Mechanical Vibration Noise Research Articles

Dynamic analysis and experimental investigation of particle damping for the vibration reduction and isolation of floating raft using the two-phase flow theory of gas-particle

ABSTRACT To ensure an effective and smooth operation of shipborne equipment and show ships’ vitality, the floating raft is universally used to reduce mechanical vibration and underwater-radiated noise. However, the vibration amplification phenomenon still occurs in low-frequency excitation of shipborne equipment. Accordingly, a new idea for enhancing vibration reduction and isolation performance of floating rafts for shipborne equipment based on particle damping is proposed. Considering particle-particle frictions and collisions inside the damper, a mathematical model of particle damping using the two-phase flow theory of gas-particle is derived for the dynamic analysis combined with the finite element method. The damping effect for vibration reduction is obtained by dynamic analysis with different dampers-installation schemes in raft structures. An experimental platform for the floating raft with particle dampers is built. Comparing its dynamic analysis with experimental investigation results, the rationality and feasibility of the mathematical model of particle damping are demonstrated. In addition, this research further indicates that particle damping enhances the vibration isolation performance of floating rafts in low-frequency excitation for shipborne equipment, which is of great practical significance to improve the combat effectiveness of ships.

Performance benchmarking of an ultra-low vibration laboratory to host a commercial millikelvin scanning tunnelling microscope

Ultra-low temperature scanning tunnelling microscopy and spectroscopy (STM/STS) achieved by dilution refrigeration can provide unrivalled insight into the local electronic structure of quantum materials and atomic-scale quantum systems. Effective isolation from mechanical vibration and acoustic noise is critical in order to achieve ultimate spatial and energy resolution. Here, we report on the design and performance of an ultra-low vibration (ULV) laboratory hosting a customized but otherwise commercially available 40 mK STM. The design of the vibration isolation consists of a T-shaped concrete mass block (∼55t), suspended by actively controlled pneumatic springs, and placed on a foundation separated from the surrounding building in a ‘room-within-a-room’ design. Vibration levels achieved are meeting the VC-M vibration standard at >3 Hz, reached only in a limited number of laboratories worldwide. Measurement of the STM’s junction noise confirms effective vibration isolation on par with custom built STMs in ULV laboratories. In this tailored low-vibration environment, the STM achieves an energy resolution of 43 μeV (144 mK), promising for the investigation and control of quantum matter at atomic length scales.

Effectiveness analysis of twelve sectors of DTC based on a newly modified switching table implemented on a wind turbine DFIG system under variable wind velocity

This paper aims to present a novel Direct Torque Control (DTC) strategy based on twelve sectors and a new Modified Switching Table (12-MST-DTC) used to control the Doubly Fed Induction Generator (DFIG) powered by Wind Turbine (WT) and operating under random wind speed. Robustness and fast dynamic performances have made Conventional DTC (C-DTC) popular and widely used, but presents major drawbacks which are high torque and flux ripples. Therefore, the 12-DTC has been proposed in the literature as an improvement but suffers from significant oscillations during super-synchronous operation mode as well as the case of overspeed. The proposed control strategy maintains the performances that offer (C-DTC and 12-DTC) and furthermore minimizes those drawbacks. The newly modified switching table is designed with additional input to cover all WT-DFIG system operation modes (sub-, super- and synchronous modes in addition to the case of over-speed) in order to diminish the flux, torque ripples and THD of the AC-grid injected currents. For optimal operating of variable-speed WT, MPPT algorithm and blade pitch control are invested. Simulation results of the 12-MST-DTC are compared with those of C-DTC and 12-DTC using MATLAB/Simulink environment treating all operation modes of WT-DFIG system and even in case of wind over speeds. The comparison results demonstrate the efficiency of the proposed control strategy in terms of flux/torque ripples and THD reduction, therefore fewer DFIG mechanical vibration and acoustic noise.

