Set Of Measured Points Research Articles

Construction of a measurement system and analytical solution for docking pose of large aircraft components based on draw-wire displacement sensors

Abstract Relative pose detection is a key technology in large component automatic docking systems. In this paper, a measurement system has been developed to detect the relative pose of large aircraft components with draw-wire displacement sensors, while an analytical calculation method has been proposed to determine the docking pose of large aircraft components. This method establishes a measurement model for the docking pose of large components and separates the position and orientation solutions based on the distances between seven sets of measurement points measured by the draw-wire displacement sensors. First, the principle of three-dimensional rendezvous positioning is refined to ascertain the relative position of the components. Then, by analyzing the properties of the rotation matrix and the coupling relationship between the position and orientation variables of the movable component, 15 compatible equations containing only two variables with a maximum degree of four are obtained. Based on this set of equations, a unique solution for the rotation matrix was obtained through the variable substitution method, gradually eliminating higher-order terms. Finally, the correctness of the method is verified through numerical examples. Unlike typical parallel mechanism models, this model can directly obtain 15 compatible equations without the need for methods such as Gröbner bases. Moreover, compared to the measurement method using six draw-wire displacement sensors, a unique solution can be directly determined, solving the problem of multiple solution selection. This measurement method only requires measuring the distance between measurement points to solve the relative pose, with low equipment costs and less susceptibility to external environmental factors.

Calibration method of laser scanning measurement system for large-scale component using a free-form surface reconstruction model

For large dimensional scanning measurement, the calibration method is limited by the standard part with the scale in millimeters or centermeters. In this paper, a novel calibration method suitable for large-scale components in meters has been developed based on the free-form surface reconstruction model. The Non-Uniform Rational B-Splines (NURBS) surface is approximated from the discrete measurement points obtained by high-precision detection using the least-squares method. The deviation between the measurement points and reference model is defined by statistical results and represented by the standard deviation of the distances from the measurement points to the corresponding closest points on the surface. Furthermore, the uncertainty components introduced in the procedure of coordinate registration and surface approximation are considered to estimate the combined uncertainty of a reconstructed surface. Finally, a scanning measurement device can be calibrated by the reconstruction model consisting of a NURBS surface expression and its uncertainty prediction. To validate the proposed calibration method, the surface of a standard part with a 4-meter diameter is detected to acquire a set of measurement points and subsequently reconstructed to a parametric surface, the uncertainty of which is analyzed considering errors introduced by both device accuracy and data processing. For the reconstruction model with degree of 4, the result shows that the calibration accuracy is superior to 30 μm with a tolerance error of less than 12 μm.

Using CoMIFs in structural modal testing

This paper reports experience in using two Componentwise Mode Indicator Functions to locate the modes of vibration of a real structure with sufficiently separated frequencies. The advantages of using selected sets of measurement points and different limited frequency bands are emphasized.

Sequential sensor selection for the localization of acoustic sources by sparse Bayesian learning.

This paper deals with the design of sensor arrays in the context involving the localization of a few acoustic sources. Sparse approximation is known to be effective to find the source locations, but it depends on different array characteristics, such as the number of sensors and the array geometry. The present paper tackles this array design problem under the form of a sequential sensor selection procedure. The proposed method alternates between two steps. One step involves a source localization estimator, given a current set of measurement points, to obtain the estimation variance. Then, the other step selects the new point where a future measurement will maximally decrease the variance from the previous step. As such, the procedure can be applied online. Both numerical and experimental studies are conducted in an indoor nearfield configuration. Results show that the proposed approach performs better than offline state-of-the-art methods, and the presented empirical study reveals a better robustness to the model mismatches originating from the room reflections.

LPWAN Coverage Assessment Planning Without Explicit Knowledge of Base Station Locations

