simulation

Accurate simulation of geometrical properties of fractures is an important goal in rock engineering. One of the most capable methods for simulating the random nature of geometrical properties of fractures is Discrete Fracture Network (DFN) random modelling, which presents the heterogeneous nature of fractured rock mass with statistically defined geometrical properties. Up to now, all properties of fractures such as location, shape, orientation, size (persistence), spacing, and opening of joints have been simulated and applied in 3D DFN modelling. In this research, a statistical solution based on Kernel’s non-parametric distribution is used for simulating roughness. Through this method, even those geometric properties of fractures which do not have their own specific distribution functions can be simulated. After simulating the roughness value, the roughness geometry should also be simulated in a way that evokes the roughness value. Therefore, in order to simulate the surface of fractures in this research, the DRS method is applied in 2D and then, developed into 3D. At the end, simulation of discontinuity’s roughness is added as a separate package to DFN-FRAC3D computer program. DFN-FRAC3D computer program, as one of the most capable tools in this field, is able to develop a 3D fracture network block model by using the surveyed data and then simulating geometrical properties of the fracture; thus, by applying the results of this research in this compute software, all geometrical properties of fractures can be simulated. Finally, in order to explain the results of this research, outcomes of DFN-FRAC3D computer program for both with and without applying the roughness property on DFN are compared.

Green's empirical function method has been used to simulate the strong motion of the Damavand earthquake. One of the conventional methods of simulation to produce strong ground motion is the use of aftershocks and foreshocks of large earthquakes using the empirical Green's function method; As a result, the ground motion simulation algorithm based on Green's empirical function, presented by Hutchings and Wu (1990), has been used to simulate the Damavand earthquake waveform.On 02/18/2019, an earthquake with a magnitude of 5 occurred in Damavand, located in Tehran province. In this study, with the aim of estimating the parameters of the source and the mode of fracture in this earthquake, the empirical Green's function method has been used to simulate the powerful movement of the earth. To simulate the main earthquake, a foreshock with a magnitude of 2.9 near the center of the main earthquake, as well as aftershocks with a magnitude of 3.9 and 4.1 recorded at the Masha and Rodhen accelerometer stations, have been considered as experimental Green's function. The length and width of the fracture in this earthquake are 2 and 3 km, respectively, in the direction of extension and slope. Calculations show that the direction, slope and tilt of the fault that caused the earthquake were 196, 76 and 156.5 degrees, respectively. The focal mechanism of this earthquake is of reverse type with strike-slip component, which is consistent with the mechanism of earthquakes in this area.

Load movement in tumbling mills involving spherical particles has been extensively studied with the discrete element method (DEM) in the past. This assumption is legitimized by the added complexity of non-spherical shape representation, contact detection and computational cost. Simulation of particles with realistic shape helps to capture the essential aspects of mechanical behavior of the particulate material. In this research, an in-house developed DEM software called KMPCDEM© was used to simulate the charge movement with spherical and non-spherical particles. At the first to calibrate the model parameters, a model tumbling mill (100 cm diameter and 10.8 cm length) with one transparent end was used. The tests were performed with steel balls and wood cubes. After calibration, a number of mill simulations were performed with the different shape of particles (spherical, cubical, and tetrahedron) to study the effect of particle shape. Comparison of the simulation and experimental results showed that the difference between the measured and predicted impact toe, shoulder angle and bulk toe angles were within 3˚-5˚ of the measured values in the model mill. The amount of in-flight of charge when using spherical and non-spherical particles was significantly different (17%). The marked difference was attributed to higher interlocking of non-spherical particles in comparison to spherical balls. The results showed that the elongation of charge was increased (5o) by considering the non-spherical shape of particles. The simulation computation time increased by 35 times when the shape of particles changed from spherical to cubical.

