Health Monitoring of Structural and Biological Systems XII, 2018
In the nonlocal theory of peridynamic the partial derivatives that appear in the classical (local... more In the nonlocal theory of peridynamic the partial derivatives that appear in the classical (local) continuum mechanics are replaced with integral equations. This is an important feature of peridynamic theory allowing it to be easily applied to problems where partial derivatives of the displacement field may not exist (e.g. sharp corners, bifurcation) inside an elastic continuum medium. Crack edge is an example where displacement field is not continuous and hence partial derivatives are undefined. In the past decade peridynamic theory has attracted researchers in modeling crack initiation and propagation, specifically phenomena like crack branching and multiple micro-crack interactions where other classical (local) theories may experience challenges. Despite its remarkable results peridynamics is still a relatively new topic and it has room for development. One area of development is coupling the peridynamics theory with the traditional multibody dynamics. This will provide a useful simulation tool in damage prediction of rotating parts such as wind turbines or helicopter rotor blades. In this paper, a coupled formulation of peridynamics and flexible multibody dynamics is presented. A floating frame of references (FFR) approach is taken to capture the large rotation and translation of a body that itself is modeled by using peridynamic theory.
Abstract The present study is focused on the phase evolution pattern and phase transition reactio... more Abstract The present study is focused on the phase evolution pattern and phase transition reactions between melt and arising solid phases during solidification of three different Mo-Si-B alloy compositions. To carry out this work, three alloy compositions from the Mo3Si, Mo5SiB2 and Mo SS primary solidification regions, in the vicinity of ternary eutectic composition of Mo-Si-B system were selected. To investigate phase evolution and solidification reactions, a phase-field simulation is conducted with MicressTM applying the thermodynamic data generated with FactsageTM. The simulations confirmed the presence of binary and ternary eutectic reactions. It was observed that, depending on the initial melt composition, a primary phase emanates at the beginning of solidification which causes a composition fluctuation in the residual melt. Depending on the composition of the residual melt, thermodynamically feasible phases tend to perform a binary reaction until the rest of liquid undergoes the ternary Mo SS -Mo5SiB2-Mo3Si eutectic reaction. However, exploring the solidification path of the considered compositions implied the uncertainties in considered thermodynamic parameters which requires the revision of thermodynamic database.
During the past decades, the Mo-Si-B alloys have received significant scientific attention since ... more During the past decades, the Mo-Si-B alloys have received significant scientific attention since they combine excellent creep behavior and acceptable oxidation resistance at high temperatures. Due to these properties, this class of refractory materials has been considered as potential candidates for high temperature applications such as aerospace engines and the power-generating industries. However, among the scientific research sufficient attention has not been paid to investigate this alloy system numerically. The present Ph.D. thesis deals with the development of phase-field based model to study the solidification behavior of Mo-rich Mo-Si-B alloy compositions including the ternary eutectic composition and near eutectic compositions which tend to form a primary phase during the solidification. In order to develop the model, thermodynamic data published within the literature and thermodynamic database have been considered within the model. The ternary alloy compositions investigat...
Substructuring methods have been used in finite element modeling of large or complex structures b... more Substructuring methods have been used in finite element modeling of large or complex structures by partitioning the entire structure into several smaller or less complex substructures. The FE model of each substructure is reduced individually via a component mode reduction technique and then assembled together with the remaining reduced substructures to obtain a reduced model for the entire system. In the standard substructuring methods that have been developed in the past decades the interface degrees-offreedom (DoF), or a transformation of them, remain in the reduced model [1–3]. Although in some problems it might be necessary to keep such DoF in the reduced model, in general the size of the model could be reduced even further if the interface DoF are reduced as well. Despite the works done on the truncation of the interface DoF [4–6], to the best knowledge of the authors, none has addressed the possibility of eliminating such DoF. In this paper a different method of substructurin...
