Frequency Of Shaft Research Articles

Utilizing porous dielectric material to enhance the performance of capacitive MEMS accelerometers for shaft monitoring

This research investigates the optimization of the performance of a capacitive-based microelectromechanical systems (MEMS) shaft monitoring accelerometer using a porous soft dielectric material with high polarization capability and low Young’s modulus. The nonlinear governing equations of a microbeam with a proof mass coupled with the squeeze motion equation of the polymeric dielectric material excited by shaft vibrations are extracted and solved in both the spatial and temporal domains. The studied model considers the stiffness, dissipative, and inertial effects of the polymeric material and incorporates porosity as a displacement-dependent variable, which introduces an additional nonlinearity. After discretizing the coupled nonlinear differential equations using the Galerkin method, the response in the frequency domain is obtained by applying an energy balance method, where the coefficients of the Fourier expansion of the response are found by arc-length continuation through a physical gradient descent learning-based approach method. The occurrence of secondary and primary resonances in different harmonic responses is studied for different harmonic acceleration inputs. The equivalent rigidity of the design is investigated for different shaft frequency magnitudes and different proof mass geometries. The effect of the initial porosity volume fraction of the elastomeric dielectric material on the dynamic response of the accelerometer is also examined. The sensor’s sensitivity is dependent on its geometry and properties and can vary based on the structure’s material parameters. Consequently, the selection of different geometries and materials may result in either an improvement or a deterioration of the sensor’s performance.

Study on the influence of guide vane opening on pressure pulsation of pump-turbine under zero flow pump condition

Abstract Reversible pump-turbine is the key equipment of energy conversion in large pumped storage power station, and it is the core of stable operation of power station. Under the pump condition, the internal pressure pulsation law of the pump-turbine has an important influence on the stable operation of the pump. In order to study the pressure pulsation characteristics of pump-turbine in pump mode under zero flow condition, this study carried out unsteady numerical simulation on three kinds of guide vane openings, and analyzed the amplitude frequency characteristics of pressure pulsation in turbine under different head and the influence of internal flow characteristics on pressure pulsation. The research shows that in the pump mode, when the guide vane opening of the turbine increases, the influence of the blade frequency and the shaft frequency on the vaneless area increases, resulting in the maximum pressure fluctuation amplitude in the vaneless area under the pump condition, especially when GVO = 19 °. At the same time, due to the influence of dynamic and static interference, the larger turbulent kinetic energy appears in the vaneless area and the connection between the guide vane flow channel and the runner flow channel, resulting in an increase in hydraulic loss. Both the experimental and simulation results show that the guide vane opening of 19 ° should be avoided to reduce the hydraulic loss in the vaneless area when the turbine is operated under the zero flow pump condition.

Unsteady Flow Behaviors and Vortex Dynamic Characteristics of a Marine Centrifugal Pump under the Swing Motion

Due to the effects of swing motion, the performances and internal flow characteristics of marine centrifugal pump undergo some unsteady variations in the marine environment. The hydraulic test system with six degree of freedom parallel motion platform is established to study the pump performance characteristics at the different heel angles of steady roll position and pitch position. The pump head gradually decreases as heel angle increases. The pump head has decreased by 7% to reach the minimum at the 15° heel angle of roll position. At the same heel angle, the head at the roll position is lower than that at the pitch position under the rated flow condition. The fluid in the impeller passage is subjected to the additional inertial force of roll motion or pitch motion under unsteady swing motion, inducing some flow bias phenomena in the velocity field. The unsteady development of flow velocity induces the intense vortex motion, and the shedding and dissipation of interblade vortices are affected. The periodic flow-induced pulsation characteristics obviously appear in the impeller passage. The pulsation periodicity and pressure amplitude are influenced due to the swing motion. The pitch motion induces the greater hydraulic excitation and fluid-induced vibration amplitude. In addition to the pressure pulsation at the low frequencies, the pulsation amplitude at 20 times the shaft frequency is evident under pitch motion.