The cleaner circuit at Miduk copper concentrator consists of 3 parallel flotation columns (4m in diameter and 12m in height). The cleaner concentrate is re-cleaned by 3 parallel flotation columns (3.2m in diameter and 12m in height), when the desired concentrate grade is not reached by the cleaner columns alone. This research work deals with simulation of the cleaner column flotation circuit at Miduk copper concentrator using USIM PAC simulator with the aim of improving the process metallurgical performance. For that purpose, the parameters of the models including flotation rate constants (kf, ks), residence time distribution (RTD), gas hold-up in collection zone (εg), mean bubble size (db), collection (Rc) and froth (Rf) zone recoveries along with some operating and geometrical variables were determined. The flotation rate constants were calculated by fitting the experimental data to the fast and slow floating components model. The residence time distribution of the flotation columns was measured by the tracer injection technique (using saturated NaCl solution as tracer). The gas hold-up and mean bubble size in the collection zone of the cleaner columns were estimated from the pressure difference and the drift flux techniques, respectively. The froth recovery was quantified by measuring the concentrate mass flow rate at different froth depths and extrapolation to the zero froth depth. The cleaner circuit was sampled five times, of which three times were used for calibration and two times for validation of the models. The mass flow rate, copper content and size distribution of the cleaner columns concentrate and tailings were accurately predicted using the simulation models. Increasing the number of operating cleaner columns improved the copper recovery (from 45.67% to 54.64%) at the expense of a reduction in the final concentrate (from 26.17% to 24.22%). The number of recleaner stages in all cases improved the the final concentrate (from 26.17% to 36.99% in the circuit with 2 cleaners and from 24.22% to 36.13% in the circuit with 3 cleaners). Increasing the feed slurry solids concentration reduced the size-by-size fractional copper recovery of the cleaner columns. Increasing the feed slurry solids concentration reduced the cleaner columns copper recovery in all size fractions. The best configuration of the cleaner and recleaner flotation columns was proposed.

Hydrocyclones are the most efficient used classifiers in the grinding circuits. Hydrocyclones are normally modeled and simulated using empirical models. These models can only be used within the range of the experimental data from which the model parameters have been derived. Computational fluid dynamics (CFD) is a powerful tool in simulating fluid flow in hydrocyclones. This research work deals with 3D simulation and modeling of fluid flow in a single phase hydrocyclone using CFD. The main simulation steps include preparing the geometry, meshing it, defining the properties of the materials involved, and setting the boundary layer and conditions. The experimenal data measured in a laboratory hydrocyclone were used for validation of the model. The simulation results indicated that the tangential velocity increased traversing towards the core, before decreasing at the interface with the air core. The liquid axial velocity inside the hydrocyclone varied from -1.59 m/s to 6.52 m/s. The axial velocity is a result of two swirling flows, the inner upward flowing inside the air core and the outer downward flowing near the cyclone wall. The liquid axial velocity inside the hydrocyclone varied from -5.58 m/s to 5.46 m/s. The LES model showed the least error on predicting the velocity profiles, the air core dimensions (7.8%), the pressure drop (7.52%) and the mass split ratio to overflow (0.18%). The effect of various geometric (spigot diameter, vortex diameter and cone angle) and process (feed flow rate) parameters on tangential velocity of the fluid was investigated.

Summary:

One of the important geometric features of rock mass discontinuities is its surface roughness. The discontinuity level has different heights that differentiate each level from the other. In practice, it is not possible to assign a roughness value to each of these levels, so to levels that are similar in height; The same amount of roughness is assigned. In analyzing the problems of stone mechanics related to coercion, it is necessary to choose one of the many levels of discontinuities that have the same amount of roughness. Discontinuity Roughness Simulation (DRS) is a random selection of different levels of surface roughness for a certain amount of surface roughness. In this method, the level of discontinuity is simplified by connecting several pieces together; So that each piece has an unevenness. By simplifying and using different layouts of components that make up the discontinuity surface, the DRS method can produce different levels, the JRC value of which is almost the same.

Several methods have been proposed to measure the roughness feature of rock mass, all of them work based on the elevation of its fracture's measurement. Precise measurements and illustration of roughness values were the subjects of the previous studies.

