A method for reconstructing equivalent loads using block sparse Bayesian learning (BSBL) is proposed for local distributed dynamic load (LDDL) without prior information on its spatiotemporal distribution. Considering the continuous variation of LDDL, a temporal distribution pattern consistency assumption is introduced, compressing LDDL into an equivalent load temporal distribution pattern function. First, the vibration response is transformed into modal loads in the modal space. Subsequently, based on BSBL, a structured redundant dictionary of basis functions derived from the pattern function is learned, enabling the reconstruction of the equivalent time distribution for the LDDL. Next, considering the structure’s spatial characteristics, a redundant dictionary of structural mode shapes is constructed. BSBL is again applied to the non-zero encoding of the basis functions for sparse decomposition, solving for the spatial distribution corresponding to the basis functions and achieving the equivalent spatial distribution reconstruction of the LDDL. The reconstructed equivalent load obtained by the proposed method not only achieves equivalence in the response field but also reflects the spatiotemporal characteristics of the actual load to a certain extent. Numerical examples validate the effectiveness of this method.

Satellite networks are significant space infrastructures. However, satellite gateway stations only can be deployed within limited geographical areas, which lead to the centralized distribution constraints of gateway stations. The local destruction-resistant routing algorithm based on segment for satellite networks is proposed to improve the serious decline of network services caused by space resource failures. Light-traffic and heavy-traffic regions are categorized based on limited gateway stations areas, while failure sections are confirmed, which are the basis of rerouting graph. Rerouting graphs are generated based on failure sections in light-traffic regions, and the rerouting source is the starting node of the failure section while the rerouting destination is the end node of the failure section. Rerouting graphs in heavy-traffic regions are entire heavy-traffic regions, and the rerouting source is the starting node of the failure section while the rerouting destination is the final target node. The rerouting time was reduced by $69 \%$, which enhances the sustained service, and ensures continuity and integrity.

This study introduces the concept of blind source separation (BSS) based on a multivariate autoregressive (AR) model in the field of operational modal analysis (OMA), with improvements and extensions. A novel blind modal identification method is proposed, which combines a non-adjacent widely linear generalized multivariate AR (GMAR) model with an extended joint eigenvalue decomposition (EJEVD) approach. First, a non-adjacent widely linear GMAR model is constructed for the analytical form of vibration response signals. Then, the GMAR coefficients are subjected to joint approximate diagonalization using EJEVD to obtain the mode shape matrix. This process converts the multi-degree-of-freedom vibration responses in the physical space into single-degree-of-freedom modal coordinates in the modal space. Finally, a simple single-modal identification method is employed to extract modal frequencies and damping parameters. The proposed method is applicable to both real and complex modal analysis, combining the practical engineering advantages of OMA with the benefit of BSS, which does not require parametric estimation of the system model. Comparative results from numerical simulations show that the proposed method outperforms methods based on second-order blind identification and complexity pursuit BSS methods in separating closely spaced modes. Experimental validation further demonstrates the effectiveness and engineering value of this method.

Pillar-shaped components with force-regulation functionality are widely utilized in shock absorption and energy dissipation fields to achieve overload protection. These components are typically required to have slender configurations to accommodate limited installation spaces. However, conventional cam mechanisms with existing standard configurations often exhibit relatively large dimensions, which hinders their engineering applications. Thus, this article presents an improved cam-based force regulation mechanism (FRM) with a compact configuration, which utilizes an obliquely placed and moved follower to reduce the lateral dimension. Compared to the conventional translational cam mechanism where the cam and follower move orthogonally, the improved configuration offers a more compact size while maintaining comparable force output characteristics, enhancing its practicality and applicability in engineering. The profile customization method with friction considered is employed to define the cam shape, ensuring that the cam that supported by the follower-spring component can deliver the desired force function within a certain stroke. Prototypes with different friction types and various (constant, linear, and quadratic) output force functions for the compact cam-based FRM were designed, assembled, and tested. The high consistency between the test results and the design objectives demonstrates the correctness and effectiveness of the presented compact design method with an obliquely placed and moved follower. The proposed inclined translational cam mechanism can be fabricated into strut or bar through shape and structural optimization design, thereby enabling its application in relevant engineering fields.

