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- 저자 : Aboutalebi (검색결과 9 건)
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Aboutalebi Payam,M’zoughi Fares,Garrido Izaskun,Garrido Aitor J 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.1
The inherent oscillating dynamics of floating offshore wind turbines (FOWTs) might result in undesirable oscillatory behavior in both the system states and the generated power outputs, leading to unwanted effects on critical, extreme, and fatigue loads, and finally to a premature failure of the facility. Therefore, this kind of system should be capable of lessening such undesired effects. In this article, four oscillating water columns (OWC) have been installed within a FOWT barge-type platform. A novel switching control technique has been developed in order to reduce oscillations of the system created by both wind and wave, as well as the fluctuations in the generated power, by adequately regulating the airflow control valves. While the impact of the coupled wind-wave loads has been considered, a set of representative case studies have been taken into account for a range of regular waves and wind speeds. The study relies on the use of response amplitude operators (RAO) that have been pre-processed and evaluated in order to apply the switching control technique. In this sense, the starting time of the switching for below-rated, rated, and above-rated wind speeds have been calculated using the platform’s corresponding pitch RAO. Additionally, the blades’ pitch and generator torque have also been regulated by means of a constant torque variable speed controller to capture maximum energy for below-rated wind speed conditions and to match the rated generator power for rated and above-rated wind speed conditions, respectively. In order to peruse the feasibility and performance of the proposed strategy, a comparison has been carried out between the uncontrolled traditional barge-type platform and the controlled OWCs-based barge FOWT. The results demonstrate that the proposed control approach can effectively and successfully decrease both the oscillations in the system’s modes and the fluctuations in the generated power.
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Assessment of Various Ductile Damage Criteria in Numerical Simulations of Machining Processes
Mojtaba Hejazi,Farhad Haji Aboutalebi 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.25 No.1
In the machining processes, chip removal can be performed by the applied forces. Therefore, predicting the required forces and energy is an essential challenge to reach the efficient processes. In this research, employing various ductile damage models of the continuum damage mechanics (CDM), a few machining processes such as 3D plane machining, 3D drilling, and turning are numerically simulated. Using the numerical simulations of finite element method (FEM), variations of the applied forces on the workpiece and the maximum force as well as the mechanism of chip formation during the machining processes are estimated. Besides, to assess the ductile damage models, the numerical simulation results are compared with the experimental results. The comparison reveals that the Ayada, Ayada negative, and Johnson–Cook damage criteria can accurately predict the required forces and respectively are the reliable models for numerical simulations of chip removal in the machining processes.
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N. Nayebpashaee,S. H. Seyedein,M. R. Aboutalebi,H. Sarpoolaky,M. M. Hadavi 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.8
Thermal barrier coating using turbine industries, application of pre- process simulation and on-line subsequent control basedon physical knowledge are greatly advantageous in order to develop the material performance despite of the time and costefficiency. Fuzzy linguistic- based model is one of the most accepted and promising approaches that is currently used in thecontrol systems of various engineering fields and applications. As for need of industrial units, physical simulation strategiesare too compound for industrial use and less efficient than soft computational techniques. A combination of fuzzy linguisticbasedmodel and finite element method (FEM) has therefore been developed in the terminology of a combined or “hybridmodel” in this study. The hybrid model was applied to predict residual stress during thermomechanical process in functionallygraded thermal barrier coating (FG-TBC). Results show that, interface shape amplitude and ceramic constituent in compositelayer have significant effect in distribution of residual stress in interface regions and can be considered as potent zones for bothvertical and horizontal cracks. In addition, this study shows excellent potential of such finite element-artificial intelligencehybrid approach for analysis of high temperature imposing of these protective coatings.
