Torsional Measurements Research Articles

A sandwich structure on Grapefruit microstructured fiber for measurement of non-coaxial torsion

A sandwich structure on Grapefruit microstructured fiber(GMF) for measurement of non-coaxial torsion is proposed and fabricated. The GMF and the single-mode fiber (SMF) are fused to make the SMF-GMF-SMF structure. The non-coaxial system is used to twist the GMF sensor. Because the two ends of the GMF are not at the same height, a tensile strain is introduced into the fiber. At the same time, the photoelastic effect and the Poisson effect also cause the phase difference to change, resulting in a transmission spectrum shift. The experimental results show that in the range of 0°∼360°, with the increase of the twist angle, the intensity of the transmission mode gradually increases, and the coupling efficiency of the higher-order mode increases. The torsion sensitivity can reaches 0.02315 dB/°. The sensor is simple in fabrication, high in sensitivity, and has a good application prospect in torsion measurement of various devices.

Helical sensor for simultaneous measurement of torsion and temperature

Based on our current research on long-period fiber gratings (LPFGs), we propose a novel fiber-based sensor for simultaneous measurement of torsion and temperature. The proposed sensor cleverly combines CO2 laser polishing with pre-twist that can introduce elliptical birefringence in the fiber to improve sensing performance. Through comparative measurement experiments, we investigate the torsion characteristic of the sensor and the effect of different degrees of pre-twist on it. Experimental results show that the highest torsion sensitivity of two resonant dips can reach 0.635 nm/(rad/m) and −0.654 nm/(rad/m) in the range of 0 rad/m − 12.6 rad/m, while in the range of −12.6 rad/m − 0 rad/m the sensitivities are 0.14 nm/(rad/m) and −0.083 nm/(rad/m) respectively due to inhomogeneous elliptical birefringence. Meanwhile, the temperature sensitivity of the two resonant dips are calculated to be 62.5 pm/°C and 66.8 pm/°C, respectively. Due to the different sensitivities of temperature and torsion, the matrix method can be used for simultaneous measurement of two parameters to ignore crosstalk. As a result, the proposed sensor shows competitiveness in practical engineering applications.

Reconstruction error model of distributed shape sensing based on the reentered frame in OFDR.

At present, the reconstruction error of optical fiber shape sensing is commonly represented by Euclidean distance error. However, the Euclidian error of shape reconstruction will be dependent on the shape complexity, which depends on length, curvature and torsion. In this paper, we establish a reconstruction error model of distributed shape sensing in optical frequency domain reflectometry (OFDR) based on the Frenet-Serret frame and the error delivering theory, which illustrates the relationship between the reconstruction error and parameters such as curvature, torsion, fiber length and strain measurement error. We experimentally verify the feasibility and applicability of the proposed reconstruction error model by distributed optical fiber shape sensing system based on OFDR. The proposed reconstruction error model can provide a prediction of the maximal reconstruction error when the estimated range of curvature, torsion, fiber length of a shape needs to be reconstructed and strain measurement errors of OFDR system are known. It is very useful to judge whether the shape reconstruction error meets the requirement according to the shape to be reconstructed.

Field Measurement on Translational and Torsional Wind-Induced Response of a High-Rise Building during Typhoon Khanun

Full measurements for the wind field atop a 32-storey building (supported by four huge columns) and for the dynamic responses of different floors were conducted on 15 October 2017 to obtain the translational and torsional responses of the high-rise building during the Typhoon Khanun. The time histories of the torsional angular acceleration responses on the 24th and 32nd floors of the high-rise building were obtained using RA013 rotational accelerometer, and those of the translational acceleration responses on the 6th, 12th, 18th, 24th, 30th and 32nd floors along axial direction were recorded by the translational accelerometer. The variation rules of the translational and torsional acceleration responses with floor height and mean wind speed were disclosed, and the response ratios between the torsional and translational acceleration were analyzed when basic time intervals were 10 min. Based on the target probability method, the value range of the acceleration peak factor with different target reliability under Typhoon Khanun was proposed. The results show that the translational and torsional acceleration peak values and root mean squares are the power functions of mean wind speed. The values of acceleration peak factors are recommended to be 3.0 and 5.0 if target reliabilities are determined as 99.38% and 100%, respectively. Research on torsional response measurements can accumulate valuable scientific data and lay solid foundations for the subsequent studies on the torsional wind-resistant design of high-rise buildings.

