The narrowband active control system is suitable for controlling low-frequency harmonic noise. In practical applications, the problem of reference signal mismatch caused by the rapid frequency changes of the original noise will seriously degrade the performance of the narrowband active control system. Existing frequency estimation algorithms often struggle to balance the speed, accuracy, and computational complexity required to track the actual frequency. This paper proposes a Notch-HAQSE frequency estimation algorithm for narrowband active control, which extracts any number of line spectrum frequency components from the reference sensor signal by combining a notch filter with a high-precision single-frequency estimation algorithm based on DFT coefficients (HAQSE). The synthesized reference signal is sent to the controller to complete secondary signal updating. Simulation and experimental results show that, compared with other frequency estimation methods used in active control, the proposed method accurately identifies and rapidly tracks multiple frequencies while significantly reducing computational complexity. It effectively addresses the problem of reference signal mismatch and multi-line spectrum vibration noise control.

To gain a deeper insight into the sorting of main launching noise sources in underwater weapons, different sub-noise sources and their contribution to the overall radiation noise are analyzed through both analytical and experimental research, focusing on the typical gas-water tank launching device trial model. The acoustic transmission channels of launching noise include hull structure and the seawater-connected domain formed by the pipeline system through which the weapons travels. In the concluded thirteen sub-noise sources, the primary components include 4 structural vibration noises and one impact vibration noise. The former are caused by gas tank seat vibration, tank cylinder wall vibration, torpedo tube wall vibration and piston axial fluctuating force source, all of which radiate noise through two transmission channels. The impact vibration is induced by the piston striking the end wall of the tank and radiates noise mainly through the connected domain. The jet noise radiated by the tube exit flow is comparable to the radiation noise of a quasi-quiet submarine in navigation and makes less contribution to the overall launching noise. The airborne noise of the launching device presents broadband white noise with stepwise elevation, mainly concentrated in high-frequency band, with minimal contribution to the structural vibration noise. The vertical vibration of the gas tank seat and the radial vibration of the tank cylinder wall are significantly affected by the piston’s startup and end crash. The instantaneous vertical impact peak value is one order of magnitude higher than a typical ship diesel engine’s periodic vibration. The radial vibration pulse peak of the tube wall is corresponded to the moment of the piston’s end crash. The ranking of the average vibration levels for the three vibration sources is as follows: gas tank seat vibration, tank cylinder wall vibration, and tube wall vibration.

Research on the identification and diagnosis of high-frequency friction signals under abnormal contact conditions of mechanical seals is limited. Therefore, a seal monitoring test-bed is established using high-frequency, wide-range, and highly sensitive acoustic emission (AE) technology. Acoustic emission signals are collected under various operating conditions of the mechanical seal, including start-stop, no pressure, low pressure, high pressure, low speed, and high speed. Then the collected data are processed and analyzed using time-domain, frequency-domain and time-frequency-domain analysis methods. A method for determining the interface friction state of the mechanical seal, based on the root mean square (RMS) change of the AE signal, is established. This method reveals the corresponding relationship between the end-face friction signal and the running state of the mechanical seal, from contact to non-contact, and further proves the seal operation process. The research identifies the evolution of the friction signal during the transition from boundary lubrication (BL) and mixed lubrication (ML) in end-face contact friction to sliding contact signals under non-contact hydrodynamic lubrication(HL). The frequency band of the AE signal during seal interface friction is found to be between 240 kHz and 320 kHz. Through time-frequency analysis of the AE signal, it is shown that continuous wavelet transform (CWT) effectively represents the time-frequency characteristics of the AE signal under different working conditions of the mechanical seal. The research results of this paper provide a theoretical foundation and data support for research on mechanical seal condition monitoring and fault diagnosis.

