In order to improve the ride comfort of the passenger vehicles, an improved MR damper is designed. The magnetic pole of the damper is sinusoidal, whose effective length can be controlled by the magnetic field. In this way, the flow area of MR fluid can be controlled. The mechanical analysis of the proposed MR damper is carried out and the theoretical analysis results show that the proposed damper can meet the damping force requirements of vehicles under various driving conditions. Half car models are established, simulation analysis is carried out under random excitation, the evaluation parameters such as body acceleration and pitch angle are analyzed comprehensively. The results show that the proposed damper is more conducive to improve the ride comfort of the vehicle.
Speech intelligibility in classrooms is shaped by the interaction of direct sound, reverberant sound, and background noise level (BNL). In classrooms, air conditioners (ACs) are often switched on and run at different fan levels, dynamically changing the BNL and affecting speech intelligibility. Objective descriptors used to evaluate speech intelligibility are articulation loss of consonants (ALC), speech transmission index (STI), and useful-to-detrimental ratio (U50). This study examined the effect of ACs on speech intelligibility through calibrated SNR measurements and IEC-compliant STI analysis in five different unoccupied university classrooms. Measurements were calibrated using reference standards, and STI values were corrected according to IEC 60268-16:2020 Annex M requirements when signal-to-noise ratios fell below 20 dB. The results demonstrate that background noise level has a stronger influence on speech intelligibility than reverberation time, with noise control taking precedence over reverberation management in typical classroom environments. Contrary to literature claims, no significant correlation was found between STI and U50 (r = 0.029, p > 0.05), challenging the interchangeable use of these descriptors in HVAC-affected spaces. Statistical modelling revealed that BNL explains 92.1% of STI variance compared to 81.4% for reverberation time (T30), with micro-perforated panels improving intelligibility primarily through noise reduction rather than reverberation control. The correlations between STI and T30 weaken substantially with increased AC noise, particularly at mid-frequencies, while high-frequency relationships (2000–4000 Hz) remain most predictive of speech intelligibility. These findings underscore the need for case-specific acoustic validation over universal correlation assumptions in real-world classroom environments.
This study delves into investigating various aspects of machinery performance and vibration analysis through experimental simulations using the Machinery Fault Simulator (MFS). It examines the influence of different masses and speeds on machinery dynamics, considering both time and frequency domain data. This study explores the effects of rotating unbalanced mass in single and multiple planes on machinery vibration, providing insights into diagnosis and mitigation strategies. The results demonstrate how the placement of an unbalanced mass in relation to each other in single and multiple planes varies the vibration effect, highlighting the importance of proper balancing and maintenance practices for optimizing machinery performance and longevity. Experimental results are validated with the 3D Finite Element (FE) result for a few cases showing excellent agreement. In general the study underscores the importance of MFS technology in advancing fault diagnosis and predictive maintenance in industrial settings.
This article presents a numerical investigation of free vibrational features of bi-directionally tapered functionally graded (BTFG) plate unified with active constrained layer damping (ACLD) on a two-parameter Winkler-Pasternak flexible support. In conjunction with the virtual work principle, the first-order shear theory for deformation is employed. The plate’s damping is actively controlled using a velocity feedback control system with 1-3 piezoelectric patches consisting of piezoelectric and viscoelastic layers. Effects of foundation/support parameters ( K w and K s), taper ratios, ACLD patch placement, and boundary conditions are systematically analysed through frequency response studies. Results demonstrate that incorporating ACLD patches significantly enhances damping features. Revealing with edge patch placement yields superior vibration suppression on the substrate plate. The study highlights the synergistic impact of ACLD patches, flexible supports, and active control, presenting a robust solution for precision vibration control in advanced structural applications.