Methodology and Approaches:

Barton's field method and determination of the maximum distance, a, between fracture and the field survey profile, L, is the foundation of the proposed method here. So fracture's length would be divided into n pieces in which its length is less than L and there exist an asperity with the height of a. By considering a number between 0 and an as the flange's height and a random number in the [0,l] interval as the distance between two adjacent flanges, locus of the fracture's flange points would be determined. The locus of the fracture's atrio points would be determined by measuring the distance between two adjacent flange and atrio points of a fracture which is a number between 0 and two adjacent flanges.

In order to validate and ensure the accuracy of the results obtained from the application of the DRS method, the validity, and reliability of the method have been checked for all possible JRCs. The results of the validity test for different JRCs indicated that the value of the mean percentage of absolute error (MAPE) for different parts of a simulated fracture is always less than 10 percent and this means that if a fracture needs to be simulated using the DRS method in order to produce a roughness value of JRC = 10, the JRC value for all parts of the simulated fractures would a number be between 9 and 11. The reliability of the DRS method for different JRCs has also been investigated. Outcomes showed that the value of MAPE in 100 of repetition of DRS method implementation for a part of the simulated fracture that is randomly determined is less than 6 percent, which is an acceptable value and a confirmation of the accuracy of the DRS method to simulate and produce fracture’s roughness.

With the increase in complexity of mineral deposits, understanding the grade variability is of high significance in getting enough information about the deposit, preventing financial losses and identifying optimized plans during and after exploitation. Likewise, mineralogical variability, grade, alteration, … can highly effect metal recovery. Modeling these parameters is seriously substantial in order to have an optimized exploitation of the mine and to minimize the risks and costs. This study used the dataset of 91 drill holes from Sari Gunay epithermal gold deposit located in north-west of Iran to model gold grade and the recovery resulted from leaching tests. Initially, the oxide and sulphide zones were distinguished using Indicator Kriging and Simulation. Then the gold grade and recovery in each zone were modeled with the application of sequential Gaussian simulation and the developed block model. The grade-recovery curve was then drawn to estimate the total tonnage amount of the deposit which was related to the sulphide zone in more than 70%. Then with the help of recovery simulation data, the grade×recovery was considered a preferable parameter in depicting the curve and estimating the reserve.

In recent years, the use of micro X-Ray images with very high resolution (as low as 100 nm) in different scientific fields has led to the development of modern methods for performing various calculations and measurements. The use of these images has become quite popular among petroleum engineers. This is because the reservoir rock-related properties like petrophysical properties and the properties that are simultaneously related to reservoir rock and fluid such as drainage and imbibition phenomena can be estimated using micro X-Ray images. To estimate these properties, some geometrical properties of grainsof two different cores are calculated and compared to each other through micro X-Ray images and somesoftware. Then, with the help of the micro X-Ray images, the necessary information for simulation of thepore network of the rock is gathered. Afterward, with the use of this information and some other software, the pore network of each of these rocks is simulated and consequently, the porosity and permeability of each of these rocks are estimated. In the simulation process, some assumptions are made to prevent the complexity of the calculations. These assumptions result in a deviation of the calculated values from real (laboratory) values. Therefore, using the calculated geometrical values obtained in the first step, a relationship is achieved by which the calculated values of the simulation are brought closer to those of the laboratory. In this research, based on the aforementioned steps and by using the sphericity, convexity, and aspect ratio of grains obtained from 2D images, a correlation is developed. Ultimately, the estimated rock properties procured by simulation are related to measured laboratory data through this correlation.

