Showing papers on "Dynamic pressure published in 2003"

Effect of solar wind pressure pulses on the size and strength of the auroral oval

Abstract: [1] It has recently been found that solar wind dynamic pressure changes can dramatically affect the precipitation of magnetospheric particles on the high-latitude ionosphere. We have examined the effect of large solar wind dynamic pressure increases on the location, size, and intensity of the auroral oval using particle precipitation data from Defense Meteorological Satellite Program (DMSP) spacecraft. Three events have been selected for study during the time period after 1997 when four DMSP spacecraft (F11–F14) were simultaneously operational. Interplanetary magnetic field (IMF) orientation is different from event to event. For each event, we determine equatorward and poleward boundaries of the auroral oval before and after an increase in solar wind pressure. Also, using measured integral fluxes, we construct precipitating particle energy input maps for the auroral oval. All cases studied show a significant change of the auroral oval location, size, and intensity in response to the solar wind pressure pulse. Most prominent are an increase of the auroral zone width and a decrease of the polar cap size when the solar wind dynamic pressure increases under steady southward IMF conditions. An increase in total precipitating particle energy flux is also observed. A smaller response is seen when the IMF Bz has a simultaneous northward turning and when it is nearly zero before the pressure enhancement. Our results also point to significant differences between the auroral precipitation response to solar wind pressure changes and its response to isolated substorms, the former inducing a global auroral reaction while the latter is related to more localized premidnight disturbances. Auroral UV observations from the Polar spacecraft during our events are found to give results consistent with the results we get from the precipitating particle observations.

Influence of the solar wind dynamic pressure on the decay and injection of the ring current

Abstract: The influence of the solar wind dynamic pressure on the decay and injection of thering current is investigated empirically, on the basis of the solar wind and the geomagneticindex Dst of the OMNI database, for the period from January 1964 to July 2001. Wefound that when the position of the ring current is closer to the Earth for a higher solarwind dynamic pressure, the decay time of the ring current decreases. The decay time, inhours, varies as follows, t = 8.70 exp(6.66/(6.04 + P)), for northward interplanetarymagnetic fields (IMF), where P is the solar wind dynamic pressure in nanopascals. It isalso found, by minimizing the root mean square errors of the hourly Dst differencebetween the calculated values and the measured ones, that the ring current injection rate isproportional to the solar wind dynamic pressure, with a power index equal to 0.2 duringsouthward IMF. This implies that the ring current injection increases when themagnetosphere is more compressed by high solar wind dynamic pressure. On the basis ofour new results we demonstrate that the predictions of Dst using O’Brien andMcPherron’s [2000a] model are improved, especially for intense geomagnetic stormswhen the influence of the solar wind dynamic pressure on the decay and injection of ringcurrent is taken into consideration.

A proxy for determining solar wind dynamic pressure at Mars using Mars Global Surveyor data

Abstract: [1] We develop a method to infer the upstream solar wind pressure at Mars using data from the Mars Global Surveyor (MGS) magnetometer instrument. The method assumes magnetic field pressure in the magnetic pileup region balances the incident solar wind dynamic pressure. Newtonian pressure balance conditions are imposed for positions off of the subflow point. Proof of concept exists from the mapping phase of the spacecraft mission, when the orbital geometry at a constant altitude allows fits to magnetic field data as a function of solar zenith angle. During the elliptical orbit phase of MGS, when the spacecraft passes through a large range of altitudes, such fits are not possible. However, the measured magnetic pressure in the magnetic pileup region is scaled by the same means as derived for the mapping orbits and reasonable upstream solar wind pressure is obtained. We compare the distribution of solar wind pressure calculated using MGS data with the solar wind pressure measured upstream of the Earth during the same time period and find good agreement, further supporting this algorithm as a valid proxy for the incident solar wind pressure. The response of the position of the Magnetic Pileup Boundary to the inferred solar wind pressure also validates the method. High solar wind ram pressure depresses the altitude of the Magnetic Pileup Boundary.

Role of Pressure in Turbulence

Abstract: There is very limited knowledge of the kinematical relations for the velocity structure functions higher than three. Instead, the dynamical equations for the structure functions of the velocity increment are obtained from the Navier–Stokes equation under the assumption of the local homogeneity and isotropy. These equations contain the correlation between the velocity and pressure gradient increments, which is very difficult to know theoretically and experimentally. We have examined these dynamical relations by using direct numerical simulation data at very high resolution at large Reynolds numbers, and found that the contribution of the pressure term is important to the dynamics of the longitudinal velocity with large amplitudes. The pressure term is examined from the view point of the conditional average and the role of the pressure term in the turbulence dynamics is discussed.