In the assembly process of an aero-turboshaft engine, the coaxiality errors of the curvic couplings are an important technical index, significantly affecting the performance and service life of the whole system. This study takes the turbine blade-casing of an aero-turboshaft engine as an example. The coaxiality errors (including both positional and orientation errors) of the curvic couplings are introduced into the clearance function of the blade tip-casing, the nonlinear dynamic model of a rotating taper-blade casing system is then proposed based on the Hamilton variational principle and the Galerkin method. The effectiveness of the proposed model is verified using ANSYS software. Two different acceleration functions are proposed: Function 1 assumes a constant acceleration value, while Function 2 adopts a cosine wave form for acceleration. The effects of different coaxiality errors of the curvic couplings on the transient response during both acceleration functions are further investigated using Newmark-β numerical method.Simulation results show that an increase in the coaxiality error of the curvic coupling leads to a reduction in the minimum clearance between the blade tip and casing, resulting in a more serious amplitude amplification induced by blade-tip casing rubbing. Compared with Function 1, Function 2 enables the system to pass through the critical speed more quickly, which advances the start time of rubbing. In addition, the maximum rubbing force and penetration depth can be effectively reduced due to the effects of the deceleration, weakening the rising and jumping phenomena in the system.

Due to the differences in data distribution caused by different locations of multiple measuring points, the fault diagnosis of the harmonic reducer is often ineffective. A fault diagnosis method for the harmonic reducer, based on a multiple feature spaces adaptation network (MFSAN), is proposed. Firstly, the vibration signal of the harmonic reducer is transformed using continuous wavelet transform to construct a time-frequency diagram that characterizes its operational state. Secondly, the data measured by sensors at different positions are divided into multiple source domain and target domain data, which are mapped to different feature spaces to obtain feature representations for each measuring point position. Then, the adaptive network is used to automatically transfer the knowledge learned from the source domain to the target domain features and automatically align the feature distribution of a specific domain to learn multiple domain-invariant representations. Finally, a domain-specific decision boundary is used to align the output of the classifier, effectively solving the data distribution differences caused by sensor location. Experimental results of harmonic reducer diagnosis of an industrial robot show that the identification accuracy of this method is 99.72%, which is higher than that of other comparison methods. The effectiveness and feasibility of this method are thus verified.

In light of investigating the interplay between the instantaneous angular speed (IAS) signal and mechanical dynamics of bearings, alongside addressing the vulnerability of rotary arm bearings within industrial robot RV reducers to failure under lowspeed conditions, this paper presents a novel three-degree-of-freedom dynamics model to explain the IAS perturbations resultant from localized roller bearing failures. The model, rooted in the Hertz line contact theory, dissects the influence mechanism of localized deformations stemming from roller-raceway interactions on the IAS. A comprehensive approach to computing the coupled tangential force and torque is outlined. The integration of failure-induced impacts into torque analysis computes torque variations introduced by the failure zone, thereby augmenting angular degrees of freedom. As a result, a three-degree-of-freedom bearing IAS disturbance dynamic model, coupling both normal and tangential forces, is established. Employing fourth-order Runge-Kutta numerical integration, the model is solved, and its results are meticulously compared and analyzed against experimental approximations under near-approximate conditions. The findings underscore the model’s ability to effectively expound upon the origins of IAS perturbations in cylindrical roller bearings while adeptly reflecting the ramifications of outer ring failures on IAS. This work contributes to the refinement of rolling bearing dynamics theory, advancing the comprehension of intricate mechanical systems.

Piezoelectric materials are often used in the fields of vibration energy harvesting and structural vibration suppression due to the excellent electromechanical coupling characteristics. This paper introduces a new shunt with switchable and manipulable force (mechanical) and electrical energy, using the primary and secondary energy conversion function of the flyback transformer based on the existing switching piezoelectric shunt. Based on the positive and negative piezoelectric effects, this paper designs the branch circuits for absorbing energy to suppress vibration and injecting energy to control vibration respectively, resulting in a highly efficient and stable structural vibration control system. The paper introduces the operating principles of the proposed new piezoelectric shunt branch and derives the decay rate models of structural amplitude under different energy manipulation conditions. The relationship between the effect of different energy manipulation methods and the amplitude of the structure is discussed through experiments. Results show that the introduced energy-manipulated shunt branch can realize highly efficient structural vibration suppression depending on the damping requirements of actual scenarios.

