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.