Discomfort, Pressure Distribution and Safety in Operator's Seat-A Critical Review

Abstract: Overall seating comfort is influenced by both static and dynamic characteristics of seat system. Therefore, the present study is an overview of work related to comfort in seat-operator interface affected by static and dynamic pressure distribution, and other related parameters involved in seat comfort, low back pain, seat design and safety in seats. A critical review has been presented on the subject, with a purpose to provide quick reference for the future researchers . The studies revealed that seat-human interface pressure on the soft seat is more evenly distributed on a larger effective contact area than on a rigid seat. The pressure distribution at human seat interface of a rigid seat is affected by seat height, posture, type of cushion and frequency and vibration. The dynamic pressure at interface is nearly sinusoidal in the vibration range of 1-10 Hz. Under vibration excitation, increase in excitation magnitude causes increased maximum ischium pressure and maximum effective contact area around resonant frequency of 4.5 to 5.0 Hz. Postural stress, whole body vibration and shocks are recognised as important factors, causing low back pain. This however, can be reduced by provision of lumbar support, side support and suitable cushion type.

Computational air data system for angle-of-attack and angle-of-sideslip

Abstract: A computational air data method and system for estimating angle-of-attack and angle-of-sideslip of an aircraft utilizing a detailed aerodynamic model of the aircraft, extended Kalman filters, inertial system measurements of body rates and body accelerations, and computation of dynamic pressure.

Static and dynamic pressure profiles of a patellar-tendon-bearing (PTB) socket:

Abstract: The purpose of this study was to evaluate the pressure distribution at the stump/socket interface in amputees wearing the patellar-tendon-bearing socket. A specially built strain gauged type pressure transducer was used for measuring this pressure distribution in four unilateral transtibial amputees. Pressure and gait parameters were measured simultaneously while they were standing and walking. Pressure profiles were compiled at 10, 25 and 50 per cent of gait cycle and compared with the pressure profiles predicted by Radcliffe in 1961. The subject's anterior-posterior pressure profiles were different from each other. However, at toe-off, each subject exhibited an increase in pressure at the patellar tendon. Their medial-lateral pressure profiles were similar: exhibiting high pressure at the medial proximal and lateral distal regions except for one subject who exhibited high pressure at the lateral proximal region instead. The subjects' pressure profiles did not resemble Radcliffe's anticipated pressure profiles. This was because ground reaction force was not the only factor affecting the resulting pressure profiles.

Method for the control of an internal combustion engine combined with a gas-dynamic pressure wave machine

Abstract: The method for the control of an internal combustion engine combined with a gas-dynamic pressure wave machine comprising a rotatable housing in order to control the process tuning over the entire performance field of the internal combustion engine as well as a variable width adjustment of the high pressure exhaust gas channel includes a certain control sequence of steps in a positive load variation and a certain control sequence of steps in a negative load variation.

Sensor for measuring wind angle

Abstract: A differential pressure-induced airflow based approach is used to measure Angle~Of-Attack (AOA) or Angle-Of-Sideslip (AOS) for an aircraft. Ports on opposing sides of an aircraft fuselage are coupled by an airway incorporating a mass airflow sensor. As the relative wind's angle of incidence changes direction with respect to the aircraft's longitudinal axis or wing chord, a differential pressure is created. The differential pressure induces an airflow between the ports whose magnitude is measured by a mass airflow sensor. The resulting airflow is a function of the respective AOA or AOS. The measured airflow and air data computer supplied parameters of airspeed (or dynamic pressure) and altitude (or static pressure) are utilized by an algorithm that reduces the data into angular AOA or AOS measurements.

Case study of solar wind pressure variations and neutral atom emissions observed by IMAGE/LENA

Abstract: [1] The Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft was designed to observe neutral atom emissions at low energy (10 eV-∼4 keV) from the high-latitude ionosphere. In this study we present data from an ion outflow event on 24 June 2000 showing increases in neutral flux that appear to be associated with dynamic pressure variations in the solar wind. Results from a correlation analysis show the neutral flux to be well correlated (∼0.64) with the solar wind dynamic pressure. The neutral atom data are most consistent with a source region at a radial distance of 2.2-2.3 R E , interpreted as the region over which the bulk ion outflow escapes the ionosphere and is partly converted to neutral atoms. Very short time delays (∼2 min) were calculated between the solar wind pressure increase and neutral atom response, indicating a prompt ionospheric response to the solar wind input.

