Search Results (1,855)

The application of tuned mass dampers (TMDs) to high-rise buildings or slender bridges can significantly decrease the dynamical vibrations due to external excitation, such as wind or earthquake loads. However, the individual properties of a TMD such as mass, stiffness and damping have to be designed carefully with respect to the dynamical properties of the investigated structure. In real-world structures, the influence of uncertain system properties might be critical for the performance of a TMD and thus the whole structure. Therefore, the design under uncertainty of such systems is an important issue, which is addressed in the current paper. For our investigations, we consider linear single-degree-of-freedom (SDOF) systems, where analytical formulas for the deterministic design already exist, and linear multi-degree-of-freedom (MDOF) systems, where a time integration and numerical optimization algorithms are usually applied to obtain the optimal TMD parameters. If the numerical optimization should be coupled with a sampling-based uncertainty quantification method, such as Monte Carlo sampling, the design procedure would require the evaluation of a coupled double-loop approach, which is very demanding from the computation point of view. Therefore, we focus the following paper on an efficient analytical uncertainty quantification approach, which estimates the mean and scatter from a Taylor series expansion. Additionally, we introduce an efficient mode decomposition approach for MDOF systems with multiple TMDs, which estimates the maximum displacements using a modal analysis instead of a demanding time integration. Different optimal design problems are formulated as single- or multi-objective optimization tasks, where the statistical properties of the maximum displacements are considered as safety margins in the optimization goal functions. The application of numerical optimization algorithms is straightforward and not limited to specific algorithms. As numerical examples, we investigate an SDOF system with single TMD and a multi-story frame with multiple TMDs. The presented procedure might be interesting for the design process of structures, where the dynamical vibrations reach a critical threshold. Full article

This study employs molecular orbital (MO) analysis, density of states (DOS) analysis, and advanced techniques such as charge density difference (CDD), transition density matrix (TDM), transition electric dipole moment density (TEDM), and transition magnetic dipole moment density (TMDM) to systematically investigate the electronic structure characteristics of Fc-[8]CPP and Fc-[11]CPP. Using density functional theory (DFT) and time-dependent DFT (TD-DFT), the π-electron delocalization properties and optical behaviors of these molecules were analyzed. Furthermore, their responses to external electromagnetic fields were explored through electronic circular dichroism (ECD) and Raman spectroscopy, comparing chiral optical responses and electron–vibration coupling effects to elucidate their photophysical properties. The results reveal that the HOMO-LUMO energy gaps of Fc-[8]CPP and Fc-[11]CPP are 5.81 eV and 5.95 eV, respectively, with a slight increase as ring size grows; Fc-[8]CPP exhibits a stronger chiral response, while Fc-[11]CPP shows reduced chirality due to enhanced symmetry. Finally, TD-DFT calculations demonstrate that their optical absorption is dominated by localized excitations with partial charge transfer contributions. These findings provide a theoretical foundation for designing conjugated macrocyclic materials with superior optoelectronic performance. Full article

Loess has poor engineering properties, including wet subsidence and dynamic fragility, and the dynamic stability of the loess subgrades can be improved by compacted modified loess mixing industrial wastes such as fly ash and lignin. However, the performance of the modified loess under complex environmental conditions, including dry and wet cycles, as well as freeze-thaw cycles, remains unclear. In this study, the dynamic and structural characteristics of modified loess mixing fly ash and lignin under the coupling effect of dry-wet/freeze-thaw cycles were investigated through laboratory tests, including dry-wet–freeze/thaw cycle tests, dynamic triaxial tests, and scanning electron microscope tests. The cumulative plastic deformation characteristics of the improved loess under different dry-wet cycles and freeze-thaw cycles were analyzed. Combined with the scanning electron microscope test results, the attenuation mechanism of the strength of the improved loess under dry-wet/freeze-thaw coupling was analyzed. The results show that the dry-wet/freeze-thaw cycles have a significant effect on the dynamic deformation of the improved loess. With the increase in dry-wet/freeze-thaw cycles, the cumulative plastic deformation of the improved loess increases logarithmically with the rise in vibration times. With the increase in the number of dry-wet/freeze-thaw cycles, the improved loess becomes loose. The micro-cracks formed in the modified loess due to the connection and directional arrangement of the pores, and become wider and wider with the increase in dry-wet/freeze-thaw cycles. The apparent porosity, average porous diameter, and pore fractal dimension of the improved loess increase, while the probability entropy decreases. Compared with freeze-thaw cycles, dry-wet cycles had a greater effect on the microstructure of the improved loess, which made the deterioration of the dynamic stability of the improved loess more obvious. Full article

