Year:2005 | Volume:38 | Issue:6 (88)|Papers Count:21

Two dimensional harmonic response of lined circular tunnel in elastic full space medium against plane P-SV waves is investigated .The solution uses hybrid direct boundary element method and finite element method for soil and lining, respectively. In the proposed ring element used in the modeling of lining, radial and tangential deformations are defined using Fourier series expansion. Therefore the direct unknowns of problem are introduced as coefficients of these series. Numerical results include the non-dimensional shear and hoop stresses in lining as well as its interface with surrounding soil for various material properties.

Based on boundary element method, a time domain solution for 3D diffraction is developed to study nonlinear interaction of ocean waves and rigid arbitrary shape structures. Solution in time is obtained from integral equation based on Green's theorem. Free surface boundary conditions are expanded and combined to change moving boundary to constant one in time. Consequently, solving simultaneous equations, resulting from discrete sizing integral equation, is required once instead of at each time step, significantly inducing time increase. The solution is separated to known incident potential and unknown scattered one, developed in time and place and should be determined. Based on these theoretical developments, software entitled "DIFFRACTION" is produced and used in assessing waves diffraction around arbitrary shape obstacles. The force and free-surface elevation for different cases are presented. Despite less elements and more convenient computations, surface-piercing circular cylinder results are in good agreement with previous studies.

In the present paper application of a one-needle and a double-needle electrical probe with developed specifications is introduced for measurement in air-water flows. The new one-needle probe has the capability of measuring air concentration and bubble count with very high sampling frequency. Another advantage of this probe is real time measurement and on-line presentation of results. More than 30 sets of tests were carried out in air-water flows to calibrate the probe and to determine the circuit threshold level. To measure the velocity of air-water mixture a double-needle electrical probe is employed. The specifications of the double-needle probe are similar to the one-needle probe with addition of one needle to make it capable of measuring flow velocity. To ensure the performance of the double-needle probe, its measurements were compared with a pitot tube. This comparison showed that the maximum difference in measurements was less than 4%.

Iranian traditional domes are of the most notable samples of traditional construction in Iran during thousands of years, many of which still standing on seismic parts of the country for many centuries. Structurally, Iranian domes can be categorized into single, double and triple-shell domes. Single-shell domes are the earliest type of domes. The single-shell is the main load bearing part. Double-shell domes consist of two shells, and they are divided into continuous and discontinuous types. In continuous double-shell domes the distance between the two shells is small and shells are connected by brick connectors. In discontinuous double-shell domes there is a considerable distance between the two shells. For structural stability of some domes meridian walls or stiffeners are built in the space between the two shells. There are also a few domes with three shells. In this paper, structural systems of a number of Iranian historical domes made of masonry materials will be discussed and their structural strength and stability due to dynamic effects of earthquake will be presented. The document will also explain the structural role of meridional stiffeners in double-shell domes.

Some methods are discussed for damage assessment of trusses. The authors developed one of these methods for suitable use of displacement and strain data. Analytical or experimental data can be used in this analysis. Also, the proposed method is able to use substructure. When the damage occurred in a part of truss, or a specific part of structure is not available, or lack of measurement devices, one can utilize substructures analysis. The damage of several plane trusses are estimated by author's computer program and the results are given in the paper.

In order to seismic microzonation of Urmai city micro tremors were measured at 220 stations during a comprehensive study. Measurements were conducted with two different approaches, those are with-reference and non-reference methods. Different aspects of site effect problem were studied by using the recorded data. Two so called Hs/Hr and H/V methods were examined in this study. Results showed that Hs/Hr method failed to give clear resonance peak at predominant frequency of the site when the distance between the site and reference station was more than 2500 meter. Whereas H/V method successfully indicated the predominant frequency at any distances. The distance of 2500 meter is introduced as the threshold distance for validity of Hs/Hr method. Suitability of micro tremor method for detection of topography effect was also examined. For this purpose the measured data at 5 stations located at Shahrake Electronic hill, south-east of Urmia city were utilized. Two horizontal components of measured micro tremors were compared to the vertical one. Results showed that at the stations located at the top portion of the hill there was significant amplification whereas for the stations located at the hill foot the amplification was negligible. This means the micro tremor method could successfully distinguish the topography effect. Moreover, the results showed that for selection of a suitable rock station the micro tremors recorded on a rock outcropping should be free of any topography effect; otherwise Hs/Hr method could not show reliable results.

