Search

In this research, a biomimetic, eagle-wing-type propeller was designed and applied to four pairs of counter-rotating propeller system to provide the necessary payload for a manned drone. The aerodynamic and noise characteristics were identified by model testing and compared with the numerical results using Ansys CFX 19.0 software. The structural analysis were also performed to reinforce the biomimetic blades by modifying the solid profiles near the hub. The aerodynamic performances of the counter-rotating propeller system were measured in terms of thrust forces by changing the distance between two counterrotating propellers and the pitch angle of the lower propeller. Based on the experiment, the best aerodynamic performance was identified at the pitch angle of 5° higher for the downstream propeller than that of upstream one and the non-dimensional distance of 0.3 between two counter-rotating propellers.

This paper investigates soft error in memories and logic circuits in 28 nm planar-FDSOI technology by neutron, alpha, proton, and gamma-ray irradiation tests, and compares with SER in bulk-FinFET. The comparison elucidates the different SER trends between planar-FDSOI and bulk-FinFET.

This paper presents the soft error rate (SER) in flip-flops of 10-nm FinFET technology, and discusses the scaling trend of SER from 14- to 10-nm FinFET technologies. Alpha and neutron irradiation test results show huge SER improvement in 10-nm FinFET technology. In a 10-nm FinFET, the alpha-induced SER decreases by $13.4\times $ , and the neutron-induced SER decreases by $3.1\times $ , compared to the 14-nm FinFET technology. The SER improvement is analyzed with the physics-based 3-D technology computer-aided design and Monte Carlo simulations. The simulation results show that fin-width scaling reduces the charge generation as well as charge collection which explains the SER improvement observed in 10-nm FinFET technology.

This paper investigates alpha-induced single event transient (SET) in combinational-logic in 10 nm bulk FinFET technology. FinFET technology improves SET in combinational-logic as well as single event upset (SEU) in flip-flops.

The coupling between the emitted energy and the acoustic energy in a thermal system, e.g. combustor, may result in system instability accompanying severe vibration. In this study, the limit curve for thermo-acoustic instability is numerically obtained by using the CFD- CAA combined method. The response function for pulsating release of heat in the Rijke tube and the distribution of mean density in the tube are computed accurately by the CFD analysis and used as inputs to CAA predictions. To verify the accuracy of the prediction method, the thermo-acoustics inside the horizontal, one meter long Rijke tube of square cross-section, which has the heating part at the location of one quarter length, is simulated. The predicted instability curve agrees well with the experimental one except the low flow- rate region of ReDo < 1.

To investigate the spatial and temporal frequency tunings for stereopsis, we measured the contrast sensitivity for depth discrimination with variable spatiotemporal frequencies and disparities using drifting sinusoidal gratings. The results showed that the contrast sensitivity changed with the stimulus disparity and the disparity tuning function varied with the spatial frequency. The disparity in the peak sensitivity decreased proportionally with the spatial frequency (size-disparity correlation). Although the temporal frequency exhibited a limited influence on the peak disparity, the temporal frequency tuning varied with the spatial frequency. The shape of the temporal frequency tuning function was lowpass for higher spatial frequencies, whereas it was bandpass for low spatial frequencies. These results suggest that more than one channel with different temporal as well as spatial frequency tunings contribute to stereopsis.

Series-resonant vibrating micromechanical resonator oscillators are demonstrated using a custom-designed single-stage zero-phase-shift sustaining amplifier together with planar-processed micromechanical resonator variants with quality factors Q in the thousands that differ mainly in their power-handling capacities. The resonator variants include two 40-/spl mu/m-long 10-MHz clamped-clamped-beam (CC-beam) resonators, one of them much wider than the other so as to allow larger power-handling capacity, and a 64-/spl mu/m-diameter 60-MHz disk resonator that maximizes both Q and power handling among the resonators tested. Tradeoffs between Q and power handling are seen to be most important in setting the close-to-carrier and far-from-carrier phase noise behavior of each oscillator, although such parameters as resonant frequency and motional resistance are also important. With a 10/spl times/ higher power handling capability than the wide-width CC-beam resonator, a comparable series motional resistance, and a 45/spl times/ higher Q of 48 000, the 60-MHz wine glass resonator reference oscillator exhibits a measured phase noise of -110 dBc/Hz at 1-kHz offset, and -132 dBc/Hz at far-from-carrier offsets. Dividing down to 10 MHz for fair comparison with a common conventional standard, this oscillator achieves a phase noise of -125 dBc/Hz at 1-kHz offset, and -147 dBc/Hz at far-from-carrier offsets.

