Torque Tube Research Articles

Current status of superconducting synchronous motor in Saga University

Since there are no iron cores in the rotor and stator windings of superconducting synchronous motors, some reactances are intrinsically smaller than those of conventional motors. Low synchronous reactance would be expected to improve the torque-ampere ratio stability and the overload capacity of superconducting machines. Two types of 30 kVA synchronous motors, such as rotating armature and rotating field types, have been constructed. The rotating armature type motor had been fabricated and tested. The results show the difficulty of holding a stator cryostat in a low-heat leak condition. The low synchronous impedance requires some control of the armature current and/or the motor field current. The rotating field type motor encountered balancing problems due to the triple-pipe configuration of the helium supplier in the torque tube.

A new technique for the analysis of torque tube heat exchangers of superconducting generators

The torque tubes of a superconducting generator belong to a unique class of heat exchangers where a single fluid stream (boil off helium vapour) exchanges heat with a metallic wall conducting heat from the ambient to the cold (liquid helium) space. The rate of heat leak to the cold space is the chief indicator of the performance of the exchanger. This rate of heat inleak has been found to be a function of two dimensionless parameters: a generalized cooling parameter Λ ∗ and a temperature range parameter Ψ. A generalized design chart is presented which expresses the dimensionless heat flow rate Q c in terms of the parameters Λ ∗ and Ψ. This chart will be useful for the design of torque tubes and vapour-cooled support members in cryogenic systems.

Large superconducting DC drives with separate torque reaction windings

A slotless-armature DC motor with multiplex winding can be designed for higher power rating compared to one with a conventional slotted armature. Conventional field systems would be very heavy and a superconducting field winding is considered in order to create an iron-free stator and lightweight machine. The superconducting field winding is relieved of reaction torque by means of a special winding attached to a separate torque tube. The reaction winding is also designed to establish the necessary commutation flux in the interpole region. Test results from a small laboratory machine demonstrate the principle of the proposed torque reaction winding. A design for a 20 MW ship propulsion motor is presented.

Vibration absorbing steering device for outboard motor

A vibration absorbing steering device for an outboard motor having a swivel bracket constructed and arranged for mounting to a transom bracket of a boat and defining a vertical passageway includes a tubular pivot shaft being pivotally engaged in the passageway, an engine mount bracket designed to mount the engine for rotation with the pivot shaft, and a vibration absorbing torque tube for absorbing vibration generated by the engine. The torque tube is vertically disposed within the tubular pivot shaft and is secured at one end to the pivot shaft. A tiller arm has a pivot end attached to the upper end of the torque tube so that the tiller arm is connected to the engine mount bracket through the torque tube, and the torque tube absorbs vibration from the engine which would normally be transmitted through the tiller arm to the operator. In addition to absorbing engine vibration, the present device also permits positive steering control of the motor by manipulation of the tiller arm.

A Triaxial Dynamometer for Force and Moment Measurements on Tillage Implements

A dynamometer was designed to measure the forces and moments acting on a tillage implement for use both in a soil bin and in the field. The instrument is able to measure the three orthogonal forces acting on the implement and the three moments acting about the orthogonal axes, up to a maximum force of 100 kN and a maximum moment of 100 kN m. The dynamometer employs two extended orthogonal rings mounted with their axes at right angles and a torque tube. The device was machined from the solid using a high tensile steel. The forces and moments acting on the dynamometer were measured by the use of strain gauge bridges using foil-type gauges. The design criteria of the rings and the torque tube and the arrangement and function of the strain gauge bridges are described in the paper. The dynamometer was calibrated by the application of known forces and moments and the voltage output of the strain gauge bridges was measured. The calibrations showed a high degree of linearity between the applied forces and moments and the bridge outputs. The hysteresis effect between loading and unloading was small, as was the effect of the position of the applied forces from the longitudinal axis of the dynamometer (<2·0%). The interaction of orthogonal forces on the response of a force measuring bridge was generally found to be 4% or less, except in two cases where practical gauging difficulties arose.

