Showing papers on "Noise (radio) published in 2018"
TL;DR: In this article, a combed-saw-tooth serration was used to mitigate turbulent boundary-layer trailing-edge noise in wind-turbine blades, and it was found that the presence of combs significantly reduced the intensity of scattered noise but not the frequency range of noise reduction.
Abstract: Trailing-edge serrations are add ons retrofitted to wind-turbine blades to mitigate turbulent boundary-layer trailing-edge noise. This manuscript studies the physical mechanisms behind the noise reduction by investigating the far-field noise and the hydrodynamic flow field. A conventional sawtooth and a combed-sawtooth trailing-edge serration are studied. Combed-sawtooth serrations are obtained by filling the empty space between the teeth with combs (i.e. solid filaments). Both serration geometries are retrofitted to a NACA 0018 aerofoil at zero degree angle of attack. Computations are carried out by solving the explicit, transient, compressible lattice Boltzmann equation, while the acoustic far field is obtained by means of the Ffowcs Williams and Hawkings analogy. The numerical results are validated against experiments. It is confirmed that the combed-sawtooth serrations reduce noise more than the conventional sawtooth ones for the low- and mid-frequency range. It is found that the presence of combs affects the intensity of the scattered noise but not the frequency range of noise reduction. For both configurations, the intensity of the surface pressure fluctuations decreases from the root to the tip, and noise sources are mainly located at the serrations root for the low- and mid-frequency range. The presence of the filaments generates a more uniform distribution of the noise sources along the edges with respect to the conventional serration. The installation of combs mitigates the interaction between the two sides of the aerofoil at the trailing edge and the generation of a turbulent wake in the empty space between teeth. As a result, the inward (i.e. from the serration edge to the centreline) and outward (i.e. from the serration centreline to the edge) flow motions, due to the presence of the teeth, are mitigated. It is found that the installation of serrations affects the surface pressure fluctuations integral parameters. Both the spanwise correlation length and convective velocity of the surface pressure fluctuations increase with respect to the baseline straight configuration. When both quantities are similar to the one obtained for the straight trailing edge, the effect of the slanted edge is negligible, thus corresponding to no noise reduction. It is concluded that the changes in sound radiation are mainly caused by destructive interference of the radiated sound waves for which a larger spanwise correlation length is beneficial. Finally, the difference between measurements and the literature is caused by an incorrect modelling of the spanwise correlation length, which shows a different decay rate with respect to the one obtained for a straight trailing edge.
114 citations
TL;DR: In this paper, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, the authors demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators.
Abstract: Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evidence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices.
94 citations
TL;DR: A 100 kHz optical parametric chirped-pulse amplifier delivering under 4-cycle (38 fs) pulses at ~3.2 µm with an average power of 15.2 W with a pulse-to-p Pulse energy stability <0.1 W presents an extreme stability, in the short and long terms.
Abstract: We demonstrate a 100 kHz optical parametric chirped-pulse amplifier delivering under 4-cycle (38 fs) pulses at ~3.2 µm with an average power of 15.2 W with a pulse-to-pulse energy stability <0.7% rms and a single-shot CEP noise of 65 mrad RMS over 8h. This source is continuously monitored, by using a fast 100 kHz data acquisition device, and presents an extreme stability, in the short and long terms.
78 citations
TL;DR: In this article, the authors demonstrate a straightforward method, employed during Advanced LIGO's second observing run, including the period of joint observation with the Virgo observatory, to separate the majority of this transient noise from potential gravitational-wave sources.
Abstract: "Blip glitches" are a type of short duration transient noise in LIGO data. The cause for the majority of these is currently unknown. Short duration transient noise creates challenges for searches of the highest mass binary black hole systems, as standard methods of applying signal consistency, which look for consistency in the accumulated signal-to-noise of the candidate event, are unable to distinguish many blip glitches from short duration gravitational-wave signals due to similarities in their time and frequency evolution. We demonstrate a straightforward method, employed during Advanced LIGO's second observing run, including the period of joint observation with the Virgo observatory, to separate the majority of this transient noise from potential gravitational-wave sources. This yields a $\sim 20\%$ improvement in the detection rate of high mass binary black hole mergers ($> 60 M_{\odot}$) for the PyCBC analysis.
69 citations
TL;DR: In this article, the authors proposed a detector design that reduces the high-frequency quantum noise with an active optomechanical filter, frequency-dependent squeezing, and high optical power.
