In this paper, two-phase rotating detonation combustion fueled by n-decane/air mixtures is simulated using Eulerian-Lagrangian method. Three-dimensional non-premixed rotating detonation chamber (RDC) with various axial lengths (45 mm, 65 mm and 85 mm) is considered. The effects of axial length on the flow filed structures, propagation characteristics and RDC performance are discussed. Numerical results demonstrate that axial length of has a significant influence on combustion product expansion, propagation stability of rotating detonation wave (RDW), and pressure gain performance of RDC. Specifically, restricting axial length of RDC induces incomplete expansion of combustion products. It is characterized by elevated pre-detonation pressure and temperature, a dominant deflagration combustion mode, and the collision and regeneration between oblique shock wave (OSW) and slip line (SL). A predictive formula for the relationship between RDC length and RDW height is established. The critical RDC length is 33 mm. Furthermore, as the axial length of RDC decreases, the intensity of the RDW weakens, the speed increases, the pressure peak first decreases and then increases, and the highest detonation stability occurs at 65 mm. The operating boundary of RDC is not affected by the axial length, and the mode transition boundary becomes narrower at larger axial length. Finally, shorter axial length of RDC can suppress the development of OSW, reduce additional entropy increase, and increase the total pressure gain of RDC from -0.14 to 0.18. The novelty of this study lies in establishing a predictive relationship between RDC length and RDW height, clarifying the operational boundary and pressure gain performance of RDC, thereby providing direct theoretical support for two-phase RDC design.

Far-field acoustic radiation prediction for large-aspect-ratio underwater vehicles remains challenging due to the poor adaptability of conventional basis function models, the ill-posedness of far-field extrapolation, high measurement density requirements, and limited robustness to noise. To address these issues, this paper proposes a far-field acoustic radiation prediction method based on the superposition of Prolate Spheroidal Wave Functions (PSWFs). Leveraging the axisymmetric characteristics of PSWFs and their energy concentration properties in the space-frequency domain, the proposed method effectively matches the axially elongated acoustic field of largeaspect-ratio structures, enabling accurate acoustic field representation with a reduced number of basis functions. Sparse Bayesian Learning (SBL) is employed to adaptively estimate the weighting coefficients, which improves the stability of solving ill-conditioned inverse problems and enhances robustness against measurement noise. By exploiting the far-field asymptotic properties of the prolate spheroidal radial wave functions, an analytical formulation for far-field directivity is derived, thereby alleviating the ill-posedness of far-field extrapolation encountered in conventional approaches. Numerical simulations of a scaled underwater vehicle model under multiple operating conditions demonstrate that the proposed method achieves significantly higher prediction accuracy and stability than conventional basis function approaches based on plane, cylindrical, and spherical waves over the frequency range of 10-200 Hz. Under sparse measurement conditions, a sampling rate of 50% yields directivity predictions comparable to those obtained using full measurements, with errors generally below 10%. The proposed method provides a robust and efficient framework for far-field acoustic radiation prediction of elongated underwater structures while significantly reducing measurement requirements.

Three-dimensional heterogeneous integration technology puts forward high standards for the reliability of multilayer heterogeneous interfaces. Delamination or micro-cracks failures frequently originate at the interfaces in under bump metallurgy layers due to high current density. Ultrasonic nondestructive testing becomes increasingly vital due to its sensitivity to interfaces. However, heterogeneous interfaces in advanced packaging, often thinner than the ultrasonic wavelength, are difficult to be detected. In this study, we demonstrate a novel method, by utilizing the peak shift of ultrasonic spectra based on ultrasonic attenuation, to reliably recognize heterogeneous interfaces with adequate real-time performance. Further experiments using a self-built platform coupled with simulations exhibit the robust capability of the method, achieving an approximate 11.16 dB improvement even in inaccurate focusing. Experimental scanning results, compared with optical images, show that the proposed method more accurately characterizes the metallurgical layer beneath the bumps than conventional constant-depth scanning. This method can also mitigate the adverse effects of multi-path echoes without the need for higher frequency transducers, ensuring the penetration capability of ultrasound into multilayer heterogeneous packaging structures. These merits making the method very suitable for non-destructive testing in advanced microelectronic packaging.