Highly sensitive temperature-independent FBG-based sensor embedded in thermoplastic polyurethane using 3D printing technology for the measurements of torsion

A new design of optical Fiber Bragg Grating (FBG)-based sensor for the measurement of torsion (twist) has been developed, which, while offering a high level of accuracy, can be fabricated inexpensively using 3D printing technology. In this sensor design, an FBG is embedded inside the thermoplastic polyurethane (TPU) filament, which acts as the sensing pad for the FBG, taking advantage of its highly elastic properties and excellent sensitivity to variations in local strain. Experiments conducted have shown that the embedded FBG-based sensor can be used effectively in the measurements of torsion or rotation, at a bonding angle of 45°, giving an average responsivity of 0.95 pm/deg in both the clockwise and anticlockwise direction over the range of − 100° to + 100°, with good linearity of up to 99%. Furthermore, the device has been developed to allow for the effects of any temperature changes to be compensated by including an additional but 'untwisted' FBG in the sensor design. It provides a temperature sensitivity of 18.90 pm/°C. This design of twist measurement sensor described in this work also shows a good response in the underground soil movement, giving an average responsivity of 0.95 pm/deg in both the clockwise and anticlockwise direction over the range of − 100° to + 100°, with good linearity of up to 99%. This proves that this fabricated device can be made applicable to a wide range of engineering applications reliably and inexpensively.

Three-Dimensional Analysis Versus Two-Dimensional Slice-Based Analysis of CT for Measuring Femoral Torsion and Its Correlation to Passive Hip Range of Motion.

IntroductionFemoral torsion is an important anatomical consideration of the hip that has major implications on the natural motion of the hip joint. Similarly, it affects pathologic conditions of the hip, including femoroacetabular impingement, dysplasia, and/or microinstability. Femoral torsion is typically measured on two-dimensional (2D) axial CT cuts by creating the angle between the femoral neck and the posterior aspect of the ipsilateral femoral condyles. Position of the leg during imaging may affect 2D measurements. Three-dimensional (3D) analysis of a hip CT with inclusion of femoral alignment may portray the anatomy of the hip more accurately as compared to a 2D slice-based analysis of a hip CT scan. It is thought that femoral torsion measured using this system could be a more accurate and reliable means of measurement. The primary purpose of this study is to assess the differences in measuring femoral torsion with 3D modeling and analysis compared to the standard 2D slice-based approach on a CT scan. Secondarily, we attempt to determine how the passive range of motion of the hip correlates with femoral torsion measured using the 3D model versus the 2D model.MethodsIn a prospective cohort study of 20 patients, femoral torsion was assessed using both 2D analysis and 3D analysis. The differences between these measurements on each of the imaging modalities were compared. Additionally, each patient had the passive range of motion of their hip measured with a goniometer. The amount of internal and external rotation was measured with the hip in a neutral position and with the hip flexed to 90°. Acetabular version, combined version, and alpha angle were added to multivariate regression analysis to evaluate their effect versus femoral torsion alone.ResultsFemoral antetorsion measured using the standard 2D slice-based approach on CT scan was 22.1° (SD: 11.1°), which was higher (p<0.001) than that using 3D analysis (8.25°; SD: 10.5°). There was a strong correlation between femoral torsion measurements using 3D analysis and 2D analysis (R=0.91). Based on 3D analysis, there was a moderate correlation between femoral torsion and passive hip external rotation measured with the hip flexed to 90° (R=0.65, p<0.002) and with the hip in a neutral position (R=0.58, p<0.007).ConclusionThere was a significant difference between femoral torsion measurements using the 3D analysis, which showed approximately 14° of less antetorsion on average. Additionally, rotation of the hip and femoral torsion was correlated to higher levels of antetorsion associated with more internal rotation of the hip.

Development and Validation of a Mobile Application for Measuring Tibial Torsion.

