Unknown Loading Conditions Research Articles

Kalman-based estimation of loading conditions from ultrasonic guided wave measurements

Abstract Ultrasonic guided wave-based structural health monitoring (SHM) of structures can be perturbed by environmental and operations conditions (EOCs) that alter wave propagation. In this work, we present an estimation procedure to reconstruct an EOC-free baseline of the structure from the only available Ultrasonic guided wave measurements. This procedure could typically be used as a prior step to increase the robustness of a more general ultrasonic imaging algorithm or SHM process dedicated to flaw detection. Our approach is model-based, i.e. we use a precise modeling of the wave propagation altered by structure loading conditions. This model is coupled with the acquired data through a data assimilation procedure to estimate the deformation caused by the unknown loading conditions. From a methodological point of view, our approach is original since we have proposed an iterated reduced-order unscented Kalman strategy, which we justify as an alternative to a Levenberg–Marquardt strategy for minimizing the non quadratic least-squares estimation criteria. Therefore, from a data assimilation perspective, we provide a quasi-sequential strategy that can valuably replace more classical variational approaches. Indeed, our resulting algorithm proves to be computationally very effective, allowing us to successfully apply our strategy to realistic 3D industrial SHM configurations.

Multiscale cascade recurrent dilation convolution network for fault diagnosis of rolling bearing under cross-load conditions

Recently, deep learning (DL) models based on convolutional neural networks have achieved satisfactory results in rolling bearing fault diagnosis. However, the bearings usually work in variable loading conditions, and their feature distribution could vary with load. The important features cannot be effectively captured in the convolution process using the existing diagnosis models, resulting in poor generalization performance. In this paper, a novel DL model, named multiscale cascade recurrent dilation convolution network, is proposed by introducing the dilated convolution and global average pooling (GAP) layer. Firstly, a new multiscale cascade structure with different convolution kernel sizes is introduced to extract multiscale features contained in the vibration signal. Secondly, a recurrent dilation convolution strategy is designed in each branch of the multiscale cascade structure to extract abundant feature information. Finally, the GAP is employed to reduce redundant feature vectors and output them, while a classifier of multilayer perceptron is used to automatically identify the fault types. The effectiveness of the proposed algorithm is evaluated by two experimental cases. The results show that the proposed method can successfully identify the labels of fault samples under unknown load conditions using the fault samples with labels under existing load conditions. Compared with other methods, this method exhibits excellent robustness and generalization performance for bearing fault diagnosis under cross-load conditions.

Adaptive guided wave-based damage identification under unknown load conditions

Damage identification methods based on guided waves (GWs) have been widely researched in the field of aircraft structural health monitoring. Notably, the existing research has not extensively considered the realization of accurate damage localization in an unknown load environment, although this aspect is of significance to the real-time safety assessment of aircraft structures. To address this issue, we propose an adaptive damage imaging method based on GW signals for typical aircraft structures subjected to unknown workloads. First, through the GW signals and load data sampled in the working load range, a mathematical model between the characteristics of the GW signal and load is established. Second, the active GW signal is adaptively compensated by the real-time identified load through the passive strain signal during the service process of the structure. Finally, the alternating time-reversal phase synthesis (ATRPS) method is used to accurately locate the damage in the monitoring area. The feasibility, applicability, and accuracy of the proposed methodology are validated by three levels of experimental cases. All results consistently indicate that reliable damage localization can be achieved under an unknown load environment.

Cyberattack Detection for Converter-Based Distributed dc Microgrids: Observer-Based Approaches

DC microgrids are complex systems connecting various renewable energy sources to different types of loads based on distributed networks. However, the strong reliance on communication networks makes dc microgrids vulnerable to intentional cyberattacks. In this article, two typical types of observer-based approaches are presented to address the attack detection problem for distributed dc microgrid systems. The disturbance decoupling approach is utilized to eliminate the influence of unknown load conditions and the coupling effect between distributed generation units (DGUs) to the residuals. The proposed method is easy to design and has less computational complexity. The performance of the provided scheme is validated by a dSPACE-based dc microgrid platform.

Investigation by Digital Image Correlation of Mixed-Mode I and II Fracture Behavior of Polymeric IASCB Specimens with Additive Manufactured Crack-Like Notch.