To investigate the effect of exposure duration on stereopsis and its spatial frequency dependency, we measured disparity threshold for the depth discrimination varying stimulus exposure duration between 0.05 and 2 s for three spatial frequencies (0.23, 0.94 and 3.75 c/deg). The results showed that disparity threshold decreased with increase in exposure duration up to a certain duration, beyond which it was approximately constant (the duration is called critical duration). The critical duration was about 150 ms for gratings with low and middle spatial frequencies (0.23 and 0.94 c/deg) while the duration was about 750 ms for gratings with high spatial frequency (3.75 c/deg). This suggests that temporal integration property varies dependently on stimulus spatial frequency. We also attempted to relate the spatial frequency dependency of the temporal integration property to the differences in temporal frequency tuning to different spatial frequency stimuli.

The BEM is a highly efficient method in the sense of economical computation. However, boundary integration is not easy for the complex geometry and moving surface, e.g. a rotating blade. Thus, Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. A Kirchhoff surface is a fictitious surface which envelopes acoustic sources of main concern. Acoustic sources may be distributed on each Kirchhoff surface element according to their acoustic characteristics. In this study, an axial fan is assumed to have unsteady loading noise as a dominant source. Dipole sources can be modeled to solve the FW-H equation. Acoustic field is then computed by determining Kirchhoff surface on which near-field is implemented, to analyze the effect of Kirchhoff surface on it. The optimal shape and the location of Kirchhoff surface are discussed by comparing with experimental data acquired in an anechoic chamber.

We measured disparity threshold for identifying the depth direction as a function of spatial frequency with various temporal frequencies and stimulus contrasts using drifting gratings. The results showed that disparity threshold depended little on temporal frequency with the exception of high temporal frequencies (≥ 10Hz) independently of stimulus contrast. Contrary to temporal frequency, contrast substantially influenced spatial frequency characteristics. The disparity threshold was approximately constant with change in spatial frequency with slight increase at high spatial frequencies for contrasts higher than 0.2 when the threshold is expressed by phase difference between the left and right eye images (phase disparity). The phase disparity threshold had a negative peak at a spatial frequency between 1 and 5c/deg (band-pass) for contrasts lower than 0.2. We discuss possible differences in the underlying mechanisms to determine disparity threshold below and above temporal frequency of 10 Hz.

In a 3D stereoscopic display, transmissive losses in the shutter glasses cause a reduction of luminance compared to a 2D display. In stereoscopic 3D, evaluation of perceptual brightness through assessment of both of bright and dark luminance levels is needed. This study compares perceptual brightness of 2D and 3D with shutter glasses between AMOLED displays and LCDs considering simultaneous contrast. When 3D luminance of an AMOLED is 12% lower than an LCD as viewed through shutter glasses, according to a comparison based on perceptual contrast length, the displays are perceived as having the same brightness range.

The effects of bulk expansion and compression on turbulence levels in supersonic boundary layers were predicted using the law of angular momentum conservation. For the compression case the present analysis predicted the amplification of turbulence level quite well when the effect of extra strain rate caused by the streamline curvature is small, where it was estimated that 90-95% of the increase in the turbulence level is caused by the bulk compression. When extra strain rate effects are present, however, the contribution of the bulk compression on the total turbulence level was reduced to about 85-90%. The predicted general trend of turbulence amplification with increasing flow-turning angle, which seems to be closely related to the linear increase in the mean density, agrees well with that of other researchers. For the expansion case, however, a quantitative comparison was challenging because the available experimental data were taken too close to the end of the perturbation region, thus not showing the relaxation behavior

An experimental investigation of the near-field pressure fluctuations on a hemisphere-nose of an axisymmetric body was conducted in three regions—laminar separation, turbulent shear layer, and developing turbulent boundary layer—at a Reynolds number (ReD) of 2.43×105 in an anechoic wind tunnel facility. A significant increase of energy level, especially at low frequencies, was noticed downstream of the laminar separation on the nose, and the positive events were observed in the turbulent shear layer region.

Effect of grid resolution on the statistics of passive scalar in a complex shear layer was investigated using a direct numerical simulation technique. The grid resolution in the shear layer which was generated from the interaction of main and injected streams strongly influences the subsequent evolution of the passive scalar. Dissipation, integral length-scale, skewness and flatness factors of the passive scalar are sensitive to the numerical resolution away from the wall where coherent structures grow very rapidly.

