Low-noise Design Research Articles

Effect of the staggered impeller on reducing unsteady pressure pulsations of a centrifugal pump

AbstractThe emitted noise and vibration induced by the unsteady flow of the centrifugal pump are always focused during its running, which is also associated with the high amplitude pressure pulsations. How to reduce pressure pulsations remains a crucial problem for the researcher considering low noise design of the centrifugal pump. In the current research, a special staggered impeller is proposed to reduce intense pressure pulsations of a centrifugal pump with ns = 69 based on alleviating rotor‐stator interaction. The numerical simulation method is conducted to illustrate the influence of staggered impeller on the pump performance and pressure pulsations, and three typical flow rates (0.8ФN–1.2ФN) are simulated. Results show that the staggered impeller will lead to the pump head increasing, and at the design working condition, the increment reaches about 3% compared with the original impeller. Meanwhile, the pump efficiency is little affected by the staggered impeller, which is almost identical with the original impeller. From comparison of pressure spectra at 20 monitoring points around the impeller outlet, it is validated that the staggered impeller contributes significantly to decreasing pressure pulsations at the concerned working conditions. At the blade passing frequency, the averaged reduction of 20 points reaches 89% by using the staggered impeller at 1.0ФN. The reduction reaches to 90%, 80% at 0.8ФN, 1.2ФN, respectively. Caused by the rib within the staggered impeller, the internal flow field in the blade channel will be affected. Finally, it is concluded that the proposed staggered impeller surely has a significant effect on alleviating intense pressure pulsation of the model pump and does not obviously alter the global performance of the pump, which is very promising during the low noise pump design considering its feasibility for manufacturing.

Vibration characteristics and power flow analysis of irregular composite coupling laminated plate structures

This article presents a predictive model to investigate the vibration and power flow characteristics of irregular composite coupling laminated plates based on the 2D Chebyshev–Ritz method. First, the simplified physical model of coupling plate with arbitrary coupling angle is specified and the coordinates are defined for better describing the displacement components of irregular structures using Chebyshev polynomials. The Lagrange energy functionals of coupling plates are derived by the first-order shear deformation theory and the employment of boundary and coupling springs. The displacement admissible functions of coupling plates are constructed based on the Chebyshev polynomials of the first kind. Then, the vibration solutions of coupling plate structure can be well evaluated by the Ritz procedure. The convergence characteristics and calculation accuracy of the model are verified by a series of numerical examples. The effects of relevant parameters on the inherent characteristics and steady-state response of the coupling plate are further investigated. The proposed vibration model, based on the 2D Chebyshev–Ritz method, is not only capable of physically revealing the complex vibration and power flow phenomena of irregular composite coupling laminated plates and similar structures, but also provides a basis for structural low-noise design engineering.

Aeroacoustic noise prediction of a vertical axis wind turbine using large eddy simulation

This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

Evaluation and Comparison of Hybrid Wing VTOL UAV with Four Different Electric Propulsion Systems

Electric propulsion technology has attracted much attention in the aviation industry at present. It has the advantages of environmental protection, safety, low noise, and high design freedom. An important research branch of electric propulsion aircraft is electric vertical takeoff and landing (VTOL) aircraft, which is expected to play an important role in urban traffic in the future. Limited by battery energy density, all electric unmanned aerial vehicles (UAVs) are unable to meet the longer voyage. Series/parallel hybrid-electric propulsion and turboelectric propulsion are considered to be applied to VTOL UAVs to improve performances. In this paper, the potential of these four configurations of electric propulsion systems for small VTOL UAVs are evaluated and compared. The main purpose is to analyze the maximum takeoff mass and fuel consumption of VTOL UAVs with different propulsion systems that meet the same performance requirements and designed mission profiles. The differences and advantages of the four types propulsion VTOL UAV in the maximum takeoff mass and fuel consumption are obtained, which provides a basis for the design and configuration selection of VTOL UAV propulsion system.

