Year:2002 | Volume:36 | Issue:3 (77)|Papers Count:19

Drilling mud is one of the important components in deep drilling of oil wells. Drilling muds consist of two phases: liquid phase (i.e. sweet water, salt water, seawater) and solid phase (such as clay minerals). Rheological characteristics of ordinary muds change in deep wells under high pressure and temperature therefore the mud is unable to perform its duties, specially transportation of the cuttings. Different methods are used for modification of these properties. One of these methods incorporates using of polymers in drilling mud. The present study investigates the properties of polymeric muds under conditions present in drilling operation in Iranwith the aim of eliminating the problems and poor efficiency of traditional muds. In this study the effects of two kinds of polymers (PHPA and XC) on the physical and rheological behavior of liquid base mud and also the effects of two kinds of pollutants (CaSO4 and MgSO4) on the behaviors and properties of polymeric muds is investigated. The results demonstrate that polymer based mud can improve rheological and thixotropic properties of the mud, decreasing of water loss, and has no effect on PH balance. Also the obove mentioned polymers become viscose when exposed to saturated salt water and are resistant to other ionic pollutants. They keep the initial specifications and viscosity in high shear rates. Increasing of temperature results in increasing of shear stress for bentonite and decreasing of shear stress for XC and PHPA polymers, Also increasing the tempreature ( of bentonite based mud ) results in increasing of yield point, viscosity and thixotropic properties, but increased temperature will have a reverse effect on mud containing XC and PHPA polymers.

This paper presents a new modeling method of induction motor under stator winding short circuit conditions. Modified winding function approach has been used for the modeling of induction motor. This model considers all the space harmonics of an induction motor. Common stator faults such as the turn-to-turn, coil-to-coil and phase-to-phase faults have been simulated. In this paper, for verification of the simulation results a 3hp induction motor has been winded with special forms that are to be easily constructing the fault conditions. Experimental results conform well with the simulation results.

Traditional fixed-rate error correction codes fail to exploit the time varying nature of the cellular communication channels. These channels are suitable most of the times, and, only occasionally, undergo deep fading. The design criterion for fixed-rate codes is base on the average or the worst channels conditions, which for these channels does not lead to an optimum design. On the other hand, Variable rate adaptive systems, can adapt to the changing channel conditions. During good channel conditions, more information can be sent with less error protection, but when the channel conditions become worse, these systems use more powerful codes for higher error protection. In this paper, an adaptive coding and modulation scheme is proposed for a DS/CDMA system used in cellular radio channels. This system uses coherent M-ary orthogonal modulation with RAKE receiver. Both Rayleigh fading and a combination of Rayleigh fading plus shadowing are discussed. Analytical bounds and simulations are used to evaluate the performance of the system. It is found there are significant improvement in bit error rate and the average throughput of the adaptive system. More important, it is found that adaptive coding scheme is relatively robust in shadowing environment.

A new concept named pseudo information measure is introduced. By this measure, Bayesian fusion of independent sources of information is extended to a wide range of possible formulations and some new fusion formulas are calculated. The coincidence between the performance of the proposed method of fusion with the results that are expected by human logic and output sensitivity of the fusion process are discussed. Also, we have discussed the resulting flexibility for map building applications. Map building by using the proposed fusion formulas has been implemented on Khepera robot. The resulting map were fed to "A*" path planning algorithm for comparative purposes. For the resulting routes, two factors are considered: length and a danger measure which is an increasing function of the least distance of the path to obstacles. The results show that by using the proposed fusion formulas, more informative maps of the environment are obtained by which more appropriate routes are achieved. Based on the selected function, there is a trade-off between the length of the resulting routes and their safety. This flexibility lets us choose the right fusion function for different map building applications.

This paper presents a 3.3-V, 18-bit sigma-delta modulator designed for digital audio. It has been simulated in a 0.6 m double poly, triple metal CMOS process using poly-poly capacitors in all process corners and considering ±10 % power supply voltage variations and -40 oC to 85oC temperature range. The integral gain coefficients of a 2-2 cascaded sigma-delta modulator are realized to achieve a higher overload level factor that is needed for high-resolution noise limited performance modulators. The achieved overload level factor is -0.6 dBFS. This modulator samples at -6.4 MHz with OSR of 128 and Nyquist rate of 50 KHz. Simulation results give SNDR and DR of 110 dB and 114 dB, respectively including of the circuit noise. The total power consumption of the modulator including that of the output buffers, voltage buffers and clock generators is 80 mW.

