Coupling Of Motion Research Articles

Development of a Variable-Pitch Flexible-Screw-Driven Continuum Robot (FSDCR) with Motion Decoupling Capability.

Tendon-driven continuum robots suffer from crosstalk of driving forces between sections, typically resulting in motion coupling between sections, which affects their motion accuracy and complicates the control strategies. To address these issues, this article proposes a mechanically designed variable-pitch flexible-screw-driven continuum robot (FSDCR) that enables motion decoupling between sections. The continuum section of the FSDCR comprises a series of orthogonally arranged vertebrae and is driven by customized variable-pitch flexible screws. The variable-pitch flexible screws apply driving forces and constraints to several threaded vertebrae in the continuum section, improving positioning accuracy and loading capacity. The flexible screws effectively balance the driving force and torque within one section through antagonistic torsional actuation, thereby achieving motion decoupling between sections. Characterization experiments have been conducted to compare the motion accuracy and load capacity of the variable-pitch FSDCR with those of the constant-pitch FSDCR. The results demonstrate that the variable-pitch FSDCR exhibits improved positioning accuracy, minimizing an average error of 0.79 mm (0.60% relative to its total length), which is 82.09% lower than that of the constant-pitch FSDCR. The load capacity of the variable-pitch FSDCR is enhanced by up to 129.09% compared with the constant-pitch FSDCR. Experiments on the motion decoupling performance of the FSDCR show that the maximum motion coupling error is 0.32 mm (0.24% relative to the section length). Additionally, the motion coupling error is minimally influenced by the rotational speed of the screw. Finally, a three-section FSDCR is constructed, and its load capacity and motion flexibility are demonstrated.

A hybrid active control method for a 3-DOF wave-compensated gangway

ABSTRACT Wave-compensated gangways are affected by forces from internal joint coupling and vessel motion, making the control process complex and challenging. Previously, three-degree-of-freedom gangways adopted passive compensation methods, utilizing end-effector sensor feedback for control. However, these methods are constrained by slow response times and significant lag. This study proposes an active hybrid compensation approach to enhance response speed and reduce tracking errors. The kinematics and dynamics of the gangway under vessel motion were analyzed. Subsequently, an improved velocity feedforward second-order super-twisting sliding mode control scheme was designed, complemented by fuzzy control for small torque compensation. Two experiments were conducted to evaluate and compare the performance of three control methods. Experiments demonstrated that the proposed hybrid control method exhibited superior performance in joint trajectory tracking, significantly reducing both root mean square and maximum errors, validating its effectiveness in improving tracking speed and accuracy.

Analysing the dynamics of the Kepler-90 planetary system

Abstract Kepler-90 system has a set of eight planets in a hierarchical structure. In this work, we used frequency analysis to study several Kepler-90 analogues to analyse in detail how the values of the eccentricity of each planet can alter the stability of the system. The system was formed by the star and eight planets for three different intervals of eccentricity (e). Our results show that for the first and second intervals all the systems are stable. However, no set of Kepler-90 system with large values of e survived up to 105 orbits of Kepler-90h. In the low eccentricity interval, planets b and c were found to be in a 5:4 mean motion resonance, and the pair g and h in a 3:2 mean motion resonance, although these two pairs are in resonance in different Kepler-90 analogues. In the medium eccentricity interval, only the pair g and h is in resonance. Kepler-90 b and c are in quasi-resonance 5:4; the critical angle circulates and librates intermittently in different periods of time. The results statistically indicate that these resonances directly affect most of them. The influence covers a wide range of possibilities: (i) a strong resonant mean motion coupling added to a coupling of the longitude of the pericentres; (ii) just a single resonant argument librating; (iii) intermittent behaviour, interleaving libration and circulation of the resonant arguments; and (iv) the quasi-resonant influence due to the near commensurability.

