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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.

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.

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.

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.

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.

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 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.

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.

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.

Research shows that ATP-dependent chromatin remodeling generates negative superhelical torsion in DNA and chromatin during gene regulation. Data indicate that all Snf2p-related ATPase motors possess this activity as exemplified by the yeast SWI/SNF complex, Xenopus Mi-2 complex, recombinant ISWI and BRG1.

When a doubly symmetric I-beam buckles elastically in a lateral-distortional mode, its web distorts, so that the two flanges have increased relative lateral displacements and may have different twist rotations. The centroid, shear center, and principal axes of the distorted cross section are all different from those of the undistorted cross section. The end connections to adjacent members may induce flange restraining moments that oppose warping deformations and modify the elastic buckling resistance. This paper investigates the effects on the lateral-distortional buckling of beams of web distortion and of the warping restraints induced by end-support conditions. It is found that a doubly symmetric I-section becomes unsymmetric during lateral-distortional buckling and that web distortion reduces the effective torsional and warping rigidities. The proposed approximations for the elastic lateral-distortional buckling resistances of beams without and with end warping restraints provide good predictions. Equations for the warping restraint stiffness induced by some commonly used end conditions are established. Comparisons with ABAQUS shell element results show that they provide good approximations.

This paper studies the possibilities of propagation of torsional surface waves in nonhomogeneous anisotropic half-space under compressive initial stress. Two types of variations in nonhomogeneity, mainly hyperbolic and quadratic, have been discussed, and it is observed that in both cases the torsional surface wave will propagate in the media under consideration. The velocities of propagation have been computed and are presented in graphs. The study shows that for hyperbolic variation of nonhomogeneity, the increase of the anisotropic factor, increases the velocity of propagation, always keeping it more than that of shear wave in homogeneous medium. The presence of initial stress increases the velocity of propagation. In the case of quadratic variation it is found that the presence of initial stresses increases the velocity of propagation. The increase of anisotropy decreases the velocity, and the decrease in the nonhomogeneity factor increases the velocity, always keeping the velocity of torsional surface waves less than that of shear wave in the homogeneous medium.

The main purpose of the present article is to exhibit the power and potential of the initial values method by means of the solution of a crucial problem. First, the initial values method is presented and a general carryover matrix is obtained for plane rods loaded perpendicular to their plane. Then an example is solved and. the advantages of the method are depicted.

Along-wind, crosswind, and torsional vibrations of structures are different aspects of the same physical phenomenon. Despite this fact, each aspect has been the object of numerous studies involving lines of research that have frequently been independent of each other. These independent lines of research have often been characterized by notable inconsistencies and clashes. This paper proposes a single coherent formulation that provides compact expressions for estimating the along-wind, crosswind, and torsional response based on a generalized gust factor approach. It presents the wind-loading model and uses a generalized equivalent spectrum technique to derive closed-form solutions of the 3D wind-excited response of slender structures and structural elements. This extends a solution previously obtained for along-wind vibrations to the crosswind and torsional response. Numerical examples are provided that illustrate the simplicity and precision of this method. Because of this simplicity and precision, the method is suitable for use in design offices as a means of providing rapid estimates of the dynamic response of slender structures to gust buffeting actions. In particular, the estimates of the crosswind and torsional response will allow the designers to make more informed decisions on when to conduct physical model studies in boundary-layer wind tunnels.

This is the second of two papers concerned with the development and the application of a smeared crack model for the description of the behavior of concrete elements in torsion. The first paper presented the development of an efficient model for the torsional analysis of concrete that utilizes a special numerical technique, which is properly adapted to include the smeared crack approach. This paper presents the validation of the analytical model by providing comparisons between analytically predicted behavior curves and experimentally obtained ones. The experimental data used in this paper comprise a series of tests in pure torsion conducted for this purpose and a database of experimental information compiled from works around the word, in an attempt to establish the validity of the proposed approach based on a broad range of parametric studies. From the comparisons between the predicted and the measured data, it is concluded that the proposed approach describes very well the behavior of concrete elements in pure torsion and yields satisfactory results for the case of nonrectangular elements subjected to combined torsion with flexure, shear, and axial force.

This is the first of two papers addressing the efficient approach of the torsional behavior of concrete elements through smeared crack analysis. This paper presents the development of an analytical model for the behavior of concrete elements in increasing torsion. The model is based on a special numerical technique that employs constitutive relations expressed in terms of normal stress and crack width, for the behavior of the crack process zones. The width of a crack process zone is considered as a material property and is estimated through comparisons between analytical and experimental data. The method is not restricted by the cross section shape because the analysis includes numerical mapping. Examination of the objectivity of the proposed analysis in relation to the used mesh density is included in the study. The proposed approach is also applicable to concrete elements subjected to torsion combined with flexure, shear, and axial force. Validation of the analytical model derived in this paper is demonstrated in a companion paper using extensive comparisons between predicted and experimentally obtained behavior curves and ultimate torque values.

A member model divided into subelements along the member axis with end fibers is developed for material and geometrical nonlinear analysis of a space frame structure. The fiber stress-strain relationship is an extended Ramberg-Osgood model. To assume appropriate stiffness on the alternative of fiber loading or unloading, a trial stiffness selection procedure is presented. Analytical increments for an overall frame are set relatively large for application to a frame with many members. Analytical results for a simple truss agreed well with experimental results and simulated the complicated behavior of a web member, which first buckled slightly, then was unloaded, and finally rebuckled in another mode under a monotonous loading.