The vibration reduction performance of NES is greatly affected by the excitation. When the excitation is too high, the system may experience bifurcation, leading to the vibration reduction failure of NES. For the above issues, a nonlinear damping parallel energy sink (NDPNES) is proposed in this paper, which utilizes damping to increase with the increase of relative motion between the NES and the controlled system to ensure efficient vibration reduction performance under strong excitation. At the same time, without increasing the total mass, to improve the stability of the NES through mass configuration. Firstly, the mathematical model of NDPNES was established, and the slowly varying equation of the system was obtained based on the complex variable averaging (CX-A) method. Then, the amplitude frequency characteristics of the controlled system were obtained, and the stability was analyzed using Lyapunov stability theorem, at the same time, the analytical results were verified by numerical methods. Afterwards, the influence of parameters on the vibration reduction performance of NDPNES was analyzed. Finally, the performance of the proposed scheme under transient and steady-state excitation was verified using numerical methods. The results indicate that, compared to existing Cubic stiffness NES (CNES), the proposed NDPNES has better vibration reduction performance and stability under strong excitation. The proposed scheme is of great significance for vibration control of machinery (such as mining machinery, engineering machinery, etc.) operating in strong excitation environments.
The stimulation of the oscillation screed systems (OSS) in the paving machine strongly affects the density and smoothness of the road surface. Thus, an experimental study of paving machine has been conducted to evaluate the actual effect of OSS on the index of the density and surface smoothness (D-SS) of the road. To ameliorate PM’s efficiency, a dynamic model of OSS is established and PID-Fuzzy control is used to analyze and control the excitation forces of OSS. The experimental and numerical simulation studies indicate that the D-SS of the road is strongly affected by both the tamper-pair excitation ( f 1 ) and vibrator-screed excitation ( f 2 ). In the working process of paving machine, a range of 16 ≤ f 1 ≤ 20 Hz and f 2 should be combined and used to enhance the road’s density, on the contrary, a range of 4 ≤ f 1 ≤ 10 Hz and without f 2 should be used to enhance the road’s surface smoothness. With the excitation forces of OSS controlled by PID-Fuzzy control, the paving machine’s efficiency has been clearly enhanced under various operation conditions.
The development of new products and services allows railway transport to constantly increase the fleet of specialised wagons, which, in comparison with the universal rolling stock, have the best technical and economic indicators. A significant part of cars is delivered by railways, and it is economically reasonable to transport them on a specialised rolling stock. In this regard, the development of a methodology for refined theoretical studies of the strength of bodies of a double-deck rolling stock for passenger cars transportation, the choice of appropriate design schemes and parameters of the bodies, the analysis of the frequencies and forms of their natural oscillations, taking into account the finite stiffness of the elements, are urgent research tasks. The research uses the methods of structural mechanics of rod systems, the applied theory of elasticity, and discrete masses. A wide range of frequencies and forms of the natural free oscillations was obtained using the discrete mass method for a structural scheme with load transfer from the upper to the lower level of the wagon with the help of four racks. The applied methodology of theoretical determination of frequencies and forms of the natural free oscillations of the car transporter wagon by the method of discrete masses is effective. It allows for the estimation of the dynamic characteristics of the wagon.
To reduce the cost of microphone array, the array structure can be optimized by optimization algorithm without affecting the location accuracy. In this paper, a sparse optimization mathematical model of microphone array structure was established under the framework of compressed sensing theory. With the minimum mean value of non-diagonal elements in Gram matrix as the optimization objective, the sparse optimal structure of 31-element nested circular array was designed by adaptive genetic algorithm, and the optimal array configuration and fitness convergence curves at different frequencies were analyzed. The performance of the optimized microphone array was verified by simulation and experiment. The results show that the root-mean-square error of the optimized array is similar to the error of the full array, and even slightly smaller than the error of the full array, indicating that the optimized array has a similar or even slightly better location performance than the full array.
The train operations on railways will inevitably induce cross-railway bridge vibrations, and it is necessary to examine the effects of train-induced vibrations on the cross-railway vehicle-bridge coupling system. In this context, this study focuses on a practical low-pylon cable-stayed bridge to analyze the behavior of the vehicle-bridge coupling system under train passage. By employing theoretical analysis, vibration experiments, and numerical simulations, a comprehensive study is conducted to analyze the vibration response of the vehicle-bridge coupling system under train-induced vibrations. The results demonstrate that vertical vibration acceleration levels at different measurement points on the bridge deck are significantly more pronounced than the horizontal vibration levels. Train passage conditions beneath the bridge exert a noteworthy influence on the vibration acceleration levels and the frequency distribution range of the bridge and vehicle. The train speed, axle load, and driving direction each have varying degrees of impact on the vibration displacement and acceleration of the vehicle-bridge coupling system, emphasizing the importance of considering these factors.
