Torsion Arm Research Articles

Analysis of aerodynamic and aeroacoustics of full scale landing gear

The aerodynamic noise of a landing gear is an important source of airframe noise. The analysis of its noise characteristics plays an important role in the design of a low-noise landing gear. Based on the FL-52 acoustic wind tunnel test technology, the coupled scale adaptive model and the acoustic disturbance equation, the results on aerodynamic noise of a full-scale landing gear model are analyzed. The high-fidelity model includes transverse strut, torsion arm, piston rod, wheel and other parts. The characteristics of static pressure distribution, power spectrum density of pulsating pressure, aerodynamic noise source distribution and directivity of overall sound pressure level are analyzed. The noise characteristics of the far-field microphone are compared with the local microphone installed in the wheel cavity. In this way, we characterize the directivity of pure tone in the wheel cavity and understand its contribution to the far-field noise. The results show that the aerodynamic noise of the landing gear can be quantified accurately by the hybrid numerical method. The pure tone has two frequencies inside and outside the wheel of the landing gear: 560 Hz and 960 Hz. The peak of the loudest sound pressure level reaches 136 dB, and the pure tone radiates to the surface of the non-separation area of the wheel of the landing gear. However, the wall pressure spectrum of the points located in the turbulence region shows a wide-frequency characteristic, and there is no obvious pure tone. From the point of view of the far-field noise directivity, the forward noise of the landing gear is larger than the rear noise, and there is a small overall sound pressure level area at the points of 65 and 110 degrees respectively. When the monitoring points are far away, the far-field noise of the landing gear shows the characteristics of wide frequency, and no obvious pure tone appears. The method can provide the technical support for predicting the aeroacoustics of a landing gear and designing a low-noise land gear.

Three-axis torque investigation of interfacial exchange coupling in a NiFe/CoO bilayer micromagnetic disk

Micrometer diameter bilayers of NiFe (permalloy, Py) and cobalt oxide (CoO) deposited on nanomechanical resonators were used to investigate exchange bias effects. The mechanical compliances of two resonator axes were enhanced by severing one torsion arm, resulting in a unique three-axis resonator that responds resonantly to torques generated by a three-axis RF field. Our technique permits simultaneous measurement of three orthogonal torque components. Measurements of the anisotropies associated with interfacial exchange coupling effects have been made. At cryogenic temperatures, observations of shifted linear hysteresis loops confirmed the presence of exchange bias from the Py/CoO interface. An in-plane rotating DC bias field was used to probe in-plane anisotropies through the out-of-plane torque. Training effects in the rotational hysteresis data were observed and showed that features due to interfacial coupling did not diminish irrespective of substantial training of the unidirectional anisotropy. The data from the rotational hysteresis loops were fit with parameters from a macrospin solution to the Landau-Lifshitz-Gilbert equation. Each parameter of the exchange bias model accounts for specific features of the rotational loop.

A New Coupling Spring Design for MEMS Tuning Fork Structures Demonstrating Robustness to Fabrication Errors and Linear Accelerations

This paper presents a new coupling spring design for the MEMS tuning fork structure. The spring design incorporates the outer arm, inner arm, and torsional arm. The outer and inner arms are connected through the torsional arm to be rotationally symmetric, constituting 180° in relation to the center of spring. The designed coupling spring always prioritizes an anti-phase motion providing robustness to linear acceleration. The operation of the spring was validated through FEM simulations and experimental results. The experimental results demonstrated that the anti-phase resonant frequency was 27,280 Hz, whereas the in-phase resonant frequency was 27,780 Hz. Furthermore, the designed coupling spring benefited from a narrow etch cavity and small surface area, making it an ideal design for consumer electronics applications.

