Dynamic Coupling Effects Research Articles

Gait coordination control of bipedal modular reconfigurable robot based on adaptive neural network

This paper proposed an adaptive neural network (NN) control method to track the desired trajectory of a bipedal modular reconfigurable robot (MRR), which can solve the gait coordination problem of bipedal MRR. The leg dynamic model and the body dynamic model of bipedal MRR are established based on the Newton–Euler iterative method, and the global dynamic model is subsequently established. Aiming at the gait coordination problem between double support phase (DSP) and single support phase (SSP), the desired trajectory is generated based on the zero-moment point (ZMP) method. The adaptive NN controller is designed to track the generated desired trajectory, which also compensates interconnected dynamic coupling (IDC) effects of the bipedal MRR. The stability of bipedal MRR system is proved by Lyapunov theory. In the end, the effectiveness of the control method is verified by comparative simulation. The simulation results show that the proposed adaptive NN method reduces the position tracking error by [Formula: see text] and the control torque by [Formula: see text] compared with the existing control methods.

Numerička analiza titrajnog odziva dalekovoda velikog raspona prijenosnih vodova izazvanog vjetrom

Based on the engineering background related to ±800 kV ultra-high voltage (UHV) transmission lines spanning the Yellow River, finite element models were developed for single-tower and transmission tower-line systems, with their wind-induced responses under wind loads were simulated and analysed. In addition, the coupling effect in a large-span transmission tower line system was investigated. The results showed that the natural vibration frequency of the tower-line system was slightly lower than that of a single tower and that the torsional natural frequency was the most significantly reduced. The transmission tower-line system has a maximum displacement of 1.92 times that of a single tower when the wind angle is 0°. The maximum axial force and stress in the tower-line system are 1.6 times and 1.37 times higher than those in a single tower. The interaction between the tower and wires significantly affects the wind-induced response of the tower body. Hence, considering the dynamic coupling effect of the tower-line transmission system is important when designing a tower.

Characterization of dynamic coupling induced shifts of frequencies in vehicle-scanning method

A comprehensive strategy combining theory and experiment is proposed to characterize the dynamic coupling induced shifts of vehicle and bridge frequencies through both experimental investigation and numerical validation, in which the effect of vehicle-bridge interaction is theoretically incorporated in the vehicle-scanning method based on the experimental model. It is known that the measurement of bridge frequencies plays an important role in structural health monitoring as the shift of frequency can be served as an indicator of possible damage occurring in a bridge. Nevertheless, the attention has been mainly drawn on the accuracy improvement in developing the vehicle-scanning method so far, with limited discussion of dynamic coupling effect on the frequency shifts. As such, a combined theoretical–experimental approach is presented to show that the influence of vehicle-bridge interaction results in the coupled frequencies of a vehicle-beam system using the vehicle-scanning method, and adopting a heavy lumped test vehicle can lead to the underestimated bridge frequency and overestimated vehicle frequency. As a new finding, the effect of rolling frequency is experimentally observed in the vehicle spectrum for the first time.

Path planning of 6-DOF free-floating space robotic manipulators using reinforcement learning

This paper presents a study on path planning for 6-DOF free-floating space robotic manipulators using Deep Deterministic Policy Gradient-based Reinforcement Learning. The focus is the development of a novel reward function tailored to address critical requirements for efficient and effective manipulation in space. These requirements include accurate pose alignment between the end-effector and the target, collision avoidance with both the target and other links of the manipulator, smoothing of joint velocities, adaptability to strong dynamic coupling between the manipulator and its base spacecraft due to high manipulator-spacecraft mass ratio, and resilience to noise in the state observations. Uniquely, the proposed reward function employs quaternions for orientation control to reduce pose misalignments and dynamic singularities, as opposed to traditional Euler angles. Our findings demonstrate that the Reinforcement Learning algorithm, when guided by this new reward function that integrates these enhancements and constraints, not only achieves the desired path planning objectives more efficiently but also exhibits faster convergence. Furthermore, the Reinforcement Learning successfully manages significant dynamic coupling effects caused by a high mass ratio between the robotic manipulator and the base spacecraft. Even under the challenge of noisy state observations, the trained agent successfully completes the path planning task, proving the Reinforcement Learning's applicability to real-space mission designs where the noise in observation is inevitable. The study highlights the critical role of reward function design in the Reinforcement Learning training process and its consequential impact on the solution quality, providing a solid foundation for future advancements in free-floating space robotic missions.

