Flexible Vibration Research Articles

Design of anti-unwinding attitude coupling controller for flexible spacecraft using positive position feedback control

Flexible vibration has a great impact on flexible spacecraft attitude control, which will reduce the pointing accuracy of the spacecraft platform and bring severe challenges to the design of a high-precision attitude control system for flexible spacecraft. Aiming at the problem of attitude and vibration coupling control of flexible spacecraft, an anti-unwinding attitude coupling controller using the positive position feedback (PPF) control is proposed in this paper. The model compensation control term is constructed based on the prior information to improve the tracking performance. The proposed attitude coupling control method can effectively suppress the flexible vibration while achieving more accurate attitude control. The obtained closed-loop system under the proposed control scheme is asymptotically stable, which is proved by the Lyapunov stability theory. The numerical simulation illustrates that the proposed method can effectively improve the attitude control accuracy of the flexible spacecraft and is capable of large-angle attitude maneuver control because of its prominent performance in attitude tracking and its unwinding-free performance.

Disturbance observer-based sliding mode control of active vertical suspension for high-speed rail vehicles

Disturbance observer-based sliding mode control (SMC) on the active vertical suspension (AVS) is developed to suppress the car body’s rigid and flexible vibration to improve ride comfort for a high-speed rail vehicle. A vertical-dynamics-intended vehicle model is foremost built with the bounce, pitch, and bending mode of the car body involved. Two sliding surfaces and disturbance observers are then designed for SMC, which only require the car body states, obviating the bogies’ states. The observer is successful in estimating the effect of unknown track irregularities perturbation as well as externally straightforwardly excitations on the car body with good accuracy. Control efficacy is verified through comparison with passive cases and sky-hook controls. With modal damping below 2% in passive cases, the mode shape function, especially with large displacement at the suspension support, would enlarge the car body acceleration. Moreover, the longitudinal traction rod can significantly multiply the flexible vibration at certain speeds. Comparative studies indicate that SMC provides satisfactory outcomes in the rigid and bending vibration suppression when all the car body’s three modes are considered in the sliding surface. However, it requires a high-frequency response actuator and allows a tighter tolerance of the control time delay than the sky-hook control.

Research on flexible beam-type nonlinear vibration isolators suitable for low frequencies

Ship vibration not only causes safety issues, but also easily generates noise pollution. Therefore, this paper introduces the quasi-zero stiffness (QZS) vibration isolator to solve the problem of low-frequency vibration. In terms of static analysis, this paper proposes a discretized beam constraint model (DBCM) to study the static properties of flexible beams with large deformation, and the finite element analysis (FEA) verifies the accuracy of DBCM. Regarding dynamic analysis, this paper combines the harmonic balance method (HBM) and the pseudo-arc length method (PALM) to analyze the dynamic response and explore the influence of excitation and damping ratio on the response stability. In addition, the performance of equivalent linear isolators is compared, revealing significant advantages of QZS isolator in terms of isolation bandwidth and peak transmissibility. The experimental data demonstrates that QZS isolator’s initial isolation frequency (2.14 Hz) is 68.5% lower than that of linear isolators (6.79 Hz), and the isolation efficiency at 5.35 Hz can reach 90%, making it suitable for low-frequency isolation. Furthermore, experimental data validate the accuracy of the theoretical model and FEA. The static and dynamic theoretical models can optimize the structural parameters of flexible beams and serve as valuable inspiration and reference for designing and improving isolator.

Highly stable and ultra-fast vibration-responsive flexible iontronic sensors for accurate acoustic signal recognition.

Wearable verbal language servers function as sophisticated and effective tools for fostering intelligent interactions between humans and machines. In the realm of collecting acoustic vibration signals, flexible iontronic pressure sensors have demonstrated their efficacy by incorporating microstructures into the functional layer, resulting in heightened pressure sensitivity. However, the substantial viscosity of the integrated iontronic materials or the lack of bonding at the heterogeneous interface emerges as a significant hindrance to capacitance recovery, leading to sluggish response speeds and mechanical instability. Here, we address the issue by introducing hydrogen bonding between naturally microstructured protein micro-fibers and hydrophilic ionic hydrogel into the dielectric layer. Due to the good resilience of protein micro-fibers and the enahnced interfacial bonding, this flexible vibration sensor demonstrates outstanding performance characteristics, featuring exceptional signal stability, a high-pressure resolution of 522 pF kPa-1, an ultra-fast response time of 0.6 ms, and a relaxation time of 0.6 ms, with a limit of detection (LOD) of 0.12 Pa, making it well-suited for acoustic vibration acquisition. By using a one-dimensional convolutional neural network (1D-CNN) deep learning to process and recognize collected acoustic signals, our sensor achieved an impressive accuracy of 98.2%. These wearable vibration sensors exemplify promising versatile applications in biometric authentication, personalized services, and human-computer interaction.