Abstract: The gravitational waveform of merging binary neutron stars encodes information about extreme states of matter. Probing these gravitational emissions requires the gravitational-wave detectors to have high sensitivity above 1 kHz. Fortunately for current advanced detectors, there is a sizeable gap between the quantum-limited sensitivity and the classical noise at high frequencies. Here we propose a detector design that closes such a gap by reducing the high-frequency quantum noise with an active optomechanical filter, frequency-dependent squeezing, and high optical power. The resulting noise level from 1 to 4 kHz approaches the current facility limit and is a factor of 20 to 30 below the design of existing advanced detectors. This will allow for precision measurements of (i) the postmerger signal of the binary neutron star, (ii) late-time inspiral, merger, and ringdown of low-mass black hole--neutron star systems, and possible detection of (iii) high-frequency modes during supernovae explosions. This design tries to maximize the science return of current facilities by achieving a sensitive frequency band that is complementary to the longer-baseline third-generation detectors: the 10 km Einstein Telescope and 40 km Cosmic Explorer. We have highlighted the main technical challenges towards realizing the design, which requires dedicated research programs. If demonstrated in current facilities, the techniques can be transferred to new facilities with longer baselines.
65 citations
TL;DR: In this paper, the authors used the k-ω SST turbulence model with the turbulence viscosity correction and the Zwart cavitation model to simulate the cavitating flow around a propeller in a non-uniform wake.
64 citations
TL;DR: It is found that the zeroth spatial order axial force is dominant for the generation of the vibration and noise in axial-flux motors.
Abstract: This paper presents a detailed analysis of the axial electromagnetic force and vibroacoustic behavior of the external-rotor axial-flux motors. First, the spatial and temporal characteristics of axial force acting on the surface of magnets are derived analytically and validated through the 2-D Fourier decomposition. Subsequently, a multiphysics model is established to calculate the vibration and noise of an external-rotor axial-flux in-wheel motor, which integrates the control model, the electromagnetic model, the structural model, and the acoustic radiation model and takes the uneven distribution of axial force into account. The accuracy of the multiphysics model is verified by the noise test. The vibroacoustic mechanism of axial-flux motors is revealed based on the multiphysics model, the influence of current harmonics and dead time effect on the vibration and noise are also analyzed. Finally, the main orders of tested noise are explained by the theoretical analysis. It is found that the zeroth spatial order axial force is dominant for the generation of the vibration and noise in axial-flux motors. The harmonic current may deteriorate the vibroacoustic behavior, but depending on its amplitude and phase. This study provides guidance for the design of low-noise axial-flux motors.
55 citations
TL;DR: In this paper, an analytic solution for aerodynamic noise generated by an unsteady wall pressure gust interacting with a spanwise-variable trailing edge in a background steady uniform flow is presented.
Abstract: This paper presents an analytic solution for aerodynamic noise generated by an unsteady wall pressure gust interacting with a spanwise-variable trailing edge in a background steady uniform flow. Viscous and nonlinear effects are neglected. The Wiener–Hopf method is used in conjunction with a non-orthogonal coordinate transformation and separation of variables to permit analytical progress. The solution is obtained in terms of a tailored modal expansion in the spanwise coordinate; however, only finitely many modes are cut-on, therefore the far-field noise can be quickly evaluated. The solution gives insight into the potential mechanisms behind the reduction of noise for plates with serrated trailing edges compared to those with straight edges. The two mechanisms behind the noise reduction are an increased destructive interference in the far field, and a redistribution of acoustic energy from low cut-on modes to higher cut-off modes. Five different test-case trailing-edge geometries are considered. The analytic solution identifies which geometries are most effective in different frequency ranges: geometries which promote destructive interference are best at low frequencies, whilst geometries which promote a redistribution of energy are better at high frequencies.
49 citations
TL;DR: In this paper, the most dominant discrete-frequency tone of an axial piston pump was suppressed using free-layer visco-elastic damping material treatment, and the reduction in the noise and vibrations at the 2nd harmonic at the rated speed of 1500 r/min were significantly reduced.
49 citations
TL;DR: In this paper, a hybrid CFD method was used to characterize the Underwater Radiated Noise (URN) of a ship at design speed, and the results showed that the predicted URN has a good correlation with the noise spectra obtained from the sea trial.