Ultrafast structural transition and electron-phonon/phonon–phonon coupling in antimony revealed by nonadiabatic molecular dynamics

Real-time time-dependent density-functional theory molecular dynamics (rt-TDDFT-MD) reveals the nonadiabatic dynamics of the ultrafast photoinduced structural transition in a typical phase-change material antimony (Sb) with Peierls distortion (PD). As the excitation intensity increases from 3.54% to 5.00%, three distinct structural transition behaviors within 1 ps are observed: no PD flipping, nonvolatile-like PD flipping, and nonstop back-and-forward PD flipping. Analyses on electron-phonon and phonon-phonon couplings indicate that the excitation-activated coherent A1gphonon mode by electron-phonon coupling drives the structural transition within several hundred femtoseconds. Then, the energy of coherent motions are transformed into that of random thermal motions via phonon-phonon coupling, which prevents the A1g-mode-like coherent structure oscillations. The electron-phonon coupling and coherent motions will be enhanced with increasing the excitation intensity. Therefore, a moderate excitation intensity that can balance the coherent and decoherent thermal movements will result in a nonvolatile-like PD flipping. These findings illustrate important roles of nonadiabatic electron-phonon/phonon-phonon couplings in the ultrafast laser-induced structural transitions in materials with PD, offering insights for manipulating their structures and properties by light.

Memory Effects Explain the Fractional Viscosity Dependence of Rates Associated with Internal Friction: Simple Models and Applications to Butane Dihedral Rotation.

Barrier-crossing rates of biophysical processes, ranging from simple conformational changes to protein folding, often deviate from the Kramers prediction of an inverse viscosity dependence. In many recent studies, this has been attributed to the presence of internal friction within the system. Previously, we showed that memory-dependent friction arising from the nonequilibrium solvation of a single particle crossing a smooth one-dimensional barrier can also cause such a deviation and be misinterpreted as internal friction. Here we introduce a simple diatom model and show that even in the absence of explicit solvent, internal memory effects arise due to coupling of the reaction coordinate motion with frictionally orthogonal degrees of freedom. This results in a fractional viscosity dependence and a deviation from Kramers' theory, typically attributed to the presence of internal friction. This model therefore mimics several biological processes where a local conformational change of a biomolecule is often influenced by its surroundings. This gives rise to an apparent "internal friction" commonly measured in terms of empirical fitting parameters α and σ. We propose a microscopic measure of this internal friction using Grote-Hynes theory which employs memory-dependent friction. We use butane to demonstrate the effect of coupling strength on the internal friction in realistic systems. This model therefore can serve the purpose of understanding internal friction in biological systems in terms of such coupling.

A novel inertial parameter identification method for the ship-mounted Stewart platform based on a wave compensation platform

To meet the requirement of time-varying inertial parameter identification of control algorithms for shipborne Stewart wave compensation platforms, this study proposes an innovative inertial parameter identification method based on a non-inertial system. Unlike traditional Stewart identification methods with a fixed frame, the proposed method does not require designing excitation trajectories to consider the condition number of the observation matrix. Namely, the proposed method requires only performing two-dimensional dynamic parameter collection for parameter identification in a six-dimensional non-inertial motion. In addition, a coupling error dimension reduction method is developed to improve the identification accuracy under the condition of coupling motion. Finally, experiments are conducted to verify the effectiveness of the proposed identification method. The experimental results show that under the coupling motion conditions, the coupling errors of the corrected singularity points are reduced by 7.9–28.1% compared to before correction, and the axial force average error correction is below 5.32%.

Floating body motion coupling study and economic evaluation of different floating photovoltaic arrangement schemes under hybrid solar-wind power generation

Abstract Reducing the number of anchor points and moorings for floating platforms is one of the ways to reduce the integration and maintenance costs of floating offshore wind and solar farms. This paper focuses on the technical feasibility and economic viability of reducing the number of anchor points and moorings for floating offshore PV platforms by using a monopile of a stationary wind turbine as a mooring anchor point and introducing a shared line system. In this paper, three different floating solar layouts and their corresponding mooring systems are numerically evaluated and optimized under different environmental loading conditions using the commercial software OrcaFlex. The results of the study show that the implementation of a shared mooring solution maximizes the cost-effectiveness economically while technically ensuring stable operation.

