查看更多>>摘要：Estimating the position, velocity, and time of GNSS receivers is based on tracking loops and extracting navigation satellite information. There are two methods for navigation satellites signal tracking: Scalar Tracking Loop (STL) and Vector Tracking Loop (VTL). The inexpensive GNSS receivers usually use STL approach, but VTL approach has advantages such as weak signal tracking, better capability against signal interference, faster tracking after temporary signal outages. Hence, using this method for tracking can improve the performance of GNSS receiver. The main drawback of the VTL method is its high computational volume. In this paper, three techniques have been proposed to reduce the computational load of this tracking method that enables the implementation of the VTL method on inexpensive receivers. The results with real data and simulations show that if these three techniques are used simultaneously, the computational load is reduced by more than 90% and on the one hand; the performance of the tracking loops shows no significant reduction compared to the standard VTL. Therefore, the simultaneous use of these three techniques to implement the VTL method can be very effective on low-cost and low-dynamic receivers. Two techniques of the three proposed techniques can also be used to implement the VTL on all types of GNSS receivers.
Beamish, S.Reddyhoff, T.Hunter, A.Dwyer-Joyce, R. S....
11页
查看更多>>摘要：Acoustic impedance is an important property used to interpret acoustic reflection measurements in tests to determine oil film thickness, a critical parameter dictating efficiency and wear rates of lubricated components. A new method to measure acoustic impedance of solid media, based on the well-established spring model, is described. The advantage of this method over existing techniques is that it can be applied to thin, multi-layered materials where individual reflections cannot be distinguished, common in many tribological systems such as bearings, piston rings and piston liners. The method is demonstrated experimentally for a range of materials. Results compare well with values calculated independently from acoustic velocity and density. The method has been applied to a bearing test rig to determine acoustic impedance of a thin-walled bearing. This study dem-onstrates that the technique is capable of measurements in dynamic systems and where traditional methods of calculating acoustic impedance are not feasible.
Vamsi, InturiHemanth, M. P.Penumakala, Pavan KumarSabareesh, G. R....
12页
查看更多>>摘要：A statistical procedure is presented for monitoring the damage of pultruded specimens using vibration data. Pultruded composite samples are processed by using continuous glass fiber rovings and epoxy matrix. Two different types of damages, a notch in the top layer and a hole at the midsection has been introduced individually in these samples. Vibration signals from healthy and damaged samples are processed using wavelet transform. various time-frequency domain statistical features have been extracted. Also, the time-domain features have been computed from the raw amplitude data. Further, both these features have been exploited to construct the feature space and significant features have been identified by evaluating the contribution rates. Finally, significant feature set is channeled as input to various machine-learning classifiers (deep neural network and support vector machine) and different classification accuracies have been estimated. The capability of these methods to early detect the damage in pultruded composites has been discussed.
查看更多>>摘要：Due to the large detection range and high sensitivity to damages, Lamb waves are widely used in the localization and quantification of structural damages in a plate structure. The dispersion curve measurement is significant in the applications of Lamb waves, especially in a material with unknown properties. In the study, a method was proposed to measure dispersion curves based on clustering. Compared with traditional methods, the proposed method could realize more accurate and reliable measurement results with less measured data. This method was experimentally verified with an isotropic aluminum plate and an anisotropic CFRP plate. The relative error between measured and real values in an aluminum plate was less than 1%. With this method, A0 mode phasevelocity dispersion curves in CFRP plate with various braiding angles were experimentally obtained. This method facilitated Lamb wave defect detection and material parameter inversion.
查看更多>>摘要：In view of the fact that it is difficult to predict the location and size of the failure of rotating machinery, the sensors sometimes cannot collect the fault information. When the fault location differs from the sensor direction by 180 degrees, the fault information in the signal is weak and may be masked by noise. Multi-channel signal acquisition is one of the methods to solve the problem. Although existing algorithms can extract fault information from a single-channel signal, they are inefficient and sometimes fail to extract weak fault information. Therefore, the information in each channel needs to be associated and combined in advance. This paper proposes a multi-channel signal processing method called quaternion empirical wavelet transform (QEWT). QEWT based on the quaternion Fourier transform can process multiple groups of vibration signals at the same time, which realizes synchronous spectral division, fusion and modal decomposition. The modal separation method based on spectral trend avoids the problems of modal aliasing and low efficiency of scale-space representation. The proposed method combines spectral negentropy with the identification of the fault characteristics of the outer ring and the inner ring, and successfully realizes the fault diagnosis of the rolling bearing.
Praveen, Hemanth MithunSabareesh, G. R.Inturi, VamsiJaikanth, Akshay...