An assessment of radio network coverage, usually in the form of a measurement campaign, is essential for multibase-station (multi-BS) network deployment and maintenance. It can be conducted by a network operator or its served consumers. However, the number of measurement points and their locations may not be known in advance for an efficient and accurate evaluation. The main goal of this study is to propose a new methodology for understanding the selection of measurement points during coverage and signal quality assessment. It is particularly tailored to multi-BS low-power wide-area network (LPWAN) deployments without explicit knowledge of BS locations. To this aim, we first conduct a large-scale measurement campaign for three popular LPWAN technologies, namely, narrowband IoT (NB-IoT), Sigfox, and LoRaWAN. Utilizing this baseline data, we develop a procedure for identifying the minimum set of measurement points for the coverage assessment with a given accuracy as well as study which interpolation algorithms produce the lowest approximation error. Our results demonstrate that a random choice of measurement points is on par with their deterministic selection. Out of the candidate interpolation algorithms, the Kriging method offers attractive performance in terms of the absolute error for NB-IoT deployments. In contrast, for Sigfox and LoRaWAN infrastructures, less complex techniques, such as the natural neighbor, linear interpolation, or inverse-distance weighting, can achieve comparable (and occasionally even better) accuracy levels.

Identification of the Minimum Number of Measurements Required for Thermal Comfort Assessment in Large Workplaces.

Optimization of resources is the key to improve our ability to perform multiple tasks with limited time and money. In the context of thermal comfort assessment, optimization becomes important in large rooms where tens of individuals perform similar tasks. This work focuses on the identification of the minimum number of measurement points that allows an accurate description of the thermal environment. Accuracy of description is assumed if no significant loss of information is associated to the transition from the 'primary' thermal map based on all available measurement points to a 'secondary' thermal map based on a reduced set of measurement points. The concept of 'no significant loss' is quantified by requiring that the difference in PMV (Predicted Mean Vote) between the two maps is kept <0.1 in the vast majority (95%) of points. PMV is a standardized synthetic index that is used worldwide for quantifying thermal comfort (ISO 7730, 2005) taking into account both environmental (thermo-hygrometric) and personal (activity, clothing) quantities. We show that the uncertainty induced by the degraded resolution of the thermal map has a limited impact on the overall uncertainty on PMV. Application of the method to a few test environments shows that the room size perpendicular to the main window and the windows orientation play the largest role in determining spatial inhomogeneity in thermal maps. A minor concurring factor is the room area.

Certainty Level of Water Delivery of the Required Quality by Water Supply Networks.

The security of water delivery of the required quality by water supply networks is identified with the concept of reliability. Therefore, a method of reliability evaluation of water distribution of the required quality was developed. The method is based on the probabilistic character of secondary water contamination in the water supply network. Data for the method are taken from monitoring of the water distribution system. The method takes into consideration the number and locations of individual measurement points and the results of the tests of water quality indicators at these points. The sets of measurement points and water quality indicators constitute a matrix research (observation) field in the model. The proposed method was implemented to assess the reliability of a water distribution process with respect to water with the required microbiological quality indicators in a real distribution system.

Guided wave time-reversal imaging of macroscopic localized inhomogeneities in anisotropic composites

Estimation of damage position and extent in the inspected structure is among the emerging problems of active structural health monitoring (SHM) with elastic guided waves. Unlike conventional non-destructive testing (NDT) techniques, which assume continuous surface scanning, SHM systems operate only with data from a limited number of sensors. Nevertheless, in the case of isotropic (metal) plate-like structures, computational time-reversal techniques have proved to be effective for estimating in situ the location and size of wave sources and/or local scatterers within the SHM concept. With composite plates, the reconstruction procedure faces additional difficulties associated with the complexity of wave phenomena caused by their lamination and anisotropy. In this article, we present an extension of the time reversal technique for the case of composite laminate plate-like structures. This technique relies on the simulation of the reversed guided waves generated by reciprocal surface loads applied at a sparse set of measurement points of a real sensor network. The proposed implementation is based on the far-field asymptotics for guided waves generated in arbitrarily anisotropic laminate waveguides by a prescribed source, which have been derived from the path integral representations in terms of Green’s matrix for the structures considered. The performance of this approach has been experimentally tested on cross-ply carbon fiber-reinforced plastic plates showing reliable and adequate results for both active (piezoactuators) and passive (artificial defects) source characterization.