An Experimental and Analytical Investigation of Composite Drive Shafts with Non-Circular End Cross-Sections

An optimization methodology is presented for the selection of the end cross-sectional shape of composite torque tubes (drive shafts) with noncircular end geometries. In a typical application, metal inserts are adhesively bonded in the ends of the tubes to allow for torque transmission. The worst case scenario of bond failure with subse quent torque transmission via insert-tube contact is considered. Optimization of the tube end cross-sectional shape under this worst case situation is the goal of this study. Employ ing facets of elasticity and the finite element method, a two step methodology is estab lished to predict the failure torque of a tube with a range of selected end cross-sections. This methodology is verified through comparison with experimental data. Results ob tained from the analytical and experimental studies indicate a spline-like cross-sectional shape as the optimal design. Failure torques on the order of 70% of the circular cross- sectional failure torque are shown to be possible.

Flexbeam helicopter rotor with improved snubber-vibration damper between the torque tube and the flexible spar member

Abstract of the Disclosure Flexbeam Helicopter Rotor With Improved Snubber-Vibration Damper Between the Torque Tube and the Flexible Spar Member A flexbeam helicopter rotor having an improved snubber-vibration damper for positioning the flexbeam spar relative to the torque tube, wherein the snubber-damper is an elastomeric bearing having a spherical and a flat portion, and whose laminates are continuous, selectively preloaded and of selected material to provide increased fatigue life, size reduction, reduced laminate stress concentration, and reduced critical design stress in the snubber-vibration damper.

Practical Design of Superconducting Generator. Electrical and mechanical design.

Since a superconducting generator (SCG) consists of a superconducting field winding, a nonmagnetic cryogenic rotor and an airgap armature winding, its design method differs from that of the conventional generator. Practical applications require establishment of its electrical and mechanical design methods.A design flowchart of the SCG was shown and the basic design method was clarified. For this method, the electrical and mechanical design of a 50MVA experimental generator was carried out. Its design specifications and size were compared with a future 1, 120MVA generator and a 778MVA conventional generator. Furthermore, synthetic stress applied on the main rotor components, such as the torque tube and room temperature damper, was obtained. From the test results of generator power loss and the V curve under synchronous condenser operation, the design method was proved to be valid.

Cryogenic isolating torque tubes for a superconducting generator-detailed model and performance analysis

Because of a suspected cryogenic insufficiency in the rotor of the 10 MVA superconducting generator a detailed analysis of the torque tubes was carried out and, to the extent possible with limited instrumentation, verified by actual experiment. The method used was a one-dimensional finite-element analysis with fixed end conditions. Nonlinear heat transfer was considered. The prediction of this analysis was that heat leak into the cold space would be small, confirming the initial design analyses. It also demonstrated that the initial analyses were robust to the major uncertainties, including steel-to-gas heat transfer. A brief description of the torque-tube system and a somewhat more detailed description of the thermal model developed for that system are given. A comparison with experimental data is shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Test results of 50 MVA superconducting generator

A 50 MVA superconducting synchronous generator with a superconducting field winding was developed. This paper describes its features and test results. The saddle-shaped field winding, impregnated with epoxy resin, was mounted on a torque tube and fastened with prestressed non-magnetic stainless steel wires. A free convection cooling system, which uses the thermosiphon effect, was adopted for the field winding. Cooldown of the rotor was carried out with a constant liquid helium feed rate of 50 l/h and it was completed smoothly within about 40 hours. After that, the rotor could rotate stably at 3600 rpm. Electrical tests of no-load, short-circuit and sudden short-circuit characteristics were also carried out. Finally, the 50 MVA generator was connected to a power network and confirmed to operate successfully for 80 minutes as a syncronous condenser with a small capacity.