In ocean engineering, assessing vibration-induced fatigue under random loads is critical, particularly for ocean structures with multiple defects, as fatigue is highly sensitive to local structural flaws. Recently, incorporating structural dynamic characteristics into vibration fatigue assessments has emerged as a significant trend and formidable challenge, involving three key obstacles: precise localization of fatigue hotspots, extraction of key modes, and determination and integration of modal damage contributions. This paper introduces a novel framework for fatigue hotspot localization and damage assessment in the context of random vibration fatigue in ocean structures. By initially identifying fatigue hotspots and hot regions using stress mode shapes, refining the finite element mesh in hot regions, and conducting reanalysis, the exact locations of fatigue hotspots can be determined, enabling structural dimensionality reduction. The introduction of a modal damage contribution factor allows for the evaluation of each mode's damage contribution and the identification of key modes, further facilitating modal reduction. For the precisely localized fatigue hotspots, the proposed method combines the damage contributions of key modes, enabling rapid and accurate assessment of fatigue damage under random vibration loads. Finite element case studies and vibration fatigue test results demonstrate that the proposed framework effectively addresses the challenges of random vibration fatigue evaluation, achieving structural and modal reduction while significantly enhancing the efficiency of damage assessment without compromising accuracy.

In order to solve the problem of the failure of SLAM algorithm due to insufficient feature information of a single point in low texture environments, an indoor visual/inertial localization algorithm combining point-line feature matching is proposed. By optimizing the LSD line feature extraction algorithm, the close fusion of vision and IMU data is achieved, and an adaptation factor is introduced in the optimization objective to reduce the processing time. This method reduces the absolute trajectory error and improves the positioning accuracy and system robustness.

In recent years, extensive research has been devoted to nonlinear piezoelectric shunt circuits for mitigating structural vibrations. However, existing studies have primarily concentrated on polynomial nonlinearity, particularly cubic nonlinearity. This paper develops a tunable non-smooth piezoelectric shunt absorber to suppress structural vibrations under harmonic excitation. We enhance the conventional resonant circuit by introducing a piecewise linear negative capacitor, which is implemented using a pair of diodes and voltage sources. The stationary response of the non-smooth system is derived using the complexification-averaging method. The effects of critical voltage and excitation intensity on the damping performance are investigated subsequently. Furthermore, we apply an adaptive control method based on the gradient descent algorithm with adaptive moment estimation (Adam) to the nonlinear circuit, improving its damping performance and enabling adaptation to changes in excitation intensity. Experimental results validate the effectiveness of the proposed adaptive nonlinear circuit, demonstrating superior stationary performance compared to linear resonant shunt circuits across a broad bandwidth of frequencies, especially at off-resonant frequencies.

This paper proposes an efficient method to evaluate the time-dependent fatigue reliability of structures under complex multilevel loads using a finite set of fatigue test data obtained under single-level loading conditions. The method preserves the simplicity of linear damage accumulation theory while considering the interactions among multiple load levels and the influence of load sequence on reliability. Leveraging the linear damage rule, a cumulative damage probability model was established under single-level constant amplitude loading. This model incorporates a fatigue life degradation function to characterize the cumulative damage effect of load cycles and corrects the fatigue reliability curve under single-level constant amplitude loading. By employing the principle of fatigue damage equivalence, the method determines the damage equivalence at the load switching point using the damage curve method, enabling the conversion of equivalent reliability under multilevel loads. The proposed method was validated by combining the test data obtained under three working conditions, including two-level loads loading, load blocks loading, and changing loads loading. The results demonstrate that the proposed method can accurately and efficiently evaluate the time-dependent fatigue reliability under different types of multilevel loads, using only a limited set of fatigue life data under single constant amplitude loads.