Analytic Hierarchy Process (AHP)-Based Evaluation of Extremely-Low-Frequency Magnetic Field Contribution Rates

The extremely-low-frequency (ELF) magnetic fields of submarines serve as key characteristics for target detection, with their formation mechanisms being complex and diverse. Effectively manipulating a submarine to reduce its magnetic signature is crucial for enhancing its magnetic stealth capabilities. However, current research on the impact of various causative factors is insufficient. This study proposes a contribution rate assessment method based on the Analytic Hierarchy Process (AHP) model, aiming to provide a theoretical basis for effective manipulation. Initially, a thorough analysis of the threat causes of a submarine’s ELF magnetic fields is conducted, and a corresponding hierarchical threat structure model is established. Subsequently, magnetic field signal characteristics generated by different causes are obtained through simulation, and threat matrices and characteristic matrices are constructed. Finally, the contribution rates of different causative magnetic fields to the total magnetic field are calculated, and the simulation results validate the effectiveness of the method. At the stern detection line, the contribution rate of the wake magnetic field is the highest, reaching 0.7649. Along the radial detection line, the contribution rate of the shaft frequency magnetic field is the highest and gradually decays, eventually falling below the wake magnetic field at 150 m and remaining at an approximately 0.5 contribution rate. This study calculates the contribution rates under different operational conditions and detection scenarios, laying a technical foundation for research on the comprehensive active control strategies of submarine ELF magnetic fields in different scenarios.

Design of hydraulic motors with rotary shaft movement for driving working equipment in modern machines

The object of research is the processes in hydraulic motors based on power cylinders, designed to drive the shaft of the working equipment in modern machines into rotational motion. When using standard motors, a problem arises relating to the need to introduce additional devices into the structure of the mechanisms of modern machines. Such devices are aimed at matching the rotation frequency of the motor shaft with the rotation shaft of the working equipment of these machines. Such a device is a reducer, the use of which leads to the appearance of a number of disadvantages. Their elimination is achieved by using the results of this study. The reported results differ from standard motors that are mass-produced, in that, based on research, motors with a rotation frequency of its shaft in the range from zero to two hundred and more revolutions per minute are proposed, which is not realized by known motors. This testifies to the construction of motors based on power cylinders, which make it possible to realize this range of rotation frequencies of its shaft. The special and distinctive features of the results are based on the application of the principle of disintegration of motor elements into two functional components. One of them includes power cylinders with a crankshaft, and the second one includes the distribution system of the working fluid. The motor implementation went through the stages of designing computer and physical models and devising schematic solutions. Calculation dependences were obtained to determine the main design parameters, according to which the motor was manufactured in the form of a full-scale sample. The scope and conditions of practical use refer to machines with working equipment capable of functioning under a mode with a low rotation frequency and a significant torque on the motor shaft

Efficient vibration analysis system using empirical mode decomposition residual signal and multi-axis data

The empirical mode decomposition (EMD) method is a technique that recursively decomposes an input signal into intrinsic mode functions (IMFs) by residual signals, primarily for identifying desirable features. The suggested algorithm observes the residual signal instead of the IMF, which lowers the computing load. The study introduces a new method for detecting bearing faults by enhancing signal extraction from sensor data using EMD and multi-axis feature extraction. This method streamlines the process by filtering out high-frequency noise and correlating residual signal information with analysis. The approach also enhances the signal-to-noise ratio (SNR) and feature signature identification using digital signal processing (DSP) techniques. The algorithm for vibration data analysis is tested for bearing failures, identifying shaft frequency and inner race bearing faults, which can be implemented in parallel. For the inner race fault bearing analysis, two-level EMD with a residual signal generates output similar to five-iteration EMD, saving 60% of computations. The use of spectral multiplication to multi-axis data processing produced a rise in the SNR of 18.32 dB to 20.92 dB for Y-axis and X-axis input, respectively. When compared to the single-axis IMF data computation, 20% fewer iterations are needed overall. A single-level EMD is adequate for calculating the rotational frequency of a healthy bearing. For the Y- and X-axis input, multi-axis analysis increases SNR by 10.68 dB and 13.14 dB, accordingly. This comprehensive strategy reduces computational complexity, improves fault detection accuracy, and minimizes noise impact, making it a promising solution for bearing fault detection.

