory test work to identify the relative agitation leaching response to cyanidation and thiourea leaching of an oxidized ore have been carried out. The ore deposits of Neishaboor area with gold grade of 4ppm are rich enough for beneficiation studies.The characterization studies show that, the ore is oxidized and gold is present partly in the form of solution in quartz veins as well as in the form of free particles in iron hydroxide specially hematite which is the product of pyrite oxidation. Quartz, hematite, calcite and feldspar are the main minerals present in the order of abundances. Sieve analysis and distribution of gold particles in different sieve fractions shows gold particles are distributed bellow 2000 microns.Based on characterization studies, the potential of an alternative lixiviant like thiourea and cyanide leach have been determined and found that under optimized conditions thiourea leaching of the ore performs (extraction of 96.7% after 16 hours) better than cyanide leaching (extraction of 47.3 after 16 hours).

Bismuth doped calcium sulfide phosphor was prepared from a solid-state reaction between a calcium salt and sulfur at presence of flux.The product was analyzed by x-ray diffraction, ICP and luminance spectrophotometry, (LS) techniques.Excitation spectra of the CaS: Bi shows three bands at 260 nm corresponds to the band gap of CaS, 320nm corresponds to IS0→1P1 transition of Be3+ and 420 nm corresponds to IS0→3P1 transition of Be+3.Emission spectra of the caS: Bi shows two bands at 450 nm (intense) from 3P1→1S0 transition of Be3+ and 580 nm (weak) that is from recombination of electron donors Bi3+Ca2+/Vs2- with Na+ Ca2+ acceptors.Also, decay curve of the CaS: Bi indicates that the material has long afterglow phosphorescence.

Economical forecasting in mining field and mathematical expectation of probability of reaching production goals has a high degree of uncertainty. Economical concepts have the imperative to develop mine scheduling. They are robust under some economical scenarios. The scenarios of blocks exploitation have the net present value that it is corresponding to the "way" and order in which the "block" is removed. There are infinite numbers of possible scenarios and each scenario has its own net present value. The "best" scenario is defined as a scenario having the maximum net present value, and the "worst" scenario has the minimum value. In real and actual cases, mine designers and decision makers sometimes need to change the exploitation scenario for an incremental pit because of prevailing conditions, which are effective and important factors in mining. Such effective factors as slope failures, presence of faults, joints, subsidence, and existence of mine water must be considered. This paper explains how the "next" scenario, between the best and the worst, can be chosen for an incremental pit to attain possible maximum net present value by using integer programming in a three-dimensional case.