Dynamic pressure probe holder and method of obtaining a dynamic pressure signal

Abstract: A component adapted to transmit a dynamic pressure signal from a high temperature environment to a location where it can be measured without causing significant attenuation of the signal. In particular, the component provides for a dynamic pressure signal transmission in the manner that will not result in the formation of condensation in the measurement system and thus eliminates the need to periodically purge condensate from the system.

Regenerator‐based thermoacoustic refrigerator for ice cream storage applications

Abstract: A regenerator‐based chiller has been built in the ‘‘bellows bounce’’ style [J. Acoust. Soc. Am. 112, 15 (2002)] to replace the vapor compression system in an ice cream sales cabinet. It utilizes a 6‐in.‐diam metal bellows to form a compliant cavity that contains the dynamic pressure oscillation (>50 kPa). The stiffness of the gas trapped in the bellows is resonated against the mass of the bellows‐cap and the mass of a moving‐magnet linear motor which is capable of high (>85%) electro‐acoustic efficiency. A second resonator, operated well below its natural frequency, uses the gas stiffness of a 1‐l volume nested within the bellows and the inertia of an ordinary loudspeaker cone to create the pressure difference across the regenerator that drives gas flow that is in‐phase with pressure. The mass of the cone can be adjusted to vary the multiplication factor that is typically 5%–10% greater than the dynamic pressure within the bellows. The loudspeaker cone suffers none of the hydrodynamic losses associated with an acoustic inertance and eliminates problems with dc gas flow in the energy feedback path. The cold heat exchanger forms one surface of the pressure vessel permitting direct contact with any thermal load. [Work supported by Ben and Jerry’s Homemade.]

Method and apparatus for charging oil into fluid-dynamic-pressure bearings, spindle motor utilizing fluid-dynamic-pressure bearings, and signal record-and-playback device utilizing fluid-dynamic-pressure bearings

Abstract: Manufacturing method enabling optimal volume oil-fill even where differing from bearing to bearing due to machining fluctuations in volume-production dynamic pressure bearings. In a first charging method, injection of oil is divided into two cycles. The first is carried out under reduced pressure, following which the pressure is raised a predetermined amount to force the oil into the bearing gap. The oil-fill status is thereupon checked, the shortage is reckoned, and in the second cycle the shortage is injected. In a second charging method, in a first cycle a surplus volume is injected under reduced pressure and the pressure is raised a predetermined amount to force the oil into the bearing gap. Following that, what is in excess of the appropriate amount is removed from the bearing. The first cycle of injection and the pressure elevation may be implemented multiple times, in between which repeat pressure-reduction can be carried out.

Static Aeroelastic Predictions for a Transonic Transport Model Using an Unstructured-Grid Flow Solver Coupled With a Structural Plate Technique

Abstract: An equivalent-plate structural deformation technique was coupled with a steady-state unstructured-grid three-dimensional Euler flow solver and a two-dimensional strip interactive boundary-layer technique. The objective of the research was to assess the extent to which a simple accounting for static model deformations could improve correlations with measured wing pressure distributions and lift coefficients at transonic speeds. Results were computed and compared to test data for a wing-fuselage model of a generic low-wing transonic transport at a transonic cruise condition over a range of Reynolds numbers and dynamic pressures. The deformations significantly improved correlations with measured wing pressure distributions and lift coefficients. This method provided a means of quantifying the role of dynamic pressure in wind-tunnel studies of Reynolds number effects for transonic transport models.