Analysis of unsteady internal flow characteristics in axial pump with varying number of blades using computational modelling and vibration techniques

Axial pumps were extensively applied in many varying applications because of their large flow and low head. In this research investigation, the comparative analysis of the findings unveiled that the predominant source of hydraulic-induced vibration in the pump stemmed from pressure pulsations at the impeller inlet. Notably, similar patterns in amplitude were observed as flow rates increased. Furthermore, time-domain analysis confirmed that pressure pulsations and vibrations are highly correlated under high flow rates. Pressure pulsation's Frequency-domain analysis also revealed that it was a multiple of shaft frequency and changed from one multiple to three multiples of vibration. While analyzing the flow rate characteristics pertaining to pressure pulsation and vibration, it was determined that pressure pulsations at the impeller inlet had the potential to generate frequency components across a broad spectrum, encompassing both low and high flow rates, as well as their respective multiples. This phenomenon was particularly pronounced in regions characterized by unstable and high flow rates. Vibration ingredients likely influenced by pressure pulsation at the impeller inlet could be as low as design flow rates and as high as high flow rates. A vibration frequency with a multiple did not seem to be influenced by pulsating pressure at the impeller entrance. The present study focuses on investigation of flow behaviors in an axial pump with varying numbers of blades. It is an important geometric parameter that significantly affects the pump's performance. Therefore, the dynamic flow patterns in a pump, considering changed flow and impeller blade configurations, are investigated by employing the sliding mesh technique in combination with SST (k-ω) turbulence model. The numerical results exhibit a commendable alignment with the existing experimental data, enhancing the predictive accuracy of pump performance. Qualitative analyses encompass static pressure, shear stress, and various velocity components. Concurrently, quantitative investigations delve into pressure fluctuations and average pressure across a spectrum of operating conditions and impeller blade configurations. These comprehensive findings underscore the substantial influence of the impeller blade on pressure, velocity magnitudes radial, axial, tangential shear stress, average pressure within the system.

DIRECTION OF ARRIVAL ESTIMATION BASED ON SMOOTH MUSIC ALGORITHM COMBINED SPECTRUM SELECTION TECHNIQUES OF NOISE CHARACTERISTICS OF MARINE TARGETS EQUIPPED PROPELLER

This article demonstrates a proposal for a direction of arrival (DOA) estimation algorithm for passive sonar systems based on the combination of the smooth multiple signal classification (Smooth MUSIC) algorithm and frequency bin selection (BS) of the sound of marine propeller-equipped targets, so-called BS-SMUSIC. The harmonics of propeller shaft and blade frequencies are considered useful information for detecting targets and estimating their parameters, including DOA. Low frequency analysis recording (LOFAR) is utilized to implement BS. By analyzing MUSIC-based algorithm together BS, passive DOA estimation algorithms have been significantly improved. Simulation results have been given in both cases: uncorrelated and correlated sources. Outcomes demonstrate that the BS-SMUSIC algorithm has the best performance in comparison to three MUSIC-based algorithms (MUSSIC, Modified MUSIC and Root MUSIC) in all investigation cases: narrow band signals at 5 dB of signal to noise (SNR); wideband signals at -5 dB of SNR. Besides, BS-SMUSIC algorithm also archives the lowest root mean square error (RMSE) in SNR range -5 dB to 20 dB. In the SNR range, the RMSE of BS-SMUSIC algorithm remains stable and is about 0.3 ◦ at -5 dB of SNR. This performance reflects its ability to ensure stable operation, super resolution and high accuracy of BS-SMUSIC algorithm for the passive sonar systems.

Research on unbalanced characteristics of axial-varying eccentric rotor based on signal demodulation

In the presence of non-uniform loads, rotor misalignment emerges as a prevalent fault in permanent magnet synchronous motors (PMSMs), leading to the manifestation of an axial-varying eccentric air–gap. Considering the three-dimensional (3D) nature of magnetic flux under axial-varying eccentric fault, 3D finite element (FE) analysis method was used in this paper. Then, the electromagnetism simulations were conducted to calculate the magnetic flux density and unbalanced magnetic pull (UMP). With the signal demodulation algorithm based on principal component analysis (DPCA), the frequency modulation of various signals from simulation and experiment was extracted. Furthermore, based on the modulation features, the relevance among magnetic flux density, UMP, and vibration acceleration was established with shaft frequency as the link. The coupling of magnetic field and vibration level shown in results was analysis, which provide important theoretical and engineering references for the safe operation of PMSM system and the exact identification of rotor tilting faults.