In this study, a new nonlinear dynamic model was established for functionally graded material (FGM) beams with layered/porous fractal microstructures, aiming to reveal the cross-scale propagation mechanism of flexural waves under large deflection conditions. The characteristics of layered/porous microstructures were equivalently mapped to the fractal dimension index. In the framework of the fractal derivative, a fractal nonlinear wave governing equation integrating geometric nonlinear effects and microstructure characteristics was derived, and the coupling effect of finite deformation and fractal characteristics was clarified. Four groups of deflection gradient traveling wave analytical solutions were obtained by solving the equation through the extended minimal (G′/G) expansion method. Compared with the traditional (G′/G) expansion method, the new method, which is concise and expands the solution space, generates additional csch² soliton solutions and csc² singular-wave solutions. Numerical simulations showed that the spatiotemporal fractal dimension can dynamically modulate the amplitude attenuation, waveform steepness, and phase rotation characteristics of kink solitary waves in beams. At the same time, it was found that the decrease in the spatial fractal dimension will make the deflection curve of the beam more gentle, revealing that the fractal characteristics of the microstructure have an active control effect on the geometric nonlinearity. This model provides theoretical support for the prediction and regulation of the wave behavior of fractal microstructure FGM components, and has application potential in acoustic metamaterial design and engineering vibration control. Full article

To address the collaborative demand for low-frequency vibration control and energy recovery, this paper proposes a dual-functional structure integrating low-frequency vibration isolation and broadband energy harvesting. The structure consists of two core components: one is a quasi-zero stiffness (QZS) vibration isolation module composed of a linkage-horizontal spring (negative stiffness) and a vertical spring; the other is an energy-harvesting component with an array of parameter-differentiated piezoelectric cantilever beams. Aiming at the conflict between the structural dynamic stiffness approaching zero and broadening the effective working range, this paper establishes a dual-objective optimization function based on the Pareto principle on the basis of static analysis and uses the grid search method combined with actual working conditions to determine the optimal parameter combination. By establishing a multi-degree-of-freedom electromechanical coupling model, the harmonic balance method is used to derive analytical solutions, which are then verified by numerical simulations. The influence laws of external excitations and system parameters on vibration isolation and energy-harvesting performance are quantitatively analyzed. The results show that the optimized structure has an initial vibration isolation frequency below 2 Hz, with a vibration isolation rate exceeding 60% in the 3 to 5 Hz ultra-low frequency range and a minimum transmissibility of the order of 10⁻² (vibration isolation rate > 98%). The parameter-differentiated piezoelectric array effectively broadens the energy-harvesting frequency band, which coincides with the vibration isolation range. Synergistic optimization of both performances can be achieved by adjusting system damping, parameters of piezoelectric vibrators, and load resistance. This study provides a theoretical reference for the integrated design of low-frequency vibration control and energy recovery, and its engineering implementation requires further experimental verification. Full article

This article focuses on the study of elastic beams with fractional-order inertial damping structures at both ends, with the aim of exploring their dynamic characteristics, damping effects, and parameter selection rules in depth, providing theoretical and practical support for engineering applications. Firstly, using the generalized Hamilton principle, two dynamic models of an elastic beam are established for two different boundary conditions. Next, using the complex modal analysis method, a design method for the critical damping of the first and second modes of an elastic beam was proposed for the first time, and the accuracy of the critical damping calculation formula was verified. Simulation analysis shows that the higher the derivative order and inertance, the lower the main resonance frequency, and the greater the critical damping. Then, using the main resonance amplitude and frequency attenuation rate (R_A and R_Ω) as indicators, an analysis was conducted on the impact of damper parameters on vibration suppression effects. The results indicate that the introduction of fractional-order inerter can reduce the main resonance amplitude and frequency, and critical damping plays a significant role in the vibration suppression process. Based on the optimal average R_A range (95–98%) and higher cost-effectiveness, selecting a damping value of 0.05~0.6 times the critical damping ensures better overall vibration suppression performance, providing an important reference for the vibration suppression design of elastic beams in practical engineering. Full article

