Displacement Correlation Research Articles

Bridge Load Classifier Based on Deep Learning for Structural Displacement Correlation

Advanced computing brings opportunities for innovation in a broad gamma of applications. Traditional practices based on visual and manual methods tend to be replaced by cyber-physical systems to automate processes. The present work introduces an example of this, a machine vision system research based on deep learning to classify bridge load, to give support to an optical scanning system for structural health monitoring tasks. The optical scanning system monitors the health of structures, such as buildings, warehouses, water dams, etc. by the measurement of their coordinates to identify if a coordinate displacement befalls that could indicate an anomaly in the structure that can be related to structural damage. The use of this optical scanning system to monitor the structural health of bridges is a little more complicated due to the vehicle’s transit over the bridge that causes a vehicle-bridge interaction which manifests as a bridge oscillation. Under this scheme, the bridge oscillation corresponds to their coordinate’s displacement due to the vehicle-bridge interaction, but not necessarily due to bridge damage. So, a bridge load classifier is required to correlate the bridge coordinates measurements behavior with the bridge oscillation due to vehicle-bridge interaction to discriminate the normal behavior of the structure to abnormal behavior or identify tendencies that could indicate bridge deformation or discover if the bridge behavior due to loads is changing through the time.

Differentiating Local and Global Vibration Modes of Heritage Masonry Buildings through the Spatial Correlation of Modal Displacements

ABSTRACT The effective differentiation between global and local modes plays a fundamental role in the selection and application of the most appropriate seismic analysis procedures. This is particularly relevant in the case of historical heritage structures and ensembles of buildings in old city centres: due to the complexity of the structural scheme, the stratification of interventions, and the irregularity of the structural configuration with the absence of seismic details, several local modes frequently characterize the dynamic response of those structures. Distinguishing local and global modes might be challenging even from the experimental point of view in the presence of few measured degrees of freedom. Nevertheless, an accurate analysis of local modes can support the identification of macro-elements and the selection of the most appropriate analysis procedure. The present paper illustrates an original approach addressing the differentiation between global and local modes through the spatial correlation of modal displacements. The proposed approach can be either automated and integrated into software for structural analysis or applied in the context of an experimental campaign, and its application to simulated case studies is discussed.

High-order stable generalized/eXtended finite element approximations for accurate stress intensity factors

This paper investigates the accuracy and robustness of stress intensity factor (SIF) extraction using the p-Hierarchical Discontinuous Interpolant Stable Generalized Finite Element Method (pFEM-DSGFEM). This method is well-conditioned and optimally convergent for fracture mechanics problems if a proper enrichment strategy and mesh refinement are used. The method performs well when calculating global quantities such as strain energy, but its ability to capture local quantities such as SIFs has not yet been explored. pFEM-DSGFEM spaces are used to solve a variety of fracture mechanics problems and their solutions are used to extract SIFs with the Displacement Correlation Method (DCM). These numerical experiments show that pFEM-DSGFEM spaces provide highly accurate SIFs, even better than standard GFEM spaces, while being well-conditioned.

Experimental investigation on the vortex-induced vibration of a three-riser group coupling interference effect

The “riser group structure—fluid between risers” is taken as the carrier, and the “three-riser system” is selected as the research object, the experiment on the vortex-induced vibration of a three-riser group coupling interference effect is performed with variable angles between the riser group and the incoming flow, and the angles are 0°, 30°, 45°, 60° and 90°. Adjacent risers are arranged at the spacing of 4 times the diameter, and the external flow changes within 0.1–0.6 m/s. Based on the strains obtained by the fiber Bragg grating sensors and the modal decomposition theory, the concepts of “frequency interference ratio” and “displacement interference efficiency” are introduced to analyze the dynamic characteristics and dynamic response evolutions of the riser group at different incidence angles. The correlation of displacement along the riser when modal competition occurs to risers is explored, and the nonlinear effect of the external flow coupled with the wake and gap flow on the structure is researched. The results indicate that the wake shadowing effect constitutes the main constraint of the midstream and downstream risers at angles 0° and 30°, which leads to the gradual reduction of the Strouhal numbers and the sudden reduction in the dominant frequencies of the midstream and downstream risers at 0°. The boundary effect is mainly reflected in the 45°-, 60°-, and 90°-riser groups, which increases the vibration frequency. The interference effect of wake and gap flow on the variable-angle riser group causes the intensity of the mode transition to be different, and the deflection of the vibration trajectory in the 45°-riser group causes the displacements in both directions to approach. Crucially, the dominant frequencies represented by the Strouhal numbers peak, and the displacement mode transition represented by the traveling wave characteristic maximize both at 60°. The frequency interference ratio and displacement interference efficiency are not exactly consistent, and the interference effects in the in-line and cross-flow directions are significantly different. For a variable-angle riser group, cross-flow displacement under high velocities would be the key consideration in engineering design, and its interference effect on the riser group at low velocities is not negligible, either.