Hydrodynamic characteristics of a seven blade highly-skewed propeller operating underneath a free surface

The performance of a highly-skewed seven-blade propeller operating underneath a free surface was simulated with different loading conditions using detached-eddy simulation and volume of fluid method. The presentation includes the hydrodynamic loads and distribution of the velocity, followed by a discussion of the vortex structure and free surface variation. Finally, the analysis delves into the power spectra of pressure and turbulence kinetic energy. The results suggest that there a decrease in the thrust, torque, and efficiency of the propeller. The blade tip vortex is observed to be distorted and delayed in merging in free surface condition. The shaft frequency, three times the shaft frequency, and blade frequency still make contributions in the far wake at J = 0.71 for free surface condition.

Study on the volute optimization and mechanism of vortex loss reduction for a centrifugal fan

Abstract In order to reduce the flow loss in the volute and improve the efficiency of the centrifugal fan further, a new type volute with a diffusion profile was designed and optimized. The effects of diffusion angles were clarified by using numerical simulations and the method of design of experiment. The mechanism of vortex loss reduction of the diffusion-type volute was revealed. The results show that diffusion-type volute can reduce the flow loss in the volute by 30.8% compared with the original volute, and increase the efficiency of the fan by 2.24%. Parametric studies show that the diffusion angle of front disc has a great influence on the efficiency of the fan, and the effect of diffusion angle of rear disc is relatively less. Mechanism analysis shows that the diffusion-type volute can greatly reduce the vortex strength in the volute, especially eliminate the high-intensity vortex near the volute tongue. As a result, the volute loss is remarkably reduced. In addition, the diffusion-type volute can effectively reduce the amplitude of pressure fluctuation in terms of shaft frequency, characteristic frequency and broadband signals in the volute.

Interstage transmission and differential analysis of pressure fluctuations in multistage centrifugal pump-as-turbine

Pumps as turbines (PATs) are used in petroleum and chemical industries to recover high-pressure residual energy. Multistage PATs allow for a wider energy recovery interval and wider range of applications. However, because multistage centrifugal pumps were not originally designed for turbine conditions, complex pressure fluctuations occur, impacting the stable operation and performance of multistage PAT. Pressure fluctuation is essentially a wave, and by analogy with the wave intensity definition, pressure fluctuations were quantified using the pressure wave energy flow density, and the pressure fluctuation patterns at different stages were investigated. The findings reveal significant differences in the intensity of pressure fluctuations at different locations within the multistage PAT. Specifically, the pressure fluctuation intensity is significantly higher from the second to the final stage, compared to the first stage. The difference in inlet flow conditions is the main reason for this difference in pressure fluctuations between stages. The inlet inflow from the second to the final stage is subject to rotational effects that exacerbate the difference in pressure fluctuation intensity between stages. Pressure fluctuations are found to be negatively related to the distance from the source of fluctuations and positively related to the flow state. Different flow conditions and interaction regions of the impeller affect the distribution of pressure fluctuation intensity and the distribution of pressure fluctuation energy across different frequency domains within the guide vanes. The main source of fluctuations in the shaft frequency and four times the shaft frequency is the impeller inlet interaction region, whereas the fluctuations in the blade passing frequency originate from the impeller outlet interaction region. This paper provides a reference for improving the stable operation of multistage PATs.

Marine shaft optimization using surrogate models and multi-objective optimization

This paper aims to obtain an application software using Ansys software in which a static, dynamic, and modal analysis for the power transmission of ships is presented. The objective functions of this research are maximum static stress, maximum dynamic stress, shaft mass, and modal shaft frequency analysis. A complete, comprehensive, and generalizable model for metal shaft types is presented. Then, using the kriging response surface and multi-objective genetic algorithm (NSGA II), these goals are optimized simultaneously. In this research, the optimization parameters are geometric parameters of the shaft design, including the position of the supports and the inner and outer diameters of the shaft. As a result of this optimization, the shaft's maximum static and dynamic stresses are reduced by 36% and 42%, respectively. The shaft's mass, which is one of the most critical factors during the shaft and its vibrations, is reduced by about 9%. In this regard, the first natural frequency of the optimized shaft increased by about 28.5% compared to the initial shaft.

