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An application of a polarization-maintaining photonic crystal fiber (PM-PCF) for torsion sensing is proposed and experimentally demonstrated. The response of the sensor is theoretically validated using the Jones matrix. High normalized sensitivity of ~0.014/[degrees] was measured within a linear twist angle range from 30[degrees] to 70[degrees]. The sensor response was observed to be highly repeatable over a 90[degrees] twist in both the clockwise and counterclockwise directions. The proposed sensor exhibits reduced temperature sensitivity due to the low thermal coefficient of PM-PCF, making it an ideal candidate for torsion sensing. OCIS codes: 060.2370, 060.3735.

The article explains the development of a new longitudinal-torsional hybrid-type ultrasonic motor, which is shown to exhibit large torque and low revolution speed. The motor is shown to be small, light and noiseless with a hollow and short cylindrical structure.

A theoretical analysis, associated simulations and tests of the coupling between the torsional waves in a semi-infinite cylindrical wave guide and a viscous fluid on the interface boundary for two viscometer configurations are presented. It is concluded that the product of the viscosity and the density of the fluid can be measured from the end reflection coefficient of the torsional wave in the wave guide.

High resolution by microwave Fourier transform spectroscopy (FTMW) is used to study the ground state rotational spectrum of B[F.sub.2]OH. The small torsional splitting is analysed using a phenomenological model developed for HN[O.sub.3].

Nonlinear torsional motions in a long circular rod with relatively large shear deformation are studied. Results prove useful in the understanding and design of devices operating with torsional modes.

The study explains the effects of the bending and torsion strains on the values of the critical current in various YBCO coated conductors. The bend of the coil is shown to be extremely sensitive to the sample-tape thickness, as well as the sample-tape width.

The study describes the critical current degradation behavior in the long length YBCO coated conductors that are subjected to torsional strain. The critical current is found to degrade gradually and slowly in these films.

Stability of a cemented implant, once the stem-cement interface has debonded, is reliant upon stem geometry and surface finish. There are relatively few studies addressing the effect of cross-sectional stem shape on cemented implant fixation. The purpose of this investigation was to compare the torsional stability of five different stem cross-sectional shapes--circular, oval, triangular, rectangular with rounded edges, and rectangular with sharp edges--under monotonically increasing and cyclic loading conditions. Seven samples of each stem geometry were tested. Stems were potted in bone cement and loaded to 5 deg of rotation. For monotonic loading, torque was applied at a constant rate of 2.5 deg/min. For cyclic loading, a sine wave torque pattern was applied, with a maximum magnitude that began at 4.5 Nm for 1500 cycles and then increased by 2.25 Nm every 1500 cycles until 5 deg of rotation. The rectangular stem with the sharp edges always provided the greatest resistance to torque, followed by the rectangular with rounded edges, triangular, oval, and circular. These results, including the effects of sharp corners, may differ for modes of loading other than torsion. These experimental results support the findings of earlier finite element models, indicating stem shape has a significant effect on resistance to torsional loading. [DOI: 10.1115/1.2720907] Keywords: implant fixation, implant design, cemented implant failure, torsional stability, arthroplasty

This paper deals with the application of neural networks (NNs) to the mechanical state estimation of the drive system with elastic joint. The torsional vibrations of the two-mass system are damped using the control structure with additional feedbacks from the torsional torque and the load-side speed. These feedbacks signals are obtained using NN estimators. The learning procedure of the NNs is described, and the influence of the input vector size to the accuracy of the state-variable estimation is investigated. The neural estimators of the torsional torque and the load machine speed are tested with open-loop and closed-loop control structures. The simulation results are confirmed by laboratory experiments. Index Terms--Neural networks (NNs), state variable estimation, torsional vibration, two-mass system.

In this paper, consideration is given to the dynamic response of a rotating cantilever twisted and inclined airfoil blade subjected to contact loads at the free end. Starting with the basic geometrical relations and energy formulation for a rotating Timoshenko beam constrained at the hub in a centrifugal force field, a system of coupled partial differential equations are derived for the combined axial, lateral and twisting motions which includes the transverse shear, rotary inertia, and Coriolis effects, as well. In the mathematical formulation, the torsion of the thin airfoil also considers a very general case of shear center not being coincident with the CG (center of gravity) of the cross section, which allows the equations to be used also for analyzing eccentric tip-rub loading of the blade. Equations are presented in terms of axial load along the longitudinal direction of the beam which enables us to solve the dynamic pulse buckling due to the tip being loaded in the longitudinal as well as transverse directions of the beam column. The Rayleigh-Ritz method is used to convert the set off our coupled-partial differential equations into equivalent classical mass, stiffness, damping, and gyroscopic matrices. Natural frequencies are computed for beams with varying 'slenderness ratio' and 'aspect ratio' as well as 'twist angles.' Dynamical equations account for the full coupling effect of the transverse flexural motion of the beam with the torsional and axial motions due to pretwist in the airfoil. Some transient dynamic responses of a rotating beam repeatedly rubbing against the outer casing is shown for a typical airfoil with and without a pretwist. [DOI: 10.1115/1.2423035]

Classical molecular dynamics simulations are used to examine the mechanical responses of several different carbon nanotube systems to applied torsional loading at various temperatures. The simulations have shown that the critical buckling moment can be modified by adjusting the system temperature and through chemical functionalization of the carbon nanotube walls.