SGBEM Analysis of Diffraction of P- and SV-Waves by a Plane Crack in an Infinite Domain

Diffraction of elastic waves by a plane crack in an unbounded domain was investigated in this work using the symmetric Galerkin boundary element method (SGBEM) for elastodynamics in the frequency domain. The types of wave considered herein are the incident plane harmonic compressional wave (P-wave) and the incident plane harmonic shear wave (SV-wave). By using the scalar and vector potential functions of these incident waves, the wave displacement field and thereby, the wave traction field can be identified. To solve for the scattered field problem of these incoming waves on a crack in an infinite plate using the SGBEM, the crack faces were loaded with tractions equal and opposite to those produced at the same position by the incident waves. The scattering displacements and tractions found were then employed in a new boundary integral formula developed for computing the dynamic T-stress (DTS) for cracks in an infinite domain, while only the scattering displacements were needed for determining the dynamic stress intensity factors (DSIFs) by the displacement correlation technique. Numerous numerical examples were presented in this work. The SGBEM results for the DSIFs agreed very well with those obtained from using the integral transform method, and to the best knowledge of the authors, the SGBEM results for the DTS were presented for the first time in this work.

Temperature dependence of dynamic dipole formation in PbTe

PbTe-based thermoelectric materials remain of great interest due to their peculiar dynamic behavior and high thermoelectric performance. The true structure of pristine PbTe has been widely discussed, since the average rocksalt structure does not adequately account for the low lattice thermal conductivity. Single crystals of PbTe exhibit large amounts of x-ray diffuse scattering, which along with additional experimental observations has led to a series of structural models containing different types of disorder. Recently, analysis of the x-ray diffuse scattering from single-crystal PbTe confirmed the formation of local dynamic dipoles proposed earlier based on inelastic neutron scattering (INS) and one-dimensional pair distribution function (PDF) experiments. Here, we study the single-crystal diffuse x-ray scattering over a wider temperature range from 30 to 622 K in order to investigate the temperature dependence of the dynamic dipole formation. We observe that the longitudinal displacement correlations along the ⟨100⟩ directions form pairwise plateaus which results in a steplike decay of the correlations with increasing interatomic distance. This is consistent with previous observations from single-crystal diffuse scattering experiments on PbTe where the same steplike trend for the correlations was observed. However, upon lowering the temperature we observe a larger relative antiphase displacement contribution to the correlations proposed to originate from the softening of the transverse optical (TO) branch. As the local dipole formation depends on the absolute amplitude of antiphase displacements, and not the relative antiphase contribution to atomic displacements, it is found that the local dipole formation increases upon heating consistent with previous INS and PDF studies. The underlying mechanism responsible for the softening of the TO branch, and thereby the formation of dynamic dipoles, is investigated by comparison to the isostructural KCl system. The different dynamics in KCl and PbTe can be explained from the different bonding mechanism, where the metavalent bonding and ability to dynamically express a stereochemically active lone pair in PbTe gives rise to long-range interactions and TO phonon softening.

Some Practical Considerations for Compression Failure Characterization of Open-Cell Polyurethane Foams Using Digital Image Correlation.