The combined reducer consisting of spiral bevel gear pair and planetary gear train is widely used in the aerospace field, and its dynamic performance seriously affects the fatigue life of the gears. However, there has been little research on the dynamic performance analysis of the combined gear reducer. In this paper, the coupling multibody dynamic models of spiral bevel gear pair and planetary gear train with and without bearing modules are established based on ADAMS software, respectively, and the influence of bearings on the dynamic performance of the coupling system is studied, and the analysis results are verified by experiments. The results demonstrate that the flexible bearings in the coupled system will induce a pronounced shaft swing that amplifies the combined reducer vibration. Because of the displacement of the sun gear, the meshing force of the planetary gear train fluctuates periodically at low frequency, which increases the maximum dynamic meshing force and is not conducive to its fatigue life. This low-frequency fluctuation can be greatly reduced by introducing additional bearings. In addition, dynamic testing confirms vibration spectral components include obvious shaft rotation frequencies except gear meshing frequencies, verifying the modeling accuracy and analytical methodology. Full article

With the increasing requirements for speed and travel distance in tracked vehicles on various terrains and the increasing mass ratio of powertrains, the vibration problem of high-power powertrains becomes a critical challenge. In this paper, in order to reflect on the vibration transmission relationship between the powertrain and the complex carrier, the magnetorheological damping system of a powertrain is studied in a whole vehicle model. The transfer matrix and equations of each component, including the magnetorheological mount, are derived by the Rui Method. Then, the electromechanical coupling multibody dynamic model of the vehicle–powertrain magnetorheological damping system is established. Consequently, the fast solution of vehicle–powertrain vibration characteristics under various road excitations is realized. The dynamic and static coupling characteristics of the powertrain system and the factors affecting its performance are analyzed in a moving vehicle. The simulation results indicate that the vibration reduction performance is the worst in the X-direction, whereas the vibration reduction performance is the best in the Y-direction. Under the E-class road condition at 10 m/s, the RMS acceleration reduction in the powertrain is 41.63% in the Y-direction relative to the chassis. Both the resonant frequency of the powertrain and chassis are 86.93 Hz in the Y-direction. Finally, the accuracy of the results is verified by simulation and driving experiments. The research results can provide theoretical guidance for the design and optimization of the powertrain mount of a tracked vehicle. Moreover, it provides a new technical means of studying the vibration characteristics of a complex multibody system. The simulation results demonstrate notable directional variations in the vibration attenuation performance of the powertrain damping system. Specifically, the X-direction shows the poorest vibration attenuation, whereas the Y-direction exhibits the best damping characteristics. Full article

As a core component of both the ship propulsion system and mission-critical equipment, shipboard motors are undergoing a technological transition from traditional fault diagnosis to multi-physical-field collaborative modeling and integrated intelligent maintenance systems. This paper provides a systematic review of recent advances in shipboard motor fault monitoring, with a focus on key technical challenges under complex service environments, and offers several innovative insights and analyses in the following aspects. First, regarding the fault evolution under electromagnetic–thermal–mechanical coupling, this study summarizes the typical fault mechanisms, such as bearing electrical erosion, rotor eccentricity, permanent magnet demagnetization, and insulation aging, and analyzes their modeling approaches and multi-physics coupling evolution paths. Second, in response to the problem of multi-source signal fusion, the applicability and limitations of feature extraction methods—including current analysis, vibration demodulation, infrared thermography, and Dempster–Shafer (D-S) evidence theory—are evaluated, providing a basis for designing subsequent signal fusion strategies. With respect to intelligent diagnostic models, this paper compares model-driven and data-driven approaches in terms of their suitability for different scenarios, highlighting their complementarity and integration potential in the complex operating conditions of shipboard motors. Finally, considering practical deployment needs, the key aspects of monitoring platform implementation under shipborne edge computing environments are discussed. The study also identifies current research gaps and proposes future directions, such as digital twin-driven intelligent maintenance, fleet-level PHM collaborative management, and standardized health data transmission. In summary, this paper offers a comprehensive analysis in the areas of fault mechanism modeling, feature extraction method evaluation, and system deployment frameworks, aiming to provide a theoretical reference and engineering insights for the advancement of shipboard motor health management technologies. Full article