Analysis and Research on Fracture Cause of Fixed Shaft of Torsion Arm of Wind Turbine Gearbox

In a wind power plant of a wind power plant limited liability company, the fixed shaft of the torsion arm of the gear box broke during the operation of a wind power generator set. In order to find out the cause of fracture, the fracture fixed shaft of torsion arm was comprehensively detected and analyzed by means of appearance morphology analysis, chemical composition analysis, mechanical properties testing, microstructure testing and fracture micro-area analysis. The results show that the main reasons for the fracture of the fixed shaft of the torsion arm of the fan gear box are as follows: improper heat treatment process of the fixed shaft of the torsion arm of the gear box causes a large amount of massive ferrite in the material structure, resulting in insufficient strength of the material; the inclusion in the material is serious, resulting in unqualified impact toughness; Shaft surface surfacing Cr - Mn stainless steel material causes the fusion zone C migration form brittle layer, at the same time the vast difference between the state of welding layer and substrate organization fusion zone caused by larger remnants stress, the embrittlement in bond layer to form the intergranular crack crack source, and in the process of the equipment operation under the action of cyclic torsional and impact load, Cracks propagate in a fatiguing manner and lead to eventual fracture.

Staple-Plate Plus Screw vs Screw Alone in Talonavicular Arthrodesis: A Cadaveric Biomechanical Study.

This study evaluated whether the addition of a nitinol staple-plate to a single cannulated screw increased the mechanical stability for a talonavicular fixation construct. Twenty matched pairs of cadaveric feet were randomized to fusion with either a single 5.5-mm cannulated screw or a screw and a plate with 2 screws and a slot with an 18-mm nitinol staple. After in situ fusion procedure, the talonavicular joint complex was dissected free and the ends were embedded in epoxy. The specimens were then cyclically loaded on a servohydraulic load frame (1000 cycles at 20 N, increasing at intervals of 20 N until failure), half of them for cantilever bending and the other half for torsion. In the bending arm of the study, the staple-plate group showed significantly higher stiffness, failure load, and cycles to failure. In the torsion arm of the study, the staple-plate group also had higher cycles to failure, stiffness in external rotation, and torque to failure. No significant difference was noted in stiffness in internal rotation. We found a significant increase in stability of the talonavicular joint when a nitinol staple-plate construct was placed to augment a single cannulated screw for the purpose of a talonavicular fusion. This information may be helpful to surgeons in implant selection for this common arthrodesis procedure.

Torsional thrust balance for electric propulsion application with electrostatic calibration device

A direct measurement torsional thrust balance for electric thrusters has been developed to test pulsed plasma thrusters (PPTs) and other electric thrusters. The current configuration is able to measure impulse bits between 14 and 79 μN · s with a resolution of 0.05 to 0.10 μN · s. The direct measurement technique, in which the thruster is mounted on the thrust balance, is considered the most suitable and accurate for applications with PPTs. The use of flexural pivots with low stiffness makes the balance compact, with a smaller torsional arm. An electrostatic calibration device (ECD) was designed and built to calibrate the thrust balance, simulate the thrust of PPTs, and to allow forthcoming tests of the double discharge pulsed plasma thrusters developed at the Associated Laboratory of Combustion and Propulsion of the Brazilian National Institute for Space Research at the Electric Space Propulsion Laboratory. The maximum impulse bit measurement error achieved was as low as 10%, lower than the average of 12%–15%, typical for this type of thrust balance. The ECD was calibrated using a previously calibrated precision analytic scale. The ECD then can carry this calibration traceability to the thrust balance, providing a higher level of accuracy.

A momentum flux measuring instrument with the variable-range for exhaust plume

A momentum flux measuring instrument (MFMI), which ranges from 1 mN∼300 N, is designed to measure the parameters related to the momentum flux of exhaust plume of attitude and orbit control thrusters covered electric and chemical thrusters. A MFMI with the variable-range provides an efficient and economy way to study the exhaust plume of both electric and chemical thrusters. The flexural pivots, replaceable strain gauge, replaceable target plate, and force arm with the variable length make it possible. The designed MFMI with the non-displacement measurement can reduce the influence of pipelines and test lines, especially the elastic force and friction due to displacement. The designed MFMI system with the range of 0∼100 mN and 0∼15 N was calibrated separately. The target indirect measurement method is a simple and economical option for measuring the thrust of electric thrusters, and is employed to measure the thrust of the LIPS-200 ion thruster using the designed MFMI. Research indicates that the sputtering contributes to the momentum transfer of plasma-surface interactions. In addition, the high-speed charged ions from the thruster will experience a charge-exchange (CEX) collision with the slow neutral background. Therefore, the influence of the sputtering and CEX on target indirect measurement method is derived in detail, and then the measured thrust is corrected. The measured average thrust, which is 40.1 mN, demonstrates that the designed MFMI is effective. The designed MFMI can also be employed as a thrust stand by directly mounting the thrusters on torsional arm, and a maximum of three thrusters can be installed on the MFMI at the same time.