(1) Background: Open-cell polyurethane foam mechanical behavior is highly influenced by microstructure. The determination of the failure mechanisms and the characterization of the deformation modes involved at the micro scale is relevant for accurate failure modeling. (2) Methods: We use digital image correlation (DIC) to investigate strain fields of open-cell polyurethane foams of three different densities submitted to compression testing. We analyze the effect of some DIC parameters on the failure pattern definition and the equivalent strain magnification at the apparent ultimate point. Moreover, we explore speckle versus non-speckle approaches and discuss the importance of determining the pattern quality to perform the displacement correlation. (3) Results: DIC accurately characterizes the failure patterns. A variation in the subset size has a relevant effect on the strain magnification values. Step size effect magnitude depends on the subset size. The pattern matching criterion presented little influence (3.5%) on the strain magnification. (4) Conclusion: The current work provides a comprehensive analysis of the influence of some DIC parameters on compression failure characterization of foamed structures. It highlights that changes of subset and step sizes have a significant effect on the failure pattern definition and the strain magnification values, while the pattern matching criterion and the use of speckle have a minor influence on the results. Moreover, this work stands out that the determination of the pattern quality has a major importance for texture analysis. The in-depth, detailed study carried out with samples of three different apparent densities is a useful guide for DIC users as regards texture correlation and foamed structures.

Dynamic transperineal ultrasonography correlates with prolonged pudendal nerve latency in female with fecal incontinence.

The pelvic floor is a complex anatomical entity and its neuromuscular assessment is evaluated through debated neurophysiological tests. An innovative approach is the study of pelvic floor through dynamic transperineal ultrasound (DTU). The aim of this study is to evaluate DTU sensitivity in recognizing patients with fecal incontinence and to evaluate its concordance with the results of the motor latency studied via pudendal nerve terminal motor latency (PNTML). Female patients affected by FI addressed to our center of coloproctology were prospectively assessed. After a coloproctological evaluation, comprising the PNTML assessment to identify pudendal neuropathy, patients were addressed to DTU to determine anterior and posterior displacement of puborectalis muscle by a blinded coloproctologist. In order to compare the data, a cohort of female healthy volunteers was enrolled. Sixty-eight subjects (34 patients and 34 healthy volunteers) were enrolled. The sensitivities of anterior displacement, posterior displacement and either anterior or posterior displacement in determining the fecal incontinence were 82%, 67% and 91%, respectively. A further high correlation of either anterior or posterior displacement with PTNML was also noted (88%). DTU is an indirect, painless and reproducible method for the identification of the pelvic floor neuromuscular integrity. Its findings seem to highly correlate with FI symptoms and with PNTML results. In the near future, after larger comparative studies, DTU would be considered a potential reliable non-invasive and feasible indirect procedure in the identification of fecal incontinence by pudendal neuropathy. Trial registration number is NCT03933683.

Signature of dynamical heterogeneity in spatial correlations of particle displacement and its temporal evolution in supercooled liquids

The existence of heterogeneity in the dynamics of supercooled liquids is believed to be one of the hallmarks of the glass transition. Intense research has been carried out in the past to understand the origin of this heterogeneity in dynamics and a possible length scale associated with it. We have done extensive molecular dynamics simulations of few model glass-forming liquids in three dimensions to understand the temporal evolution of the dynamic heterogeneity and the heterogeneity length scale. We find that although the strength of the dynamic heterogeneity is maximum at a timescale close to characteristic $\alpha$-relaxation time of the system, dynamic heterogeneity itself is well-developed at timescale as short as $\beta$-relaxation time and survives up to a timescale as long as few tens of $\alpha$-relaxation time. Moreover, we discovered that temperature dependence of heterogeneity length remains the same in the whole time window although its absolute value changes over time in a non-monotonic manner.

A displacement-based and explicit non-planar 3D crack propagation model in the generalized/extended finite element method

The displacement-based methods for the extraction of the Stress Intensity Factors (SIFs) were created decades ago and, since them, they have been used in a wide range of numerical analysis, most of them based on standard 2D Finite Element Method (FEM). Although the accuracy of the SIFs computed by the displacement-based methods generally be inferior compared with the energy release methods, the use of the former methods have been motivated by its simplicity, ease of implementation and low computational cost, even though it may yield less accurate SIFs when compared with the latter methods. A major use of the SIFs is the prediction of the crack path direction in crack propagation analysis. The modelling of crack propagation is the most frequent application of the Generalized Finite Element Method (GFEM) and Extended Finite Element Method (XFEM) and a large number of crack propagation models presented in literature uses energy release methods for SIFs evaluation. Very few works using displacement-based methods for the computation of the SIFs have been published in literature in the context of the GFEM and XFEM. This paper presents a propagation model for an explicit non-planar 3D crack in a GFEM/XFEM background. The proposed model uses the Displacement Correlation Method (DCM) for the SIFs extraction. Some crack propagation problems are investigated and the resultant crack paths are compared with reported results from literature. This work demonstrates that the model here proposed generates very reasonable crack paths even for relatively coarse meshes using linear elements.