Measurement of alternating and rotational magnetostrictions of Non-oriented silicon steel sheets

Extensive numerical analyses and experimental tests have shown that while major regions of magnetic cores in electromagnetic devices, such as transformers and rotating electric machines, are dominated by the alternating magnetic fields, the rotating magnetic fields exist in the corner joints of multi-phase transformers and the yoke area behind the teeth of rotating electric machines. These magnetic fields cause core losses due to hysteresis and eddy currents, mechanical vibration and acoustic noises due to magnetostriction. Many studies have been reported in the literature on alternating and rotational core losses and alternating magnetostriction, but not so much on rotational magnetostriction, especially in non-oriented (NO) silicon steel sheets. The vibration and noise caused by rotational magnetostriction are much higher than those caused by alternating magnetostriction. This paper reports the development of a magnetostriction measurement system consisting of a 2D symmetrical single sheet tester (SST) and resistance strain gauges. The selection considerations of resistance strain gauges are summarized. The alternating and rotational magnetostriction characteristics of a NO silicon steel, B35A300 (0.35 mm), are measured. Because the rotating magnetic field in the stator is not always ideally circular but more often elliptical, the magnetostriction under elliptical magnetizations with different axis ratios is also measured. The magnetostriction anisotropy of the NO steel sheet is observed and analyzed. The elongation and contraction under alternating, circular and elliptical rotating magnetizations with different axis ratios are discussed. The results can provide data support for calculating and designing multi-phase transformers and rotating electric machines under different types of magnetizations. The research can provide theoretical and practical guidance for mitigating mechanical vibration and acoustic noise caused by magnetostriction.

Experimental study on electromechanical performance decoupling and vibration suppression of crystal oscillator

In the mechanical vibration environment, the phase noise of crystal oscillator would deteriorate sharply, which would lead to the decline of the stability of crystal oscillator and affect the comprehensive performance of the whole electronic equipment. In this paper, the mechanism of electromechanical coupling between mechanical vibration and phase noise is analysed theoretically. The relationship between phase noise and vibration magnitude and the sensitivity of phase noise to different vibration frequencies and directions are studied experimentally, then the decoupling of mechanical performance and electrical performance is realized. Based on this, a vibration isolator for crystal oscillator is designed, which can achieve 15-2000Hz full frequency band random vibration attenuation, the vibration acceleration RMS value is reduced by 95%, and the phase noise degradation of crystal oscillator is less than 5dB. The research has a certain reference value for the vibration isolation design of electromechanical coupling vibration sensitive devices.

Marine self-potential measurement tool for autonomous underwater vehicle.

Marine self-potential (SP) measurement is commonly conducted for seafloor sulfide detection and hydrothermal vent studies in deep water using instruments towed close to the seafloor. However, this method has the following shortcomings: (1) It relies on ships for deep towing, and the need for a dedicated ship time lowers its efficiency. (2) Owing to complex topography, most towed instruments are located far from the seafloor to ensure safety, resulting in large effective signal attenuation and low signal-to-noise ratio. (3) The measurement direction is generally a single axis, with only the electric field of the axial component observed, providing limited information. With the gradual maturity of autonomous underwater vehicle (AUV) technology, it has become possible to mount marine SP measurement tools on AUVs for detection. Compared with conventional methods, this method has significant advantages in terms of efficiency, signal-to-noise ratio, and multicomponent observation. The proposed tool is a lightweight underwater device having a compact design and low power consumption, making it suitable for AUVs. The overall volume of the tool is D50mm × L350mm, and the underwater weight is 0.6kg. Chopper amplification technology ensures the low-noise measurement of electric field signals. In addition, the reformed electrodes enhance stability, thereby reducing the mechanical vibration noise. Laboratory test results show that the noise of the data logger is 7.8 nV/rt (Hz)@1Hz. The marine test conducted in the southwest Indian Ocean verified the reliability of the proposed marine SP measurement tool. The maximum working depth was 4000m. The test lasted ∼25 h, and the effective electric field data were collected for ∼17 h. This survey found a maximum SP anomaly of 0.55 mV/m in the Yuhuang hydrothermal field, which provided effective data support for the discovery of new seafloor sulfide anomalies.