A bistable parallel nonlinear energy sink (BPNES) is proposed in this paper to improve the vibration reduction performance and stability through inter-well chaotic response and mass configuration, so as to achieve vibration control of the engine under broadband and wide energy excitation. In order to provide the design theory of BPNES, the relationship between structure parameters and thresholds of the inter-well chaotic response and strongly modulated response (SMR) are obtained by Melnikov theory and multiscale analysis, and the numerical results indicate that the analytical solution is reliable. The concepts of energy dissipation and energy spectrum were defined to analyze the vibration reduction performance of BPNES under transient and steady-state excitation, respectively. The analysis results indicate that compared to Cubic stiffness NES(CNES), BPNES has better vibration reduction performance under wide energy excitation, especially when the excitation intensity is low. The results under steady-state excitation also indicate that BPNES is less likely to generate high branching under different excitation intensities, indicating better stability. The results of this study indicate that the proposed BPNES is very suitable for vibration control with a wide vibration frequency band and a wide range of vibration intensity changes, such as engines, machine tools, etc.
Acoustic energy is the primary source of vibration input to a Space Launch Vehicle. The Sound Pressure Level produced by high velocity gases can have adverse effect on subsystem reliability if not subsided to an allowable limit. In this research, the theory underlying the transfer matrix approach is described first followed by a description of the experimental setup using Impedance tube. Various results, including the absorption coefficient and normal incidence Transmission Loss are presented for an acoustic insulation of variable Melamine Foam thickness from 25 mm to 70 mm; different Honeycomb / Carbon sandwich; and metallic structures. The results are first estimated numerically using COMSOL and later validated experimentally. The working frequency range is described with the placement of small and large diameter tubes from 31.5 Hz to 8000 Hz. The resonance features are obtained due to sample constraint around its edges. The acoustic characteristics of Melamine Foam with different thicknesses are presented to optimize acoustic insulation blanket within Payload Fairing to protect satellite and other avionics from harmful Sound Pressure Level. Since the primary vibroacoustic environment occurs at the very beginning of a mission, such failures are likely to have a greater mission impact than failures induced by other space environments over time. Consequently, an optimized acoustic insulation is mandatory for Payload Fairing to attenuate acoustic loads up to a desired level. This approach of sound attenuation is equally applicable for other applications which are vulnerable against acoustic loads.
Natural fibers, like coconut shells, offer an eco-friendly and renewable alternative for brake pads, providing promising performance in terms of friction and durability. Research has shown that these reinforced materials can perform comparably to commercial options, particularly in areas such as wear resistance and mechanical stability. While many studies have focused on chemical and mechanical properties, there is still limited understanding of their impact on noise phenomena in braking systems. Further exploration is needed to evaluate their potential in reducing noise. Train noise pollution is a significant issue, largely due to vibrations and high-pitched sounds caused by friction in braking systems. This noise impacts passengers and arises from complex friction interactions where excess energy is converted into vibrations and sound. Advances in computing have enabled the application of the Finite Element Method to analyze these vibrations and their connection to noise phenomena in braking systems. This study proposes an iterative method to correlate brake component properties with instability parameters through finite element and complex eigenvalue analyses. The objective is to compare the performance of commercial and coconut shell-reinforced friction materials in mitigating brake squeal, with the aim of reducing vibrational instability and improving braking efficiency in train systems. The results demonstrate that the coconut shell-reinforced material outperforms the commercial material in reducing instability and noise across various parameters. The commercial material exhibits more unstable points and higher noise, while the reinforced material maintains better stability, lower noise, and more consistent performance in terms of friction, stiffness, and thickness variations. Overall, the reinforced material shows superior noise reduction and stability compared to the commercial option under the conditions studied.
This article discusses the issue of how a harmonic plane wave interacts with an infinite homogeneous steel plate in a soil environment, specifically an elastic environment. The load compensation method is used to address this problem. The Kirchhoff-Love equation describes the equation of motion for the plate. The soil motion equations may be described using several mathematical frameworks, including elastic theory equations, Cauchy relations, physical equations, and Lame equations. The boundary conditions for the contact between the plate and the soil medium include ensuring that the normal displacements at the boundary of the obstacle and the soil medium are equal. Additionally, it is assumed that the pressure amplitudes and normal stresses are also equal. Calculate the influence functions of the displacement perpendicular to the infinite plate when subjected to a concentrated force in the form of the Dirac delta function. Once the value of compensatory loads has been established based on the boundary conditions. The normal displacement values of the plate may be calculated by summing the convolution of the influence function with the compensating loads and displacements of the infinite plate that are influenced by plane harmonic waves.