Optimized Drilling Through Use Of Downnhole Motors

Abstract It has been established that rate of penetration (ROP) is directly related to rotational speed (RPM) of the drill bit in most formations. The Wembley area of northwest Alberta shows a proportionate increase in drilling rate with increases in rotary speed. Pan Canadian Petroleum Ltd. (PCP) optimized bit RPM by supplementing the rig's rotary capability with downhole motors. This paper will summarize the results of using downhole motors to Increase penetration rates in the Wembley field and will provide the drilling plan which PanCanadian uses to optimize vertical drilling with downhole motors. Introduction The relationship for soft and medium soft formations, between rate of penetration and rotational speed has been established as(1): (1) R = KWN a where: R = Rate of penetration K = Lithology factor N = Rotary speed W = Weight on bit a = exponent (equal to 1 for Wembley) For Wembley area this equation may be reduced to: (2) R = constant ( N ) Although the constant includes the bit weight, which is a variable, by drill off tests and manufacturer's recommendations bit weight has been optimized at a relatively constant value between 18 000 and 20 000 daN. Equation (2) suggests the rate of penetration can be enhanced through rotary speed increases. Factors which place an upper limit on rotary speed include:Drill string limitations.Drilling rig limitations on rotary speed.Drill bit limitations.Mechanical hole erosion.Casing wear. Drill string limitations include resonant vibration, joint strength, wear due to erosion and cyclic bending fatigue. Contractors limit rotary speed to 150 RPM or less and will not warrant the operational integrity of the string at higher rotary speeds. An excellent reference paper has been prepared by D. Dareing of Maurer Engineering Inc. (Ref. SPE 11228). Therefore most conventional drilling rigs are limited to rotary speeds of 150 RPM. Chain drive rotary tables are in common use and are usually coupled from the drawworks power take-off directly to the rotary drive pinion. Due to substructure space limitations it is not often possible to include a transmission on the rotary table. Chain sprockets also tend to be fixed by rotary torque requirements and chain speed limits. Torque tubes and electric drive rotaries have added flexibility to available RPM but these systems are not always available. Retrofit on existing rigs cannot be economically justified unless a long-term rig commitment is possible. Drill bit manufacturer's suggest RPM limits for their products but recent developments in premium sealed bearings have allowed greater flexibility. Also, insert bits have been improved in the bonding of carbide teeth to the cone matrix, allowing higher rotary speeds. Casing wear is a concern to all operators and, in some cases, optimum drilling performance has been sacrificed to limit wear. Non-rotating stabilizers have been used successfully but, again, stabilizer wear increases substantially when the drill string is rotated above 100 RPM.

An Approach to Optimal Thermal Design of Superconducting Generator Rotor

To stabilize the superconducting condition of field winding of a superconducting generator and to ensure high-efficiency operation of the machine, heat penetrating the inner rotor of the superconducting rotor must be suppressed. This makes it necessary to recognize quantitatively and accurately heat penetrating from such parts as current leads, torque tubes, and radiation shields. Since the temperatures of such structures and the coolant rise from around 4K to 300K, such physical quantities as density of the coolant and thermal conductivities of the structures depend nonlinearly on temperatures. This prevents adequate accuracy from being obtained simply by the analysis of penetrating heat by using the mean values of properties. To improve this inaccuracy, we developed nonlinear thermal analysis methods. Many experiments, including those with a 3000kVA superconducting generator, have proved that this technique accurately estimates the temperature distribution in structures and the heat penetrating an inner rotor. The technique enabled us to obtain important knowledge on parameters concerning heat penetrating from current leads, torque tubes, and radiation shields for trial designing of a 1000MVA machine.

Duration of load tests for shear strength

The strength of wood falls with time under load, and in current design codes the short-term strength of wood is reduced by about 40% to account for duration of load effects. This figure is based on tests made on small bending specimens. In this paper are described tests made on wooden torque tubes to investigate the effect of duration of load on shear strength. A control sample was tested to establish a curve for short-term strength, and four groups of 80 specimens each were then tested under various levels of constant long-term load. Stress ratio at failure was estimated by assuming that the short-term strength of each group could be represented by the control curve, and that under long-term loading specimens would fail in the order of their short-term strength. In each group the stress ratio at failure fell with time under load, and this reduction appears to be related to that predicted by a viscoelastic plastic model. It is concluded that the Madison curve presently used to predict duration of load effects may be conservative at normal levels of applied stress. Key words: wood, shear, long-term loading, duration of load.