IF 기동방식 센서리스 압축기의 소음 및 진동 저감 제어

This paper presents a simple mechanical vibration and acoustic noise reduction of IF(current-frequency) starting sensorless controlled compressor. The adopted compressor is controlled by the sensorless estimation using back EMF observer in the normal speed range. In order to increase the speed up to normal sensorless speed range, the IF open-loop starting method is used. At the IF starting, the speed variation from the fluid load makes a mechanical vibration and acoustic noise. In order to reduce the mechanical vibration and acoustic noise, a simple variable torque slope with initial rotor position estimation method is proposed in this paper. The proposed method uses an initial rotor position estimation than a conventional rotor alignment method. And, the torque reference slope according to the increased open-loop speed is changed by the hysteresis error between the open-loop reference speed and the estimated speed. Because of the initial rotor position and the variable current according to the speed can reduce the collision of the compressor at standstill and low-speed region. Consequently the mechanical vibration and acoustic noise can be reduced.BRThe proposed simple variable IF starting method is verified 2.2kW IPMSM driven HVAC(Heating, Ventilation & Air conditioning) compressor. Experimental results shows the reduced vibration and acoustic noise at the starting to normal speed range.

A high degree of direct torque control applied to a grid-connected wind energy system based on a DFIG

This paper presents the performances improvement of a doubly fed induction generator (DFIG) driven by a wind turbine (WT) using direct torque control (DTC). However, the major drawbacks related to DTC are high torque/flux ripples that produce mechanical vibration and disagreeable noise. The use of multilevel inverters seems to be an interesting solution. A three-level voltage source (inverter) converter (3LVSI) connected to the rotor side of the DFIG is considered in this paper. The high freedom degree of the voltage vectors selection in the 3LVSI allows a control with minimal torque and flux ripples. In addition, a fuzzy logic approach is introduced, to ensure an intelligent extraction of the energy sweeping the WT blades. A variable adjustment step enables an optimal extraction in a minimum tracking time with significant reduction of oscillations in the steady state. Simulation results obtained using MATLAB/SIMULINK demonstrate the effectiveness of the 3LVSI-DTC control based on Fuzzy MPPT in the wind energy conversion system (WECS).

A System Phase Noise Model for Frequency-Modulated MEMS Gyroscopes

A system phase noise model is proposed in this paper for frequency-modulated (FM) gyroscopes, which gives us a clearly guidance for different noise and how to improve the final performance. The author here introduces a mathematical calculation method to deal with the time domain noise and transforms the time-varying noise into phase modulation paths to analyze the frequency noise effect. Meanwhile, the proposed model reveals the relationships about mechanical vibration noise mechanical additional loop noise and performance indicators. In this way, combing frequency spectrum and Allan variance curves, the weight of each noise can be determined. Here, we get different physical noise sources from actual circuit chip by the proposed phase noise decomposition method and analyze the whole noise contribution. After that, we can clearly understand the performance indicators required to design the circuit. Finally, this work offers a whole theory instructions to quantitate different frequency noise for FM gyroscopes.

Experimental and Informational Modeling Study of Sustainable Self-Compacting Geopolymer Concrete

Self-compacting concrete (SCC) became a strong candidate for various construction applications owing to its excellent workability, low labor demand, and enhanced finish-ability, and because it provides a solution to the problem of mechanical vibration and related noise pollution in urban settings. However, the production of Portland cement (PC) as a primary constituent of SCC is energy-intensive, contributing to about 7% of global carbon dioxide (CO2) emissions. Conversely, the use of alternative geopolymer binders (GBs) in concrete can significantly reduce the energy consumption and CO2 emissions. In addition, using GBs in SCC can produce unique sustainable concrete with unparallel engineering properties. In this outlook, this work investigated the development of some eco-efficient self-compacting geopolymer concretes (SCGCs) obtained by incorporating different dosages of fly ash (FA) and ground blast furnace slag (GBFS). The structural, morphological, and mechanical traits of these SCGCs were examined via non-destructive tests like X-ray diffraction (XRD) and scanning electron microscopy (SEM). The workability and mechanical properties of six SCGC mixtures were examined using various measurements, and the obtained results were analyzed and discussed. Furthermore, an optimized hybrid artificial neural network (ANN) coupled with a metaheuristic Bat optimization algorithm was developed to estimate the compressive strength (CS) of these SCGCs. The results demonstrated that it is possible to achieve appropriate workability and mechanical strength through 50% partial replacement of GBFS with FA in the SCGC precursor binder. It is established that the proposed Bat-ANN model can offer an effective intelligent method for estimating the mechanical properties of various SCGC mixtures with superior reliability and accuracy via preventing the need for laborious, costly, and time-consuming laboratory trial batches that are responsible for substantial materials wastage.