A number of common fallacies regarding various theories of relativity and methods of falsification thereof are considered in this paper. A 'weak' principle of relativity implicitly applied in theories of [...]

To investigate the flutter characteristics of cascading blades in multiple blade rows, the computation program to calculate the unsteady blade loading based on the unsteady lifting surface theory for contra-rotating annular cascades was formulated and coded. Then a computation program to solve the coupled bending-torsion flutter equation for the contra-rotating annular cascades was also developed. Some results of the flutter analysis are presented. It is shown that the presence of the neighboring blade row gives rise to substantial change in the critical flutter condition irrespective of the blade row gap when the main acoustic duct mode is of cut-on state. The effect of the neighboring blade row is also significant irrespective of the state of the main acoustic duct mode when the blade rows are very closely placed. DOI: 10.2514/1.22561

This paper investigates the shear buckling of flat, stiffened panels of specially orthotropic skin material, for which the stiffeners are assumed to possess both flexural and torsional rigidity. It is shown that the shear buckling behavior can be captured by four generic, nondimensional panel parameters, two of which relate to the skin orthotropy, the other ones representing the flexural and torsional stiffness of the stiffeners. Several design curves, showing the nondimensional shear buckling load as a function of these four panel parameters, are generated using the STAGS FEM code. The validity of the FEM method is demonstrated through comparison with an analytical procedure based on the Rayleigh-Ritz and Lagrangian multiplier methods. Furthermore, to assess the accuracy of the design curves a number of Glare panels containing stiffeners of different shapes and attachment methods typically applied in aerospace structures are analyzed as well. These particular FEM analyses are more realistic than the ones used to generate the design curves in the sense that the exact shape of the stiffeners is modeled and the attachment method is explicitly accounted for. It is shown that the predictions from the design curves are in reasonable agreement with the detailed FEM results.

The torsional buckling analysis of multiwalled carbon nanotubes subjected to thermal load is studied and numerical results of the general case are presented for thermal effect. It is concluded that at room or lower temperature the critical torsional load of a multiwalled carbon nanotube increases as the value of temperature change increases, while at higher temperature than room temperature the critical torsional load decreases as the value of the temperature change increases.

A dynamic analysis is performed for torsional resonance (TR) and lateral excitation (LE) modes of atomic force microscopy (AFM) by considering the coupling between the cantilever torsion and lateral bending. Parametric analyses show that in TR and LE modes, the pure torsional approximation can provide accurate cantilever responses if the lateral tip-sample interaction is weak when compared to the cantilever torsional stiffness.

In structural design of steel structures in fire, the failure criterion needs to be checked for all members under individual design actions or a combination of them. For space frames, combined design actions usually include forces due to bending, axial, shear, and torsion. An increase in temperature will result in changes to these forces as well as the diminution of the failure criterion due to reduced member capacities as a result of these combined design actions. This paper presents an elastic method for the prediction of limiting temperature of members in space steel frames. Since the critical temperature of the structure corresponds to the ultimate failure of the member with the lowest limiting temperature, this elastic method is equivalent to finding the location of the first plastic hinge in a general plastic analysis. By considering the degradation of the mechanical properties of steel in fire, a formulation based on the failure criterion of combined design actions including torsion is presented for limiting temperature calculation. The fundamentals of the solution strategy are also explained. CE Database subject headings: Torsion; Temperature; Steel structures; Fire hazards; Fire resistance.

This paper introduces a small-signal dynamic model of a fixed-frequency (induction machine based) wind farm connected to an electrical power system. The model represents the system small-signal dynamics in the frequency range of a fraction of Hz to 50/60 Hz. The model includes the dynamics of the wind energy capturing mechanism, the rotating shaft system, the generator electrical system of each wind energy unit, the wind farm collector system, and the utility grid. Based on the proposed model, two performance indices are introduced to i) investigate sensitivity of the system modes, e.g., torsional modes, to the system parameters, and ii) evaluate the system capability to reject electrical and mechanical disturbances, e.g., a wind gust. The application of the model to the analysis of a system with two wind units is presented and the study results are validated based on comparison with the time-domain simulation results obtained in the PSCAD/EMTDC environment. Index Terms--Fixed-speed wind farm, sensitivity analysis, small-signal dynamics, torsional phenomenon.