RF MEMS for Reconfigurable Antenna Using Gravitational Search Optimization and Artificial Neural Network

The projected method explains about the problems occurred in the combination of the MEMS switches and the complete scheme plan is resolved through choosing the finest devise limits for the plan. The devise limits, namely, length of beam, width of beam, torsion arm length, switch thickness, holes and gap were measured. At this point, the finest value of the devise limit is forecast by the aid of artificial neural network (ANN). Furthermore, the method contains the optimization method of Gravitational Search Algorithm (GSA) to optimize the input signal and so dropping the Mean Square Error (MSE). The complete scheme is executed in the operational platform of MATLAB and the outcomes were examined.

Configurations and Key Issues of Low Thrust Measurement for Microspacecrafts

Microthrusters on microspacecrafts are of interest and its output thrust must be characterized for a particular applicaton. The technology of micro thrust measurement can evaluate the performance of microthrusters. The measurement principles of steady-state thrust, pulse impulse, average thrust and instantaneous thrust are introduced. The classical thrust stands at home and broad are summarized and they are classified into torsional arm type, balance type, hanging pendulum type and flexure vibration type according to their dynamics configurations. The characters, purpose, advantages and disadvantages are analyzed. The key problems, such as error influence factors and its countermeasure, calibration, and measurement automatization, are pointed out.

Step-response of a torsional device with multiple discontinuous non-linearities: Formulation of a vibratory experiment

A vehicle clutch damper is intentionally designed to contain multiple discontinuous non-linearities, such as multi-staged springs, clearances, pre-loads, and multi-staged friction elements. The main purpose of this practical torsional device is to transmit a wide range of torque while isolating torsional vibration between an engine and transmission. Improved understanding of the dynamic behavior of the device could be facilitated by laboratory measurement, and thus a refined vibratory experiment is proposed. The experiment is conceptually described as a single degree of freedom non-linear torsional system that is excited by an external step torque. The single torsional inertia (consisting of a shaft and torsion arm) is coupled to ground through parallel production clutch dampers, which are characterized by quasi-static measurements provided by the manufacturer. Other experimental objectives address physical dimensions, system actuation, flexural modes, instrumentation, and signal processing issues. Typical measurements show that the step response of the device is characterized by three distinct non-linear regimes (double-sided impact, single-sided impact, and no-impact). Each regime is directly related to the non-linear features of the device and can be described by peak angular acceleration values. Predictions of a simplified single degree of freedom non-linear model verify that the experiment performs well and as designed. Accordingly, the benchmark measurements could be utilized to validate non-linear models and simulation codes, as well as characterize dynamic parameters of the device including its dissipative properties.

Precision electromagnetic calibration technique for micro-Newton thrust stands

This paper introduces a new direct non-contact electromagnetic calibration technique for high precision measurements of micro-thrust and impulse. A ring-shaped electromagnet with an air gap is used in the calibration. The calibration force is produced by the interaction of a uniform magnetic field with a copper wire current in the air gap. This force depends linearly on this current as well as the steady angular displacement of the torsion arm of the thrust stand. The range of calibration force is very large and the calibration force is easy to generate and insensitive to the arm displacement. The calibration uncertainty for a 150-μN force is 4.17 μN. The more influential factor on the calibration uncertainty is the magnetization of the electromagnet core due to the copper wire current. In the impulse calibration, the exerted impulse is linearly dependent on the maximal angular displacement of the torsion arm. The uncertainty in the impulse calibration is determined by uncertainties in both the force calibration and the pulse time.