47 citations
TL;DR: In this article, a new method of active incoherent microwave imaging is presented that uses noise signals and spatial frequency sampling, which is based on interferometric spatialfrequency sampling arrays developed in radio astronomy, to implement the first active imaging method that samples in the spatial frequency domain.
Abstract: A new method of active incoherent microwave imaging is presented that uses noise signals and spatial frequency sampling. Building on interferometric spatial frequency sampling arrays developed in radio astronomy, active incoherent microwave imaging utilizes the transmission of noise signals to implement the first active imaging method that samples in the spatial frequency domain. In comparison to passive microwave imaging systems, active incoherent imaging requires receivers with far less sensitivity, and thus less overall cost. We present the theory behind the imaging technique and show experimental results from a 5.85-GHz system imaging in one and two dimensions. For 1-D images, the transmitter consisted of two noise generators, while the receive array was a synthesized linear array with elements placed in $1\lambda $ increments with the widest spacing of $15\lambda $ . For 2-D images, the transmitter consisted of three noise generators, while the receive array was a synthesized T-array with elements placed in $0.5\lambda $ increments. We demonstrate the reconstruction of 1-D and 2-D scenes consisting of spherical reflecting targets, using only 25 MHz of signal bandwidth and 10 $\mu \text{s}$ of integration time, both of which are an order of magnitude less than passive microwave and millimeter-wave imaging systems.
TL;DR: In this article, a systematic study reveals distinct fast and slow components to the noise, which are compatible with the hypothesis of electrons which were trapped below the liquid surface, and can be reduced by increasing the electric field across the liquid/gas interface.
Abstract: Single electron noise which persists for many milliseconds is known to follow ionizing events in liquid/gas xenon emission detectors. Due to the long timescale, this noise can be mistaken for a genuine signal. Therefore, it is a limiting background to the low-energy threshold of dark matter searches, and could prevent discovery-class searches for MeV scale hidden sector dark matter. A systematic study reveals distinct fast and slow components to the noise. The fast component is compatible with the hypothesis of electrons which were trapped below the liquid surface, and can be reduced by increasing the electric field across the liquid/gas interface. However, the slow component increases linearly with electric field. Hypotheses for the origin of this effect are discussed, and techniques for mitigation are suggested.
01 Mar 2018
TL;DR: In this paper, the loss and noise of an aluminium on silicon quarter-wavelength (λ/4) resonator in the single photon regime was investigated. But, the loss mechanism has not yet been investigated in the context of superconducting circuits.
Abstract: © Published under licence by IOP Publishing Ltd. The loss and noise mechanisms of superconducting resonators are useful tools for understanding decoherence in superconducting circuits. While the loss mechanisms have been heavily studied, noise in superconducting resonators has only recently been investigated. In particular, there is an absence of literature on noise in the single photon limit. Here, we measure the loss and noise of an aluminium on silicon quarter-wavelength (λ/4) resonator in the single photon regime.
TL;DR: In this paper, the effect of multiple transverse jets on the turbulent boundary layer developing over a flat plate is experimentally investigated for aeroacoustic purposes, where a single line of jet nozzles with different spanwise spacings is located parallel to the trailing-edge of the plate, at approximately 30 jet diameters upstream of the trailing edge.
Abstract: In this work, the effect of multiple transverse jets on the turbulent boundary layer developing over a flat plate is experimentally investigated for aeroacoustic purposes. A single line of jet nozzles with different spanwise spacings is located parallel to the trailing-edge of the plate, at approximately 30 jet diameters upstream of the trailing-edge. The axes of the jet nozzles have an inclination of 15° with respect to the streamwise direction. Two values of the jet velocity ratio (r = ujet/u∞) are considered, r = 1 and r = 2. The simultaneous measurement of streamwise velocity and surface pressure fluctuations is performed with hot-wire anemometry and flush-mounted microphones, respectively. The mean velocity profiles show that the low inclination angle of the multiple jets prevents the formation of adverse pressure gradients, and therefore, the multiple jets injection does not lead to flow separation, at least at the range of downstream locations under investigation. From the velocity measurements, the jets merge downstream of the jet nozzles and form a layer of jet fluid characterized by a low energy content. The estimates of the far-field noise show that jets injection at a velocity ratio of r = 1 leads to noise attenuation over the whole range of frequencies under analysis. At a velocity ratio of r = 2, jets injection enables to gain a larger noise reduction than at r = 1 at low frequencies, but the estimated far-field noise is expected to increase at high frequencies.