Numerical modeling has been largely developed in soil mechanics behavior by different methods. Among them, the development of the boundary element method, which is the most suitable one for domains with infinite boundary conditions like soils media, has been restricted by the necessity of deriving the Green's functions of the governing differential equations. Indeed, attempting to solve the three-dimensional boundary value problems for unsaturated soils leads one to search for the associated Green's functions of the governing differential equations.In this paper the governing differential equations of the phenomena are presented which consist of three main groups of equations: 1- equilibrium and constitutive equations of soil's solid skeleton, 2- conservation and transfer equations for air phase and 3- conservation and transfer equations for moisture phase.The associated Green's functions have been manipulated with a few assumptions to first linearize the completely non-linear governing differential equations and next to make possible deriving the results, mathematically. After applying the Laplace transform to eliminate the time variable, Green's functions of the governing differential equations have been derived using the straightforward Kupeadze's method. Then using the inverse Laplace transforms, the completely closed-form Green's functions have been derived in the time domain.Finally, for verification of the results it has been demonstrated that when the conditions approach to the poroelastostatic case, the Green's functions approach to the corresponding poroelastostatic Green's functions as well. As no analytical solutions are available in the literature for the mentioned Green's functions, it seems to be a new experience to introduce a set of fundamental solutions for the unsaturated case for the first time.

Presented is a rigorous solution for the three-dimensional stability analysis of convex slopes with corners in plan view. The method is based on the upper-bound theorem of limit analysis approach. A rigid-block translational collapse mechanism is considered, with energy dissipation taking place along planar velocity discontinuities. This mechanism is optimized to obtain the minimum factor of safety for stability of the corners. The algorithm can also be used to determine the ultimate limit load of a foundation located on a corner. Based on comparisons with known solutions, the method was generally found to be accurate in predicting the stability of such slopes. The numerical results indicate that the unloaded corners are more stable than the straight slopes. Dimensionless diagrams for various corner angles are also presented.

In this paper we are presenting a methodology, which can remove the effect of ionosphere refraction (ionosphere error) on the coordinates derived by single frequency GPS receivers up to 85 percent at a radius of 1400 km around the computational point. The method is based on the GPS observations being made at the permanent GPS stations, according to the following procedure: (i) The real-time GPS observations being made at the permanent GPS station is compared, epoch-wise, with precisely known coordinates of the permanent station and the time series of coordinate variations in x, y, and z component {∆xi, ∆x, ∆z} is derived. (ii) Fast Fourier technique is applied in order to transfer each components of the variations vector from the time domain into frequency domain. (iii) The plot of the resulted period gram provided us with the frequency vector {fx, fy, fz} of the ionosphere refraction (ionosphere error) with nearly 24 hour period. (iv) Having derived the frequency vector of the ionosphere refraction, a sinusoidal models of the form Sxi =ai0+ai1cos(wit-ψi ) (where w=2πƒ ) is fitted to the coordinate differences {∆x, ∆y, ∆z} via least squares technique. As a case study, 25 day observations of the permanent GPS station of Tehran National Cartographic Center (NCC) is used.

A thorough study on the possibility of using Topex-Poseidon satellite altimetry data for DTM generation over the land area has been conducted.The geographical region of Iran has been selected as the test region. The study proves that repeated observations of Topex-Poseidon satellite are a valuable source for increasing the precision and resolution of existing DTM's.The theoretical details and the results of the case study will be presented.

In this paper Abel-Poisson boundary value problem with boundary data of the type gravity intensity (from gravimetry) and sea surface height (from satellite altimetry) as a solution to geoids computation problem is presented. This method besides its high accuracy from its theoretical point of view, addresses the problem of high-accuracy geoids computations in the coastal areas. The highlights of the method are: - Application of ellipsoidal harmonic expansion up to degree/order and ellipsoidal centrifugal field for the removal of the effect of global gravity and isostasy field from the gravity intensity observations at the surface of the earth.- Application of ellipsoidal Newton integral on the multi-cylindrical equal area map projection surface for the removal of the residual mass effects within a radius of around the computational point from the gravity intensity and astronomical observations at the surface of the earth.- Application of ellipsoidal harmonic expansion up to degree/order and ellipsoidal centrifugal field for the removal of the effect of global gravity and isostasy on the geoidal undulations from the geoidal undulations derived from satellite altimetry.- Application of ellipsoidal Newton integral on the multi-cylindrical equal area map projection surface for the removal of the effect of the water masses outside the reference ellipsoid within a radius of around the computational point from the geoidal undulations derived from satellite altimetry.- Least squares solution of the observation equations of the incremental quantities derived from aforementioned stages in order to obtain the incremental gravity potential at the surface of reference ellipsoid.- Restore of the removed effects at the application points on the surface of reference ellipsoid.- Application of ellipsoidal Bruns formula for converting the potential values on the surface of the reference ellipsoid into the geoidal heights with respect to the reference ellipsoid.As the case study, computation of the high-resolution geoids of Iran based on gravity intensity and sea surface height from Topex-Posseidon satellite altimetry data is presented.

