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Showing 8 results for Tangent
Volume 13, Issue 15 (3-2014)
Abstract
In this study a new approach for investigating the flutter speed of nonlinear aeroelastic systems is proposed. In this approach, the compatibility of nonlinear random vibration analysis based on the statistical properties of response is used and extended to the nonlinear aeroelastic systems to analyze the instability of these systems with using neither time domain analysis nor limit cycle oscillations. To this aim a 2-degree nonlinear airfoil with cubic torsional spring under quasi steady flow is considered as an aeroelastic system. At first, one random Gaussian white noise is added to the aerodynamic lift force then the statistical linearization and the random vibration analysis of the nonlinear systems are used to obtain a nonlinear map of response-variance with flow velocity as the control parameter. This nonlinear map leads to a nonlinear algebraic equation which consists of two parameters as the flow velocity and variance of the response. By solving this nonlinear equation for various flow velocities, the flutter speed is considered as the maximum of response-variance. Finally the jump phenomenon is also investigated where tangent bifurcation occurs.
Experiments on Variable-mass Threshing of Rice in the Tangential-longitudinal-flow Combine Harvester
Volume 15, Issue 7 (12-2013)
Abstract
The existing studies of threshing process of combine harvesters adopt the assumption of constant mass, which is contradictory to the phenomenon of separation of grains and short stalks in actual threshing process. Therefore, the characteristics of threshing and separation are not accurately described. Aiming at this problem, this study established the tangential-longitudinal threshing and separation test-bed with tangential-flow device, auxiliary feed beater, and longitudinal-flow device of tangential-longitudinal-flow combine harvester and conducted experiments and analysis of rice threshing with feed rates of 5, 6, and 7 kg s-1. The results showed that the changes in rates of material flow along the arc-length of concave in tangential-flow device and longitudinal-flow device were equal to the changes in rates of material density with time. In the process of variable-mass and constant-mass rice threshing, when the feeding rates were 5, 6, and 7 kg s-1 in the test-bed, the flow rates from the tangential-flow device were 4.07, 5.01, and 5.95 kg s-1, respectively. The average power consumption of the tangential-flow drum in variable mass threshing process was higher than that in the constant mass threshing process by 2.16, 2.73, and 3.09kW, respectively. The flow rate at the outlet of the longitudinal-flow device was 3.34, 4.04, and 4.72 kg s-1, respectively. The average power consumption rate of the longitudinal-flow drum in variable mass threshing process was lower than that in the constant mass threshing process by 7.32, 10.44, and 12.17kW, respectively. The results of material flow rate and power consumption would offer the basis for the design of longitudinal-tangential flow threshing and separation device.
Tina Shayan, Vahid Hakimzadeh, Mostafa Shahidi Noghabi,
Volume 16, Issue 88 (6-2019)
Volume 16, Issue 88 (6-2019)
Abstract
The ultrafiltration process as one of the membrane processes based on pressure can replace with the conventional method of liming-carbonation as a new method in sugar industry. In this research, reduction of hardness, increasing the non-sugar rejection components and improving the purity of permeate flow were modeled during the treatment of raw beet syrup with ultrafiltration by artificial neural network. The ultrafiltration process was carried out at three temperatures of 30, 40 and 50 ° C, three pressures in the membrane 1, 2 and 3 times in eight intervals of equal time of 1 to 60 minutes. The best model for reduction of hardness was obtained with a hidden layer, the number of 13 neurons, the tangent transfer function, the momentum learning law, and the percentage of data 40, 35, and 25 for training, evaluation, and test, respectively. The variation of non-sugar rejection compounds with a hidden layer, 15 neurons, tangent transfer function, Levenberg learning law, and assigning 50, 5 and 45 percent of the data to training, evaluating and testing with the least error and the highest correlation coefficient during modeling. Improvement of the purity of permeate flow during ultrafiltration with a hidden layer, 18 neurons, sigmoid transfer function, Levenberg learning law and data percentages 60, 15 and 25 for training, evaluation, and testing created the best network. Also, the highest correlation coefficient between laboratory data and predicted values with the model was obtained for hardness variation, non-sugar rejection compounds and purity, 0.892, 0.985 and 0.985 respectively.
