Vibration and stability of internally damped rotating composite Timoshenko shaft

The mechanical model for the dynamic behavior of an internally damped rotating composite shaft is derived using a refined variational asymptotic method and the principle of virtual work. The composite shaft is considered as an anisotropic thin-walled Timoshenko beam. The internal damping of composite shaft is modelled by adopting the multi-scale damping analysis method. Galerkin’s method is employed to discretize and solve the equations of motion. The effect of design parameters including fiber orientation, length aspect ratio, stacking sequences and boundary conditions on the free vibration and stability of composite shaft is investigated

Modeling and dynamic analysis of rotating composite shaft

Structural modeling and dynamical analysis of rotating composite shaft are conducted in this paper. A thin-walled composite shaft structure model, which includes the transverse shear deformation of the shaft, rigid disks and the flexible bearings, is presented and then used to predict natural frequencies and dynamical stability. Based on the thin-walled composite beam theory referred to as variational asymptotically method (VAM), the displacement and strain fields of the shaft are described. Hamilton’s principle is employed to derive the equations of motion of the shaft system. Galerkin’s method is used to discretize and solve the governing equations. The validity of the model is proved by comparing the results with those in literatures and convergence examination. The effects of fiber orientation, ratios of length over radius, ratios of radius over thickness and shear deformation on natural frequency and critical speeds are investigated. Finally the unbalance transient responses of the composite shaft system are also given by using the time-integration method

Physics-Based Trajectory Design for Cellular-Connected UAV in Rainy Environments Based on Deep Reinforcement Learning

Cellular-connected unmanned aerial vehicles (UAVs) have gained increasing attention due to their potential to enhance conventional UAV capabilities by leveraging existing cellular infrastructure for reliable communications between UAVs and base stations. They have been used for various applications, including weather forecasting and search and rescue operations. However, under extreme weather conditions such as rainfall, it is challenging for the trajectory design of cellular UAVs, due to weak coverage regions in the sky, limitations of UAV flying time, and signal attenuation caused by raindrops. To this end, this paper proposes a physics-based trajectory design approach for cellular-connected UAVs in rainy environments. A physics-based electromagnetic simulator is utilized to take into account detailed environment information and the impact of rain on radio wave propagation. The trajectory optimization problem is formulated to jointly consider UAV flying time and signal-to-interference ratio, and is solved through a Markov decision process using deep reinforcement learning algorithms based on multi-step learning and double Q-learning. Optimal UAV trajectories are compared in examples with homogeneous atmosphere medium and rain medium. Additionally, a thorough study of varying weather conditions on trajectory design is provided, and the impact of weight coefficients in the problem formulation is discussed. The proposed approach has demonstrated great potential for UAV trajectory design under rainy weather conditions

Primary resonance of a rotating composite shaft with geometrical nonlineary

The primary resonance of a simply supported rotating composite shafts with geometrical nonlineary is studied. The composite shaft is modeled as a thin-walled Euler-Bernoulli beam. A variational-asymptotical method (VAM) applied to anisotropic thin-walled closed-cross-sectional beams is used to describe the displacement and strain fields of the composite shafts. The geometrical nonlineary is considered in the relationships of strain and displacement of the shaft. The nonlinear extensional-bending-torsional equations of motion for the composite shaft are derived by using the Hamilton principle. In order to emphatically study nonlinear transverse bending vibration, the effects of extensional and torsional deformations are ignored. By means of the method of multiple scales the approximation solution of primary resonance of transverse bending vibration is obtained. The Galerkin method is employed to reduce the governing equations to the ordinary differential equations. By using fourth-order Runge-Kutta method the time histories, phase diagrams and power spectrums are plotted. The study shows the effect of the external damping, ply angle, eccentricity, ratios of length over radius, ratios of radius over thickness and rotating speed on nonlinear dynamic behavior of the shaft. Specifically, the numerical simulation results show that the shaft exhibits the complex dynamic behavior including periodic, quasi-periodic and chaotic motion

An analytical model for dynamic simulation of the composite rotor with internal damping

A theoretical model for the dynamics of composite rotor is presented. The composite shaft that includes rigid disks and is supported on rigid bearings is considered as a thin-walled Euler-Bernoulli beam. Internal damping of the composite shaft is taken into account. The equations of motion are derived using the thin-walled composite beam theory based on variational asymptotic method and Hamilton’s principle. The internal damping of shaft is introduced by adopting the multi-scale damping analysis method. Galerkin’s method is used to discretize and solve the governing equations. To demonstrate the validity of the present model, the convergence of the method is examined and the results are compared with those available in the literature. Numerical study shows the effect of design parameters on the natural frequencies, critical rotating speeds and instability thresholds of composite shaft. In addition, the free vibration responses due to the initial perturbations and the forced responses to unbalance for composite shaft are also presented

