Publications
197 results found
Stapelfeldt SC, Parry AB, Vahdati M, 2015, Validation of time-domain single-passage methods for the unsteady simulation of a contra-rotating open rotor, ISSN: 2313-0067
The growing pressure to reduce fuel consumption and cut emissions has triggered renewed interest in contra-rotating open rotor technologies. Open rotors achieve a significant reduction in fuel consumption by allowing large increases in bypass ratio without the weight and drag penalties which arise from simply scaling up a turbofan bypass duct. However, in addition to potential noise issues, open rotors are susceptible to self-exited or forced vibration because of their unducted, light-weight, highly swept blades. The prediction of aeroelastic instabilities requires numerical methods which can accurately model the unsteady environment. Compared to full circumference simulations, single-passage multi-row (SPMR) methods with phase-lagged boundary conditions can offer significant savings in computational time but need to be validated for contra-rotating open rotor geometries operating at incidence. This paper presents the application of a time-domain single-passage method for the unsteady simulation of a contra-rotating open rotor rig at take-off operating conditions. The single-passage solution is compared to the reference full circumference solution as well as experimental measurements. It is demonstrated that the SPMR approach provides a good approximation for open rotors operating at angles of attack at significantly reduced computational cost.
Zhao F, Nipkau J, Vahdati M, 2015, Influence of acoustic reflection on flutter stability of an embedded blade row, ISSN: 2313-0067
The aim of this work is to understand the effects of acoustic reflections on flutter stability of an embedded rotor in a multi-stage compressor. To achieve this goal, flutter analysis of an embedded rotor blade in a high pressure compressor is undertaken using a validated 3D unsteady RANS solver with mesh movement. In the first part of this work, flutter computations are performed on the rotor with and without the presence of its adjacent blade rows and the influence of reflections on aerodynamic damping of the embedded row is studied. In the second part of this work reflective boundary conditions are used to reflect pressure waves from known locations. A wave-splitting procedure is performed to split the unsteady pressure into an outgoing wave and a reflected wave. Using this technique a relationship between the phase of the reflected wave and the susceptibility to flutter is established.
Zhao F, Nipkau J, Vahdati M, 2015, Influence of acoustic reflection on flutter stability of an embedded blade row, ISSN: 2410-4833
The aim of this work is to understand the effects of acoustic reflections on flutter stability of an embedded rotor in a multi-stage compressor. To achieve this goal, flutter analysis of an embedded rotor blade in a high pressure compressor is undertaken using a validated 3D unsteady RANS solver with mesh movement. In the first part of this work, flutter computations are performed on the rotor with and without the presence of its adjacent blade rows and the influence of reflections on aerodynamic damping of the embedded row is studied. In the second part of this work reflective boundary conditions are used to reflect pressure waves from known locations. A wave-splitting procedure is performed to split the unsteady pressure into an outgoing wave and a reflected wave. Using this technique a relationship between the phase of the reflected wave and the susceptibility to flutter is established.
Zhao F, Nipkau J, Vahdati M, 2015, INFLUENCE OF ACOUSTIC REFLECTION ON FLUTTER STABILITY OF AN EMBEDDED BLADE ROW, 11th EUROPEAN CONFERENCE ON TURBOMACHINERY FLUID DYNAMICS AND THERMODYNAMICS, Publisher: EUROPEAN TURBOMACHINERY SOC-EUROTURBO
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- Citations: 3
Stapelfeldt SC, Parry AB, Vahdati M, 2015, VALIDATION OF TIME-DOMAIN SINGLE-PASSAGE METHODS FOR THE UNSTEADY SIMULATION OF A CONTRA-ROTATING OPEN ROTOR, 11th EUROPEAN CONFERENCE ON TURBOMACHINERY FLUID DYNAMICS AND THERMODYNAMICS, Publisher: EUROPEAN TURBOMACHINERY SOC-EUROTURBO
Amelian S, Koofigar HR, Vahdati A, et al., 2014, Digital optimal control of multi-stand rolling mills with measurement and input delays, Journal of Engineering Science and Technology, Vol: 9, Pages: 261-272, ISSN: 1823-4690
In this paper, the problem of designing an optimal control algorithm for rolling processes is addressed. Deriving a mathematical model for a general class of rolling mills, the optimal control problem is defined. In the design procedure, time delays in thickness measurment and control input are taken into account. The proposed strategy significantly improves the results of previous investigations from practical point of view. Simulation results are also studied to highlight the effictiveness of the method. © School of Engineering, Taylor's University.