Train-track-circular tunnel spatially coupled dynamics model and coupling effects of dynamic track-tunnel interactions

Train-track-circular tunnel spatially coupled dynamics model and coupling effects of dynamic track-tunnel interactions

Investigation of dynamic coupling effect on bridge frequency measurement

Investigation of dynamic coupling effect on bridge frequency measurement

Dynamic coupling effects of injection on spray and mixture formation in an asymmetrically vibrating combustion engine

Enhanced methods of energy conversion present a viable solution for addressing energy load challenges. This study introduces a vibrating combustion engine designed to enhance energy conversion efficiency by harnessing flexible dynamics and variable asymmetric motion. However, the consideration of its unique dynamic effects has emerged as a pivotal challenge in fuel-air mixing and combustion research. This study introduces a fuel spray and mixing simulation method that facilitates the reciprocal exchange of coupling parameters between the combustion and dynamics models. It iterates the simulation outcomes of motion and combustion to predict mixture formation. Subsequently, the method is employed to explore the impact of injection position on fuel spray and mixture formation. Results show that there is an optimum injection position for the operation frequency, and retarding or advancing leads to slow compression and weak gas motion for fuel spray and mixing, although retarded injection provides high in-cylinder gas pressure and temperature. The early injection generally causes long penetration, small droplet diameter, slight impingement, and fast evaporation, unless it is too early. The results further indicate that when IAP = 6 mm, a more uniform mixture can be attained at the beginning of combustion, leading to a thermal efficiency of up to 42.9% for the engine.

Dynamics of bridges during proof load tests and determination of mass-normalized mode shapes from OMA

Modal shapes derived from Operational Modal Analysis (OMA) lack normalization with respect to masses, hindering direct estimation of effective mass or modal participation factors. The mass-change method is suitable to solve this issue since it proposes an experimental derivation of scaling factors for modes based on OMA results in different load conditions. However, in the case of bridges, the method application is challenging, as significant static masses are required on the deck for OMA in loaded conditions. To address this challenge, trucks can be used as added masses during standard static proof load tests for bridges, making the mass-change method feasible. However, the presence of trucks introduces dynamic coupling effects among bridge and vehicles, potentially complicating the dynamic identification. This paper proposes a methodology to exploit data obtained from OMA on bridges loaded with stationed trucks within the framework of the mass-change method in order to get the modal scaling factors for the mass normalisation of mode shapes and taking into account possible effects of the dynamic coupling between the two systems. To this purpose, the bridge dynamics with added stationed trucks is studied by introducing a finite element model to address the bridge-vehicles dynamic coupling. Then, a simple but effective 2-degree of freedom system is introduced to develop a parametric investigation in a non-dimensional manner in order to provide a practical tool for engineers to account for the bridge-truck dynamic coupling effects. Finally, numerical applications are proposed to derive some conclusions about the effectiveness of the proposed procedure and its suitability in real applications.