Synchronized switch damping (SSD) techniques have been developed for structural vibration suppression in recent years. In SSD control, a self-sensing approach can invert the voltage on piezoelectric materials at displacement extrema without sensors or real-time controllers. However, tracing extrema from the voltage on piezoelectric materials has become challenging since the voltage generated by the vibration of controlled mode is minor compared with noises as the increase of damping performance. Furthermore, the voltage decay caused by the current leakage is dominant when the host structure vibrates at a low frequency. This paper proposes a self-sensing approach based on the zero-crossing detection technique with voltage decay compensation. The switching delay and voltage decay are considered in the electromechanical model of the SSD system. Accordingly, a band-limited proportional-differential circuit is implemented to offset the voltage decay and generate zero-crossings at displacement extrema simultaneously. Experiments show that the proposed method is still effective when the voltage decay in the SSD control is dominant.

差分放大电路是模拟电子技术课程中的一个重要知识点.传统教学模式下,差分放大电路一般先求解静态工作点,然后根据信号的双端或单端输入方式以及输出方式,将输入信号等效为共模信号与差模信号,再结合电路的对称性,分别分析差分放大电路的差模特性与共模特性[1].目前,国内外教材与文献中,对差分放大电路交流通路等效方法主要有两种,一种是数学等效[1-2],另一种是输入信号耦合传输等效[3-4],这两种等效方法均引入了差模与共模概念,由于放大电路信号的激励和输出方式组合共4种,学生习惯于单入单出的电路模型分析,理解上难度较大,公式容易混淆.本文提出一种新的差分放大电路的交流分析通用模型,利用该模型可推导出差分放大电路的一般性结果,与教材上对比分析,有助于学生深入理解差分放大的概念并掌握电路的内在本质.

The quasi-zero-stiffness (QZS) vibration isolator is usually composed of positive and negative stiffness elements in parallel. The negative stiffness element usually requires specific constraint boundaries to form negative stiffness characteristics, which cannot meet the lightweight design of spacecraft structures. So the bi-stable hybrid symmetric laminate (BHSL) is presented as a negative stiffness element. A finite element model (FEM) is developed to carry out static and dynamic analyses of this vibration isolator. An equivalent theoretical model is developed based on the restoring force–displacement curve of BHSL. The approximate analytical solutions and direct numerical solutions are obtained by employing the averaging method and the Runge-Kutta method, respectively. Different types of the steady-state response are obtained, namely the symmetrical multi-harmonic response, the asymmetric multi-harmonic response and the single-harmonic response. There exists a small gap between the analytical solutions and the Runge-Kutta solutions or the FEM results only at the low frequency excitation due to the super-harmonics. The displacement transmissibility is used to quantify the vibration isolation performance of this vibration isolator. The experiment is designed to verify the theoretical and FEM models from static and dynamic analysis perspectives. The results show adjusting geometric parameters and lay-up designs can improve the vibration isolation performance.

The satellite-borne data transmission antenna is the main disturbing source of low-frequency microvibration of spacecraft, which immensely affects the image quality of remote sensing satellite. In this paper, the dynamic characteristics of flexible load driven by stepping motor on flexible boundary are studied. The dynamic equation of the stepping motor driven by current subdivision is simplified by linearization method. The dynamic model of flexible load driven by stepping motors on flexible boundary is established by using the Dynamic Substructure Method, and the analytical expression of microvibration of the data transmission antenna is given. The coupling relationship between the stepping motors and the flexible structure is analyzed by modal coordinate transformation. The microvibration model is verified by simulation and experiment, and the main causes and coupling factors of microvibration are explained. The results show that the model can accurately predict the microvibration of the satellite antenna and can be applied to the microvibration prediction in orbit. The reasonable selection of the working velocity of the stepping motors can effectively reduce the microvibration, which provides the basis for the design of the antenna control system.

Backlash is the inherent characteristic of gear transmission system. It is an important mean to measure and compensate backlash to improve transmission performance. When the driving gear reverses, due to the existence of backlash, the driven gear will still keep its original steering due to inertial motion until the driven gear collision with the driving gear. In this paper, based on the analysis of the tooth gap of the driving gear and the driven gear, an on-line measurement method of the meshing tooth gap combining the angular velocity of the load end with the information of the Angle position of the two axes of the master-slave gear is presented. This method uses the gyroscope at the load end (driven wheel) to monitor the sudden change of angular velocity at the moment of gear reverse impact and re contact, and the signal is used as the judgment basis for the reverse contact moment of the driving gear and driven gear. Then, the angular position data of driving gear and driven gear are fused at the time of reverse rotation and contact impact, and the backlash of the gear is calculated online. Finally, setting up an experimental platform for measuring backlash, and the proposed method is verified. The experimental results show that the proposed method can achieve accurate backlash measurement.