Spatiotemporal Analysis of Nonaffine Displacements in Disordered Solids Sheared Across the Yielding Point

The time evolution and spatial correlations of nonaffine displacements in deformed amorphous solids are investigated using molecular dynamics simulations. The three-dimensional model glass is represented via the binary mixture, which is slowly annealed well below the glass transition temperature and then sheared at a constant strain rate. It is shown that with increasing strain, the typical size of clusters of atoms with large nonaffine displacements increases, and these clusters remain spatially homogeneously distributed, until the yielding point when mobile atoms become localized within a system-spanning shear band. Furthermore, the yielding transition is associated with an abrupt change in the spatial correlation of nonaffine displacements, which varies from exponential to power-law decay. We also find that the height of the first peak in the pair correlation function of small atoms exhibits a distinct increase at the yielding strain. These results are discussed in relation to the yielding transition in amorphous materials under cyclic loading.

Dense active matter model of motion patterns in confluent cell monolayers

Epithelial cell monolayers show remarkable displacement and velocity correlations over distances of ten or more cell sizes that are reminiscent of supercooled liquids and active nematics. We show that many observed features can be described within the framework of dense active matter, and argue that persistent uncoordinated cell motility coupled to the collective elastic modes of the cell sheet is sufficient to produce swirl-like correlations. We obtain this result using both continuum active linear elasticity and a normal modes formalism, and validate analytical predictions with numerical simulations of two agent-based cell models, soft elastic particles and the self-propelled Voronoi model together with in-vitro experiments of confluent corneal epithelial cell sheets. Simulations and normal mode analysis perfectly match when tissue-level reorganisation occurs on times longer than the persistence time of cell motility. Our analytical model quantitatively matches measured velocity correlation functions over more than a decade with a single fitting parameter.

Generalized displacement correlation method for mechanical and thermal fracture of FGM

The main objective of this work is to present a numerical modeling of mixed-mode fracture in isotropic functionally graded materials (FGMs), under mechanical and thermal loading conditions. In this paper, the displacement-based method, termed the generalized displacement correlation (GDC) method, is investigated for estimating stress intensity factor (SIF). Using the ANSYS Parametric Design Language (APDL), the continuous variations of the material properties are incorporated by specified parameters at the centroid of each element. This paper presents various numerical examples in which the accuracy of the present method is verified. Comparisons have been made between the SIFs predicted by the GDC method and the available reference solutions in the current literature. A good agreement is achieved between the results of the GDC method and the reference solutions.

Impact of visual signals on axial segmental control during walking in patients with vestibular disorder and healthy persons

Head and trunk control during standing in patients with vestibular disorder may depend on intact visual signal to override vestibular disturbance. It is unknown if such process during walking would change. Therefore, the aims of this study were to quantify (1) head and trunk control in healthy participants (HPs) and patients with unilateral vestibular hypofunction (UVH) during walking with and without visual manipulation; and (2) the correlation/association between vestibular function and head/trunk control during walking with visual manipulation in patients. Seventeen UVH patients and 15 HPs completed all the tests. They participated in the caloric test, which was used to examine vestibular function, and walked on a treadmill with and without visual manipulation. Head and trunk angular displacement and velocity were primary outcome measures, deviation of center of mass and step variability were secondary. Head roll angular displacement (7.38° ± 1.38 [mean ± SE] v.s. 12.95° ± 1.48, p = 0.004) and head-trunk correlation (in the pitch/sagittal plane: 0.22 ± 0.05 v.s. 0.38 ± 0.05, roll/frontal plane: 0.35 ± 0.06 v.s. 0.55 ± 0.06, p < 0.05) were significantly lower in patients compared to HPs. Head pitch angular velocity (8.58°/s ± 2.17 v.s. 14.23°/s ± 1.22, p = 0.026) and step width variability (0.075 ± 0.010 v.s. 0.083 ± 0.009, p = 0.04) increased with visual manipulation only in patients. No significant correlation/association was found between vestibular function and head/trunk control. Lower head-trunk correlation in patients suggests an independent head-trunk control strategy in response to vestibular impairment. Visual input could be used by patients to compensate for vestibular disturbance for head control and foot placement. Severe UVH may not lead to worse postural control compared to mild disorder.

