Adjustable Speed Control and Damping Analysis of Torsional Vibrations in VSD Compressor Systems

This paper proposes a model-based two-degree-of-freedom (2DOF) speed control for a medium voltage (MV) variable speed drive (VSD) connected to a centrifugal compressor (CC) train. Torsional mode excitations in the drive shaft due to converter switching behaviour are considered. An effective description of the harmonics transfer is proposed. The tuning strategy aims to optimize the tracking behaviour of the step and ramp command, taking care of critical speed excitations. The stability of the closed-loop dynamics against time delay and drive parameter variations are studied by means of Nyquist diagrams and time-domain simulations. A descriptive method for the process damping behaviour is proposed. The control strategy is evaluated through simulations as well as an experimental setup, based on a hardware in the loop (HIL) in a master–slave configuration.

Comparative theoretical study of the resonance frequencies of the longitudinal-shear and torsion modes of the magnetoelectric effect in a two-layer magnetostrictive-piezoelectric structure Metglas / GaAs

The article is devoted to a comparative theoretical study of the frequencies of the electromechanical resonance (EMR) of the magnetoelectric (ME) effect in the magnetostrictive-piezosemiconductor structure Metglas / GaAs of the longitudinal-shear and torsional modes. It is found that the resonance frequencies for the torsional mode are approximately 2 times higher than the corresponding frequencies for the longitudinal-shear mode. Therefore, it is quite possible to observe the torsional mode of the ME effect against the background of the longitudinal-shear mode, since the resonance frequencies are well distinguishable. The results obtained can find application in the construction of new ME devices.

Flexural–Torsional Free Vibration Analysis of a Double-Cantilever Structure

This paper aims to investigate the free coupled flexural–torsional vibrations of a double-cantilever structure. The structure consists of two identical Euler–Bernoulli cantilever beams with a piezoelectric layer on top. The beams are connected by a rigid tip connection at their free ends. The double-cantilever structure in this study vibrates in two distinct modes: flexural mode or coupled flexural–torsional mode. The flexural mode refers to the in-phase flexural vibrations of the two cantilever beams resulting in translation of the tip connection, while the coupled flexural–torsional mode refers to the coupled flexural–torsional vibrations of the cantilever beams resulting in rotation of the tip connection. The latter is the main interest of this research. The governing equations of motion and boundary conditions are developed using Hamilton’s principle. Two uncoupled equations are realized for each beam: one corresponding to the flexural vibrations and the other one corresponding to the torsional vibrations. The characteristic equations for both the flexural and the coupled flexural–torsional vibration modes are derived and solved to find the natural frequencies corresponding to each mode of vibration. The orthogonality condition among the mode shapes is derived and utilized to determine the modal coefficients corresponding to each mode of vibration. Moreover, the analytical and experimental investigations show that the coupled flexural–torsional fundamental frequency of the structure is dependent on dimensional parameters including the length of the cantilever beams and the length of the tip connection.

Role of Active Morphing in the Aerodynamic Performance of Flapping Wings in Formation Flight

Migratory birds have the ability to save energy during flight by arranging themselves in a V-formation. This arrangement enables an increase in the overall efficiency of the group because the wake vortices shed by each of the birds provide additional lift and thrust to every member. Therefore, the aerodynamic advantages of such a flight arrangement can be exploited in the design process of micro air vehicles. One significant difference when comparing the anatomy of birds to the design of most micro air vehicles is that bird wings are not completely rigid. Birds have the ability to actively morph their wings during the flapping cycle. Given these aspects of avian flight, the objective of this work is to incorporate active bending and torsion into multiple pairs of flapping wings arranged in a V-formation and to investigate their aerodynamic behavior using the unsteady vortex lattice method. To do so, the first two bending and torsional mode shapes of a cantilever beam are considered and the aerodynamic characteristics of morphed wings for a range of V-formation angles, while changing the group size in order to determine the optimal configuration that results in maximum propulsive efficiency, are examined. The aerodynamic simulator incorporating the prescribed morphing is qualitatively verified using experimental data taken from trained kestrel flights. The simulation results demonstrate that coupled bending and twisting of the first mode shape yields the highest propulsive efficiency over a range of formation angles. Furthermore, the optimal configuration in terms of propulsive efficiency is found to be a five-body V-formation incorporating coupled bending and twisting of the first mode at a formation angle of 140 degrees. These results indicate the potential improvement in the aerodynamic performance of the formation flight when introducing active morphing and bioinspiration.

Feasibility of Lead Fast Reactor Heat Exchanger Tube Online Monitoring

Online structural health corrosion monitoring in advanced lead fast reactor heat exchangers and molten salt reactor heat exchangers is desirable for detecting tube degradation prior to leaks that may allow mixing of heat exchanger fluids or release of radiological contamination beyond the design containment boundary. This program demonstrates feasibility for a torsional mode sensor to attach to the outside of a long (30-m) heat-exchanger tube in the stagnant flow area where the tube joins the heat-exchanger plenum and where it is possible to protect a sensor and cable from high-force flows. The sensor must be connected by a cable to a monitoring instrument near the heat exchanger. The sensor and cable management approach will be impractical to implement on existing heat exchangers; rather, sensors must be installed in conjunction with heat exchanger fabrication. Previous work has shown the ability of low-temperature lead zirconate titanate (PZT) piezoceramic sensors to detect anomalies of interest in 3-m tubes. These sensors have subsequently been extended to a 30-m tube more representative of commercial power heat exchanger designs. The program will continue to investigate higher-temperature piezoelectric ceramics and long-term performance of high-temperature adhesives and sealants for 350 C lead reactor environments and higher-temperature (700 °C) molten salt environments.

The interaction of fundamental torsional guided waves from axial and oblique defects in pipes

A quantitative study of the interaction of the T(0,1) torsional mode with axial and oblique defects in a pipe is presented in this paper. A mode decomposition technique employing the chirplet transform is used to separate the multimodal signals reflected from the defects. Reflection signals are obtained from experiments on a carbon steel pipe. The influence of the crack length and inclination angle on the reflection is investigated. The reflection from an axial defect is found to consist of a series of wave pulses with gradually decaying amplitude. The results show that the reflection coefficient of an axial crack initially increases with the crack length but finally reaches an oscillating regime. Furthermore, for an oblique crack, it is revealed that the reflection coefficient is linearly dependent on the equivalent circumferential extent of the defect and is independent of the axial length.

Effect of Boundary Conditions on Fluid–Structure Coupled Modal Analysis of Runners

To predict the resonance characteristics of hydraulic machinery, it is necessary to accurately calculate the natural modes of the runners in the operating environment. However, in the existing research, the boundary conditions of the numerical modal analysis of the runner were not unified. In this paper, numerical modal analysis of a prototype Francis pump turbine runner was carried out using the acoustic–structure coupling method. The results of three different constraints were compared. The influence of the energy loss on the chamber wall on the natural modes of the runner was studied by the absorption boundary. The results show that the constraint condition (especially the rotating shaft) has significant impacts on the torsional mode, the radial mode, the 1 nodal-diameter mode, and the 0 nodal-circle mode, and the maximum differences in the natural frequencies under different conditions are 69.3%, 56.4%, 35.1%, and 9.4%, respectively. The change of the natural frequencies is closely related to the modal shapes. On the other hand, the energy loss on the wall mainly affects the nodal-circle modes, and the influence on other modes is negligible. The results can provide references for the design and resonance characteristics analysis of hydraulic machinery runners.