MONITORING AND EVALUATION OF A LONG-SPAN RAIWAY BRIDGE USING SENTINEL-1 DATA

Abstract. This paper is focused on displacement monitoring of a bridge, which is one of the key aspects of its structural health monitoring. A simplified Persistent Scatterer Interferometry (PSI) approach is used to monitor the displacements of the Nanjing Dashengguan Yangtze River High-speed Railway Bridge (China). This bridge is 1272 m long and hosts a total of 6 railway lines. The analysis was based on a set of twenty-nine Sentinel-1A images, acquired from April 2015 to August 2016. A dense set of measurement points were selected on the bridge. The PSI results show a maximum longitudinal displacement of 150 mm, on each side of the bridge. The displacements are strongly correlated with the temperature, showing that they are due to thermal expansion. Using the PSI results, the Coefficient of Thermal Expansion (CTE) of the whole bridge was estimated. The result agrees well with the CTE of the bridge materials. Using a regression model, the PSI-measured displacements were compared with in-situ measurements. The paper proposes a procedure to assess the performance of the movable bearings of the bridge, which is based on the PSI measurements.

Optimal placement of measurement points on large aircraft fuselage panels in digital assembly

A large aircraft fuselage panel is commonly composed of a variety of thin-walled components. Most of these components are large, thin and compliant, and they are also prone to some flexible deformation during assembly and remain deformed after assembly. Besides, many different fabrication and assembly manners are adopted in order to guarantee the complicated assembly relationships between each component. The above characteristics often cause large aircraft fuselage panels to exhibit low stiffness and weak strength, thereby inducing deformation during assembly. Since the posture of a large aircraft fuselage panel is commonly evaluated by matching the theoretical and actual positions of the measurement points placed on it, and its assembly deformation is also represented by the position errors of the measurement points, a reasonable measurement point placement is significant for the large aircraft fuselage panel in digital assembly. This article presents a method based on the D-optimality method and the adaptive simulated annealing genetic algorithm to optimize the placement of the measurement points which can cover more deformation information of the panel for effective assembly error diagnosis. By taking the principle of the D-optimality method, an optimal set of measurement points is selected from a larger candidate set through adaptive simulated annealing genetic algorithm. As illustrated by an example, the final measurement point configuration is more effective to maximize the determinant of the corresponding Fisher Information Matrix and minimize the estimation error of the assembly deformation than those obtained by other methods.

A Noncontacting Approach for Full-Field Strain Monitoring of Rotating Structures

The three-dimensional point-tracking (3DPT) measurement approach is used in conjunction with finite element (FE) method and modal expansion technique to predict full-field dynamic response on a rotating structure. A rotating three-bladed wind turbine rotor was subjected to different loading scenarios, and the displacement of optical targets located on the blades was measured using 3DPT. The out-of-plane measured displacement of the targets was expanded and applied to the FE model of the turbine to extract full-field strain on the turbine. The sensitivity of the proposed approach to the number of optical targets was also studied in this paper. The results show that the dynamic strain on a structure can be extracted with a very limited set of measurement points (optical targets) placed on appropriate locations on the blades. It was shown that the proposed technique is able to extract dynamic strain all over the entire structure, even inside the structure beyond the line of sight of the measurement system. Because the method is based on a noncontacting measurement approach, it can be readily applied to a variety of structures having different boundary conditions.

A field experiment on a steel Gerber-truss bridge for damage detection utilizing vehicle-induced vibrations

A field experiment was conducted on a real continuous steel Gerber-truss bridge with artificial damage applied. This article summarizes the results of the experiment for bridge damage detection utilizing traffic-induced vibrations. It investigates the sensitivities of a number of quantities to bridge damage including the identified modal parameters and their statistical patterns, Nair’s damage indicator and its statistical pattern and different sets of measurement points. The modal parameters are identified by autoregressive time-series models. The decision on bridge health condition is made and the sensitivity of variables is evaluated with the aid of the Mahalanobis–Taguchi system, a multivariate pattern recognition tool. Several observations are made as follows. For the modal parameters, although bridge damage detection can be achieved by performing Mahalanobis–Taguchi system on certain modal parameters of certain sets of measurement points, difficulties were faced in subjective selection of meaningful bridge modes and low sensitivity of the statistical pattern of the modal parameters to damage. For Nair’s damage indicator, bridge damage detection could be achieved by performing Mahalanobis–Taguchi system on Nair’s damage indicators of most sets of measurement points. As a damage indicator, Nair’s damage indicator was superior to the modal parameters. Three main advantages were observed: it does not require any subjective decision in calculating Nair’s damage indicator, thus potential human errors can be prevented and an automatic detection task can be achieved; its statistical pattern has high sensitivity to damage and, finally, it is flexible regarding the choice of sets of measurement points.