Optimal control of a space shuttle, and numerical simulations

Abstract: We study the Earth re-entry problem of a space shuttle where the control is the angle of bank, the cost is the total amount of thermal flux, and the system is subject to state constraints on the thermal flux, the normal acceleration and the dynamic pressure The optimal solution is approximated by a concatenation of bang and boundary arcs, and is numerically computed using a multiple-shooting code

Reference Static and Dynamic Pressures in Automotive Wind Tunnels

Abstract: The reference pressures are determined in automotive wind tunnels by measurement of pressures and pressure differences at upstream positions along the wind tunnel nozzle. For closed wall wind tunnels usually the so callednozzle method is used, where the volume flux is calculated from a pressure difference measured at the nozzle contour and a calibration factor determined in the empty test section. For open jet wind tunnels a choice is available between nozzle and plenum method. For the plenum method the reference static pressure is taken from the plenum chamber and the dynamic pressure also refers to the plenum conditions. The static reference pressure in closed wall tunnels is calculated by subtracting the dynamic pressure from the total pressure in the settling chamber. In this paper, the definitions and the differences between the two methods are discussed in detail. Possible sources of errors, such as velocity-dependent calibration factors, interference with boundary layer suction and empty test section velocity distribution are discussed. Special focus will be laid on the investigation of the interference of model displacement (blockage) and measured dynamic pressure. It will be shown, that local effects of the pressure build up in front of the model usually do not affect the accuracy of the measured dynamic pressure. Nevertheless model blockage does affect the measured results for aerodynamic forces as well as for pressure distributions. A short discussion of the sources of errors and of possible theoretical corrections to force coefficients and pressure distributions will be given. In this case special focus will be laid on the influence of the distance between model and nozzle in an open jet wind tunnel. The measured effect on the pressure distribution of a vehicle will be analysed and it will be shown, that neither nozzle nor plenum method deliver correct pressure distribution results without additional correction, if the blockage level is high.

Gas turbine combustor hybrid dynamic-static probe

Abstract: A removable instrumentation assembly and probe for use in simultaneously measuring dynamic pressure, at least one static pressure, and temperature for a gas turbine combustor. The instrumentation assembly allows combustor performance analysis as well as monitoring of component integrity through dynamic pressure fluctuations. The instrumentation assembly includes a probe having a plurality of passages, each connected to tubular conduits for measuring and recording respective pressures. In the preferred embodiment, dynamic pressures from within a combustion chamber are measured and recorded along with static pressures within the combustion chamber and outside of the combustion chamber, along with external air temperature.

Fluid dynamic-pressure bearing, spindle motor and recording disk driver

Abstract: PROBLEM TO BE SOLVED: To provide a fluid dynamic-pressure bearing, a spindle motor equipped with the fluid dynamic-pressure bearing and a recording disc driver capable of preventing negative pressure or excess floating of a rotor from occurring and reducing cost. SOLUTION: A radial-bearing part is structured with a dynamic pressure generating groove formed with an outer peripheral surface of a shaft and an inner peripheral surface of a sleeve. A thrust-bearing part is structured with an end face of a sleeve and a dynamic pressure generating groove formed on a lower face of a hub facing against the end face of the sleeve. A gap for structuring the radial-bearing and the thrust-bearing is integrally connected and filled with communicating oil. An end of the radial-bearing gap and the thrust-bearing is connected by a communicating hole which allows the oil to circulate. At the thrust-bearing, two of inner and outer dynamic pressure generating grooves are formed; the outer dynamic pressure generating groove increases static pressure of the oil and the inner hydrodynamic pressure generating groove circulates oil maintained by the radial-bearing through the communicating hole. COPYRIGHT: (C)2004,JPO&NCIPI

Gas dynamic pressure bearing, spindle motor comprising a gas dynamic pressure bearing, and recording disk drive device and polygon scanner comprising a spindle motor

Abstract: A gas dynamic pressure bearing is disclosed in which dynamic pressure generating grooves in a radial bearing pump out gas toward a thrust bearing, and dynamic pressure generating grooves in the thrust bearing pump in gas toward the radial bearings. This structure generates high pressure in the lubrication gas in the connecting portions of the radial bearings and thrust bearings. In order to compensate for the movement of gas by means of this pump-out and pump-in operation, a structure is provided that links the two portions of the radial and thrust bearings where the gas pressure is reduced, or connects these two portions with the space surrounding the bearing.

Development of a new piezoelectric dynamic pressure generator for high pressure periodic and aperiodic calibration

Abstract: The need for dynamic pressure calibration has been increasing in the past years. Many solutions have been developed to satisfy this demand; nevertheless both present periodic and aperiodic systems do not cover the whole range of needs, calling for further development effort. In this contribution is presented a newly designed piezoelectric-actuated dynamic high-pressure calibration system that operates both periodically, 70×10 5 Pa peak-to- peak at 300 Hz, and aperiodically, almost 50×10 8 Pa/s. Concept, design and first experimental results are described. First encouraging results foster further enhancement of performances.