Clear differences in the phase noise performance of a 10 MHz MEMS-based micromechanical resonator oscillator have been measured using sustaining circuits with and without automatic-level control (ALC), and with differing mechanisms for ALC. In particular, low output power oscillators referenced to high-Q clamped-clamped beam /spl mu/mechanical resonators exhibit an unexpected 1/f/sup 3/ phase noise component without ALC, a 1/f/sup 5/ phase noise component when an ALC circuit based on resonator dc-bias adjustment is used, and finally, removal of these components when an ALC circuit based on sustaining amplifier gain control is used, in which case the expected 1/f/sup 2/ phase noise component is all that remains. That ALC is able to remove the 1/f/sup 3/ phase noise seen in non-ALC'ed oscillators suggests that this noise component emanates primarily from nonlinearity in the voltage-to-force capacitive transducer, either through direct aliasing of amplifier 1/f noise, or through instabilities introduced by spring softening (i.e., Duffing) phenomena.

A 10-MHz series resonant micromechanical resonator oscillator has been demonstrated using a custom-designed, single-stage, zero-phase-shift sustaining amplifier together with a clamped-clamped beam micromechanical resonator, designed with a relatively large width of 40 /spl mu/m to achieve substantially lower series motional resistance R/sub x/ and higher power handling than previous such devices. Using automatic level control (ALC) circuitry to remove an unexpected 1/f/sup 3/ close-to-carrier phase noise component, this oscillator achieves a phase noise density of -95 dBc/Hz at 1 kHz offset from the carrier, while consuming only 820 /spl mu/W of power.

LES formulation was applied to simulate the flow fields around rotating fan blades tested by DLR. The turbulent flows around fan blade rotating with 500 RPM were simulated and the far-field noise was exactly computed by using the Ffowcs Williams and Hawkings equation with an inclusion of quadrupole source formulation. Variations of lift forces and deviation angles in the spanwise direction were analyzed to correlate flow parameters with acoustics parameters and identify noise sources. The dipole noise computed at the far-field by computed drag and lift forces was in good agreement with experimental data and the dipole source was also found to be the major contributor to overall far-field noise from unsteady calculation.

Mounted on the body of a fan blade is a micro-electro mechanical system which includes at least one thin silicon film forming an integrated circuit, and an actuator connected to the circuit for generating vibrations. If used as a noise-killing system, the actuator generates vibrations which offset (reduce) unstable air flows along the blade body. If used in a heat exchanger to improve the heat exchange effect, the system generates vibrations which amplify the unstable air flow, e.g., to amplify turbulence and vortexes.

Acoustic mechanical power from fluctuating fluid flows forms but a tiny part (about 10−5) of the power within the flow. The familiar, far‐field solution to the Lighthill equation is used and is written as

The breakdown process of the initial large‐scale structures into substructures near the end of the potential core is examined and the production of aerosound as a result is discussed. The quadrupole‐like directivity pattern of jet noise is numerically obtained by applying the large‐eddy simulation (LES) technique for the fluid flow. The Lighthill analogy is used to obtain the acoustic far field. Most of the sound comes from a region near the end of the potential core. A discussion to explain this quasiaxisymmetric directivity pattern is given. The directivity maximum is obtained at about 45° from the axis of the jet exhaust. This will be explained in terms of turbulent velocities. The convective effect on sources is introduced by ray tracing to calculate retarded times. The result is to obtain more radiation downstream, as is observed. The relation of this correction to the Lighthill theory will be discussed.

Acoustic radiation from turbulent fluids, aeroacoustics, has been a major research area especially since the pioneering work of Lighthill. The fundamental mechanism of acoustic radiation from homogeneous turbulence has been discussed, using a similarity hypothesis [W. C. Meecham and G. W. Ford, J. Acoust. Soc. Am. 30, 318 (1958)]. This paper presents a new application of large eddy simulation (LES) techniques to the calculation of the acoustic far field produced by turbulent fluids. The acoustic radiation problem consists of two steps; in the first step one simulates homogeneous turbulent fields using LES; and in the second step one generates the far‐field sound using Lighthill’s analogy. It is found that the radiated power spectrum is proportional to ω4M3, where M is the Mach number, at high frequencies as predicted in the early work. Other features of the sound field support the early theory. Similar calculations for jet noise will be discussed. Color computer graphics will be shown.

The quadrupole‐like directivity patterns of jet noise, created by jet impingement on a large fiat plate were experimentally obtained by the authors previously [J. Acoust. Soc. Am. Suppl. 1 88, S8 (1990)]. Theoretical considerations have been examined to explain physically this directivity phenomena, and a model coherent structure called the “orientated vortex motion” is proposed. The model hypothesizes that a train of partially organized, large‐scale vortices exists inside the boundary layer flow near the plate. By including their images in the rigid plate an oscillation is formed, resulting in a quadropole acoustical source, which explains the experiments quite well. This is analogous to the low Reynolds number free jet case that predicts a possible, similar directivity pattern for the noise from the free jet. A large eddy simulation (LES) computational technique for the simulation of turbulent flows seems to be a feasible approach to investigate the proposed organized motion. A simulated statistically s...