Vahdati M, Smith N, Zhao F, 2014, INFLUENCE OF INTAKE ON FAN BLADE FLUTTER, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
Dodds J, Vahdati M, 2014, ROTATING STALL OBSERVATIONS IN A HIGH SPEED COMPRESSOR PART 1: EXPERIMENTAL STUDY, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
Dodds J, Vahdati M, 2014, ROTATING STALL OBSERVATIONS IN A HIGH SPEED COMPRESSOR PART 2: NUMERICAL STUDY, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
Vahdati A, Vahdati M, Mahdavinejad RA, 2013, Simulating the buckling deflection of carbon nanotube-made detectors used in medical detections by applying a continuum mechanics model, Life Science Journal, Vol: 10, Pages: 186-191, ISSN: 1097-8135
Carbon nanotubes are increasingly used in fabrication of nano-detectors and other nano devices. Herein, the buckling of a carbon nano-tube made detector is simulated. In order to obtain nonlinear constitutive equation of the detectors we assume the distributed electrostatic and Van der Waals attractions along the CNT length. By considering the nano forces in a continuum mechanics model we were able to achieve the differential equation of the CNT. In the next step by applying Adomian series solution, we provided an analytical closed-form solution of CNTs. The deflection and the buckling parameters are determined and discussed in detail. The analytical obtained results are compared with those of literature as well as numerical solution. The obtained results revealed that the presented continuum based model is in good agreement with experimental result. Moreover it is found that the analytical solution can be considered as a reliable approach to study the buckling stability of detectors in nanoscales where the presence of van der Waals force is important.
Choi M, Smith NHS, Vahdati M, 2013, Validation of Numerical Simulation for Rotating Stall in a Transonic Fan, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 135, ISSN: 0889-504X
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- Citations: 55
Vahdati A, Vahdati M, 2012, The instability of multi walled carbon nanotube probes near graphite sheets, Life Science Journal, Vol: 9, Pages: 5593-5596, ISSN: 1097-8135
In this paper the deflection and instability of a freestanding carbon nanotube (CNT) probe/sensor in the vicinity of the graphene layers are investigated. Modeling the buckling of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite has been carried out using numerical finite difference method. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. Minimum nanotube-graphite initial gap and stable length of freestanding CNT are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers.
Vahdati A, Vahdati M, 2012, The instability and of multi walled carbon nanotube with small number of layers probes near graphite sheets, Life Science Journal, Vol: 9, Pages: 5597-5600, ISSN: 1097-8135
In this paper the deflection and instability of a freestanding carbon nanotube (CNT) probe/sensor in the vicinity of the graphene layers are investigated. Modeling the buckling of multi walled carbon nanotube (MWCNT) probes/actuators in the vicinity of thin and thick graphite has been carried out using numerical finite difference method. A hybrid nano-scale continuum model based on Lennard-Jones potential is applied to simulate the intermolecular force-induced deflection of MWCNT. Minimum nanotube-graphite initial gap and stable length of freestanding CNT are determined as basic parameters for engineering applications and nano-devices design. The stable length of MWCNT is determined as a function of its geometrical and material characteristics, initial gap and number of graphene layers.
Hafshejani MK, Vahdati A, Vahdati M, et al., 2012, Study of the mercury removal for health care and the effect of PH in mercury removal from aqueous solutions by activated carbons, Life Science Journal, Vol: 9, Pages: 1846-1848, ISSN: 1097-8135
A serious environmental threat from heavy metal ion pollution, especially mercury, has generated a great deal of attention in recent years. Mercury is one of the priority pollutant listed by USEPA as it can easily pass the blood-brain barrier and affect the fetal brain. High concentration of Hg (II) causes impairment of pulmonary function and kidney, chest pain and dyspnoea. Consequently, removal of mercury in water and wastewater assumes importance. In this review paper, we have evaluated the efforts which have been done for controlling the mercury emissions from aqueous solutions. According to the EPA agency, the tolerance limit for Hg (II) for discharge into inland surface water is 10μg/l and for drinking water is 1μg/l. Mercury (Hg) is one of the heavy metals of concern and has been found in the waste waters coming from manufacturing industry, and natural sources. Among several types of technology for removing of Hg in water (chemical precipitation, reverse osmosis, ion-exchange, etc.), adsorption is one of most frequently used. It is a complex process involving physical, chemical, and electrical interactions at sorbent surfaces. Therefore, in this study will investigate effective parameters such as pH, initial concentration and surface characteristic.
Vahdati A, Dadjoo F, Alimoradi F, et al., 2012, Simulating the cooling of medical CT-scanners: Part 1: Formulation, Life Science Journal, Vol: 9, Pages: 1029-1034, ISSN: 1097-8135
CT-scanners are used as an non-invasive detecting method in medical applications as a powerful radiological device. Many patients are used CT-scanners for detecting disease. However CT-scanners required cooling due to the huge heat generated during the operation. In this work we modeled a convection-diffusion cooling process of CT-scan devices. A flow in a rectangular body with symmetry, constant heat flux and constant temperature boundary conditions has been considered. The governing equation has been discredited based on the finite volume method and has been solved using a fully implicit method. This paper is mostly concerned with the problem description and the results presents in part 2 of this paper.