Dynamic stability of hingeless and bearingless rotors in forward flight

The aeroelastic stability of flap bending, lead-lag bending and torsion of hingeless and bearingless rotor blades in forward flight is examined, using a finite element formulation based on Hamilton's principle. The hingeless blade is idealized as an elastic beam, and is discretized into beam elements. Each beam element consists of fifteen nodal degrees of freedom. Between the elements there is a continuity of displacement and slope for lag and flap bending, and a continuity of displacement for twist and axial deflection. For a bearingless rotor blade the flexbeam, the torque tube and the main blade are assumed as elastic beams, and these are discretized into beam elements. Quasisteady strip theory is used to evaluate the aerodynamic forces, and the unsteady aerodynamic effects are introduced approximately through a dynamic wake induced inflow modelling. The natural vibration characteristics of a rotating blade are calculated from the finite element equations. The blade finite element response equations are transformed to the model space in the form of a few normal mode equations. These nonlinear response equations containing periodic terms are solved iteratively using Floquet theory. The periodic perturbation equations linearized about the nonlinear response position are solved for stability using Floquet transition matrix theory as well as constant coefficient approximation in the fixed reference frame. Results are presented for both stiff-inplane and soft-inplane blade configurations. Stability results are also obtained for a bearingless blade configuration consisting of single flexbeam with a wrap-around type torque tube and the pitch links located, one on the leading edge and the other on the trailing edge of the torque tube. The effects of several parameters on the blade stability are examined, including, the blade modelling, lag stiffness, dynamic inflow, constant coefficient approximation and forward speed.

Dynamic Stability of a Bearingless Circulation Control Rotor Blade in Hover

The aeroelastic stability of flap bending, lead-lag bending and torsion of a bearingless circulation control rotor blade in hover is investigated using a finite element formulation based on Hamilton's principle. The flexbeam, the torque tube and the outboard blade are discretized into beam elements, each with fifteen nodal degrees of freedom. Quasisteady strip theory is used to evaluate the aerodynamic forces and the airfoil characteristics are represented either in the form of simple analytical expressions or in the form of data tables. A correlation study of analytical results with the experimental data is attempted for selected bearingless blade configurations with conventional airfoil characteristics.

Finite Element Analysis for Bearingless Rotor Blade Aeroelasticity

A conventional articulated rotor blade has mechanical flap and lag hinges, a lag damper, and a pitch bearing. In connection with an interest in designs of greater mechanical simplicity and increased maintainability, hingeless and bearingless rotors have been developed. A hingeless blade lacks the hinges and is cantilevered at the hub. It does have a pitch bearing for pitch control. A bearingless design eliminates the hinges and the pitch bearing as well. In the present investigation of bearingless rotor blade characteristics, finite element analysis has been successfully applied to determine the solutions of the nonlinear trim equations and the linearized flutter equations of multiple-load-path blades. The employed formulation is based on Hamilton's principle. The spatial dependence of the equations of motion is discretized by dividing the flexbeams, the torque tube, and the outboard into a number of elements.

Structural models and undamped torsional natural frequencies of a superconducting turbogenerator rotor

Superconducting turbogenerators with a “double rotor structure” have a torsional natural frequency within the generator, the outer rotor moving in opposition to the inner rotor. For large machines this natural frequency may approach 100 Hz. In this paper a finite element model and simple lumped mass and spring models of the rotor, for the calculation of the undamped torsional natural frequencies, are described and compared. A method by which equivalent spring stiffnesses for both the inner and outer rotors can be derived is described, allowing one to use a rotor model with one lumped mass and equivalent spring stiffness for each of the inner and outer rotors. Such a rotor model can be readily used for studying electromagnetic interaction effects and assessing fault torques in the outer rotor and inner rotor torque tubes.

