Search Results (89)

Amid the ongoing decarbonization of the international shipping industry, methanol has emerged as a promising alternative fuel for marine auxiliary boilers owing to its environmental advantages and engineering feasibility. However, its low viscosity and surface tension make the atomization process highly sensitive to operating conditions, posing challenges to stable and efficient burner operation. Existing studies have predominantly focused on engine applications, whereas systematic investigations into the atomization characteristics and operating-parameter matching of primary-air swirl-cup nozzles for marine auxiliary boilers remain limited. To address this gap, the present study combines experimental measurements and numerical simulations to investigate the effects of fuel flow rate, atomizing-cup rotational speed, and primary-air damper opening on spray characteristics. Spray imaging was employed to characterize the spray cone angle and macroscopic morphology, while PIV and PDA were used to measure the outer-flow-field velocity and droplet-size characteristics, respectively. Numerical simulations of liquid-film formation and breakup were performed using a coupled VOF-DPM framework. The predicted spray angle and outer-flow-field velocity showed good agreement with the experimental measurements, with overall deviations within 3–12%. Increasing the atomizing-cup speed generally promoted droplet refinement, while adjustment of the primary-air supply further influenced the droplet-size distribution. Under high-speed operating conditions, the atomized droplet size was generally maintained below 100 μm, and the SMD in the investigated near-field region was approximately 60–80 μm. Based on the multi-load experimental results, primary-air parameter-matching relationships were established for fuel flow rates ranging from 100 to 500 kg/h, providing guidance for maintaining stable atomization performance over a wide operating-load range. This study provides a quantitative basis for the operating-parameter design and stable operation of primary-air swirl-cup nozzles in marine methanol-fired auxiliary boilers and offers useful guidance for their engineering application. Full article

Vibration damper detection in unmanned aerial vehicle (UAV)-based transmission line inspection presents distinctive task-specific challenges: the targets are not only small and weakly textured, but also characterized by slender structures. Their effective identification therefore depends on the preservation of local contour cues and the appropriate organization of deep contextual responses. To address the limitations of conventional lightweight detectors in structural feature representation, cross-scale semantic consistency, and bounding-box localization, this paper proposes CARE-Net (Cascaded Attention and Refinement Enhanced Network), a compact detection framework for vibration damper detection. CARE-Net adopts an asymmetric design consisting of front-end structural enhancement and back-end contextual refinement. Specifically, the Cascaded Residual Attention Block (CRAB) is deployed in the backbone to strengthen the representation of slender contours and local structural features of vibration damper targets. The Dynamic Context Refinement Network (DCRN) is introduced at the backbone–neck transition to improve the contextual organization of deep features and the quality of cross-scale feature fusion. Meanwhile, an Adaptive Focal Complete IoU Loss (AF-CIoU) is proposed to optimize bounding-box regression for difficult samples without altering the inference architecture. A UAV-based vibration damper dataset covering three condition categories, namely normal, rusted, and dilapidated, is constructed in this study. Experimental results show that CARE-Net achieves an mAP^@0.5 of 0.951 and an mAP^@0.5:0.95 of 0.628 with 2.44 M parameters and 6.2 GFLOPs. Further configuration experiments indicate that, compared with repeatedly introducing attention enhancement into high-level features, stage-specific feature modeling is better suited to the slender small-object detection task investigated in this study. The proposed method provides a solution for intelligent vibration damper inspection of transmission lines that balances detection accuracy, model compactness, and potential for terminal-side application. Full article

