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Robust Optimum Design of Thrust Hydrodynamic Bearings for Hard Disk Drives

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Applied Mathematics 2012年第10期3卷 1368-1379页

作者： Hiromu Hashimoto yuta sunami Department of Mechanical Engineering Tokai University Hiratsuka Japan

This paper describes the robust optimum design which combines the geometrical optimization method proposed by Hashimoto and statistical method. Recently, 2.5″ hard disk drives (HDDs) are widely used for mobile devices such as laptops, video cameras and car navigation systems. In mobile applications, high durability towards external vibrations and shocks are essentials to the bearings of HDD spindle motor. In addition, the bearing characteristics are influenced by manufacturing error because of small size of the bearings of HDD. In this paper, the geometrical optimization is carried out to maximize the bearing stiffness using sequential quadratic programming to improve vibration characteristics. Additionally, the bearing stiffness is analyzed considering dimensional tolerance of the bearing using statistical method. The dimensional tolerance is assumed to distribute according to the Gaussian distribution, and then the bearing stiffness is estimated by combining the expectation and standard deviation. As a result, in the robust optimum design, new groove geometry of bearing can be obtained in which the bearing stiffness is four times higher than the stiffness of conventional spiral groove bearing. Moreover, the bearing has lower variability compared with the result of optimum design neglecting dimensional tolerance.

关键词： Robust Optimum Design Hard Disk Drive Hydrodynamic Bearing Tolerance Statistical Method

Vibration Response Characteristics against the Radial and Axial Shocks on Small Size Hard Disk Drive Spindle Supported by Oil Film Bearings

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Journal of Mechanics Engineering and Automation 2014年第7期4卷 547-554页

作者： Masayuki Ochiai yuta sunami Hiromu Hashimoto Department of Mechanical Engineering Tokai University Kanagawa 259-1292 Japan

This paper describes the experimental study on shock response of FDB （fluid dynamic bearing） spindle for HDDs （hard disk drives）. The FDBs are widely used as rotating shaft support elements for HDD spindle motors. Recently, the opportunity for the HDD spindle motors exposed to external vibration has been increasing because the HDDs are used for various information related equipment such as mobile PCs （personal computers）, video cameras, car navigation systems and so on. Hence, the rotating shaft has a possibility to come in contact with the bearing by external shocks and it causes wear or seizure to the bearing surface. To avoid the problem, it is extremely important to know how the spindle moves against the large shock on HDDs experimentally. However, as far as the authors know, there are few experimental studies treating the shock response of HDD spindles. In this paper, firstly, we propose a new test rig and experimental method for shock response of FDB spindles. Then the shock tests against the radial and axial disturbance on FDB spindle for 2.5＂ HDD are conducted. Finally, the experimental results of shock response waveforms and maximum displacement of disk are shown.

关键词： Tribology fluid film bearing hard disk drive spindle motor shock test shock response

Identification Method of Dynamic Coefficients of Fluid Film Bearings for HDD Spindle Motors

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Journal of Mechanics Engineering and Automation 2014年第2期4卷 123-129页

作者： Masayuki Ochiai yuta sunami Hiromu Hashimoto Department of Mechanical Engineering Tokai University Hiratsuka 259-1292 Japan

Fluid film bearings are widely used as support elements of rotating shaft for HDD （hard disk drive） spindle motors. Recently, the opportunity for the HDD spindle motors exposed to external vibration has been increasing because the HDDs are used for various information related equipments such as mobile PCs, car navigation systems. Hence, the rotating shaft has a possibility to come in contact with the bearing and it causes wear or seizure to the bearing surface. In order to avoid the problems, it is extremely important to enhance the dynamic characteristics of the fluid film bearings for spindles. However, verification from both theory and experiment of dynamic characteristics such as spring coefficients and damping coefficients is rare and few. In this paper, the bearing vibration characteristics when the HDD spindle is oscillated are investigated theoretically and experimentally. And then the identification method ofoil film coefficients of fluid film bearing spindles is described.

关键词： Tribology fluid film bearing hard disk drive spindle motor dynamic coefficient vibration identification.

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Research in Astronomy and Astrophysics 2021年第5期21卷 43-70页

作者： yuta Ito Department of Physics The Graduate Center of CUNY365 Fifth AvenueNew YorkNY 10016USA Department of Physics and Astronomy The College of Staten Island of CUNY2800 Victory BoulevardStaten IslandNY 10314USA

Fitting parametric models to globular clusters’structural profiles has been essential for the study of stellar *** provides their important structural parameters,such as the concentrations and core radii of the ***,existing parametric models can apply only to non-collapsing-core clusters in the early relaxation-evolution ***,a single parametric model cannot provide globular clusters’structural parameters in both the early and late evolution *** have recently found an accurate spectral solution for the self-similar orbit-averaged Fokker-Planck(OAFP)equation to model collapsingcore clusters at the late evolution *** present work establishes a new parametric model by combining the self-similar OAFP-and *** it is a single-mass and isotropic model,the new model applies to at least fifty-five Galactic globular clusters with resolved cores in all the evolution *** a main result,we show the characteristics of the relaxation times against the concentrations of the *** also affirm that the structures of low-concentration clusters are polytropic in the Milky Way.

