فصلنامه مدل سازی در مهندسی
پیاپی 32 (بهار 1392)

Dynamic compaction is a useful method of soil improvement especially for Granular soils. In this method، a tamper falls from a specified height on the soil to compact it. This method is developed and applied in many countries in land reclamation projects. Several researchers have worked on simulating dynamic compaction process using numerical tools and implemented solutions for prediction of the appropriate patterns of compaction. However، less attention has been paid on prediction of useful patterns of compaction considering minimum distance limitations from adjacent structures. Indeed، in reclaimed areas like petrochemical complexes and other facilities، pipelines and other structures exist which are very sensitive to the impact energy and heavy tamping. As a result، dynamic compaction should be performed considering these limitations to avoid cracking or collapse of near field structures. The criterion for considering the minimum distance of adjacent structures is dependent to the minimum soil particle velocity. In the present research، ABAQUS 6. 10-1 software is used for modeling of dynamic compaction process (DC). Ground vibration measurements were carried out and result of field measurements and Numerical analysis are compared. The ability of isolation trenches on active isolation of the dynamic compaction process is also modelled and it has been indicated that the isolation trenches have low effects on reducing the soil particle velocity in adjacent structures at the range of considered parameters.

Post-tensioned steel connections are new type of connections in which bending moment and shear force at the end of the beam are transmitted to the column using high strength strands. In these connections، energy dissipaters are used for increasing energy dissipation and controlling plastic deformations. In the present paper، the complete numerical model of the experimentally tested connection has been created using ABAQUS software; and cyclic response of this model is compared with the experimental results. Then، simplified numerical model of the connection with the shorter time of modeling and analysis has been created. In this simplified simulation، to model strands، the beam elements are used instead of solid elements، and welding is used instead of bolts for connecting the energy dissipater angles to the beam. A good agreement between cyclic response of numerical model and experimental result was obtained. Also، the results of the full model and simplified model are very close to each other. Therefore، the use of simplified model is confidence and it needs less time for analysis. In addition، the size of software output data is much less. Because، the construction of laboratory samples needs more time and cost compared to computer simulations، therefore، the numerical models can be created simply for modeling the connections with post-tensioned and energy dissipation systems، and effects of these systems on the connection behavior can be studied.

Calculation of hydrodynamic resistance is one of the most important steps in design of vessels. Nowadays، using numerical methods and specially Computational Fluid Dynamics (CFD) for calculation of ship resistance is one of marine engineering fields. In this research، flow around the hull of a catamaran vessel is investigated numerically and resistance is calculated. Numerical modeling is done with FLUENT CFD code. This software solves governing equations by Finite Volume Method (FVM). Modeling is carried out for two ratios of separation to length of vessel (S/L) and finally numerical results are compared to experimental results from model tests. At low speeds، numerical results have a good agreement with experimental results but in higher speeds، the difference between numerical and experimental results increases about 10-20%. Also، by the increase of hull separation، the total resistance of catamaran decreases due to reduction of demi-hulls interferences.

In recent decades the use of special truss moment frames has been developed as relatively new steel frame systems in high seismic zones. These frames dissipate the seismic energy through the specific ductile parts that are located near the middle of the span of the truss beam. In this study the response modification factor of steel moment frames with specific truss beams due to the ductility and over strength was determined. The analysis was carried out using linear static analysis (pushover). In order to consider the nonlinear behavior of the material in formation of the plastic hinge، it was used the elasto-plastic behavior and it was assumed that the plastic hinge are created at the top and bottom of the column and beam. The analyses are carried out for two types of the frames، Vierendeel and across diagonals frames. These frames are evaluated for two cases، two and three spans، and also for different stories، 3 to 8-story. The results are shown that the response modification factor of the Vierendeel frame is more than the across diagonal frame’s and has a better seismic performance. The results also show that the response modification factor is dependent on the height of the structure، so that this factor is increased with increasing the height of the structure.

By applying BOR-FDTD method، fluorescence enhancement by using nano-antennas is investigated. Details of computational method are described including، updating equations، source، detector، absorbing boundary conditions. It is shown that fluorescence enhancement depends on nano-antenna features، ambient environment، the wavelength of incident light and the distance between emitter and nano-antenna. By the precise investigation of the impact of distance on the parameters effective in fluorescence enhancement (Purcell factor، antenna gain، the electric field intensity) we show that by setting the appropriate emitter distance from nano-antenna the highest enhancement can be obtained.

This paper studies an analytical method which combines the superposition technique along with the solution structure theorem such that a closed-form solution of the hyperbolic heat conduction equation can be obtained using fundamental mathematics. In this paper، Non-Fourier heat conduction in a slab that has an adiabatic left boundary and a right boundary with convection has been investigated. A complicated problem is split into multiple simpler problems which in turn can be combined to obtain a solution to the original problem. The original problem is divided into four subproblems by setting the heat generation term، the initial conditions and the boundary condition to different values in each subproblem. All solutions given in this paper can be easily proven by substituting them into the governing equation.

In this study، the extraction of Zataria multiflora Boiss essential oil with subcritical water was investigated. The most and the most important part of Z. multiflora essential oil was thymol. One two-phase mathematical model was employed for simulating of extraction yield at different operating conditions in packed bed. Three important mass transfer steps consist of diffusion of solutes through particles، convection of solutes through a layer of stagnant fluid outside particles and elution of solute by the flowing bulk of fluid were considered. The unsteady state mass balance of the solute in solid and subcritical water phases led to two partial differential equations that were solved numerically using a linear equilibrium relationship. This model consists of three parameters mass transfer coefficient، axial dispersion coefficient and effective diffusivity. The last parameter was selected to be the model tuning parameter and the others were estimated by existed experimental correlations. The effective diffusivity and mean relative error of data for flow rates 1، 2 and 4 ml/min were 5×10-12 m2/s، 0. 073، 0. 180 and 0. 294 respectively.