Cross-influence of cavitation and flow rate on pressure pulsation of a volute mixed flow pump

Mixed-flow pump is a general purpose hydraulic machinery in many fields of fluid transport for its advantages of wide efficient operation flow rate range, but its operation stability is restricted by cavitation. To obtain the cross effect of cavitation and flow rate on its pressure pulsation, a high-precision experimental system was first established to monitor the pressure signals at four key positions, obtaining their time domain; second, based on this tested results, time frequency domain analysis technique based on continuous wavelet transform was adopted to capture the temporal evolution; third, wavelet coherence value analysis was further adopted to diagnose the cavitation development speed at different spatial positions. Primary findings are as follows: (1) the secondary peaks induced by cavitation generated the discrete disturbance in low-frequency range, and the amplitudes at shaft frequency and blade passing frequency were both increased, with a worse time continuity. (2) Under 1.0 QBEP, the mixed flow pump had a best anti-cavitation performance. Under 0.8 QBEP, its internal flow pattern was easily to be disturbed by cavitation flow, while that under 1.2 QBEP had the fastest cavitation development speed. (3) Under the action of unstable potential flow, within the flow field near the rotor–static interface and the downstream, a close flow exchange was established between the cavitation bubbles and mainstream; thus, the pressure pulsation inside the volute became more sensitive to the cavitation development.

A fast method for robust estimation of gearbox instantaneous speed

Under non-stationary condition, estimating the instantaneous frequency (IF) of shaft from vibration signal is an ideal way for gearbox fault monitoring without tachometer. Among them, the method based on harmonic phase demodulation has always occupied a dominant position. In the low signal-to-noise ratio (SNR) condition, the noisy harmonic components may cause greater IF estimation error. In this work, an improved approach for estimating the IF of gearbox reference shaft is proposed based on the short time Fourier transform spectrogram. The theoretical derivation proves that the high-order meshing harmonic can reduce the IF estimation error of gearbox reference shaft. By constructing the spectrogram weight factor, an improved maximum tracking algorithm is proposed to redefine the IF estimation range. On this basis, the robust IF estimation of high-order meshing harmonic with low SNR is realized. Finally, it is equivalent to the estimated IF of gearbox reference shaft. The proposed strategy is compared with the two advanced IF estimation methods. The civil aircraft engine dataset and the wind turbine gearbox dataset provided in the Safran contest demonstrate that the proposed strategy works. In the case of heavy load and large speed change, the proposed method has extremely low consumption time while maintains good estimation accuracy.

The effect of the impeller eccentricity on the hydrodynamic characteristics of a centrifugal pump

To explore the effect of impeller eccentricity caused by shaft parallel misalignment on the hydrodynamic characteristics of a centrifugal pump, a numerical simulation model based on computational fluid dynamics (CFD) is established. The SST k-ω turbulence model is used to describe the flow field in centrifugal pump. The eccentric motion of the impeller is described by the sliding mesh method (SMM). The results indicates that the nonuniformity and instability of flow field will be aggravated with the increment of impeller eccentricity, which then reduce the pump head and efficiency to a certain extent. The radial force exerted on the impeller is directly proportional to the eccentricity of the impeller. In addition, the impeller eccentricity has a significant impact on the peak rotation frequency of shaft frequency. This study can provide a numerical reference for eccentricity fault diagnosis and vibration control of centrifugal pump impellers to carry out optimal design and vibration reduction.