Study on Characteristics of the Vibration and Noise of High-Power Scroll Compressor

With the rapid development of a high-power scroll compressor (HSC), the dynamic performance of a scroll compressor has an important impact on the vibration and noise of the whole compressor. So, the dynamic characteristics and structural acoustic radiation characteristics of HSC under dynamic excitation are studied by simulation and experiment in this paper. Firstly, the dynamic simulation model of HSC is established to analyze the time-domain and frequency-domain characteristics of bearing excitation and upper support excitation. At the same time, the finite element models of housing, upper support, and lower support are constructed to analyze the transient dynamic response of housing under the excitation source. Based on the vibration displacement of the housing surface, the prediction model of the housing radiated noise is also established, and then the radiated noise of the housing surface and the noise spectrum of the standardized test points are analyzed. Finally, the accuracy of the prediction model is verified by acoustic experiments. The experimental results show that the vibration and radiation noise of the housing can be accurately predicted by reasonable modeling to calculate the gas force and approximate the actual gas load. The vibration of the housing coupling system is the main source of the vibration characteristics of the HSC. The conclusions of the study can provide a reference for the low noise design of the HSC.

A Hybrid and Efficient Low-noise assessment Platform for Urban aerial mobility (HELPU)

Urban aerial mobility (UAM) is a promising approach to improve the traffic situation in gigantic cities, which, however, may encounter significant noise pollution issues. An integrated research platform, which is being established at HKUST, to include noise generation, long-distance propagation, and perception at the observers is timely to assess the environmental impact of UAM noise and to develop low-noise designs and flight planning. A high-quality test rig in the anechoic aerodynamic facility at HKUST is employed to measure the propeller aeroacoustics and aerodynamics, and to enable the innovative noise control device and design studies. The measurements and high-fidelity simulations using an in-house computational aeroacoustics solver can lead to comprehensive databases to facilitate and validate the development of physics-oriented noise prediction models. Also, high-efficient implementation of the boundary element method is conducted to account for the noise scattering due to the fuselage and then to evaluate the impact of UAM layout on the directivity patterns, which will then be efficiently projected to the far-field observers using the advanced Gaussian beam tracing with the effects due to moving source, atmospheric attenuation, and refraction, complex boundary absorption and reflection incorporated. Low-noise flight planning is then be made accordingly.

Urban 110 kV indoor substation noise analysis and control schemes: A real case study

As an important node in urban city, power substation provides the clean energy to thousands of households, ensuring a stable and high quality of urban life. However, the influence of noise emission from substation is always underestimated. With the improvement of environmental consciousness, making the substations quietly hidden in urban cities becomes an urgent issue which should be thoroughly considered. A real case is presented in this paper to vividly reflect how such a comprehensive noise issue is faced and tackled through proper techniques and novel applications. Based on the low-frequency noise characteristics of 110 kV power transformers and the limited space features of indoor substation, integrated noise control schemes are proposed with consideration of low-noise design of ventilation and heat dissipation systems. Dynamic vibration absorber is firstly investigated and designed to minimize the vibration of transformer tank. After the practical implementation, the acoustic environment is reevaluated and the measurement results verified the noise control effect. Consequently, the acoustic environment quality within and out of substation is improved and the negative impact of urban substation is controlled.

Noise Reduction Design of Steam Control Valve

The internal steam fluid pressure pulse force is the excitation source of control valve. Based on the Lighthill equation and the orifice injection shunt noise reduction theory, the flow noise and air noise calculations of throttling devices are carried out for the eccentric rotary control valve and the cage sleeve control valve, and the design improvements are presented for noise control of the valves. When there is no noise reduction internals, the air noise caused by the steam control valve with a pressure of 4.5MPa in front of the valve is greater than 95dB. The preset orifice plate reduces the pressure in the control valve to 50% of that before the valve, then the small hole Shunt method for noise reduction can be employed. When the two-stage orifice plate is installed and the number of second-stage holes is greater than 100, the air noise of the eccentric rotary steam control valve is lower than 80dB, and the first-stage orifice plate is installed. The air noise of the bored sleeve type steam control valve with preset orifice plate is also lower than 80dB, but it is easier to meet the low noise design requirements of the steam control valve than the improving method used in above sleeve type steam control valve.