An Investigaton of Minimum-Weight Dual-Material Symmetrically Loaded Wheels and Torsion Arms

A cylindrically symmetric layout of two opposite families of logarithmic spirals is shown to define the layout of minimum-weight, symmetrically loaded wheel structures, where different materials are used for the tension and compression members, respectively; referred to here as dual-material structures. Analytical solutions are obtained for both structure weight and deflection. The symmetric solutions are shown to form the basis for torsion arm structures, which when designed to accept the same total load, have identical weight and are subjected to identical deflections. The theoretical predictions of structure weight, deflection, and support reactions are shown to be in close agreement to the values obtained with truss designs, whose nodes are spaced along the theoretical spiral layout lines. The original Michell solution based on 45 deg equiangular spirals is shown to be in very close agreement with layout solutions designed to be kinematically compatible with the strain field required for an optimal dual-material design.

Dynamics of flexible-link and flexible-joint manipulator carrying a payload with rotary inertia

A dynamic model of a flexible-arm and flexible-joint manipulator carrying a payload with rotary inertia is presented. The Lagrangian approach in conjunction with the finite element method is employed in deriving the equations of motion, within the assumption of a small deformation theory. All the dynamic coupling terms between the system reference rotational motion, joint torsional deformations and arm bending deformations are accounted for. The dynamics of a payload with rotary inertia are incorporated in the model in a consistent manner. Furthermore, the effects of axial shortening due to beam and bending deformations and motions induced inertial forces as well as the effects of gravity are included in the model. The resulting model and simulation results have shown that the joint flexibility has a pronounced effect on the dynamic behavior of rotating flexible arms that should not be simply neglected. The effect is shown to be due to the nonlinear dynamic interaction between the joint torsional deformations, the arm bending deformations and the system reference rotational motion. Simulation results of the nonlinear and the linearized models are compared and the results are discussed. The effects of the payload are shown to be increasing the elastic deformations’ amplitudes and reducing the frequency of oscillations. Due to the model nonlinearity, different combinations of system parameters are expected to develop different effects. This makes the proposed model valid in the design process as well as in the performance evaluation.

An Automatic Magnetic Balance for the Study of Ferromagnetic Materials

An instrument is described for plotting, automatically, magnetization-temperature curves for ferromagnetic substances. The sample is placed on a torsion arm in an inhomogenous magnetic field, and the force to which it is subjected is opposed by a torque applied to a torsion wire by a reversible motor. The shaft of the motor is connected to a Beckmann Helipot, and the motion of the shaft is converted into a change in emf. which is recorded by a Leeds and Northrup Speedomax. The temperature of the sample is also controlled and recorded by the Speedomax. Data on the performance of the instrument are given and sample plots of thermomagnetic runs for Ni, Fe3O4, and Fe3C are shown.

A simple spring torsion balance

A simple and inexpensive spring torsion balance is described, the elastic element of which is a helical spring of phosphor-bronze wire which is arranged to act as the only support of the torsion arm. The relative sensitivity is about 0.002 of the maximum load, while the absolute sensitivity attainable is at least 0.001 mg., by direct reading.

The Magnetic Balance of MM. P. Curie and C. Cheneveau

This balance is intended for the determination of the coefficient of specific magnetization, susceptibility, and permeability of feebly paramagnetic and diamagnetic bodies. The body under investigation is suspended from one arm of a torsion balance, which measures the force exerted on the body when it is placed in the non-uniform field of a permanent magnet. The torsion balance is formed by a horizontal rod suspended by a long fine platinum wire and carrying at one end a hook from which the substance under investigation can be suspended in a small enclosing glass tube. On the other end of the torsion arm a copper sector is fixed which moves between the poles of an auxiliary magnet and thus provides efficient damping. A second branch arm is also provided upon which may be placed suitable counterweights to balance the specimen. The suspension carries a mirror, and the movements are read on a translucent scale in the ordinary way. The magnetic field is that of a large circular permanent magnet mounted in such a way that the vertical gap may be made to describe a semicircle of radius equal to the length of the torsion arm, and the movements of this magnet are controlled by the observer at the screen by means of cords. An empty containing tube is first mounted on the balance, and the maximum deviation on both sides of the zero is obtained by bringing up the magnet towards each side of the specimen. The tube is now filled to a given mark with a known mass of pure distilled water and the variations observed as before. The water is now replaced by a known mass of the substance to be examined occupying the same volume or the same vertical height, and again the deviations are observed. The paper indicates how the value of K may be calculated from these observations. Experiments have been performed with various metals and alloys, and the results are tabulated and discussed in the paper.