In helicopter rotor systems, effective suppression of lead–lag vibration requires dampers with reliable load transfer, appropriate stiffness matching, tunable damping, and efficient energy dissipation. However, conventional lead–lag dampers often suffer from limited stiffness–damping adjustability and sealing-related constraints. Here, we developed a magnetorheological fluid elastomeric (MRFE) damper by integrating magnetorheological fluid with a rubber elastomer. An elastomer system with a target shear modulus of 0.72 MPa was obtained through systematic design of the rubber formulation, rubber–metal bonding, and vulcanization process. Dynamic characterization showed that the dissipated energy increased markedly with amplitude but only slightly with frequency, whereas applied current exerted the strongest influence on the MRFE response. As the current increased from 0 to 1.5 A, the dissipated energy, effective stiffness, and equivalent damping coefficient increased by 1901.5%, 491.0%, and 961.1%, respectively. The zero-current effective stiffness of 0.443 kN/mm closely matched the required baseline stiffness of 0.44 kN/mm. For inverse current prediction, the improved Transformer model with hyperparameters optimized using PSO achieved a 72.04% lower RMSE than the differential evolution-assisted one-dimensional long short-term memory (DE-1DLSTM) model. These results suggest the potential of the MRFE for stiffness-matched support, controllable energy dissipation, and data-driven current prediction in rotor lead–lag vibration mitigation. Full article

Addressing the opportunistic behavior of retailers operating within the unique spaces of transportation hub ecosystems, which exploit strong temporal and spatial constraints and geographic monopolies, this paper constructs a three-party evolutionary game model involving transportation hub authorities, micro-merchant enterprises, and transient consumers. Using China’s high-speed rail hubs as the research context, this study develops a theoretical evolutionary game model with numerical simulations and endogenously embeds the backlash from informal digital public opinion into the regulatory decision-making framework. The study thoroughly deconstructs the mechanisms of behavioral evolution and control pathways within highly constrained micro-spaces. The study reveals that: (1) Static, constant regulation, lacking negative feedback linked to the system’s state, inevitably causes the system to fall into a non-convergent “regulation-speculation” cyclical oscillation; (2) A state-dependent dynamic regulatory mechanism can effectively serve as an adaptive damper to quell strategic oscillations; however, because it fails to eliminate speculative premiums, the system becomes locked in a mediocrity trap characterized by low compliance rates; (3) Endogenous digital public opinion leverage can reconfigure the phase space structure and trigger topological bifurcations in the system, breaking the attractor region of the mediocrity equilibrium and driving the game system to undergo a structural transition, with asymptotic convergence to the pure-strategy ideal point. Furthermore, digital empowerment drives consumers to exhibit an inverted U-shaped transient behavioral trajectory of “forced silence—awakening to rights advocacy—rational self-governance,” thereby scientifically deconstructing the public’s dual silence paradox in the digital age. This study not only provides a mathematical basis for the public sector to achieve a paradigm shift from rigid regulation to flexible adaptive governance and structural safe retreat at the micro level, but also offers strategic insights for intertemporal compliance management by micro-merchants. Full article

The rapid adoption of electric vehicles, together with increased battery mass and altered load distribution, is placing greater demands on ride comfort and suspension adaptability, while controller optimization may still request forces beyond the instantaneous capability of the physical semi-active actuator if experimentally supported force limits are not explicitly enforced. This study proposes a unified experimentally constrained optimization framework for a magnetorheological damper (MRD)-based semi-active suspension system using a two-degree-of-freedom quarter-car model. The damper is characterized at eleven current levels and represented by a branch-dependent lookup model that provides the zero-current baseline and instantaneous feasible force range. Proportional–integral–derivative (PID) and linear quadratic regulator (LQR) controllers are independently tuned using a genetic algorithm (GA) and particle swarm optimization (PSO) under identical vehicle dynamics, objective functions, tuning excitation, and MRD force constraints. Each candidate force demand is projected onto the experimentally derived feasible range throughout optimization. The controllers are tuned on a composite B–C–D profile and subsequently evaluated over nine road–speed scenarios. PID-PSO reduces the RMS sprung-mass acceleration by 15.91% and achieves the best acceleration performance in six cases, whereas LQR-PSO provides more balanced improvements in body motion, suspension travel, tire response, and force feasibility. The proposed framework therefore provides a more physically constrained basis for the comparative design and evaluation of MRD-based semi-active suspension control. Full article