A Theoretical Model for the Self-Noise of a Velocity-Broadband Seismometer

ABSTRACTA theoretical model of the seismometer self-noise can be used to predict the self-noise. Its inputs are mechanical and electrical parameters of the seismometer. In this article, we studied the theoretical model of the self-noise of the velocity-broadband seismometer, using the CS60 seismometer as an example. Velocity-broadband seismometer is a type of feedback seismometer. The previous theoretical model of the self-noise of the feedback seismometer only involved noise sources in the forward path of the feedback system. Our model involved not only noise sources in the forward path, but also noise sources in the feedback path and external to the feedback loop.We introduced noise sources in the feedback system of the seismometer and the method of calculating their levels with mechanical and electrical parameters, developed expressions for referring all noise sources to the input terminal of the feedback system, and finally established the model. We compared the CS60 seismometer’s predicted self-noise calculated using this model with the measured self-noise, and we found good agreement between them.The contribution of each noise source to the total noise was studied, and it was found that the dominant noise source in CS60 is different over different frequency bands. Over the frequency band below 0.0095 Hz, the noise of the integrator (in the feedback path) is the dominant noise source. Over the frequency band from 0.0095 to 0.21 Hz, suspension noise is the dominant noise source. Over the frequency band from 0.21 to 39 Hz, the noise of the differential driver (external to the feedback loop) is the dominant noise source. Over the frequency band above 39 Hz, the noise of the preamplifier (in the forward path) is the dominant noise source. In addition, some viewpoints about the low-noise design of seismometers were proposed.

Prediction of vibration radiation noise from shell of straw crushing machine

In order to predict the radiation noise of the vibrating shell of the straw crusher in the design phase, the computational fluid dynamics–discrete element coupling method is initially used to simulate the airflow–straw coupled flow field in the straw crusher, and the pulsating pressure generated by the coupled flow field is applied to the inner surface of the shell of the crusher. Then, the harmonic response of the shell is analyzed, and its results are used to be the acoustic boundary condition. Finally, the finite element and acoustic boundary element combined test methods are used to predict vibration noise of the straw crusher shell. The results indicate that the produced vibration noise of the straw crusher shell changes as the excitation frequency of the rotor rotation changes. The maximum vibration noise is achieved at the excitation fundamental frequency, and radiation noises at the harmonic frequencies decrease as the frequency increases. The simulated value of the sound pressure level of each measuring point at the excitation fundamental frequency and harmonic frequencies is basically the same as those of the experiment. Moreover, it is found that the maximum difference between the simulated and experimental value of measuring points is 1.69 dB(A). Therefore, it is concluded that the numerical model of the vibration radiation noise is accurate. The vibration noise of the shell at the inlet is the largest, and the main noise source of the vibration radiation noise is the dipole sound source of the rotating hammer rotor. The corresponding design method provides the reference for the low-noise design of straw crushers.

Noise simulation and low noise design of skinned panel structure of scientific experiment rack

The noise of the scientific experiment rack radiates into the space station through the skinned structure, which directly affects the safety and health of astronauts in orbit for a long time, so it is necessary to carry out low-noise design. Firstly, the finite element model of the panel structure is established, and the correctness of the model is verified by modal test. Secondly, select a point as the vibration excitation point on the finite element model of the plate structure to simulate the vibration input of the excitation source, obtain its vibration response through the modal superposition method, take the vibration response as the boundary condition of the acoustic boundary element, use the modal acoustic transfer vector technology to calculate the radiation noise of the plate structure, and verify it through the noise test in the half anechoic chamber. Then, the acoustic pressure contribution analysis of the radiated noise from the skinned panel structure is carried out, and the panel area which can reduce the radiated noise of the target is determined. The constrained damping layer is applied in this area. The results show that the radiated noise at the target position is significantly reduced.