The possibility of modeling gravity field of the Earth along the leveling lines using the gravity observations at the leveling benchmarks has been studied. As the case study, gravity observations along the first order-leveling network of Iran has been considered. The mathematical models that have been developed for this purpose are polynomials of degree 4 and degree 8. The efficiency of the aforementioned models has been compared with the ellipsoidal harmonic expansion to degree and order 20, 180, 360 and the Somigliana-Pizzeti gravity field. The test computations have proven that a polynomial model of degree 4 can be considered as the best choice for the gravity field modeling along the leveling lines. Based on the case study of gravity field modeling along the leveling lines of Iran, the polynomial model of degree 4 can provide 20 mGal accuracy which is quite enough to provide the accuracy level of the gravity data needed for the precise leveling based on the current demands. Therefore, by applying such a model the need for the gravity observations along the leveling lines will be reduced and as such great reduction in the expense of the precise leveling observations will be achieved.

Measurement and modeling of the surface of the human face have found extensive applications in the surgical operations and computer animations in recent years. Varieties of approaches including laser scanning, coded lights, stereo imaging, etc. are available. This paper deals with the reconstruction of the human face using stereo images employing an amateur camera utilized in a digital close range photogram metric approach. To model the calibration parameters of the camera, a 3D control network was constructed and a rigorous 3D network adjustment was performed. The accuracy of the points in the adjusted network is estimated to be about 0.7 mm. These points are utilized in a self calibration co linearity model yielding the camera calibration parameters. In the next stage, based on a simple camera placement rule, the optimum positions of the camera stations are determined and seven convergent photographs are taken from these stations. As the texture of the human face is normally quite low, an artificial pattern was applied over the face prior to photography. The well known adaptive least squares multi image matching was then applied to the scanned images to detect the conjugate points. Nearly 18000 conjugate points are extracted. Space intersection of conjugate collinear rays provided the object coordinates of the matched points using the direct linear transformation model. The reconstructed surface of the face was generated by Delaney triangulation of the object coordinates of the matched points. To facilitate the visualization of the surface, contour lines and the shaded relief are generated. Statistical test indicated an overall accuracy of 0.7 mm for the reconstructed surface.

This research work is concerned with the digital surface reconstruction of Cheshmeh Ali historical site using the method of digital close range photogrammetry. Regarding the size of the site and other photogram metric factors such as film resolution, camera frame size, etc. four imaging stations were considered. Hasselblad non metric camera was installed on each predetermined station successively and four %80 overlapping images were taken to cover the entire area of the site. These images were then scanned with Intergraph scanner with a resolution of 14 micron pixel size. Non-linear image distortions, which were mainly due to the camera low geometric stability, were then modeled using the Multi Quadric (MQ) interpolation function. The MQ coefficients were determined using a dense pattern of control points. The object space coordinates of the control points were measured by total station. The statistical tests indicated an accuracy level of ±36 micrometer in image space for the checkpoints. The MQ coefficients were then used in the later stage to resample the original images and hence effectively the generated resample output data were nearly free from distortions. These images were then fed into the Parade yes DSP system to generate a three dimensional photogram metric model. The X, Y and Z coordinates of the site were then extracted manually from the 3D models using the operator's interactive capability offered by the DSP. The connectivity of the common features in the adjacent models was ensured using the stereo superimposition potentials of Parade yes system. The geometric accuracy of the reconstructed 3D surface is estimated about ± 5 millimeter.

Multi Quadric (MQ) interpolation function is used as a post-processing tool for the refinement of the object coordinates of the tie points obtained by the aerial triangulation (AT) technique. To apply the MQ function, initially a low order polynomial AT is applied to a photogrammetric block consisting of 4 strips and 77 photographs. The trend of the residual vector errors of the ground control points was then modeled by the MQ function. The calculated MQ coefficients were subsequently utilized to refine the ground coordinates for all tie points of the block.The accuracy achieved by the MQ approach is compared with the standard polynomial, independent model and bundle adjustment AT techniques. The evaluated accuracy is based on the uniformly distributed checkpoints whose coordinates were determined by differential GPS receivers. The test results indicate that MQ function gives a marginal improvement of +-0.2; +-0.1 and +-0.2 meter RMSE for the X, Y and Z coordinates of the check points respectively as compared with the polynomial AT method. However, comparing the accuracy figures with the standard independent model and bundle adjustment, noticeable improvements were not observed.Furthermore, the MQ potential for the elimination of the residual systematic errors for tie points due to imperfect interior orientation parameters was also investigated by introducing defective interior orientation parameters during tie data capture stage. The MQ function was then applied again as a post processor for removing the systematic trend. The results show an overall improvement of +-0.80, +-1.08 and +-2.90 meter RMSE for the X, Y and Z coordinates of the tie points respectively. It could be concluded that the MQ interpolation function is an effective trend removal technique if camera interior orientation parameters are not known with the required accuracy. Test results also indicate that the MQ is superior to the polynomial interpolation functions as far as systematic trend removal in aerial triangulation is concerned.