Dynamics of a hydropower generator subjected to unbalanced magnetic pull

2011 ◽  
Vol 225 (9) ◽  
pp. 2076-2088 ◽  
Author(s):  
Y Calleecharan ◽  
J-O Aidanpää
Keyword(s):  
Periodic Motion ◽  
Critical Speed ◽  
Radial Component ◽  
Electrical Machines ◽  
External Forcing ◽  
New Model ◽  
Unbalanced Magnetic Pull ◽  
Wide Range ◽  
Jeffcott Rotor ◽  
Rotor Model

Eccentricity leading to unbalanced magnetic pull (UMP) in electrical machines is a significant concern in industry. The UMP is known to be composed of two components: a radial component and a tangential one. Models that are used in industry tend to include the radial component alone. In this article, a Jeffcott rotor model together with a new UMP model that incorporates both radial and tangential UMP constituents is studied for an industrial hydropower generator. Characterizing the UMP as springs permits the model to inherit UMP stiffness contribution. Interesting dynamics are observed with the new model for a wide range of external forcing frequencies. It is shown firstly that the new UMP model is sensitive to forcing frequency in the rotor movements. Secondly, it is found that this sensitivity to forcing frequency increases with decreasing rotor system stiffness. Moreover, quasi-periodic motion in the rotor displacements is observed and it is noted that the rotor does not need to be forced by frequencies above its critical speed for this less desirable motion to occur. Thus, it becomes interesting to be able to account for the UMP stiffness contribution in order to curb machine malfunction which might result from these UMP forces.

The Limited-Torque Acceleration Through Critical Speed Phenomenon in Rotating Machinery

2012 ◽  
Author(s):  
Anand Srinivasan ◽  
Trent W. Thurston
Keyword(s):  
Critical Speed ◽  
Equations Of Motion ◽  
Drive Train ◽  
Transient Solution ◽  
Acceleration Rate ◽  
Jeffcott Rotor ◽  
Full Speed ◽  
Lateral Displacements ◽  
Design Speed ◽  
Rotor Model

Rotor-bearing systems of modern day turbomachinery are generally designed to operate at speeds well above the lateral critical speed(s). Acceleration from rest to design speed of turbomachines is usually accomplished by a driver such as a motor or a turbine. The driver provides the torque required to bring the drive-train to full speed. If the torque delivered by the driver is less than the torque demanded by the driven machine, the drive-train stalls at a speed below running speed. If this speed coincides with a lateral critical speed of the turbomachine, the amplitude of vibration may increase to levels high enough to trip the machine. In extreme cases, damage due to rubs from vibration excursions may occur on the rotating components. Such a phenomenon is referred to as a limited-torque-acceleration of rotors through the critical speed. A theoretical analysis of this phenomenon requires a time-transient solution of the lateral equations of motion, with the acceleration rate determined from the torque equation. In this paper, the acceleration of the Jeffcott rotor model with a variable torque input has been studied, and the time-transient response of the shaft lateral displacements has been presented. Data recorded from a turbomachine that incurs vibration excursions during limited-torque acceleration through critical speed has also been presented. The importance of fast acceleration rates through critical speeds for rotating equipment has been stressed in this paper.

Interrogating the Lead-up to a Critical Speed in Rotordynamics

2021 ◽  
pp. 1-18
Author(s):  
Lawrie Virgin
Keyword(s):  
Critical Speed ◽  
Stress Test ◽  
Equations Of Motion ◽  
Rotating Shaft ◽  
Small Perturbations ◽  
New Approach ◽  
Naturally Occurring ◽  
Jeffcott Rotor ◽  
Random Disturbances ◽  
Rotor Model

Abstract This paper presents a new approach to predicting an incipient critical speed in a rotating shaft. Based on the classical governing equations of motion for an eccentric mass on a flexible shaft (the Jeffcott rotor model), the approach is centered on examining the behavior of small perturbations or random disturbances to infer the approach of a critical speed (resonance). Such disturbances, that may be based on intentional probing, or simply the result of naturally occurring fluctuations, cause small transients. It is the changing nature of these transients (as characterized by their associated eigenvalues) that is used to assess the proximity to a critical speed. In this paper the material developed is based on analysis, but generating the data from simulations or experiments will be the next step. The approach is a kind of stress-test, conceptually not dissimilar to structural health monitoring and damage detection, but here directed toward the lead-up to resonance.

scholarly journals Effciency of an Electrical Machine in Electric Vehicle Application

2016 ◽  
Vol 11 (1) ◽  
pp. 20-29 ◽  
Author(s):  
S. B. Shah ◽  
B. Silwal ◽  
A. Lehikoinen
Keyword(s):  
Electric Vehicle ◽  
Standard Method ◽  
Operating Cost ◽  
Electrical Machines ◽  
Electrical Machine ◽  
Test Machine ◽  
Current Component ◽  
Element Analysis ◽  
Voltage Drops ◽  
Wide Range

