Strain Waveforms Research Articles

Differences in left ventricular contraction in left bundle branch block with preserved and reduced ejection fraction: an evaluation using 2-dimensional speckle tracking echocardiography

Abstract Background Left ventricular (LV) contraction in left bundle branch block (LBBB) is characterized by early septal contraction and delayed contraction of the lateral wall, but the process may differ depending on myocardial contractility in addition to the degree of conduction block. Purpose This study aimed to evaluate LV contraction in patients with LBBB by analysis of longitudinal strain (LS) and to compare it between patients with preserved LV ejection fraction (pEF: EF>50%) and reduced LV EF (rEF: EF<40%). Methods We studied 87 patients with LBBB. Fifty had pEF (EF 59±7%) with a mean QRS duration of 144±12ms, and 38 had rEF (EF: 29±4%) with a mean QRS duration of 147±12ms (p=0.32 vs. pEF). We also studied 43 patients without conduction block (Narrow-QRS; pEF, n=23; rEF, n=20). Patients with a heart rate less than 60 or greater than 80 beats/min during echocardiography or with a history of myocardial infarction were excluded. Three standard apical images were recorded, and the LS of one heartbeat starting at the beginning of the QRS was evaluated in 18 LV segments. When the strain waveform showed a negative peak during the pre-ejection period, it was identified as early systolic contraction (ESC), and the first negative peak that appeared after aortic valve opening (AVO) was identified as late systolic contraction (LSC). The time from the beginning of QRS to the peak of the LSC (Q-Peak) and the strain value at the end of the QRS were measured in each segment. Results In patients with LBBB, the septum contracted early, and ESC was seen mainly in the early contracted area. The lateral wall contraction was delayed, and the difference between the maximum and minimum Q-Peak was greater than the Narrow-QRS in the same EF category. Patients with rEF and LBBB had a larger number of segments with ESC and a smaller minimum Q-Peak than those with pEF. The difference between the maximum and minimum Q-Peak was greater for patients with rEF than for patients with pEF. Conclusions Although patients with LBBB had significant dyssynchrony due to conduction block even those with pEF, LV contractile properties were altered in patients with rEF and associated with further increased dyssynchrony.

Simulation and Measurement of Strain Waveform under Vibration Using Fiber Bragg Gratings.

The work is devoted to the consideration of methods for determining the strain of objects using fiber Bragg gratings under a high-frequency vibration or pulsed mechanical action, which is difficult to perform using widespread methods and devices. The methods are based on numerical processing of the time dependence of the radiation power reflected from the fiber Bragg grating at various wavelengths, which makes it possible to measure strain parameters in a wide range of magnitude and frequencies. The efficiency of the proposed methods is demonstrated by numerical simulation. It is shown that it is possible to restore the strain dependence on time in the range ±1000 μϵ or more from simultaneously measured power dependencies reflected by the fiber Bragg grating using common fiber-optic components. The case of sequential registration of reflected radiation power at different wavelengths to determine the probability density of the distribution of the strain values is also considered. The results of signal processing obtained both by numerical simulation and experimentally for the case of a linear vibration are presented. The technical problems of using the proposed methods are discussed.

Evaluation of equivalent axle load factors for multi axles based on fatigue tests using actual strain waveforms

Equivalent axle load factor (EALF) is used to characterize the fatigue damage effect of multi-axle loads on asphalt pavement. EALF is calculated as the ratio of the pavement’s fatigue resistance under a single axle load to that under a multi-axle load. Existing studies use the same fatigue life function to predict the fatigue life of asphalt mixture under both single- and multi-axle loads, primarily focusing on the differences in pavement strains under these two configurations. However, strain waveforms in asphalt pavement caused by multi-axle loads differ from those under single-axle loads, altering the mixture’s fatigue behavior. To address this issue, this research tests the fatigue responses of asphalt mixtures under actual loading waveforms from single-axle, tandem-axle, and tridem-axle loads. Based on the test results, fatigue life functions are developed for each axle configuration and used to establish an updated EALF model. Since the applied fatigue life functions are based on test results from more realistic strain waveforms, the calculated EALFs provide more reliable predictions of the damaging effect of multi-axle loads on asphalt mixtures.