Abstract Quantitative defect evaluation using high-frequency scanning acoustic microscopy remains challenging when echoes from multilayer structures are strongly overlapped. A multiresolution matching pursuit (MRMP) method is proposed for echo separation and defect quantification. The method integrates a physically motivated band-limited echo-atom model and a hierarchical sparse decomposition scheme that combines coarse localization, recursive segmentation, and local dictionary refinement. This strategy improves echo-atom alignment while avoiding the computational cost of a globally dense dictionary. Finite-element simulations and experiments on bonded wafers and flip-chip (FC) package are used to validate the method. The MRMP separates adjacent echo components with a demonstrated axial spacing of 16.86 μm in silicon under the present 1 GSa s −1 sampling condition, corresponding to sub-wavelength spacing. For bonded-wafer signals, the MRMP achieves a signal-to-noise ratio of 18.7 dB and a normalized reconstruction error of 11.52%. For FC solder-bump void evaluation, the estimated void ratio decreases from 35.22% using conventional C-scan and 30.02% using fixed-dictionary orthogonal matching pursuit to 18.75%, close to the x-ray reference of 15.35%. The results show that the MRMP improves echo separability and quantitative reliability for ultrasonic inspection of advanced packaging.

Common shell of revolution, such as cylindrical, conical, and spherical shells, are widely used in marine, aerospace, and other engineering fields due to their excellent support and pressure-resistant properties. Research on their vibration characteristics has progressed from single shells to composite shells, from ribbed shells to those with complex internal substructures, and from uniform to discontinuous connections. The discontinuities in wave propagation at the boundaries of discontinuously connected cylindrical shells result in highly complex equation of vibration control, leading to limited studies in this area. This study first models the uniform cylindrical shell and annular plate as spectral elements, using trigonometric and Bessel functions to describe displacement solutions and obtain vibration responses for arbitrary boundary conditions. Then, based on artificial virtual spring theory and the weighted least squares method, the discontinuous connection between the cylindrical shell and annular plate is modeled as a circumferentially varying stiffness distribution, leading to the derivation of dynamic stiffness matrices for both continuous and discontinuous connections. Finite element simulations are conducted using ABAQUS to analyze the vibration characteristics of the discontinuously connected cylindrical shell under free, clamped, and simply supported boundary conditions. Finally, an experimental setup is used to measure the vibration response under harmonic excitation and perform impedance testing with an impact hammer. The results show that the spectral element method accurately calculates the natural frequencies of the stiffened cylindrical shell, with an overall error of less than 2 %, while the maximum error for the experimental shell is 5.8 %.

With the rapid development of precision instruments, aerospace, and automotive industries, the demand for compact vibration isolators capable of suppressing low-frequency vibrations has surged. Although prior reviews have established the theoretical framework of quasi-zero stiffness (QZS) isolators, critical gaps persist in addressing their compact design under strong nonlinear dynamics and diverse engineering constraints. This review systematically analyzes the dynamic characteristics of QZS systems under nonlinear effects and evaluates five innovative design methodologies for compact QZS isolators: special spring type, magnetic type, bionic type, metamaterials-based type, and origami-inspired type. Key findings reveal that special spring-type isolators are simple to design and space-efficient but difficult to machine. Magnetic-type isolators achieve ultra-low start-up frequencies but face thermal instability. Metamaterial designs enable multifunctional integration at the cost of manufacturing complexity, while bionic-inspired and origami-inspired isolators are difficult to abstract for practical applications. We find that current research tends to prioritize miniaturization over the synergistic optimization of load capacity, broadband isolation, and adaptability. Future research should focus on multi-degree-of-freedom systems, coupled metamaterials-bionic structures, and active magnetic control. This work provides a key roadmap for advancing compact QZS technology in space-constrained applications.

The energy supply of microelectronic products mostly depends on chemical batteries with limited life that not only need to be replaced regularly, but also easily cause environmental pollution. Mechanical energy capture has attracted more and more attention in recent years. As a new type of self-sustaining micro power supply, the micro mechanical energy collector can convert the widely existing mechanical energy in the environment into electrical energy. It has the advantages of small size, light weight, convenient processing, reliable work, good environmental adaptability, and long life. It can almost replace traditional batteries,wired power supplies and micro batteries, supplying power for various micro wireless sensor products and embedded devices. For this reason, this paper aims at the problem of difficult power supply of a wireless sensor for equipment vibration monitoring, breaking through the limitation of single function of traditional vibration isolation and energy capture system, innovatively designng a mechanical vibration energy capture micro generator with multi-function vibration isolation and energy capture integration, models and analyzes the overall structure of the device and conducts theoretical derivation. It tests the output characteristics of the device under different load resistances. The test results show that the mechanical vibration energy capture micro generator can efficiently collect mechanical energy and convert it into electrical energy, which proves that the mechanical vibration energy acquisition device based on radial magnetic field designed in this paper is a practical energy acquisition system.

