Showing papers on "Torsion (mechanics) published in 1993"

Vibration control of 2 mass resonant system by resonance ratio control

Abstract: This paper presents a position control method to suppress torsional vibrations of 2 mass resonant systems without using position sensor on the arm portion. Instead of using a position sensor, the reaction torque caused by the shaft torsion is utilized for the suppression of the vibration. In this paper, the reaction torque is estimated by an observer using motor portion parameters and state variables. The feedback of the reaction torque makes it possible to control the "resonance ratio", which is a novel concept for vibration controls. The proposed control system is based on both the conventional PD control and the resonance ratio control, and the controller gain determination method is discussed. The validity of the proposed method is also confirmed by several experiments. >

An Edge Crack Torsion Method for Mode III Delamination Fracture Testing

Abstract: A new fracture toughness test, the edge crack torsion method, has been developed for characterizing the mode III delamination behavior of composites. The test is based on a laminate specimen subjected to torsion to propagate an edge delamination crack in its midplane. The crack growth mode of the specimen has been deduced to be mode III from fracture mechanics principles. The torsional behavior and the corresponding fracture parameter GIIIC have been analyzed on the basis of plate torsion and laminate theory. Edge crack torsion tests were performed to measure GIIIC of several carbon fiber/epoxy composite systems. Laminate layups were optimized to yield linear elastic fracture behavior of the specimens. The specimens were also sufficiently compliant to allow GIIIC to be readily obtained by using the compliance calibration method. The deformation characteristics of the specimens were found to follow the laminate torsion description. SEM observations showed fracture surface morphology varying with resin microstructures and, for the case of an untoughened matrix, were consistent with what was reported in the literature for other proposed mode III fracture tests.

Torsion balances, torsion pendulums, and related devices

Abstract: The torsion pendulum is not only a mainstay instrument in the world of precision measurement and gravitational physics, but is important in electrical science, biophysics, petrology, metallurgy, and various other fields of endeavor Whether used in the ‘‘static’’ (deflection) mode, the ‘‘dynamic’’ (oscillating) mode, or in some more complex configuration, instrumentation of this kind enables one to isolate and measure weak effects that would otherwise be difficult if not impossible to observe against the background gravitational field of the earth In this review, we present a brief history of fiber‐suspended apparatus and assess the fundamental limits of performance of the dumbbell pendulum We then inventory the different versions of such systems presently used by gravitational physicists and discuss the various interrogation techniques used to monitor the movement of the suspended test mass Next, we tabulate some of the applications for torsion instruments outside of gravitational physics, and close with a few comments on the direction of research in this area

Vibration Control of a 2 Mass Resonant System by the Resonance Ratio Control

Abstract: Recently, with the progress of robust control techniques, the resonance of mechanical systems becomes a more important problem. This paper presents a position control method to suppress the torsional vibration of a 2 mass resonant system. Here we propose a sensorless control of arm portion. In this case, it is necessary to estimate some states of the arm portion. When motor portion parameters are well known due to several identifications, the reaction torque caused by the shaft torsion can be estimated. This reaction torque feedback makes it possible to control the resonance frequency between the torque current and the motor position. Here, we introduce a new concept which is called “Resonance Ratio”. The resonance ratio is determined arbitrarily by the feedback of the reaction torque. The proposed method is a reasonable concept from a mechanical point of view.The proposed control system is based on both the conventional PD control and the resonance ratio control. Then any sensor information of the arm portion is not used, and the proposed controller is a very simple structure. This is one of the remarkable points of the proposed method. We discuss an idea of the determination method of controller gains. The validity of the proposed method is also proved by several experiments.

Torsion in Base‐Isolated Structures with Elastomeric Isolation Systems

Abstract: Torsion in baseisolated structures with inelastic elastomeric isolation systems due to bidirectional lateral ground motion is studied. In a companion paper by the writers, torsional coupling in sli...