To estimate the fatigue life of connections in structures which are under cyclic loads, Stress Concentration Factors (SCF) are required. Few researches exist in the literature for multiplanar connections made up of rectangular hollow sections (RHS). Therefore, in the absence of such reliable results, existing relevant planar formulations are being used in fatigue life evaluations, which are mostly uneconomical. In this paper the connection is modeled using finite element method in three dimensional frame and elements; the selected mesh density and details are verified against existing experiments in planar connections. The effect of out-of-plane braces into the SCF of XX and TT multiplanar RHS is studied using the similar model extended to contain the out of plane members. The effect of various geometrical parameters on SCF of XX & TT type connections are compared with conventional formulas and discussed via figures; the resulting stress contours are also presented for each case study

Trip production modeling is the process of representing the effect of various socioeconomic parameters on human trip-making behavior. Whereas making a trip appears to be related to the socioeconomic characteristics through some functional form. This paper describes the use of an advanced type of NFSs, Adaptive Network-Based Fuzzy Inference Systems (ANFIS), for modeling trip production pattern. The proposed trip production model used a four-step hybrid learning strategy. At first, by using a linear regression model, a suitable initial situation was developed for the NFS and then this initial system was trained until reaching the final model. The data used in this research were collected from 55 traffic zones (47 zones in inner regions and 8 zones in outer regions) throughout Shiraz comprehensive study in 1990. In 1990s Shiraz comprehensive study, linear regression analysis was used to model the trip production. In that study the models were developed for four major trips: work trips, school trips, shopping trips, and recreational trips. In order to be comparable with the previous practice, we also used this classification and made the new models for those four trip purposes. We also use the same variables that were used in conventional models for building the new models. The predictions of the conventional models were compared with those from the new proposed models. The results indicate that the new models have capability to represent the relationship between the trip demands and the independent variables more accurately than the conventional models.

A three dimensional slope stability analysis based on the upper-bound technique of limit analysis is presented. A transitional rigid block collapse mechanism and an admissible velocity field are considered, and energy dissipation taking place along planar velocity discontinuities together with the work done by external forces are calculated. The minimum upper-bound solution is determined by optimizing the shape of the blocks. The software prepared on this basis can be used to calculate the safety factor in slope stability problems as well as the bearing capacity of shallow foundations near slopes in three dimensional situations.

A finite element program based on elastic - perfect plastic soil model of Mohr- Coulomb criteria was used to study the effect of load inclination and load eccentricity on the bearing capacity coefficients of surface footing. The existing formulae for iγ, ic, ieγ and iec have also been reviewed for the sake of comparison, and the shape and the size of rupture zones have been discussed. The results obtained from the present computations were compared to the available experimental results and others proposed relationships. The results showed that there are many factors which influence the computational results so that it is not that easy to judge clearly at this stage. Some distinct and general conclusions could, however, be made as follows : 1) Application of a suitable finite element program based on the elastic - perfect plastic soil model with Mohr - Coulomb criteria is able to illustrate the the effects of influential factors in determining the soil bearing capacity . 2) The factors of inclination and eccentricity are dependent on the friction angle of the soil, so as for large values ofφ ,the descending rate of these factors becomes more distinguished . This effect has not been included in the previous formulae.3) The effect of dilatancy angle can basically change the descending rate of the mentioned factors .This effect has not been considered in the previous literature. 4) The shapes of the rupture zones are similar to the experimentally observed shapes, but their sizes obtained from the present study are smaller than those have been measured in the tests with the same conditions.

Straight lines extraction is considered used as an important case in image analysis. It is also applied in different sciences such as computer vision, image processing, remote sensing and photogrammetry. Whit the development of digital photogrammetry since 80s, mapping has extremely been successful. Due to the much complicated nature of aerial and satellite images of earth, the automatic extraction of plan metric features such as roads and buildings to produce plan metric maps is experiencing some difficult. One of the important parts of the solution is straight lines extraction. In this paper, a method based on conceptual organization for extraction of straight lines from aerial images has been suggested. Based on the suggested method, in the first stage, the original image is converted to a binary image. In the second stage, the binary image is labeled and chain code, then features that have specific structure is separated. Based on the ability of conceptual organization, in the third stage, segment lines are extracted from structured features. Due to the noise, the segment lines are grouped together to make bigger lines. The proposed method has been tested and evaluated on aerial images in 1/10000 scale from Kish region.