The antibacterial activities of eight snake crude venom (Macrovipera lebetina obtusa, Pseudoceras... more The antibacterial activities of eight snake crude venom (Macrovipera lebetina obtusa, Pseudocerastes persicus, Pseudocerastes urarachnoides, Echis carinatus sochureki, Gloydius halys caucasicus, Naja (naja) oxiana, and two species of true sea snakes Enhydrina schistose and Hydrophis cyanocinctus) were assessed against five important standard pathogenic bacterial strains (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, vancomycin resistant Enterococcus faecium and Streptococcus pneumoniae). Broth micro-dilution method, standard disk diffusion assay and bio-autography based on polyacrylamide gel electrophoresis were used for this purpose. Snake venom revealed inhibitory effects against S. aureus and E. faecium strains. The moderate effects on S. aureus were showed by venomof P. urarachnoides, P. persicus and N. oxiana with MIC values of 20, 10 and 10 μg/ml respectively. Moreover, venom of E.carinatus, M.lebetina and G. halys showed strong effects (MICs= 40, 80, 160 μg/...
International Journal of Sports Physiology and Performance, 2021
Context: Several studies report static-stretch-induced deficits and dynamic-stretch performance i... more Context: Several studies report static-stretch-induced deficits and dynamic-stretch performance improvement after intervention. Purpose: To investigate the muscle activation of the forehand and backhand in table tennis players after experiencing static- and dynamic-stretching protocols. Methods: A total of 24 elite male table tennis players (age 22.7 [3.46] y, height 1.78 [0.03] m) were tested before and 0, 10, 20, and 30 min after the 3 conditions (dynamic stretch, static stretch, and no stretch). The MEGA ME6000 (Mega Electronics, Kuopio, Finland) was used to capture the surface EMG data of the anterior deltoid, middle deltoid, posterior deltoid, biceps, and triceps muscles. Muscle activation data of the pretest were compared with posttest 0, 10, 20, and 30 min. These data were also compared between 3 different conditions (dynamic stretch, static stretch, and no stretch). Results: A 2-way repeated-measures analysis of variance indicated significant differences in the forehand and ...
This work gives an insight into the transient softening at the fusion boundary of resistance spot... more This work gives an insight into the transient softening at the fusion boundary of resistance spot welds on hot stamped steel. Metallographic investigations and hardness mapping were combined with finite phase–field modeling of phase evolution at the fusion boundary. Saturation of weld nugget growth in the welding process was observed. For industrially relevant, long welding times, the fusion boundary of a spot weld is therefore isothermally soaked between the peritectic and solidus temperatures. This leads to a carbon segregation to the liquid phase due to higher carbon solubility and possibly to δ-Fe formation at the fusion boundary. Both results in a local carbon depletion at the fusion boundary. This finding is in good agreement with carbon content measurements at the fusion boundary and the results of hardness measurements.
IOP Conference Series: Materials Science and Engineering, 2017
A Mo-10.9Si-20.3B (if not stated otherwise all compositions are given in at.%) alloy was modeled ... more A Mo-10.9Si-20.3B (if not stated otherwise all compositions are given in at.%) alloy was modeled using the phase field method with linearized phase diagrams and thermodynamic data. The simulation results showed that there are two specific microstructural constituents. According to the simulations and experimental microstructural investigations the primary Mo5SiB2 phase observed in this study was combined by the Moss-Mo3Si-Mo5SiB2 eutectics. The overall composition of the both primary and eutectic area was probed and the phase evolution along with the concentration change of the core areas were explored and visualized in the solidification domain. To verify the accuracy of the simulation results, they were comprised with the experimental achievements. In terms of the fraction of phases, the portion of the primary phase and the eutectic constituent and the phase distribution pattern our results were in good agreement with the experimental observations.
Various challenges such as new technologies, growing complexity and competitive environment, requ... more Various challenges such as new technologies, growing complexity and competitive environment, require the main contractor to assign some of the project’s tasks to other parties, the so-called subcontractors. Although subcontracting is a usual phenomenon in the construction industry, insufficient attention to the subcontractor selection strategy may pose some major threats to a project. Having in mind the significance of such risks, the optimization of subcontractor selection is essential for the success of the project. The importance of risk management in selecting subcontractors and the direct relation between risks and returns in most projects are two main motives for using the concept of portfolio in this paper. The main objective of this paper is to propose a model to allocate the best portion of project’s task to some subcontractors in order to reach the optimized portfolio of subcontractors and main contractor. This is a new approach in the subcontractor management; therefore,...
Journal of Mechanical Science and Technology, 2015
This paper presents a methodology for constructing a finite element based tire model suitable for... more This paper presents a methodology for constructing a finite element based tire model suitable for ride and handling simulations of vehicles. The model is based on available high-resolution finite element models developed by tire manufacturers. Such high-resolution models contain detailed structural and material characteristics of a tire that exhibit degrees-of-freedom in the order of 105 or greater. Consequently, for multibody dynamic analysis, the main objectives of the presented methodology become to reduce the number of degreesof-freedom and to preserve as much of the essential characteristics of the original model as possible. The presented tire model is formulated with a non-rotating reference frame that uses the rotational invariant characteristic of the tire.
