ESTEGHLAL
Year:2003 | Volume:22 | Issue:1|Papers Count:14

Abstract: Overhead transmission lines are influenced by different factors which are ‎mostly electrical and mechanical. These factors can cause problems for lines, ‎distortions in network and outage of line. In designing transmission lines mechanical ‎properties are evaluated after selecting a suitable conductor and clearance with regard ‎to electrical properties. In lines designing, an important mechanical parameter for ‎estimating of phase distance is oscillations. Strong wind or icefall from conductor ‎surfaces or simultaneous presence of ice and wind may cause different oscillations. ‎These oscillations are classified to aeoliane‏,‏ galloping, and swing. Aeoliane is of high frequency (5-100Hz,-) and low amplitude ‎‎(about a few centimeters), galloping is of low frequency (0.1 to 0.3Hz) and high ‎amplitude (about of span sagging), also swing is of horizontal oscillation. In this ‎paper, the mechanism of conductor galloping oscillation and its different types are ‎described also these oscillations are simulated on the typical span by personal ‎computer‏.‏

Abstract: This paper presents a new super-element with twelve degrees of freedom for latticed columns. This elements is developed such that it behaves, with an acceptable approximation, in the same manner as a reference model does. The reference model is constructed by using many Solid elements. The cross section area, moments of inertia, shear coefficient and torsoinal rigidity of the developed new element are derived Since the reference model has a large number of degrees of freedom (especially for nonlinear cases), computation of the equivalent essential parameters of the proposed element is very time consuming, so, a model using only beam elements is also presented For the super element, a general purpose program is developed that is capable of performing linear and nonlinear analysis of 3D frames with latticed columns. In order to derive the essential parameters of the proposed super-element, many latticed columns are analyzed while shear deformations are taken into consideration. Using these essential equivalent parameters approximate relations are proposed for the compution of parameters of arty latticed column based on geometric characteristics. Finally, to show the accuracy of the proposed element, several examples are presented

In this paper, Forchheimer equation is used as the constitutive equation for flow through rock fill, and the nonlinear two-dimensional governing equation with free surface is solved by a new finite element method in a fixed grill. The model is verified by applying it to different flow conditions. The first scenario, which is assumed to be one-dimensional with analytical solution available for it, is used to verify the developed code. Other scenarios, which are two-dimensional free surface tests on a laboratory rockfill, are used to verify the modeL The model shows satisfactory performance in this regard. For example, on average, a mean absolute relative error of about 2.3%, in terms of pressure head was found to exist between modelling results and observed values. Further capabilities of the model are discussed by simulating overflow through self- spillway rockfill dams.

Abstract: There is a worldwide interest in the proper design of embankment darns to ‎resist earthquake loadings. For the first time in Iran, a complete ambient vibration ‎survey due to low-level loads such as wind, machinery activities, low level tectonic ‎activities, and water exit from bottom outlet was performed on Marun embankment ‎dam. These kinds of ambient vibration tests are suitable for manifesting the lower ‎vibration modes of the dam body. Using different signal processing methods such as ‎Power Spectra Density, the results of in-situ tests have been used to evaluate the ‎natural frequencies, mode shapes and modal damping of the dam body. Besides ‎ambient vibration tests, the 3-D modal analysis of the dam body was performed using ‎ANSYS software. The foundation and abutment flexibility effects on dynamic ‎characteristics of the dam body were investigated and the dynamic soil properties ‎were used from Engineer s report and some empirical relations. Also initial shear ‎modulus of the dam body and foundation materials was evaluated by refraction ‎survey. In this paper, the test procedures, related signal processing results, numerical ‎analysis results and its comparison with the dynamic characteristics of the dam body ‎obtained from the full-scale dynamic tests will be presented Finally, calibrating ‎procedures of the numerical model (based on increasing the accuracy of dam body ‎geometry, soil and rock material parameters and foundation and abutment flexibility) ‎will be discussed‏.‏

In hot forming process ,the workpiece undergoes plastic deformation at high ‎temperature and the microstructure of the workpiece changes according to the plastic ‎deformation .These changes affect the mechanical properties of workpiece .in order ‎to optimize this process .both the plastic deformation of workpiece and it is ‎microstructure changes should be taken into consideration-since material behaviors at ‎elevated temperatures are usually rate-sensitive , the analysis of the hot forming ‎processes requires a thermo -viscoplastic model. In this paper, by coupling the flow ‎stress prediction model developed with finite element analysis of thermo-viscoplastic ‎of the hot upsetting process, temperature, strain rate, flow stress distributions and ‎geometry of the workpiece at each time step can be calculated .At each time step, the ‎strain rate and temperature at each element are obtained .From these values and ‎history of deformation, the changes in microstructure and flow stress can be ‎determined. ‎

Abstract: An analysis of the demands of ULSI and GSI technologies shows the ‎necessity of multi-layer devices to reduction of signal transmission delay time. This ‎reduction is realized by using a better conductor metal, such as Cu and a surrounding ‎insulator with low capacity than actually used, such as Dow Cyclotene 3022. In this ‎paper, the results of evaporated and sputtered Cu to Dow Cyclotene 3022 were ‎studied .After presentation of interfacial reaction that causes adherence; the methods ‎of enhanced adherence as surface modification of polymer by nitrogen plasma have ‎been investigated

Abstract; in this paper, shear localization due to strain softening in sidepressed cylinders, is inverstigated. Shear localization causes formation of macroscopic shear bands, which can be obsserved in the metallographic cross-section. In this paper, for the first time a method is presented in which a simple two-slice model is used to study the formation of shears bands. The results obtained form this model are in perfect agreement with the results obtatained form experimental works force-a#+B# and B#` micrcrostructures in Ti-6242Si alloy.

Dense Silicon nitride was investigated to determine the effect of its microstructural parameters and densification on thermo-mechanical properties and thermal stress resistance to fracture initiation during a hot or cold mechanical and thermal shock testing. The different materials and microstructures were obtained by changing the parameters such as the type of the powder, additive, forming process and sintering condition. Maximum crack growth and thermal shock resistance of dense Si3N4 are achieved after complete conversion of the a®b transformation, and after the change in grain morphology towards elongated grain and the relative crystallization of the second phases have been obtained. The characteristics are obtained by a high a phase content of the starting powder, high Y2O3 and sintering condition of higher temperature (2000o C), longer soaking times (1h) and load application at the beginning of the thermal cycle.