Influence of different parameters on nonlinear friction-induced vibration characteristics of water lubricated stern bearings

To investigate the mechanism of friction-induced vibration and noise of ship water lubricated stern bearings, a two-degree-of-freedom (2-DOF) nonlinear self-excited vibration model is established. The novelty of this work lies in the detailed analysis of influence of different parameters on the stability and nonlinear vibration characteristics of the system, which provides a theoretical basis for the various friction vibration and noise phenomenon and has a very important directive meaning for low noise design of water lubricated stern bearings. The results reveal that the change of any parameter, such as rotating speed of shaft, contact pressure, friction coefficient, system damping and stiffness, has an important influence on the stability and nonlinear response of the system. The vibration amplitudes of the system increase as (a) rotating speed of shaft, contact pressure, and the ratio of static friction coefficient to dynamic friction coefficient increase and (b) the transmission damping between motor and shaft decreases. The frequency spectrum of the system is modulated by the first mode natural frequency, which is continuous multi-harmonics of the first mode natural frequency. The response of the system presents a quasi-periodic motion.

A Miniature Transformer-Coupled Low-Noise Preamplifier for Low Source Resistance Sensors at Low Frequency

Transformer-coupling technique plays a key role in low-noise design methodology. Recently, there has been an increasing amount of research undertaken on developing dedicated transformer-coupled low-noise preamplifiers for particular sensors or systems. However, no research exists which combines an in-depth analysis of analytical models with a thorough under-standing of performance specifications in terms of background noise, input range, bandwidth, and size. In this research, we present a small-signal model and a noise model for these preamplifiers along with fundamental design parameters. We design, construct, and test a prototype miniature transformer-coupled low-noise preamplifier for a specific resistive sensor with a source resistance below 0.1Ω in a frequency band of interest between several Hertz and 1kHz. Proposed models are validated by the excellent agreement between the simulation and experiment results. Results show the input-referred voltage noise at room temperature settles to about 25pV/√Hz and 35pV/√Hz at 10Hz when the source resistance is 6mΩ and 36mΩ, respectively. This research will serve as a basis for future studies on high resolution resistive sensors and systems.

Experimental investigation of the ring-planet gear meshing forces identification

The dynamic gear meshing forces are the primary sources of vibration and noise in planetary gear transmissions (PGTs), leading to lower transmission accuracy and shorter service life. An accurate estimation of dynamic meshing forces is valuable for the low vibration and noise design and condition monitoring of PGTs. In this paper, we aim to evaluate the dynamic ring-planet gear meshing forces in PGTs, and a moving forces identification model is developed to evaluate the ring-planet meshing forces. Firstly, the ring-planet meshing forces are modelled as moving forces acting on the inner wall of the ring gear. Extend frequency response functions (EFRFs) are proposed to represent the time-varying vibration transmission path of the PGTs. Then, a moving force identification (MFI) model is established to evaluate the meshing forces. Besides, singular value decomposition (SVD) and regularization techniques are employed to solve the ill-posed inverse problem. A simplified ring model is taken as an example for numerical investigation to access the accuracy and feasibility of the proposed method. Finally, experimental vibration signals are used to identify ring-planet meshing forces. Compared with the testing meshing forces derived from dynamic strain signals, identification results indicated that the presented method can evaluate the dynamic ring-planet meshing forces with acceptable results.

Tonal-Noise Assessment of Quadrotor-Type UAV Using Source-Mode Expansions

The present work deals with the modeling of the aerodynamic sound generated by the propellers of small-size drones, taking into account the effects of horizontal forward flight with negative pitch and of installation on supporting struts. Analytical aeroacoustic formulations are used, dedicated to the loading noise. The fluctuating lift forces on the blades are expanded as circular distributions of acoustic dipoles, the radiated field of which is calculated by using the free-space Green’s function. This provides descriptions of the sound field, valid in the entire space. The stationary mean-flow distortions responsible for the lift fluctuations and at the origin of the sound are estimated from existing numerical flow simulations and from ad hoc models. Installation and forward-flight effects are found to generate much more sound than the steady loading on the blades associated with thrust. Therefore, the models are believed reliable fast-running tools that could be used for preliminary low-noise design through repeated parametric calculations, or for noise-impact estimates corresponding to prescribed urban traffic.