High-frequency optimally windowed chirp rheometry for rapidly evolving viscoelastic materials: Application to a crosslinking thermoset

Knowledge of the evolution in the mechanical properties of a curing polymer matrix is of great importance in composite parts or structure fabrication. Conventional rheometry, based on small amplitude oscillatory shear, is limited by long interrogation times. In rapidly evolving materials, time sweeps can provide a meaningful measurement albeit at a single frequency. To overcome this constraint, we utilize a combined frequency- and amplitude-modulated chirped strain waveform in conjunction with a homemade sliding plate piezo-operated rheometer (PZR) and a dual-head commercial rotational rheometer (Anton Paar MCR 702) to probe the linear viscoelasticity of these time-evolving materials. The direct controllability of the PZR, resulting from the absence of any kind of firmware and the microsecond actuator-sensor response renders this device ideal for exploring the advantages of this technique. The high frequency capability allows us to extend the upper limits of the accessible linear viscoelastic spectrum and, most importantly, to shorten the length of the interrogating strain signal (OWCh-PZR) to subsecond scales, while retaining a high time-bandwidth product. This short duration ensures that the mutation number (NMu) is kept sufficiently low, even in fast-curing resins. The method is validated via calibration tests in both instruments, and the corresponding limitations are discussed. As a proof of concept, the technique is applied to a curing vinylester resin. The linear viscoelastic (LVE) spectrum is assessed every 20 s to monitor the rapid evolution in the time and frequency dependence of the complex modulus. Comparison of the chirp implementation, based on parameters such as duration of the experiment, sampling frequency, and frequency range, in a commercial rotational rheometer with the PZR provides further information on the applicability of this technique and its limitations. Finally, FTIR spectroscopy is utilized to gain insights into the evolution of the chemical network, and the gap dependence of the evolving material properties in these heterogeneous systems is also investigated.

Coupled thermo-mechanical phase field modeling for shear ductile fracture at high strain rate and temperature

The objective of the current study is to introduce a coupled thermo-mechanical phase field model to elucidate shear ductile fracture under varying strain rates and temperatures. Both the plastic work threshold and fracture energy exhibit dependence on the strain rate and temperature. To explore this in detail, hat-shaped specimens are adopted to systematically investigate shear ductile fracture under distinct strain rates and temperatures by the split Hopkinson pressure bar apparatus. The simulated and experimental strain waveforms are then compared to calibrate and validate the damage parameters of the presented phase field model. The results demonstrate that the numerical simulations are in agreement with the experiments. Moreover, the fracture process of the hat-shaped specimen is also examined. The numerical results furnish a reliable description of the hat-shaped specimen from damage initiation to complete fracture. It's found that the influences of strain rate on shear stress and fracture initiation are less pronounced than that of temperature for U75V steel. In summary, the developed phase field model can reproduce shear ductile failure of the hat-shaped specimen under diverse strain rates and temperatures.

Mechanical loading of ex vivo bovine trabecular bone in 3D printed bioreactor chambers

Previous ex vivo bone culture methods have successfully implemented polycarbonate (PC) bioreactors to investigate bone adaptation to mechanical load; however, they are difficult to fabricate and have been limited to a 5 mm maximum specimen height. The objective of this study was to validate a custom-made 3D printed MED610TM bioreactor system that addresses the limitations of the PC bioreactor and assess its efficacy in ex vivo bone culture. Twenty-three viable trabecular bone cores (10 mm height by 10 mm diameter) from an 18-month-old bovine sternum were cultured in MED610TM bioreactors with culture medium at 37 °C and 5% CO2 for 21-days. Bone cores were ranked based on their day 0 apparent elastic modulus (Eapp) and evenly separated into a “Load” group (n = 12) and a control group (n = 11). The Load group was loaded five times per week with a sinusoidal strain waveform between −1000 and −5000 με for 120 cycles at 2 Hz. Eapp was assessed on day 0, 8, and 21 using quasi-static tests with a −4000 με applied strain. Over 21-days, the Eapp of Load group samples tended to increase by more than double the control group (53.4% versus 20.9%) and no visual culture contamination was observed. This study demonstrated that bone organ culture in 3D printed MED610TM bioreactors replicated Eapp trends found in previous studies with PC bioreactors. However, further studies are warranted with a larger sample size to increase statistical power and histology to assess cell viability and bone mineral apposition rate.