Vehicle suspension significantly influences the safety of cargo transportation. This study presents a 14-degree-of-freedom vehicle–cargo coupling model that explicitly incorporates the frequency-dependent stiffness of air springs. Systematic parametric investigations of air spring orifice resistance, loading mass, and cargo stiffness reveal the following: (a) Compared with leaf spring suspension, air suspension vehicles attenuated the first peak of acceleration power spectral density by over 50%, while slightly amplifying the second peak; (b) When replacing leaf spring suspension with air suspension, the upper-layer cargo exhibited significantly larger vibration reductions (14% vertical, 28% pitch) than the lower-layer cargo under identical cargo parameters. The roll angle should be controlled to prevent the cargo overturning when equipping air suspensions; (c) Under light loading conditions, the vertical vibration response in upper-layer cargo is amplified. This amplification can be effectively suppressed through two complementary approaches, i.e., employing low-stiffness cushion materials and reducing orifice resistance through tunable orifices, which collectively attenuate characteristic peaks in the frequency-domain response and comprehensively mitigate the vertical vibration of cargo. These findings provide guidance for designing transportation schemes for cargo in air suspension vehicles to enhance cargo safety. Full article

High-pier partially cable-stayed bridges, with their significant pier heights and relatively low structural stiffness and stability, experience pronounced vehicle–bridge coupling effects during vehicle transit, influencing their dynamic response and safety. This study developed a co-simulation analysis program using easy language and ANSYS to investigate the dynamic behavior of a prestressed concrete five-tower partially cable-stayed bridge under vehicle–bridge interaction, considering factors such as vehicle speed, bridge deck grade, and cable force. The research findings indicate that a reduction in bridge deck grade leads to increases in peak dynamic responses and impact factors, with the dynamic amplification factor showing a deteriorating trend across all cross-sections. Structural responses fluctuate with vehicle speed and exhibit sensitivity to speed variations, with the maximum response observed at a speed of 80 km/h. Adjusting cable forces can reduce the impact factor: a 5% change in cable tension causes the mid-span impact factor to drop sharply from 0.38 to 0.04, a substantial decrease of 89.5%. The structural system can exert an impact on the impact factor by as much as several times: while the dynamic displacement and bending moment of the fixed system are smaller than those of the continuous beam system, its impact factor is as high as 4.22 times that of the continuous beam system. Additionally, dynamic responses are closely related to the position of the fixed bearing, with responses near the fixed bearing being reduced. Notably, the maximum impact factors of critical sections all exceed the 0.05 limit specified in the code for this type of bridge, with values of 0.54 at the mid-span, 0.91 at the pier top, and 0.43 at the tower top anchor zone. This indicates that the provisions regarding dynamic amplification factors in the current code are inappropriate for such bridges. The difference in impact factors between bridge components can reach 2.12 times, this indicates that specific impact factors should be assigned to individual components to achieve an optimal balance between safety and economic performance. Full article

A time-domain semi-empirical simulation model based on the wake oscillator approach is developed to investigate the coupled in-line (IL) and cross-flow (CF) vortex-induced vibration (VIV) of a flexible riser in uniform oscillatory flow. A novel nondimensionalization method is introduced by utilizing the dimensionless parameter $StKC$, which effectively replicates the fundamental lift frequency caused by the complex vortex motion around the riser. The structural responses of the riser are described using the Euler–Bernoulli beam theory, and the van der Pol equations are used to calculate the fluid forces acting on the riser, which can replicate the nonlinear vortex dynamics. The coupled equations are discretized in both time and space with a finite difference method (FDM), enabling iterative computations of the VIV responses of the riser. A total of six cases are examined with four different Keulegan–Carpenter ($KC$) numbers (i.e., $KC=31$, 56, 121, and 178) to investigate the VIV characteristics of small-scale and large-scale risers in uniform oscillatory flow. Key features such as intermittent VIV, amplitude modulation, and hysteresis, as well as the VIV development process, are analyzed in detail. The simulation results show good agreement with the experimental data, indicating that the proposed numerical model is able to reliably reproduce the riser VIV in uniform oscillatory flow. Overall, the VIV characteristics of the large-scale riser resemble those of the small-scale riser but exhibit higher vibration modes, stronger traveling wave features, and more complex energy transfer mechanisms. Full article

