Iranian Journal of Science and Technology Transactions of Civil Engineering
Volume:38 Issue: 1, 2014

Ant Colony Optimization (ACO) has been used as one of the popular meta-heuristic algorithms in structural optimization. In this algorithm, the selected cross sections are chosen according to a parameter called “probability ratio”. This parameter and the way to choose the cross sections from a list of cross sections, are the most important points in the optimization process. Though the Ant Colony algorithm has a special ability in achieving the optimal point, in some cases in order to avoid local optima, the utilization of special techniques is needed. In the present paper, the first aim is to use Harmony Search (HS) algorithm to increase the local search ability of the ACO. In this way a combined algorithm, denoted by HACOHS, is obtained with special abilities to achieve a global optimum. For this purpose, optimal design of skeletal structures such as trusses and steel frames is considered using the HACOHS. However, in the process of optimization by HACOHS method, several GA selections are employed at the cross section selection stage. Utilizing the Tournament (HACOHS-T), Roulette wheel (HACOHS-Ro), and Rank (HACOHS-Ra) methods it is found that the HACOHS-T is the most efficient of these algorithms for optimal design of skeletal structures.

This research examines performance of semi-active control of structures using Magneto-Rheological (MR) dampers. Mechanical specifications of this smart fluid damper change by falling into the magnetic field, so by increasing intensity of magnetic field the resulting damper power consequently increases. In this paper, two models of 9 and 20-story buildings were first selected as case studies and respective specifications of these structures (mass, stiffness and damping matrices) were calculated using valid sources as well as analysis of structures ignoring axial deformations against imposed loads. Then, sample structures were simulated in a Simulink environment. Consequently, optimum force determination processor, control system and MR damper were modeled in Simulink environment and were installed on a structural system. Finally, the obtained results from damper equipped structure were compared with non controlled structure. In semi-active control case, clipped optimal algorithm was considered as control algorithm and optimal classic linear control method was used to determine control power. Based on the obtained results, it is observed that using this control method will significantly decrease structure response, such that MR damper can be about 12% to 36% effective in reducing maximum lateral drift and up to 21% in reducing maximum acceleration. Two mechanisms are eventually offered to improve the function of dampers and their performance. The proposed mechanism is shown to be effective in reducing the capacity and number of dampers required.

Presented is a method of three-dimensional stability analysis of slopes due to earthquake forces based on the Lower-bound theorem of the limit analysis approach. The method’s aim is to determine the factor of safety of such slopes using numerical linear finite element and lower bound limit analysis to produce seismic stability charts for three dimensional (3D) homogeneous slopes. The rigorous limit analysis results in this paper together with results of other researchers were found to bracket the slope stability number and therefore can be used to benchmark for solutions from other methods. It was found that using a two dimensional 2D) analysis to analyze a 3D problem will lead to a significant difference in the factors of safety depending on the slope geometries. Numerical 3D seismic results of the proposed algorithm are presented in the form of some dimensionless graphs which can be a convenient tool to be used by practicing engineers to estimate the initial stability for excavated or man-made slopes.

This paper reports the effect of addition of quarry dust and billet scale on the properties of fly ash bricks. Bricks were made with fly ash and cement and varying percentages of quarry dust and billet scale. All the mixtures were made to be flowable in fresh state. The bricks were then tested for strength, modulus of rupture, ultrasonic pulse velocity, initial rate of suction, water absorption, and efflorescence. The strength of bricks ranged from 0.8 MPa to 18.9 MPa, modulus of rupture ranged from 0.13 MPa to 3.7 MPa, water absorption from 15 to 32 %, and initial rate of suction between 0.27 and 2.21 kg/m2.min. All the bricks were categorised as non efflorescent. It is concluded that the optimum ratio of fly ash and billet scale and quarry dust and billet scale is 1:1 to get improved strength. Furthermore, it is shown that fly ash bricks incorporating 25% of quarry dust and billet scale gives reduction in the various properties observed.