To improve the seismic performance and post-earthquake recoverability of low- and mid-rise steel frames, this study investigates the seismic performance and layout strategy of a self-centering friction damper (SCFD) through experimental and numerical studies. The SCFD combines the superelastic restoring capability of shape memory alloy (SMA) bars with the energy dissipation provided by non-asbestos organic (NAO) friction materials. Monotonic and cyclic tests were conducted to characterize the mechanical behavior of Ni–50.8 at. % Ti SMA bars and the hysteretic performance of the SCFD, based on which a numerical model of the damper was established and validated. An uncontrolled frame and four controlled frames employing diagonal, chevron, improved lower toggle-brace, and improved upper toggle-brace layouts were comparatively investigated to evaluate the effects of brace configuration, installation position, and damper quantity on seismic performance. The proposed damper exhibited an equivalent damping ratio ranging from 24% to 32%. When the SMA strain exceeded 6%, the residual deformation of the damper increased significantly, indicating that excessive SMA deformation should be avoided in practical design. Among the investigated configurations, the improved upper toggle-brace layout, combined with additional dampers installed at the first story, showed the best overall performance. Compared with the uncontrolled multi-story structure, the residual inter-story drift ratio was reduced by 76.7–93.5%, while the maximum acceleration reduction reached 28.9%. However, local acceleration amplification was observed in some cases because of the increased structural stiffness. These findings provide practical guidance for the layout design and engineering application of self-centering friction dampers in low- and mid-rise steel frames. Full article

To elucidate the influence of operational conditions on the seismic responses of offshore wind turbines (OWTs) and the vibration mitigation efficacy of tuned mass dampers (TMDs) under multi-hazard scenarios, time-domain dynamic analyses are performed for OWT systems subjected to combined wind, wave and seismic excitations. Five typical operational conditions are considered, including cut-in operation, rated-power operation, cut-out shutdown, 1-year return-period extreme shutdown, and 50-year return-period extreme shutdown. The nacelle acceleration and tower-top displacement responses of the uncontrolled structure are comparatively characterized, the peak and root-mean-square (RMS) vibration reduction ratios of the TMD for fore-aft vibrations are quantitatively assessed, and the intrinsic mechanism governing the response discrepancies across operational conditions is elucidated. Numerical results demonstrate that seismic excitation dominates the extreme structural responses of the OWT system. Under the rated-power condition, the peak acceleration and displacement under coupled seismic loading reach 6.90 and 2.19 times the corresponding values under wind–wave loads alone, respectively. Substantial discrepancies in structural responses are observed across operational conditions, with aerodynamic damping magnitude and the spectral properties of hub rotational loads identified as the key influencing factors. The TMD exhibits reliable vibration control performance overall: the optimal control efficacy is achieved under the 1-year return-period shutdown condition, with a peak acceleration reduction ratio of 34.8%—by contrast, its mitigation performance degrades significantly under the 50-year return-period extreme-turbulence condition, with the peak acceleration reduction ratio dropping to merely 15.8%. Full article

Slender cantilever precision positioning actuators are highly susceptible to ambient low-frequency micro-vibrations, which severely deteriorate dynamic positioning accuracy and operational stability. To address this challenge, this paper proposes a passive vibration attenuation method utilizing a customized partitioned particle damper. A micro-vibration-adapted discrete element method (DEM) coupled dynamic model is established to quantitatively characterize the underlying multi-mechanism energy dissipation driven by micro-slip friction and weak inelastic collisions. Through systematic numerical parametric analysis and physical experimentation, the optimal damper configuration is identified. Experimental results rigorously demonstrate that the optimized particle damper effectively suppresses broadband micro-vibrations (10–100 Hz), achieving a maximum steady-state vibration damping efficiency of 63.24% and a transient peak acceleration attenuation of 67.5% at the cantilever tip. This work provides a highly compact, energy-free, and robust structural vibration suppression strategy, demonstrating significant potential for application in high-precision actuation systems. Full article