Response and fragility of long-span truss structures in ultra-high voltage substation subjected to near-fault pulse-like and far-field ground motions

This study numerically investigates the seismic responses, bearing capacities, and fragilities of long-span truss structures (LSTSs) in ultra-high voltage substations subjected to near-fault pulse-like (NFP) and far-field (FF) earthquakes. The finite element model established in ABAQUS software considers the tower-line dynamic coupling effect, and it is excited by 20 NFP and 20 FF earthquakes. The seismic responses and bearing capacities are analyzed to generate the design recommendations for LSTS. According to five performance levels, the fragility curves are developed by performing a fragility method based on intensity measure. The peak displacement, acceleration amplification factor, bearing capacity, and fragility results significantly indicate that the seismic risk of LSTS under FF earthquakes is much higher than that under NFP earthquakes. Moreover, there are three typical failure modes (i.e., I – III) of LSTS under strong earthquakes. Mode I is a brittle failure while mode III is a ductile failure. Furthermore, the bearing capacity basically obeys a lognormal distribution, and the distributions subjected to NFP and FF ground motions are very close.

Fragility assessment of sea-crossing cable-stayed bridge subjected to multi-hazard action via TKC and R-vine copula

Seismic fragility analysis methods commonly used for assessing structural components and systems have certain limitations. This paper introduces a new semi-parametric approach for structural component fragility analysis, the TKC method. This method is based on log-transformed kernel density estimation (log-TKDE) and copula functions, which establish the joint probability distribution (JPD) of a structural response value (d) and a disaster-inducing factor strength parameter (α) using log-TKDE and match the marginal cumulative distributions (MCDs) of d and a via bivariate copula functions. A novel method for evaluating structural system fragility is also proposed based on the R-vine copula function. This approach accounts for the intricate correlations among different components, providing a precise estimation of the multidimensional JPD. The reliability and accuracy of the proposed methods are demonstrated through a seismic fragility analysis of a sea-crossing cable-stayed bridge under earthquake load. Furthermore, a multi-hazard fragility analysis of bridge components and systems is conducted considering hazards such as earthquake, wind, and wave loads. A comparison is made with the seismic fragility of bridges subjected to earthquake loads alone. The results show that the median and 95% confidence of the damage probability of structural components calculated by the TKC method and Monte Carlo simulation (MCS) closely match, which validates the proposed method. The TKC method is also more accurate and computationally efficient than the MCS method with the same Bootstrap sample size and confidence level (95%). The proposed structural system fragility assessment method based on the R-vine copula accounts for complex correlations between components and yields more accurate results than the first-order boundary method. Load spectrum characteristics, structural component characteristics, and other factors cause the multi-hazard fragility of bridge components and systems to differ substantially from their seismic fragility. The difference rate of system damage probability can reach 28.82%. In evaluating the anti-disaster performance of sea-crossing bridges, it is necessary to incorporate the marine environmental load and consider the dynamic response coupling effect of the bridge excited by seafloor ground motions with extreme wind and wave loads. This approach can guide the optimization of bridge designs and facilitate multi-hazard fragility analysis in accordance with real damage probabilities.

Nonlinear seismic response of seabed with terrain variation and seawater-seabed coupling

Understanding the seismic characteristics of submarine sites and conducting seismic response analysis for such locations are crucial for the safety of marine engineering. However, due to a shortage of strong motion records, the ground motion of offshore earthquakes has not yet been fully characterized. The actual seabed conditions are highly intricate, necessitating consideration of factors such as the dynamic coupling effect between seawater and seabed, the strong nonlinearity of seafloor soft sediments, and the diverse nature of natural submarine terrain. In this study, the modified Davidenkov dynamic constitutive model is used to simulate the nonlinear behavior of the soil. The Coupled Acoustic-Structure method is utilized to simulate the interaction between seawater and seabed. Three typical and simplified terrains, namely flat terrain, valley terrain, and hilly terrain, are individually modeled. The measured seafloor ground motions with different frequency components are used as bidirectional seismic excitations input from the bedrock. The amplification factor in terms of CAV is introduced to evaluate the amplification of seismic ground motion characteristics at seabed surface with respect to those at the bedrock surface. The acceleration response spectra in both horizontal and vertical directions, as well as the corresponding vertical-to-horizontal response spectral ratios, at the representative points are obtained, respectively. Several key findings are consistent with the features of the observed offshore and onshore earthquake ground motions. Numerical examples are presented to illustrate the different influence rules of terrain condition, overlying water depth, and seismic intensity on the nonlinear seismic response characteristics.