TL;DR: In this article, the authors investigated anomalous ion-motional heating, a limitation to multi-qubit quantum-logic gate fidelity in trapped-ion systems, as a function of ion-electrode separation.
Abstract: We investigate anomalous ion-motional heating, a limitation to multi-qubit quantum-logic gate fidelity in trapped-ion systems, as a function of ion-electrode separation. Using a multi-zone surface-electrode trap in which ions can be held at five discrete distances from the metal electrodes, we measure power-law dependencies of the electric-field noise experienced by the ion on the ion-electrode distance $d$. We find a scaling of approximately $d^{-4}$ regardless of whether the electrodes are at room temperature or cryogenic temperature, despite the fact that the heating rates are approximately two orders of magnitude smaller in the latter case. Through auxiliary measurements using application of noise to the electrodes, we rule out technical limitations to the measured heating rates and scalings. We also measure frequency scaling of the inherent electric-field noise close to $1/f$ at both temperatures. These measurements eliminate from consideration anomalous-heating models which do not have a $d^{-4}$ distance dependence, including several microscopic models of current interest.
TL;DR: It turns out that the analytical model can predict the electromagnetic vibration and noise of the AFWM quickly and effectively over a wide speed range, which is of great significance for the design of low-noise axial-flux motors.
Abstract: This paper presents an analytical model of the electromagnetic vibration and noise for an external-rotor axial-flux in-wheel motor (AFWM). First, the air-gap flux density is calculated and the influence of edging effect is taken into account through a radial correction function. On this basis, the electromagnetic force acting on the surface of the magnets is obtained. Then, the modal parameters and shapes are calculated and the surface displacement of the AFWM is obtained via a modal superposition method. Finally, sound radiation efficiency is explored to predict the electromagnetic noise. The analytical model is validated through simulation and experiment, respectively. It turns out that the analytical model can predict the electromagnetic vibration and noise of the AFWM quickly and effectively over a wide speed range, which is of great significance for the design of low-noise axial-flux motors.
TL;DR: In this article, a pure silica photonic crystal fiber with a group velocity dispersion of 4 ps$^2$/km at 1.55 $\mu$m and less than 7 ps$+1.34$-$1.82$m low-noise spectrum with a relative intensity noise below 2.2
Abstract: A pure silica photonic crystal fiber with a group velocity dispersion ($\beta_2$) of 4 ps$^2$/km at 1.55 $\mu$m and less than 7 ps$^2$/km from 1.32 $\mu$m to the zero dispersion wavelength (ZDW) 1.80 $\mu$m was designed and fabricated. The dispersion of the fiber was measured experimentally and found to agree with the fiber design, which also provides low loss below 1.83 $\mu$m due to eight outer rings with increased hole diameter. The fiber was pumped with a 1.55 $\mu$m, 125 fs laser and, at the maximum in-coupled peak power (P$_0$) of 9 kW, a 1.34$-$1.82 $\mu$m low-noise spectrum with a relative intensity noise below 2.2\% was measured. The numerical modeling agreed very well with the experiments and showed that P$_0$ could be increased to 26 kW before noise from solitons above the ZDW started to influence the spectrum by pushing high-noise dispersive waves through the spectrum.
TL;DR: In this paper, both experimental and numerical methods are used to shed more light on the noise generation mechanism of this narrowband tip clearance noise and provide a unified description of this source.
TL;DR: In this paper, the magnetic search coil (MSC) was used for magnetic field observations in a few kHz frequency range, which may cause local acceleration and/or rapid loss of radiation belt electrons.
Abstract: This paper presents detailed performance values of the Magnetic Search Coil (MSC) that is part of the Plasma Wave Experiment on board the Arase (ERG) satellite. The MSC consists of a three-axis search coil magnetometer with a 200-mm-long magnetic core. The MSC plays a central role in the magnetic field observations, particularly for whistler mode chorus and hiss waves in a few kHz frequency range, which may cause local acceleration and/or rapid loss of radiation belt electrons. Accordingly, the MSC was carefully designed and developed to operate well in harsh radiation environments. To ascertain the wave-normal vectors, polarizations, and refractive indices of the plasma waves in a wide frequency band, the output signals detected by the MSC are fed into the two different wave receivers: one is the WaveForm Capture/Onboard Frequency Analyzer for waveform and spectrum observations in the frequency range from a few Hz up to 20 kHz, and the other is the High Frequency Analyzer for spectrum observations in the frequency range from 10 to 100 kHz. The noise equivalent magnetic induction of the MSC is $$20\,{\hbox {fT/Hz}}^{1/2}$$
at a frequency of 2 kHz, and the null depth of directionality is − 40 dB, which is equivalent to an angular error less than $$1^{\circ }$$
. The MSC on board the Arase satellite is the first experiment using a current-sensitive preamplifier for probing the plasma waves in the radiation belts.