Concussion case classification based on brain strain waveforms using dynamic time warping and cluster analysis

Concussion case classification based on brain strain waveforms using dynamic time warping and cluster analysis

Creep-fatigue life and damage evaluation under various strain waveforms for Ni-based Alloy 740H

This paper presents creep-fatigue life evaluation of a nickel-based Alloy 740H, for evaluating its performance as a material of advanced ultra-supercritical power plants. Strain controlled creep-fatigue tests were performed under six strain waveforms using solid bar specimens at 700 °C, and the effect of strain waveform on creep-fatigue life was discussed. Creep-fatigue lives were shorter than pure fatigue life depending on the strain waveform. The failure life in symmetrical waveform was reduced to about half as the strain rate decreased by one order of magnitude. The failure lives in the unsymmetrical waveforms were smaller than that in the symmetrical waveform and tensile slow straining was more detrimental to fatigue life than compressive slow straining. The creep-fatigue life decreased significantly due to strain hold, and tensile peak strain hold had more enhanced effect on fatigue life than compressive strain hold. Applicability of five existing approaches based on linear damage summation rule were discussed. In addition, a new approach based on modified ductility exhaustion model with several modifications was proposed in order to improve the life predictability of the classical approach. Time fraction rule with ASME failure envelope and new approach satisfactorily predicted the creep-fatigue lives almost within a scatter band of 2.

A coupled thermo-mechanical cohesive zone model for strain rate-dependent fracture of hat-shaped specimens under impact

A coupled thermo-mechanical cohesive zone model for strain rate-dependent materials is proposed to illustrate the shear failure in the hat-shaped specimens made of U75V rail steel at various impact loads and temperatures.The cohesive energy and the maximum cohesive stress in the proposed cohesive zone model depend on strain rates and temperatures. The coefficients in the functions of cohesive energy, maximum cohesive stress, and the cohesive law are obtained through a combination of experimental and simulation data. The experimental strain waveforms are obtained by a split Hopkinson pressure bar system and the cohesive zone model is implemented using ABAQUS finite element software with the assistance of user subroutines.The findings substantiate the efficacy of the proposed cohesive zone model in accurately predicting the shear failure of hat-shaped specimens under high-speed impacts, as evidenced by the notable concurrence between experimental and computational outcomes within an acceptable margin of error. Notably, the cohesive energy and maximum cohesive stress in the model demonstrate a dual dependency on strain rates and thermal conditions, emphasizing the significance of considering both thermal and mechanical effects when simulating shear failure in materials experiencing high temperatures and high strain rates.

Temporally probing the thermal phonon and charge transfer induced out-of-plane acoustical displacement of monolayer and bi-layer MoS2/GaN heterojunction

Acoustical behavior of semiconducting transition metal dichalcogenides determines the heat transfer pathway, and thus plays a crucial role in the electronics and optoelectronics design. In this research, van der Waals heterojunctions (vdWHs) consisting of transferred monolayer and bi-layer MoS2 on GaN substrate were studied. We observed an asymmetric bipolar acoustic strain wave with ∼5 ps duration, which describes the surface of substrate undergoing strong compressive deformation after weak tensile deformation in the out-of-plane direction. We developed a theory to explain the mechanisms responsible for the observed strain waveform in the vdWHs elastic system, and obtained the critical parameters of the carrier dynamics by temporal fitting. Our results not only report a coherent acoustic phonon generated in the vdWHs, which will complement our understanding of the thermal transfer at the 2D/substrate interface, but also provide information about the intrinsic properties in the vdWHs, which would benefit the design of the 2D-based devices in the future.

Real-Time Damage Self-Diagnosis and Self-Localization Brillouin Distributed Optical Fiber–Fiber-Reinforced Polymer Composite Smart Cables

Cables are important components of long-span space structures, cable-supported bridges, slopes, and so on. However, they often suffer from damage such as wire breakage, corrosion, and anchor head loosening, which threatens structural safety seriously. Therefore, it is very important to diagnose and localize their damage. To address this problem, a real-time damage self-diagnosis and self-localization smart cable is proposed. It is made of a polyethylene cover pipe and some parallel intelligent steel strands with the Brillouin distributed monitoring capability. Fiber-reinforced polymer (FRP) and optical fiber are put together in the thermosetting molding process to form the intelligent central wire of each intelligent steel strand. When the side wire of the steel strand reaches the ultimate load, the intelligent central wire only reaches about 50% of its ultimate load, so it can be used in the real-time monitoring of side wires. Numerical models of seven-wire steel strands with different lengths were established, and the broken wire damage was simulated by changing coupling conditions in single and multiple damage cases. To further verify the proposed smart cable, experiments were carried out based on two intelligent steel strands with the length of 34.5 m. Experimental damage cases were simulated by cutting side wires at different positions under different loads. Both numerical and experimental results show that the change in the tension strain of the intelligent central wire can indicate the damaged location of the broken side wire. For a healthy steel strand, the tension strain of the central wire is a constant value; for a damaged steel strand, damage can be localized according to the strain waveform of the intelligent central wire and its ratio of peak strain to stable strain. The proposed smart cable has functions of real-time stress self-sensing, damage self-diagnosis, damage self-localization, damage self-warning of any side wire, and its central wire has excellent corrosion resistance; it can be well used in life-cycle real-time structural health monitoring of cable structures/substructures, which dramatically reduces the probability of cable accidents, and lays a good foundation for smart civil structures.

