End Leakage Research Articles

Magnetic End Leakage Flux in a Spoke Type Rotor Permanent Magnet Synchronous Generator

The spoke type rotor can be used to obtain magnetic flux concentration in permanent magnet machines. This allows the air gap magnetic flux density to exceed the remanent flux density of the permanent magnets but gives problems with leakage fluxes in the magnetic circuit. The end leakage flux of one spoke type permanent magnet rotor design is studied through measurements and finite element simulations. The measurements are performed in the end regions of a 12 kW prototype generator for a vertical axis wind turbine. The simulations are made using three dimensional finite elements to calculate the magnetic field distribution in the end regions of the machine. Also two dimensional finite element simulations are performed and the impact of the two dimensional approximation is studied. It is found that the magnetic leakage flux in the end regions of the machine is equal to about 20% of the flux in the permanent magnets. The overestimation of the performance by the two dimensional approximation is quantified and a curve-fitted expression for its behavior is suggested.

A Spoke-Type IPM Machine With Novel Alternate Airspace Barriers and Reduction of Unipolar Leakage Flux by Step-Staggered Rotor

This paper proposes a spoke-type interior permanent magnet (IPM) machine with novel alternate airspace barriers, through which higher torque capability and better manufacturability can be obtained, without remarkable deterioration in mechanical strength. Further, the influence of end leakage flux in the novel IPM design is investigated by three-dimensional finite element method, including the leakage flux characteristics and torque capability. Furthermore, a step-staggered rotor is proposed to reduce the unipolar leakage flux and magnetization of the end shaft. As an extension, unipolar leakage flux is further investigated in consequent-pole PM machines, as well as the validity of step-staggered method. Finally, prototypes are fabricated and tested to verify the foregoing analyses, including the magnetic field at the end shaft and the output capability.

SU-F-T-366: Dosimetric Parameters Enhancement of 120-Leaf Millennium MLC Using EGSnrc and IAEA Phase-Space Data

Purpose: Recently, the multileaf collimators (MLC) have become an important part of any LINAC collimation systems because they reduce the treatment planning time and improves the conformity. Important factors that affects the MLCs collimation performance are leaves material composition and their thickness. In this study, we investigate the main dosimetric parameters of 120-leaf Millennium MLC including dose in the buildup point, physical penumbra as well as average and end leaf leakages. Effects of the leaves geometry and density on these parameters are evaluated Methods: From EGSnrc Monte Carlo code, BEAMnrc and DOSXYZnrc modules are used to evaluate the dosimetric parameters of a water phantom exposed to a Varian xi for 100cm SSD. Using IAEA phasespace data just above MLC (Z=46cm) and BEAMnrc, for the modified 120-leaf Millennium MLC a new phase space data at Z=52cm is produces. The MLC is modified both in leaf thickness and material composition. EGSgui code generates 521ICRU library for tungsten alloys. DOSXYZnrc with the new phase space evaluates the dose distribution in a water phantom of 60×60×20 cm3 with voxel size of 4×4×2 mm3. Using DOSXYZnrc dose distributions for open beam and closed beam as well as the leakages definition, end leakage, average leakage and physical penumbra are evaluated. Results: A new MLC with improved dosimetric parameters is proposed. The physical penumbra for proposed MLC is 4.7mm compared to 5.16 mm for Millennium. Average leakage in our design is reduced to 1.16% compared to 1.73% for Millennium, the end leaf leakage suggested design is also reduced to 4.86% compared to 7.26% of Millennium. Conclusion: The results show that the proposed MLC with enhanced dosimetric parameters could improve the conformity of treatment planning.