Coupled Motion Response Analysis for Dynamic Target Salvage under Wave Action

The strategic recovery of buoys is a critical task in executing deep-sea research missions, as nations extend their exploration of marine territories. This study primarily investigates the dynamics of remotely operated vehicle (ROV)-assisted salvage operations for floating bodies during the recovery of dynamic maritime targets. It focuses on the hydrodynamic coefficients of dual floating bodies in this salvage process. The interaction dynamics of the twin floats are examined using parameters such as the kinematic response amplitude operator (RAO), added mass, damping coefficient, and mean drift force. During the “berthing stage”, when the double floats are at Fr = 0.15–0.18, their roll and yaw Response Amplitude Operators are diminished, resulting in smoother motion. Thus, the optimal berthing speed range for this stage is Fr = 0.15–0.18. During the “side-by-side phase”, the spacing between the ROV and FLOAT under wave action should be approximately 0.4 L to 0.5 L. The coupled motion of twin floating bodies under the influence of following waves can further enhance their stability. The ideal towing speed during the “towing phase” is Fr = 0.2. This research aims to analyze the mutual influence between two floating bodies under wave action. By simulating the coupled motion of dual dynamic targets, we more precisely assess the risks and challenges inherent in salvage operations, thus providing a scientific basis for the design and optimization of salvage strategies.

Memory-extraction-based DRL cooperative guidance against the maneuvering target protected by interceptors

This paper presents an open and interesting issue for missiles, i.e., achieving collaborative parameters constrained cooperative guidance, despite the interference of pursing interceptors (INTs) and the maneuvering target, by the fact that the target-missile-interceptor (TMI) engagement induces their complex and time-varying relationships. The Memory-Extraction-based Soft-Actor-Critic (ME-SAC) approach is proposed, which enhances the collaborative performance of missiles by implicitly extracting coupling motion characteristics among TMI from historical state, achieving the joint optimization of situation awareness and strategy. Firstly, the cooperative guidance task is formulated as a multi-order Markov decision process (MOMDP) to better represent the dynamic evolution of engagement, and a memory-extraction process is introduced to alleviate the curse of dimensionality. Secondly, a memory-decision-oriented maximum entropy framework combined with memory update modules is designed for enhancing strategy search ability. Then, a domain-knowledge-based pre-training is implemented to improve convergence speed. Finally, in simulation evaluation with various scenarios, the proposed ME-SAC shows more promising than the typical DRL-based and model-based algorithms in task success rate, learning efficiency, and adaptability.

Three-dimensional simulation on phase change heat transfer of moving spherical particle

Investigating the motion process of paraffin particle under a mesoscopic scale is very helpful to master the heat transfer mechanism of the mushy zone in solid–liquid phase change. Prior researches predominantly focused on either particle motion or phase change, without accounting for their coupling. In this study, the three-dimensional finite element method is used to solve the motion and heat transfer of the particle, taking into account the coupling of motion and phase change. The moving grid is employed to trace the interface of moving particles and liquid using the Arbitrary Lagrangian-Euler method, which is able to calculate flow and heat transfer in fluid region and allow grid deformation in solid region. The results indicate that uneven fluid velocity around the particles results in non-uniform temperature gradients on particle’s surface. In areas with larger temperature gradient, it melts more quickly and its deformation is obvious. The maximum is located at particle orientation angle 30°. Changing the size and direction of fluid velocity will reinforce or inhibit the movement of particle. The changing time of motion direction when fluid velocity is −0.03 m/s shorten 2.7 times than when fluid velocity is −0.01 m/s. The initial temperature of the surrounding fluid has a positive relationship with the particle melting rate. The channel width affects significantly the motion and melting of particle. The initial position of particle has an important effect on it’s falling movement, and the closer is close to the wall of channel, the greater the displacement of left and right movement.

Modeling ultrafast anharmonic vibrational coupling in gas-phase fluorobenzene molecules.

In this work, we study the energy flow through anharmonic coupling of vibrational modes after excitation of gas-phase fluorobenzene with a multi-THz pump. We show that to predict the efficiency of anharmonic energy transfer, simple models that only include the anharmonic coupling coefficients and motion of modes at their resonant frequency are not adequate. The full motion of each mode is needed, including the time while the mode is being driven by the pump pulse, because all the frequencies present in the multi-THz pump contribute to the excitation of the non-resonantly excited vibrational modes. Additionally, the model gives us the insight that modes with either A1 or B2 symmetry are more actively involved in anharmonic coupling because these modes have more symmetry-allowed energy transfer pathways.