Chain position optimization of a 4UPS−UPU parallel mechanism considering dynamic coupling effects

The strong dynamic coupling effects among kinematic chains are not beneficial to the control of parallel mechanisms. This paper deals with the chain position optimization of a 4UPS−UPU parallel mechanism to reduce dynamic coupling effects among kinematic chains. Using the kinematic model, the Jacobian matrix is derived, and a method is proposed to transform it into a non-dimensional form and being independent of scaling factors. A singularity index is formulated based on the normalized determinant of the modified Jacobian matrix, guiding the optimization of chain positions at the base platform. Subsequently, the dynamic model is derived by using the principle of virtual work and a novel dynamic coupling index is proposed by taking both the inertia and centrifugal terms in the dynamic model into account. The neural network is then employed to enhance the calculation efficiency of the dynamic coupling index. Finally, the chain positions at the moving platform are optimized using Particle Swarm Optimization algorithm. This optimization process significantly reduces the dynamic coupling effects among kinematic chains in the parallel mechanism, thereby conferring advantageous benefits to its overall control.

20CrMnTi surface strengthening based on laser-assisted carburizing grinding

Highly wear-resistant 20CrMnTi surfaces with gradient properties are urgently demanded in manufacturing core components such as shafts and gears. However, balancing productivity, production costs, and energy consumption with existing surface machining and strengthening methods are challenging. Therefore, laser-assisted carburizing grinding is proposed, which combines laser micro-carburizing and grinding tempering to realize the integration of processing and strengthening of the 20CrMnTi surface. The optimal laser power is determined to be 300 W by the dynamic thermal-force coupling effect. A 1300 μm thick metamorphic layer is formed on the surface of 20CrMnTi, and its formation mechanism is analyzed based on the microstructural phase transformation. The surface hardness after laser-assisted carburizing grinding can reach 550 HV. The failure form of the carburized surface is mainly abrasive wear, and the wear loss is reduced to 50% compared to uncarburized surfaces. This study developed an efficient, energy-saving, and controllable integrated method of 20CrMnTi surface machining and strengthening. Meanwhile, the surface strengthening mechanism is explained based on laser micro-carburizing and grinding tempering. The findings provide technical references for manufacturing high-performance 20CrMnTi surfaces and theoretical support for carburized grinding strengthening technology.

Microgravity Decoupling in Torsion Pendulum for Enhanced Micro-Newton Thrust Measurement

To enhance the accuracy of micro-Newton thrust measurements via a torsion pendulum, addressing microgravity coupling effects caused by platform tilt and pendulum mass eccentricity is crucial. This study focuses on analyzing and minimizing these effects by alleviating reference surface tilt and calibrating the center of mass during thrust measurements. The study introduced analysis techniques and compensation measures. It first examined the impact of reference tilt and center of mass eccentricity on the stiffness and compliance of the torsion pendulum by reconstructing its dynamic model. Simscape Multibody was initially employed for numerical analysis to assess the dynamic coupling effects of the tilted pendulum. The results showed the influence of reference tilt on the stiffness and compliance of the torsion pendulum through simulation. An inverted pendulum was developed to amplify the platform’s tilt angle for microgravity drag-free control. Center of mass calibration can identify the gravity coupling caused by the center of mass position. Based on the displacement signal from the capacitive sensor located at the end of the inverted pendulum, which represents the platform’s tilt angle, the pendulum’s vibration at 0.1 mHz was reduced from 5.7 μm/Hz1/2 to 0.28 μm/Hz1/2 by adjusting the voltage of piezoelectric actuator. Finally, a new two-stage torsion pendulum structure was proposed to decouple the tilt coupling buried in both pitch and roll angle. The study utilized theoretical models, numerical analysis, and experimental testing to validate the analysis methods and compensation measures for microgravity coupling effects in torsion pendulums. This led to a reduction in low-frequency noise caused by ground vibrations and thermal strains, ultimately improving the micro-Newton thrust measurement accuracy of the torsion pendulum through the platform’s drag-free control.

