查看更多>>摘要：The BeiDou Regional Navigation Satellite System (BDS-2) and BeiDou Global Navigation Satellite System (BDS-3) satellites will be utilized in conjunction to provide positioning, navigation and timing (PNT) services. Precise orbit products are essential preconditions and guarantees for providing PNT services. To improve the quality of the BeiDou Navigation Satellite System (BDS) orbits determination, a method for eliminating the biases caused by code inter-system biases (ISBs) between the BDS-2 and BDS-3 at overlapping frequencies on BDS doubledifference (DD) ambiguity resolution (AR) is proposed. To validate the contribution of the proposed method, the dataset spanning from day of year (DOY) 170, 2019, to DOY 170, 2020 is analyzed in the BDS precise orbit determination (POD) with different processing strategies. The results show that the fractional cycle biases (FCBs) in wide-lane and narrow-lane ambiguities are related to the receiver types, which are stable and can be estimated as constants in a POD arc length. After applying the proposed calibration method, the success fixing rate for the BDS-2/3 inter-system wide-lane ambiguities is improved by more than 25%, and that of the narrow-lane ambiguities by approximately 6%. Compared with that for BDS-2/2 and BDS-3/3 intra-system AR independently, the overlapping accuracy is improved by 13.7%, 4.8% in the along-track, cross-track directions, respectively, after adding BDS-2/3 inter-system AR.
Gupta, Munish KumarKorkmaz, Mehmet ErdiSarikaya, MuratKrolczyk, Grzegorz M....
12页
查看更多>>摘要：Aluminium alloys are widely used in modern engineering applications such as automobile, aerospace etc because of its characteristics. The machining of aluminium alloys are also considered as difficult because of its sticky and soft nature, low thermal conductivity, strain hardening effect etc. The cooling conditions employed at cutting zone improved the machining performance but the resources, material consumption, skilled labor etc. are also required for performing the machining experiments. Therefore, the simulation of process parameters with the help of Finite Element Modelling (FEM) during machining is highly researched topic these days. In this work, a new practice from measurement science i.e., FEM simulation was performed with AdvantEdge software and the prediction models were developed for evaluating the cutting forces and cutting temperature while machining AA2024-T351 alloy under dry, liquid nitrogen (LN2) and carbon dioxide (CO2) conditions. Initially, the 3D turning model was developed and the results were compared with experimental findings. The results obtained from simulation model are very close with experimental results with minimum standard value of 0.67 (5.7%) for cutting forces and 4.58 (6.16%) for cutting temperature. Thus, it is worthy to mention that the 3D FE model is efficient and effective to predict and measurement results with minimum error.
查看更多>>摘要：In the detection using guided waves, the signal often carries a high level of non-Gaussian noise. The traditional denoising method cannot estimate and use the prior information of the signal, which leads to poor denoising effect. To tackle this problem, this paper proposed a denoising network based on the combination of generative adversarial network (GAN) and autoencoder (AE). First, GAN is used to estimate the distribution characteristics of the extracted noise and generate samples. Second, according to the characteristics of the guided wave, a pair of datasets are generated to train DAE network. The trained denoising AE has strong robustness. As a result, the proposed GAN-AE based denoiser (GAD) can effectively can effectively reduce the noise level and has the ability to accurately recover the peak time of the wave packet. In particular, the proposed method significantly outperforms conventional denoising methods in low signal-to-noise (SNR) conditions.
查看更多>>摘要：The laser ultrasonic (LU) technique has the advantages of a wide frequency band, small non-detection zone, high resolution and non-contact compared to conventional ultrasonic testing, which makes it potential for on-line inspection of the wire arc additive manufacturing (WAAM) process. To investigate the influence of surface profile on the LU inspection of WAAM defects, multiscale analysis was adopted in the mathematical characterization of the sample surface profile. Finite Element (FE) models of LU inspection of WAAM defects with different surface profiles were established using COMSOL software. The propagation of acoustic waves and their interaction with surface profile and defects were numerically analyzed. The LU inspection methods, that is, superficial crack detected by through-transmission of Rayleigh wave and internal hole detected by pulsed-echo of shear wave were put forward. A set of WAAM samples with different surface topographies was manufactured by the robotic gas metal arc welding (GWAM) system through varying the process parameters and filler materials. LU inspection experiments were conducted to obtain B-scan images and A-scan signals of the defects in these samples. The experimental results indicate that surface roughness has a significant effect on the signal-to-noise ratio (SNR) of internal through hole detection, and surface waviness has a significant effect on the sensitivity of superficial crack detection. The experimental results are consistent with the numerical results, which validate the proposed FE model. The proposed FE model can be used for the quantitative study of the influence of WAAM sample profile on the LU inspection. Furthermore, it is also a guidance for the formulation of key process parameters in LU inspection, such as the maximum generating-receiving laser distance and the laser's layout. At last, a robotic LU inspection system was built and preliminarily achieved the automatic inspection of a WAAM part. This research provides a theoretical basis for the on-line application of LU techniques in WAAM process monitoring.