Tibial torsion lacks a single and reliable method for its measurement. While physical examination, computed tomography (CT), and EOS imaging are used complementarily, three-dimensional (3D) CT is the most widely used method for intuitive documentation and visualization. However, concern regarding the associated radiation hazard limits its use in the evaluation of pediatric patients. Moreover, EOS machines are too expensive and too large to be placed in every clinic requiring the measurement of tibial torsion. Therefore, a new method for 3D reconstruction is needed. In the present study, we tested the validity and reliability of a novel reconstruction tool for the lower leg. A statistical shape model and Laplacian constraint were adopted for the development of a new reconstruction tool for measuring tibial torsion. Tibial torsion measurements based on a 3D reconstruction application and CT images for 36 patients were evaluated for intraobserver and interobserver reliability. Tibial torsion measurements for 75 patients were compared for validation. A 3D reconstruction system for the lower leg was developed as a mobile application and was installed in a portable device for easy access in the clinical setting. In terms of interobserver reliability, the intraclass correlation coefficient among 3 clinicians was 0.896 (95% confidence interval [CI], 0.828 to 0.941). The correlation coefficient between tibial torsion measured with use of 3D CT and that measured with the mobile application was 0.865 (p < 0.001). The mobile application showed excellent reliability and validity for measuring tibial torsion. Concurrent utilization with mobile application for the femur allows visualization of the rotational profile of the leg without the need for CT or EOS. Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Influence of limb positioning during image acquisition on femoral torsion measurements: implications for surgical planning

ABSTRACT Femoral torsion is an important parameter to accurately quantify when planning for the correction of structural pathomorphology. The purpose of this study was to quantify the influence of limb positioning during image acquisition and of alignment techniques on femoral torsion measurements, by measuring the change in femoral torsion angle, upon digital rotations that simulate flexion/extension and adduction/abduction positions of the femur. Femoral torsion measurements were reduced up to 1° and increased up to 0.35° per each degree of flexion and abduction, respectively. The estimation of femoral torsion measurements yielded a difference up to 5.8° between the aligned and non-aligned cases.

Axial-torsional mode correlation analysis of a drill string system with non-smooth characteristics

Axial-torsional coupling vibrations are dangerous and complex vibrations that can cause abnormal working conditions in the drilling system. Therefore, the vibration mode correlation is essential in the dynamic analysis of the response complexity of the system to reduce the vibration risk level. In this paper, an axial-torsional lumped parameter model with 5-DOF (degrees of freedom) is proposed to investigate the axial-torsional mode correlation of a drill string system with non-smooth characteristics. Numerical simulations are carried out by using the 4th-5th order Runge-Kutta method with adaptive time steps, and the simulation results are compared and verified by the 5-DOF torsional lumped parameters model and field measurement data. It also performs time domain, frequency domain, and correlation coefficient analysis. The results reveal the mode shape and correlations of an axial-torsional mode in coupled vibrations with and without a bit-bounce. Bit-bounce and stick-slip coupling vibration can be produced by increasing the rotary table speed. The torsional angular velocity of the proposed model is smaller than that of the comparative model, which is in good agreement with the field data.

Simultaneous measurement of torsion and strain at high temperature by using a highly birefringent cladding fiber Bragg grating.

We demonstrate the fabrication of a new highly birefringent cladding fiber Bragg grating (Hi-Bi CFBG) consisting of a pair of sawtooth stressors near the fiber core by using a femtosecond laser direct writing technology. The unique sawtooth structure serves as in-fiber stressor and also generates Bragg resonance due to its periodicity. After optimization of laser pulse energy, the Hi-Bi CFBG with a high birefringence of 2.2 × 10-4 and a low peak reflectivity of ∼ -24.5 dB (corresponding to ∼ 0.3%) was successfully fabricated in a conventional single-mode fiber (SMF). And then, a wavelength-division-multiplexed Hi-Bi CFBGs array and an identical Hi-Bi CFBGs array were successfully constructed. Moreover, a simultaneous measurement of torsion and strain at high temperature of 700 °C was realized by using the fabricated Hi-Bi CFBG, in which the torsion can be deduced by monitoring the reflection difference between the two polarization peaks and strain can be detected by measuring polarization peak wavelength. A high torsion sensitivity of up to 80.02 dB/(deg/mm) and a strain sensitivity of 1.06 pm/µɛ were achieved. As such, the proposed Hi-Bi CFBG can be used as a mechanical sensor in many areas, especially in structural health monitoring at extreme conditions.