Abstract: Through out this paper an experimental study was carried out to study the static torsion capability of hybrid aluminum glass fiber composite shaft. A hybrid shaft was fabricated using [...]

Ab initio calculations for determining the relative stabilities and the sizes of the torsional barriers that hinder the internal rotation are discussed. This method produces observable parameters and represents an improvement of the usual way consisting in the direct determination of the parameters from ab initio force fields.

A torsional dependence of electron spin-spin exchange coupling in trimethylenemethane (TMM)-type dinitroxide biradicals is described. This torsional dependence is compared with an analogous series of TMM-type bis(semiquinone) biradicals.

This paper presents a study developed on a three-phase 11-MW synchronous motor with a solid salient-pole rotor of a blower drive system of a blast furnace at the Companhia Siderurgica Belgo-Mineira, Joao Monlevade, Brazil. A mechanical model including motor, gears, couplings, and blower is used in a simulation study to evaluate the torsional dynamics and stresses during motor startup and voltage sag conditions. In addition, the operation of the synchronous motor under voltage sag is analyzed with a comparative study between complete and approximated models of the motor. The utilization of a dynamic voltage restorer to protect the drive system under this abnormal situation is also evaluated. Index Terms--Power quality, simulation models, synchronous motors.

A Ch stretching methyl torsional model is used to simulate the methyl band overtone profiles. This model is applied to a series of molecules with torsional barriers ranging from 5 to about 500 cm(super -1), and the methyl CH-stretching overtone band structure for most barrier heights is explained.

Steel angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion. However, many design codes do not have any design rules for torsion, while some recommendations are unnecessarily conservative, or are of limited application, or fail to consider some effects which are thought to be important. In this paper, proposals are developed for the section capacities of angle sections under bearing, shear, and uniform torsion. In a companion paper, consideration is given to the first-order elastic analysis of the biaxial bending of angle section beams, including the effects of restraints, and proposals are developed for the section moment capacities of angle sections under biaxial bending. The proposals in this and the companion paper can be used to design steel angle section beams which are laterally restrained so that lateral buckling and second-order effects are unimportant. DOI: 10.1061/(ASCE)0733-9445(2002)128:11(1394) CE Database keywords: Bearing capacity; Shear; Torsion; Angle section; Steel; Biaxial bending; Elastic analysis.

The paper introduces the circular cross-section corner-filleted flexure hinges as connectors in three-dimensional compliant mechanism applications. Compliance factors are derived analytically for bending, axial loading and torsion. A circular cross-section corner-filleted flexure hinge belongs to a domain delimited by the cylinder (no fillet) and the right circular cross-section flexure hinge (maximum fillet radius). The analytical model predictions are confirmed by finite element simulation and experimental measurements. The circular cross-section corner-filleted flexure hinges are characterized in terms of their compliance, precision of rotation and stress levels. [DOI: 10.1115/1.1480022]

The active twist rotor investigated in this research is a derivative of the previously developed smart-active-blade-tip (SABT) rotor. On the SABT rotor, the blade tips are independently pitched, with respect to the main blade. A novel piezo-induced bending-torsion coupled actuator beam, located spanwise in the hollow midcell of the main rotor blade, is used to actuate the blade tip. When the blade tip is locked to the main blade, the actuator beam twists the entire blade. A Mach scale rotor with a 1.542 m diameter was hover tested, open loop, to evaluate the control authority for vibration reduction. A nonrotating tip-twist amplitude of 0.78 deg was achieved (below resonance, 150 V rms). Analysis indicates that no significant twist actuation degradation is expected at full rotor speed. In 2000-rpm hover (tip Mach 0.47), at 8-deg collective, and for a single blade actuation of 150 V rms at 1, 2, and 3 per revolution, respectively, the measured oscillatory thrust coefficients are 1.4 x [10.sup.-3], 0.55 x [10.sup.-3], and 0.7 x [10.sup.-3]. The corresponding finite element model estimated blade twist amplitudes are 0.8, 1,0, and 1.9 deg. Good correlation of the predicted and measured rotor thrust was achieved up to 3 per revolution. The hover test demonstrates the potential of the active twist rotor system using an internal actuation beam and warrants further research for a dedicated next-generation model-scale design and full-scale feasibility study.

