Small Number Of Measurement Points Research Articles

Damage Identification of Stay Cables Based on a Small Amount of Deflection Monitoring Data

For the problem of cable damage identification in cable-stayed bridges, we have presented a method for identifying cable damage based on deflection monitoring data from a small number of measurement points. We first describe the method to reduce the number of measurement points. We analyzed the distributional characteristics of the deflection difference before and after cable damage in cable-stayed bridges with optimized measurement points. The first derivative of the deflection difference is transformed by a wavelet transform to identify the location of the damaged cable. Then, the Kriging proxy model with exponential and deflection differences is established. The objective function is constructed from the residual deflection difference formed by the deflection difference and the measured deflection difference. With the particle swarm optimization algorithm, the damage parameters in the surrogate model are modified to minimize the objective function, and the damage to the cables is then identified. It is shown that the location of the damaged cable can be identified from the deflection data of a small number of measurement points with small error. The degree of damage can be accurately determined using the surrogate model.

Comparison of Measured and Derived Thermal Conductivities in the Unsaturated Soil Zone of a Large-Scale Geothermal Collector System (LSC)

The design, energetic performance, and thermal impact of large-scale geothermal collector systems (LSCs) are dependent on the thermal conductivity of unsaturated soils (λ). The aim of this study was to investigate the benefits of two different λ measurement methods using single-needle sensor measuring devices on a laboratory scale. Since large-scale determinations are required in the context of LSCs, the potential for deriving λ from electrical resistivity tomography measurements (ERTs) was also examined. Using two approaches—the continuous evaporation method and the punctual method—thermal conductivities of soil samples from Bad Nauheim (Germany) were measured. The results were compared with averaged λ derived from three ERT sections. With the evaporation method, significant bulk density changes were observed during the experimental procedure, which were caused by the clay content and the use of repacked samples. The punctual method ensures a sufficiently constant bulk density during the measurements, but only provides a small number of measurement points. The thermal conductivities derived from ERTs show largely minor deviations from the laboratory measurements on average. If further research confirms the results of this study, ERTs could provide a non-invasive and unelaborate thermal exploration of the subsurface in the context of large-scale infrastructure projects such as LSCs.

Single-Camera-Based Bridge Structural Displacement Measurement with Traffic Counting.

Vision-based structural displacement methods allow convenient monitoring of civil structures such as bridges, though they are often limited due to the small number of measurement points, constrained spatial resolution, and inability to identify the acting forces of the measured displacement. To increase the number of measurement points in vision-based bridge displacement measurement, this study introduces a front-view tandem marker motion capture system with side-view traffic counting to identify the force-inducing passing vehicles on the bridge’s deck. The proposed system was able to measure structural displacement at submillimeter resolution on eight measurement points at once at a distance of 40.8–64.2 m from a front-view camera. The traffic counting system with a side-view camera recorded the passing vehicles from two opposing lanes. We conducted a 35-min experiment for a 25 m-span steel road bridge with hundreds of cars passing over it and confirmed dynamic displacement distributions with amplitudes of several millimeters when large vehicles passed.

Spatial extrapolation of early room impulse responses in local area using sparse equivalent sources and image source method

The room impulse response (RIR) is important in most acoustic applications, such as the design of concert halls and sound field control, because it characterizes the sound propagation. The measurement of RIRs at multiple points is challenging, as it requires a huge microphone array or repeating the experiment by microphone replacement. Several RIR interpolation and extrapolation methods of RIRs have been developed for obtaining RIRs from multiple measurement points efficiently. Extrapolation methods offer more efficient RIR measurement compared to interpolation. However, previous studies focused on extrapolation at frequencies below 1 kHz, and the extrapolation at higher frequencies was difficult. In this study, we propose an extrapolation method for RIRs of direct sound and early reflections in a local area using a small number of measurement points. The proposed method represents the RIRs around the microphones using superpositions of sparse equivalent sources located around the loudspeaker and image sources. We conducted a measurement experiment in an anechoic chamber to estimate RIRs around microphones using sound-reflecting boards. From the experimental results with 2.5 dimensional conditions, the proposed method achieved about above 10 dB of signal to noise ratio (SNR) near the microphone array from 0.5–8.5 kHz. For the extrapolation accuracy over the entire evaluation area (0.6 × 0.54 m2), the proposed method improved the SNR by about 5–6 dB compared to results using the plane wave decomposition.