Torsional natural frequencies in the superconducting turbogenerator

In the design of superconducting AC generators the inner and outer rotors aie supported on thin torque tubes. This type of rotor structure introduces a torsional natural frequency, whereby the inner and outer rotor of the generator move in opposition, the frequency of which is influenced by the rotor electromagnetic structure. In this paper an analysis of the torsional natural frequencies within the turbine and generator is presented using eigenvalue techniques. The analysis is used to investigate the influence of the rotor structure on the frequency and damping of both the inter-rotor torsional mode and the rigid-body hunting oscillation mode. A simple formula for damping of rotor-hunting oscillations is presented. The eigen-value technique is also used to examine the influence of generator loading condition on the two oscillation modes.

A sensitive rolling moment balance for use in supersonic blowdown tunnels

STRAIN-GAGE balance is a standard device for measurement of aerodynamic loads acting on models in a wind tunnel. The most common type—the six component internal balance—is employed for general, routine testing while special-purpose balances designed to meet exclusive requirements are used for specialized tests. Design of balances meant for use in supersonic blowdown tunnels can often be complicated on account of the need to withstand large transient loads that occur on the models during tunnel starting and stopping and yet have adequate sensitivity. These problems become particularly severe when the loads to be measured are of low magnitude, such as in some special tests. Successful solutions to these problems are often obtained by adoption of some unconventional design concepts and schemes. A recent example of a novel scheme for measurement of low rolling moments in low speed wind tunnels is found in Ref. 1. A special-purpose internal strain-gage balance was developed to measure low rolling moments in a trisonic blowdown tunnel. The capability of the balance to withstand large magnitudes of all the six components of load while retaining a high sensitivity to rolling moment is an important and special feature. The balance was required to measure maximum rolling moments varying between 0.2 and 10 kg-cm with a resolution of 0.002 kg-cm on wing-body models of 36 mm diameter and 380 mm length. The tunnel starting/stopping loads that the balance had to withstand were large owing not only to the relatively large size of models but also to the high pressure ratios required for starting the tunnel (starting pressures at Mach 2.5 and 3 were 5 and 6.5 atm, respectively). The above combined requirements could not be met by the usual balance arrangements employing cruciform or torque tube element and a balance incorporating some unusual design features, described below, was developed. Description The balance is of floating-frame type and the sensing element is essentially a crossed-flexur e pivot formed by four strips connecting the outer sleeve to the inner rod (Fig. 1). The strips are arranged in pairs in two transverse planes and the distance between the strips in each plane is kept as large as possible to resist high pitching and yawing moments. The strips, made of heat treated high strength alloy steel, are 1 mm thick by 9 mm wide and provide adequate sensitivity to low rolling moments. In order to increase the capability of the balance to withstand large rolling moment, an overload safeguard that automatically limits the rolling moment in the strips is provided. The safeguard, Fig. 2, is formed by a stop connected to the outer sleeve and passing through slots in the inner rod. When the balance is subjected to a rolling moment

Effect of Warping Restraints on I-Beam Buckling

Elastic lateral buckling moments are computed for six wide-flange beams under uniform moment for a comprehensive range of length to depth and depth to flange width ratios. Support conditions considered are fully fixed about the minor axis, hinged about the minor axis and free to warp, and hinged about the minor axis and warping suppressed. The last condition is reproduced in a prototype by welding a troughlike shape to the web and flanges in a manner that produced a warp restraining torque tube between the flanges. A numerical method is used to obtain buckling moments for the hinged-warp restrained case. The fixed-support condition is easily the superior way of suppressing buckling but that condition is often not easily producible in a practical design detail. On the other hand, the hinged-warped restrained support condition results in significant improvement in the buckling moments and has the advantage of being relatively easy to produce in a design detail.