TL;DR: In this article, a single trapped ion was used as a sensor to investigate the temperature dependence of electric-field noise both before and after ex situ ion milling of the trap electrodes.
Abstract: Electric-field noise from ion-trap electrode surfaces can limit the fidelity of multiqubit entangling operations in trapped-ion quantum information processors and can give rise to systematic errors in trapped-ion optical clocks. The underlying mechanism for this noise is unknown, but it has been shown that the noise amplitude can be reduced by energetic ion bombardment, or ``ion milling,'' of the trap electrode surfaces. Using a single trapped $^{88}\mathrm{Sr}^{+}$ ion as a sensor, we investigate the temperature dependence of this noise both before and after ex situ ion milling of the trap electrodes. Making measurements over a trap electrode temperature range of 4 K to 295 K in both sputtered niobium and electroplated gold traps, we see a marked change in the temperature scaling of the electric-field noise after ion milling: power-law behavior in untreated surfaces is transformed to Arrhenius behavior after treatment. The temperature scaling becomes material-dependent after treatment as well, strongly suggesting that different noise mechanisms are at work before and after ion milling. To constrain potential noise mechanisms, we measure the frequency dependence of the electric-field noise, as well as its dependence on ion-electrode distance, for niobium traps at room temperature both before and after ion milling. These scalings are unchanged by ion milling.
TL;DR: In this article, an experimental investigation of the near-field pressure of a compressible jet is presented, where the proper orthogonal decomposition (POD) of the pressure fluctuations measured by a linear array of microphones is performed in order to provide the streamwise evolution of the jet structure.
Abstract: In this work an experimental investigation of the near-field pressure of a compressible jet is presented. The proper orthogonal decomposition (POD) of the pressure fluctuations measured by a linear array of microphones is performed in order to provide the streamwise evolution of the jet structure. The wavenumber–frequency spectrum of the space–time pressure fields re-constructed using each POD mode is computed in order to provide the physical interpretation of the mode in terms of hydrodynamic/acoustic nature. Specifically, non-radiating hydrodynamic, radiating acoustic and ‘hybrid’ hydro-acoustic modes are found based on the phase velocity associated with the spectral energy bumps in the wavenumber–frequency domain. Furthermore, the propagation direction in the far field of the radiating POD modes is detected through the cross-correlation with the measured far-field noise. Modes associated with noise emissions from large/fine scale turbulent structures radiating in the downstream/sideline direction in the far field are thus identified.
Journal Article•
TL;DR: In this article, the authors investigated anomalous ion-motional heating, a limitation to multi-qubit quantum-logic gate fidelity in trapped-ion systems, as a function of ion-electrode separation.
Abstract: We investigate anomalous ion-motional heating, a limitation to multi-qubit quantum-logic gate fidelity in trapped-ion systems, as a function of ion-electrode separation. Using a multi-zone surface-electrode trap in which ions can be held at five discrete distances from the metal electrodes, we measure power-law dependencies of the electric-field noise experienced by the ion on the ion-electrode distance $d$. We find a scaling of approximately $d^{-4}$ regardless of whether the electrodes are at room temperature or cryogenic temperature, despite the fact that the heating rates are approximately two orders of magnitude smaller in the latter case. Through auxiliary measurements using application of noise to the electrodes, we rule out technical limitations to the measured heating rates and scalings. We also measure frequency scaling of the inherent electric-field noise close to $1/f$ at both temperatures. These measurements eliminate from consideration anomalous-heating models which do not have a $d^{-4}$ distance dependence, including several microscopic models of current interest.
TL;DR: An improved noncontact current probe for locating the noise source to estimate the electromagnetic interference emission on printed circuit board (PCB) based on measured surface scan method and two near-field measurement results compared with the reference probe are used to illustrate the new features.