The geomagnetic map is an important factor affecting the performance of geomagnetic matching navigation. The random error of the geomagnetic map seriously affect the accuracy of the matching positioning, which even leads to matching failure. In order to improve the geomagnetic matching performance, a method for modeling and compensating the random error of geomagnetic map data is proposed. Based on the analysis of the random error characteristics of the geomagnetic map data, this method establishes a nonstationary time series model of the data, takes this model as the state equation, takes the real-time data as the measurement, and uses Kalman filter to filter the geomagnetic map data to compensate the random error of geomagnetic map data. The effectiveness of the filtering method is indirectly proved through the navigation and positioning experiments based on the geomagnetic data before and after filtering. The processing results of the actual geomagnetic map data show that the geomagnetic map data filtered by the method in this paper can improve the positioning accuracy by 54.7% when it's used for navigation.

This paper presents a passive quasi-zero-stiffness (QZS) vibration isolator via a cam mechanism (CM), where the cam has a user-defined profile to generate the desired force-displacement relation that yields the QZS characteristic. Without using the common configurations connecting positive and negative stiffness in parallel, this CM based QZS isolator is much simpler in structure due to utilizing fewer key components. Unlike previous studies where the high calculation complexity must be simplified by Taylor expansion for the convenience of dynamic analyses, this QZS isolator has the superiority that the ideal simplest restoring force with QZS property can be directly realized through the well-designed CM, which can eliminate the approximation error between the theoretical design and actual implementation. The nonlinear differential motion equations based on pure-cubic restoring force and both viscous and friction damping are derived and solved with the harmonic balance method, followed by the discussion of the relevant dynamic characteristics. Experiments on the fabricated physical prototype of the QZS isolator are carried out. The static results verify the proposed design principle due to the agreement between the tested and designed force-displacement curves. The vibration tests show the advantages of QZS isolator in most cases, since it can exhibit the wider isolation frequency bandwidth and much weaker resonance effect than the corresponding linear counterpart. The actual transmissibility characteristics of the QZS and linear isolators under different force and base motion excitation levels are obtained and comprehensively compared to reveal the specific isolation efficiency and how excitation amplitudes affect the vibration attenuation performance.

Aiming at the requirements of positioning under emergency situations such as terrorist activities, natural disasters, etc., we propose an emergency positioning method of indoor pedestrian in non-cooperative navigation environment based on virtual reference node array/inertial navigation system in this paper. This method bases only on a reference node that has been placed indoor temporarily, and uses the distance information between the single reference node and the move node carried by pedestrian. In this emergency positioning method, we establish the virtual reference node array and virtual ranging overdetermined equations to obtain the pedestrian’s three-dimensional positioning coordinates without accumulated error by using the surface intersection physical model and least square method. Furthermore, we combine the positioning results of inertial navigation and wireless virtual reference node array method, so that the fluctuation of wireless positioning error is suppressed, and long-term and high-precision positioning is achieved. Finally, we choose LinkTrack’s UWB local positioning result as the reference comparison standard, and conduct experimental verification and performance evaluation of the proposed method. The experimental result shows that the average error of the proposed positioning method along X-axis and Y-axis are 0.049m and 0.056m respectively, which indicates that this method has similar positioning accuracy with LinkTrack’s UWB local positioning system, and it can realize the accurate positioning and tracking of indoor pedestrian in non-cooperation navigation environment.