Machines have always made life simpler, directly or indirectly. They have been developed for a very wide range of applications. For the per- formance analysis of any machine, one important parameter to be considered is the machine loss. This consideration has signifcances like determining the effciency of the machine which in turn infuences the operating cost, determining the heating of machine and for accounting the voltage drops or current component associated with the cause of the losses and many more. Losses in electrical machines can be categorized according to the causes or phenomena that produce them. The effciency of an electrical machine directly depends on different kind of losses in the machine. Therefore, in this paper we primarily focus on the losses in the machine. First, all possible losses, their causes and effects in an electrical machine have been explained. A brief account of calculating those losses has also been explained. The standard method of calculating the effciency follows after that. Finally, a fnite element analysis is performed for a test machine and the losses and the effciency of the test machine is stud- ied. Journal of the Institute of Engineering, 2015, 11(1): 20-29 

Stability-Optimized Clearance Configuration of Fluid-Film Bearings

2006 ◽  
Vol 129 (1) ◽  
pp. 106-111 ◽  
Author(s):  
Koichi Matsuda ◽  
Shinya Kijimoto ◽  
Yoichi Kanemitsu
Keyword(s):  
Fourier Series ◽  
Load Capacity ◽  
Fluid Film ◽  
Eccentricity Ratio ◽  
Rotating Speed ◽  
Fluid Film Bearings ◽  
Wide Range ◽  
Jeffcott Rotor ◽  
The Stability ◽  
Frequency Ratios

The whirl instability occurs at higher rotating speeds for a full circular fluid-film journal bearing, and many types of clearance configuration have been proposed to solve this instability problem. A clearance configuration of fluid-film journal bearings is optimized in a sense of enhancing the stability of the full circular bearing at high rotational speeds. A performance index is chosen as the sum of the squared whirl-frequency ratios over a wide range of eccentricity ratios, and a Fourier series is used to represent an arbitrary clearance configuration of fluid-film bearings. An optimization problem is then formulated to find the Fourier coefficients to minimize the index. The designed bearing has a clearance configuration similar to that of an offset two-lobe bearing for smaller length-to-diameter ratios. It is shown that the designed bearing cannot destabilize the Jeffcott rotor at any high rotating speed for a wide range of eccentricity ratio. The load capacity of the designed bearings is nearly in the same magnitude as that of the full circular bearing for smaller length-to-diameter ratios. The whirl-frequency ratios of the designed bearing are very sensitive to truncating higher terms of the Fourier series for some eccentricity ratio. The designed bearings successfully enhance the stability of a full circular bearing and are free from the whirl instability.

scholarly journals Professional characteristics of an educator: A survey of literature

2013 ◽  
Vol 25 (1) ◽  
pp. 1-22
Author(s):  
J. Anitha ◽  
R. Krishnaveni
Keyword(s):  
Student Outcome ◽  
Wide Scope ◽  
Review Of Literature ◽  
New Model ◽  
Professional Characteristics ◽  
Wide Range ◽  
Made In ◽  
Comprehensive Study

Literature has shown that various studies have dealt with different professional features of teaching and they have focused on one or few professional characteristics of educators. In spite of the immense amount of literature on educator characteristics, a comprehensive study that would encompass the vital professional characteristics of an educator in total is lacking. This has instigated the researcher to take up the study to identify the professional characteristics of an educator. An attempt was made in identifying the educators' characteristics using student outcome as a boundary criterion to select the characteristics from among several that are available in the literature. Therefore, a new model of professional characteristics of educators was proposed. This paper discusses in detail, the characteristics of a profession in general and the wide range of educator’s characteristics as studied in previous researches. The paper presents a wide scope for the models developed to be studied in depth to appreciate and investigate more about the professional characteristics identified through this review of literature. The models may also be tested empirically for further accumulation of knowledge in the field.

Dynamics and Stability of Partial Immersion Milling Operations

1999 ◽  
Author(s):  
M. X. Zhao ◽  
B. Balachandran ◽  
M. A. Davies ◽  
J. R. Pratt
Keyword(s):  
Hopf Bifurcation ◽  
Time Variation ◽  
Periodic Motion ◽  
Contact Time ◽  
Period Doubling ◽  
Experimental Investigations ◽  
Partial Immersion ◽  
Milling Operations ◽  
Wide Range ◽  
The Stability

Abstract In this paper, numerical and experimental investigations conducted into the dynamics and stability of partial immersion milling operations are presented. A mechanics based model is used for simulations of a wide range of milling operations and instabilities that arise due to regeneration and/or impact effects are studied. Poincaré sections are used to assess the stability of motions. The studies reveal that apart from Hopf bifurcation of a periodic motion, a period-doubling bifurcation of a periodic motion may also lead to chatter in partial immersion milling operations. Issues such as tooth contact time variation and structure of stability charts are also discussed.

Part A: Articles: A Non-Governmental Human Rights Strategy for Peacekeeping?