TU-FG-201-02: Is Weekly MLC QA Necessary? Two Year EPID-Based Weekly MLC QA Experience at the University of Maryland

Purpose: Appropriate MLC QA is important to assure treatment accuracy. In addition to the TG-142 recommended picket fence test, our institution performs four MLC tests on a weekly basis. The purpose of this study was to evaluate the clinical necessity of our weekly MLC QA program after a two-year run. Methods: Our Weekly MLC QA tests: 1) MLC positioning; 2) Interdigitation for testing hard MLC motion; 3) Picket fence at static gantry angle; 4) Leaf-end leakage and 5) dose match between a VMAT plan and the same plan with static-gantry-sliding window. For this study, a total of 794 Weekly MLC QA plans using EPID systems (3878 in total) for 10 machines from June 2014 to February 2016 were analyzed. Failure Mode Effect Analysis (FMEA) was performed with five failure modes. For each failure mode, a risk probability number (RPN) was calculated for a Weekly MLC QA (Monthly + Weekly) and for a Monthly MLC QA Only scheme. The probability of occurrence was evaluated from the Weekly QA experience. Results: Total number of failures for 794 cases were 24 (0.23%, for MLC Position test, 0.11% for Interdigitation test, 0.11% for Picket Fence Test, 0% for Leaf end Leakage test and 2.5% for VMAT test). The QA goal was to maintain the RPN score < 125. The RPN scores for the Monthly MLC QA Only ranged from 144–180, while those with Weekly (Monthly + Weekly) MLC QA decreased to 96–120. Conclusion: The Weekly MLC QA decreased the RPN numbers to the desired level (RPN<125), while those from the program of Monthly QA only were found to be higher or borderline. This objectively proves the clinical necessity for comprehensive weekly MLC QA.

Investigation of the Transient Inductance for a Pulsed Alternator With Fully Passive Compensation

The passively compensated pulsed alternator (PCPA) is one of the most competitive pulsed power technologies for future electromagnetic launcher systems. The PCPA is mostly designed for the high pulse repetition frequency military applications, such as the railgun, coilgun, and electrothermal chemical gun. The PCPA is a high-energy and high-power (sub-GW) electrical synchronous generator operating in a fast-transient, short-pulse regime. Due to its low internal impedance during the discharge, the pulsed alternator is capable of extremely high output current, almost two orders of magnitude higher than similar rotating synchronous generators of the same size. This paper has investigated the transient inductance of the armature winding of a PCPA, including the internal inductance and the end leakage inductance. A novel method is proposed to decrease the end leakage inductance in which the end windings are surrounded by totally enclosed conductive shields settled at the stator ends. The analytic formulas of the internal inductance and the end leakage inductance are deduced using the magnetic vector potential method. The concept of end winding shielding can be generalized to other types of compensated pulsed alternators, such as the selective PCPAs and actively compensated pulsed alternators.

Analytical Algorithm for Strand End Leakage Reactance of Transposition Bar in AC Machine

Calculation of circulating current in transposition bars is the key problem in the design of stator windings, which will determine the transposition type of stator windings. The circuit equation method, in which the calculation of strand end leakage reactance in transposition bars is the premise, is widely used in engineering to calculate circulating current. This paper describes an analytical algorithm for the calculation of strand end leakage reactance in transposition bars, which is based on mirror image principle. The end leakage reactance of strands in transposition bar is calculated by the integral of transposition path discretized into many key points. Contrary to the existing calculation method, the analytical algorithm proposed in this paper is a general method for calculating the end leakage reactance, which can simulate the transposition path of strands in the end region for different transposition types. In order to validate the proposed method, the end coil self and mutual leakage reactance are calculated by proposed analytical algorithm and finite element method.

Influence of Underexcitation Operation on Electromagnetic Loss in the End Metal Parts and Stator Step Packets of a Turbogenerator

The leading operation of large generators is an effective method to adjust the electric reactive power surplus, and the leading-power factor was restricted by the temperature rise of the end parts. In this paper, a three-dimensional (3-D) electromagnetic field of a 330-MW water-hydrogen-hydrogen-cooled turbogenerator in the end region was investigated, and the effect of end leakage magnetic flux on stator step packets was considered in the calculation process. The magnetic flux density distribution was analyzed, and the eddy current losses of metal parts in the end region and core losses of stator step packets were calculated under lagging and leading operations. The influences of the leading-power factor on the losses of end components were analyzed, which could provide a theoretical basis for the safety of the leading operation.