Bistable structures are widely used for vibration energy harvesting due to their wide bandwidths and extraordinary performance. However, the dynamics of bistable structures are complicated, and inter-well, intra-well, chaotic, superharmonic, and subharmonic vibrations may coexist in some frequency ranges. Inter-well vibration is typically the most desired because of its large oscillation amplitude, which means more kinetic energy can be converted into electricity via different energy transduction mechanisms. In this study, a modified bistable beam-slider vibration energy harvester consisting of a cantilever beam and a movable slider on the beam is investigated experimentally. The slider can move along the beam under the combined effect of the inertial and magnetic forces. Moreover, magnetic nonlinearity is incorporated into the beam to achieve bistability instead of the linear or monostable configurations typically found in existing literature studies. The slider trajectory and the bistable cantilever beam time responses show that the slider can help the bistable beam system transfer from the chaotic to the inter-well vibration orbit. The results show that inter-well vibration can be maintained even with disturbance introduced with 3.92 m/s(2) base excitation over the 15 Hz-18 Hz frequency range. The whole transfer process is self-regulating and does not require any external intervention. Therefore, the harvester we designed is self-adaptive, with a substantially broadened operating bandwidth.

Weak fault detection is still a hotspot in these years. The key of this work is to enhance the ratio of signal to noise (SNR). Then a new extraction method of weak fault impact based on amplification algorithm is proposed. Since the fault impact is related to bigger derivative, the amplification function combined with the derivative of the vibration signal is used to amplify the amplitude of the impact. Then Sparse Spike Deconvolution (SSD) which has been widely used in earthquake for impact detection is able to extract small impact from the signal processed by amplification function. Then, in order to enhance the periodicity of fault impacts, the compression function is used to compress the amplitude of bigger impacts according to different scales. At last, the experiment result shows that the proposed method is more effective than the common envelope analysis.

Low-frequency radiated noise, characterized by a distinctive “acoustic fingerprint” is generated when vibrations from marine machinery propagate through a ship’s hull into the ocean. This type of noise travels long distances with concentrated and stable energy, posing a significant threat to a ship’s acoustic stealth capabilities. Active-passive hybrid isolation is the primary method for reducing low-frequency radiated noise from ships; however, technical challenges remain, such as effectively integrating active and passive components, achieving high output force in a compact design, and addressing the poor linearity of actuator output at low frequencies. To address these issues, this paper presented an innovative electromagnetic-hydraulic-rubber integrated vibration isolator. Firstly, the study analyzed the dynamic characteristics of a two-degree-of-freedom isolation system and investigated the influence of active-passive hybrid vibration isolator parameters on control force and vibration reduction performance. Secondly, it was established that the magnetic circuit model and magnetic field strength expressions for the electromagnetic actuator using magnetic circuit analysis derive the analytical relationship between electromagnetic force, current amplitude, and frequency using the energy method. Subsequently, a mathematical model was developed for the rubber-hydraulic suspension component to examine its dynamic characteristics, hydraulic damping, and hydraulic force amplification transmission laws. Lastly, we organically combine the electromagnetic actuator with the rubber-hydraulic suspension and conduct a multi-physics joint simulation of the integrated vibration isolator using Comsol software to verify the effectiveness of the optimized design and vibration isolation control. Experimental research was carried out on the dynamic characteristics, output force properties, and fatigue characteristics of the integrated vibration isolator prototype. Results indicated that the established models and methods can achieve over 90% accuracy in predicting the performance of the electromagnetic actuator’s output force and exhibit good linearity within the 5–400 Hz range. The rubber-hydraulic suspension can achieve an amplification factor of up to 1.5 for the electromagnetic force while reducing the transmission of vibrations to the base. The research findings can enhance the low-frequency vibration isolation performance of marine machinery equipment and improve their acoustic stealth capabilities.

