Torsional Phenomena Research Articles

Geometric torsion in idiopathic scoliosis: three-dimensional analysis and proposal for a new classification.

Three-dimensionally reconstructed spines of 62 subjects with idiopathic scoliosis were reviewed for three-dimensional pattern classification based on the measurement of geometric torsion. To evaluate the relevance of geometric torsion as a three-dimensional index of scoliosis, and to develop a three-dimensional classification of deformity for idiopathic scoliosis as opposed to the current classifications based on two-dimensional frontal views. Attempts have been made to measure the geometric torsional shape of scoliotic curves represented curvilinearly. However, the geometric torsion phenomenon has never been properly analyzed and thus has never been precisely defined. Standardized stereoradiographs of 62 patients with idiopathic scoliosis were obtained and used to generate three-dimensional reconstructions. A continuous parametric form of the curved line that passes through the vertebrae was created by least square fitting of Fourier series functions. Frenet's formulas then were used to calculate the geometric torsion. Analysis of geometric torsion associated with 94 major scoliotic curves allowed three basic categories of torsion curve patterns to be identified. Scoliotic spines with multiple major curves are described by a combination of basic torsion patterns, one for each curve. A three-dimensional analysis of the spine in terms of geometric torsion has defined three distinct patterns of torsion in a group of scoliotic curves. Geometric torsion had extreme values at the levels of upper and lower vertebrae, but zero or nearly zero values at the levels of the apices. The torsional phenomenon can be unidirectional or bidirectional in both single and double major curves.

SOME DESIGN PRINCIPLES RELEVANT TO TORSIONAL PHENOMENA IN DUCTILE BUILDINGS

Recent studies provided opportunities to review some of the principles, which have been used in the formulations of internationally accepted code-recommendations relevant to the seismic design of ductile buildings also subjected to torsional phenomena. With the progress of this study, features emerged which are considered to have contributed to a better understanding of structural behaviour. Moreover, the identification of deeply embedded fallacies, relevant to ductile response, suggested the introduction of some changes in seismic design strategies, yet not widely known or appreciated. Reasons for necessary re-interpretations of traditional structural properties, together with illustrative examples, demonstrating applications, rather than set code-type rules, are offered.

Understanding torsional phenomena in ductile systems

Recent studies provided opportunities to review some of the principles, which have been used in the formulations of internationally accepted code-recommendations relevant to the seismic design of ductile buildings also subjected to torsional phenomena. With the progress of this study, features emerged which are considered to have contributed to a better understanding of structural behaviour. Moreover, the identification of deeply embedded fallacies, relevant to ductile response, suggested the introduction of some changes in seismic design strategies, yet not widely known or appreciated. Reasons for necessary re-interpretations of traditional structural properties, together with illustrative examples, demonstrating applications, rather than set code-type rules, are offered.

Torsion in the cohomology of finite loop spaces and the Eilenberg–Moore spectral sequence

We use the Eilenberg–Moore spectral sequence to study torsion phenomena in the integral cohomology of finite loop spaces with maximal torus generalizing some results for compact Lie groups due to Kac.

Analysis of shaft torsional phenomena in governing large steam turbine generators with non-linear valve stroking

The paper focuses on how shaft torsional problems can be initiated in some situations by the fast action of steam control valves. It demonstrates that shaft flexibility can exert a significant influence on steam turbine-generator response following severe supply system disturbances, particularly for large machines where the turbine has nonlinear valve stroking and fast valving. The effect can be minimised by careful location of the speed sensor on the turbine shaft and by filtering to reduce speed input or acceleration signals due to troublesome low-frequency torsional vibrations to an insignificant level. Digital implementation of steam-turbine control systems is described. Response for a range of control philosophies where digital control procedures are used are given. Two large machines where digital speed sensing and filtering techniques in steam valve control are implemented are examined.