Multizone Sound Field Reproduction Based on Equivalent Source Method

In this paper, the two-zone sound field reproduction problem is investigated with a newly proposed method. The aim of the two-zone reproduction problem is to achieve sound field reproduction in the bright zone while keeping the sound field energy in the dark zone as low as possible. The main difference between the proposed method and the conventional method is that the sound field control in the dark zone is not limited to a small number of measurement points on the region boundary but to measurement points throughout the whole dark zone. For practical reasons, the whole region is discretized into a grid, and the grid selection method is also provided in this paper. Simulations are performed to compare the performances of the proposed and conventional methods with different virtual source directions, and a comparison of the robustness to the regularization parameter shows that the proposed method is less sensitive to the selection of the regularization parameter. Finally, an experiment is performed with a circular loudspeaker array in a real listening room. A quieter dark zone is achieved by the proposed method while keeping the reproduction error in the bright zone close to that of the conventional method, similar to the simulation results. These outcomes verify that the proposed method performs well in both free-field and reverberation environments.

Inspection of blade profile and machining deviation analysis based on sample points optimization and NURBS knot insertion

As the core component of aviation industry, the machining accuracy of blade has great impact on the performance of aeroengine. Blade inspection can get knowledge of machining accuracy and can be used to compensate the machining error. In consideration of measuring time and efficiency, measuring trace planning based on sample points optimization (SPO) is introduced, and NURBS knot insertion (NURBS-KI) method is proposed to reconstruct the blade contour. Then, the designed model and the reconstructed model are compared to analyze the machining error. The reconstruction result shows that the presented method can better restore the blade contour, and NURBS-KI algorithm is proved in this paper to be an effective method to reconstruct blade curve and surface based on small number of measurement points. As illustrated in deviation analysis results, the machining error is within the design tolerance, and the finishing allowance can be removed afterwards.

선박 곡부재 계측 포인트에 대한 곡면 모델링 방법

Forward and afterward parts of ship and offshore structures are composed of curved plates with a thick thickness. It takes mush time to process the curved plate. If the fabricated curved plate has some dimensional errors, the additional cost is incurred in the assembling process. So, it is important to assess accurate dimensions for fabrication. Recently, photometric systems and 3D laser scanners have been used for this purpose. The dimensional assessment for fabrication is evaluated by comparing the surface created from the measurement points with the design surface. A B-spline surface interpolation is generally used to create the measurement surface, but there may be errors depending on the number and position of measurement points. In this study, we propose a method to improve the generation of the measurement surface. The mesh refinement method is used to obtain an accurate curved surface using a small number of measurement points. A Hermite curve interpolation is applied to reduce the error of the final generated surface. For accurate interpolation, the exact tangential direction is calculated at the vertex of an element, and errors are evaluated for various calculation methods.

Reconstruction of low-frequency bridge noise using an inverse modal acoustic transfer vector method

Low-frequency noise emitted by elevated viaducts in light rail transit lines has considerable adverse effects on inhabitants living nearby. Reliable prediction of the acoustic field radiating from the viaduct using forward numerical models is challenging because the model parameters that influence viaduct vibration are difficult to obtain. To avoid directly quantifying these parameters, such as wheel–rail combined roughness, an inverse method is presented to reconstruct the acoustic field using modal acoustic transfer vectors and the sound pressures at a small number of measurement points. First, a forward numerical method based on the train–track–bridge interaction analysis is performed to predict the structure-borne noise of a concrete box girder viaduct. Then, the calculated sound pressures are treated as virtual measurement results to illustrate the inverse method procedure. Both QR decomposition and singular value decomposition with Tikhonov regularisation are used in the inverse analysis. Third, the proposed inverse method is validated by comparing the sound pressure levels computed using the inverse method with the results simulated using the forward prediction method. Finally, the reliability of the inverse procedure is further validated through field tests of two U-shaped girder viaducts.