In this article the destructive effects of low velocity impact on the residual compressive strength of composite plates with three different size studies. Using a closed from solution and a finite element method the mechanical behavior of the composite plates under impact loading is simulated. Using an experimental program, the results of simulation are evaluated. The composite plates are subjected to impact loading and then they are tested under compression loading conditions. The results of experiments show that the size of the damaged area decreases by increasing the size of the specimen. Therefore, in the real situation that the size of the structure in greater than that of the test specimen, the magnitude of damage is supposed to be smaller. Using Hertz method the magnitude of the impact loading is calculated. The damage area of the impacted specimen is also calculated. By changing the mechanical properties of the material in the damaged area the residual strength of the damaged specimen is simulated. The results obtained from simulation are in good agreement with experimental results

In this paper, a control law is developed based on the sliding mode control for electro hydraulic active suspension. The law is derived from simulation of hydraulic system, which contains valve and actuator dynamics. Controller is designed for a half vehicle model in such a way that the displacement and acceleration, as two independent set points, to approach to zero. The input servo valve voltage is determined in such a way that, actuators apply required force to sprung mass in order to increase ride comfort. The comparison of passive and active systems for half vehicle model shows that the controller with this strategy can increase ride behavior. Also the robustness of the controller has been investigated and the results show that the controller is worked very good even with the presence of road noise and vehicle parameters variation

Storage of natural gas in liquid hydrocarbons is one procedure for automotive natural gas usage that reduces the requirements of high-pressure or cryogenic storage needed in other common techniques such as CNG and LNG. Model solutions of Methane in 52 solvents and Tehran Refinery productions were simulated using various equations of state to determine the pressures necessary to maintain a liquid phase at ambient temperature. The calculation results show that the storage pressure can be reduced to 15 MPa, and due to the storage condition in the liquid phase, the energy density is increased up to almost 40% of the energy density of gasoline. With this technology, the low storage density of CNG and the very low storage temperature of LNG are both overcome, thus dramatically improving the technical feasibility of large-scale commercialization of natural gas powered vehicles.

Drilling mud is one of the important components in deep drilling of oil wells. Drilling mud consists of two phases: liquid phase (i.e. sweet water, salt water, seawater) and solid phase (such as clay minerals). Rheological characteristics of ordinary mud change in deep wells under high pressure and temperature, therefore, the mud is unable to perform its duties specially transportation of the cuttings. Different methods are used for modification of these properties. One of these methods incorporates use of polymers in drilling mud. The present study investigates the properties of polymeric muds under conditions present in drilling operation in Iran with the aim of eliminating the problems and poor efficiency of traditional muds. In this study the effects of two kinds of polymers (PHPA and XC) on the physical and theological behavior of liquid base mud is investigated together with the effects of two kinds of pollutants (CaSO4 and MgSO4) on the behavior and properties of polymeric mud. The results demonstrate that polymer based mud can improve theological and thixotropic properties of the mud, decreasing of water loss, and has no effect on PH balance. Also, the above mentioned polymers become viscose when exposed to saturated salt water and are resistant to other ionic pollutants. They keep the initial specifications and viscosity in high shear rates. Increasing of temperature results in increasing of shear stress for bentonite and decreasing of shear stress for XC and PHPA polymers. Also increasing the temperature (of betonies based mud) results in increasing of yield point, viscosity and thixotropic properties, but has a reverse effect on mud containing XC and PHPA polymers.

The objective of the present study is to demonstrate how the depth of burial of under exploration structures, affect the optimum distance between sampling points. In this respect, the magnetic field of buried structures in the yard of the Geophysical Institute of Tehran University has been measured. Then, the optimum distance of data collection points for each structure has been calculated. The present study proposed a distance of 0.5 to 1 meter for planar structures, a distance of 2.5 m for fault structures and finally a distance of 1 meter for cylindrical structures

Titanium-Phosphate ore deposit of Ghareh Aghadj, NW of Urumieh, has been developed in conjunction with maphic and ultramaphic intrusions of the region. Major rock types are wehrlite and diorite, followed by microgranodiorite, gabbro and gneiss. According to the geological and magneto metric studies three boreholes have been located. Based on data from two of these boreholes and results from samples measured for magnetic susceptibility properties, a network of boreholes has been designed for further exploration of the ore deposit.

This paper considers the problem of dynamic multi-item single level Capacitated Lot Sizing Problem with Setup Carry-over, which is abbreviated as CLSPSC. First the formulation of CLSPSC is presented as a Mixed Integer Programming (MIP) problem. Then two new heuristics for CLSPSC, consist of three elements of lot size determination, feasibility conditions and setup carry-over determination are described. Based on the algorithms a computer program in C++ is prepared for the algorithms. The computational results demonstrate that the heuristic algorithms are efficient to gain good quality solutions with high speed. The computational efficiency makes it possible to solve realistically large problem instances routinely on a personal computer.