Numerical Analysis of Flutter in Variable Geometry Compressors

Aeroelastic behaviour of a transonic rotor in a newly designed 1.5 stage compressor with variable geometry is studied numerically in this paper. The stage is intended to be the front part of a one-shafted large frame industrial gas turbine (IGT) compressor. The compressor was designed using open-source software MULTALL and numerical computations were performed using the three-dimensional aeroelasticity code AU3d, which has been tested and validated for many aeroelastic test cases over the past 25 years. Flutter analysis for the 1F mode was performed at various design and off-design operating conditions which are typically experienced in IGT (varied inlet temperature and inlet guide vane angle). Although in all the cases the rotor remained stable, clear trends in aerodynamic damping were observed, which can be explained by shock position. In the last phase, the effects of increased tip gap size on the flutter stability were studied. The increase in tip clearance did not result in flutter; unsteady computations without blade motion showed a tip rotating instability with 11 cells travelling at 84% of the shaft speed in the stationary frame. Due to the frequency proximity between the rotating instability and blade natural vibration mode, large amplitude displacement driven by lock-in was observed in the fluid-structure coupled simulation. It was concluded that this type of aeroelastic instability which can be mistaken for flutter is the main threat for this IGT compressor.

Directivity pattern of the sound radiated from square stepped-plate radiators

A square flat-plate radiator driven by a longitudinal vibrator at the resonant frequency of its fourth-order natural vibration mode at its center for the generation of highly directional ultrasonic radiation in air is studied herein. The radiator was able to create a bending vibration mode whose four straight nodal lines were located at a 45° angle on each side. To obtain highly directional sound, the surrounding area of the four right isosceles triangles formed by a nodal line and two sides is modified to be raised one by half the wavelength of sound radiated in the propagation medium so that surface elements vibrate in phase. Then, the relation among the frequencies, nodal lines of the rhombus mode, and geometrical dimensions of the radiator is determined. The calculated directivity pattern of the stepped-plate radiator is equivalent to that of its corresponding theoretical piston, i.e., a stepped plate is a piston-like radiator. Results show that the measured vibrational-mode shape of the stepped-plate radiator is consistent with the calculated one, and the calculated directivity pattern is almost similar to the measured one.

DETERMINATION OF ASPHALT CONCRETE VISCOSITY BY THE FOUR-POINT BENDING TEST

In this work, a model for the dynamical four-point bending test is present, with particular emphasis on application to an asphalt concrete (AC) composite, a viscoelastic material, based on the Euler-Bernoulli theory, which approaches an equation where the Young modulus E can be substituted by the operator (E + γ∂/∂t), where γ is an internal damping parameter associated to the binder viscoelasticity and t is the time. As course aggregate in the composition of the AC mixture, the sintered aggregate of calcined clay was used, interesting to be employed as an alternative to the lack of natural course aggregate in some regions of the planet, where the presence of sedimentary rocks prevails. The results indicated that γ decreases with the temperature and loading frequency and the apparent noise in the stiffness versus strain curve is resulted from the natural vibration mode of the beam.

Analysis and Optimization of Impact Condition of Power Conditioning Inverter Based on ANSYS

This paper uses the professional finite element analysis software ANSYS to process a certain type of power regulating inverter. The overall finite element model of the inverter is established then the three-way impact condition is analysed according to the requirements of GJB 1060.1-91. Through the modal analysis in ANSYS software, the natural frequency and natural vibration mode of the inverter are calculated. Based on modal analysis of the inverter, the DDAM shock spectrum analysis function is used to analyse the impact condition of the inverter. Through the calculation of the impact condition, the deformation and stress state of the inverter structure under various working conditions are obtained. By analysing the calculation results, the weak position of the inverter structure is found and the corresponding optimization scheme is proposed to improve the dynamic performance and improve the electron. The overall dynamic performance of the inverter cabinet also provides an important reference for the design of subsequent electronic cabinets.

RESEARCH ON THE TYMPANIC MEMBRANE FREE VIBRATION MODEL BASED ON THIN PLATE THEORY

Myringoplasty is one of the routine surgeries in the treatment of tympanic membrane (TM) perforation. Since the anatomic structure of the middle ear cannot be simulated in clinical treatment, the surgery is mainly directed by experiences. Based on the mechanical properties of TM in the anatomy, four hypotheses are presented and TM is simplified as a sectorial annulus plate with fixed boundary condition. This paper proposes a free vibration model of TM. Its natural frequencies of free vibration are obtained by variables separation method and Bessel function. The system of fundamental solutions of fourth-order homogeneous equations can be solved for the analytical expressions of corresponding natural vibration mode. The theoretical model is proved to be valid since the natural frequency of the model is consistent with the experimental data. The effect of geometric parameters and material parameters on TM natural frequency is subsequently discussed in the numerical examples. Especially, the diameter and thickness of TM will cause different natural frequency errors above 40%, while the Young’s modulus and density of TM cause errors below 15% as well.

Vibration Characteristics of Roundabout Swing of HAWT Wind Wheel

Modal testing was used to show that the roundabout swing was a natural vibration mode of the wind wheel of a horizontal-axis wind turbine (HAWT). During the vibration, the blade root was simultaneously subjected to bending and rotary shear stresses. A method for indirect testing and determination of the dynamic frequencies of the typical vibrations of the wind wheel was developed, based on the frequency-holding characteristic of each subsignal during the transmission of the multiple mixed-vibration signals. The developed method enabled simple and accurate acquisition of the dynamic frequencies without destruction of the flow and structural fields. The dynamic vibration stress of the roundabout swing was found to be significantly stronger than those of the first- and second-order flexural vibrations of the blades. By a combination of numerical simulations and tests, it was determined that the pneumatic circumferential force was the primary determinant of the roundabout swing vibration frequencies, the relationship being quadratic. The roundabout swing vibration potentially offers new explanations and analytical pathways regarding the behavior of horizontal-axis wind turbines, which have been found to be frequently involved in fatigue-damage accidents within periods shorter than their design lives.