Translated article] A 3D method to estimate the effect of derotational osteotomies over femoral maltorsion

Introduction and objectivesAccurate measurement of femoral torsion is essential to diagnosing, correct surgical decision-making, and the preoperative planning of derotational osteotomies in a subgroup of anterior knee pain patients and patellofemoral instability. Several measurement techniques have been described with great variability in the magnitude of the values. Moreover, none of them can predict the effect of rotational osteotomy on the femoral version value. The purpose of the present work is to develop a method to reliably measure femoral torsion as well as to evaluate the effects of osteotomy on the femoral version angle. Material and methods30 patients without previous signs neither symptoms of patellofemoral pain or patellofemoral instability and with a lower limbs CT were selected. Their femoral torsion was measured using the classic Jeanmart and the Murphy's method by two independent radiologists. Independently, two orthopedic surgeons measured femoral torsion with the 3D method described in this study. The intraclass coefficient correlation and the Bland-Altman tests were used to analyze qualitatively and quantitatively the intraobserver and interobserver variability of the method regarding the Jeanmart's and Murphy's method. The confidence interval of the Normal values of the new method were defined and a lineal regression analysis between the 3D-Jeanmart's and 3D-Muphy's methods was performed. ResultsThe mean femoral version with the 3D method was 12.74° (SD 5.96°, 95% CI: 11.67°–13.82°). With Jeanmart's method, it was 12.84° (SD 8.60°, 95% CI: 11.28°–14.39°) and 15.87° (SD 10.68°, 95% CI: 13.94°–17.80°) with Murphy's method, being these differences not statistically significant. Both interobserver and intraobserver agreement of the 3D method were high. ConclusionThe method presented in this study allows for the reliable quantification of femoral torsion in a reproducible way. This method can be applied in several open access 3D image programmes what makes its implementation in the healthcare centres possible from now on.

Ultra-low-dose computed tomography for torsion measurements of the lower extremities in children and adolescents

BackgroundQuantifying femoral and tibial torsion is crucial in the preoperative planning for derotation surgery in children and adolescents. The use of an ultra-low-dose computed tomography (CT) protocol might be possible for modern CT scanners and suitable for reliable torsion measurements even though the bones are not completely ossified.MethodsThis is a retrospective review of 77 children/adolescents (mean age 12.7 years) who underwent a lower extremity CT for torsion measurements on a 64-slice scanner. A stepwise dose reduction (70%, 50%, 30% of the original dose) was simulated. Torsion measurements were performed on all image datasets, and image noise, interrater agreement and subjective image quality were evaluated. Effective radiation dose of each original scan was estimated. As proof of concept, 24 children were scanned with an ultra-low-dose protocol, adapted from the 30% dose simulation, and the intra-class correlation coefficient (ICC) was determined. Ethics approval and informed consent were given.ResultsTorsion measurements at the simulated 30% dose level had equivalent interrater agreement compared to the 100% dose level (ICC ≥ 0.99 for all locations and dose levels). Image quality of almost all datasets was rated excellent, regardless of dose. The mean sum of the effective dose of the total torsion measurement was reduced by simulation from 0.460/0.490 mSv (boys/girls) at 100% dose to 0.138/0.147 mSv at 30%. The ICC of the proof-of-concept group was as good as that of the simulated 30% dose level.ConclusionPediatric torsion measurements of the lower extremities can be performed using an ultra-low-dose protocol without compromising diagnostic confidence.

Investigation on the Dependence of Directional Torsion Measurement on Multimode Fiber Geometry

The torsion measurement and torsion direction discrimination characteristics of a multimode fiber (MMF) geometry in a singlemode-multimode-singlemode (SMS) fiber structure are investigated theoretically and experimentally. Three different geometries of MMFs, including circular symmetric MMF, axisymmetric MMF, and asymmetric MMF were fabricated based on a fiber polishing technique. The torsion response characteristics of a MMF depends on the birefringence within the MMF, as birefringence is related to the twist rate of the fiber. The experimental results demonstrate that the unpolished MMF with a circular asymmetric refractive index (RI) distribution has no wavelength response to torsion, and the single-side polished MMF with an axisymmetric RI distribution can measure torsion, but it does not have the ability to discriminate torsion direction. It is found that an MMF section with two polished surfaces at an angle to each other results in a departure from the symmetrical RI distribution, which introduces elliptical birefringence into the MMF. As a result, directional torsion measurement is achieved with sensitivities of 0.162 nm/(rad/m) clockwise and -0.139 nm/(rad/m) counterclockwise. The MMF geometry presented provides a new approach to torsion direction discrimination and shows good application potential in practical torsion vector measurement.