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Arman Ahmadi‑Binahri,Mandana Adeli,M. Reza Aboutalebi,Sergey Krasikov 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.6
In this study, the application of thermite reactions in Nb2O5–Al system in the fabrication of novel NbAl3/Al2O3 compositeswas investigated. Combining the thermite reactions with self-propagating high-temperature synthesis (SHS) techniquein compressed powder mixtures of Nb2O5+ Al resulted in layer-by-layer progress of the exothermic reaction, controlledformation of the desired products and their coexistence in each reacted layer. Characterization of the products using X-raydiffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) techniques showedthat all samples were composed of a metallic matrix including NbAl3as the main compound, along with Al2O3as ceramicreinforcing phase. Differential thermal analysis (DTA) analysis was used to study the mechanism of reaction using bothstoichiometric and over-stoichiometric amounts of aluminum. The effect of such parameters as stoichiometry and greendensity of the samples on the combustion temperature, formed phases, microstructure, and hardness of the obtained compositeswas investigated using samples with stoichiometric as well 20 wt% and 40 wt% excess aluminum, and samples withgreen densities of 75%, 85%, and 95% of theoretical maximum density (TMD). The presence of excess aluminum resultedin prolonged reaction times, lower combustion temperatures, and lower mean values of hardness. While the variations ingreen density had no remarkable effect on the microstructural features of products within the density range under study, themost intensive reactions, highest combustion temperature, and highest mean value of hardness were encountered in sampleswith green density of 85%TMD.
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Mohsen Rezaei,Mehrdad Poursina,Shahram Hadian Jazi,Farhad Haji Aboutalebi 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.8
Time-dependent mesh stiffness is a most important reason of vibration and dynamic excitation in gear sets. In this research, analytical formulas of the helical gear set and the planetary gear system are combined to calculate the time-dependent mesh stiffness of the helical planetary gear system. For this purpose, at the first step, the analytical equations are derived for the spur gear pair. Then by dividing a helical tooth into the several independent thin spur tooth slices, the helical gear pair mesh stiffness is extracted. Finally, these equations are extended to the helical planetary gear system. The suggested analytical results and those which obtained by the finite element method (FEM) are compared and are in good agreement when the helix angle is less than 15 degrees. Also, the helical planetary gear system mesh stiffness in different cases such as fixed carrier, fixed sun gear and fixed ring gears is calculated. These results show that the value of mesh frequency ratio in each case scales the mesh stiffness shapes in the rotation angle direction. In other words, mesh frequency ratio parameter determines the number of meshing period in each rotation of planets.
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Majid Emadi,Hamid Beheshti,Mohammad Heidari-Rarani,Farhad Haji Aboutalebi 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5
Thin-walled aluminum tubes have been widely used in engineering structures, aerospace and transportation industries due to their excellent properties. In this paper, the effect of tempering and annealing on the crushing behavior of aluminum alloy tubes, in brittle or ductile manner, under quasi-static compression were investigated. The chemical composition, the Brinell hardness number and the tensile stress-strain curves of various types of Al alloys, i.e., Al 2024, Al 7075 and Al 6061 were obtained in both tempered and annealed state. Then, the axial compression tests were performed on the tubes by a universal testing machine at a controlled displacement rate of 5 mm/min. The crushing mode, load-displacement curve, and crashworthiness characteristics were achieved to obtain specifications of mentioned aluminum tubes. Annealing process, apart from changing the deformation mode and material strength, has often reduced energy absorption in the ductile alloy, Al 6061, and increased in brittle alloys, Al 2024-T3, T4 and Al 7075-T651. This process could also be used as a triggering mechanism to decrease the initial peak force. These experimental results give useful information regarding the material behavior of aluminum alloys to be utilized in the design process of crashworthy components.
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Multi crack detection in helical gear teeth using transmission error ratio
Mohsen Rezaei,Mehrdad Poursina,Shahram Hadian Jazi,Farhad Haji Aboutalebi 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.3
Gear systems are used to transmit power in the industry when accuracy and synchrony are needed and helical gear systems are used in more accurate and high-speed industries. It is important to ensure that these systems work faultlessly, therefore the detection of the crack location and situation is very efficient in the gear systems. In this research, a new approach is proposed to detect the multi crack location and length in the helical gear teeth. To this end, after giving an explanation of helical gear mesh stiffness and demonstrating the helical gear pair dynamic modeling, the transmission error ratio method is used to detect the cracks locations and lengths. Then, according to solved examples, when the cracks locations are far enough that their effects on the transmission error are completely separated, the cracked teeth and the lengths of cracks can be detected exactly, and when the cracks are in adjacent teeth, according to the cracks lengths and depths and their effects overlap, the number of cracks and their lengths can be detected exactly, approximately or absolutely undetectable.
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