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Optimum kinetic and gas hold up distribution study in an NDMA hydrogenation reactor
, Article 18th International Congress of Chemical and Process Engineering, CHISA 2008, Prague, 24 August 2008 through 28 August 2008 ; 2008 ; Kazemeini, M ; Sharif University of Technology
2008
Abstract
Unsymmetrical Dimethyl hydrazine (UDMH) is used as stabilizer, fuel promoter, chemical in photography, and liquid fuel for fighter jet engines. Catalytic liquid phase hydrogenation of nitrosodimethylamine (NDMA) is one of the most efficient methods for the production of UDMH. Hydrogenation of NDMA to UDMH using a commercial 5% Pd/C catalyst in aqueous solution of NDMA was studied under constant temperature at 40°-70°C, ≤ 15 bar, and NDMA concentrations of 40-70 wt %. The effects of temperature, pressure, and NDMA concentration on NDMA conversion and yield of UDMH product in presence of undesired Dimethylamine (DMA) were studied. At NDMA concentration of > 50 wt %, the UDMH yield was < 0.89,...
Size-dependent vibrational behavior of a Jeffcott model for micro-rotor systems
, Article Journal of Mechanical Science and Technology ; Volume 30, Issue 1 , 2016 , Pages 35-41 ; 1738494X (ISSN) ; Asghari, M ; Sharif University of Technology
Korean Society of Mechanical Engineers
Abstract
In this study, several analytical expressions are obtained for the vibrational characteristics of a Jeffcott model for micro-rotor systems based on the strain gradient theory to investigate the small-scale effects on the model. The Jeffcott model consists of a massless microrotating shaft and a disk as a rotor with eccentricity. The disk is mounted on the middle of the shaft. Two second-order differential equations associated with the oscillating motion of the rotor in the plane perpendicular to the longitudinal axis are presented and transformed into a complex form. The stiffness of the system is determined by obtaining the deflection of a strain-gradient-based nonrotating microbeam...
Vibration and Stability Analysis of Rotor with Initial Bow and Non-Linear Supports
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Rouhollah (Supervisor)
Abstract
In this study, the effect of the initial bow on vibrations and stability of the rotor with nonlinear supports has been investigated. Using the energy method, the rotor’s equations of motion for the four-degree of freedom Jeffcott rotor and the elastic rotor assuming Tymoshenko beam relations are calculated. It is very important to study the initial bow as one of the common faults in rotating machines that has a great effect on system vibrations. A method was proposed to reduce rotor vibrations and balancing systems. Choosing a way to eliminate machine defects is one of the points considered by rotor dynamic engineers. Many factors can cause a bow in the rotor, some of the most important of...
Unbalance-induced rub between rotor and compliant-segmented stator
, Article Journal of Sound and Vibration ; Volume 429 , 2018 , Pages 96-129 ; 0022460X (ISSN) ; Alvandi, M ; Sharif University of Technology
Academic Press
2018
Abstract
Today, turbomachinery designers are trying to attain zero clearances for optimizing performance and efficiency of machine by designing advanced compliant-segmented seals. This trend involves secondary issues such as rotor-to-stator contact interaction which is to be treated with more technical knowledge in rotordynamic design and condition monitoring programs. The aim of this paper is to gain insight into dynamic interaction between a flexible rotor and a set of compliant arc-shaped segments as stator system. Specifically, the unbalanced-induced forward rubbing response is investigated in tight clearance condition during resonance-passing situations. A Jeffcott rotor modeling is used for...