When vibrations generated by marine machinery propagate through a ship's hull into the ocean, they produce low-frequency radiated noise with distinct "acoustic fingerprint" characteristics. This noise, characterized by stable and concentrated energy, long transmission distances, and difficulty in elimination, becomes the primary target for enemy sonar detection. Active vibration isolation serves as a critical method for reducing low-frequency vibrations in ships and enhancing their acoustic stealth performance. However, control challenges persist, including multi-frequency excitation, frequency fluctuation, multi-channel coupling, and slow convergence speed. To address these issues, this paper introduced an innovative multi-channel decentralized decoupling filtered-x least mean square (DMFxLMS) algorithm. Firstly, a recursive least squares identification algorithm with a forgetting factor was proposed, taking into account the characteristics of single-input, multi-output and multi-input, and multi-output control systems, effectively enhancing the algorithm's convergence speed and control accuracy. Secondly, based on the decentralized decoupling control concept, the multi-channel control system was simplified into parallel single-channel control loops. The control weight coefficient updates were only related to adjacent error signals, significantly reducing the algorithm's computational complexity. Thirdly, an anti-impact link was designed to improve the algorithm's robustness, considering the interference caused by other mechanical equipment during the control process. The influence of abnormal error signals in the control weight coefficient correction term was suppressed, and a percentage function was introduced to limit the output signal. Finally, the feasibility and effectiveness of the DMFxLMS algorithm were verified through simulations and experiments. The results demonstrated that the DMFxLMS algorithm achieved significant control effects for both constant frequency line spectrum excitation and frequency fluctuating line spectrum excitation, fulfilling the objective of reducing base vibration. The DMFxLMS algorithm exhibited fast convergence and excellent robustness, making it suitable for practical engineering applications.

Near-field acoustic holography is a cutting-edge sound field visualization technique that allows the acquisition of sound pressure amplitude and phase information in a region near a sound source to reconstruct the surface “acoustic highlights” of the sound source by means of area array, near-field measurements. Near-field acoustic holographic measurements in the free sound field, and the related algorithms to locate and identify noise sources, have many applications in engineering. However, there are still many problems to be studied for the accurate localization and identification of noise sources in non-free fields for large size underwater body sources. Firstly, the theoretical derivation of the sound field separation method based on the virtual double holographic planes is carried out. Secondly, to study the key parameters of the sound field separation method based on the virtual double holographic planes, the genetic algorithm is introduced to select the optimal number of expansion terms for the spherical waves, to give the regularized combination method, and to perform simulations. Then, the simulation studies of air acoustic field and water acoustic field in complex environment are conducted for the sound field separation method based on virtual double holographic planes, and to discuss the effects of measurement parameters on the sound field separation errors. Finally, the feasibility and effectiveness of the sound field separation method based on the virtual double holographic planes are verified in the hydroacoustic tests. Moreover, the reconstruction error in the test is analyzed and a method to reduce the error is given. The results show that the sound field separation method based on virtual dual holographic planes only needs to measure the sound pressure value of a single holographic plane, and there is no requirement for the shape of the holographic plane. This method has the advantages of simple sound field testing, no requirement for the measurement array, and high accuracy of sound field separation compared with the traditional sound field separation method.

Abstract Dynamic designs for ship propulsion shafting can be categorised as complex multi-disciplinary coupling systems. The traditional single disciplinary optimisation design method has become a bottleneck, restricting the further improvement of shafting design. In this paper, taking a complex propulsion shafting as the object, a dynamic analysis model of the propeller-shafting-hull system was established. In order to analyse the coupling effect of propeller hydrodynamics on shafting dynamics, the propeller’s hydrodynamic force in the wake flow field was calculated as the input for shafting alignment and vibration analysis. On this basis, the discipline decomposition and analysis of the subdisciplines in design of shafting dynamics were carried out. The coupling relationships between design variables in the subdisciplines were studied and the Multi-disciplinary Design Optimisation (MDO) framework of shafting dynamics was established. Finally, taking the hollowness of the shaft segments and the vertical displacement of bearings as design variables, combined with the optimal algorithm, the MDO of shafting dynamics, considering the coupling effect of the propeller-shafting-hull system, was realised. The results presented in this paper can provide a beneficial reference for improving the design quality of ship shafting.