Online Moisture Measurement of Bio Fuel at a Paper Mill Employing a Microwave Resonator.

This paper investigates online moisture measurement of biofuel employing a strip line cavity resonator at approximately 366 MHz, attached above and below the conveyor belt. An existing sensor design is modified for the factory assembly, and the correct operation has been tested prior to this paper with a small number of measurement points and collected reference samples (n = 67). The purpose is now to concentrate on the accuracy of the measurement and increase the number of measurement points (n = 367). The measurements were made in 5 different lots, and the thickness and moisture properties of the biomaterial mat were varied between minimum and maximum levels by adjusting the settings of the belt filter press that presses pulp slush into a mat. In order to further reduce inaccuracy, at the maximum one standard deviation was allowed from the average height of the equivalent water layer for each dataset, and consequently the number of samples was reduced to 235. A linear fit and a parabola fit were determined for thickness of the equivalent water layer vs. the relative resonant frequency shift: R2 = 0.82 and R2 = 0.78.

Fast Antenna Far-Field Characterization via Sparse Spherical Harmonic Expansion

A procedure is proposed to significantly reduce the amount of time to characterize 3-D antenna far-field patterns. The measured far field is expanded into spherical harmonics, and a sparse recovery algorithm is used to recover the spherical wave coefficients giving access to the field radiated by the antenna everywhere. A small number of measurement points are required, since the relevant information of the most antenna patterns is concentrated in only a few spherical wave coefficients. Sampling strategies enabling fast spherical scans are discussed, which makes the approach both efficient and easy to implement in existing far-field measurement facilities. Simulations are first provided to show the potentialities of this compressive sensing-based approach. The proposed strategy is then applied to characterize 3-D far-field patterns radiated by several antennas operating in different frequency bands measured in far field in direct line of sight configuration and in a compact antenna test range. Experimental results show that a saving in the number of measurement points up to 70% can be achieved compared with standard approaches. These results pave the way to a more efficient use of far-field measurement facilities.

Firefly algorithm combined with Newton method to identify boundary conditions for transient heat conduction problems

ABSTRACTFirefly algorithm combined with Newton method (FA–NM) is proposed for identifying time-dependent boundary conditions of two-dimensional transient heat conduction problems with a heat source. The dual reciprocity boundary element method (DRBEM) is applied to solve the direct problem. The improved firefly algorithm has not only a good global search ability, but also a good local search ability. FA–NM can acquire accurate results with much less iterations. Furthermore, different measurement points and noises are also considered. A small number of measurement points cannot obtain precise results. With the increase in the measurement points to a certain value, the results are more accurate. When the measurement noises are not very large, FA–NM can get desirable results. With the decrease in measurement noises, the results are in better agreement with the exact solutions. Numerical results also indicate that the more front the time substep is, the more accurate the estimated boundary conditions are.

Structural damage detection based on virtual element boundary measurement

A “weak” formulation of the pseudo-excitation (PE) approach was recently proposed for structural damage detection in thin-walled structures. The method was shown to exhibit some appealing features including high noise tolerant ability. However, the method requires very dense displacement field measurement within the inspection region. To tackle the problem, a new damage detection method based on virtual element boundary measurement (VEBM) under the “weak” formulation framework is proposed in this paper. VEBM based “weak” formulation divides the entire structure into several “virtual elements” (VE). By tuning the vibration frequency to the natural frequency of the VE, the “weak” formulation is shown to provide a “region-by-region” detection strategy, allowing reliable damage detection by using only a small number of measurement points at the VE boundaries. The effectiveness of the proposed method was first validated numerically using a cantilever beam containing a small damage. Influences of various factors such as measurement noise levels and frequency discrepancies between the ideal and the actual elements were discussed. An experiment was carried out through a Laser Doppler Vibrometer (LDV) measurement. Results demonstrated that VEBM method can achieve good detection results by using a small number of measurement points, whilst providing enhanced noise tolerant capability against measurement uncertainties.