The purpose of this study was to compare the push-out bond strength of mineral trioxide aggregate... more The purpose of this study was to compare the push-out bond strength of mineral trioxide aggregate (MTA) and calcium enriched mixture (CEM) as root end filling materials. A total of 40 root dentin slices (1 ± 0.2 mm) were prepared from freshly extracted human maxillary central teeth and their lumens were enlarged to 1.3 mm. The slices were randomly divided into two groups (n = 20). MTA and CEM cement were mixed according to manufacturer's instruction and introduced into the lumens. The specimens were wrapped in pieces of wet gauze soaked in distilled water and incubated at 37°C for 3 days. The push-out bond strength was measured using a universal testing machine. The slices were then examined under a light microscope at ×10 magnification to determine the nature of bond failure. The data were analyzed using Mann-Whitney test (P < 0.001). The mean push-out bond strength for CEM cement and MTA were 1.68 ± 0.9 and 5.94 ± 3.99 respectively. The difference was statistically signific...
International Journal of Operations Research and Information Systems, 2010
Simulating large-scale systems usually entails exhaustive computational powers and lengthy execut... more Simulating large-scale systems usually entails exhaustive computational powers and lengthy execution times. The goal of this research is to reduce execution time of large-scale simulations without sacrificing their accuracy by partitioning a monolithic model into multiple pieces automatically and executing them in a distributed computing environment. While this partitioning allows us to distribute required computational power to multiple computers, it creates a new challenge of synchronizing the partitioned models. In this article, a partitioning methodology based on a modified Prim’s algorithm is proposed to minimize the overall simulation execution time considering 1) internal computation in each of the partitioned models and 2) time synchronization between them. In addition, the authors seek to find the most advantageous number of partitioned models from the monolithic model by evaluating the tradeoff between reduced computations vs. increased time synchronization requirements. I...
Health Monitoring of Structural and Biological Systems XII, 2018
In the nonlocal theory of peridynamic the partial derivatives that appear in the classical (local... more In the nonlocal theory of peridynamic the partial derivatives that appear in the classical (local) continuum mechanics are replaced with integral equations. This is an important feature of peridynamic theory allowing it to be easily applied to problems where partial derivatives of the displacement field may not exist (e.g. sharp corners, bifurcation) inside an elastic continuum medium. Crack edge is an example where displacement field is not continuous and hence partial derivatives are undefined. In the past decade peridynamic theory has attracted researchers in modeling crack initiation and propagation, specifically phenomena like crack branching and multiple micro-crack interactions where other classical (local) theories may experience challenges. Despite its remarkable results peridynamics is still a relatively new topic and it has room for development. One area of development is coupling the peridynamics theory with the traditional multibody dynamics. This will provide a useful simulation tool in damage prediction of rotating parts such as wind turbines or helicopter rotor blades. In this paper, a coupled formulation of peridynamics and flexible multibody dynamics is presented. A floating frame of references (FFR) approach is taken to capture the large rotation and translation of a body that itself is modeled by using peridynamic theory.
Abstract The present study is focused on the phase evolution pattern and phase transition reactio... more Abstract The present study is focused on the phase evolution pattern and phase transition reactions between melt and arising solid phases during solidification of three different Mo-Si-B alloy compositions. To carry out this work, three alloy compositions from the Mo3Si, Mo5SiB2 and Mo SS primary solidification regions, in the vicinity of ternary eutectic composition of Mo-Si-B system were selected. To investigate phase evolution and solidification reactions, a phase-field simulation is conducted with MicressTM applying the thermodynamic data generated with FactsageTM. The simulations confirmed the presence of binary and ternary eutectic reactions. It was observed that, depending on the initial melt composition, a primary phase emanates at the beginning of solidification which causes a composition fluctuation in the residual melt. Depending on the composition of the residual melt, thermodynamically feasible phases tend to perform a binary reaction until the rest of liquid undergoes the ternary Mo SS -Mo5SiB2-Mo3Si eutectic reaction. However, exploring the solidification path of the considered compositions implied the uncertainties in considered thermodynamic parameters which requires the revision of thermodynamic database.