VEHICLE DRIVELINE DYNAMIC BEHAVIOUR: EXPERIMENTATION AND SIMULATION

The work presented is of a study of torsional vibrations of a driveline under static torque and excited by engine torque fluctuations. It includes the design of an experimental set-up and a computer software to predict dynamic behaviour and seek efficient technical solutions. A finite element model is used to study current systems and perform transient analysis. Basic linear elements are used and non-linearities such as a multi-staged clutch with dry friction and gear backlash are taken into account. The time response is calculated and a pseudo-modal method is used. An experimental set-up of the whole driveline has been designed and built to allow simulation of the basic torsional phenomena occurring on the vehicle driveline under input torque from 0 to 200 Nm, and, moreover, to validate numerical models. Furthermore, prediction and experiments on two new vehicles are in quite good agreement.

SEISMIC TORSIONAL EFFECTS ON DUCTILE STRUCTURAL WALL SYSTEMS

With a distinct design rather than analysis-oriented approach, some torsional phenomena, arising during the elasto-plastic seismic response of building structures, are addressed. It is postulated that existing code recommendations, expressed only in terms of the properties of elastic structures, are largely irrelevant when the design needs to be based on ductile system behaviour. Torsional restraint provided by elastic elements of a system, is claimed to be the desirable property controlling the amplification of inelastic translatory deformations of critical elements by storey twist. With the identification of the sources of inelastic element deformations, a simple behaviour-based design strategy is proposed. This should ensure that the displacement ductility demand, expected to be imposed on the system, does not result in deformations that, as a consequence of storey twist, may exceed the displacement ductility capacity of critical elements.

DYNAMIC MODELLING OF RAILWAY TRACK BASED ON WAVE PROPAGATION

In order to reduce the noise generated in the environment during a train's passage, studies have been carried out to model the track behaviour in dynamics. Models based on a rail description by Timoshenko beams were found to be insufficient, especially for lateral motion where torsion phenomena caused a large discrepancy between calculations and experimental measurements. Therefore a model was developed allowing for rail section strains and based on a description of waves travelling through the rail. A very satisfactory agreement with experimental data was reached both for lateral and vertical motions in a low to medium frequency range with a cheap calculation time cost.

複合材料の三次元熱応力解析

A computer program for three-dimensional thermal stress analysis of anisotropic materials such as composites has been developed. As an example, the deformations of bi-metal and angle- ply laminates under thermal conditions were analyzed. From the computational results, the torsional phenomenon, which is caused by the coupling and the effect of free edge on stress, was recognised. When the residual stress is taken into consideration, the tensile strength of angle-ply laminates was also analyzed. The effect of property of matrix on the tensile strength of angle-ply laminate was investigated. As a results, it was shown that the fracture pattern can be changed by property of matrix.

Turbine generator laboratory model tests to damp torsional oscillations with supplementary signals

The improvement of generator stability by the use of supplementary signals into the voltage regulator and governor loops using discrete-time linear optimal control theory has been studied with particular emphasis on providing better damping for torsional oscillations. A multi-inertia laboratory model equipped with data acquisition and control computers was constructed to model the shaft dynamics of a 660 MW Drax turbine-generator. It is shown that the shaft torsional phenomena can be adequately simulated on a micro-synchronous-generator at least as far as the dominant shaft torsional modes of vibration are concerned. The practical implementation of multi-mode linear quadratic Gaussian (LQG) controllers has been shown to enhance system stability and provide better damping to the lower frequency torsional modes, which are those most susceptible to excitation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Non-linear three-dimensional large-amplitude damped free vibration of a stiff elastic stretched string