A comprehensive analysis of short-circuit fault in wound-rotor resolvers
, Article IEEE Transactions on Vehicular Technology ; Volume 69, Issue 12 , December , 2020 , Pages 14884 - 14892 ; Nasiri Gheidari, Z ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2020
Abstract
This paper presents a detailed analysis of short circuit fault (SCF) in wound rotor (WR) resolvers. For this purpose, an analytical model based on winding function (WF) method is developed considering the stator and rotor windings fault, the severity of the fault, the phase of the stator faulty winding, and the tooth of shorted turns. The proposed model leads to a comprehensive understanding of the SCF behavior of WR resolvers and also leads to define proper fault detecting signatures. All the predictions are verified by time stepping finite element analysis as well as the experimental tests on two prototyped resolvers. IEEE
Subspace identification of fault modes for a twin-rotor system
, Article International Journal of Intelligent Unmanned Systems ; Volume 9, Issue 4 , 2021 , Pages 313-335 ; 20496427 (ISSN) ; Bintul Huda, A ; Rasool, A ; Bukhari, S. H. R ; Sharif University of Technology
Emerald Group Holdings Ltd
2021
Abstract
Purpose: The purpose of this paper is to identify the fault modes of a nonlinear twin-rotor system (TRS) using the subspace technique to facilitate fault identification, diagnosis and control applications. Design/methodology/approach: For identification of fault modes, three types of system malfunctions are introduced. First malfunction resembles actuator, second internal system dynamics and third represents sensor malfunction or offset. For each fault scenario, the resulting TRS model is applied with persistently exciting inputs and corresponding outputs are recorded. The collected input–output data are invoked in NS4SID subspace system identification algorithm to obtain the unknown fault...
Stability assessment of bowed asymmetric rotors on nonlinear supports
, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 44, Issue 12 , 2022 ; 16785878 (ISSN) ; Mousavi, S. M. R ; Firouz Abadi, R. D ; Farajolahi, M ; Chasalevris, A ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
This paper investigates the influence of residual bow on the stability of a rotating system consisting of an unbalanced Jeffcott rotor with anisotropy and two nonlinear journal bearing supports. The motion equations of the rotor system are formulated and analyzed considering most common faults and features including coupling effects of unbalance, anisotropy and residual shaft bow, by applying Lagrangian dynamics and Floquet theory. Time varying system properties of stiffness and damping are introduced into the equations of motion affecting the rotor behavior, and the influence is studied with respect to the extent of the bearing nonlinearity and the rotor anisotropy. Increasing area of...
Dynamic Analysis of Rotors with Imbalance, Bent and Misalignment
, M.Sc. Thesis Sharif University of Technology ; Behzad, Mehdi (Supervisor) ; Mehdigholi, Hamid (Co-Advisor)
Abstract
In this thesis a comprehensive software code has been developed for analyzing dynamic behavior of rotary systems. Dynamic analysis of rotors consists of calculating critical speeds, mode shapes and vibrational response. The code is also capable to model unbalance, bend and misalignment faults. Due to the complexity of current misalignment models, a simplified model was developed. Rotor, disks and bearings were modeled and joined together to build the complete model. A novel procedure was suggested for modeling of multisectional rotors (such as, Tie-rod and Tie-bolts). Vibrational response has been calculated for each of the faults and effect of shaft and bearing parameters has been observed....
A survey on rotor faults in brushless doubly fed machines
, Article Proceedings of the 2011 3rd International Youth Conference on Energetics, IYCE 2011, 7 July 2011 through 9 July 2011 ; July , 2011 , Page(s): 1 - 8 ; 9781457714948 (ISBN) ; Gorginpour, H ; Saket, M. A ; Oraee, A ; Ahmadian, M ; Oraee, H ; Sharif University of Technology
2011
Abstract
The cause of about 10% of faults in induction machines is related to the rotor part. In this paper, an analytical method for general modeling of brushless doubly-fed machines (BDFMs) with broken rotor loops and end ring is presented. The approach is based on calculation of resistance and inductance matrices through the winding function of the machine, so the assumption of sinusoidal MMF is not needed. It is also shown that a fault in a loop can lead to faults in other parts of the rotor. To validate the method a simulation in MATLAB/Simulink is performed based on the D180-frame prototype BDFM
Numerical and experimental investigation of the vibration of rotors with loose discs
, Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 224, Issue 1 , 2010 , Pages 85-94 ; 09544062 (ISSN) ; Asayesh, M ; Sharif University of Technology
2010
Abstract
In this study, the energy method has been used to develop a finite-element code for studying the effects of loose rotating discs on the rotor-bearing systems' response. A mathematical model of the loose disc has resulted in terms similar to unbalance and gyroscopic effects in the equation of motion of the system. Results of this study show that rotor response and beating phenomena are a function of measurement location, loose disc mass and inertia, ratio of rotating speed to the speed of loose disc, and clearance between the loose disc and shaft considering constant speed for loose disc and shaft. The developed finite-element model can numerically give the response of rotors with any number...