Correlation tensor magnetic resonance imaging

Diffusional Kurtosis Magnetic Resonance Imaging (DKI) quantifies the extent of non-Gaussian water diffusion, which has been shown to be a sensitive biomarker for microstructure in health and disease. However, DKI is not specific to any microstructural property per se since kurtosis may emerge from several different sources. Q-space trajectory encoding schemes have been proposed for decoupling kurtosis arising from the variance of mean diffusivities (isotropic kurtosis) from kurtosis driven by microscopic anisotropy (anisotropic kurtosis). Still, these methods assume that the system is comprised of multiple Gaussian diffusion components with vanishing intra-compartmental kurtosis (associated with restricted diffusion). Here, we develop a more general framework for resolving the underlying kurtosis sources without relying on the multiple Gaussian diffusion approximation. We introduce Correlation Tensor MRI (CTI) – an approach harnessing the versatility of double diffusion encoding (DDE) and its sensitivity to displacement correlation tensors capable of explicitly decoupling isotropic and anisotropic kurtosis components from intra-compartmental kurtosis effects arising from restricted (and time-dependent) diffusion. Additionally, we show that, by subtracting these isotropic and anisotropic kurtosis components from the total diffusional kurtosis, CTI provides an index that is potentially sensitive to intra-compartmental kurtosis. The theoretical foundations of CTI, as well as the first proof-of-concept CTI experiments in ex vivo mouse brains at ultrahigh field of 16.4 T, are presented. We find that anisotropic and isotropic kurtosis can decouple microscopic anisotropy from substantial partial volume effects between tissue and free water. Our intra-compartmental kurtosis index exhibited positive values in both white and grey matter tissues. Simulations in different synthetic microenvironments show, however, that our current CTI protocol for estimating intra-compartmental kurtosis is limited by higher order terms that were not taken into account in this study. CTI measurements were then extended to in vivo settings and used to map heathy rat brains at 9.4 T. These in vivo CTI results were found to be consistent with our ex vivo findings. Although future studies are still required to assess and mitigate the higher order effects on the intra-compartmental kurtosis index, our results show that CTI's more general estimates of anisotropic and isotropic kurtosis contributions are already ripe for future in vivo studies, which can have significant impact our understanding of the mechanisms underlying diffusion metrics extracted in health and disease.

Learning to Explore Saliency for Stereoscopic Videos via Component-Based Interaction.

In this paper, we devise a saliency prediction model for stereoscopic videos that learns to explore saliency inspired by the component-based interactions including spatial, temporal, as well as depth cues. The model first takes advantage of specific structure of 3D residual network (3D-ResNet) to model the saliency driven by spatio-temporal coherence from consecutive frames. Subsequently, the saliency inferred by implicit-depth is automatically derived based on the displacement correlation between left and right views by leveraging a deep convolutional network (ConvNet). Finally, a component-wise refinement network is devised to produce final saliency maps over time by aggregating saliency distributions obtained from multiple components. In order to further facilitate research towards stereoscopic video saliency, we create a new dataset including 175 stereoscopic video sequences with diverse content, as well as their dense eye fixation annotations. Extensive experiments support that our proposed model can achieve superior performance compared to the state-of-the-art methods on all publicly available eye fixation datasets.