Estimation of uncertainty of mean velocity of flue gas in a conduit as determined by the traverse method within the gravimetric measurement of particulate concentration

In gravimetric measurements of dust emissions from industrial technological plants, the required mean gas velocity in a conduit is often determined by Pitot traverse method. It is commonly seen as a method giving good approximate values of mean gas velocity, although the actual rate of this approximation is not considered in the analysis of measurement results. It was seen that there was a need to establish what magnitude of error might occur in practice due to the small number of measurement points and typical non-uniformity of the gas velocity profiles in conduits of rectangular cross-section. The calculations were based on the concept of treating a measurement plane as one consisting of a set of elementary planes. The elementary gas velocity profiles in these elementary planes were simulated, the mean velocity for these profiles were calculated based on point velocity values, and the measurement uncertainty of this mean velocity determined. This uncertainty results in the uncertainty of the mean velocity across the entire measurement plane. It appears that, depending on the number of measurement points and gas velocity profile non-uniformity, the value is not small and is of the order of several percent, and hence needs to be taken into account in the budget of the combined uncertainty of mean velocity, which in turn contributes to the uncertainty of gas volumetric flow rate and dust pollutant mass flow rate.

Improving the accuracy of assessing the position deviation in coordinate measurements of GTE compressor and turbine blade profiles

The paper proposes a method for increasing the accuracy of the iterative closest point (ICP) algorithm used in metrology problems in determining position deviation. The target of using the method for determining deviation profiles were compressor blades of a gas turbine engine (GTE). We propose to formulate the problem of the optimal match in the developed method as a multicriterion task including the criteria of the minimum of squared distances, differences of normal vectors and difference values of the depth of camber at the appropriate points of the superposed profiles. Different variants of reducing the problem to the use of a single integral criterion including the above-mentioned ones are considered. The problems of optimization were solved using the quasi-Newtonian methods of sequential quadratic programming. The proposed new method of improving the ICP algorithm based on geometric features showed greater accuracy in comparison with the discussed methods for optimizing the distance between the fitting points, especially in the case of a small number of measurement points on the profiles.

Water pollution estimation based on the 2D transport–diffusion model and the Singular Evolutive Interpolated Kalman filter

In this paper, the 2D mathematical water pollution model describing the transport–diffusion processes of some contaminant substances in Thanh Nhan Lake in Hanoï is considered. The finite-volume method is used to solve the model equations. The Singular Evolutive Interpolated Kalman filter is applied to evaluate the pollution level at arbitrary mesh point based only on a small number of measurement points.

TH‐C‐144‐02: Experimental Study of Discrete Prompt Gamma Lines for In‐Vivo Proton Range Verification

Purpose: A novel method for in vivo proton beam range verification is presented, using energy‐resolvable proton‐induced prompt gamma lines. Methods: Prompt gamma‐rays emitted near the end‐of‐range of a clinical proton beam originate from transitions between the lower states of excited nuclear reaction products. We developed a prompt gamma‐ray detection system with the aim of resolving the resulting discrete gamma lines. The ability to quantify the strength of these lines can provide valuable information for in vivo range verification: known cross sections may be used as prior knowledge, and uncertainties resulting from differences in tissue composition could be reduced. A LaBr3:Ce scintillation detector was used, which provides high energy resolution. The pulses from the photomultiplier tube were acquired with analog‐to‐digital converters at high sampling rates, synchronized to the cyclotron radiofrequency to separate the quasi‐continuous neutron‐induced background from the prompt gamma signals of interest. Results: Preliminary measurements were performed with a 150 MeV proton pencil‐beam targeted on the center of a water phantom with a 15 cm diameter. A 1 cm lead slit collimator was used perpendicular to the beam direction, centered at the end‐of‐range. The acquired gamma spectra show the 6.13 MeV gamma line from oxygen‐16, and its escape peak, can be clearly resolved with an energy resolution of ∼1% FWHM. Conclusion: Our results show the feasibility of measuring discrete prompt gamma lines using a practical detection system. These gamma lines can be attributed to specific nuclear reactions with established properties, potentially enabling accurate proton range verification using a small number of measurement points. Experiments with different collimators and proton energies are currently being performed to determine an optimal configuration for range verification.