A mine ventilation system is an important component of an underground mining system. It provides a sufficient quantity of air to maintain a suitable working environment. Therefore, the mine ventilation system should be kept at a highly reliable level and also be maintained at a very reliable level during the whole service time of the coal mine. However, in reality, failures of a mine ventilation system do occasionally happen. Most of such failures can result in potential risk for the workers. For example, the insufficient quantity of fresh air to the underground mine working face may lead to the increased concentration of coal gas to the lower flammable limit. Once an ignition source exists, a gas explosion can take place. Hence, some failures become an immediate cause of a mine accident and can cause fatalities and/or property damage. By an in-depth analysis, one of the reasons contributing to the mine ventilation failure is that most systems lack enough technical considerations when they were initially designed. Underestimating the components can substantially lead to a poor quality system. In order to improve coal mine safety, in this paper, a model scientifically allocating the reliability practice is introduced into the mine ventilation systems design process. Such a model can well consider the indeterminate problems in both the decision-making process and the system itself, to achieve the optimum reliability allocation. In detail, first, based on previous research findings, the hierarchical structure of a mine ventilation system is identified by the analytic hierarchy process (AHP) method. Second, the proposed reliability allocation model using the fuzzy mathematics calculation is applied to complete and optimize the reliability allocation works. Application of this model is also demonstrated at the end of this paper.

The mechanical parameters of coarse-grained soils are often obtained via indoor or field tests. In these tests, it is necessary to reduce the particle size of the original graded soils due to the size limitation of the testing apparatus. Therefore, several scale methods (e.g., the equivalent substitute method and parallel gradation method) have been proposed to reduce the size of the original graded soils to the proper testing size. However, the mechanical parameters will be different if different scale methods are adopted, a phenomenon that has been termed the “scale effect”. In this research, a group of large-scale oedometer tests were conducted with specimens that were downsized using different scale methods. The results show that (1) when adopting the same scale methods, the compression modulus increases with the increase in the nominal maximum particle size. (2) For the same nominal maximum particle size, samples that are downsized using the equivalent substitute method have a higher compression modulus and degree of particle breakage than those adopting the parallel gradation method. (3) Then Duncan Chang EB model parameters were back calculated from oedometer tests using an immune genetic algorithm (IGA). These mechanical parameters were also used in a three-dimensional (3D) finite element method analysis of the Pankou Rock-fill Dam. The manner in which the scale method influences rock-fill dam deformation is also discussed.

Knowing flow pattern, especially stream tube dimensions at the vicinity of a lateral intake is important to study flow discharge and sediment rate entering to the intake as well as to better design a measure for controlling sediment entry into the intake. Previous studies have been focused on intake from rectangular channels. In the present study, however, different experimental tests were carried out at a 30 degree water intake installed at bank of a trapezoidal channel to measure the three components of flow velocities; these data were then applied to calibrate the numerical SSIIM2 model; by running the SSIIM2 model for different flow conditions, more data were obtained. From the analysis of both experimental and numerical data the flow patterns upstream of intake were plotted and the stream tube dimensions were obtained for all flow conditions. It was found that the dividing stream width for intake from trapezoidal canal at the bottom is less than it is for intake from rectangular canal for the same flow conditions; the width at any elevation was found to depend directly on the diversion flow ratio. Relations for predicting dividing stream width as a function of diversion flow ratio have been presented for intake from both rectangular and trapezoidal cross sections. Also, computed secondary current strength at the intake entrance, which is an effective parameter in transporting sediment to the intake, showed that it is a function of flow diversion ratio and for intake from trapezoidal channel it is less than from rectangular channel.

In this paper, the optimum inlet shape of morning-glory spillway is discussed. The effect of some parameters including maximum discharge coefficient and minimum possibility of cavitation (cavitation index) are investigated. For this purpose, using computational fluid dynamics (CFD) in the form of finite volume method, 3D Navier-Stokes equations of flow at different inlet shapes are solved. Free water surface is modeled by water-air two phase flow and equations are solved by volume of fluid (VOF) method. Flow turbulence is modeled by “K-Є model”. Based on experimental results, models are verified and discharge, velocity, pressure and cavitation index for different inlet shapes are computed and compared with each other. The morning-glory spillway inlet is modeled using different types of equations including WAGNER equation (Y=aX^3.88), CREAGER equation (Y=aX^1.87) and circular form for their funnel profile shapes. In each model changing the head (h) versus discharge (Q) diagram is drawn and results are compared.