SU‐E‐T‐430: Modeling MLC Leaf End in 2D for Sliding Window IMRT and Arc Therapy

Purpose:To develop a 2D geometric model for MLC accounting for leaf end dose leakage for dynamic IMRT and Rapidarc therapy.Methods:Leaf‐end dose leakage is one of the problems for MLC dose calculation and modeling. Dosimetric leaf gap used to model the MLC and to count for leakage in dose calculation, but may not be accurate for smaller leaf gaps. We propose another geometric modeling method to compensate for the MLC round‐shape leaf ends dose leakage, and improve the accuracy of dose calculation and dose verification. A triangular function is used to geometrically model the MLC leaf end leakage in the leaf motion direction, and a step function is used in the perpendicular direction. Dose measurements with different leaf gap, different window width, and different window height were conducted, and the results were used to fit the analytical model to get the model parameters.Results:Analytical models have been obtained for stop‐and‐shoot and dynamic modes for MLC motion. Parameters a=0.4, lw' =5.0 mm for 6X and a=0.54, lw' =4.1 mm for 15x were obtained from the fitting process. The proposed MLC leaf end model improves the dose profile at the two ends of the sliding window opening. This improvement is especially significant for smaller sliding window openings, which are commonly used for highly modulated IMRT plans and arc therapy plans.Conclusion:This work models the MLC round leaf end shape and movement pattern for IMRT dose calculation. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation and verification.

Numerical analysis of spiral oil wedge sleeve bearing including cavitation and wall slip effects

AbstractThe modified Reynolds equation is established on the basis of critical shear stress model, in which the circumferential and axial wall slip of sleeve and journal surface is considered. Cavitation is treated using modified Elrod algorithm that simplifies the solution of modified Reynolds equation in the full‐film region. The modified Reynolds equations considering wall slip and cavitation effect for two‐dimensional sleeve bearing are established. The results show that wall slip decreases oil film pressure, carrying capacity, friction drag and temperature rise but increases end leakage and cavitation region. The obtained results using the mass‐conserving boundary condition are compared with the Reynolds boundary condition. Copyright © 2014 John Wiley &amp; Sons, Ltd.

An Analytical Model for Leakage Effect in the Electrical Generator of Rim-Driven Marine Current Power System

This paper presents an equivalent magnetic circuit model to predict the leakage effect, especially the end leakage effect, of surface-mounted permanent magnet synchronous machine (SPMSM) in rim-driven marine current power (RMCP) system. The end leakage effect is usually neglected in most conventional permanent magnet (PM) machines. However, it is significant in the electrical generator of RPCM due to the short axial length. The idealized path and analytical expressions of end leakage permeance are given in this paper. Finite Element Method (FEM) 3D/2D and experimental values are presented to validate the proposed analytical model. With no need for the time-consuming FEM-3D calculation, a correction factor base on the analytical mode is proposed to adjust the results (e.g. back-EMF, torque) of conventional design when end leakage is ignored in the calculation. The calculation results and experimental values show that the proposed analytical model is accurate to analyze the leakage effects of SPMSM in RMCP system.

Analytical Calculation of Slotless Permanent Magnet Motor Based on Soft Ferrite

High-speed slotless permanent magnet brushless motor based on soft ferrite adopts a large effective air gap structure. For the large effective air-gap, the air-gap flux distribution becomes uneven and the end leakage flux significantly increases. Thus, the traditional analytical method of the phase EMF is inapplicable. This paper deduces the analytical expression of the phase EMF based on the analytical calculation of the air-gap field and analyzes the distribution of the end leakage flux by 3D finite elements methods. Then the end leakage flux is considered by a correction factor of the core length. Finally the analytical calculation method is proved to be feasible by the comparison between the finite elements results and the prototype test results.