The escalating security risks associated with unauthorized unmanned aerial vehicles (UAVs) in advancing smart cities necessitate the development of robust active countermeasures. This work presents a novel approach centered on a UAV-borne flexible net system and provides a rigorous investigation into its complex nonlinear dynamics. This study establishes a lumped-mass, semi-spring–damper dynamic model of the flexible capture net, characterizing its key dynamic properties, including deployment performance, aerodynamic attitude, and the high-impact phenomena of collision and entanglement with the target UAV. To verify the reliability of the proposed method, numerical simulations are combined with field tests for systematic validation. Comparative analysis reveals excellent quantitative agreement, with over 80% conformity in the net’s spatial configuration between simulated and experimental results. This paper illuminates the fundamental principles governing energy dissipation and transient tension dynamics pre- and post-capture. This study provides preliminary evidence for the feasibility of the proposed method and identifies key directions for future investigation. The findings offer guidance for the design and optimization of future systems intended to neutralize low, slow, and small (LSS) aerial threats. Full article

This study presents an experimental characterization and numerical assessment of Cu–Al–Be (CAB) shape memory alloys (SMAs) for potential applications in U-shaped flexural plate (UFP) seismic dampers. Six alloy compositions were evaluated through monotonic tensile tests, ASTM F2516 superelastic protocols, and increasing-amplitude cyclic loading to identify the material exhibiting stable superelastic behavior at room temperature. Among the tested materials, alloy CAB4.76-A showed the most favorable response, with high transformation stress, stable pseudoelastic behavior, and strain recovery exceeding 95% for strains up to 2.5%. A phenomenological finite element model based on the Auricchio constitutive formulation was calibrated using experimental data within the validated strain range (ε ≤ 0.025), showing good agreement in stiffness and stress prediction. The calibrated model was subsequently applied to simulate the response of a UFP device under orthogonal cyclic loading. The results indicate a strong dependence on loading orientation due to coupled bending–torsion effects, with the 90° direction exhibiting significantly higher strength and energy dissipation capacity. Comparison with analytical formulations originally developed for steel UFPs showed that these expressions provide approximate estimates when applied to SMA-based devices. The results suggest that Cu–Al–Be alloys are a promising alternative for UFP applications, while highlighting the importance of loading orientation and the need for future experimental validation at a device scale. Full article

The present work investigates fluid–structure instabilities and flow-induced oscillations of a pitching NACA0012 airfoil through numerical simulations. The flow is modeled using the compressible Navier–Stokes equations in a non-inertial rotating reference frame, while the structural dynamics are represented by a torsional spring–mass–damper system. The analysis focuses on the effects of reduced velocity, equilibrium angle of attack, and elastic axis position on the aeroelastic behavior at low Reynolds number ($Re=1000$). Particular attention is devoted to characterizing the transition from vortex-shedding-dominated oscillations to fully developed limit-cycle oscillations and to assessing its sensitivity to aerodynamic and structural parameters. The results show a transition from steady flow to vortex shedding and, at higher reduced velocities, to limit-cycle oscillations. Increasing the equilibrium angle of attack promotes an earlier onset of instability and stronger aerodynamic forcing, while moving the elastic axis downstream has a similar destabilizing effect due to the larger aerodynamic moment arm (up to approximately 20% reduction of the critical reduced velocity). The nature of the transition is found to depend strongly on the equilibrium angle of attack, with distinct behaviors observed at low and high incidence. Frequency analysis highlights the progressive coupling between fluid and structural dynamics: vortex shedding dominates in the weakly coupled regime, whereas the structural frequency governs the response in the limit-cycle regime. The study provides a consistent description of the mechanisms driving flow-induced oscillations and of the parameters controlling aeroelastic stability. Full article

From the perspective of human vibration perception, reducing vibration stimuli transmitted to occupants is essential for improving ride comfort and reducing fatigue. Intelligent dampers, as key actuators in semi-active suspension systems, provide adjustable damping capabilities for vibration control. This article combines them with biomimetic control principles to study the vibration control of semi-active suspension. The effects of damper forward and inverse models, damping force ranges, and time delays on suspension performance were analyzed. The results show that a function prediction-based damper model, a damping force range below 0.2 times and above 1.4 times the passive curve, and a 10 ms delay could balance vibration reduction and economy. Particle swarm optimization is used to optimize LQR control parameters for different road grades and typical speeds. Inspired by the adaptive behavior of chameleons, graded weights are assigned according to road characteristics, with greater emphasis on comfort on Grade A and B roads and driving stability on Grade C and D roads. The results show that proper matching of damper models and parameter constraints can fully exploit the adjustable damping capability of smart dampers. These findings provide a theoretical basis for designing and optimizing semi-active suspension control strategies. Full article