In the numerous works trying to describe the free vibration of stretched elastic strings, phenomena due to non-linear geometrical modifications in a three-dimensional large amplitude motion are separated from those due to the string's stiffness, in which case torsional vibrations cannot be taken into account. In order to fill this gap with a more complete model and to specify its field of validity the problem set up again, starting from three-dimensional elasticity for finite displacements with small strains of a slender homogeneous elastic cylindrical rod under initial stress. The original geometrical construction which gives the cross-section's orientation during the motion is detailed. With the symmetry of the problem preserved, it provides a description of simple physical meaning and in particular the torsion is used as a parameter. The goal of this study being the determination of the deformed shape of the central line, the three spatial variables are reduced to one through expressions for the resultant forces and moments on the cross-sections, leading to macroscopic equations of motion which are simplified in the case of uncoupled transverse and longitudinal modes. For the first time, the equations of motion introduce a coupling torsion term and include existing string and beam models, which can thus be considered as particular cases. The assumptions and generalizations are discussed and the influences of the different terms are described. While this work is based on the limits imposed by material linearity, it provides a useful basic tool for the study of the transverse vibrations of slender elastic beams, including the commonly avoided torsional phenomena.

A coupled tortional vibration of a rotating blade and shaft system of axial-flow-type machinery. (Continued report. Application of the equivalent reduced modeling method).

An analytical and experimental study on the coupled torsional vibration was carried out in the previous paper in order to determine the influencing factors in the coupled effect. In this paper, an equivalent reduced modeling method, which has been recently proposed as a new numerical analysis procedure, is applied for the previous torsional blade and shaft system. The results obtained are in good agreement with the experimental data of the previous paper, and the method seems to be effective for numerical estimation of the coupled torsional phenomena.

Torsional Oscillations of Unequally-Loaded Parallel Identical Turbine-Generators

This paper provides a detailed analytical investigation of the torsional phenomenon of closely coupled parallel identical T-G sets, under unequal loading conditions. The impact of important factors, i.e., 1) load difference of generators, 2) mechanical damping torque components and 3) series capacitor compensation level on the torsional modes of unequally loaded parallel T-G set, are examined. The studies are conducted on a system composed of two parallel identical T-G sets. An eigenvalue method is used for the studies and the analytical results are verified by detailed digital computer simulation of the system, using the EMTP. The T-G sets also represented by the so called EGM, and whenever applicable, the study results are compared with those obtained from the EGM. The studies indicate that the corresponding torsional modes of the parallel T-G sets under unequal loading conditions, are not in-phase. The phase-deviation depends on: 1) the load-difference of the generators and 2) the mechanical damping torque components. Among the mechanical damping coefficients, i.e., mutual-damping coefficient, absolute-speed self-damping coefficient and speed-deviation, self-damping coefficient, the first two are constants and the third one is load dependent. The mechanical damping torque components corresponding to the speed-deviation self-damping coefficients have a noticeable impact on the phase-deviation. This paper also reports the results of an investigation in which an SVC system is used to mitigate the torsional oscillatory modes of the unequally loaded T-G sets.

Surface faulting caused by the Kalamata (Greece) earthquakes (13.9.86)

A great number of neotectonic faults traverse the Messinian gulf and its geological prolongation on the continent towards the north, which forms the Kalamata-Kyparissia tectonic graben. On the 13th September 1986, the whole Messinia area was shaken by an earthquake ( M = 6.2); it caused much damage, mainly in the city of Kalamata. Catastrophes were limited to a relatively small area, in the form of a triangle. The striken area is a second-order tectonic graben (called the Dimiova-Perivolakia graben) which is developed on the eastern margin of the greater Kalamata-Kyparissia tectonic graben. Alpine and post-Alpine (Neogene and Quaternary) formations outcrop in the graben. The recent earthquakes caused small fractures (4–5 m long) and small-scale reactivation of neotectonic faults. Both have been observed in almost all formations. The seismic fractures form a zone or zones. They consist of small parallel fractures arranged en échelon, which allows us to conclude that in some places the fracture zones are of right-lateral and in others of left-lateral character. This, in fact, coincides with the kinematics of the main neotectonic fault-zones of the graben. This, in conjunction with other morphotectonic observations, suggests that the deformation of the area is connected with coupling or even torsion phenomena.