Abstract: This paper develops an improved noncontact current probe for locating the noise source to estimate the electromagnetic interference emission on printed circuit board (PCB). The miniature current probe is fabricated in a four-layer PCB with high-performance dielectric RO4003C. The designs of isolated via array and matching via-pad structures are used to optimize the performance of probe. The probe can then be used for wideband electromagnetic compatibility test from 9 kHz to 10 GHz under narrow and complex conditions. The current probe can be sensitive enough to detect the weak current signal as small as −130 dBA and has a spatial resolution of 1 mm. The application of current probe in noise location on PCBs based on measured surface scan method is investigated in this paper. And two near-field measurement results compared with the reference probe are used to illustrate the new features of the probe.
TL;DR: In this article, the authors used industrial particle boards with eight different colors (black, white, grey, red, green, blue, brown, and yellow) and two different sheens (flat and semi-gloss) to explore how noise and plane residuals vary with scanning geometry and target-color.
Abstract: Abstract Point-cloud coordinate information derived from terrestrial Light Detection And Ranging (LiDAR) is important for several applications in surveying and civil engineering. Plane fitting and segmentation of target-surfaces is an important step in several applications such as in the monitoring of structures. Reliable parametric modeling and segmentation relies on the underlying quality of the point-cloud. Therefore, understanding how point-cloud errors affect fitting of planes and segmentation is important. Point-cloud intensity, which accompanies the point-cloud data, often goes hand-in-hand with point-cloud noise. This study uses industrial particle boards painted with eight different colors (black, white, grey, red, green, blue, brown, and yellow) and two different sheens (flat and semi-gloss) to explore how noise and plane residuals vary with scanning geometry (i.e., distance and incidence angle) and target-color. Results show that darker colors, such as black and brown, can produce point clouds that are several times noisier than bright targets, such as white. In addition, semi-gloss targets manage to reduce noise in dark targets by about 2–3 times. The study of plane residuals with scanning geometry reveals that, in many of the cases tested, residuals decrease with increasing incidence angles, which can assist in understanding the distribution of plane residuals in a dataset. Finally, a scheme is developed to derive survey guidelines based on the data collected in this experiment. Three examples demonstrate that users should consider instrument specification, required precision of plane residuals, required point-spacing, target-color, and target-sheen, when selecting scanning locations. Outcomes of this study can aid users to select appropriate instrumentation and improve planning of terrestrial LiDAR data-acquisition.
TL;DR: In this paper, the electrochemical noise of a polymer membrane hydrogen-air fuel cell operating at different load currents was measured in serial experiments and the spectral power densities of the noise were divided into three regions.
Abstract: The electrochemical noise of a polymer membrane hydrogen-air fuel cell operating at different load currents was measured in serial experiments. Spectral power densities of the noise are shown to be divided into three regions. At frequencies greater than 3–10 Hz, the spectrum dependence has a constant slope of − 2 in the bilogarithmic coordinates. At frequencies 0.3–5 Hz, there is a horizontal plateau in which length is determined by the value of a load. At frequencies less than 0.3 Hz, the dependence of spectral power density has a slope of − 2. Medium-frequency plateau and high-frequency slope of spectral power densities of the noise were approximated by model RC circuits. The values of Faradic resistance and double-layer capacitance connected in parallel were obtained from the electrochemical impedance data. At load voltages higher 0.5 V, the height of the plateau was shown to be proportional to the 2.68 power of the load current value.
01 Mar 2018
TL;DR: In this paper, the influence of pole and slot number combinations on noise and vibration characteristics of fractional-slot PM motors with either single- or double-layer concentrated windings was investigated, and the explicit magnetic field equations were developed for analyzing the radial vibration force and the torque pulsation by the aid of Schwarz-Christoffel conformal mapping.
Abstract: The radial force and the torque pulsation are identified as two main causes of electromagnetic noise and vibration in permanent magnet (PM) motors for electric vehicle (EV) and hybrid EVs systems. The aim of this paper is to systematically investigate the influence of pole and slot number combinations on noise and vibration characteristics of fractional-slot PM motors with either single- or double-layer concentrated windings. Preferentially, the explicit magnetic field equations are developed for analyzing the radial vibration force and the torque pulsation by the aid of Schwarz-Christoffel conformal mapping. Subsequently, an in-depth investigation of pole ( $2p$ ) and slot ( $Q_{s}$ ) number combinations is carried out to provide a detailed finding of noise behaviors due to the electromagnetic origins. The investigation on the electromagnetic noise is performed depending on the several major $S_{\mathrm{ pp}}$ families. Finally, the relationship between the vibration mode order and the torque variation is established to provide the comprehensive characteristics of the electromagnetic noise.