12页
查看更多>>摘要：Condition monitoring of a modern wind turbine gearbox is quite challenging as it comes with multiple stages which operate at different frequencies. A gearbox is made up of multiple components and fault diagnosis (single or multi-component) could be challenging owing to the interaction between the mating parts and the damaged component. In this investigation, a simplified signal segmentation technique that segments the non-stationary vibration signals to match a specific speed stage and component within a multi-stage gearbox is proposed. This technique improves the features within the dataset and allow even simpler algorithms to be more effective while performing fault diagnosis. The segmentation approach is also evaluated for its robustness with three different machine-learning algorithms, namely Decision tree, Support Vector Machine and Deep Neural Network. The overall classification accuracy of the datasets prepared with the proposed approach is found to be 97%, which is higher when compared to the conventional approach.
查看更多>>摘要：Microwave attenuation method has been one of the possible methods to measure the carbon content in fly ash online with high accuracy in recent years. However, the uncertainty of the shape of fly ash accumulation in waveguide brings many errors to the measurement of carbon content. To correct the errors, based on the study of ash level measurement, the influences of different inclined planes on the measurement of medium height and transmission attenuation are compared. Then, a model was established to quantify the influence of slope degree on carbon content of fly ash. Finally, the interference of different inclined planes on the measurement of carbon content in fly ash is analyzed. The result shows that with the increase of the inclination angle of the dielectric top slope in the waveguide, the transmission attenuation effect gradually increases. This will lead to the large measured value of carbon content in fly ash.
查看更多>>摘要：The multi-row bearings of rolling mills are subject to axial and radial loads. Due to the complex working conditions, it is difficult to achieve better results in fault diagnosis by analyzing signal directional vibration signals. In order to realize the fault diagnosis of bearings subjected to multiple directional loads, this paper introduces the idea of cooperative processing of multi-sensing signals and proposes a fault feature extraction method of improved multivariate variational mode decomposition (IMVMD) combined with multivariate composite multiscale weighted permutation entropy (MCMWPE). First, reconstruct the signal by variational modal decomposition (VMD). Upgrade VMD to multi-channel decomposition mode by considering the correlation of the multichannel signal and optimizing its parameters. Secondly, propose the method to calculate multi-channel signal entropy. Represent bearing fault features by calculating the MCMWPE of multi-channel reconstructed signals. The method proposed in this paper is validated on experiment rolling mill datasets and actual rolling mill datasets from a factory. Entropy curves and PSO-SVM classification results show that IMVMD-MCMWPE can extract fault features better than other methods.
查看更多>>摘要：Ultra wide band (UWB) radio positioning technology is widely used in indoor high-precision positioning scenes, while obstacles in the wireless signal propagation path will cause the non-line of sight (NLOS) propagation of UWB signal and the reduction of positioning reliability. In this paper, an efficient NLOS identification scheme based on multiple input learning (MIL) neural network model with channel impulse response (CIR) and time frequency diagram of CIR (TFDOCIR) is proposed by direct detection in UWB positioning system. It is experimentally demonstrated that the average NLOS identification accuracies reach 86.82%, 92.53%, 91.61%, 92.91%, 92.02% corresponding to five different obstacles including wooden door, concrete wall, metal plate, human body and glass window, respectively. Additionally, the overall NLOS identification accuracy achieves 91.74%. Through the proposed NLOS identification scheme with weight least squares (WLS), the indoor UWB-based positioning tests are performed with the average error 7.35 cm, thereby proving its ability of ranging error preventation.
查看更多>>摘要：Flat slab systems made of reinforced concrete (RC) are popular structural solutions widely used in practical applications. The knowledge about their behaviour under extreme loading conditions, including the loss of the columns, is still being developed worldwide. Also, new materials are tested for this purpose. The research pre-sented hereafter in the article includes the progressive collapse simulation caused by removing the external column in the flat slab system reinforced with B600B steel. One of the aims of the research was to assess the effectiveness of the applied reinforcement after losing the column, depending on the degree of horizontal tie reinforcement. The structural behaviour of the entire reinforced concrete system during the experiment was controlled using advanced reference techniques, including distributed fibre optic sensing DFOS, optical image correlation system, total station as well as conventional strain and displacement transducers. The article focuses on the possibilities of DFOS sensing in an extensive range of strains caused by the steel yielding and the cracks directly in concrete. Thanks to distributed measurements and monolithic composite sensors, it was possible to detect all the cracks and reflect their patterns during all load stages until structural failure. The article describes the methodology and discusses the results of this pioneer measurement approach. Despite the extensive state of the art in distributed sensing, the paper provides the new knowledge gained during research. It is mainly related to a DFOS-based solution for extremely high strain measurements thanks to the excellent bonding properties and strain transfer to the optical fibre, from both steel reinforcement and surrounding concrete.
NSTL
Elsevier