During the past decades, the Mo-Si-B alloys have received significant scientific attention since ... more During the past decades, the Mo-Si-B alloys have received significant scientific attention since they combine excellent creep behavior and acceptable oxidation resistance at high temperatures. Due to these properties, this class of refractory materials has been considered as potential candidates for high temperature applications such as aerospace engines and the power-generating industries. However, among the scientific research sufficient attention has not been paid to investigate this alloy system numerically. The present Ph.D. thesis deals with the development of phase-field based model to study the solidification behavior of Mo-rich Mo-Si-B alloy compositions including the ternary eutectic composition and near eutectic compositions which tend to form a primary phase during the solidification. In order to develop the model, thermodynamic data published within the literature and thermodynamic database have been considered within the model. The ternary alloy compositions investigat...
Substructuring methods have been used in finite element modeling of large or complex structures b... more Substructuring methods have been used in finite element modeling of large or complex structures by partitioning the entire structure into several smaller or less complex substructures. The FE model of each substructure is reduced individually via a component mode reduction technique and then assembled together with the remaining reduced substructures to obtain a reduced model for the entire system. In the standard substructuring methods that have been developed in the past decades the interface degrees-offreedom (DoF), or a transformation of them, remain in the reduced model [1–3]. Although in some problems it might be necessary to keep such DoF in the reduced model, in general the size of the model could be reduced even further if the interface DoF are reduced as well. Despite the works done on the truncation of the interface DoF [4–6], to the best knowledge of the authors, none has addressed the possibility of eliminating such DoF. In this paper a different method of substructurin...
The antibacterial activities of eight snake crude venom (Macrovipera lebetina obtusa, Pseudoceras... more The antibacterial activities of eight snake crude venom (Macrovipera lebetina obtusa, Pseudocerastes persicus, Pseudocerastes urarachnoides, Echis carinatus sochureki, Gloydius halys caucasicus, Naja (naja) oxiana, and two species of true sea snakes Enhydrina schistose and Hydrophis cyanocinctus) were assessed against five important standard pathogenic bacterial strains (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, vancomycin resistant Enterococcus faecium and Streptococcus pneumoniae). Broth micro-dilution method, standard disk diffusion assay and bio-autography based on polyacrylamide gel electrophoresis were used for this purpose. Snake venom revealed inhibitory effects against S. aureus and E. faecium strains. The moderate effects on S. aureus were showed by venomof P. urarachnoides, P. persicus and N. oxiana with MIC values of 20, 10 and 10 μg/ml respectively. Moreover, venom of E.carinatus, M.lebetina and G. halys showed strong effects (MICs= 40, 80, 160 μg/...
International Journal of Sports Physiology and Performance, 2021
Context: Several studies report static-stretch-induced deficits and dynamic-stretch performance i... more Context: Several studies report static-stretch-induced deficits and dynamic-stretch performance improvement after intervention. Purpose: To investigate the muscle activation of the forehand and backhand in table tennis players after experiencing static- and dynamic-stretching protocols. Methods: A total of 24 elite male table tennis players (age 22.7 [3.46] y, height 1.78 [0.03] m) were tested before and 0, 10, 20, and 30 min after the 3 conditions (dynamic stretch, static stretch, and no stretch). The MEGA ME6000 (Mega Electronics, Kuopio, Finland) was used to capture the surface EMG data of the anterior deltoid, middle deltoid, posterior deltoid, biceps, and triceps muscles. Muscle activation data of the pretest were compared with posttest 0, 10, 20, and 30 min. These data were also compared between 3 different conditions (dynamic stretch, static stretch, and no stretch). Results: A 2-way repeated-measures analysis of variance indicated significant differences in the forehand and ...
This work gives an insight into the transient softening at the fusion boundary of resistance spot... more This work gives an insight into the transient softening at the fusion boundary of resistance spot welds on hot stamped steel. Metallographic investigations and hardness mapping were combined with finite phase–field modeling of phase evolution at the fusion boundary. Saturation of weld nugget growth in the welding process was observed. For industrially relevant, long welding times, the fusion boundary of a spot weld is therefore isothermally soaked between the peritectic and solidus temperatures. This leads to a carbon segregation to the liquid phase due to higher carbon solubility and possibly to δ-Fe formation at the fusion boundary. Both results in a local carbon depletion at the fusion boundary. This finding is in good agreement with carbon content measurements at the fusion boundary and the results of hardness measurements.