Aeroelastic response, loads, and stability of a composite rotor in forward flight

Abstract: The aeroelastic response, blade and hub loads, and shaft-fixed aeroelastic stability are investigated for a helicopter with elastically tailored composite rotor blades. A finite element analysis including nonclassical effects such as transverse shear, torsion related warping, and in-plane elasticity is integrated with the University of Margland Advanced Rotorcraft Code. The analysis is correlated against both experimental data and detailed finite element results. Correlation of rotating natural frequencies of coupled composite box-beams is generally within 5-10%

Bending and torsion models of beams with induced-strain actuators

Abstract: This paper develops one-dimensional pure bending, coupled bending and extension, and combined bending, extension and torsion models of isotropic beams with induced strain actuation. A finite thickness adhesive layer between the crystal and beam is included to incorporate shear lag effects. Experimental tests evaluate the accuracy and limitations of the models. The bending and coupled bending and extension models show acceptable correlation with static test results whereas the combined extension, bending, torsion model poorly predicts the system behavior and needs refinement.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

All universal coverings of two‐dimensional gravity with torsion

Abstract: Global solutions of two‐dimensional gravity with torsion are found and elucidated. The model admits complete analysis of possible maximally continued space‐times by means of Penrose’s diagrams. There are 13 types of orientable universal coverings. For zero cosmological constant there is flat two‐dimensional Minkowskian space‐time. For nonzero cosmological constant the universal covering of zero torsion covers one‐sheet hyperboloid with Lorenzian metric of constant curvature. All other universal coverings are the surfaces of nonzero torsion and nonconstant curvature. The global solutions include surfaces of a black hole configuration.

Stuck pipe locator system

Abstract: A system for locating a stuck pipe is disclosed which, in one aspect, includes a tool with a removable bi-sensor cartridge assembly which has at least two autonomous independent sensors, one for sensing torsion and one for sensing tension. The sensors may also be used to indicate temperature downhole. A method is disclosed for locating stuck pipe using such a sensor and using a slip joint according to the present invention. In one aspect the slip joint has a housing, a mandrel, and a two conductor coil cord assembly.

Torsion bar suspension for operator's platform

Abstract: A suspension for the operator's platform of agricultural or industrial vehicles uncouples the platform from vibrations of the vehicle chassis, in particular vertical vibrations acting in the vehicle's fore-and-aft plane. To do this, at least one essentially horizontally and laterally aligned torsion rod is fixed with its ends between the platform and a first end of a pair of links. The second end of each link is pivotally mounted to the vehicle chassis, with the pivot axis parallel to the torsion rod axis. The torsion rod is supported in the vehicle platform by a bearing which is close to the link.

Macroscopic three-dimensional motion patterns of the left ventricle

Abstract: The pattern of displacements in the left ventricle (LV) can be described by 13 modes of motion and deformation. Three functional modes of deformation are essential for ejection: a decrease in cavity volume, torsion, and ellipticalization. Four additional modes are used to describe asymmetric deformation. Six modes of rigid body motion describe rotation and translation. In the LV 14–20 radiopaque markers were inserted in the wall of the LV. They were distributed more or less evenly from base to apex and around the circumference. Torsion and volume changes require the definition of a cardiac coordinate system. The point at which ejection focusses is used as the origin, and the torsion axis is used as the z-axis. In the present study the coordinate system was positioned objectively by a least squares fit of the kinematic model to the measured motion of markers. In five dogs in the control state the kinematic parameters were determined as a function of time for all 13 modes. The torsion axis was displaced 4 ± 2 mm (mean±sd) from the center of the cross-section of the LV towards the lateral free wall. The direction of the torsion axis closely coincided with anatomical landmarks at the apex and base. During systole, a unique relation was found between the ratio of cavity volume to wall volume and torsion. This relation was universal to all LVs, the cylinder-symmetric mathematical model of cardiac mechanics inclusive. In diastole the patterns of deformation seem less universal and reproducible.

Saint-venant’s torsion problem for a composite circular cylinder with aninternal edge crack

Abstract: In this paper the writer uses Muskhelishvili single-layer potential function solution and single crack solution for the torsion problem of a circular cylinder to discuss the torsion problem of a composite cylinder with an internal crack, and the problem is reduced to a set of mixed-type integral equation with generalized Cauchy-kernel. Then, by using the integration formula of Gauss-Jacobi, the numerical method is established and several numerical examples are calculated. The torsional rigidity and the stress intensity factors are obtained. The results of these examples fit the results obtained by the previous papers better.