Origin and tuning of bandgap in chiral phononic crystals

The wave equation revealing the wave propagation in chiral phononic crystals, established through force equilibrium law, conceals the underlying physical information, such as the essence of the motion coupling and the inertial amplification effect. This has led to a controversy over the bandgap mechanism. In this article, we theoretically unveil the reason for this controversy, and put forward an alternative approach from wave behavior to formulate the wave equation, offering an alternative pathway to articulate the bandgap physics directly. Based on the physics revealed by our theory method, we identify the obstacles in coupled acoustic and optic branches to widen and lower the bandgap. Then we introduce an approach based on spherical hinges to decrease the barriers, for customizing the bandgap frequency and width. Finally, we validate our proposal through numerical simulation and experimental demonstration.

Prediction model of grinding roughness for worm with complicated space tooth surface

Optimum grinding parameters are crucial for achieving high-quality grinding of helical tooth surfaces for worm drives. The complex coupling motion relationship and formation mechanism between the worm blank and the grinding head make it difficult to predict the effect of grinding parameters on tooth surface roughness. Therefore, we developed a prediction model for the worm tooth surface roughness under conjugate grinding and applied it to the Roller Enveloping Worm Reducer (REWR). The forming process of the theoretical worm tooth surface during the grinding process was modeled by using the conjugate meshing principle. Considering the plowing and cutting effects of grinding particles on the tooth surface at different design parameters, feed speeds, and rotational speeds of the grinding head, the roughness prediction equation was established based on the theory of the maximum depth of valley bottom. Through the coupling analysis of the theoretical tooth surface model and the roughness prediction model, the prediction of the worm tooth surface roughness is realized. Based on the validated model, the influences of grinding parameters on the worm tooth surface roughness of REWR were quantitatively discussed. This study is of great significance for optimizing process parameters in the grinding of complex spatial surface transmissions.

Quantum advantage of one-way squeezing in weak-force sensing

Cavity optomechanical (COM) sensors, featuring efficient light–motion couplings, have been widely used for ultrasensitive measurements of various physical quantities ranging from displacements to accelerations or weak forces. Previous works, however, have mainly focused on reciprocal COM systems. Here, we propose how to further improve the performance of quantum COM sensors by breaking reciprocal symmetry in purely quantum regime. Specifically, we consider a spinning COM resonator and show that by selectively driving it in opposite directions, highly nonreciprocal optical squeezing can emerge, which in turn provides an efficient way to surpass the standard quantum limit which is otherwise unattainable for the corresponding reciprocal devices. Our work confirms that breaking reciprocal symmetry, already achieved in diverse systems well beyond spinning systems, can serve as a new strategy to further enhance the abilities of advanced quantum sensors, for applications ranging from testing fundamental physical laws to practical quantum metrology.

Impact of Various Coupled Motions on the Aerodynamic Performance of a Floating Offshore Wind Turbine Within the Wind–Rain Field

Impact of Various Coupled Motions on the Aerodynamic Performance of a Floating Offshore Wind Turbine Within the Wind–Rain Field

Dynamic Ultrastrong Coupling in a 2 nm Gap Plasmonic Cavity at the Sub-Picosecond Scale.

Localized surface plasmon resonances (LSPRs) can enhance the electromagnetic fields on metallic nanostructures upon light illumination, providing an approach for manipulating light-matter interactions at the sub-wavelength scale. However, currently, there is no thorough investigation of the physical mechanism in the dynamic formation of the strongly coupled LSPRs on sub-5 nm plasmonic cavities at the sub-picosecond scale. In this work, through femtosecond broadband transient absorption spectroscopy, we reveal the dynamic ultrastrong coupling processes in a nanoparticle-in-trench (NPiT) structure containing 2 nm gap cavities, and demonstrate a coherent motional coupling between vibrating AuNPs and the nanogaps. We achieve a maximum Rabi splitting energy of ∼660 meV in the sub-picosecond hot-electron relaxation time scale under the resonant excitation of the nanogap cavity's LSPR, reaching the ultrastrong coupling regime. This leads to a change of global vibration modes for the 2 nm gap cavity, potentially related to the dynamical Casimir effect with nanogap resonators.