To address the insufficient damping and instability tendency of metal coil spring isolators subjected to intense impact loading, a multi-stage vibration isolation configuration integrating polyurethane, springs, and eddy current dampers is proposed. Dynamic models for both single-stage and multi-stage isolation systems are formulated, and a corresponding simulation model is developed in MATLAB R2023b/Simulink to investigate the peak suppression and attenuation characteristics of the multi-stage isolation under impact. To characterize the nonlinear finite deformation and time-dependent response of polyurethane, a hyperelastic-viscoelastic constitutive model is established by coupling the Ogden hyperelastic model with a generalized Maxwell viscoelastic model, with model parameters identified through quasi-static compression and stress relaxation tests. Drop impact experiments are performed to compare the displacement response, top- and bottom-plate peak accelerations, and vibration isolation rate between a polyurethane-spring-eddy-current multi-stage isolator and a spring-spring-eddy-current multi-stage isolator. The results demonstrate that the multi-stage structure enables staged dissipation of the impact energy, substantially reducing both the peak acceleration and the displacement stroke of the isolated mass. Under all drop test conditions, the polyurethane-based multi-stage isolator yields lower top-plate output peak acceleration and higher isolation rate than its all-spring counterpart, confirming its superior isolation performance. Envelope fitting of the simulation-based output acceleration with experimental inputs reveals that the all-spring multi-stage isolator exhibits a higher attenuation rate and equivalent damping ratio, whereas the polyurethane-based isolator achieves more effective suppression of the output peak level under severe impact conditions. Full article

Accurate modeling of smart composite dampers is crucial for simulation and model-based control. This study focuses on the constitutive modeling of a novel damper that synergistically combines an Entangled Metallic Wire Mesh (EMWM) with a magnetorheological (MR) fluid. Unlike traditional MR dampers, the interaction between the field-responsive MR fluid and the rate-sensitive, deformable EMWM matrix introduces strong coupled current–frequency dependence. To capture this essential characteristic, a control-oriented, bivariate (current–frequency) hysteresis model is formulated, wherein all parameters are explicit, continuous functions of both the control current (I) and excitation frequency (f). A systematic two-step identification method is employed to derive these functions from dynamic tests. A key finding is that the identified damping exponent (α) consistently exceeds unity across the tested operational range. This quantitatively indicates a transition from viscous-dominated to inertial-flow-dominated dissipation within the EMWM matrix, a distinctive mechanism attributed to non-Darcian flow in its porous structure. The fully parameterized model demonstrates high fidelity (R² > 0.99) within the characterized low-frequency, small-amplitude regime and shows reliable predictive capability for interpolated conditions. The presented model serves as a ready-to-use constitutive tool for the simulation and design of low-frequency vibration isolation systems utilizing EMWM-MR composites, and the revealed inertial flow mechanism provides fundamental insight for the development of next-generation adaptive dampers. Full article

Since the inception of utility-scale wind turbines, there has been a continual increase in the size of the devices used. One drawback of turbine size increase is that the weight of the rotor blades has grown dramatically. Technological advancements have allowed for the creation of light blades to overcome this issue. These lighter rotors are also less stiff than their predecessors and prone to experiencing aeroelastic vibrations that can lead to fatigue damage. Aerodynamic damping occurring during blade vibration has the potential to mitigate those oscillations; thus, understanding its underlying physics provides an extremely useful tool for future blade design. In a series of previous publications, the authors presented a novel reduced-order characterization technique for the oscillatory response of wind turbines, which allows for the analysis of rotor vibrations when excited by wind gust pulses. In this paper, the authors will apply the same gust pulse technique to analyze the physics of blade’s aerodynamic damping, identifying two physical mechanisms. The first acts either as a damper, or as an energy feeder, depending on operational conditions. The second operates in a purely dissipative manner. Results of numerical experiments on several operational scenarios illustrating these behavioral responses will be presented and discussed. Full article