Background: South African mineworkers are exposed to excessive noise which leads to occupational noise-induced hearing loss (ONIHL). However, there is a dearth of literature on the contribution of personal noise exposure measurements to predict the development of ONIHL. Aim: We aimed to determine the predictive ability of age, sex, personal noise measurements, and work shift duration as early signs of hearing deterioration associated with ONIHL for mineworkers at a large-scale platinum mine in South Africa. Methods: Two merged electronic datasets, comprising records of 521 mineworkers, were analysed, viz. a dataset of personal noise exposure measurements and an audiometry screening dataset, for the period 2014 to 2018. Pearson Chi 2 test described the associations between personal noise measurements, age, sex and shift duration, and hearing deterioration (STS). LOWESS assessed the correlation between personal and area noise measurements and hearing deterioration and personal noise measurements. Multinomial logistic regression analysis was used to identify risk for ONIHL, classified as mild, moderate, moderate-severe and profound hearing loss. Results: Most of the mineworkers were male ( n = 480; 92.1%), aged 26-55 years ( n = 452; 86.6%), and most were exposed to personal noise measurements less than 85 dB(A) ( n = 303; 61.1%). Pearson Chi 2 indicated age as a significant risk factor associated with STS. LOWESS indicated a positive association between personal and area noise measurements, but no association between personal noise measurements and STS. Multinomial logistic regression showed age as a significant risk for STS, mostly for mineworkers with STSs at mild, moderate and moderate-severe hearing loss in both ears. Conclusion: Mineworkers’ age was associated with STSs and was a risk factor that had a significant predictive ability for ONIHL. We highlighted the usefulness of personal noise measurements as risk-based assessment tools for audiometry surveillance that the South African mines could use to evaluate noise reduction strategies and outcomes for ONIHL prevention.
Using the multi-body dynamics simulation software Simpack, a dynamic model of the subway vehicle-track system with elastic wheelsets on curved lines is established. The influence of corrugation excitation with different characteristics on wheel-rail forces and wear, as well as the vertical vibration characteristics of the system, are studied. The results indicate that when the vehicle passes a straight creep point with a corrugation depth of 0.20 mm, the wheel-rail force reaches a value of 0 and exceeds the safety limit, resulting in decreased vehicle stability. When the vehicle passes the middle section of the curve and the corrugation depth is 0.20 mm, stress concentration occurs on the left wheel flange and right wheel tread, and the maximum contact stress is greater than the material yield limit, which leads to increased wheel-rail wear. The variation of corrugation wavelength causes a change in the peak range of vehicle structural vibration, and short-wavelength corrugation excitation leads to an increase in the peak energy, resulting in more obvious resonance. It is recommended to control the corrugation depth within 0.14 mm and conduct timely inspection and rail grinding of the line.
Effective fault diagnosis is critical for the safe and efficient operation of rotating machinery in nuclear facilities. This paper proposes a deep learning-based approach that integrates multi-domain signal analysis and transfer learning to classify rotor conditions as either healthy or faulty. Vibration signals are transformed into 2D images and processed using pretrained models: ResNet50, GoogleNet, and a custom Deep Convolutional Neural Network (DCNN). Signal transforms, including the Fast Fourier Transform (FFT), Fractional Fourier Transform, Short-Time Fourier Transform (STFT), Continuous Wavelet Transform (CWT), and Fractional Wavelet Synchrosqueezing Transform, are applied to enhance feature representation. ResNet50 achieved up to 100% accuracy on the primary dataset and over 99% on the secondary dataset. GoogleNet and DCNN also demonstrated excellent performance, achieving accuracies of up to 100% in specific domains. Additionally, transfer learning using YamNet enabled effective sound-based classification of vibration signals. These results show that using advanced signal processing together with deep learning can lead to very accurate and quick fault detection in important safety situations.
