Influence of the Blade Bifurcated Tip on the Correlation between Wind Turbine Wheel Vibration and Aerodynamic Noise

To reduce the vibration and aerodynamic noise of wind turbines,a new design is proposed relying on a blade with a bifurcated apex or tip.The performances of this wind turbine wheel are tested at the entrance of a DC(direct-action)wind tunnel for different blade tip angles and varying centrifugal force and aerodynamic loads.The test results indicate that the bifurcated apex can reduce the vibration acceleration amplitude and the vibration fre-quency of the wind wheel.At the same time,the bifurcated apex can lower the maximum sound pressure level corresponding to the rotating fundamental frequency of the wind wheel.According to all thesefindings,the tip angle of the bifurcated apex is the main factor enhancing the effect of the modification.

A critical review of wheel/rail high frequency vibration-induced vibration fatigue of railway bogie in China

Purpose–This review aims to give a critical view of the wheel/rail high frequency vibration-induced vibration fatigue in railway bogie.Design/methodology/approach–Vibration fatigue of railway bogie arising from the wheel/rail high frequency vibration has become the main concern of railway operators.Previous reviews usually focused on the formation mechanism of wheel/rail high frequency vibration.This paper thus gives a critical review of the vibration fatigue of railway bogie owing to the short-pitch irregularities-induced high frequency vibration,including a brief introduction of short-pitch irregularities,associated high frequency vibration in railway bogie,typical vibration fatigue failure cases of railway bogie and methodologies used for the assessment of vibration fatigue and research gaps.Findings–The results showed that the resulting excitation frequencies of short-pitch irregularity vary substantially due to different track types and formation mechanisms.The axle box-mounted components are much more vulnerable to vibration fatigue compared with other components.The wheel polygonal wear and rail corrugation-induced high frequency vibration is the main driving force of fatigue failure,and the fatigue crack usually initiates from the defect of the weld seam.Vibration spectrum for attachments of railway bogie defined in the standard underestimates the vibration level arising from the short-pitch irregularities.The current investigations on vibration fatigue mainly focus on the methods to improve the accuracy of fatigue damage assessment,and a systematical design method for vibration fatigue remains a huge gap to improve the survival probability when the rail vehicle is subjected to vibration fatigue.Originality/value–The research can facilitate the development of a new methodology to improve the fatigue life of railway vehicles when subjected to wheel/rail high frequency vibration.

PHENOMENON OF CARVED DRIVING WHEELS

A newly found phenomenon of carved driving wheels of a rear-wheel-drive tractor used in an airport is discussed. The circum of every driving wheel is damaged at three regions, which distribute regularly and uniformly. Everyday, the tractor tows a trailer which are times heavier than the tractor, and moves on the same road in the airport. The phenomenon is explained by the torsional self-excited vibration system of the powertrain. The simplified torsional vibration system is discribed by a 2-order ordinary differential equation, which has a limit circle. Experiments and numerical simulations show the followings： Because of the heavy trailer, the slip ratio of the tractor＇s driving wheels is very large. Therefore, there is severe torsional self-excited vibration in the tractor＇s drivetrain, and the self-excited vibration results in severe and regular fluctuations of the rear wheel＇s velocity. The severe fluctuations in velocity fastens the damage of the driving wheels. At the same time, the time interval in which an arbitrary point in the circum of the driving wheel contacts with the road twice is two times more than the period of the torsional self-excited vibration, and this times explained the existence of three damaged regions. At last, it points out that the phenomenon can be avoided when the torsional damping is large enough.

Analysis and Testing of Microvibrations Produced by Momentum Wheel Assemblies

The microvibrations produced by momentum wheel assemblies（MWA） can degrade the performance of instruments with high pointing precision and stability on spacecraft.This paper concentrates on analyzing and testing the microvibrations produced by MWA.We analyze the disturbance sources produced by mass imbalance,structural mode,bearing irregularity and nonlinear stiffness,and random noise;then,test a well-balanced MWA by a highly sensitive measurement system consisting of a Kistler table and an optical tabletop.The results show that the test system has a resolution of less than 0.003 N in the frequency range of 3-300 Hz.The dynamic imbalance of the MWA cannot excite the radial rocking mode,but there are dynamic amplifications when the poly-harmonic disturbances intersect with the structural modes.Especially at high rotational speed（〉3 000 rev/min）,the main disturbance sources of the MWA come from the bearing irregularity interacting with radial translation mode in the high frequency range.Thus,bearing noise deserves more attention for the well-balanced MWA,and alternative of high quality bearings are proposed to reduce the microvibrations.