Volume 17, Issue 10 (1-2018)
Abstract
In this research, a general mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials. Various experimental tests show that cracks always propagate in an isotropic medium and along fiber direction in orthotropic materials. With a novel material model titled an Equivalent Reinforced Isotropic Model (ERIM), fracture criterion can be extended for investigation of fracture in orthotropic materials. This inspires that fracture in orthotropic materials follows the fracture mechanism in isotropic materials. This new criterion is developed based on extension of MTS which is widely used for isotropic materials. Also in this research the effects of T-stress in fracture of some specimens has been studied. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that non-singular T-stress term has a significant impact on orthotropic material failure, especially when the second mode is dominant mode. It is shown that unlike isotropic materials, fracture toughness of orthotic materials in mode I (K_IC) cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode I (├ K_IC ┤|ortho) is defined. Considering ease of access, wood is used as experimental specimen for the purpose of comparing the results.
Volume 21, Issue 2 (1-2021)
Abstract
Composites that withstand high temperatures are one of the parameters that always is the focus of attention. Especially when this type of material in sensitive parts flying craft is used. Generally, sensitive parts of flying craft should be also, radar transparency, have good mechanical strength at high temperatures. PTFE matrix composite is one of the options suitable for this purpose. PTFE is one of the polymers that have high heat resistance and low dielectric constant. This article processing preparation of glass fiber reinforced PTFE polymer matrix composites with conventional sintering methods. Then composite sheets made from E-glass woven fabric with PTFE have been produced with conventional sintering methods. To achieve optimal sintering processing of PTFE matrix composite, various cycles of time and temperature were selected and the optimal sintering cycle for such composite materials is obtained by the design of the experimental method. Then the mechanical properties of composites with different sintering processes were measured. To determine the mechanical properties, a tensile test was performed, and to determine the electrical and electromagnetic properties, a dielectric constant test in X-band was performed. The loss tangent, as well as composite products obtained. The maximum tensile strength and tensile modulus were achieved in this research respectively equal to 130 Mpa and 3.65 GPa. Constant dielectric and Loss tangent of the samples produced in the x-band are 2.37 and 0.096, respectively. Finally, to validate results in this research, the results of the performed tests were compared with the results of other references in this context.
Fakhreddin Salehi, Moein Inanloodoghouz,
Volume 21, Issue 146 (3-2024)
Volume 21, Issue 146 (3-2024)
Abstract
The use of ultrasonic waves to change the structure of the gums leads to the modification and improvement of their functional characteristics and rheological properties. In this research, the effects of ultrasonic intensity and treatment time on apparent viscosity, consistency coefficient, and flow behavior index of different concentrations of xanthan gum were investigated and modeled. Genetic algorithm-artificial neural network method with three inputs (ultrasonic power, treatment time and gum concentration) and three outputs (viscosity, consistency coefficient, and flow behavior index) was used to model the process. The apparent viscosities of the xanthan gum control sample (untreated) at concentrations of 0.1, 0.15, and 0.2% were 21.0, 39.9, and 66.5 mPa.s, respectively. The results of this research showed that gum viscosity decreased with increasing intensity and duration of ultrasound application. Ultrasonic treatment for 20 min significantly reduced the apparent viscosity of xanthan gum from 39.9 to 23.2 mPa.s (p< 0.05). The genetic algorithm-artificial neural network modeling results showed that the network with 3-5-3 structure in a hidden layer and using the hyperbolic tangent activation function can predict the rheological parameters of xanthan gum with high correlation coefficient and low error value. Values of mean squared error (MSE), normalized mean squared error (NMSE), mean absolute error (MAE), and correlation coefficient (r) to predict the apparent viscosity of xanthan gum were 73.17, 0.20, 6.48, and 0.90, respectively. Based on the results of the sensitivity analysis test, ultrasonic treatment intensity was the most effective factor in changing the apparent viscosity, consistency coefficient, and flow behavior index of xanthan gum.
Volume 23, Issue 3 (8-2023)
Abstract
Regarding the dependence of ductility response in structural components on their ability to keep stability after yielding of the material, in this paper, the influence of change in tangential modulus of work-hardening part of stress-strain response, was observed on the load carrying capacity and plastic buckling response of stainless-steel tubular columns. To keep cost-effectivity in the research, the objective of the study was followed by FE modeling, which was verified by simulation of plastic buckling in an experimental specimen with D/t=60, made of duplex stainless-steel. For all components of the models, S4R elements were used and both material and geometrical nonlinearity were included in the models. To conduct deformation of the columns according to the experimental observations, an initial imperfection equal to t/100 to combination of first three mode shapes of the columns was imported. The material stress-strain response after yield point was determined for the model by a multilinear curve according to the tensile stress-strain curve, obtained experimentally. The main parameters for comparison of the FE model and experimental observation were force-displacement curves. The FE study was extended by modeling of stainless-steel columns with various D/t ratios in range of D/t=30-120. Two main parameters comprised of energy absorption capacity and deformation of the column related to yield of the section and collapse threshold (e/g) were compared to the columns with various D/t ratios.