The gearbox system faults are the main causes of the failure of the rotating components, therefore dynamic gearbox features are necessary. The article attempts to clarify the gearbox’s dynamic characteristics as the consequence of the preliminary pitting circumstance. Three operating variables such as shaft loading, shaft speed and defect size were selected to observe the parametric effect and the experiment was conducted according to Taguchi L9 orthogonal arrays (OA). A dedicated experimental test rig has been developed for experiments with different speeds and loading conditions to implement and simulate industrial-based applications. The accelerometer was used to record the vibration signals while simulating faults. The response parameters used to monitor the gearbox conditions comprise time-domain indices notably kurtosis and root mean square. Investigating the impact of defects on vibrations is made easier by the interplay of defect size, load, and speed. To determine the relationship between the inputs and outputs of a physical system, statistical analytic approaches have been employed. Analysis of variance has been shown to be a dependable technique for assessing the key elements connected to the gearbox’s vibration. It was revealed from the Analysis of variance table that dynamic characteristics in terms of response performance were significantly influenced by defect size. To mitigate the dynamic features and prolong the life of rotational systems, it is recommended that these optimal input parameter conditions might be applied to gearbox fault diagnosis.
In response to the challenges of identifying and reducing noise from multiple sources in construction machinery, this study focuses on a hydraulic source cart as the research subject and employs a sound-vibration fusion diagnostic method for noise identification. Firstly, by analyzing the noise distribution of hydraulic source car under different speed, the main source of noise is deduced. Then, by analyzing the vibration spectrum of each part and comparing with the noise test results, the frequency and location of the main noise are determined. The results show that this method can accurately identify the main noise source frequencies and locations under different gear positions. At 800 r/min, 1500 r/min, and 2600 r/min, the maximum sound pressure levels of the hydraulic source cart are 73.08 dB at the valve side, 75.89 dB at the reducer side, and 78.67 dB at the pump side, with the main source frequencies being 602 Hz, 450 Hz, and 390 Hz, respectively. The main source frequencies are 602 Hz, 450 Hz and 390 Hz, all of which are integer multiple frequencies of the gear pump meshing frequency at this gear position, so the gear pump is the main noise source, and the main noise reduction object of the cart is the gear pump and its valve body.
Enhancing the control performance of the tractor-trailer air suspensions can improve the driving efficiency and handling ability (DP-HA) of the driver. Based on the dynamic model of a multi-axle tractor-trailer using air suspensions, three different control cases including the control of the damping values in dampers, the control of the stiffness values in airbags, and the control of both the damping and stiffness values of the air suspensions are studied and simulated under different working conditions of the tractor-trailer, respectively. A new control method combining fuzzy controller and genetic algorithm program is also examined and applied to control the damping and stiffness values of the air suspensions. The study indicates that the air suspensions using the different control approaches improve the DP-HA of the driver better than without the control. Besides, the control performance of the damping values is better than that of the stiffness values under all various operation conditions of the tractor-trailer. Significantly, by combining both control methods of the damping values and stiffness values, the isolation performance of the tractor-trailer air suspensions is strongly enhanced in comparison with using the controlled damping or controlled stiffness values. Therefore, the combined control method of both damping values and stiffness values should be developed to further improve the DP-HA of the driver.
No comparative research has investigated the effect of tonal noise and background speech on cognitive functions. Therefore, this study aims to determine the impacts of tonal noise and background speech noise on cognitive function and noise annoyance based on personality traits. Twenty-five male students of Hamadan University of Medical Sciences with normal and healthy hearing participated in 4 simulated 50-min scenarios in an indoor environment. The cognitive functions including reaction time, sustained attention, and working memory were measured by PVT, CPT, and n-Back tests respectively. At the end of each test session, the noise annoyance was evaluated by the ISO-15666 questionnaire. According to the results of the repeated measures ANOVA test, a significant difference in mean reaction time in the n-Back and PVT tests was observed ( p < .05). The significant difference in mean correct response in the n-Back test was not observed. The highest rate of perceived noise annoyance has been observed in exposure to 65 dB tonal noise with a mean and standard deviation of 41.52 ± 7.56. A positive correlation was observed between the reaction time of PVT and CPT tests and the neuroticism dimension, and its values were reported as 0.410 and 0.423, respectively. Tonal noise and background speech can reduce cognitive performance and acoustic comfort considering noise sensitivity and age of participants. These have special rules for causes of employees’ distraction in office room.
