Modeling and Analyzing Dynamic Response for An Offshore Bottom-Fixed Wind Turbine with Individual Pitch Control

The asymmetric or periodically varying blade loads resulted by wind shear become more significant as the blade length is increased to capture more wind power.Additionally,compared with the onshore wind turbines,their offshore counterparts are subjected to additional wave loadings in addition to wind loadings within their lifetime.Therefore,vibration control and fatigue load mitigation are crucial for safe operation of large-scale offshore wind turbines.In view of this,a multi-body model of an offshore bottom-fixed wind turbine including a detailed drivetrain is established in this paper.Then,an individual pitch controller(IPC)is designed using disturbance accommodating control.State feedback is used to add damping in flexible modes of concern,and a state estimator is designed to predict unmeasured signals.Continued,a coupled aero-hydro-servo-elastic model is constructed.Based on this coupled model,the load reduction effect of IPC and the dynamic responses of the drivetrain are investigated.The results showed that the designed IPC can effectively reduce the structural loads of the wind turbine while stabilizing the turbine power out-put.Moreover,it is found that the drivetrain dynamic responses are improved under IPC.

Improving Functionality of 2DOF Piezoelectric Cantilever for Broadband Vibration Energy Harvesting Using Magnets

This paper presents a 2DOF nonlinear piezoelectric energy harvester for improving the efficiency of energy harvesting in low frequency range.The device consisted of an L-shaped piezoelectric cantilever with a magnet at the tip of the first beam and two external magnets on the pedestal.The distance between the magnets which generated nonlinear magnetic attraction was adjusted such that the system can exhibit monostable or bistable characteristics.First,the model of this piezoelectric energy harvester was established and the dynamic equation was derived based on the magnetic attractive force.Then,the nonlinear dynamic responses of the system subject to harmonic excitation were explored by a numerical method and validated by experiments.At an excitation level of 4 m/s^(2)in reverse sweep test for the proposed nonlinear harvester,nearly 240%increase in frequency bandwidth was obtained compared to 2DOF linear one in the first two resonance regions under both monostable and bistable states.Moreover,the nonlinear device yielded a closer frequency band gap between the first two resonance regions.The findings provide insight for the design of a broadband energy harvester when there is nonlinearity using magnets.

Coupled evolution of piston asperity and cylinder bore contour of piston/cylinder pair in axial piston pump

The wear condition of the piston/cylinder pair is crucial to the performance and reliability of the axial piston pump.The hard piston surface,the soft cylinder bore surface,and the interface oil film affects each other during the wear process.Specifically,in the mixed lubrication region,the geometry of the hard piston surface asperity directly affects the wear of soft cylinder bore surface,while the asperities may deform or even degrade when penetrating and sliding against the cylinder bore.So far,there is no suitable method to simulate their coupled evolution.This paper proposed a wear process simulation model considering the real-time interaction between the elasto-plastic deformation of the piston surface asperity,the wear contour of the cylinder bore,and the lubrication condition of the interface.An offline library of the elasto-plastic constitutive behavior of the asperity based on the finite element method(FEM)is established as a part of the simulation model to precisely analyze the deformation and degradation of the asperity and quickly invoke them in the numerical wear process simulation.The simulation and experimental results show that the piston asperity and the cylinder bore contour converge to a steady state after running-in for about 0.5 h.The distribution of the simulated asperity degradation and wear depth is also verified by the experiment.

适应液氧煤油发动机变推力工况的伺服机构设计方案

An electro-hydraulic actuator for the thrust vector control(TVC)of a throttlable kerolox rocket engine is introduced in this paper.The creative feature is an integrated hydraulic power drive unit,where a constant speed kerosene motor is used to draw high pressure kerosene from the engine and to drive a constant pressure variable displacement piston pump,acting as the power supply for the actuator.Its operational mechanism,to accommodate the varying pressure from the turbo-pump of a throttling engine,lies in a pressure-reducing flow regulator inserted at the motor inlet.Another key point is that the displacement of the motor is reasonably bigger than the pump so that a sufficiently wide range of pressures can be adapted.Modeling analysis and flight test results were well matched,which show the outstanding performance of this novel type actuator.

Performance optimization for high speed axial piston pump considering cylinder block tilt

Increasing the rotating speed is considered as an efficient approach to upgrade the power-to-weight ratio in an axial piston pump,but penalized by more leakage and more severe wear resulting from the adverse cylinder block tilt.Previous studies mainly focused on the bearing characteristic of the valve plate/cylinder block pair,but the spline coupling also plays a key role in the undesired cylinder block tilt,which has been little studied.A theoretical model for the rotating assembly is presented to investigate the effect of the spline coupling length on the cylinder block tilt and the performance of the valve plate/cylinder block pair.A typical high-speed axial piston pump with the displacement of 5.2 mL/r at 10000 r/min was studied by simulation and experiment.It shows that the optimal spline coupling length is one value increased by 2 mm from the original,bringing a remarkable leakage reduction under the high-speed condition by decreasing the cylinder block tilting angle.The experiment result matches well with the simulation.The influences of the spline coupling on the cylinder block tilt and the leakage were demonstrated.