Enhanced weathering during glacial periods and its dynamic response to climate and sea-level changes inferred from the northern South China Sea sediments

Secondary weathering of exposed continental shelf sediment at low-latitudes may play a significant role in atmospheric CO2 consumption during glacial periods, which is negative feedback for climate stability. However, more lines of evidences are required to verify the link of glacial weathering with climate. This study presents a comprehensive analysis of geochemical proxies that indicate the silicate weathering intensity in the northern South China Sea (SCS) over orbital timescales since ∼244 ka. Provenance discrimination results, based on the Sr-Nd isotopes values and the patterns of rare earth elements (REEs), suggest that the terrigenous sediment was primarily derived from Taiwan Island. The silicate weathering records revealed two different weathering regimes during glacial periods in the northern SCS, corresponding to changes in monsoon climate and sea-level. During the early period of Marine Isotope Stage 6 (MIS 6), the increase in weathering intensity was in response to climate variability, and the rapid delivery of terrigenous sediment through contour currents allowed for the preservation of climate signals in the continental margin. In contrast, the significant increase in weathering intensity during the glacial periods at late MIS 2 and late MIS 6, was a result of the sedimentary recycling process dominated by sea-level rises. In this case, the marginal sea weathering records did not truly reflect climate changes, due to secondary weathering processes on the exposed continental shelf. Our new geochemical results emphasize the dynamic coupling effects of climate and sea-level changes in transmitting and preserving silicate weathering signals at low-latitude during glacial periods. When using marginal sea sediments for paleoclimatic and paleo-weathering reconstruction, one should be cautious of the complex influence of sediment source-to-sink processes on sediment composition, and a holistic approach may provide more robust constraints.

Linear permanent magnet electrodynamic suspension system: Dynamic characteristics, magnetic-mechanical coupling and filed test

This study investigates the dynamic electromagnetic characteristics and thermo-mechanical coupling effect of the linear permanent magnet electrodynamic suspension system (PMEDS) via high-speed test rig. Besides, a physical prototype weighing 1.5 tons along with a 50-m linear copper guideway is developed and tested. Firstly, the topology structure along with fundamental operation model is introduced, followed by establishing the analytical model. Subsequently, a multi-functional test rig is utilized to experimentally determine its speed characteristics, lateral stability, and vertical vibration, while also validating the simulation and analytical models. Additionally, thermo-mechanical coupling analysis is conducted through co-simulation, experimentation and calculation to determine the dependence of temperature on the levitation and drag forces. Finally, a prototype vehicle integrated with auxiliary components, is fabricated and tested on a copper guideway. The vehicle is suspended freely via levitation force in the air above 30 mm, with tested suspension height generally aligning with dynamic simulation results.

Modeling and Hover Flight Control of a Micromechanical Flapping-Wing Aircraft Inspired by Wing–Tail Interaction

This article intends to give a comprehensive model to a brand new micromechanical flapping-wing aircraft inspired by wing–tail interaction. In this aircraft, the flapping-wing induced flow contributes to the tail control torque generation. However, this also makes the wing–tail interaction nonnegligible, and this flow would be disturbed by the relative flow produced by the body motion. The dominant unsteady aerodynamic effects of the flapping wing are considered. The flapping-wing induced flow over the tail is included when analyzing the tail aerodynamics. Especially, the aerodynamic–dynamic coupling effect of both the wing and the tail is considered to account for the force due to the body motion. A nonlinear and time-periodic simulation model of the aircraft is, thus, established. The model is averaged and linearized around hover status. Because of the combination of the wing–tail interaction with the aerodynamic–dynamic coupling, the state and control matrixes, including both the induced flow effect and the body motion effect, can be obtained. The pitch dynamics are analyzed, and it is found that the tail can push the two unstable oscillatory poles closer to the imaginary axis. The role of the tail is fully demonstrated by considering the induced flow. Cascade controllers are also designed according to the root-locus plot based on the built model. Due to the inclusion of the wing–tail interaction and the aerodynamic–dynamic coupling, the controllers are proved to be efficient in the attitude stabilization during statistic hover, descent, and ascent flights. Our proposed model can be easily applied to the modeling of other flapping-wing aircraft with similar structures, and it makes the controller design process more efficient and targeted.