Dynamic Modeling and Stability Analysis of a Control Moment Gyroscope Considering the Influence of a Flexible Vibration Isolator

Dynamic Modeling and Stability Analysis of a Control Moment Gyroscope Considering the Influence of a Flexible Vibration Isolator

Effect of Rigid Pitch Motion on Flexible Vibration Characteristics of a Wind Turbine Blade

Effect of Rigid Pitch Motion on Flexible Vibration Characteristics of a Wind Turbine Blade

Research on solar sail attitude maneuvering method based on adaptive sliding mode control

A solar sail is a spacecraft propulsion system that uses the pressure of light to push a spacecraft. It consists of a lightweight support structure that deploys a large area of flexible film. During attitude maneuvering in space, the solar sail will excite vibrations in the flexible support structure and film, which can affect the accuracy of the attitude control system. To address this issue, this article first establishes a rigid-flexible coupled dynamic model of the solar sail that includes attitude motion and flexible structure elastic vibrations. Then, based on an adaptive sliding mode control method, a solar sail attitude maneuvering method is proposed. Finally, a numerical simulation is conducted using a hexagonal-shaped solar sail as the object. The numerical simulation results show that the attitude maneuvering method has the performance of attitude tracking and attitude stabilization, can meet the requirements of large-angle attitude maneuvering for solar sail spacecraft, and has strong robustness to model parameter uncertainty.

Design and analysis of a novel flexible variable stiffness damping mechanism for grinding electric spindle

The purpose of this research is to design a flexible variable stiffness damping mechanism to solve the load impact problem in the grinding process of permanent magnet electric spindle. Firstly, combined with the structure and usage scene of the grinding permanent magnet electric spindle, according to the design principles and technical indicators, a novel flexible variable stiffness vibration damping joint is proposed. Then the stiffness and energy storage model of the flexible variable stiffness damping mechanism is established, and the stiffness and energy storage characteristics of the mechanism are analyzed. The strength and dynamic characteristics of the flexible variable stiffness mechanism are analyzed by Ansys and Adams, respectively. Finally, an experimental platform for the comprehensive performance verification of the flexible variable stiffness damping mechanism is built to verify the dynamic characteristics and damping effect of the mechanism. The research results show that the designed flexible variable stiffness structure has better vibration damping effect and can improve the grinding performance of the permanent magnet electric spindle.

Splashing of droplet under the vibration effect of flexible membrane

The impact dynamics of a droplet falling onto a substrate is significant in various applications such as inkjet printing, spray coating, and bioprinting. Generally, several factors, such as the fluid properties (e.g. viscosity or surface tension) and substrate characteristics (e.g. surface roughness or flexibility) govern whether falling droplets spread or splash. In this study, we experimentally investigate droplet impact dynamics on a thin, flexible membrane for various Weber numbers (230 < We < 600) and membrane stiffnesses, which can be controlled by the applied tensile force. In addition, the effect of membrane vibration on impact behavior is considered. In the high Weber number regime, splashing is dominant, regardless of the membrane stiffness. In contrast, in the low Weber number regime, a transition between splashing and deposition is observed, depending on the membrane stiffness. In short, flexible membrane vibration induces droplet splashing despite the insufficient kinetic energy of the droplet. Increasing the stiffness of the membrane contributes to the suppression of droplet splashing by minimizing membrane vibration.

Train/track coupled dynamics model of long heavy haul train based on substructure and parallel computing

To consider the coupled effect on the running safety between elastic track and longitudinal impulse of Long Heavy Haul Train(LHHT), a train/track coupled dynamics model is established by using connection substructure theory. The ballasted track is divided into several segments called sub-tracks: a sub-track includes rail, sleepers and ballast. In the sub-track model, the sleepers and ballast are modelled as lumped mass. The rail is divided into the contact and connection rail. The contact rail is modelled as an Euler beam to reflect the wheel/rail interaction and the flexible vibration of the rail. The connection rail is modelled as a super element to reflect the interaction between adjacent contact rail. To increase the simulation speed, a new parallel computing method is proposed: a train/track coupled dynamics model is divided into different submodule, a submodule includes a sub-track and a vehicle on the sub-track. A submodule is calculated by a single computer core. The submodule is connected by connection rail, couplers and ballast. The advantage of this parallel method is that the load of each computer core is almost uniform. The simulation speed depends on the number of parallel computing cores instead of one core with a particularly large load. Finally, taking the 10,000-ton train as an example, the distribution of coupler force, the derailment coefficient and wheel unloading rate are given during the train braking on a curve, which shows the application and necessity of the train/track coupled dynamics model based on substructure and parallel computing.