1996 ◽  
Vol 14 (2) ◽  
pp. 127-145
Author(s):  
Reinhard Marx
Keyword(s):  
Human Rights ◽  
Moral Dilemma ◽  
International Community ◽  
Human Rights Violations ◽  
Neutral Position ◽  
New Model ◽  
Wide Range ◽  
Human Rights Movement ◽  
Protection Of Human Rights ◽  
Domestic Jurisdiction

The human rights movement has never accepted that human rights belong to the domestic jurisdiction, but the new model of peacekeeping, which to some extent is based on a human rights component, causes severe problems for the movement, particularly because of its selectivity and its often biased implementation. This obstacle to an impartial combat against massive human rights violations and a wide range of other problems make it difficult for the movement to develop a consistent and plausible policy on peacekeeping. Although the international community may have good reasons to deploy soldiers in order to save lives and to bring an end to genocide, a supportive attitude by the human rights movement may jeopardise its principles of impartiality and non-violent campaigning and hence weaken the system of protection of human rights. But it has to be underscored that massive human rights violations will cause a moral dilemma for the movement if it cannot justify its neutral position on compelling grounds.

Extension of the Transfer Matrix Method for Rotordynamic Analysis to Include a Direct Representation of Conical Sections and Trunnions

1980 ◽  
Vol 102 (1) ◽  
pp. 122-129 ◽  
Author(s):  
M. S. Darlow ◽  
B. T. Murphy ◽  
J. A. Elder ◽  
G. N. Sandor
Keyword(s):  
Transfer Matrix ◽  
Cross Sections ◽  
Transfer Matrix Method ◽  
Matrix Method ◽  
Critical Speed ◽  
Axial Direction ◽  
Matrix Analysis ◽  
Beam Elements ◽  
Conical Section ◽  
Rotor Model

The transfer matrix method for rotordynamic analysis (alternately known as the HMP or LMP method) has enjoyed wide popularity due to its flexibility and ease of application. A number of computer programs are generally available which use this method in various forms to perform undamped critical speed, unbalance response, damped critical speed and stability analyses. For all of these analyses, the assembly of the transfer matrices from the rotor model is essentially the same. In all cases, the rotor model must be composed entirely of cylindrical beam elements. There are two situations when this limitation is not desirable. The first situation is when the rotor being modelled has one or more sections whose cross sections vary continually in the axial direction. The most common of these sections is the conical section. Presently, a conical section must be modelled as a series of “steps” of cylindrical sections. This adversely affects both the simplicity and accuracy of the rotor model. The second situation when current transfer matrix techniques are not accurate is when the rotor being modelled has one or more sections that do not behave as beam elements. The most common example is a trunnion which behaves as a plate. This paper describes the analytical basis and the method of application for direct representation of conical sections and trunnions for a transfer matrix analysis. Analytical results are currently being generated to demonstrate the need for and advantages of these modelling procedures.

scholarly journals On the Role of Nonsynchronous Rotating Damping in Rotordynamics

2000 ◽  
Vol 6 (6) ◽  
pp. 467-475 ◽  
Author(s):  
Giancarlo Genta ◽  
Eugenio Brusa
Keyword(s):  
General Model ◽  
Degrees Of Freedom ◽  
Dynamic Behaviour ◽  
System Parameters ◽  
Spin Speed ◽  
Rotating Systems ◽  
Jeffcott Rotor ◽  
The Stability ◽  
Rotor Model

Nonsynchronous rotating damping, i.e. energy dissipations occurring in elements rotating at a speed different from the spin speed of a rotor, can have substantial effects on the dynamic behaviour and above all on the stability of rotating systems.The free whirling and unbalance response for systems with nonsynchronous damping are studied using Jeffcott rotor model. The system parameters affecting stability are identified and the threshold of instability is computed. A general model for a multi-degrees of freedom model for a general isotropic machine is then presented. The possibility of synthesizing nonsynchronous rotating and nonrotating damping using rotor- and stator-fixed active dampers is then discussed for the general case of rotors with many degrees of freedom.

Application of the POD Method for Cracked Rotors

2017 ◽  
Author(s):  
Ayesha Al Mehairi ◽  
Mohammad A. AL-Shudeifat ◽  
Shadi Balawi ◽  
Adnan S. Saeed
Keyword(s):  
Covariance Matrices ◽  
Cracked Rotor ◽  
Force Vector ◽  
Highly Sensitive ◽  
Jeffcott Rotor ◽  
Unbalance Force ◽  
Proper Orthogonal ◽  
Integration Response ◽  
Cracked Rotor System ◽  
Rotor Model

The application of the proper orthogonal decomposition (POD) method to the vibration response of a cracked Jeffcott rotor model is investigated here. The covariance matrices of horizontal and vertical whirl amplitudes are formulated based on the numerical integration response and the experimental whirl response, respectively, for the considered cracked rotor system. Accordingly, the POD is directly applied to the obtained covariance matrices of the numerical and experimental whirl amplitudes where the proper orthogonal values (POVs) and the proper orthogonal modes (POMs) are obtained for various crack depths, unbalance force vector angles and rotational speeds. It is observed that both POVs and their corresponding POMs are highly sensitive to the appearance of the crack and the unbalance angle changes at the neighborhoods of the critical. The sensitivity zones of the POVs and POMs to the crack propagation coincide with the unstable zones of the cracked system obtained by Floquets theory.

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