In this work, the fracture mechanics properties of polyamide (PA) specimens manufactured by the selective laser sintering (SLS) technology are investigated, in which an embedded crack-like notch was inserted in the design and produced during the additive manufacturing (AM) phase. To cover a wide variety of mode I/II mixity levels, the inclined asymmetrical semicircular specimen subjected to three points loading (IASCB) was employed. The investigation was carried out by analyzing the full displacement field in the proximity of the crack tip by means of the digital image correlation (DIC) technique. To characterize the material, which exhibits a marked elastic-plastic behavior, the quantity J-integral was evaluated by two different methods: the first one exploits the full fields measured by the DIC, whereas the second one exploits the experimental load–displacement curves along with FEM analysis. The DIC methodology was experimentally validated and proposed as an alternative method to evaluate the J-integral. It is especially suited for conditions in which it is not possible to use the conventional LDC method due to complex and possibly unknown loading conditions. Furthermore, results showed that the AM technique could be used effectively to induce cracks in this type of material. These two aspects together can lead to both a simplification of the fracture characterization process and to the possibility of dealing with a wider number of practical, real-world scenarios. Indeed, because of the nature of the additive manufacturing process, AM crack-like notches can be sintered even having complex geometry, being three-dimensional and/or inside the tested structure.

Effect of Bench Press Load Knowledge on Repetitions, Rating of Perceived Exertion, and Attentional Focus.

Beaudoin, CM, Cox, Z, Dundore, T, Thomas, T, Kim, J, and Pillivant, D. Effect of bench press load knowledge on repetitions, rating of perceived exertion, and attentional focus. J Strength Cond Res 32(2): 514-519, 2018-Few studies have examined the role of the teleoanticipation during resistance training. The purpose of this study was to examine the effect of bench press (BP) load knowledge on repetitions completed, ratings of perceived exertion (RPEs), and attentional focus (% associative). Thirty-six recreationally active resistance-trained men (n = 25) and women (n = 11) participated in this study (age = 20.97 ± 1.87 years; ht = 174.12 ± 9.41 cm; and mass = 80.14 ± 14.03 kg). All subjects completed 3 testing sessions: (a) 1 repetition maximum (1RM) BP determination; (b) submaximal BP repetitions to fatigue known load (KL); and (c) submaximal BP repetitions to fatigue unknown load (UL). Known load and UL sessions were randomized and counterbalanced and both completed at 70% 1RM. An estimated weight ratio was computed using the subject's estimate of the UL weight relative to the KL weight. An independent samples t-test revealed no significant testing order difference for the estimated weight ratio. Two-way repeated-measures analysis of variances revealed no significant differences in the number of repetitions (p = 0.63), RPE (p = 0.18), or attentional focus (% associative) (p = 0.93) between the KL and UL conditions. Pearson correlations found a moderate positive association between KL repetitions completed and % associative focus when the UL was completed before the KL. Load knowledge did not influence the number of repetitions, RPE, or attentional focus while completing the BP. Further research examining the use of pacing strategies, RPE, and attentional focus during KL and UL conditions are warranted.

비선형 부하에서 커패시터 전류 궤환을 통한 고성능 UPS 설계

This paper presents a digital control solution to process capacitor current feedback of high performance single-phase UPS for non-linear loads. In all UPS the goal is to maintain the desired output voltage waveform and RMS value over all unknown load conditions and transient response. The proposed UPS uses instantaneous load voltage and filter capacitor current feedback, which is based on the double regulation loop such as the outer voltage control loop and inner current control loop. The proposed DSP-based digital-controlled PWM inverter system has fast dynamic response and low total harmonic distortion (THD) for nonlinear load. The control system was implemented on a 32-bit Floating-point DSP controller TMS320C32 and tested on a 5[KVA] IGBT based inverter switching at 11[Khz]. The validity of the proposed scheme is investigated through simulation and experimental results.