Survey of Primary Flow Measurement Parameters at the NASA Langley Transonic Dynamics Tunnel

Abstract: An assessment of the methods and locations used to measure the primary flow conditions in the NASA Langley Transonic Dynamics Tunnel was conducted during calibration activities following the facility conversion from a Freon-12 heavy-gas test medium to R-134a A survey of stagnation pressure, plenum static pressure, and stagnation temperature was undertaken at many pertinent locations in the settling chamber, plenum, and contraction section of the wind tunnel and these measurements were compared to those of the existing primary flow measurement systems Local flow velocities were measured in the settling chamber using a pitot probe Results illustrate that small discrepancies exist between measured primary tunnel flow conditions and the survey measurements These discrepancies in tunnel stagnation pressure, plenum pressure, and stagnation temperature were found to be approximately +/- 1-3 psf and 2-3 degrees Fahrenheit The propagation of known instrument errors in measured primary flow conditions and its impact on tunnel Mach number, dynamic pressure, flow velocity, and Reynolds number have been investigated analytically and shown to require careful attention when considering the uncertainty in measured test section conditions

Using of the Dynamic Pressure-Step Method for Mass Transfer Coefficient Measurement in the Internal-Loop Airlift Reactor

Abstract: The principle of the dynamic pressure-step method, consists insimultaneous measurement of both the oxygen concentration and the totalpressure in the internal-loop airlift reactor (ALR). After reaching steadyoxygen concentration in liquid (0.3 M-Na2SO4 solution) atthe atmospheric pressure, the pressure in the column was increased by about 15kPa. The pressure in the column changed in about 10-15 s, therefore this methodis called the non-ideal pressure-step method. Then, the instantaneous values ofboth the column pressure and the oxygen concentration could be used forcalculation of instantaneous driving force for the oxygen mass transfer withoutthe need of immediate pressure step. Measurements were carried out in the ALRs with a working volume of 40 dm3. Pureoxygen, air, and 0.3 M-Na2SO4 aqueoussolution were used as the model gas and liquid media. Measurements showed verygood agreement between k L a valuesmeasured with air and pure oxygen, respectively in the whole range of usedsuperficial velocities of input gas. Further experiments proved instantaneous changeof oxygen concentration in the whole volume of liquid phase. Measured data weredescribed by correlation based on superficial gas velocity of the input gas andby linear dependence on overall gas hold-up in the liquid.

Test section pressure measurements at the research wind tunnel of the aeronautical institute of technology

Abstract: This work presents pressure measurements at test section of ITAs subsonic open-circuit research wind tunnel. The test section, rectangular in shape, is 1.2 m wide, 1.0 m high and 4.0 m long. The contraction ratio is 10:1. The maximum velocity at the test section is approximately 70 m/s, which corresponds to a Reynolds number (Re) around 10 6 considering an airfoil with chord of 0.3 m. Test section dynamic pressure variations with the fan rotational speed were measured using two techniques: Pitot-Prandtl tube and two rings of static orifices (a ring at the settling chamber and the other one at the test section). Results were obtained over a complete operational rate of the tunnel. Dynamic pressure uniformities at the test section transversal area also are shown.

Global magnetospheric‐ionospheric oscillations initiated by a solar wind pressure impulse

Abstract: [1] We present simultaneous observations of long-period (∼1 hour) global magnetospheric-ionospheric oscillations with multiple spacecraft and ground-based instruments. These oscillations occurred following a major increase in the solar wind dynamic pressure. When the solar wind pressure impulse impinged on the magnetosphere, oscillations of energetic plasma particles in the ring current region were excited. The strongest oscillations came from electrons in the energy range of 75–225 keV with periods of 55–80 min. Ground magnetometers measured periodic (∼1 hour) enhancements of ionospheric currents from the auroral to equatorial latitudes. However, the solar wind pressure and IMF in this event did not show variations similar to the energetic particle oscillations and/or ground magnetometer deviations. We suggest that the magnetosphere has an intrinsic period of ∼1 hour during quiet times. The magnetospheric oscillations with this period can be initiated by a solar wind pressure impulse. After the initiation the solar wind no longer plays a role in the subsequent evolution of the magnetospheric oscillations.