Optimizing river discharge measurements using Monte Carlo Markov Chain

► We perform Monte Carlo simulation to improve efficiency of river discharge measurement. ► We find that the number of measurements may be reduced without significant increase of uncertainty. ► We propose a “recipe”, where sparse measurements are used within the proposed computational scheme. In this work we implement Monte Carlo Markov Chain (MCMC) dynamics in the search of rules that may lead to optimizing river discharge measurements, which should prove useful in situations when resources are scarce. The MCMC dynamics is based on a recently proposed computational interpolation scheme, where the velocity profile for each vertical section is first determined by applying polynomial regression, and then a continuous approximation for the velocity across the entire vertical section is obtained through interpolation. To this end, we use the data obtained experimentally on rivers Exu and Capibaribe, state of Pernambuco, in the northeast of Brazil. By considering the velocity profile obtained through this procedure using all the available measurement points as the “best known profile”, or benchmark, we proceed by randomly choosing a small number of measurement points, repeating the above procedure, and comparing the result with the benchmark. The deviation of the reduced point approximation from the benchmark is then used as an objective function, which is minimized through an iterative MCMC process of moving the individual measurement points in different directions, and accepting or rejecting these movements. MCMC dynamics is applied for different choices of the reduced number of measurements, and finally a “recipe” is proposed for the practical choice of the number of measurement points and their placement, which optimizes the river discharge measurement. More precisely, instead of performing the full set of measurements at k vertical sections using several points for each vertical in order to apply the standard area-velocity method, one may perform just a single measurement close to the surface for every other of the k verticals, and then apply the proposed computational scheme. If the image of the velocity profile keeps changing as new measurements are incorporated, and one is interested in the details of the multiple flow structure, additional measurements should be made between adjacent high velocity observations. The software implementing the numerical procedure is available for free download at the internet page http:/www.pgbiom.ufrpe.br/downloads/discharge .

A plane wave generation method by wave number domain point focusing

A method for generation of a wave-field that is a plane wave is described. This method uses an array of loudspeakers phased so that the field in the wave-number domain is nearly concentrated at a point, this point being at the wave-number vector of the desired plane wave. The method described here for such a wave-number concentration makes use of an expansion in spherical harmonics, and requires a relatively small number of measurement points for a good approximate achievement of a plane wave. The measurement points are on a spherical surface surrounding the array of loudspeakers. The input signals for the individual loudspeakers can be derived without a matrix inversion or without explicit assumptions about the loudspeakers. The mathematical development involves spherical harmonics and three-dimensional Fourier transforms. Some numerical examples are given, with various assumptions concerning the nature of the loudspeakers, that support the premise that the method described in the present paper may be useful in applications.

Perceptible Grouping of Cracks in Nuclear Piping Using Wavelet Transformation

This paper presents an application of the wavelet transform for damage detection or crack detection based on digital image processing measurements. A number of important issues that need to be considered when image sequences are used for vibration analysis are discussed. These include: correspondence of image features from image to image, image calibration and spatial resolution. The principles of image edge detection are discussed and a comparison between the wavelet approach and the classical method is presented. A digital image damage detection method based on converting image to data, then filtering and converting from 2D to 3D data measured. The method is illustrated using a simple programming for matlab and Fortran for image to data and wavelet transformation model. The major advantage of the method is the significantly increased number of discrete points used to describe mode shapes. This is in contrast to classical techniques where in practice a small number of measurement points are obtained from a limited number of sensors. Keywords—Crack detection, Wavelet transformation

Damage Detection Using Optical Measurements and Wavelets

The paper presents an application of the wavelet transform for damage detection based on optical measurements. A number of important issues that need to be considered when image sequences are used for vibration analysis are discussed. These include: correspondence of image features from image to image, image calibration and spatial resolution. The principles of image edge detection are discussed and a comparison between the wavelet approach and the classical method is presented. A novel damage detection method based on optically measured mode-shape data is proposed. The method is illustrated using a simple cantilever beam experiment. The major advantage of the method is the significantly increased number of discrete points used to describe mode shapes. This is in contrast to classical techniques where in practice a small number of measurement points are obtained from a limited number of sensors.