Adaptive bearing fault diagnosis using reference frequency and modified scalogram

Previous studies on the diagnosis of natural faults in rolling element bearings have primarily concentrated on detecting an increase in the frequency amplitude across a broad frequency spectrum within the measured signal when a fault occurs in the bearing. However, this study introduces an adaptive method centered on the conspicuous distinction in frequency amplitude between the shaft and bearing fault frequencies as the bearing fault progresses. Specifically, we propose a bearing fault diagnosis approach leveraging the shaft frequency amplitude as a constant reference independent of prevailing conditions, as it consistently maintains a relatively steady level regardless of the presence of bearing faults. Moreover, we devised a modified scalogram to enhance the diagnostic performance for bearing faults by consistently and prominently visualizing information pertinent to faults. We comprehensively assessed fault diagnosis accuracy between a convolutional neural network employing the scalogram and one employing the modified scalogram to verify the diagnostic performance of the adaptive method. This analysis yielded accuracies of 93.6% and 99.3%, respectively. Furthermore, the relationship between the bearing fault diagnosis results and the visualized fault-related information in the scalogram and modified scalogram was analyzed using gradient-weighted class activation mapping, providing evidence supporting improved fault diagnosis performance using the adaptive method.

Experimental Measurement of Dynamic Characteristics of Structural Units

The aim of this study is to investigate and optimize the dynamic properties of an entire structural unit. Using modal analysis and experimental measurements of the propulsion system, natural frequencies with close agreement were identified. The drive was able to work within the frequency range during start-up and normal operation, but due to various influences, including the inherent oscillations of structural elements, complex dynamic phenomena occurred. The presence of a conveyor with rubber and plastic wheels also affected the results. Important information on the input shaft, tooth frequency, driveline oscillation and output shaft was obtained. Research has identified resonant frequencies and increased drive oscillation that are created by the interaction between the input shaft and tooth frequency. The significant frequency of bent screws in the conveyor pipe affects the shafts and the drive screw, which in turn causes problems with material fatigue and microcracks. Corrective measures include the possibility of replacing or balancing the screw and increasing the diameter of the pipe. Regular monitoring and diagnostics have a preventive nature and serve to minimize serious consequences. Implementing a controller with a PID system offers the potential to suppress oscillations and improve dynamic and strength characteristics, while accurate calibration of this implementation is of key importance.

Analysis of three-dimensional thermal vibration coupling characteristics of composite shaft under axial load

The Carrera unified formulation (CUF) is employed to simplify the complete three-dimensional dynamic model based on the three-dimensional elasticity theory into a hierarchical one-dimensional dynamic model that maintains three-dimensional solution accuracy. The displacement function is formulated using Taylor polynomials and the improved Fourier series method (IFSM). Subsequently, the study solves the thermal vibration characteristics of the composite shaft under axial load through the application of energy functional and Hamilton's principle. The accuracy and stability of the present method are verified by comparing the present results with simulation. This study investigates the influence of thermal effects, structural parameters, and axial load on the vibrational characteristics of the composite shaft. The analysis results indicate that temperature, structural parameters, and axial load all significantly affect the fundamental properties of the composite shaft. As temperature and length-radius ratio increase, the natural frequency of the composite shaft gradually decreases. Regarding axial load, axial tension exhibits a positive correlation with the structure's natural frequency, whereas axial pressure shows a negative correlation. These findings hold significant engineering implications for utilizing composite shaft in the marine engineering sector.

A Numerical Study of the Hydrodynamic Noise of Podded Propulsors Based on Proper Orthogonal Decomposition

Podded propulsors have become a focal point of research in the field of marine propulsion in recent years due to their high efficiency, low noise, and excellent maneuverability. To investigate the acoustic characteristics induced by the flow field of podded propulsors, a high-precision unsteady numerical simulation was conducted using the Delayed Detached Eddy Simulation (DDES) coupled with Ffowcs Williams–Hawkings (FW-H) equations. Multiple spatial acoustic receiving arrays were employed, and analysis methods including Proper Orthogonal Decomposition (POD) and Fast Fourier Transform (FFT) were utilized to determine the spatial distribution of the acoustic field of the podded propulsor. The results show that the blade passing frequency and the shaft frequency consistently dominate as the primary characteristic frequencies. On the plane of the propeller disk, the distribution of sound pressure levels is uniform without distinct directivity. Across the space curved surface, approximately the first ten POD modes encompass 99.8% of the total energy, and their spatial distribution characteristics of sound pressure are closely related to the pod structure. Additionally, these modes exhibit characteristic frequencies such as the blade passing frequency and shaft frequency. The spatial distribution of sound pressure at a single frequency on the spatial surface corresponds well with the results obtained from the POD analysis.