This paper proposes a novel hybrid scheme through read-first-LSTM (RLSTM) encoder-decoder and broad learning system (BLS) for bearings degradation monitoring and remaining useful life (RUL) estimation, which aims to describe the nonlinear characteristics of the degradation process. Firstly, the raw signals are processed premier by complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and a novel dimensionality reduction method composed of t-distribution stochastic neighbor embedding (t-SNE) and density-based spatial clustering of application with noise algorithm (DBSCAN). Then, the health indicator is constructed with the Hilbert-Huang transform (HHT) corresponding to the bearings’ natural fault frequency, which can be employed as the hybrid scheme training label. Linear rectification technology (LRT) and exponentially weighted moving average (EWMA) control chart are adapted to define the exact process of the degradation. Secondly, a novel RLSTM is proposed. And simultaneously, an encoder-decoder model, where RLSTM is utilized as an encoder, and LSTM is adopted as a decoder, is designed for degradation monitoring. Finally, a broad learning system (BLS), which differs from deep learning with a deeper structure, is established in a flat network to estimate the RUL of bearings. Compared with the state-of-the-art techniques, the better efficacy of the proposed hybrid scheme is illustrated using the PRONOSTIA platform dataset.

轴系动力学特性直接影响到舰船航行的安全性、隐蔽性和可靠性,为分析清楚轴段空心度对舰船推进轴系动力学特性的影响,以某复杂推进轴系为研究对象,基于有限元法建立其动力学分析模型;采用雷诺方程计算轴承油(水)膜刚度,基于螺旋桨升力线理论近似计算螺旋桨轴承力作为振动激励,研究得到螺旋桨轴、艉轴及中间轴空心度变化对轴系校中及振动特性的影响规律;在此基础上,以各轴段空心度为变量,应用多目标优化算法开展轴系动力学特性综合优化.优化结果表明:轴系前后艉轴承负荷差减小了4.1kN,回旋振动和纵向振动的最大振幅均有所减小,轴系动力学特性得到改善.

针对滚动轴承故障冲击信号难以提取的问题,提出了一种改进辛几何模态分解(Improved Symplectic Geometry Modal Decomposition,ISGMD)滚动轴承故障特征提取方法.首先将振动信号进行辛几何模态分解,然后,利用k均值聚类的方法对分解得到的辛几何分量进行聚类,通过包络谱稀疏度指标筛选出故障特征明显的聚类辛几何分量(Cluster Symplectic Geometry Component,CSGC)并进行重构,对重构分量进行包络解调,提取出故障特征.将该方法运用到轴承故障仿真和实验信号,结果表明,这里提出的方法能够有效提取出滚动轴承故障特征.

To improve the isolation ability of the existing equipment for low-frequency line spectrum, this paper presents an electromagnetic double-layer vibration isolation system (ED-VIS) for the first time. The negative and positive stiffness values of the ED-VIS are provided by the electromagnet and the linear spring, respectively. To better analyze the vibration isolation system designed in this paper, the dynamic model of the ED-VIS is established, and the effects of damping ratio, excitation force amplitude, and mass ratio on the force transmissibility feature of the isolator are analyzed. Then, the ED-VIS test bench is built, and the low-frequency vibration isolation capability of the ED-VIS is measured by a frequency sweep test. According to the sweep test results, a method to improve the low-frequency vibration isolation capability of the isolator is proposed. Finally, the reliability of the system in isolating low-frequency vibration is verified. The results show that compared with the equivalent linear vibration isolation system, ED-VIS is more sensitive to low-frequency vibration and has a lower initial vibration isolation frequency. Therefore, this paper designs the ED-VIS has better low-frequency vibration isolation performance.

针对现有高静低动刚度隔振器的设计参数均已固定,磁负刚度机构无法在线调整的问题,本文设计一种新型负刚度可调的电磁隔振器.利用永磁体与螺旋线圈设计电磁负刚度元件,并对其进行有限元仿真分析.通过静力分析,推导负刚度可调高静低动刚度隔振器力-位移-电流和刚度-位移-电流的数学表达式,得到系统在平衡位置获得准零刚度特性的条件.建立高静低动刚度隔振系统动态模型,利用平均法研究不同参数对系统幅频特性及力传递率的影响.研制原理样机,搭建试验台架并进行隔振性能测试试验,试验结果表明本文研究的高静低动刚度隔振器具有更宽的有效隔振频域和更低的传递率峰值.

动力装置监测诊断课程是机电管理人才培养的主干课程之一.将精准教学引入动力装置监测诊断课程教学,在课前、课中和课后收集可衡量、可调控的数据信息,能够达到"以生为本,私人订制"的个性化教学目标,从而实现个性化人才培养.