Design Modification and Comparative Analysis of Flexible Multi-configuration Beam Vibration Rig

Design Modification and Comparative Analysis of Flexible Multi-configuration Beam Vibration Rig

Nonlinear finite time attitude control of flexible spacecraft based on a novel output redefinition method

A finite time attitude controller is designed for a flexible spacecraft based on a novel output redefinition method, in this paper. To make the flexible appendages vibration suppression effective, the appendage tip-point is selected as the output. First, a novel output redefinition method is proposed to overcome the non-minimum phase property of the dynamic model. The proposed method not only makes the system model minimum phase but also improves the attitude control system performance. Consequently, the precise attitude pointing and stabilization are achieved. Then, a nonlinear finite time H∞ controller is designed based on the backstepping approach. For the situation where the modal variables measurements are not available, a modal observer is also designed. The simulation results show the effectiveness of the proposed method in the presence of the model uncertainties and environmental disturbances.

Low-frequency vibration isolation via an elastic origami-inspired structure

This paper presents a new elastic origami-inspired structure with quasi-zero-stiffness (QZS) characteristics to provide effective low-frequency vibration isolation performance. The geometric structure of the origami mechanism is first introduced, followed by the establishment of its mechanical model through the integration of elastic joints with compression springs. The derived strong nonlinear stiffness characteristics of the elastic origami mechanism are conducive to exploring a QZS isolator with high performance. Then by using the multiscale method, the dynamic behavior of the origami-inspired isolator is obtained, and the parameter influencing investigations validate that the proposed vibration isolation system has strong design flexibility and superior vibration suppression capability. An experimental prototype was fabricated and a series of vibration testing experiments under different working conditions were carried out. The experimental results demonstrated the effectiveness of the established theoretical model. Furthermore, the comparison with typical nonlinear passive isolators verified the advantages of the developed origami-inspired vibration isolation system. This work has the potential to advance the practical applications of origami-based mechanisms and also provides a new technical candidate for high-performance vibration isolation systems.

Nonlinear dynamics of time-varying curvature balance rope coupled with time-varying length hoisting rope in friction hoisting system

Mine friction hoisting system is a typical multi-body system composed of traction sheave, conveyance, hoisting rope, and balance rope. Hoisting rope is of large-scale and flexible tension, leading to large amplitude elastic vibration and huge tension fluctuation during hoisting movement. Balance rope is of small tension amplitude and bending modulus, undergoing significant curvature changes, large displacement, and large deformation. Considering the complex coupling vibrations between the moving hoisting rope and balance rope in the ultra-kilometer-deep shaft, a coupling modeling method of the variable-length hoisting rope with the variable-curvature balance rope is proposed. Based on the absolute nodal coordinate formulation(ANCF), the balance rope is modeled by non-equal-length and variable-number elements, and the hoisting ropes on both sides are modeled by variable-length and variable-number elements. A flexible rope vibration experiment platform is built in the laboratory to verify correctness of the proposed theoretical model.The experimental results are in good agreement with those in theoretical simulation. Besides, the nonlinear coupling dynamic behaviors of hoisting rope and balance rope in an ultra-kilometer-deep well are studied. It reveals the non-stationary phenomenon of hoisting rope and balance rope with a long-time range. Both sides of flat balance rope undergo large bending deformation and non-stationary response when transient resonance occurs in hoisting ropes.

Investigation on Numerical Simulation of VIV of Deep-Sea Flexible Risers

The vortex-induced vibration (VIV) of flexible risers is a complex fluid–structure interaction (FSI) phenomenon. In this study, we conducted a numerical simulation method based on the slicing method to study the vortex-induced vibration (VIV) of deep-sea flexible risers with different slenderness ratios and uniform flow velocities. The method combines the finite element model of the riser structure with the two-dimensional flow field slices solved by the Fluent solver. The fluid–structure interaction was realized by a self-compiled UDF program and the overset mesh technique. The numerical results were validated by comparing them with experimental data. The VIV characteristics of the riser, such as the vibration track, vibration mode, vibration frequency and wake vortex shedding mode, were analyzed. The article reveals the nonlinear dynamic features of flexible riser vibration, such as multi-frequency vibration, wide-frequency vibration and multi-modal vibration. The article also provides insights into the fluid–structure interaction mechanism of VIV of deep-sea flexible risers.

Dynamic modeling and control of a solar sail considering large-amplitude nonlinear vibration

The solar sail spacecraft utilizes Solar Radiation Pressure (SRP) to achieve propulsion, which can realize long-term acceleration without fuel consumption, making it an appealing option for deep space exploration and polar-sitter observation. However, because of the large-scale and high-flexibility of the membrane structure, the solar sail poses challenging dynamic and control issues. Precise dynamic modeling and effective control design can provide theoretical guidance for the efficient functioning of solar sail, which are of great significance and urgently need to be studied. In this paper, a dynamic model that can describe the large-amplitude vibrations of the solar sail is established. Additionally, an attitude tracking controller and a cable-based nonlinear vibration controller are designed to control the attitude motion and flexible vibration of the solar sail. The results show that the established nonlinear rigid-flexible coupling dynamic model is more accurate compared to the linear dynamic model. The polynomial fitting method can characterize the nonlinear dynamics of the solar sail extremely effectively while cutting the program runtime to 5% of the original. Two controllers designed in this paper can make the solar sail maneuver follow the desired trajectory accurately while reducing the sail surface vibration by more than 40%. The research outcomes of this paper can provide references for the dynamic study and active control of large-scale membrane spacecraft.