Study on Self Compacting Geopolynmer Concrete

Self-compacting concrete (SCC) became a strong candidate for various construction applications owing to its excellent workability, low labor demand, and enhanced finish-ability, and because it provides a solution to the problem of mechanical vibration and related noise pollution in urban settings. However, the production of Portland cement (PC) as a primary constituent of SCC is energy-intensive, contributing to about 7% of global carbon dioxide (CO2 emissions. Conversely, the use of alternative geopolymer binders (GBs) in concrete can significantly reduce the energy consumption and CO2 emissions. In addition, using GBs in SCC can produce unique sustainable concrete with unparallel engineering properties. In this outlook, this work investigated the development of some eco-efficient self-compacting geopolymer concretes (SCGCs) obtained by incorporating different dosages of fly ash (FA) and ground blast furnace slag (GBFS). The structural, morphological, and mechanical traits of these SCGCs were examined via non-destructive tests like X-ray diffraction (XRD) and scanning electron microscopy (SEM). The workability and mechanical properties of six SCGC mixtures were examined using various measurements, and the obtained results were analyzed and discussed. Furthermore, an optimized hybrid artificial neural network (ANN) coupled with a metaheuristic Bat optimization algorithm was developed to estimate the compressive strength (CS) of these SCGCs. The results demonstrated that it is possible to achieve appropriate workability and mechanical strength through 50% partial replacement of GBFS with FA in the SCGC precursor binder. It is established that the proposed Bat-ANN model can offer an effective intelligent method for estimating the mechanical properties of various SCGC mixtures with superior reliability and accuracy via preventing the need for laborious, costly, and time-consuming laboratory trial batches that are responsible for substantial materials wastage.

Imaging error compensation method for through-focus scanning optical microscopy images based on deep learning.

Through-focus scanning optical microscopy (TSOM) is a model-based nanoscale metrology technique which combines conventional bright-field microscopy and the relevant numerical simulations. A TSOM image is generated after through-focus scanning and data processing. However, the mechanical vibration and optical noise introduced into the TSOM image during image generation can affect the measurement accuracy. To reduce this effect, this paper proposes a imaging error compensation method for the TSOM image based on deep learning with U-Net. Here, the simulated TSOM image is regarded as the ground truth, and the U-Net is trained using the experimental TSOM images by means of a supervised learning strategy. The experimental TSOM image is first encoded and then decoded with the U-shaped structure of the U-Net. The difference between the experimental and simulated TSOM images is minimised by iteratively updating the weights and bias factors of the network, to obtain the compensated TSOM image. The proposed method is applied for optimising the TSOM images for nanoscale linewidth estimation. The results demonstrate that the proposed method performs as expected and provides a significant enhancement in accuracy.

Research on the Method of Suppressing the End Detent Force of Permanent Magnet Linear Synchronous Motor Based on Stepped Double Auxiliary Pole

Permanent magnet linear synchronous motors have the advantages of high thrust density, high acceleration, high speed, and high efficiency, which are widely used in CNC lathes, lithography machines, rail transportation, etc. In high-speed, high-precision servo control systems, detent force fluctuation caused by end effect can easily cause problems such as speed fluctuation, mechanical vibration and electromagnetic noise, which affect the servo performance of permanent magnet linear synchronous motors. Aiming at the detent force fluctuation caused by the end effect of permanent magnet linear synchronous motor, this paper proposes a stepped double auxiliary pole method. The method has a good suppression effect on the end normal force fluctuation and the end thrust fluctuation, which improves the servo performance of the permanent magnet linear synchronous motor in the high-precision servo system. In the traditional methods of suppressing the fluctuation of end detent force, two common methods are using a magnetic isolation aluminum plate and optimizing the auxiliary pole size. The former needs a magnetic isolation aluminum plate to connect the auxiliary pole and the primary mover. Therefore, it needs to add the connection device to connect those three parts. The connection device complicates the auxiliary pole part and increases manufacturing difficulty. The latter does not change the manufacturing process, but in the early design process, the optimum size of the auxiliary needs to be considered. Compared with these two methods, the one proposed in this paper avoids the complex structure of magnetic isolation aluminum plate, the stepped double auxiliary pole is integrated with the primary mover. Moreover, it has a fixed structure with optimum size. Therefore, the method in the paper does not change the manufacturing process, improves the strength of the initial pole structure, and reduces design period. Finally, the finite element analysis by ANSYS was performed to illustrate the correctness and effectiveness of the method.