Improved finite-time prescribed performance super-twisting sliding mode united control framework for underwater vehicle-manipulator system

This paper investigates the trajectory tracking control problem for underwater vehicle-manipulator system (UVMS) with model uncertainties, dynamic coupling effects and external disturbances. Firstly, an improved finite-time performance function (IFTPF) is proposed to ensure the prescribed tracking accuracy with predefined convergence time while avoiding singularities in the system and enhancing robustness. Additionally, to reduce the controller’s dependence on the system model and compensate for unknown external disturbances, a neural network (NN) estimator is proposed to estimate the combination of system uncertainties and dynamic coupling effects, while a neural network-based nonlinear disturbance observer (NNDO) addresses the unknown external disturbances. Furthermore, an improved finite-time prescribed performance super-twisting sliding mode control framework using neural network-based disturbance observer (NNDO-IFTPPSTSMC) is proposed to ensure control accuracy and robustness while reducing chattering phenomenon. Theoretical analysis demonstrates that corresponding error variables of the system are bounded, and the trajectory tracking errors satisfy the prescribed performance constraints. Finally, simulation results validate the effectiveness and feasibility of the proposed method.

An experimental demonstration of level attraction with coupled pendulums

We have experimentally demonstrated dissipative coupling in a double pendulum system through observation, which shows three distinctly different patterns of motion over the accessible parameter space. The described dissipative coupling apparatus is easy to manufacture and budget-friendly. The theoretical calculations are also suitable for the undergraduate level. Our experiment can serve as a novel demonstration for ubiquitous dynamic coupling effects encountered in many disparate physical systems. Unlike the well-known spring-coupled pendulums, our experiment employs Lenz's effect to couple the pendulums through electromagnetic damping, which, to the best of our knowledge, has not been demonstrated in the classroom. Our pendulums exhibit level attraction behaviour between two modes, induced by the dissipative coupling. This stands in contrast to the traditionally taught concept of level repulsion (avoided crossing) with spring-coupled pendulums. This experiment showcases distinctly different time domain dynamics of the dissipatively coupled pendulums over the parameter space, characterized by different oscillation patterns, damping rates, and relative phase between the two pendulums, which is a valuable lesson elucidating the dynamics of synchronization in linear systems for undergraduate students.

Experimental and numerical studies of the dynamic coupling effect in the primary-secondary system

Many complicated dynamic coupling effects(DCE) exist in the primary-secondary system(PS system) under earthquakes, among which the dynamic interaction and tuning effect have a more significant influence. However, the existing numerical analysis methods and experimental works are mostly based on the assumption of a small mass ratio, resulting in no significant interactions within the coupled system to be discussed. Therefore, a series of dynamic characteristics tests and shaking table tests were conducted to determine the working of the DCE works on the PS systems with appropriate mass ratios, and test results were used for the validation of an analysis method without the mass limitation and for the extended numerical analyses. According to the results, the dynamic interaction could reduce the responses of the secondary system(S system), and the reduction was positively related to the mass ratio, the tuning effect could cause a divergence of the natural frequencies and about 10–40% decrease in the primary system(P system) response and approximately 7–34 times increase in the S system response. The results of the extended analysis demonstrate the effectiveness of increasing the damping of connection, and decoupled analysis will yield more than double the security redundancy.