Multiaxial creep-fatigue constitutive modeling and damage evaluation for type F82H steel under non-proportional loading conditions

In this study, the deformation behaviors of F82H steel at 823 K under uniaxial and non-proportional loading conditions were described using a unified viscoplasticity model. The multiaxial creep–fatigue life was predicted using a strain energy damage parameter in collaboration with cycle-by-cycle concept. The creep–fatigue tested conditions includes tension holding and slow strain rate strain waveforms. Our findings showed that the cyclic deformation behaviors were well described using the unified viscoplasticity model. The creep–fatigue life was well predicted by the proposed energy-based model within a factor of 2.

Viscoelastic glucose theory (VGT #27): Applying the Concept of Viscoelasticity Theory and using the Estimated Daily Glucose (eAG) over a 3.8-Year Period from 5/8/2018 to 2/17/2022 as the Strain to Study the Role and Influences of the Corresponding Stress as well as their Impact on the Predicted eAG Results Based on the GH-Method: Math-Physical Medicine (No. 608)

Recently, the author applied theories of elasticity, plasticity, viscoelasticity, and viscoplasticity from engineering and perturbation theory from quantum mechanics, along with the wave theory and energy theory from physics to conduct his biomedical research on certain output biomarkers, such as glucose (symptoms or behaviors) resulting from a selected input biomarker, such as the carbs/sugar amount, exercise level, or others (causes or stressors). In this article, he chose his synthesized estimated daily glucose (eAG) data and waveform over the past 3.8 years as the strain (ε or output, symptom). Since 5/8/2018, he has been utilizing a continuously monitoring glucose (CGM) sensor device to collect 96 glucose data each day at 15-minute time intervals. In order to investigate and learn the behaviors of the strain (ε) or eAG, and its stress (σ) or input/cause as defined to be the eAG change rate multiplied by a selected viscosity factor (η), he purposely select two values of η as 1 and 2. After conducting the stress-strain analysis based on 1 and 2 as his viscosity factors (η), he then uses another set of measured values: average daily carbs/sugar intake amount of 41.13 grams and average daily walking exercise of 16.02 k-steps, as the second set of viscosity factors (η). There are two main purposes of this research article. First, to check the stress-strain diagram’s sensitivity due to the selection of different viscosity factors. Second, to examine the correlation between predicted strain (eAG) waveform using the viscoelastic perturbation model and the measured CGM sensor eAG waveform due to the selection of different viscosity factors. The following two defined equations from viscoelasticity glucose theory (VGT) are utilized to study the stressstrain relationship for this case study. At first, he selects his eAG as the strain, which is his target research item: strain = ε = individual output biomarker value (eAG) at present time Furthermore, he wants to use the strain rate or his overall eAG change rate to be multiplied by a selected viscosity factor as the stress: Stress = σ = η * (dε/dt) = η * (d-strain/d-time)

Realization of an ultra-high pressure dynamic calibrate system by drop hammer based on fiber Bragg grating strain sensor.

In this letter, we propose a novel technique for dynamic ultra-high pressure calibration that measured pressure by FBG based strain sensor. Generally, the traditional method of dynamic ultra-high pressure calibration by standard sensor is costly and it is difficult to improve the accuracy. Therefore, we prefer FBG strain sensor to replace the standard sensor to calibrate the ultra-high pressure. In this proposal, the calibration process is that the central wavelength of the FBG attached to the elastic element changes rapidly with the strain of the elastic element during the drop hammer impact, synchronously. This allows the calibration accuracy to be easily increased to 0.02% and the cost to be reduced by 1/100 compared to traditional calibration techniques. The experiment results show that coefficient of linear correlation between the strain waveform and the pressure signal reaches 0.999. The strain calibration based on FBG is of great significance to the measurement and calibration of dynamic ultra-high pressure sensors.