Reliability and agreement analysis among 5 subjective methods of ocular torsion measurement

ObjectiveTo evaluate the reliability in the measurement of ocular torsion and the agreement of the following subjective methods: double Maddox test, synoptophore, Gracis torsionometer, Harms screen and Awaya cyclodeviation test. MethodPatients with vertical strabismus acquired in adulthood were recruited and ocular torsion was measured with the 5 methods described on three occasions. As a gold standard test does not exist, the one that obtained the best repeatability data was chosen as the reference test. Results25 patients were included in the study. The repeatability of each test was studied: double Maddox test (ICC = 0.783, CV = 29.33%), synoptophore (ICC = 0.976, CV = 6.71%), Gracis torsionometer (ICC = 0.937, CV = 20.10%), Harms screen (ICC = 0.962, CV = 11.86%) and Awaya test (ICC = 0.987, CV = 52.58%). The reference test to compare the agreement was the synoptophore. Statistically significant differences were found when comparing the ocular torsion ranges between the synoptophore and the Gracis torsionometer (p = 0.008) and between the synoptophore and the Awaya test (p = 0.02). ConclusionsThe double Maddox test, the synoptophore, the Gracis torsionometer, and the Harms screen are reliable methods with good reproducibility indices. Among them, the synoptophore is the most consistent method. The Awaya test did not show good reliability. The bilateral Maddox test, the Gracis torsionometer, and the Harms screen were methods with good agreement with the synoptophore, which was determined as the reference test. The Awaya test did not show good agreement with the synoptophore.

Identification of torsional frequencies of a large rotor blade based on measurement and simulation data

With increasing size of wind turbines, the aerodynamic and structural properties of the rotor blades become more and more important. However, studies investigating the torsional properties using measurement data and simulation results on full-size turbines are still scarce. In this study, torsional measurements are carried out on a large wind turbine with a rotor diameter of 180 m and compared with model results. In this study, torsional measurements on a large wind turbine with a rotor diameter of 180 m are conducted and compared with model results. Torsional parameters of a rotor blade are identified using two different measurement methods, the first based on strain gauges and the second based on accelerometers. Both methods show frequencies that can be associated with the natural frequencies of the two first torsional modes of the rotor blade. To extract the natural frequencies and to reduce external effects, a manual pitching procedure is evaluated. Here, the first two natural frequencies associated with torsional modes can be identified. In a second step, the behaviour of the blade during power production is investigated and compared with the simulation results.

Análisis de fiabilidad y concordancia entre 5 métodos subjetivos de medición de la torsión ocular

ObjectiveTo evaluate the reliability in the measurement of ocular torsion and the agreement of the following subjective methods: double Maddox test, synoptophore, Gracis torsionometer, Harms screen and Awaya cyclodeviation test. MethodPatients with vertical strabismus acquired in adulthood were recruited and ocular torsion was measured with the 5 methods described on 3 occasions. As a gold standard test does not exist, the one that obtained the best repeatability data was chosen as the reference test. ResultsTwenty-five patients were included in the study. The repeatability of each test was studied: double Maddox test (ICC=0.783, CV=29.33%), synoptophore (ICC=0.976, CV=6.71%), Gracis torsionometer (ICC=0.937, CV=20.10%), Harms screen (ICC=0.962, CV=11.86%) and Awaya test (ICC=0.987, CV=52.58%). The reference test to compare the agreement was the synoptophore. Statistically significant differences were found when comparing the ocular torsion ranges between the synoptophore and the Gracis torsionometer (P=.008) and between the synoptophore and the Awaya test (P=.02). ConclusionsThe double Maddox test, the synoptophore, the Gracis torsionometer, and the Harms screen are reliable methods with good reproducibility indices. Among them, the synoptophore is the most consistent method. The Awaya test did not show good reliability. The bilateral Maddox test, the Gracis torsionometer, and the Harms screen were methods with good agreement with the synoptophore, which was determined as the reference test. The Awaya test did not show good agreement with the synoptophore.