Design and Simulation of On-Orbit Assembly System Based on Insect-Inspired Transportation

In response to the requirements of large-scale space in-orbit assembly and the special environment of low gravity in space, this paper proposes a small robot structure with the integration of assembly, connection, and vibration reduction functionalities. Each robot consists of a body and three composite mechanical arms-legs, which can dock and transfer assembly units with the transport spacecraft unit, and also crawl along the edge truss of the assembly unit to a designated location to complete in-orbit assembly while ensuring precision. A theoretical model of robot motion was established for simulation studies, and in the research process, the vibration of the assembly unit was studied, and preliminary adjustments were made to address the vibration issue. The results show that this structure is feasible for in-orbit assembly schemes and has good adjustment ability for flexible vibration.

Optimal phase compensation for a rotor-AMB system considering interface contact

Rotor-Active magnetic bearing (rotor-AMB) systems offer significant advantages in power consumption and are increasingly being applied in fluid machinery. However, in such machinery, the impeller and the rotor are commonly connected by bolt fastening. Once a certain pre-tightening force is applied to the bolted connection and the interface contact between the rotor and the impeller is formed, the flexible modal vibration will be excited when the rotor is levitated. The conventional Proportional-Integral-Derivative (PID) controller is limited in this vibration suppression and it is essential to increase the damping at bending mode to inhibit vibration. However, the calculation of the optimal phase compensated is based on the rotor-AMB model considering interface contact. In this work, the effect of the interface contact is equivalent to massless spring units, and the disturbance generated by spring units is acted upon the mechatronic system in the way of positive feedback. The detailed description of the transfer function from the disturbance to rotor deformation at fourth bending mode is obtained by theoretical model and system identification. The optimal phase of the system needed to inhibit the disturbance is determined by minimizing the gain of the transfer function at fourth bending mode. A combination of PID control and phase compensation is implemented in the experiment. The results show that the optimal phase is 50° as the calculation and the optimal phase compensation control can sufficiently inhibit the modal vibration.

Finite-Time Attitude Optimization Maneuver Control for Coupled Spacecraft Under Attitude Measurement Errors and Actuator Faults

The large-angle attitude maneuver trajectory design and tracking control for flexible spacecraft with slosh structure under attitude measurement errors and actuator faults are investigated in this article. Considering that rapid attitude maneuvers can lead to severe flexible vibrations and liquid sloshing, which in turn affects system stability. Therefore, under the requirement of fast maneuvering, the attitude trajectory is optimized to maximize the system’s stability by establishing a new indicator function, while satisfying multiple physical constraints. Furthermore, the novel adaptive multivariable command filtering backstepping fault-tolerant controller is proposed for the coupled spacecraft, to achieve the finite-time attitude tracking to the optimized trajectory, despite the measurement errors and actuator faults. The merits lie in the modified auxiliary signals and virtual commands design, which can compensate the filter errors, caused by the applied filters to deal with the “explosion of terms” of conventional backstepping control, in finite time with better control performance. The numerical simulations are performed to verify the effectiveness of the proposed method.

Vibration Suppression Trajectory Planning of Underwater Flexible Manipulators Based on Incremental Kriging-Assisted Optimization Algorithm

It is of great significance to expand the functions of submarines by carrying underwater manipulators with a large working space. To suppress the flexible vibration of underwater manipulators, an improved sparrow search algorithm (ISSA) combining an elite strategy and a sine algorithm is proposed for the trajectory planning of underwater flexible manipulators. In this method, the vibration evaluation function is established based on the precise dynamic model of the underwater flexible manipulator and considering complex motion and vibration constraints. Simulation results show that the ISSA algorithm requires only 1/3.68 of the time of PSO. Compared to PSO, SSA and the opposition-based learning sparrow search algorithm (OBLSSA), the optimization performance is improved by 17.3%, 13.1% and 9.7%, respectively. However, because the complex dynamics model of the underwater flexible manipulator leads to large computational effort and a long optimization time, ISSA is difficult to apply directly in practice. To obtain a large number of optimization results in a shorter time, an incremental Kriging-assisted ISSA (IKA-ISSA) is proposed in this paper. Simulation results show that IKA-ISSA has good nonlinear approximation ability and the optimization time is only 3% of that of the ISSA.