High precision ringdown modeling: Multimode fits and BMS frames

Quasi-normal mode (QNM) modeling is an invaluable tool for characterizing remnant black holes, studying strong gravity, and testing GR. Only recently have QNM studies begun to focus on multimode fitting to numerical relativity (NR) strain waveforms. As GW observatories become even more sensitive they will be able to resolve higher-order modes. Consequently, multimode QNM fits will be critically important, and in turn require a more thorough treatment of the asymptotic frame at $\mathscr{I}^+$. The first main result of this work is a method for systematically fitting a QNM model containing many modes to a numerical waveform produced using Cauchy-characteristic extraction (CCE), an extraction technique which is known to resolve memory effects. We choose the modes to model based on their power contribution to the residual between numerical and model waveforms. We show that the all-mode strain mismatch improves by a factor of $\sim10^5$ when using multimode fitting as opposed to only fitting the $(2,\pm2,n)$ modes. Our most significant result addresses a critical point that has been overlooked in the QNM literature: the importance of matching the Bondi-van der Burg-Metzner-Sachs (BMS) frame of the numerical waveform to that of the QNM model. We show that by mapping the numerical waveforms$-$which exhibit the memory effect$-$to a BMS frame known as the super rest frame, there is an improvement of $\sim10^5$ in the all-mode strain mismatch compared to using a strain waveform whose BMS frame is not fixed. Furthermore, we find that by mapping CCE waveforms to the super rest frame, we can obtain all-mode mismatches that are, on average, a factor of $\sim4$ better than using the publicly-available extrapolated waveforms. We illustrate the effectiveness of these modeling enhancements by applying them to families of waveforms produced by NR and comparing our results to previous QNM studies.

Viscoelastic glucose theory (VGT #27): Applying the Concept of Viscoelasticity Theory and using the Estimated Daily Glucose (eAG) over a 3.8-Year Period from 5/8/2018 to 2/17/2022 as the Strain to Study the Role and Influences of the Corresponding Stress as well as their Impact on the Predicted eAG Results Based on the GH-Method: Math-Physical Medicine (No. 608)

Recently, the author applied theories of elasticity, plasticity, viscoelasticity, and viscoplasticity from engineering and perturbation theory from quantum mechanics, along with the wave theory and energy theory from physics to conduct his biomedical research on certain output biomarkers, such as glucose (symptoms or behaviors) resulting from a selected input biomarker, such as the carbs/sugar amount, exercise level, or others (causes or stressors). In this article, he chose his synthesized estimated daily glucose (eAG) data and waveform over the past 3.8 years as the strain (ε or output, symptom). Since 5/8/2018, he has been utilizing a continuously monitoring glucose (CGM) sensor device to collect 96 glucose data each day at 15-minute time intervals. In order to investigate and learn the behaviors of the strain (ε) or eAG, and its stress (σ) or input/cause as defined to be the eAG change rate multiplied by a selected viscosity factor (η), he purposely select two values of η as 1 and 2. After conducting the stress-strain analysis based on 1 and 2 as his viscosity factors (η), he then uses another set of measured values: average daily carbs/sugar intake amount of 41.13 grams and average daily walking exercise of 16.02 k-steps, as the second set of viscosity factors (η). There are two main purposes of this research article. First, to check the stress-strain diagram’s sensitivity due to the selection of different viscosity factors. Second, to examine the correlation between predicted strain (eAG) waveform using the viscoelastic perturbation model and the measured CGM sensor eAG waveform due to the selection of different viscosity factors.

Bridge Response and Heavy Truck Classification Framework Based on a Two-Step Machine Learning Algorithm

Collecting information on heavy trucks and monitoring the bridges which they regularly cross is important for many facets of infrastructure management. In this paper, a two-step algorithm is developed using bridge and truck data, by deploying sequentially unsupervised and supervised machine learning techniques. Longitudinal clustering of bridge data, concerning strain waveforms, is adopted to perform the first step of the algorithm, while image visual inspection and classification tree methods are applied to truck data concurrently in the second step. Both bridge and truck traffic must be monitored for a limited, yet significant, amount of time to calibrate the algorithm, which is then used to build a classification framework. The framework provides the same benefits of two data collection systems while only one needs to be operative. Depending on which monitoring system remains available, the framework enables the use of bridge data to identify the truck’s profile which generated it, or to estimate bridge response given the truck’s information. As a result, the present study aims to provide decision-makers with an effective way to monitor the whole bridge-traffic system, bridge managers to plan effective maintenance, and policymakers to develop ad hoc regulations.