Clustering of atomic displacement parameters in bovine trypsin reveals a distributed lattice of atoms with shared chemical properties

Low-frequency vibrations are crucial for protein structure and function, but only a few experimental techniques can shine light on them. The main challenge when addressing protein dynamics in the terahertz domain is the ubiquitous water that exhibit strong absorption. In this paper, we observe the protein atoms directly using X-ray crystallography in bovine trypsin at 100 K while irradiating the crystals with 0.5 THz radiation alternating on and off states. We observed that the anisotropy of atomic displacements increased upon terahertz irradiation. Atomic displacement similarities developed between chemically related atoms and between atoms of the catalytic machinery. This pattern likely arises from delocalized polar vibrational modes rather than delocalized elastic deformations or rigid-body displacements. The displacement correlation between these atoms were detected by a hierarchical clustering method, which can assist the analysis of other ultra-high resolution crystal structures. These experimental and analytical tools provide a detailed description of protein dynamics to complement the structural information from static diffraction experiments.

Hygro-thermally induced stress intensity factor of an edge crack piezo laminated composite plate

Purpose The purpose of this paper is to evaluate hygro-thermo-mechanically induced normalized stress intensity factor (NSIF) of an edge crack symmetric angle-ply piezo laminated composite plate (PLCP) using displacement correlation method. Design/methodology/approach In the present work, the governing equations are solved through conventional finite element method combined with higher order shear deformation plate theory utilizing the micromechanical approach. Findings The effects of crack length, the thickness of the plate and piezoelectric layer, stacking sequences, fiber volume fraction, position of piezoelectric layer, change in moisture and temperature, and voltage on the NSIF are examined. The numerical results are presented in the form of a table for the better understanding and accuracy. The present outlined approach is validated with results available in the literature. These results can become a benchmark for future studies. Research limitations/implications The mathematical models theoretically have been developed by considering different parameters. The results are generated using MATLAB 2015 software developed by the authors’ side. Originality/value The fracture analysis of a single edge crack PLCP with the effect of a piezoelectric layer at the different location of cracked structures, plate thickness, and actuator voltage and hygro-thermo loading is the novelty of research for health monitoring and high-performance analysis.

Assessment of spinal cord motion as a new diagnostic MRI-parameter in cervical spinal canal stenosis: study protocol on a prospective longitudinal trial

BackgroundIncreased spinal cord motion has been proven to be a relevant finding within spinal canal stenosis disclosed by phase-contrast MRI (PC-MRI). Adapted PC-MRI is a suitable and reliable method within the well deliberated setting. As the decision between conservative and operative treatment can be challenging in some cases, further diagnostic marker would facilitate the diagnostic process. We hypothesize that increased spinal cord motion will correlate to clinical course and functional impairment and will contribute as a new diagnostic marker.MethodsA monocentric, prospective longitudinal observational trial on cervical spinal canal stenosis will be conducted at the University Medical Center Freiburg. Patients (n = 130) with relevant cervical spinal canal stenosis, being defined by at least contact to the spinal cord, will be included. Also, we will examine a control group of healthy volunteers (n = 20) as proof-of-principle. We will observe two openly assigned branches of participants undergoing conservative and surgical decompressive treatment (based on current German Guidelines) over a time course of 12 month, including a total of 4 visits. We will conduct a broad assessment of clinical parameters, standard scores and gradings, electrophysiological measurements, standard MRI, and adapted functional PC-MRI of spinal cord motion. Primary endpoint is the evaluation of an expected negative correlation of absolute spinal cord displacement to clinical impairment. Secondary endpoints are the evaluation of positive correlation of increased absolute spinal cord displacement to prolonged evoked potentials, prediction of clinical course by absolute spinal cord displacement, and demonstration of normalized spinal cord motion after decompressive surgery.DiscussionWith the use of adapted, non-invasive PC-MRI as a quantitative method for assessment of spinal cord motion, further objective diagnostic information can be gained, that might improve the therapeutic decision-making process. This study will offer the needed data in order to establish PC-MRI on spinal cord motion within the diagnostic work-up of patients suffering from spinal canal stenosis.Trial registrationGerman Clinical Trials Register, ID: DRKS00012962, Register date 2018/01/17

Correlations of non-affine displacements in metallic glasses through the yield transition

We study correlations of non-affine displacements during simple shear deformation of Cu–Zr bulk metallic glasses in molecular dynamics calculations. In the elastic regime, our calculations show exponential correlation with a decay length that we interpret as the size of a shear transformation zone in the elastic regime. This correlation length becomes system-size dependent beyond the yield transition as our calculation develops a shear band, indicative of a diverging length scale. We discuss these observations in the context of a recent proposition of yield as a first-order phase transition.