Free vibration analysis for wind turbine structure by component mode synthesis method

Based on free interface component modal synthesis method, the free vibration behavior of wind turbine structures is investigated. The wind turbine structure is divided into three parts including tower, wheel hub-cabin and rotor. The tower is modeled as an isotropic metal cantilever beam, the blade as thin-walled composite beam and the wheel hub-cabin as a rigid body due to its large extensional stiffness, bending stiffness and torsion stiffness compared with tower and blades. The displacements of the blades are described by thin-walled composite beam theory. Galerkin’s method is used to discretize blades and tower. Employing Lagrange method, the motion equations of blades are derived and then stiffness and mass matrices are obtained. The natural frequencies and mode shapes of the wind turbine structure are predicted by numerical simulations. Numerical results using the present model are validated by ANSYS software results

Near-Field Communications: A Degree-of-Freedom Perspective

Multiple-antenna technologies are advancing towards large-scale aperture sizes and extremely high frequencies, leading to the emergence of near-field communications (NFC) in future wireless systems. To this context, we investigate the degree of freedom (DoF) in near-field multiple-input multiple-output (MIMO) systems. We consider both spatially discrete (SPD) antennas and continuous aperture (CAP) antennas. Additionally, we explore three important DoF-related performance metrics and examine their relationships with the classic DoF. Numerical results demonstrate the benefits of NFC over far-field communications (FFC) in terms of providing increased spatial DoFs. We also identify promising research directions for NFC from a DoF perspective.Comment: 8 page

Flood mitigation performance of low impact development technologies under different storms for retrofitting an urbanized area

Low impact development technologies (LIDs) have been reported as alternatives to mitigate urban waterrelated hazards, particularly for urban flooding. However, the effectiveness of LIDs on flood mitigation is still not well understood. This study assessed the mitigation extent of urban flooding by LIDs for retrofitting an urbanized area at a feasible level using a hydrological model. A range of storms with different rainfall durations and amounts from intensity-duration-frequency curves were used to evaluate the hydrological performances of LIDs. The results indicated that LIDs were effective alternatives to mitigate urban flooding in the urbanized area. Surface runoff and peak flow decreased by 18.6e59.2% and 8.0 e71.4%, respectively. However, the flood mitigation performance decreased markedly with the increase of rainfall amount. Although LIDs were less effective in flood mitigation during shorter and heavier storms, the performance was better with the increase of rainfall duration. This research provides an insight into flood reduction capabilities of LIDs under different rainfall characteristics for retrofitting built up areas, which is useful for urban storm management

A Experimental Research On The Anti-erosion Material For Hydraulic Machinery

International audienceHydraulic machinery used in many fields was badly eroded, but it was found that not enough has been done on the erosion mechanism and the anti-erosion material. By using a rotating jet erosion testbed, four kinds of materials were tested under different dynamics parameters. At the same time, aluminum bronze was tested under different size of sand particle. Some conclusions can been obtained after observing material surface by SEM. With the increase of Impacting velocity , the damage of material surface became serious and weight loss got bigger. With the increase of the impacting angle, the weight loss first increased and then decreased. At the same dynamics parameters, because surface damages of 06Cr19Ni10 and 45Cr are small, so 06Cr19Ni10 and 45Cr had the better anti-erosion performance. However, Q235 had worse anti-erosion performance. With the increase of sand size, the erosion of material surface got worse, and weight loss had an obviously change between 0.4mm and 0.5mm

Investigating Sparse Reconfigurable Intelligent Surfaces (SRIS) via Maximum Power Transfer Efficiency Method Based on Convex Relaxation

Reconfigurable intelligent surfaces (RISs) are widely considered to become an integral part of future wireless communication systems. Various methodologies exist to design such surfaces; however, most consider or require a very large number of tunable components. This not only raises system complexity, but also significantly increases power consumption. Sparse RISs (SRISs) consider using a smaller or even minimal number of tunable components to improve overall efficiency while maintaining sufficient RIS capability. The versatile semidefinite relaxation-based optimization method previously applied to transmit array antennas is adapted and applied accordingly, to evaluate the potential of different SRIS configurations. Because the relaxation is tight in all cases, the maximum possible performance is found reliably. Hence, with this approach, the trade-off between performance and sparseness of SRIS can be analyzed. Preliminary results show that even a much smaller number of reconfigurable elements, e.g. only 50%, can still have a significant impact.Comment: EuCAP 202