Numerical Research on a Three-Dimensional Solid Element Based on Generalized Elasticity Theory

A finite element equation is established based on generalized elasticity theory by applying a virtual work principle. Then, a penalty function term is added to the virtual work equation by imposing rotation and displacement as independent variables. An 8-node element with full integration, an 8-node element with reduced integration, and a 20-node element with full integration are constructed using difference integration schemes and shape functions. The influences of structural degrees of freedom and the penalty parameter on convergence are analyzed via the three elements. It is shown that the 8-node element with reduction integration and the 20-node element with full integration are convergent, whereas the 8-node element with full integration is divergent. The scale effects of a slender beam, a short beam, a thin plate, and a medium-thick plate are numerically analyzed. Lastly, the scale effects of the frequencies that correspond to the bending mode, torsion mode, and tension-compression mode for a pretwisted plate are studied. It is found that the frequencies that correspond to the bending mode and torsion mode exert a scale effect, whereas the frequency that corresponds to the tension-compression mode does not. The essence of the scale effect is that the rotational deformation of the microstructure is amplified.

Cosmological dark sector from a mimetic–metric–torsion perspective

We generalize the basic theory of mimetic gravity by extending its purview to the general metric-compatible geometries that admit torsion, in addition to curvature. This essentially implies reinstating the mimetic principle of isolating the conformal degree of freedom of gravity in presence of torsion, by parametrizing both the physical metric and torsion in terms of the scalar ‘mimetic’ field and the metric and torsion of a fiducial space. We assert the requisite torsion parametrization from an inspection of the fiducial space Cartan transformation which, together with the conformal transformation of the fiducial metric, preserves the physical metric and torsion. In formulating the scalar–tensor equivalent Lagrangian, we consider an explicit contact coupling of the mimetic field with torsion, so that the former can manifest itself geometrically as the source of a torsion mode, and most importantly, give rise to a viable ‘dark universe’ picture from a mimicry of an evolving dust-like cosmological fluid with a nonzero pressure. A further consideration of higher derivatives of the mimetic field in the Lagrangian leads to physical bounds on the mimetic–torsion coupling strength, which we determine explicitly.

Coupled and Multimode Tailboom Vibration Control Using Fluidic Flexible Matrix Composite Tubes

This paper covers the modeling and testing of a helicopter tailboom integrated with a fluidic flexible matrix composite (F2MC) damped vibration absorber. In an advance over previous work, the F2MC absorber presented in this paper treats a combination of tailboom lateral, torsional, and vertical vibrations. A finite element structural model of a laboratory-scale tailboom is combined with a model of attached F2MC tubes and a tuned fluidic circuit. Vibration reductions of over 75% in a coupled 26.8-Hz lateral bending/torsion tailboom mode are predicted by the model and measured experimentally. These results demonstrate that F2MC vibration control is viable at higher frequencies and for more complex vibration modes than previous research had explored. A new absorber with a fluidic circuit that targets two tailboom vibration modes is designed and experimentally tested. On the lab-scale tailboom testbed, the absorber with this circuit is shown to provide vibration reductions of over 60% in both a 12.2-Hz vertical mode and a 26.8-Hz lateral bending/torsion mode. Using this new absorber, vertical and lateral/torsion mode damping are achieved with almost no added weight relative to a purely vertical absorber.

Analysis of Detection Quality for Ultrasonic Guided Wave With L(0,2) and T(0,1) in the Pressure Pipe

Torsion mode and longitudinal mode are used primarily in ultrasonic guided wave inspection, especially L (0, 2) mode and T (0, 1) mode. There are some differences between them, like excitation method, mode of particle vibration, inspection ability and impact factor. So, it is very important to select the appropriate mode between L (0,2) and T(0,1). In this paper, the detection ability of two guided wave modes are compared and analyzed with regard to four aspects in the pipe: fluid, liquid level, defects, the angle between defect and wave propagation direction. The experimental results show that L (0,2) mode is more suitable for defect detection in pressure pipe than T (0,1) mode, but L (0,2) mode is more sensitive to fluid in a pipe. This paper provides a basis for selecting the mode of guided waves in ultrasonic detection.

A Mechanical Beam Resonator Engineered at Nanoscale for Ultralow Thermoelastic Damping

ABSTRACTA mechanical beam resonator engineered at nanoscale for suppressing thermoelastic damping to obtain ultrahigh quality factor is reported. The resonator employs the torsion mode of a spring beam to excite the rotation oscillation of a nanoscale resonant beam. The ultralow thermoelastic damping in the resonator is obtained by employing torsion oscillation. Optimal study of thermoelastic damping is carried out by varying the dimensional parameters of the resonator. The resonator operating in the MHz regime with the quality factor over one million is obtainable by the proposed oscillation exciting method and appropriate design of dimensional parameters of the beams. In order to obtain such overall intrinsic quality factor, virtual supports are employed to eliminate attachment loss in the resonator.

Vibration Suppression of a Cantilever Plate Using Magnetically Multimode Tuned Mass Dampers

For a few decades, various methods of suppressing structural vibration have been proposed. The present study proposes and exploits an effective method of suppressing the vibration of cantilever plates similar to the solar panels of a satellite. Magnetically tuned mass dampers (mTMDs) are a tuned mass damper (TMD) with eddy current damping (ECD). We introduce the mTMD concept for the multimode vibration suppression of the cantilever plate. The design parameters of the mTMD are determined based on the parametric study of the theoretical four-degree-of-freedom model, which was derived for a cantilever plate with TMDs. Two TMDs are optimized for the first bending mode and first torsion mode of the plate, and they are verified analytically and experimentally. To increase the damping performance of the TMDs, ECD is introduced. Its damping ratios are estimated analytically and verified experimentally.

Hot Torsion Tests - A Reliable Rolling Simulation Method for C-Mn Steels

Torsion tests have been proven to be a successful method to simulate the hot rolling of steels. Simulation work performed at a laboratory scale together with the analysis of the resulting mean-flow-stress behavior, leads to important metallurgical information to be considered during full-scale rolling processes. In this work, two different hot deformation schedules of C-Mn steels have been performed on a Gleeble simulation system in hot torsion mode. In addition to the torsion tests, the mean-flow-stresses of industrial rolling data were analyzed. Industrial hot deformation schedules simulated using hot torsion and the mean-flow-stress values were plotted versus the inverse of absolute temperature in the same graph. All points match the same behavior showing that torsion testing is a reliable hot working simulation method.