SU‐E‐T‐380: Modeling MLC Leaf End in 2D for Sliding Window IMRT and Arc Therapy

Purpose: To develop a 2D geometric model for MLC accounting for leaf end dose leakage for IMRT and arc therapy. Methods: Leaf‐end dose leakage is one of the problems for MLC dose calculation and modeling. Dosimetric leaf gap used to model the MLC and to count for leakage in dose calculation, but may not be accurate for smaller leaf gaps. We propose another geometric modeling method to compensate for the MLC round‐shape leaf ends dose leakage, and improve the accuracy of dose calculation and dose verification. A triangular function is used to geometrically model the MLC leaf end leakage in the leaf motion direction, and a step function is used in the perpendicular direction. Dose measurements with different leaf gap, different window width, and different window height were conducted, and the results were used to fit the analytical model to get the model parameters. Results: Analytical models have been obtained for stop‐and‐shoot and dynamic modes for MLC motion. Parameters a=0.4, lw=5.0 mm for 6X and a=0.54, lw=4.1 mm for 15x were obtained from the fitting process. The proposed MLC leaf end model improves the dose profile at the two ends of the sliding window opening. This improvement is especially significant for smaller sliding window openings, which are commonly used for highly modulated IMRT plans and arc therapy plans. Conclusion: This work models the MLC round leaf end shape and movement pattern for IMRT dose calculation. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation and verification.

Analysis of static and dynamic performance characteristics of THD journal bearing operating under lubricants containing nanoparticles

In this paper, the static and dynamic performance characteristics of journal bearing in terms of load capacity, attitude angle, end leakage, frictional force, threshold speed and damped frequency are presented when the bearing operating under lubricants, which contain nanoparticles and viscosity of these lubricants varies with temperature. The nanoparticles used for the present work are copper oxide (CuO), cerium oxide (CeO2) and aluminum oxide (Al2O3). Viscosity models for the lubricants are developed with the available experimental data. The modified Reynolds and energy equations are used to obtain pressure and temperature distribution across the lubricant film and these equations are solved by using the finiteelement method and a direct iteration scheme. The static and dynamic performance characteristics of journal bearing are computed for various values of eccentricity ratios for isoviscous and thermoviscous lubricants. The computed results show that in isoviscous case, addition of nanoparticles does not change performance characteristics considerably but in thermoviscous case, changes are significant.

Comparative performance of squeeze film air journal bearings made of aluminium and copper

Two tubular squeeze film journal bearings, made from Al 2024 T3 and Cu C101, were excited by driving the single-layer piezoelectric actuators at a 75-V AC with a 75-V DC offset. The input excitation frequencies were coincident with the 13th modal frequency, at 16.32 and 12.18 kHz for the respective Al and Cu bearings, in order to produce a ‘triangular’ modal shape. The paper also provided a CFX model, used to solve the Reynolds equation and the equation of motion, to explain the squeeze film effect of an oscillating plate with pressure end leakage. The dynamic characteristics of both bearings were studied in ANSYS and then validated by experiments with respect to their squeeze film thickness and load-carrying capacity. It was observed that whilst both bearings did levitate a load when excited at mode 13, the Al bearing showed a better floating performance than Cu bearing. This is due to the fact that the Al bearing had a higher modal frequency and a greater amplitude response than the Cu bearing.

The numerical analysis of the radial sleeve bearing with combined surface slip

In order to improve the carrying capacity and reduce the temperature rise in high speed and precise spindle systems, a combined surface radial sleeve bearing using the interfacial slip technique was discussed. An extended Reynolds equation was derived based on the modified slip length model considering the limiting shear stress. By means of the finite differential methods, the characteristic analysis and optimization of the slip region of the combined surface sleeve bearing were carried out, and it has been proved that there is still a considerable large load support in a parallel sliding gap. Comparing with the general journal bearing, the load capacity and end leakage rate of the combined surface sleeve bearing can be increased greatly and the load capacity can be increased by 1.75 times. The attitude angle, friction drag, temperature rise of the combined bearing can be decreased distinctly and the temperature rise can be decreased by 92.4%.

Effect of nanoparticles additives on the performance of an externally adjustable fluid film bearing

This paper presents the effect of CuO, TiO 2 and Nano-Diamond nanoparticles additives in API-SF engine oil, on static characteristics of an externally adjustable fluid-film bearing. Modified form of Reynolds equation is solved numerically for various simulated operating conditions. Static characteristics evaluated are in terms of load carrying capacity, end leakage and friction. This study predicts that, a bearing having negative radial and negative tilt adjustments, and operating with API-SF engine oil blended particularly with TiO 2 nanoparticles, results in better load capacity with reduced end leakage and increased friction, as compared to API-SF engine oil and Base oil without nanoparticle additives.