Multi-parameter sensor with high sensitivity based on a long-period fiber grating prepared by a polarization-maintaining fiber.

We propose what we believe to be a novel long-period fiber grating (LPFG) based on a polarization-maintaining fiber (PMF) and single-mode fiber. Due to the principal axis of stress, the resonance peak is strongly dependent on the polarization state of the input light. Under different polarization states, the response of the resonance peak to the change of the external environment is different. A single resonance peak can measure several physical quantities without wavelength overlap using polarization multiplexing. The experimental results show that the PMF-LPFG realizes a high sensitivity torsion and bending measurement under different polarization states (-3.27 nm/rad*m and -13.38 nm/m) and can also measure the ambient temperature (84.10 pm/°C). The PMF-LPFG unit has the advantages of small size, high sensitivity, and multi-parameter measurement. The design scheme of the sensor provides a new idea for a multi-parameter sensor.

Bearing inner race fault detection and size estimation using the variable reluctance sensor

The variable reluctance sensor (VRS) has been widely used in the speed measurement system in the fields of automobile, helicopter, and ship, because of its high robustness. In recent years, most studies have verified the effectiveness of the application in rotor torsional vibration measurement and blade monitoring by the VRS. However, there is less research devoted to the VRS in bearing fault diagnosis, and its influencing mechanism between bearing faults and signal characteristics is not clear. In this paper, the raw signal of the VRS is used for bearing diagnosis. The mechanism of bearing partial fault signal response is analyzed by establishing the bearing inner ring fault model and the sensor signal response model. The characteristics of the VRS signal are given and verified by experiments. The results show that the gearwheel tooth-pass frequency is modulated by the bearing fault characteristic frequency, and there is an obvious double peak phenomenon in the high-frequency part. Moreover, the fault data with widths of 1 mm and 2 mm are analyzed by using the interval time of double peak. It is found that the fault sizes estimated are close to the actual defect size, and have small standard deviations. The original signal of the VRS has great potential in bearing diagnosis.

Fiber Ring Laser Based on Side-Polished Fiber MZI for Enhancing Refractive Index and Torsion Measurement

A fiber ring laser based on a side-polish fiber Mach-Zehnder interferometer (MZI) for effective improving refractive index (RI) and torsion sensing is proposed and investigated. The side-polished fiber MZI sensor can not only enhance the evanescent wave but also break circular symmetry of optical fiber face section, so it can be used for the surrounding RI and torsion sensing. A spectrum 3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dB</i> bandwidth of less than 0.15 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nm</i> has been achieved which makes the fiber ring laser torsion sensing system to have higher measurement resolution. Experiment results show that the RI and torsion sensitivity of proposed sensor is dependent on the polish depth: the thicker the polish depth, the higher the sensitivity. For a sensor with side polish depth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$47~\mu {m}$ </tex-math></inline-formula> , the measured RI sensitivity reaches −81.36 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nm</i> /RIU, the torsion sensitivity is as high as −0.019nm/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sup> , the sensitivity converted to torsional rate is −0.267 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nm</i> /( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rad</i> . <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m} ^{-1}$ </tex-math></inline-formula> ).

Phase Demodulation of Rotor Torsional Vibration Measurement under Time-Varying Speed

When torsional vibration is measured with the zebra-tape method, the modulation signals can be contaminated by electrical noise, environmental noise, step noise, sensor nonlinearities, and so on. Although the amplitudes of these types of noise are very weak relative to the amplitude of the ideal pulse test signal, they may introduce large-scale random broad-spectrum noise to the signal phases. Such noise is difficult to remove using frequency domain, time-frequency-domain, or threshold sampling methods and seriously affects the accuracy of torsional vibration measurements. This paper presents a phase demodulation algorithm based on downsampling and local resampling (DSLR) to improve the accuracy of torsional vibration measurements. To verify the proposed DSLR algorithm, torsional vibration simulations and experiments are conducted under a time-varying rotation speed. The results show that the angular displacement signal obtained from the torsional vibration test using zebra tapes is the superposition of the dynamic and static angular displacements, with the latter generated because of the varying rotation speed with respect to time. The DSLR algorithm effectively reduces the phase noise and demodulates the pulse signal phases. The work in this paper provides a method for obtaining reference torsional vibration measurements of rotors based on the zebra-tape method under time-varying speeds.