Vahdati A, Alimoradi F, Yekrangi A, et al., 2012, An investigation on physical response of modified adhesives used in medical applications, Life Science Journal, Vol: 9, Pages: 1025-1028, ISSN: 1097-8135
Glues and adhesives are increasingly used in medical applications. They can be utilized in disposal medical devices, structural bonds, bone cement, prostheses and other applications. For improve the adhesion of these materials, the liquid Hycar modifier is added and mixed. However, despite liquid modifier might modify the adhesion properties of glues and adhesives, the physical properties of these materials might be deteriorated. In this paper the physical response i.e. thermal and mechanical behavior of the adhesive modified with liquid rubber has been investigated for medical applications. In addition, scanning electron microscopy (SEM) is utilized in this work for better understanding the behavior of adhesive.
Vahdati M, Cumpsty N, 2012, The mechanism of aeroelastic instability in transonic fans, 13th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT13)
Choi M, Smith NHS, Vandati M, 2012, VALIDATION OF NUMERICAL SIMULATION FOR ROTATING STALL IN A TRANSONIC FAN, ASME Turbo Expo 2011, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1667-1676
Vahdati M, Simpson G, Imregun M, 2011, Mechanisms for Wide-Chord Fan Blade Flutter, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 133, ISSN: 0889-504X
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- Citations: 37
Choi M, Vahdati M, Imregun M, 2011, Effects of Fan Speed on Rotating Stall Inception and Recovery, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 133, ISSN: 0889-504X
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- Citations: 47
Choi M, Vahdati M, 2011, Numerical strategies for capturing rotating stall in fan, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY, Vol: 225, Pages: 655-664, ISSN: 0957-6509
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- Citations: 5
choi M, vahdati M, 2011, Recovery Process from Rotating Stall in a Fan, Journal of Propulsion and Power, Vol: 27, Pages: 1161-1168
Vahdati A, Vahdati M, 2010, Experimental, statistical and simulation study on spring-back behavior in incremental sheet metal forming (ISMF) process, Pages: 607-612, ISSN: 0094-243X
Recently, considerable attention has been paid for the many kinds of flexible production processes. Most concerned one is the incremental sheet metal forming (ISMF) process, which does not require any high capacity press machine and a set of dies with specified shape for the product. ISMF process apparatus requires a traveling tool with simple shape and a holder which holds the sheet stationary at its periphery. In this research, spring-back and its effect on dimensional precision of ISMF process has been studied. The influence of process parameters such as: vertical step size (ν), sheet thickness (t), tool diameter (d), feed rate (f) and spindle speed (n) have been investigated. A series of experimental tests have been implemented for a straight groove bead-shape part made of aluminum sheets (Al 1050-O). In first section, a reliable statistical analysis has been carried out to extract the importance of each parameter. The obtained model permits to select appropriate process parameters to reduce spring-back effectively. In second section, simulation process has been implemented by FEM software. In final, experimental results confirm the results of simulation and comparisons between experimental and simulation results of spring-back have shown good agreement. © 2010 American Institute of Physics.
Vahdati M, Sedighi M, Khoshkish H, 2010, An analytical model to reduce spring-back in incremental sheet metal forming (ISMF) process, Pages: 1113-1120, ISSN: 1022-6680
In this paper, spring-back and its effect on geometrical and dimensional accuracy of incremental sheet metal forming (ISMF) process has been studied. The influence of process parameters such as: vertical step size, sheet thickness, tool diameter, feed rate and spindle speed have been investigated. A series of experimental tests have been carried out for a straight groove bead-shape part made of aluminum sheets. A reliable statistical analysis has been carried out to extract the importance of each parameter. The obtained model permits to select appropriate process parameters to reduce spring-back effectively. © (2010) Trans Tech Publications.
Choi M, Vandati M, Imregun M, 2010, EFFECTS OF FAN SPEED ON ROTATING STALL INCEPTION AND RECOVERY, ASME Turbo Expo 2010, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 2593-2603
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- Citations: 1
di Mare L, Vadati M, Mueck B, et al., 2009, AEROELASTIC INSTABILITY OF FAN BLADES AT HIGH ALTITUDES, 54th ASME Turbo Expo 2009, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1765-1772
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- Citations: 2
Vahdati M, Simpson G, Imregun M, 2009, MECHANISMS FOR WIDE-CHORD FAN BLADE FLUTTER, 54th ASME Turbo Expo 2009, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 585-593
Vahdati M, Simpson G, Imregun M, 2008, Unsteady flow and aeroelasticity behavior of aeroengine core compressors during rotating stall and surge, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 130, ISSN: 0889-504X
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- Citations: 40
vahdati M, Simpson G, imregun M, 2008, Unsteady Flow and Aeroelasticity Behavior of Aeroengine Core Compressors During Rotating Stall and Surge, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 130, ISSN: 0889-504X
Vahdati M, Breard C, Simpson G, et al., 2008, FORCED RESPONSE ASSESSMENT USING MODAL FORCE BASED INDICATOR FUNCTIONS, 53rd ASME Turbo Expo 2008, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 665-672
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