In this research, the adverse hydraulic jump formed in a gradually expanding stilling basin of rectangular cross section is investigated both theoretically and experimentally. The experiments were conducted in a specially designed model for a wide range of bed slopes and diverging angles of the basin walls in addition to classic jump for a wide range of Froude numbers. A momentum-based theory is presented to determine the sequent depth ratio. The results show that there is good agreement between theoretical and experimental data. Comparison of important parameters of a diverging hydraulic jump on the adverse slope, such as length, sequent depth and energy loss, with those in the classic jumps indicated that any increase in the adverse bed slope and the diverging angle of basin wall would cause a reduction of the sequent depth and relative length of jump and increase in the relative energy loss in comparison to the classical hydraulic jump.

River sediment discharge estimation is a very important process for the water resource management. Sediment discharge is usually calculated either from the direct measurements of sediment concentration or sediment transport empirical equations. Due to several difficulties in applying empirical equations and direct measurements, in this study a general equation is developed to estimate the total sediment load with a good accuracy. An artificial intelligent model based on Honey Bee Mating Optimization (HBMO) is used to estimate the parameters of the proposed equation. The set of variables in the model is based on evaluating some of the existing empirical equations and also the prior researches to find the dominant parameters in the sediment transport formulas. Based on these investigations some parameters such as average flow velocity, water surface slope, average flow depth, median particle diameter, water temperature and width of the rivers are more effective and have been selected as the dominant variables in this research. With consideration of the mentioned variables, this model tries to determine the coefficients and powers of the general equation. Three data sets of different rivers have been chosen to demonstrate the model. The model has been calibrated by 75% of the data and validated by the remaining 25%. To calculate the proposed model efficiency and validity, the results have been compared with two common models. Therefore, the Sediment Rating Curve (SRC) and Non Linear Regression (NLR) models have been applied and the statistical results have been proposed to show the model efficiency.

Uranium in the environment is hazardous to human health and requires better methods for detection and remediation. Bioadsorbent coated on nanocrystalline iron oxides offers a number of advantages as sorbents for water purification and environmental remediation. In this study, first highly uniform and crystalline iron oxide nanocrystals (nMAG) were prepared using iron salts in presence of NaOH by co- precipitation process and then sugarcane bagasse coated on synthesized iron oxide nanocrystals has been used as a bioadsorbent for uranium solution with low concentration. The effect of different parameters on optimum function of this process has been analyzed. The results showed that maximum uranium absorption occurs at pH levels of about 3. Optimum amounts of biomass, uranium concentration and contact time are 0.1 gr, 50 ppm and 120 min, respectively. Thus, the uranium biosorption by magnetic biosorbent can be considered a potential technology of treatment process for uranium removal in which the adsorbents and the adsorbed pollutant can be quickly recycled by simply applying a magnet.

Adsorption of Reactive Yellow 145 (RY145) and Remazol Black RL (RBRL) onto pine needles (PN) was investigated with respect to initial dye concentrations, adsorbent dosage, and pH in a batch manner. The obtained data in the study were described according to the Langmuir and Freundlich isotherm models and the Langmuir model describes the experimental data very well with a qmax value of 13.831 and 7.225 for RBRL and RY145 respectively. As the pH decreased, adsorption density increased gradually and the highest adsorption density was obtained at pH 2 for both adsorbents (91.57 and 64.77% for RBRL and RY145 respectively). Equilibrium adsorption rates of 70.15% with RY145 and 86.72% with RBRL onto PN were observed at 90 min. In order to better model the kinetics of adsorption, first order, pseudo second order and second order models were applied. Among these models, the pseudo-second order kinetic model provided a good correlation for the adsorption of RY145 and RBRL by PN with a R2> 0.999. Results showed that pine needles have great potential to remove Reactive Yellow 145 (RY145) and Remazol Black RL from aqueous solutions.