IOP Conference Series: Materials Science and Engineering, 2017
A Mo-10.9Si-20.3B (if not stated otherwise all compositions are given in at.%) alloy was modeled ... more A Mo-10.9Si-20.3B (if not stated otherwise all compositions are given in at.%) alloy was modeled using the phase field method with linearized phase diagrams and thermodynamic data. The simulation results showed that there are two specific microstructural constituents. According to the simulations and experimental microstructural investigations the primary Mo5SiB2 phase observed in this study was combined by the Moss-Mo3Si-Mo5SiB2 eutectics. The overall composition of the both primary and eutectic area was probed and the phase evolution along with the concentration change of the core areas were explored and visualized in the solidification domain. To verify the accuracy of the simulation results, they were comprised with the experimental achievements. In terms of the fraction of phases, the portion of the primary phase and the eutectic constituent and the phase distribution pattern our results were in good agreement with the experimental observations.
Various challenges such as new technologies, growing complexity and competitive environment, requ... more Various challenges such as new technologies, growing complexity and competitive environment, require the main contractor to assign some of the project’s tasks to other parties, the so-called subcontractors. Although subcontracting is a usual phenomenon in the construction industry, insufficient attention to the subcontractor selection strategy may pose some major threats to a project. Having in mind the significance of such risks, the optimization of subcontractor selection is essential for the success of the project. The importance of risk management in selecting subcontractors and the direct relation between risks and returns in most projects are two main motives for using the concept of portfolio in this paper. The main objective of this paper is to propose a model to allocate the best portion of project’s task to some subcontractors in order to reach the optimized portfolio of subcontractors and main contractor. This is a new approach in the subcontractor management; therefore,...
Journal of Mechanical Science and Technology, 2015
This paper presents a methodology for constructing a finite element based tire model suitable for... more This paper presents a methodology for constructing a finite element based tire model suitable for ride and handling simulations of vehicles. The model is based on available high-resolution finite element models developed by tire manufacturers. Such high-resolution models contain detailed structural and material characteristics of a tire that exhibit degrees-of-freedom in the order of 105 or greater. Consequently, for multibody dynamic analysis, the main objectives of the presented methodology become to reduce the number of degreesof-freedom and to preserve as much of the essential characteristics of the original model as possible. The presented tire model is formulated with a non-rotating reference frame that uses the rotational invariant characteristic of the tire.
The purpose of this study was to compare the push-out bond strength of mineral trioxide aggregate... more The purpose of this study was to compare the push-out bond strength of mineral trioxide aggregate (MTA) and calcium enriched mixture (CEM) as root end filling materials. A total of 40 root dentin slices (1 ± 0.2 mm) were prepared from freshly extracted human maxillary central teeth and their lumens were enlarged to 1.3 mm. The slices were randomly divided into two groups (n = 20). MTA and CEM cement were mixed according to manufacturer's instruction and introduced into the lumens. The specimens were wrapped in pieces of wet gauze soaked in distilled water and incubated at 37°C for 3 days. The push-out bond strength was measured using a universal testing machine. The slices were then examined under a light microscope at ×10 magnification to determine the nature of bond failure. The data were analyzed using Mann-Whitney test (P < 0.001). The mean push-out bond strength for CEM cement and MTA were 1.68 ± 0.9 and 5.94 ± 3.99 respectively. The difference was statistically signific...
International Journal of Operations Research and Information Systems, 2010
Simulating large-scale systems usually entails exhaustive computational powers and lengthy execut... more Simulating large-scale systems usually entails exhaustive computational powers and lengthy execution times. The goal of this research is to reduce execution time of large-scale simulations without sacrificing their accuracy by partitioning a monolithic model into multiple pieces automatically and executing them in a distributed computing environment. While this partitioning allows us to distribute required computational power to multiple computers, it creates a new challenge of synchronizing the partitioned models. In this article, a partitioning methodology based on a modified Prim’s algorithm is proposed to minimize the overall simulation execution time considering 1) internal computation in each of the partitioned models and 2) time synchronization between them. In addition, the authors seek to find the most advantageous number of partitioned models from the monolithic model by evaluating the tradeoff between reduced computations vs. increased time synchronization requirements. I...
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Papers by Omid Kazemi