Upgraded Fiber-Optic Sensor System for Dynamic Strain Measurement in Spallation Neutron Source

We describe an upgraded fiber-optic sensor system and its performance in measuring the dynamic strains in a mercury target of the Spallation Neutron Source (SNS). Strains result from dynamic pressure waves in the stainless-steel mercury target induced by short (~700 ns), intense (up to 23.3 kJ), high-energy (~1 GeV) proton pulses. In the upgraded sensor system, the output of each sensor head is interrogated with a compact, all-fiber based Faraday Michelson interferometer, which generates interference signals with a steady phase shift. Strain waveforms are recovered from the phase-shifted interference signals using a high-speed digital signal processing procedure developed in our previous work. We demonstrate successful measurements of dynamic strain pulses, e.g., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400 \mu \varepsilon $ </tex-math></inline-formula> over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$190 \mu \text{s}$ </tex-math></inline-formula> , on a recently installed SNS target using the upgraded sensor system. The measured strain waveforms are analyzed for more than 20 sensor locations and/or orientations, and provide information regarding the temporal structure of strain profiles and dependence of the strain magnitude on the proton powers of 200 – 1400 kW. The new interrogator also measures the radiation-induced-attenuation (RIA) in the optical fiber, enabling experimental investigations of RIA profiles induced by a 700-ns radiation pulse. The radiation effects on the strain measurement performance are discussed over a radiation dose range of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${4}\times {10}^{{8}}$ </tex-math></inline-formula> Gy and an RIA compensation method is proposed. The measurements allow insight into the response of this unique piece of equipment and can be used for validation of simulations.

Residual limb shear strain during gait is correlated with patient reported outcomes for persons with transfemoral amputation

The purpose of this study was to measure residual limb skin strain and strain rate within the socket during gait in individuals with a transfemoral amputation and to determine if skin strain during gait is related to patient-reported comfort and function. It was hypothesized that greater skin strain and skin strain rate would correlate to worse patient-reported outcomes. It was also hypothesized that skin strain would progressively increase from the distal to the proximal end of the residuum and maximum strain would occur shortly after heel strike. Dynamic biplane radiography (DBR), combined with conventional motion capture, was used to measure skin deformation within the socket during treadmill walking for 10 persons with unilateral transfemoral amputation. The questionnaire for persons with a transfemoral amputation (Q-TFA) was administered to assess prosthetic use, mobility, health problems, and global health. Q-TFA Prosthetic Use score and Problem score were negatively correlated with the peak shear strains in the proximal and distal regions of the residuum, respectively. Maximum shear strain increased progressively from proximal to distal regions of the residual limb. Within-subject variability in shear strain waveforms during gait was 0.7% or less, but between-subject variability was 3.3% to 5.0% shear. This study demonstrates that skin shear within the socket of persons with transfemoral amputation can be measured during gait using DBR and the results suggest that greater skin shear in the proximal region of the socket is related to decreased prosthetic use.

Fatigue Damage Monitoring of Wind Turbine Blades by Using the Kalman Filter

Fatigue damage accumulation needs to be monitored for extending the lifetime of horizontal axis wind turbines. To monitor accumulation of fatigue damage, this paper proposes a blade load and fatigue damage monitoring system consisting of physics models coupled with the Kalman filter (KF). The proposed monitoring system estimates bending moment distribution along the blade as a time series from 1 Hz data collected by a supervisory control and data acquisition (SCADA) system and from 20 Hz strain sensor data collected at the blade root. Static load is computed on the basis of blade element and momentum theory from SCADA data, whereas dynamic response of the blade is computed by assuming a mass–spring–damper system. The KF corrects the estimated moment distribution with moment measured at the blade root. The monitoring system is demonstrated and validated by installing it on a 2 MW floating downwind turbine and estimating strain and fatigue damage at the medium span position of the blades, where a strain sensor is installed. The validation results show that strain wave forms and fatigue damage estimated by the monitoring system with the KF are consistent with those computed from the strain measurement with sufficient accuracy for structural health monitoring.