Noise and Vibration Originated From UMF due to Rotor Eccentricity of the HDD Spindle System

2013 ◽  
Author(s):  
S. J. Sung ◽  
G. H. Jang ◽  
K. J. Kang
Keyword(s):  
Degrees Of Freedom ◽  
Acoustic Noise ◽  
Fluid Dynamic ◽  
Rotating Disk ◽  
Spindle Motor ◽  
Noise And Vibration ◽  
Spindle System ◽  
Cogging Torque ◽  
Outer Rotor ◽  
Numerical And Analytical Methods

Cogging torque and UMF (unbalanced magnetic force) are major excitation sources of acoustic noise and vibration originated from HDD spindle motors. They are generally outer rotor type motors with fluid dynamic bearings (FDBs). The FDBs support and constrain the rotating disk-spindle system in five degrees of freedom except axial rotating direction. Unbalanced mass of the disk-spindle system generates whirling motion and changes the characteristics of UMF. Several researchers have investigated the harmonic contents of cogging torque and UMF by numerical and analytical methods [1]–[3]. Lee and Jang [4] experimentally and numerically investigated the characteristics of the UMF of a HDD spindle motor due to manufacturing errors such as the uneven magnetization of permanent magnet (PM) and the eccentricity of rotor and stator. However, they discussed only the cogging torque and UMF, and did not investigate the effect of the cogging torque and UMF on acoustic noise and vibration of a HDD spindle system.

Effect of an Hourglass-Shape Tapered Sleeve on the Performance of the Fluid Dynamic Bearings of a HDD Spindle Motor

2013 ◽  
Author(s):  
J. H. Lee ◽  
M. H. Lee ◽  
G. H. Jang
Keyword(s):  
Rough Surface ◽  
Fluid Dynamic ◽  
Dynamic Performance ◽  
Rotating Disk ◽  
Groove Depth ◽  
Spindle Motor ◽  
Spindle System ◽  
Thrust Bearings ◽  
Steel Sleeve ◽  
Bearing Ball

Fluid dynamic bearings (FDBs) of a HDD spindle motor support the rotating disk-spindle system through the pressure generated in the fluid lubricant. The radial and axial clearances of a 2.5″ HDD spindle motor are approximately 2 and 30 micro-meters, respectively, and herringbone or spiral grooves are inscribed in the sleeve of journal or thrust bearings to provide pumping pressure. One of the difficult manufacturing processes is to inscribe uniform grooves, especially groove depth in the range of several micro meters. Grooves are inscribed on the surface of the stainless steel sleeve by the electro chemical machining (ECM) which generally generates rough surface of the sleeve in grooved bearing. Ball-sizing process is used to scrape down rough surface. When a ball passes through the sleeve of FDBs to make rough surface smooth, compressive pressure is generated between ball and sleeve inlet and between ball and sleeve outlet, respectively. It forms an hourglass-shape tapered sleeve as shown in Figure 1, and tapered sleeve generally decreases the static and dynamic performance of the FDBs and the HDD spindle system, consequently.

scholarly journals Model forB1Imaging in MRI Using the Rotating RF Field

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Adnan Trakic ◽  
Jin Jin ◽  
Ewald Weber ◽  
Stuart Crozier
Keyword(s):  
Degrees Of Freedom ◽  
Acoustic Noise ◽  
Bloch Equation ◽  
Gradient Coil ◽  
Imaging Method ◽  
Nonuniform Field ◽  
Rf Coil ◽  
Image Encoding ◽  
Magnetic Resonance Imaging Mri ◽  
Space Requirements

Conventionally, magnetic resonance imaging (MRI) is performed by pulsing gradient coils, which invariably leads to strong acoustic noise, patient safety concerns due to induced currents, and costly power/space requirements. This modeling study investigates a new silent, gradient coil-free MR imaging method, in which a radiofrequency (RF) coil and its nonuniform field (B1+) are mechanically rotated about the patient. The advantage of the rotatingB1+field is that, for the first time, it provides a large number of degrees of freedom to aid a successfulB1+image encoding process. The mathematical modeling was performed using flip angle modulation as part of a finite-difference-based Bloch equation solver. Preliminary results suggest that representative MR images with intensity deviations of <5% from the original image can be obtained using rotating RF field approach. This method may open up new avenues towards anatomical and functional imaging in medicine.

scholarly journals Hydrodynamic limits of kinetic equations for polyatomic and reactive gases

2017 ◽  
Vol 8 (1) ◽  
pp. 23-42 ◽  
Author(s):  
M. Bisi ◽  
G. Spiga
Keyword(s):  
Degrees Of Freedom ◽  
Continuum Limit ◽  
Fluid Dynamic ◽  
Energy Levels ◽  
Kinetic Equations ◽  
Navier Stokes ◽  
Bgk Model ◽  
Hydrodynamic Limits ◽  
Stress Diffusion ◽  
Reactive Gases

Abstract Starting from a kinetic BGK-model for a rarefied polyatomic gas, based on a molecular structure of discrete internal energy levels, an asymptotic Chapman-Enskog procedure is developed in the asymptotic continuum limit in order to derive consistent fluid-dynamic equations for macroscopic fields at Navier-Stokes level. In this way, the model allows to treat the gas as a mixture of mono-atomic species. Explicit expressions are given not only for dynamical pressure, but also for shear stress, diffusion velocities, and heat flux. The analysis is shown to deal properly also with a mixture of reactive gases, endowed for simplicity with translational degrees of freedom only, in which frame analogous results can be achieved.

Fluid dynamic bearing for HD-DVD single-phase spindle motor

2003 ◽  
Author(s):  
Hung-Kuang Hsu ◽  
Chien-Chang Wang ◽  
Mei-Lin Lai ◽  
Yu-Hsiu Chang ◽  
Der-Ray Huang
Keyword(s):  
Single Phase ◽  
Fluid Dynamic ◽  
Spindle Motor ◽  
Fluid Dynamic Bearing

Commercialization of Active Isolation for Jet Aircraft

1997 ◽  
Author(s):  
Steve C. Southward ◽  
Douglas E. Ivers ◽  
Geoff C. Nicholson
Keyword(s):  
Control System ◽  
Vibration Control ◽  
Acoustic Noise ◽  
Development Program ◽  
Flight Test ◽  
Test Time ◽  
Vibration Source ◽  
Noise And Vibration ◽  
Transmission Path ◽  
Active Isolation

Abstract Active Noise and Vibration Control (ANVC) technology is a proven solution for noise and vibration problems in aircraft. The challenges in commercializing this solution range from the development issues of choosing the best actuation, sensor, and control technology to obtaining sufficient flight test time and satisfying FAA requirements. This paper examines significant case histories in the progression of the Lord active vibration control program from conception to market. Throughout the development program, several important discoveries were made regarding the performance, reliability, and economics of Active Isolation Systems (AIS) in jet aircraft. First, practical speaker-based solutions cannot achieve global acoustic noise cancellation for engine tones above about 200 Hz. A comparatively small array of structural actuators placed in the dominant transmission path, such as in or near the engine mounts, are capable of global cancellation in the cabin up to at least 500 Hz. Second, the performance is generally better when cabin microphones are used as error sensor inputs because the AIS control system can compensate for flanking paths better than if accelerometers are used as error sensors. Third, when the actuators are placed in the dominant transmission path and close to the vibration source, the control system will simultaneously achieve global acoustic noise reduction in the cabin and vibration reduction in the aircraft structure without affecting the engine casing vibration levels.

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