Research on Radial Force of Permanent Magnet Synchronous Motor Based on Maxwell

In the existing permanent magnet motor drive system, the vibration and noise problems caused by motor and driver are more and more obvious and complex. Among them, the radial electromagnetic force fluctuation problem of permanent magnet synchronous motor (PMSM) stator is the most important cause of vibration and noise. The radial electromagnetic force fluctuation of PMSM stator is the main source of vibration and noise. In order to lay a solid foundation for studying the distribution of vibration and noise, the radial electromagnetic force of 12 slot 14 pole PMSM is calculated by combining Maxwell stress method and Lorentz force method. Based on the Maxwell platform, a solution model is established to analyze the radial electromagnetic force of motor in time and space. The time–space analysis diagram of radial electromagnetic force in no-load section and load section is given; it is helpful to avoid resonance point and realize low-noise design of motor.

Multi-Rate Low-Noise Optical Receiver Front-End

Conventional optical receivers are mostly optimized for single data rate. In this work, after examining conventional optical front-ends, we present the low-noise tunable front-end (LNTF) topology, which is able to achieve optimized noise performance at multiple data rates. In addition, colored noise optimization techniques including capacitive noise scaling and CMOS inverter based transimpedance amplifier (TIA) are also studied, which together with the LNTF form a low-noise design methodology for silicon photonics based CMOS optical receiver. Employing these techniques, the implemented 3D hybrid-integrated silicon photonics receiver achieves excellent noise performance of 0.91 μArms and 0.5 μArms input-referred noise current at 25 and 10 Gb/s, respectively, which enables high sensitivity of −14.6 dBm and −16.5 dBm OMA at BER = 10−12, correspondingly.

V-Band GaAs Metamorphic Low-Noise Amplifier Design Technique for Sharp Gain Roll-Off at Lower Frequencies

In this letter, we present the design of a V- band low-noise amplifier for intersatellite crosslink receivers. The test vehicle, realized on industrial metamorphic gallium arsenide technology, operates from 57 to 66 GHz exhibiting 23-dB gain and an average 1.8-dB noise figure. Particular attention was devoted to the analysis and synthesis of an alternative bias injection topology to obtain a sharp gain roll-off at lower frequencies, thus avoiding the insertion, at system level, of an image-reject filter.

Rapid functional optoacoustic micro-angiography in a burst mode.

Optoacoustic microscopy (OAM) can image intrinsic optical absorption contrast at depths of several millimeters where state-of-the-art optical microscopy techniques fail due to intense light scattering in living tissues. Yet, wide adoption of OAM in biology and medicine is hindered by slow image acquisition speed, small field of view (FOV), and/or lack of spectral differentiation capacity of common system implementations. We report on a rapid acquisition functional optoacoustic micro-angiography approach that employs a burst-mode laser triggering scheme to simultaneously acquire multi-wavelength 3D images over an extended FOV covering ${50}\;{\rm mm} \times {50}\;{\rm mm}$50mm×50mm in a single mechanical overfly scan, attaining 28 µm and 14 µm resolution in lateral and axial dimensions, respectively. Owing to an ultrawideband low-noise design featuring a spherically focused polyvinylidene difluoride transducer, we demonstrate imaging of human skin and underlying vasculature at up to 3.8 mm depth when using per-pulse laser energies of only 25 µJ without employing signal averaging. Overall, the developed system greatly enhances performance and usability of OAM for dermatologic and micro-angiographic studies.

Suppression of reverberations at fiber tips for optical ultrasound sensing

Fabry-Perot-based ultrasound sensors at fiber tips have performed high sensitivity and immunity of electromagnetic interference with a relatively compact size. Nevertheless, the reverberation at fiber tips causes a strong noise that degrades the sensing capability. Here we propose a fiber optical-based ultrasound sensor with three design approaches to reduce the reverberation, including designs with an eccentric core, absorptive shield, and arc edge. The effect was experimentally validated with a photoacoustic signal excitation. Compared with bare single-mode fibers in simulation, the low-reverberation design increased the signal-to-noise ratio by 32.1 dB with identical excitation. The experimental results demonstrated the "clean" response with almost invisible reverberations, which was validated by a commercial hydrophone. This research solved the reverberation problems and provided a low-noise design for fiber optic ultrasound sensing.