Capable of capturing offshore wind energy, the floating wind turbine is one of the primary research interests for researchers in the wind energy community. Researchers usually adopt two-dimensional low-degree-of-freedom simplified planar models for offshore barge-type wind turbines, where the model parameters are identified by the nonlinear least square method. In this case, the accuracy of these models depends highly on parameter fitting. Given the unique structure of offshore floating wind turbines and the surrounding environment, a multi-degree-of-freedom coupled dynamical model is necessary to yield more realistic dynamic behaviors. In this paper, we present a coupled dynamic model with 16 degrees of freedom for the multi-body system of barge-type offshore floating wind turbines under the combined action of wind and waves. The model accuracy is verified through numerical simulation using OpenFAST, developed by the National Renewable Energy Laboratory (NREL). In particular, the modified Blade Element Momentum theory is used to calculate the blade aerodynamic load, the linear potential flow theory is used to determine the wave load, and the quasi-static method is used to obtain the tension of the mooring systems. Besides the generator torque control and blade pitch control, a bi-directional tuned mass damper (TMD) is placed in the nacelle to mitigate the structural vibration of the floating wind turbine of the barge-type, where a limiting device is introduced to limit the TMD stroke. Subsequently, the control parameters are optimized by the method of exhaustion and the genetic algorithm. The simulation analyses show that the model proposed in this paper accurately alculates yields the dynamic response of the barge-type offshore floating wind turbine. The bi-directional TMD with collision mechanism is efficient in mitigating the structural response.

This paper presents a dynamic analytical model of periodic corrugated sandwich structures by using the dynamic stiffness(DS) method. In the model, the coupled structure is decoupled into several open cylindrical shells and rectangular plates, and then based on Kirchoff’s thin plate theory and Flügge’s thin shell theory, the DS matrices of substructures under the condition of simply supported on the opposite side are derived. According to the continuity condition and equilibrium conditions on the coupling boundary, the coordinate transformation matrix of each substructure is derived, and the global DS matrices of the periodic structure are assembled using a similar strategy to the finite element method (FEM). Based on the assembled global DS matrices, the vibration characteristics for the three types of periodically corrugated sandwich structures are calculated, and the results are compared with those from FEM solutions. The results show that the presented model can obtain accurate calculation results with fewer degrees of freedom. In addition, the effects of different core styles and geometric parameters on the band gap characteristics of the periodic sandwich structure are also explored.

In the field of low-frequency vibration isolation, aiming at the issues of insufficient bearing capacity of linear system and stiffness hardening and instability caused by nonlinear jump of traditional quasi-zero stiffness vibration isolation system, a mechanical model of the bionic limb-like quasi-zero stiffness isolation system was established by using the bionic limb-like structure as the negative stiffness element and the positive stiffness spring in parallel. The static characteristics of the system were analyzed; A dynamic model was established based on the Lagrangian equations, and the harmonic balance method was used to analyze the dynamics equations of the system analytically; Through theoretical analysis and experimental research, the isolation characteristics of linear and traditional quasi-zero stiffness isolation system and bionic limb quasi-zero stiffness isolation system were compared and analyzed, as well as the influence of excitation amplitude on the isolation performance and stability characteristics of the system. The results show that compared with the linear system and the traditional quasi-zero stiffness isolation system, the bionic limb-like quasi-zero stiffness isolation system not only ensures the system has a higher bearing capacity, but also effectively reduces the displacement transmissibility and expands the vibration isolation through the design of structural parameters. The frequency bandwidth improves the stability and vibration isolation performance of the system in complex excitation environments.