Passive cervical spine flexion: The effect of age and gender

BackgroundPrevious studies reported passive cervical range of motion under unknown loading conditions or with minimal detail of subject positioning. Additionally, such studies have not quantitatively ensured the absence of active muscle during passive measurements. For the purpose of validating biomechanical models the loading condition, initial position, and muscle activation must be clearly defined. A method is needed to quantify the passive range of motion properties of the cervical spine under controlled loading conditions, particularly in the pediatric population where normative clinical and model validation data is limited. MethodsHealthy female pediatric (6–12years; n=10), male pediatric (6–12years; n=9), female adult (21–40years; n=10), and male adult (20–36years; n=9) volunteers were enrolled. Subjects with restrained torsos and lower extremities were exposed to a maximum 1g inertial load in the posterior–anterior direction, such that the head–neck complex flexed when subjects relaxed their neck musculature. Surface electromyography monitored the level of muscle relaxation. A multi-camera 3-D target tracking system captured passive neck flexion angle of the head relative to the thoracic spine. General estimating equations detected statistical differences across age and gender. FindingsPassive cervical spine flexion equaled 111.0° (SD 8.0°) for pediatric females, 102.8° (SD 7.8°) for adult females, 103.8° (SD 12.7°) for pediatric males, and 93.7° (SD 9.9°) for adult males. Passive neck flexion significantly decreased with age in both genders (P<0.01). Females exhibited significantly greater flexion than males (P<0.01). InterpretationThis study contributes normative data for clinical use, biomechanical modeling, and injury prevention tool development.

Nonlinear control of a variable displacement axial piston pump

AbstractIn this contribution a mathematical model of a variable displacement axial piston pump controlled by a solenoid valve is derived. For the purpose of a controller design the mathematical model is simplified using singular perturbation arguments. The goal of the controller design is to track prescribed trajectories in the load pressure for arbitrary unknown load conditions. The control concept being proposed comprises a feedforward controller and a nonlinear backstepping controller combined with a load estimator for the trajectory error system. The feasibility of this control concept is shown by means of measurements on a test‐stand. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Parameter identification of concrete lining for a subway tunnel

The key factor in filling the gap between the real and predicted behaviour of structures is the use of field measurements not only to monitor the stability of structures, but also to re-evaluate the input data of the parameters used in the numerical analysis. Based on this re-evaluation of the input data, the original model is continuously modified to achieve minimum discrepancy between the behaviour of the model and the real structure. This can be done by using the back analysis procedures. Till now most of the researchers concentrate on the parameter identification of the soil constants only and consider the constants of the supporting elements (concrete or shotcrete) as fixed known values although the true constants of the supporting elements may be different than their assumed values. In a previous paper, the parameter identification of the concrete constants has been done and checked with some theoretical examples. In this study, the parameter identification of the constants of the tunnel concrete lining had been achieved. A two-dimensional element, called BEAM 6 element, is used to simulate the tunnel concrete lining while another element, called, LST element (Linearly Varying Strain Triangular element), is used to simulate the surrounding soil. The back analysis was done based on the dual boundary control method. The parameter identification has been applied on two real tunnels. The first application has been done for the soil constants only while the identification of the constants of the tunnel shotcrete lining simultaneously with the soil parameters had been applied on the second tunnel. Although more than one region of concrete are used, the parameters of the concrete lining have been identified simultaneously with the soil parameters. The obtained displacements are compared with the measured ones and the obtained results have been discussed. The main points can be summarized as: Although only parts of the measurements were used, satisfactory results were obtained at most measuring points. The calculated curve of displacements matches the measured curve very well, except for the lower region of measurements and some points in the middle part. The difference between the measured and the calculated displacements for the lower region may be due to unknown loading conditions of air pressure and water level. Another reason of this difference may be due to the accuracy of the sliding micrometers in this region because the measurements are very small. The forces of shotcrete lining in cases of identification of shotcrete parameters simultaneously with the soil parameters are higher than those in cases of identification of soil parameters with fixed shotcrete parameters. Therefore, it is preferable to identify the shotcrete parameters simultaneously with the soil parameters to ensure the safety in tunnelling process. Although the tunnel is still safe, the predicted factor of safety is reduced. Hence, the back analysis helps in making a reliable assessment of tunnelling safety. The identification of soil parameters only and considering the shotcrete parameters as constant parameters gives displacements far from the observed displacements while the identification of all soil layers simultaneously with the shotcrete parameters has a big effect on the calculated displacements. This application can be considered as a successful application of the parameter identification of shotcrete lining although the poor available measurements data. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

ANALYSIS OF THE PERFORMANCE OF OPERATIONAL DATA ANALYSIS METHODS

Operating data are measurements taken from a system under operating conditions. They contain a combination of the system characteristics and generally unknown loading conditions. The scope of this paper is to describe several methods of investigating operational phenomena and to discuss some of their limitations. The use of transmissibilities, monophase representation of operating shapes and principle response analysis will be illustrated from results obtained from a noise-free 11 dof discrete system, or from industrial results obtained from measurements on the guiding system of a vehicle with tyres.