Cyber Security Analysis of Power Networks by Hypergraph Cut Algorithms

This paper presents exact solution methods for analyzing vulnerability of electric power networks to a certain kind of undetectable attacks known as false data injection attacks. We show that the problems of finding the minimum number of measurement points to be attacked undetectably reduce to minimum cut problems on hypergraphs, which admit efficient combinatorial algorithms. Experimental results indicate that our exact solution methods run as fast as the previous methods, most of which provide only approximate solutions. We also present an algorithm for enumerating all small cuts in a hypergraph, which can be used for finding vulnerable sets of measurement points.

Efficient 2.5D electromagnetic modeling using boundary integral equations

Fast and accurate simulation of responses of logging-while-drilling (LWD) electromagnetic (EM) tools in complex 2D and 3D formations is very important for reconstruction of the resistivity distribution in proactive geosteering. Currently, real-time interpretation is based on the 1D parametric inversion. Advances in fast simulation beyond the 1D model would open a way for real-time 2D inversion. We developed, implemented numerically, and tested an efficient method for simulation of LWD EM tools in complex 2D formations with an arbitrary 3D position of the tool. The method is based on the boundary integral equations for the tangential components of the field and the Fourier transform, which reduces the problem to a series of 1D integral equations. Computations are carried out simultaneously for the whole set of measurement points with the same matrix, which provides a short computation time per point. We verified the method by comparing our results with those obtained by the well-known explicit 1D method and by commercial software in the 2D case. Numerical results justified that the method is accurate and time efficient. Also, as an example, we simulated the signals of real propagation and azimuthal resistivity tools for a complex 2D formation model with fault. The software based on our method can be useful in planning geosteering jobs in complex formations.

Methods for estimating relative accuracy of ALS data.

The data acquired by airborne laser scanning is a set of measurement points with certain XYZ coordinates (the so-called cloud of points), located at places where laser pulses sent by the scanning system are refl ected. The coordinates of these points are determined based on the distance measured from the scanner system to the ground along the predetermined laser beam, and the scanning angle at which the beam is sent. The position and orientation of the scanner during the measurement is determined with the use of the GPS/INS system integrated with the scanner [7]. The coverage of the developed area with data from the ALS is done by executing a fl ight in multiple parallel strips that partly overlap, thus ensuring the continuity of the development. The accuracy of the designated coordinates of ALS points depends on the accuracy of observation (distance, scan angle, position and orientation) and on the mathematical model used to determine the coordinates of these points [2]. In connection with the occurrence of errors in the measurement devices and in the defi nition of the mathematical model, there exist some discrepancy in the data from the adjacent strips in overlapping area. Therefore, in order to improve the position of the measuring points, we use ALS data alignment methods by basing on the adjustment of data from adjacent strips and their best integration in the exterior coordinate system. The use of ALS data for the purposes of subsequent developments, such as the DTM (Digital Terrain Model) and DSM (Digital Surface Model) requires the determination of their accuracy. By measuring the diff erences between the adjacent strips, we can estimate the relative accuracy of the ALS, and by sett ing the position of the examined control objects in the exterior coordinate system independently, we can also estimate their absolute accuracy. However, the specifi c nature of data

Damage detection by modal curvatures: numerical issues

This work is concerned with modal curvature-based damage detection in slender beam-like structures, whereby the modal curvatures are computed by numerical differentiation of noisy mode shapes sampled at a finite number of measurement points. Within this framework, most common techniques greatly amplify the measurement errors and their application leads to unreliable outcomes, especially when a large set of measurement points is considered. Preliminary signal processing, even if beneficial for reducing the noise level, does not solve the problem in that neither the detection of damaged zones nor the reduction of false alarms exhibit significant improvements. In a comparative fashion, we herein demonstrate that a modified Savitzky–Golay filter and the cubic smoothing spline method can provide a more affordable way for detecting damages when using numerically obtained modal curvatures. In doing so, the robustness against the measurement errors and the role of the adopted formulation for the modal curvature-based damage index are considered. A simple statistical procedure that can further improve the detection of damaged regions together with the identification of possible false positives is also presented.