The torsion of a compound bar is studied by eigenfunction expansion and collocation. The bar has a regular polygonal cross section bonded with a circular core of different material. It is found that the torque is insensitive to the core size when the latter is less than 0.2 of the maximum dimension. Otherwise, the torque is highly dependent on the core size ratio and the shear moduli ratio of the two materials. The results obtained should be useful in the design of torsion members.

The objective of this paper is to present the feasibility of applying Vlasov's theory of thin walled bars to model the behavior of rib-reinforced cantilevered plates. A simple analytical model based on Vlasov's theory is presented and validated against experimental results. It is shown that the presented theoretical method is simple and sufficiently accurate to be used as a design tool. The presented approach is also valid for plates fabricated from composite materials.

The tension-torsion problem for pretwisted antisymmetric laminated composite strips is formulated without ad hoc shell-type assumptions. No restrictions regarding the thickness-to-width aspect ratio are made. The elasticity equations are derived first and solved exactly for the torsional rigidity of orthotropic strips. An approximate solution is derived for angle-ply laminates. The torsional rigidity predictions are compared with a shell-type closed-form solution and finite-element simulations. An iterative method, which allows for the development of closed-form one-term approximations in a number of boundary-value problems, is presented. The accuracy of the method is illustrated by comparison with exact solutions for two benchmark problems.

This paper extends a simple method of analyzing the plastic torsion collapse of compact equal flange I-section beams to monosymmetric and point-symmetric beams. The method can be used manually, is much easier than elastic analysis, and is no more difficult than the plastic collapse analysis of beams in bending. The use of plastic torsion analysis avoids the conservatism of first yield analysis and design because it accounts for the spread of plasticity through the cross section and the redistribution of torque that occurs in redundant members after the first hinge forms. Designs based on plastic analyses of torsion will lead to significant economies over the first yield designs based on elastic analysis. Equations are developed in this paper for the uniform torsion plastic torques and for the plastic bimoments of monosymmetric I-sections, lipped and unlipped channels, and equal flange lipped angles, and of point-symmetric lipped and unlipped Z-sections. A worked example of the plastic torsion collapse and design of a lipped channel is present.

In the resonance ratio control, which we proposed for vibration suppression and disturbance rejection in a torsional system, the estimation speed of the disturbance observer should have been much faster than the resonance frequency of the controlled system. However, a too fast disturbance observer sometimes causes an implementation problem. In this paper, we give the optimal speed of the disturbance observer and propose a novel technique named 'slow resonance ratio control.' It does not have any fast part in the controller. It also enables us to design the speed control and the vibration suppression control almost completely independently. Index Terms - Disturbance observer, disturbance rejection, observer pole design, resonance ratio, robust control, speed control, suppression, torsional system, vibration.

In a previous paper, the writers presented a one-dimensional analytical model for the static analysis of multicell, thin-walled beams with nonhomogeneous cross sections. The proposed model accounts for shear deformations due to nonuniform bending and torsion supplementing the primary effects considered by the classical models. Here, the constitutive relations for the beam model are given and the dynamic analysis of the shear core is considered by a proper generalization of the continuous formulation. An algebraic procedure is given to evaluate the equivalent mechanical properties of the cross section. Moreover, a one-dimensional hierarchical finite element formulation is proposed for displacements and rotations. The proposed model is shown to cover the analysis of multicell, thin-walled beams, having regular cutouts, as is typical of shear cores of tall buildings. The applications include solutions to both the continuous and the discrete models.

The paper explores the dependence of torsional modes of turbogenerator on the uncertainty in the shaft spring constant (stiffness). The analysis is performed on a typical single machine infinite bus system. Small-signal stability analysis as well as large-disturbance analysis are performed on five rotational mass mechanical system. Different operating conditions of the generator are examined. It is shown that the spring constant (stiffness) of the shaft can significantly influence damping and frequency of torsional modes. Effects on maximum torsional torques developed in the shaft following large disturbance in the electrical system are also analysed. The paper underlines the importance of accurate modelling of the turbine-generator shaft for studies of torsional oscillations and subsynchronous resonance.

A general formulation for torsional-flexural analysis of beams with arbitrary cross section is presented in a general coordinate system. The theory maintains Vlasov's approach in terms of generalized strains and stresses and yields the same system of differential equations. The common hypothesis of transversely rigid cross section, which overestimates the effective flexural and torsional section stiffness, is replaced by the assumption that stresses in the plane of the cross section are small. The resulting theory reduces to the exact solution of Timoshenko when warping effects are neglected. Shear stresses due to shear forces, warping torsion, and Saint-Venant torsion are determined as the gradient components of a unique potential function. These equations are solved with the finite element method, which also provides the flexural and torsional section stiffness and the shear center. Numerical examples are presented and results are compared with full three-dimensional finite element analyses. The formulation is simple and, in spite of the limitations of the simplifying hypotheses, sufficiently accurate for many engineering applications, bypassing costly three-dimensional finite element analyses.

Kinematic relations, equilibrium equations, buckling equations and related boundary conditions for laminated, cylindrical, moderately thick shells, including the effect of transverse shear are studied. Buckling applications for moderately thick, torsionally loaded, laminated, cylindrical shell with fixed ends are presented. Results are obtained for the classical and first-order, and higher-order shear deformation theories based on Donnell-type and Sanders-type kinematics relations.