The effect of shell liners on mill performance has been the subject of various studies, but little known about the effect of dry SAG mills end liners on throughput and grinding efficiency. In particular, in the case of dry Aerofall mill types where it has been claimed that the end liners play a key role in the crushing and grinding actions. This paper experimentally characterizes the role of end liners in dry SAG mills with the objective of obtaining a thorough understanding of the effects of end liners design on the load trajectory and SAG mill performance. It was thought the characterization study will lead to design new end liners which eliminate or reduce the shortcomings of the current liners and improve the comminution efficiency mainly by prolonging liner life. The test works conducted in a scale down mill with a diameter of 1m indicated that conventionally used "deflector" type liners did not provide efficient environment for grinding. Direct observations obtained from the model mill during tests by various visualization techniques, along with simulations using the KMPCDEM software were the main sources of understanding flow behavior of charge inside the mill. In this research, to improve the grinding efficiency, a new design using low profile end liners incorporating radial ribs of proper height was investigated. The special design of model mill made it possible to increase the radial ribs height in steps of 6mm up to 18.5mm. The transparent end of the mill enabled accurate trajectory determination by image analysis. The results indicated that the new lower height profile deflectors and 15.5mm-height (14.5cm in industrial scale) radial ribs improved the mill performance while avoiding excessive pressure drop across the mill and wear on the liner. The image analysis showed that the use of new liners increased the distribution of coarse particles across the mill cross section from 28% to 35%. A new liner design was proposed by decreasing the number of liners in each slice from 5 to 4 pieces. The thickness of the inner head liners reduced from 45cm to 30cm and the outer deflector liners replaced by14.5 cm radial ribs. The distance between the feed and discharge liners increased from the original 115cm to 176cm which increased the effective length of the mill by 53%. The new design reduced the weight and volume of end liners by 9% and 23%, respectively. On account of installation of the new liners in Aerofall SAG mills the throughput increased from 441 to 465 t/h, the product size decreased from 519 to 480 μm and the amount of recycled material from the SAG mill product decreased from 10 to 6%. The most significant improvement was observed in the liner life; an increase of 50 to 200 % in liner life depending on the location of end liners was achieved. The relining time also reduced by 37.5% with the new liners.

The main production operations in most mines are drilling, blasting, loading, and hauling. Therefore, the optimization of each part causes an increase in profits and a decrease in mining costs. About 50 to 60 percent of mining costs are related to machinery, and the major share of them belong to loading and hauling machine. So, the correct utilization of the haulage fleet is very important step to increase productivity and to reduce production costs of the systems. In this study, by using simulation method and utilization of Arena software, the operation of the current production system of Abadeh Fireclay mine have been studied. Results showed that the productivity of loading machines in mine is low and due to the shortage of trucks the unit production costs of haulage system be increased.  By using the high-capacity machines in mining operations, mine production will be increased and also production costs will be reduced significantly. Moreover, when flexible dispatching approach is used with proportionate loading and hauling machines, production will incr ease by 4 to 8 percent with a given number of trucks and also production costs will decrease by 5 to 7 percent.

When comminution precedes mineral beneficiation processes, the liberation spectrum of the particles in a comminution process is of great importance. The calculation of the liberation spectrum in a continuous closed milling circuit is a vastly more difficult task. Here, a method has been incorporated into the CMCS simulation software to calculate the product size distribution and liberation spectrum in ball mills. The model requires a minimum amount of experimental data and is capable of calculating the detailed liberation spectrum. While, other existing methods account only for the completely liberated particles and a broad group of unliberated particles are not represented. An easy-to-use ball mill simulation environment has been developed and the results are compared with measured grinding data and previously existing simulators, particularly MODSIM, demonstrating firmly tested performance both in terms of accuracy and precision of obtained results.