Static pressure calculation from dynamic pressure for rotary air-data system and methodology therefor

Abstract: A Rotary Air-data System (RADS) periodically samples pressure data from a main rotor blade mounted pitot-scoop integrated with a high accuracy pressure sensor to compute a velocity vector that is resolvable into the aircraft's coordinate system. Mathematical techniques are employed which provide accurate computations of static pressure without a static pressure sensor. The RADS also computes the direction of the relative wind which is particularly useful when the pilot executes hover or low speed, low altitude maneuvers in restricted visibility. The availability of relative wind velocity information coupled with navigation data enhances the ability of rotary aircraft to perform accurate low altitude hover, fire control and other autopilot maneuvers.

Comparing hydrostatic and nonhydrostatic navier-stokes models of internal waves

Abstract: Internal waves occur at a variety of temporal and spatial scales and are mechanisms by which momentum, energy, nutrients and biota are transported in lakes, estuaries and coastal oceans. In stratified systems, accurate prediction of water quality effects requires modeling internal wave evolution and propagation. Lake, estuary, and coastal ocean models typically apply the hydrostatic approximation to the Navier-Stokes equations, which limits the accuracy of internal wave predictions. The hydrostatic approximation exploits the small aspect ratio (vertical:horizontal length scale) of natural systems, which makes the vertical acceleration and dynamic pressure negligible relative to the horizontal acceleration and hydrostatic pressure (Marshall et al, 1997). The hydrostatic approximation also eliminates the need to solve a three-dimensional Poisson problem for dynamic pressure, thereby dramatically decreasing computational requirements. The hydrostatic approximation is adequate for large-scale ocean processes, but breaks down for scales less than ten kilometers (Kantha and Clayson, 2000). At the mesoscale (10-100 km in horizontal extent, depths of order 1000 m, and horizontal velocities of 0.1 – 1 m s -1 ), the aspect ratio may no longer be considered small, therefore dynamic pressure and vertical acceleration are not negligible and the hydrostatic approximation will not effectively model system dynamics. The exclusion of dynamic pressure in a model may distort the balance between internal wave steepening and dispersion such that the small error of neglecting dynamic pressure accumulates into a large error in the long-term prediction of wave propagation. Thus, inclusion of vertical acceleration and nonhydrostatic pressure is necessary to properly model the evolution of internal waves (Long, 1972). As a simple, monochromatic wave in a nonlinear system evolves, the system’s nonlinearities cause the internal wave to slowly steepen. If there is no force balancing the steepening, the wave will propagate unabated, shorten, and eventually overtop itself causing a mixing event to occur. The full Reynolds-averaged Navier-Stokes (RANS) momentum equation contains both vertical acceleration (the advective term) and dynamic pressure, Eq. (1):

Cooling mechanism of dynamic pressure bearing device

Abstract: PROBLEM TO BE SOLVED: To satisfactorily cool a dynamic pressure bearing by a compact and inexpensive mechanism. SOLUTION: A cooling means 30 having a medium transfer pipe 31 for self-circulating a cooling operation medium between a high temperature side region and a low temperature side region relative to dynamic pressure bearings RB, SB is provided in a cooling body storage part 18 provided in at least either of a shaft member 12 and a bearing member 21 to absorb and radiate heat from the dynamic pressure bearings RB, SB by self-circulating the cooling operation medium by the medium transfer pipe 31 itself so that a forced transfer means such as a conventional pump device is unnecessary to cool the dynamic pressure bearings in order to simplify the cooling mechanism and the whole device greatly. COPYRIGHT: (C)2004,JPO&NCIPI

Hybrid dynamic pressure bearing of spindle motor

Abstract: The present invention relates to a bearing of a spindle motor for a hard disk drive which includes an aero dynamic pressure bearing which is fixedly installed in a space formed by a base and hub, a fluid dynamic pressure bearing which rotatably pivots the center of a hub in a radial direction and a thrust direction, and an air groove formed in such a manner that a certain space is formed between the hub and the aero dynamic pressure bearing after the hub is driven, wherein the aero dynamic pressure bearing and the fluid dynamic pressure bearing are directed to forming an upper side plane of which an upper side is extended in an outer radial direction like a spinning top for thereby implementing a conical shape in which a width of a lower side is decreased in a vertical direction.