Mu2e Magnetic Measurement Studies

The Mu2e experiment at Fermilab is designed to explore charged lepton flavor violation by searching for muon-to-electron conversion. The magnetic field generated by a system of solenoids is a crucial component of Mu2e and requires accurate characterization to detect any potential flaws and to produce a detailed field map. In order to design and build a precise field mapping system consisting of Hall and NMR probes, tolerances and precision for such a system need to be evaluated. To generate a final magnetic field map of the Mu2e solenoids, a continuous field has to be extracted from a discrete set of measurement points. A design for the Mu2e field mapping hardware, and results from simulations to specify parameters for Hall and NMR probes are presented. A fitting procedure for the analytical treatment of our expected magnetic measurements is introduced.

Modal scaling in operational modal analysis using a finite element model

Operational modal analysis (OMA) is a technique that has been widely used on civil and mechanical structures in the last 10 years. As the force is unknown, mode shapes cannot be mass normalized from the responses used for modal identification. In the past few years, several formulations have been proposed to scale mode shapes using the mass-change method, which consists of repeating modal testing after changing the mass at different points of the structure where the mode shapes are known. This technique is easy to use in small systems but it has important drawbacks in medium and large structures due to the difficulties of applying masses of sufficient magnitude. In this paper a more simple methodology is proposed based on scaling the experimental mode shapes of a structure using the mass matrix of a finite element model. Two approaches are compared; one approach where the mass matrix is reduced to the set of measurement points using SEREP and a second approach where the experimental mode shapes are expanded to all DOFs in the model using a newly published principle called the local correspondence (LC) principle. The two approaches are compared in two case studies: a numerical example and a real experimental case. In the numerical example a finite element model was assembled in MATLAB, which was considered the experimental model, and then one thousand finite element models were simulated changing the material and the section properties of each element of the model, in order to study the accuracy provided by the different techniques. As regarding the experimental case, the scaling factors of a cantilever beam were estimated by the mass change method and with the equations that consider the mass matrix of the finite element model. The effect of discretization of the finite element model was studied by assembling several finite element models with different numbers of degree of freedoms.

Computationally efficient simulation of extracellular recordings with multielectrode arrays

In this paper we present a novel, computationally and memory efficient way of modeling the spatial dependency of measured spike waveforms in extracellular recordings of neuronal activity. We use compartment models to simulate action potentials in neurons and then apply linear source approximation to calculate the resulting extracellular spike waveform on a three dimensional grid of measurement points surrounding the neurons. We then apply traditional compression techniques and polynomial fitting to obtain a compact mathematical description of the spatial dependency of the spike waveform. We show how the compressed models can be used to efficiently calculate the spike waveform from a neuron in a large set of measurement points simultaneously and how the same procedure can be inversed to calculate the spike waveforms from a large set of neurons at a single electrode position. The compressed models have been implemented into an object oriented simulation tool that allows the simulation of multielectrode recordings that capture the variations in spike waveforms that are expected to arise between the different recording channels. The computational simplicity of our approach allows the simulation of a multi-channel recording of signals from large populations of neurons while simulating the activity of every neuron with a high level of detail. We have validated our compressed models against the original data obtained from the compartment models and we have shown, by example, how the simulation approach presented here can be used to quantify the performance in spike sorting as a function of electrode position.

Decrease of Total Subcutaneous Adipose Tissue From Infancy to Childhood

The observation and research of body composition is a topic of present interest. For the assessment of health and variables influencing growth and nutrition, it is of utmost interest to focus on the population of young children. The measurements of subcutaneous body fat distribution in a sample of clinically healthy children ages 0 to 7 years were examined. The optical device LIPOMETER was applied to measure the thickness of subcutaneous adipose tissue layers (in millimeters) at 15 well-defined body sites. This set of measurement points defines the subcutaneous adipose tissue topography. In the present study, subcutaneous adipose tissue topography was determined in 275 healthy children (128 girls and 147 boys) divided into 3 age groups. The results of the measurements are presented in 3 levels: total subcutaneous adipose tissue, 4 body regions, and 15 body sites. Our results show a clear physiological decrease in subcutaneous body fat in boys (-43.8%) and girls (-39.8%). One interesting finding was that the decrease occurs mainly in the trunk, abdomen, and lower extremities, whereas the body fat distribution of the upper extremities did not differ. Furthermore, slight subcutaneous adipose tissue topography differences between both sexes were found. The present study provides basic documentation of subcutaneous adipose tissue topography in healthy children ages 0 to 7 years. An accurate description of subcutaneous adipose tissue topography in healthy subjects could help to characterize various diseases in relation to overnutrition and malnutrition throughout childhood.