The variation of feed characteristics of the Choghart Iron Processing Plant has resulted in the reduction of AG mill efficiency. In this research, the possibility of converting the Choghart AG mill to SAG mill to stabilize the mill power draw and improve the grinding process was investigated. The JKSimMet software was used to simulate the circuit and predict the effect of charging steel balls to the AG mill. The results of grinding tests on the ore samples were used to simulate the circuit. The product size distribution predicted by the software was very close to the actual product size of the AG mill. The simulation of the circuit, using different tonnage of 100 mm steel balls showed that the mill throughput could increase by around 6 percent with a slight increase in the mill product size. The actual results of adding the steel ball to the plant were in agreement with the simulation results. Summary: simulation of Choghart AG mill circuit was performed and the effect of charging steel ball on the mill performance was evaluated. The possibility of grinding the Choghart oxidized and high ratio ore in this circuit, at a reasonable throughput, was investigated. Based on the simulation results a plant-scale experiment on a batch of oxidized ore was also performed. It was shown that charging 100 mm steel balls, at around 5% volume of the AG mill, facilitated the grinding of oxidized ore. The throughput of Choghart AG mill circuit was lower than the expected level for grinding the oxidized (or high Fe/FeO ratio) ores. Converting the AG mill to SAG mill to increase the grinding of this type of ore was an option which was investigated. The circuit was simulated by JKSimMet software and then adding of steel ball to the system was evaluated. The results were validated using the plant-scale studies. Methodology and Approaches: Sampled from the feed and product streams were collected, the relevant grinding tests were conducted and the selection and breakage functions of the ore were determined. The ore breakage test results and the specification of the feed material and AG mill and vibrating screen were used as input data to the JKSimMet software. Then charging different tonnage of the steel balls to the AG mill was evaluated. Plant-scale experiments were also conducted. Results and Conclusions: Based on the impact and abrasion tests of the feed samples this ore was considered as a medium hard type ore. The simulation result for the mill product size distribution was very close to the actual data of the plant. Therefore this software could be used to predict other changes in the circuit. The simulation results showed that by adding 5 and 10 percent (volume) of 100 mm steel balls to the Choghart AG mill its throughput could be increased by around 3 and 7 percent, respectively. The plant scale experiments with the same type of steel ball were in agreement with the simulation results. As it was expected the mill product size slightly increased.

Summary Geometry of joints or joint shapes is one of the geological characteristics, which is important for determining the strength and stability of rock mass. Here joint shapes mean the geometric forms of joints when looking from the direction normal to the joint planes. There is not enough literature and references about the shape of the joints. Some of them consider approximately the joint shapes as square, rectangular, circular or even elliptical forms. We usually observe the traces of joints as segments in rock outcrops but it is difficult to see their shapes in the outcrops of underground openings. In this research the parallel joints which form a joint set, are created by the statistical simulation for different joint shapes. Then by comparing the simulated joint distribution with the real joint set distribution from outcrop measurements, it is possible to predict the shape of joints in rock masses. The simulation results showed that the joint set distributions will not follow the classic statistical distributions such as logarithmic, power, exponential or Poisson. They are complex in nature and have a skewness to the left.
Introduction One of the important parameters of discontinuities in rock mass is the shape and geometry of joints. The effects of joint shape and its geometry in rock mass resistance properties are defined by many rock mechanics and engineering geologist specialists. They assumed the shape of joints as square, rectangle, circular and elliptical features.
Methodology and Approaches For determination the shape of joints in rock masses in this research the statistical engineering is applied. The joints and discontinuities are considered two-dimensional planes. Then by intersection of a random plane normal to the joint set planes the simulation of joints in outcrop were obtained. At the end by the distribution of the joints obtained from the simulation, one can determine the shape of the joints.
Results and Conclusions The results showed that the joints with circular, uniform shapes and with the relative movements have the exponential distribution of trace length. But for nonuniform cases the distribution approaches the normal distribution. A uniform distribution was observed for the square or the diamond shape of the joints.

It is well documented that in gas treatment units in addition to H2S absorption, a large percentage of CO2 is absorbed to solvent. CO2 absorption in gas treatment units causes loss of energy and a reduction in the capacity of sulfur recycling unit. According to the fact that higher amont of CO2 exists in Sarakhs gas region and also that loss of chemical solvent (Amine) is higher in a unit with higher CO2 content, this research deals with CO2 absorption performance with physical and chemical solvent mixture ,Sulfinol-M. The results indicates an overall flow rate reduction of MDEA solvent from 400-480 m3/hr for 40-50 %wt MDEA to 315-420 m3/hr with the relative compound of H2O 20-40 %wt, Sulfolane 40-50 %wt , MDEA 20-40 %Wt for Sulfinol-M solvent mixture. Also Co2 absorption by this solvent will be 0,001555 moles less than MDEA solvent. Therefore with relative change in water level, Sulfolane and MDEA we can control and optimize the regenerative energy required to achieve required market characteristic, investment cost, the increase of Sulfur recovery unit capacity and the decrease of solvent flow equipment.