This article presents a quasi–zero-stiffness isolator with a cam-based negative-stiffness mechanism, where the cam has a user-defined noncircular profile to generate negative stiffness to counterbalance the positive stiffness of the vertical spring and yield the quasi–zero-stiffness characteristic around the equilibrium position. Unlike previous studies, the proposed quasi–zero-stiffness isolator has the preferable feature that the desired cubic restoring force can be directly obtained through the well-designed profile of the cam in the negative-stiffness mechanism with the friction considered during the model design, rather than through the Taylor expansion and friction-ignoring assumption, which can avoid the approximation error between the theoretical design and the specific realization. The pure-cubic nonlinear differential equation of motion of the quasi–zero-stiffness isolator is derived and solved with the harmonic balance method, followed by the discussion of the relevant dynamic characteristics. Experimental studies are carried out based on the physical prototype of the quasi–zero-stiffness isolator. The results show that the quasi–zero-stiffness isolator can greatly extend the isolation frequency bandwidth and has a much lower resonance peak. In the low-frequency band, the quasi–zero-stiffness isolator greatly outperforms the corresponding linear system but is equivalent or even inferior in the high-frequency range with the increase of excitation force.

Navigation and positioning services are related to national security, economic development and social livelihood, they're playing a decisive and indispensable role in both military and civilian fields. Urbanization is accelerating and indoor sites are increasing. People spend more than 80% of their time living and working in the indoor environments (including large buildings, underground sites, mines, tunnels, etc.), How to achieve high-precision navigation and positioning in such a complex navigation environment? This is not only an urgent social problem but also a technical problem. Based on the introduction of indoor navigation background, an inertial measurement information/UWB combined indoor positioning method is proposed in this paper, to solve the problem of long-term positioning in a complex indoor environment, and the experimental researches have been performed. Firstly, based on the research of human motion model, the method extracts motion parameters related to navigation and establishes the mapping model between human motion parameters and navigation parameters in order to implement autonomous pedestrian navigation which is based on inertial measurement information/human motion model. Then, using the position information provided by UWB as the measurement, the Kalman filter based on inertial measurement information/ human motion model/UWB combined system is designed to integrate positioning information from the combined system of inertial measurement information/human motion model and UWB, so that it can provide long-term and high-precision relative navigation for indoor pedestrians. The paper develops a prototype of the inertial measurement information/human motion model/UWB combined system, which provides a physical platform for the experimental verification of the proposed method. What's more, it also optimizes and verifies the proposed method referring to experiments under the environment of NOKOV high-precision indoor 3D-motion capture system by Beijing measurement technology co., LTD. There are bright application prospects that the method can be extended in single-soldier system, urban anti-terrorism operations and pedestrian positioning in the field of emergency rescue.

Satellite navigation system can produce large errors or even cannot locate the target when its signals get obscured. To meet the local positioning demands of unmanned aerial vehicle(UAV) in GPS denied environment, we proposed a relative navigation method using wireless ranging information to construct virtual base stations. This method needs only one actual base station prepared on the ground in advance, and then construct virtual reference base station array by using ranging information of the UAV carried mobile node and the UAV displacement vector, finally, realize wireless positioning by listing virtual location equations and using the least square method to solve three-dimensional location coordinates of UAV. In this paper, the proposed method is validated and the accuracy is evaluated by testing EuRoC data set. The experiment results show that the method can realize precise positioning of UAV.

In order to study the failure mechanism of fractured rock mass under different loading and unloading conditions, marble was used as the test material, which contained 45° double pre-existing cracks. The main processes, which initiation, propagation, coalescence of the cracks, were recorded by a high speed camera. To analyze the crack modes, it could be seen that shear stress played a main effect on the failure process of the uniaxial and biaxial loading of specimens. While shear stress played a significant role in the initial stage of unloading, tensile stress was dominated in the final stage of failure under unloading. At the same time, the numerical models under different loads have been established by ANSYS. It was found that the initiation and propagation characteristics of the main cracks in the experiment were basically consistent with the Mises stress distribution characteristics in the numerical simulation. Finally the effective shear stress (τe) was defined by combining with the stress field theory and power function of Mohr-Coulomb failure criterion. The critical zones of the crack initiation were estimated. Compared with the experimental results, it could be proved that the angle between danger zone and pre-existing crack was about 40° and -140°.