TL;DR: In this article, the impact of solar surface magneto-convection on absorption line profiles was analyzed from the solar disk center to the solar limb, and the authors found that the visible plasma flows and geometry of the corrugated surface significantly impact the resultant line profiles and induce center-to-limb variations in shape and net position.
Abstract: Manifestations of stellar activity (such as star-spots, plage/faculae, and convective flows) are well-known to induce spectroscopic signals often referred to as astrophysical noise by exoplanet hunters. For example, setting an ultimate goal of detecting true Earth analogs demands reaching radial velocity (RV) precisions of ∼9 cm s-1. While this is becoming technically feasible with the latest generation of highly stabilized spectrographs, it is astrophysical noise that sets the true fundamental barrier on attainable RV precisions. In this paper, we parameterize the impact of solar surface magneto-convection on absorption line profiles, and extend the analysis from the solar disk center (Paper I) to the solar limb. Off disk-center, the plasma flows orthogonal to the granule tops begin to lie along the line of sight, and those parallel to the granule tops are no longer completely aligned with the observer. Moreover, the granulation is corrugated and the granules can block other granules, as well as the intergranular lane components. Overall, the visible plasma flows and geometry of the corrugated surface significantly impact the resultant line profiles and induce center-to-limb variations in shape and net position. We detail these herein, and compare to various solar observations. We find our granulation parameterization can recreate realistic line profiles and induced radial velocity shifts, across the stellar disk, indicative of both those found in computationally heavy radiative 3D magnetohydrodynamical simulations and empirical solar observations.
TL;DR: In this paper, a semi-empirical method is presented that predicts broadband hull-pressure fluctuations and underwater radiated noise due to propeller tip vortex cavitation, using a hump-shaped pattern for the spectrum and predicts the centre frequency and level of this hump.
Abstract: A semi-empirical method is presented that predicts broadband hull-pressure fluctuations and underwater radiated noise due to propeller tip vortex cavitation. The method uses a hump-shaped pattern for the spectrum and predicts the centre frequency and level of this hump. The principal parameter is the vortex cavity size, which is predicted by a combination of a boundary element method and a semi-empirical vortex model. It is shown that such a model is capable of representing the variation of cavity size with cavitation number well. Using a database of model- and full-scale measured hull-pressure data, an empirical formulation for the maximum level and centre frequency has been developed that is a function of, among other parameters, the cavity size. Acceptable results are obtained when comparing predicted and measured hull-pressure and radiated noise spectra for various cases. The comparison also shows differences that require adjustments of parameters that need to be further investigated.
TL;DR: In this paper, a new leading edge serration geometry is proposed which provides significantly greater noise reductions compared to the maximum noise reductions achievable by single-wavelength serrations of the same amplitude.
Abstract: Aerofoils operating in a turbulent flow generate broadband noise by scattering vorticity into sound at the leading edge. Previous work has demonstrated the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading edge noise. All of this work has focused on sinusoidal (single-wavelength) leading edge serration profiles. In this paper, a new leading edge serration geometry is proposed which provides significantly greater noise reductions compared to the maximum noise reductions achievable by single-wavelength serrations of the same amplitude. This is achieved through destructive interference between different parts of the aerofoil leading edge, and therefore involves a fundamentally different noise reduction mechanism from conventional single-wavelength serrations. The new leading edge serration profiles simply comprise the superposition of two single-wavelength components of different wavelength, amplitude and phase with the objective of forming two roots that are sufficiently close together and separated in the streamwise direction. Compact sources located at these root locations then interfere leading to less efficient radiation than single-wavelength geometries. A detailed parametric study is performed experimentally to investigate the sensitivity of the noise reductions to the profile geometry. A simple model is proposed to explain the noise reduction mechanism for these double wavelength serration profiles and shown to be in close agreement with the measured noise reduction spectra. The study is primarily performed on flat plates in an idealized turbulent flow. The paper concludes by introducing the double-wavelength serration on a 10% thick aerofoil, where near-identical noise reductions are obtained compared to the flat plate.