Inspired by naturally occurring bis-isochromans such as penicisteckins, we envisaged the first synthesis of biaryl-type bis-1-arylisochromans containing a stereogenic ortho-trisubstituted biaryl axis. We achieved the stereoselective synthesis of 5,5′-linked heterodimeric bis-isochromans containing both central and axial chirality elements by performing diastereoselective Suzuki–Miyaura biaryl coupling reactions on two optically active 1-arylpropan-2-ol derivatives, followed by two oxa-Pictet–Spengler cyclizations with aryl aldehydes or methoxymethyl chloride. We studied the diastereoselectivity of the cyclization step, separated the stereoisomeric products with chiral preparative HPLC and determined the absolute configuration through a combination of vibrational circular dichroism (VCD), NMR and single-crystal X-ray diffraction analysis. We demonstrated that different aryl groups could be introduced into the two isochroman subunits, since the dimethoxyaryl subunit reacted faster, enabling the two oxa-Pictet–Spengler cyclizations to be performed separately with different aryl aldehydes. We also explored the acid-catalyzed isomerization and oxidation to axially chiral ortho-quinones in order to produce stereoisomeric and oxidized analogs, respectively. We identified the antibacterial activity of our target bis-isochromans against Bacillus subtilis and Enterococcus faecalis with minimum inhibitory concentrations down to 4.0 and 0.5 μg/mL, respectively, which depend on the stereochemistry and substitution pattern of the bis-isochroman skeleton. Full article

The influence mechanism and identification of mass defects in hemispherical resonators are currently highly challenging and significant research directions. This paper first establishes a shell–rod coupling vibration model under the influence of mass error, and, based on this model, constructs a characterization system for the vibration characteristics (quality factor and frequency split) of the resonator. The influence of the first four harmonic components of the mass defect on the quality factor and frequency split of the resonator was systematically studied, and the analytical expression of its quantitative representation was derived, which reveals the internal physical relationship between the mass defect and the vibration characteristics. Subsequently, the theoretical model was verified by using finite element simulation. Finally, an efficient and high-precision method for identifying the first four harmonics of hemispherical resonator mass defects was proposed, and an experimental device was set up to successfully achieve the synchronous identification of the first four harmonic components. An innovative beam-split optical system that streamlines displacement metrology reduced test complexity by >60%. Full article

This study investigates the performance of Distributed Acoustic Sensing (DAS) for detecting gas pipeline leaks under controlled experimental conditions, using multiple fiber cable types deployed both internally and externally. A 21 m steel pipeline with a 1 m test section was configured to simulate leakage scenarios with varying leak sizes (¼”, ½”, ¾”, and 1”), orientations (top, side, bottom), and flow velocities (2–18 m/s). Experiments were conducted under two installation conditions: a supported pipeline mounted on tripods, and a buried pipeline laid on the ground and covered with sand. Four fiber deployment methods were tested: three internal cables of varying geometries and one externally mounted straight cable. DAS data were analyzed using both time-domain vibration intensity and frequency-domain spectral methods. The results demonstrate that leak detectability is influenced by multiple interacting factors, including flow rate, leak size and orientation, pipeline installation method, and fiber cable type and deployment approach. Internally deployed black and flat cables exhibited higher sensitivity to leak-induced vibrations, particularly at higher flow velocities, larger leak sizes, and for bottom-positioned leaks. The thick internal cable showed limited response due to its wireline-like construction. In contrast, the external straight cable responded selectively, with performance dependent on mechanical coupling. Overall, leakage detectability was reduced in the buried configuration due to damping effects. The novelty of this work lies in the successful detection of gas leaks using internally deployed fiber optic cables, which has not been demonstrated in previous studies. This deployment approach is practical for field applications, particularly for pipelines that cannot be inspected using conventional methods, such as unpiggable pipelines. Full article