The Acoustic Emission Testing Technology on Large Crane Structure Damage

The Acoustic Emission testing application on Crane steel structure is greatly limited, because of the factors such as the random transmission path of sound wave, the influence of dynamic load noise and the discontinuity of structure. In this paper, the feasibility of Acoustic Emission detection for crane structure damage is discussed from two aspects: mechanism test and field detection. Based on the analysis of the whole test process, when lifting heavy objects and braking, the metal structure is subjected to the instantaneous gravity load of tens of tons, so that a large number of AE signals are collected by various monitoring sensors. It mainly includes active defect damage, mechanical vibration, structural friction and electrical noise, etc. At this time, the effective defect expansion signal is compared with the noise signal. However, in the load maintenance phase, the noise signal disappears or drops to a very low level. At this point, if a sensor still collects a strong active AE signal, it is highly likely that there is a damage source in this area. Compared with the traditional mechanical properties of materials, AE characteristic parameters, such as amplitude, ringing count and energy count, can reflect the microscopic damage changes of materials under load in a more detailed way. By summing up the distribution range of AE parameters corresponding to different damage mechanisms and typical signal characteristics, such as the double peaks phenomenon in the material yield stage, it can provide a scientific foundation for the application of AET in the metal structure damage of large lifting machinery.

Active omni wheel possessing seamless periphery and omnidirectional vehicle using it

Vehicles that are capable of achieving omnidirectional movement will work very efficiently in factories and warehouses. To meet this requirement, various omnidirectional vehicles have been proposed, but the wheel mechanism makes precise movement difficult. The active omni wheel (AOW), which can drive itself in an arbitrary direction at any time, can address this issue, but our previous design had mechanical vibration and acoustic noise due to gaps in the outer circumference of the wheel, and its complicated structure had a large number of parts. To solve these problems, this study developed a new AOW possessing a seamless periphery and simple structure. By using barrel-shaped friction-driven outer rollers arranged alternately on the left and right sides of the wheel, gaps between the outer rollers are eliminated and a smooth periphery is realized. Additionally, the power transmission paths were simplified to reduce the number of parts. This paper explains the AOW structure and then presents analyses of structural conditions and kinematics of the AOW. A two-wheel-drive omnidirectional vehicle using the AOW was built and kinematically analyzed. Finally, experiments using the developed AOW and vehicle were conducted and their effectiveness was verified.

Iterative Learning Identification and Compensation of Space-Periodic Disturbance in PMLSM Systems With Time Delay

This paper aims to solve a closed-loop identification problem for the space-periodic force ripple in permanent-magnet linear synchronous motor (PMLSM) systems. Conventional identification schemes use the overall error signal to update estimates. However, the error caused by mechanical vibration and measurement noise could affect and even deteriorate the identification performance. In this paper, a novel iterative learning identification method that utilizes the partial but most pertinent information in the error signal is proposed to identify the force ripple. First, the effective error signal caused by the reference trajectory and the force ripple are extracted by projecting the overall error signal to a subspace. The subspace is spanned by some basis functions selected on the basis of the physical model of the PMLSM and the sinusoidal model of the force ripple. The time delay of the PMLSM system is compensated in these basis functions. Then, a norm-optimal approach is proposed to design the learning gain. The monotonic convergence of the iterative learning identification is further analyzed. Numerical simulation and experiments are provided to validate the proposed method and confirm its feasibility and effectiveness in force ripple identification, as well as its compensation.

Vibration and Noise in Magnetic Resonance Imaging of the Vocal Tract: Differences between Whole-Body and Open-Air Devices.