According to force-deformation curves, by decrease of D/t ratio, the energy absorption capacity increased considerably for the columns, for example the energy absorption capacity and e/g ratio increased by 12% and 12%, respectively for comparison of the columns with D/t=60 and D/t=30, however, e/g ratio for the columns of D/t=120 and 100 were less than two, categorized as a force-controlled column. Two models with D/t=30, 60 were selected to follow the objective of the study. The work-hardening response of the material was approximated by two linear segments, the first by a tangential modulus equal to E=7.9 GPa and the second was by the tangential modulus equal to E=2.4 GPa. The influence of change in tangential modulus through a range between 0-200% was observed on the structural parameters related to ductility, comprised of energy absorption capacity up to collapse threshold and deformation of column at the collapse threshold. The results showed different reaction of the columns with different D/t ratios, increase of tangential modulus at the first work-hardening part was more significant than increase of the influence by the later part of the work-hardening response for the column of D/t=60, however an inverse effect was observed for the column of D/t=30, i.e. the influence of tangential modulus at the later part was more significant for this column. By doubling the tangential modulus of earlier part of the work-hardening response, the energy absorption capacity and e/g ratio for the column of D/t=60 increased by 26% and 46%, respectively. By doubling the tangential modulus of later part of work-hardening response, the energy absorption capacity and e/g ratio for the column of D/t=30 increased by 111% and 71%, respectively. The results showed significant parts of work-hardening response of duplex stainless-steel, to be exploited for development of ductility in the tubular columns.
Volume 23, Issue 6 (11-2023)
Abstract
Vortex drops are compact hydraulic structures used in surface water and sewer collection systems to convey runoff from higher to lower elevations by creating a rotational flow inside vertical shafts. These structures are composed of three main parts: the intake, drop shaft, and dissipation chamber. Tangential intake is a steep tapering channel that generally has a junction with a rectangular approach channel with the horizontal bottom at the beginning and a narrow slot at the connection with the drop shaft. Many factors need to consider in the design of vortex drop shafts with proper hydraulic performance. The review of previous studies and the guideline designs for this structure indicates that most design relations were obtained either based on simplified assumptions or by conducting limited tests on laboratory scale models, which can cause desirable operation in practice. These conditions have forced engineers to set up laboratory models or numerical simulations of the initial design to evaluate the proper performance of the structure in big projects. With this introduction, one of the problems in the surface water collection network of Tehran is conveying high volumes of runoff from the surface of streets at the highway intersections to a lower level in the underground tunnels or pipes. Therefore the authorities pay more attention to necessary considerations in the design and use of these types of structures for the safe transfer of runoff downstream. In this paper, using numerical modeling, the hydrodynamics of flow in a real vortex drop shaft with tangential intake has been studied. In the design stage, a vortex drop structure in Tehran's urban drainage has been selected and evaluated by the Flow-3D numerical model. Based on the latest available design methods, Several tangential intakes with different geometry were assessed separately. Finally, the performance of the final drop shaft was simulated and analyzed using the numerical model. The final design simulation results showed that the flow in the tangential intake would enter the vertical shaft without forming a hydraulic jump. The flow in the vertical shaft is spirally attached to the wall with a central air core. A key design parameter is the ratio of the air core area to the drop shaft cross-sectional area that was greater than 0.49. The efficiency of energy losses at the tangential intake is about (9-15%), in the vertical shaft is about (23-40%), and in the energy dissipating chamber is (70-71%) depending on the flow rate. The energy loss efficiency in the whole structure was about (80-84%). The depth size needed to create a water cushion in the energy dissipation chamber was considered for three depths of 0.4D, 0.5D, and 0.6D. After numerical modeling, the appropriate depth for the water cushion was determined to be 0.6D. The results of the simulations indicated that the use of existing design methods only sometimes leads to optimal hydraulic performance in the structure. Therefore, reviewing the existing design methods, simulating the flow in the designed drop shaft, or setting up a laboratory model before finalizing the design is necessary.
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