Sliding mode control method for a machine having an operating section operatively coupled to a servomotor and wherein a switching variable is determined based on a torsion amount and a torsion speed

Abstract: A sliding mode control method is provided capable of improving the following ability of a control system with respect to a command at the time of change in the operating condition of a machine, and preventing vibration which tends to occur by the action of a spring element of the machine at the time of change in the operating condition. The processor of a servo circuit derives position deviation (e) and speed deviation (e) based on a command position (θr) and an actual position (θ), estimates an torsion amount (en) and torsion speed (en) by effecting observer processing (Steps 100 to 101), and derives a switching variable (s) (102). The processor derives each of the first to fourth terms of the switching input in dependence on the positive or negative sign of the switching variable, and the positive or negative sign of a corresponding one of the position deviation, the second derivative of the command position, the torsion amount, and the torsion speed (103 to 129), and then derives, on the basis of the switching input derived by adding the four terms together, a torque command (T) sufficient to cause the switching variable to converge on 0 (130, 131). The servo system properly follows the command even when nonlinear parameters associated with the spring element of the machine have varied, thereby preventing vibration of the machine.

Flexure-torsion behavior of prismatic beams. I - Section properties via power series

Abstract: The behavior of a tip-loaded cantilever beam with an arbitrary cross section is studied using Saint-Venant's semi-inverse method along with a power series solution for the out-of-plane flexure and torsion warping functions. The power series coefficients are determined by solving a set of variationally derived linear algebraic equations. For complex cross sections, the calculated coefficients represented a 'best-fit approximation' to the exact warping function. The resulting warping functions are used to determine the cross-sectional properties (torsion constant, shear correction factors, shear deformation coefficients, and shear center location). A new linear relation is developed for locating the shear center, where the twist rate is zero about the line of shear centers. Moreover, the kinematic relations for a new fully compatible one-dimensional beam theory are developed. Numerical results are presented first to verify the approach and second to provide section data on NACA four-series airfoils not currently found in the literature.

Improved wide-column-frame analogy for shear/core wall analysis

Abstract: The wide-column-frame analogy is popular in design offices for the analysis of shear/core wall buildings. However, it has been found to yield erroneous results in cases where shear deformation of the walls is significant, e.g. core walls subjected to torsion. There are two sources of error. First, due to discrete modeling of the vertical joints between adjacent planar wall units, the wall elements are subjected to parasitic moments, which cause artificial flexure of the elements and eventually excessive shear deformation of the walls. Second, the rotations of the coupling beams at the beam-wall joints have been mistaken as equal to the rotations of the horizontal rigid arms and, as a result, the beam end rotations are underestimated by amount equal to the shear strain in the walls. It is proposed that these problems be resolved by: (1) Adjusting the shear deformation factor of the wall elements to compensate for the errors in shear deformation due to artificial flexure; and (2) using beam elements with vertical rigid arms for the coupling beams, so as to eliminate the errors in beam end rotations. Substantial improvement in accuracy is achieved with these modifications.

Fiber reinforced concrete beams under torsion

Abstract: The effect of steel fibers on the behavior and ultimate strength of reinforced concrete beams under torsion is studied. Glued standard bright wires of designation ZC 60/0.8 were used. A total of 6 beams was cast and tested. Three beams reinforced with longitudinal reinforcements only had fiber percentages of 0, 0.6, and 1.2 respectively. The other 3 beams reinforced with longitudinal reinforcement and stirrups had the same percentages of fibers as the first group. Improvements in the first crack and ultimate strengths were noticed. These improvements depend on the volume percentages of fibers. The experimental ultimate strength values were compared with theoretical values obtained from torsion formulas. A good correlation of results is clearly shown.

Kalusa-Klein approach in higher-dimensional theories of gravity with torsion

Abstract: The Kaluza-Klein approach is investigated in the Einstein-Cartan-Sciama-Kibble (ECSK) theory and in a Brans-Dicke-type model with torsion. In particular, the authors focus their attention on the possible coupling of gauge fields and torsion, the principle of minimal coupling and the possible physical meaning of the fields which originate from the higher-dimensional torsion fields. Also, it is known that Brans-Dicke-type models with torsion have an extended conformal symmetry. They investigate the fate of this symmetry when going (via dimensional reduction) to four dimensions. They find that the vectorial part of the torsion acquires a nonvanishing value, thus breaking the symmetry of the original five-dimensional theory.

Torsion damper, especially for a motor vehicle

Abstract: A torsion damper, especially for a motor vehicle, comprises coaxial primary and secondary parts mounted for relative rotation or one with respect to the other. A circumferentially acting resilient element, at least partially mounted within a cavity formed in a sealing element, acts between the primary and secondary parts via a torque limiter. The torque limiter comprises a damper plate fixed with respect to one of the primary and secondary parts, and two counter plates secured together with suitable fasteners. The two counter plates frictionally embrace the damper plate, and the sealing element is secured to the counter plates by the fasteners.