查看更多>>摘要：The roughness of rock joint surfaces plays a vital role in the hydrological and mechanical properties of discontinuous rock masses. Applicable and reliable measurements are important for investigating the roughness characterization of rock joints. This research comprehensively evaluates the performance of smartphone photogrammetry for rock joints through a roughness characterization method. Five laboratory-sized rock joint specimens were selected and operated by 24 experimenters to assess the trueness and precision of smartphone photogrammetry based on Structure from Motion- Multi View Stereo (SfM-MVS) photogrammetry technique. Benchmark data from a structure light scanner were used to assess the usability of smartphone photogrammetry through the directional roughness metric method. The results show that it can be applied to achieve acceptable trueness and precision of joint roughness measurements for engraving rock and replica rock joints with no reflective or translucent materials. In addition, the roughness errors of the subsampled models with point intervals of 0.25 mm, 0.5 mm, and 1.0 mm are close to each other.
Xu, GuangyaPu, YuanyuanHogan, Sean A.Kennedy, Deirdre...
6页
查看更多>>摘要：Acid-induced milk coagulation is a key processing step in the manufacture of dairy products i.e. yoghurt, and could benefit from process analytical technologies for monitoring the kinetics of milk coagulation. This study evaluates a novel, bulk acoustic wave (BAW) sensor technology to monitor acid-induced (glucono-delta-lactone (GDL)) coagulation of skim milk. The effects of GDL concentration (2.5, 3 and 3.5%) and temperature (22, 31 and 40 degrees C) on skim milk coagulation kinetics were evaluated using rheometry and the BAW sensor. A parameter tAVg, determined from acoustic viscosity (AV), was established to monitor the onset of gelation. Changes observed in tAVg at the onset of gelation were due to changes in particle size of samples at pH -5.3 and -5.2. A positive linear relationship (R2 = 0.97) were found between gelation point (G ' > 1 Pa) and tAVg, and was capable to monitor early stages of gel formation.
查看更多>>摘要：BLDC motor applications require precise position and speed measurements, traditionally obtained with sensors. This article presents a method for estimating those measurements without position sensors using terminal phase voltages with attenuated spurious, acquired with a FPGA that also operates a PWM-controlled inverter. Voltages are labelled with electrical and virtual rotor states using an encoder that provides training and testing data for two three-layer ANNs with perceptron-based cascade topology. The first ANN estimates the position from features of voltages with incremental timestamps, and the second ANN estimates the speed from features of position differentials considering timestamps in an acquisition window. Sensor-based training and sensorless testing at 125-1,500 rpm with a loaded 8-pole-pair motor obtained absolute errors of 0.8 electrical degrees and 22 rpm. Results conclude that the overall position estimation significantly improved conventional and advanced methods, and the speed estimation slightly improved conventional methods, but was worse than in advanced ones.
查看更多>>摘要：For the high strength, good corrosion resistance and stability, carbon fiber reinforced polymer (CFRP) composites can be made into pipes to transfer gasses and oils in submarine environment. Structural performance and shape of CFRP composite pipes are particularly important to sustain the regular operation of the delivery system. To obtain the in-field shape and identify the local buckling of CFRP composite pipes, quasi-distributed optical fiber sensing techniques have been developed based on the multiplex of fiber Bragg grating (FBG) sensors. Theoretical investigation on shape profile configuration of the pipes based on the measured strains has been performed. Relationship between the accuracy of configuration algorithm and the sensor layout has also been explored. Experiments have been conducted to check the effectiveness and accuracy of the proposed sensing technique and curve configuration algorithm. Results validate good measurement performance of the proposed sensors and high accuracy of the shape-configuration algorithm. Suggestions on the sensor layout of long-distance pipe structures are provided with the comprehensive consideration of overall structural shape control and economical factor. The study can be adopted to instruct the establishment of the structural health monitoring system, identify the buckling and assess the safety operation of pipe structures.
查看更多>>摘要：To improve the spatial resolution of electrical capacitance tomography (ECT) images for visualizing large-scale concentric-annulus measuring area, ECT sensors with 12 external electrodes (EE) and different number of internal electrodes, 4, 6 and 8 are designed. The outer radius of the sensors is 500 mm and inter radius is 100, 150, 200, 250 mm respectively. Two excitation strategies are used, which are external-opposite-internal (EOI) and external-opposite (EO). The obtained capacitance data are used to reconstruct images using linear back projection (LBP) and Landweber iteration. Based on numerical simulation and experimental measurement, it is found that increasing the number of internal electrodes does not improve the quality of images. When LBP is used with normalized sensitivity matrix, the 12-4 internal-external-electrode (IEE) sensor with EOI excitation strategy has advantages over the EE sensor and other IEE sensors in terms of image quality and contrast. When Landweber iteration is used, the IEE sensors with EO excitation strategy can effectively eliminate the influence of abnormal capacitances. Landweber iteration can reconstruct high quality images when the sensitivity matrix is normalized according to discrete elements of measurement area, while the reconstructed images are more sensitive to the noise level.
查看更多>>摘要：This paper investigates the possibility of using photogrammetry to obtain the sound radiation into free-field from flexural vibrations of distributed thin structures. A simple model problem is considered, where multiple (i.e. two or more) cameras are used to track at a regular grid of target points the flexural vibration of a baffled thin rectangular flat plate structure. The sound radiation into free-field is then derived from the Rayleigh integral, which is approximated into a finite sum assuming the plate is discretised into a regular mesh of elements whose centres correspond to the grid of points where the flexural vibrations are measured with the cameras. The paper shows that the vibration measurement errors produced by the image pixelisation in the cameras compensate over the grid of target points so that the estimate of the radiated sound field with the Rayleigh integral formulation is comparatively more accurate.
NSTL
Elsevier