Investigating Nonlinear Vibration of a Turbine-Shaft in the Start-up Process Using Timoshenko Beam Theory
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Rohollah (Supervisor)
Abstract
In this study, the nonlinear vibrations of an elastic rotor that is under the elastic support and under the follower force caused by the airflow passing through the rotating plane are investigated. The elastic shaft is modeled by the Timoshenko beam theory, which is connected to a motor through a flexible coupling and the motor increases the rotational speed of the rotor by applying torque. Gibbons’ equations have been used to model the misalignment forces. First, the kinetic energy of the rotating system is calculated nonlinearly to take into account the effect of nonlinear terms due to the rotational inertia of the system, and then the potential energy and The work of external forces on...
Dynamic Behavior and Stability Analysis of Rotor-Seal System
, M.Sc. Thesis Sharif University of Technology ; Mohammmad Navazi, Hossein (Supervisor)
Abstract
The present research aims to achieve two main objectives in the Rotordynamic. The first one is, study and calculate the linear dynamic coefficients of a tapered gas seal, and the second one is, analysis the dynamic behavior and stability of the Timoshenko rotor supported with tapered gas seal. Classical Reynolds equation is used to calculate the dynamic coefficients of tapered gas seal. At first, using the perturbation method, the perturbed equations for gas film thickness and pressure are obtained. The finite difference method (FDM) is utilized to transfer the obtained PDEs to the algebraic system of equations. The algebraic system of equations then solved, and the zeroth and first-order...
Generalized vector model for the brushless doubly-fed machine with a nested-loop rotor
, Article IEEE Transactions on Industrial Electronics ; Volume 58, Issue 6 , August , 2011 , Pages 2313-2321 ; 02780046 (ISSN) ; Shao, S ; Abdi, E ; Oraee, H ; McMahon, R ; Sharif University of Technology
Abstract
This paper presents a generic vector model for the brushless doubly-fed machine (BDFM) with a nested-loop rotor. The vector model is presented for a generic p1/p2 pole-pair BDFM which may have any number of loops per nest. The vector transformations utilized in the derivation of the vector model are provided in general form such that the model can be represented in any appropriate reference frames according to the specific application of the model, such as BDFM analysis, simulations, or control system synthesis. The derived vector model benefits from the feature of reduced order in comparison with the coupled-circuit model, which is the most detailed model for the BDFM, while maintaining the...
A low-cost linearized analog resolver-to-DC converter
, Article 30th International Conference on Electrical Engineering, ICEE 2022, 17 May 2022 through 19 May 2022 ; 2022 , Pages 619-623 ; 9781665480871 (ISBN) ; Khajueezadeh, M ; Nasiri Gheidari, Z ; Sheikhaei, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
High-efficiency Permanent Magnet Synchronous Motors (PMSMs) are widely used in industry. Subsequently, resolvers' employment is increasing in the drive of PMSMs. Measuring the rotor angle using a resolver needs a costly Resolver to Digital Converter (RDC). Therefore, a low-cost analog RDC is designed against the conventional Angle Tracking Observers (ATOs) in the following study. The designed RDC has satisfactory accuracy, simplicity, and enduring against excitation frequency. Firstly, an overview of the resolver is shown, and subsequently, the circuit of the designed RC is described thoroughly. Ultimately, the simulations' outcomes are displayed, and comparing our design with others...
Vibration Analysis of Rotor-Disk Systems
, M.Sc. Thesis Sharif University of Technology ; Behzad, Mehdi (Supervisor) ; Mehdigholi, Hamid (Supervisor)
Abstract
Utilization of the rod fastened rotors in gas turbines as well as induction motors increased recently due to several advantages. Rods in rod fastened rotors are connected to shafts in both sides of the rotors and pre-tightened using bolts in each ends. Predictions of dynamic characteristics of these rotors have specific complications as a result of effects of contact interfaces raised due to applied pre-tightening load. Studies carried out in the field of vibration analysis of rotors consist of investigation of vibration of shafts, bearings and other connected components to the rotors. One of the best methods for modeling and analyzing complicated structures such as rod fastened rotors is...