Torsional oscillations of unequally-loaded parallel identical turbine-generators

This paper provides a detailed analytical investigation of the torsional phenomenon of closely coupled parallel identical T-G sets, under unequal loading conditions. The impact of important factors, i.e., 1) load difference of generators, 2) mechanical damping torque components and 3) series capacitor compensation level on the torsional modes of unequally loaded parallel T-G set, are examined. The studies are conducted on a system composed of two parallel identical T-G sets. An eigenvalue method is used for the studies and the analytical results are verified by detailed digital computer simulation of the system, using the EMTP. The T-G sets also represented by the so called EGM, and whenever applicable, the study results are compared with those obtained from the EGM. The studies indicate that the corresponding torsional modes of the parallel T-G sets under unequal loading conditions, are not in-phase. The phase-deviation depends on: 1) the load-difference of the generators and 2) the mechanical damping torque components. Among the mechanical damping coefficients, i.e., mutual-damping coefficient, absolute-speed self-damping coefficient and speed-deviation, self-damping coefficient, the first two are constants and the third one is load dependent. The mechanical damping torque components corresponding to the speed-deviation self-damping coefficients have a noticeable impact on the phase-deviation. This paper also reports the results of an investigation in which an SVC system is used to mitigate the torsional oscillatory modes of the unequally loaded T-G sets.

Stable Operating Regions of Torsional Interaction Phenomenon in Synchronous Generators

This paper shows that the unstable torsional interaction phenomenon, which had been the cause of shaft failures, is restricted only to the condition when the network resonance frequency and the interacting torsional resonance frequency are both subsynhronous. The interactions, in which this condition is not fulfilled, are positively damped and therefore, safe. The paper also presents physical and analytical insights into the characteristics of the damping torque-vs-frequency curve of the synchronous generator.

Torsional oscillations and the solar cycle

Both the net torsional pattern and its derivative, the shear oscillation, are studied in relation to the solar activity cycle using data collected at Mount Wilson from 1967–1986. The shear is seen as the better quantity for study, since it is both more fully determinable with these data and has straighter ties to the zones of activity. The shear zones run from pole to equator, clearly indicating that the cycle begins at the poles. Total transit, roughly at constant speed, takes roughly 18 years, and the active zones emerge to span the zones of shear enhancement after the latter have reached sunspot latitudes. This 18-yr transit time is seen as the proper duration of the cycle: successive cycles begin roughly 11 years apart and thus overlap. The polar origin of the torsional pattern is found to be phenomenologically connected with variations in the polar field amplitude. It is also noted in both the magnetic and torsional patterns that, for the past few cycles, the activity portion begins earlier and thus lasts longer in the northern hemisphere. In a general discussion of torsional oscillations and their role in the solar cycle, the ‘net pattern’ and ‘k = 2 wave’ interpretations of the torsional phenomenon are contrasted and reasons for preferring the net pattern are presented. A model is proposed in which the torsional oscillations are the surface signature of an azimuthal convective-roll pattern. This model could provide the original Babcock model with a mechanism for trapping and further amplifying the toroidal field.

The Interction of Torsional Reasonances with Network Resonances in Synchronous Generators

Subsynchronous torsional resonances have interacted with subsynchronous network resonances to cause shaft failures-in synchronous generators. But what of their interactions in the supersynchronous span of the frequency spectra? Are they safe? These questions have become relevant as more network resonances are being added to the power system through the increasing use of static VAR compensators and their smoothing filters. The paper offers a few answers to these questions using the phase modulation theory of the torsional interaction phenomenon.

Shaft Torsional Phenomena in Governing Large Turbine-Generators with Non-Linear Steam Valve Stroking Constraints

The paper examines shaft torsional phenomena i governing large synchronous-generators followinng (severe system disturbances and (b) load rejectiona)

Shaft Torsional Phenomena in Governing Large Turbine-Generators with Non-Linear Steam Valve Stroking Constraints

Shaft Torsional Phenomena in Governing Large Turbine-Generators with Non-Linear Steam Valve Stroking Constraints