Understanding the instability phenomena of rotor-shaft and driveline systems incorporating universal joints is becoming increasingly important because of the trend towards light-weight, high-speed supercritical designs. In this paper, a nondimensional, periodic, linear time-varying model with torsional and lateral degrees-of-freedom is developed for a rotor shaft-disk assembly supported on a flexible bearing and driven through a U-joint. The stability of this system is investigated utilizing Floquet theory. It is shown that the interaction between torsional and lateral dynamics results in new regions of parametric instability that have not been addressed in previous investigations. The presence of load inertia and misalignment causes dynamic coupling of the torsion and lateral modes, which can result in torsion-lateral instability for shaft speeds near the sum-type combinations of the torsion and lateral natural frequencies. The effect of angular misalignment, static load-torque, load-inertia, lateral frequency split, and auxiliary damping on the stability of the system is studied over a range of shaft operating speeds. Other than avoiding the unstable operating frequencies, the effectiveness of using auxiliary lateral viscous damping as a means of stabilizing the system is investigated. Finally, a closed-form technique based on perturbation expansions is derived to determine the auxiliary damping necessary to stabilize the system for the least stable case (worst case). [DOI: 10.1115/1.1460907]

An important design issue of electrostatic torsion actuator is the relative locations of the actuating electrodes, where the bias voltage is applied. These geometrical design parameters affect both the Pull-In angle as well as the Pull-In voltage. In this paper, a new approximated analytical solution for the Pull-In equation of an electrostatic torsion actuator with rectangular plates is derived. The analytical expression is shown to be within 0.1% of the one degree of freedom (1DOF) lumped-element model numerical simulations. Moreover, the analytical expressions are compared with the full coupled-domain finite-elements/boundary-elements (FEM/BEM) simulations provided by MEMCAD4.8 Co-solve tool, showing excellent agreement. The approach presented here provides better physical insight, more rapid simulations and an improved design optimization tool for the actuator. [661] Index Terms--Actuator, design, electrostatic, pull-in, torsion.

It is well known that the homogeneous elastic half space does not allow the torsional surface wave to propagate. The present article attempts to study the possibility of propagation of such waves in a liquid-filled initially stressed poroelastic layer over nonhomogeneous half space. The study concludes that torsional surface waves may propagate in the poroelastic layer. The presence of fluid in pores and initial compressive stresses diminishes the velocity. The nonhomogeneity in rigidity and density of the half space also has a certain role to play in initiating, enhancing, or diminishing the velocity of torsional surface waves. DOI: 10.1061/(ASCE)0733-9399(2002)128:2(184) CE Database keywords: Porous media; Anisotropic materials; Surface waves; Velocity.

The Saint-Venant torsion problem of a circular cylinder reinforced by a nonconcentric circular bar of a different material with an imperfect interface is studied. Conformal mapping together with a Laurent series expansion are employed to analyze the problem. The jump condition in either the warping function or the shear traction, characterizing the imperfect interface, is simulated in the transformed domain in an exact manner. Unlike the problem with perfectly bonded interface, the series solution has to be resolved by a truncation. Numerical illustrations are provided for the torsional rigidity of the cross section. In the case of perfect bonding case, our results agree with that reported in Muskhelishvili. [DOI: 10.1115/1.1406962]

Analytically predicted results of blade-vortex interaction (BVI) airloads, using the second-generation comprehensive helicopter analysis system (2GCHAS), are presented with the experimental results obtained from the higher-harmonic-control aeroacoustic rotor test (HART) program using a 40-percent, Mach-scaled model of the hingeless BO-105 main rotor. Correlations include airloads, blade tip deflections, and tip vortex geometry. The effects on blade airload predictions are studied with higher-harmonic pitch controls (HHC). It was concluded that the blade torsional deflection and the wake system play a very important role in predicting BVI airloads. [DOI: 10.1115/1.1401025]

The mechanism of torsional chatter in drilling differs qualitatively and quantitatively from other types of chatter. In this paper we show that torsional chatter can be explained by the torsional-axial coupling inherent in a twisted beam; the beam 'untwists' and extends in response to an increase in cutting torque. Based on a model of this mechanism, predictions of stability boundaries and chatter frequencies are derived by frequency domain analysis, and confirmed by numerical simulation and experimental tests. The effect of the torsional-axial coupling is opposite that of traditional cutting in that an increase in cutting forces leads to axial extension and greater chip load. Because of this sign difference, the limiting depth of cut is governed by the positive real part of the frequency response function, which explains the unexpected fact that torsional chatter occurs below the natural frequency of the tool. [DOI: 10.1115/1.1381399]

Density functional theory (DFT) calculations are employed at the Becke-3-Lee-Yang-Parr (B3LYP) level using the 6-31+G(d,p) basis set to explain geometrical optimizations on the ground and triplet states of the cis- and trans-stilbenes and of 2,3-diphenylnorbornene. Results on theoretical calculations support that in 2,3-diphenylnorbornene and in cis- and trans-stilbenes torsional motion about the CC double bonds offers more stabilization in the triplet state, instead of phenyl-vinyl torsion.