Levitation characteristics of a squeeze-film air journal bearing at its normal modes

A tubular squeeze-film journal bearing was designed such that it flexed its shell at its normal modes producing a triangular modal shape. The shell motion was created by a single-layer piezoelectric actuator powered at 75 V AC with a 75 V DC offset and the driving frequency coincided with the modal frequency of the bearing. The paper provided a theory that shows the existence of a positive pressure in a squeeze film responsible for the levitation phenomenon. The various modes of vibration of the tubular bearing, made from AL2024-T3, were obtained from a finite element model implemented in ANSYS. Two normal modes, the 13th and 23rd, at the respective theoretical frequencies of 16.37 and 25.64 kHz, were identified for further investigation by experiments with respect to the squeeze-film thickness and its load-carrying capacity. While the bearing at both modes could cause levitation, the 13th mode has a greater load-carrying capacity because its modal shape produced a much lower end leakage.

Effect of turbulence on the static performance of a misaligned externally adjustable fluid film bearing lubricated with couple stress fluids

Static analysis of a misaligned externally adjustable fluid-film bearing is carried out thereby including turbulence and couple-stress effects in lubricants blended with polymer additives. A modified form of Reynolds equation, incorporated with the theory of micro-continuum and the concept of adjustability, is solved numerically, for various simulated operating conditions. The effects of turbulence and couple-stress on key performance parameters are presented. This study predicts that, an externally adjustable fluid-film journal bearing operating with negative adjustment configuration and lubricants with couple-stress, results in superior load carrying capacity with reduced friction and end leakage, as compared to a conventional partial arc bearing.

Research on the Effect of Whole Cylinder Block on EHL Performance of Main Bearings Considering Crankshaft Deformation for Internal Combustion Engine

In this paper, the analyses of elastohydrodynamic lubrication (EHL) of crankshaft bearings considering the deformation of the whole cylinder block and crankshaft under load were carried out for the crankshaft bearing system of a four-stroke four-cylinder internal combustion engine. The lubrication of crankshaft bearing was analyzed by dynamic method. The deformation of bearing surface under pressure of oil film was calculated by compliance matrix method. The results show that when the crankshaft deformation under load is considered, compared with the results of not considering the deformation of cylinder block, the maximum film pressure decreases, the minimum film thickness increases, and the end leakage flow-rate and frictional coefficient of journal surface change little in an engine working cycle when considering the deformation of cylinder block. The models of the whole cylinder block and the single main bearing housing were used, respectively, to calculate the deformation of main bearing surface in the analyses. The results show that the calculation accuracy of the elastohydrodynamic lubrication analyses of crankshaft main bearings can be met basically by applying the simple model based on the single main bearing housing to calculate the elastic deformation of main bearing surface.

Thermohydrodynamic Lubrication Analysis of Misaligned Plain Journal Bearing With Rough Surface

Journal misalignment exists generally in journal bearings. When severe journal misalignment takes place, the minimum film thickness of journal bearings reduces greatly. In this condition, the surface roughness, the oil viscosity-pressure relationship (VPR), and the thermal effect have obvious effects on hydrodynamic lubrication performance of misaligned bearings. In this paper, the oil film pressure, oil film temperature, load-carrying capacity, end leakage flow rate, frictional coefficient, and misalignment moment of a journal bearing with different angles of journal misalignment and surface roughness, and considering oil VPR and thermal effect, were calculated based on the generalized Reynolds equation, energy equation, and solid heat conduction equation. The results show that the oil VPR and surface roughness have a significant effect on the lubrication of misaligned journal bearings under large eccentricity ratio. The thermal effect will affect obviously the lubrication of misaligned journal bearings when eccentricity ratio and angle of journal misalignment are all large. In the present design, the size of the journal bearing is compact more and more, and the eccentricity ratio and angle of journal misalignment are usually large in operating conditions. Therefore, it is necessary to take the effects of journal misalignment, surface roughness, oil VPR, and thermal effect into account in the design and analyses of journal bearings.