This article compares open-air and whole-body magnetic resonance imaging (MRI) equipment working with a weak magnetic field as regards the methods of its generation, spectral properties of mechanical vibration and acoustic noise produced by gradient coils during the scanning process, and the measured noise intensity. These devices are used for non-invasive MRI reconstruction of the human vocal tract during phonation with simultaneous speech recording. In this case, the vibration and noise have negative influence on quality of speech signal. Two basic measurement experiments were performed within the paper: mapping sound pressure levels in the MRI device vicinity and picking up vibration and noise signals in the MRI scanning area. Spectral characteristics of these signals are then analyzed statistically and compared visually and numerically.

Comb-referenced frequency-sweeping interferometry for precisely measuring large stepped structures.

A precise 3D surface measurement method for large stepped structures without height ambiguity is proposed based on optical-frequency-comb-referenced frequency-sweeping interferometry and Fourier-transformed fractional phase retrieval. Unlike other interferometry that depends on the absolute phase value for several certain wavelengths, this method obtains results from the phase change during frequency sweeping and thus remains free from the confined non-ambiguity range. By reference to an optical frequency comb, the relative uncertainty from the tunable laser frequency was reduced by three orders of magnitude, and the sweeping frequency range can be precisely determined. Besides, the fractional phase can be rapidly retrieved in only one step using a Fourier transform method, with advantages of high accuracy and immunity to light intensity fluctuation and mechanical vibration noise. Samples of step heights from 1μm to 1mm were measured, and the standard uncertainty was 45nm. This permits applications such as quality assurance in microelectronics production and micro-electro-mechanical system (MEMS) manufacture.

Influence of DC-Link Voltage on Commutation Torque Ripple of Brushless DC Motors with Two-Segment Pulse-width Modulation Control Method

The commutation process causes current ripple to be generated in the drive system of brushless DC (BLDC) motor. This, in turn, leads to output torque ripple. Mechanical vibration and acoustic noise are its influences which are undesirable phenomenon in some applications. A new method is presented in this paper which reduces torque ripple and commutation period in the entire range of motor speed. This method is designed and implemented based on two-segment pulse-width modulation (PWM) and DC-link voltage doubling during commutation. Based on the presented theory and given the influence of DC-link voltage on ripple magnitude, some experiments are carried out in which simultaneous association of the above mentioned factors in reducing current ripple and commutation time in the entire speed range of rotor has been proved. The experimental results show that the current ripple magnitude in high speed range is almost 20 times less than conventional method based on H-PWM_L-ON technique.

Principle analysis of snapshot Mueller matrix imaging polarimeter using birefringent crystal

Conventional Muller matrix imaging polarimeter (MMIP) with several rotating elements suffers mechanical complexity, vibration noise, heat generation, and other unwanted problems. To overcome those shortcomings, we present a snapshot Muller matrix imaging polarimeter (SMMIP) using a birefringent crystal with high extinction ratio. The snapshot imaging polarimeter allows a single image to be used to measure the polarization of a scene without electronic control units or moving mechanical components. This new polarimeter combines the technique of Muller matrix spectropolarimetry with a snapshot imaging polarimeter through using modified Savart polariscope (MSP-SMMIP). It contains both a generator and an analyzer module. Spatial polarization fringes are localized on a sample by incorporating modified Savart polariscope into a polarization generator module. These fringes modulate the Mueller matrix components of the sample, which are subsequently isolated with modified Savart polariscope in an analyzer module, and the analyzer and the imaging lens combine with 16 beams to create interference, resulting in spatial modulation on the two-dimensional CCD camera. Expressions for interference intensities, optical system analysis, theory of calibration and method of reconstruction are presented. Finally, the numerical simulation is used to demonstrate theoretical analysis and the feasibility of MSP-SMMIP. The layout is very easy to calibrate and the reference target is only a linear polarizer at 22.5°. Moreover, the remarkable advantages of the proposed instrument, compared with conventional Muller matrix imaging polarimeter, are that it is also simple, compact, snapshotted, and static (no moving parts). Therefore we believe that the proposed snapshot imaging polarimeter will be very useful in many applications, such as biomedical imaging and remote sensing.