关键词： (Galaxy:)globular clusters:general Galaxy:kinematics and dynamics methods:numerical

Drag-reduction behavior of an unusual nonionic surfactant in a circular pipe turbulent flow

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Journal of Hydrodynamics 2014年第3期26卷 400-405页

作者：蔡书鹏 HIGUCHI yuta Institute of High Pressure Water Jet Hunan University of Technology Graduate School of Science and Technology Kobe University

The Alkyl Polyglucoside（APG） is a nonionic surfactant with no toxicity and with high biodegradability, its drag-reduction behavior in a circular pipe flow is measured, and the rheological characteristics are investigated with a rheometer with a cone-plate flow cell. From the measured results, the APG is shown to have a high drag-reduction capacity, whose shear viscosity is shear-ratedependent at high concentrations, while its solution at concentrations with drag-reduction effects is non-viscoelastic as verified by zero relaxation time in the relaxation process of the shear stress, which contradicts the general viewpoint that there is a correlation between the viscoselastic characteristics and the turbulent drag reduction for the drag-reduction surfactant. However, the APG solution is birefringent as observed through a birefringent test, which indicates that there are rod-shaped micelles in the solution under the shearing flow. The higher extensional viscosity inferred from the extensional phenomenon observed in the measurements of the shear viscosity could be responsible for the drag reduction property of this nonionic surfactant.

关键词： drag reduction shear stress relaxation relaxation time viscoelasticity

Lepton mass matrix from double covering of A_(4) modular flavor symmetry

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Chinese Physics C 2022年第12期46卷 162-171页

作者： Hiroshi Okada yuta Orikasa Asia Pacific Center for Theoretical Physics(APCTP)-Headquarters San 31 Hyoja-dongNam-guPohang 790-784Korea Department of Physics Pohang University of Science and TechnologyPohang 37673Republic of Korea Institute of Experimental and Applied Physics Czech Technical University in PragueHusova 240/511000 Prague 1Czech Republic

We study a double covering of modular A_(4)flavor *** this end,we construct lepton models for canonical and radiative seesaw *** irreducible doublet representations,heavier Majorana fermion masses are characterized by one free parameter that would differentiate from A_(4)***χsquare numerical analysis,we demonstrate that both scenarios produce some predictions in case of normal hierarchy reproducing neutrino oscillation ***,no solution satisfies the neutrino oscillation data in case of radiative seesaw of inverted hierarchy.

关键词： flavor physics neutrino and Lepton mass beyond the standard model

MicroRNA-based targeting of the Rho/ROCK pathway in therapeutic strategies after spinal cord injury

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Neural Regeneration Research 2023年第2期18卷 311-312页

作者： Tetsu Kimura yuta Horikoshi Department of Anesthesia and Intensive Care Medicine Akita University Graduate School of MedicineAkitaJapan

Spinal cord injury(SCI)is one of the leading causes of disability and is a devastating condition that requires long-term care,reduces social productivity,and gives an immense emotional burden on patients and their fa *** frequently occurs due to traffic accidents,falls,slips,violence,sports,and medical accidents in today's *** initial mechanical damage triggers a secondary injury cascade that induces more intractable damage(Silva et al.,2014).Secondary injury mechanisms have been postulated,including neuronal apoptosis,inflammation,oxidative stress,and excitotoxicity.

关键词： damage injury emotional

Is the magic texture of Majorana neutrinos immanent in Dirac nature?

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Chinese Physics C 2023年第4期47卷 66-73页

作者： yuta Hyodo Teruyuki Kitabayashi Graduate School of Science and Technology Tokai University4-1-1 KitakanameHiratsukaKanagawa 259-1292Japan Department of Physics Tokai University4-1-1 KitakanameHiratsukaKanagawa 259-1292Japan

Magic textures are successful candidates of the correct texture for Majorana *** this study,we demonstrate that several types of magic textures of Majorana neutrinos are approximately immanent in the flavor mass matrix of Dirac *** addition,the normal mass ordering of Dirac neutrino masses is slightly preferable to inverted mass ordering in the context of magic textures.

关键词： neutrino mixing mass matrix magic texture

Counter-Rotating Type Tidal Stream Power Unit Boarded on Pillar(Performances and Flow Conditions of Tandem Propellers)

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Journal of Thermal Science 2013年第6期22卷 580-585页

作者： yuta Usui Toshiaki Kanemoto Koju Hiraki Kyushu Institute of Technology: Sensui 1-1 TobataKitakyushuFukuoka804-8550Japan

The authors have invented the unique counter-rotating type tidal stream power unit composed of the tandem pro- peUers and the double rotational armature type peculiar generator without the traditional stator. The front and the rear propellers counter-drive the inner and the outer armatures of the peculiar generator, respectively. The unit has the fixftful advantages that not only the output is sufficiently higher without supplementary equipment such as a gearbox, but also the rotational moment hardly act on the pillar because the rotational torque of both propel- lers/armatures are counter-balanced in the unit. This paper discusses experimentally the performances of the power unit and the effects of the propeller rotation on the sea surface. The axial force acting on the pillar in- creases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Be- sides, the force vertical to the stream also acts on the pillar, which is induced from the Karman vortex street and the dominant frequencies appear owing to the front and the rear propeller rotations. The propeller rotating in close to the sea surface brings the abnormal wave and the amplitude increases as the stream velocity is faster and/or the drag is stronger.

关键词： Tidal stream Counter rotation Tandem propellers Generator Armature