Collision-Free Trajectory Planning Optimization Algorithms for Two-Arm Cascade Combination System

As a kind of space robot, the two-arm cascade combination system (TACCS) has been applied to perform auxiliary operations at different locations outside space cabins. The motion coupling relation of two arms and complex surrounding obstacles make the collision-free trajectory planning optimization of TACCS more difficult, which has become an urgent problem to be solved. For the above problem, this paper proposed collision-free and time–energy–minimum trajectory planning optimization algorithms, considering the motion coupling of two arms. In this method, the screw-based inverse kinematics (IK) model of TACCS is established to provide the basis for the motion planning in joint space by decoupling the whole IK problem into two IK sub-problems of two arms; the minimum distance calculation model is established based on the hybrid geometric enveloping way and basic distance functions, which can provide the efficient and accurate data basis for the obstacle-avoidance constraint condition of the trajectory optimization. Moreover, the single and bi-layer optimization algorithms are presented by taking motion time and energy consumption as objectives and considering obstacle-avoidance and kinematics constraints. Finally, through example cases, the results indicate that the bi-layer optimization has higher convergence efficiency under the premise of ensuring the optimization effect by separating variables and constraint terms. This work can provide theoretical and methodological support for the efficient and intelligent applications of TACCS in the space arena.

Wheel Drive Driverless Vehicle Handling and Stability Control Based on Multi-Directional Motion Coupling

Wheel Drive Driverless Vehicle Handling and Stability Control Based on Multi-Directional Motion Coupling

Spatial And Temporal Modes On A Generic Tandem Configuration In Transonic Shock Buffet

Certain combinations of upstream flow conditions in transonic flight may incite a highly unsteady shock-wave/boundary-layer interaction, often referred to as transonic buffet. The coupling of periodic shock motion and intermittent separation is seen to convey a characteristic unsteadiness in the evolution of the turbulent wake. This article uses high-speed focusing Schlieren and PIV measurements at high spatial resolution to characterize the temporal and spectral modes governing the flow past a generic 2D tandem configuration. This interaction, consisting of an OAT15A supercritical airfoil as the main wing and a NACA 64A-110 profile representing the tailplane, is investigated at chord-based Reynolds numbers of 2 million and 1 million, respectively and compared against fully-established shock buffet conditions in an isolated airfoil scenario operated at identical inflow conditions. The strongest buffet is observed in both configurations for a Mach number of 0.72 and an angle of attack of 5 deg, occurring at frequencies of 112 Hz and 103 Hz. Despite an equally periodic nature of the buffet unsteadiness, both shock amplitude and frequency are seen to decrease slightly in the tandem interaction. Global spectral analysis performed on the entire field of view identifies the buffet instability as the governing mode in both flow scenarios, imposing its unsteadiness even far downstream of its origin, allowing the extraction. of relevant sensor locations for a subsequent localized assessment of the involved time scales. Except for the buffet mode, complementing DMD analyses reveal a strong influence of a vortex-shedding mode throughout the entire buffet cycle. Mode shapes and associated frequencies furthermore suggest an intermittent low-frequency/large wavelength and high-frequency/low wavelength behavior, involving leading contributions between 2000 Hz and 4000 Hz.

Decoupling of rotation and translation at the colloidal glass transition.

In dense particle systems, the coupling of rotation and translation motion becomes intricate. Here, we report the results of confocal fluorescence microscopy where simultaneous recording of translational and rotational particle trajectories from a bidisperse colloidal dispersion is achieved by spiking the samples with rotational probe particles. The latter consist of colloidal particles containing two fluorescently labeled cores suited for tracking the particle's orientation. A comparison of the experimental data with event driven Brownian simulations gives insights into the system's structure and dynamics close to the glass transition and sheds new light onto the translation-rotation coupling. The data show that with increasing volume fractions, translational dynamics slows down drastically, whereas rotational dynamics changes very little. We find convincing agreement between simulation and experiments, even though the simulations neglect far-field hydrodynamic interactions. An additional analysis of the glass transition following mode coupling theory works well for the structural dynamics but indicates a decoupling of the diffusion of the smaller particle species. Shear stress correlations do not decorrelate in the simulated glass states and are not affected by rotational motion.