Design, Manufacturing and Control of High Speed Spindle Resistant to Speed Fluctuations and Sudden Mass Unbalance
, M.Sc. Thesis Sharif University of Technology ; Durali, Mohammad (Supervisor)
Abstract
Industrial rotating parts experiencing high angular velocities must be examined for structural integrity and strength before being installed in an operating machine. This includes performing non-destructive tests such as rotating at high speeds that generate near yield stresses in part critical points. The dangers associated with performing such tests require that these tests be performed in devices named “Spin Testers”. In this device the test is normally carried out in vacuum and within armored walls. A critical component of the spin tester is the spindle to which the rotating part is attached. Besides carrying weight of the test piece and rotating at high speeds, the spindle must be...
Behavior of a Four Degree of Freedom Jeffcott Rotor with Clearance and Rubbing in Supports
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Roholla (Supervisor)
Abstract
different phenomena occur between rotor and support rub impact causing system parts failure. Still Increasing the accuracy of manufacturing and decreasing the clearance of supports but the probability of rub impact between the rotor and support grows and this phenomenon is going to be more critical. This research would rub impact at two ends of four degrees of freedom Jeffcott rotor considering supports directional degree of freedom. Because the contact points are at two ends of the rotor, the rotational degree of freedom of the rotor is also considered. The system is modeled with 8-DOF and after numerical solving and comparison, the results with other papers, the system's behavior including...
Vibration Modeling and Stability of Two Rigid Rotors Under the Influence of Internal Friction Caused by Slip on the Contact Surface of the Shrink-fit Connection
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Ruhollah (Supervisor)
Abstract
In this study, the modeling of shrink-fit connection was performed by considering the effect of friction on the connection. The behavior of a beam with shrink-fit connection was compared with the results of Adams software and the modeling accuracy was shown. Using both energy and Newton methods, the equations of motion of a rigid rotor consisting of two shafts connected by shrink-fit connection were obtained and the dynamic behavior of the rotor was investigated. Finally, the coupling parameters affecting the vibrations and stability of this rotor were introduced and the effect of each on the system behavior was shown.
Low voltage ride-through capability improvement of DFIG-based wind turbines under unbalanced voltage dips
, Article International Journal of Electrical Power and Energy Systems ; Vol. 60,Issue , 2014 , pp. 82-95 ; ISSN: 01420615 ; Parniani, M ; Sharif University of Technology
Abstract
This paper proposes a competent and effective scheme to enhance the ride-through capability of DFIG-based wind turbines under unbalanced voltage dip conditions. The proposed method is realized through joint use of the rotor-side converter control and a three-phase stator damping resistor (SDR) placed in series with the stator windings. By means of an asymmetrical SDR idea, during the unbalanced voltage dip the SDR resistors are activated only in phase(s) experiencing low voltage. Then, the rotor current is controlled such that no unbalance voltage appears on the stator voltage. The proposed ride-through approach limits the peak values of the rotor inrush current, electromagnetic torque and...
Experimental study of parameters affecting the nusselt number of generator rotor and stator
, Article Heat Transfer Engineering ; Volume 31, Issue 3 , 2010 , Pages 243-249 ; 01457632 (ISSN) ; Nili Ahmadabadi, M ; Hashemi, A ; Sharif University of Technology
2010
Abstract
In this research, the parameters affecting the Nusselt number of a generator rotor and stator under varying heat transfer rate are experimentally studied. In spite of the stator having no grooves, the rotor has four large triangular grooves. The temperature and then heat transfer rate of the rotor and stator are experimentally measured in three longitudinal and two angular positions. First, the effect of axial Reynolds number and rotor rotational speed on the rotor and stator Nusselt number with constant heat transfer rate ratio is studied. The range of the axial Reynolds number and rotational speed used is from 4000 to 30,000 and from 300 to 1500 rpm, respectively. Next, the effect of...