Vibration responses of structures with inherent nonlinear behaviors can degrade the performance of linear theory based damage detection methods. This paper integrates the phase space reconstruction and Koopman operator to provide a linear representation of strongly nonlinear systems. Similar to the modal analysis of linear systems, the linearized model allows for handling nonlinear vibration responses as a superposition of the discovered nonlinear coordinate basis. This property provides opportunities to identify the structural condition change of structures with initial nonlinearity. The eigen-frequencies extracted from the Koopman operator are served as damage features. The performance of using the eigen-frequencies from dynamic mode decomposition for nonlinear structural damage detection is compared with the natural frequencies obtained from fast Fourier transformation and the time-frequency analysis method to emphasize the superiority of the proposed approach. Two experimental structures exhibiting inherent nonlinearity, namely, a magneto-elastic system and a precast segment beam, are employed to demonstrate the feasibility and effectiveness of using the proposed method for identifying condition change of nonlinear structures. Results demonstrate that the presented nonlinearity linearization framework and the damage feature defined in this study are suitable for reliably identifying the occurrence of structural damage and condition change in structures with inherent nonlinearities.
ABSTRACT During hydraulic fracturing of shale oil wells, fracturing fluid enters the formation causing dynamic changes in in-situ stress in the near-wellbore region, which in turn affects the wellbore stress. This paper takes into account the change of in-situ stress caused by fracturing fluid pumped into the formation, derives the analytical solution of wellbore stress under non-uniform in-situ stress conditions, and analyzes the effects of surface pumping pressure, delivery rate, casing wall thickness, formation Young's modulus and Poisson's ratio on casing stress. The results show that: with the increase of pump pressure and Poisson's ratio of the formation, the Mises stress increase of the casing inner wall increases, and the non-uniformity of stress increases; with the increase of delivery rate and Young's modulus of the formation, Mises stress of the casing inner wall increases, and the non-uniformity of stress decreases sharply; With the increase of the casing wall thickness, the Mises stress in the inner wall of the casing decreases, but the non-uniformity increases slightly; When the Young's modulus and Poisson's ratio of the formation is high, the pumping pressure and displacement should be reasonably controlled and the wall thickness of the casing should be increased to reduce the risk of casing change. INTRODUCTION In recent years, more and more shale oil resources have been discovered with the continuous development of China's economy and the continuous updating of exploration technology (Xu et al., 2021; Wang et al., 2018; Ning et al., 2021). The typical terrestrial mixed-phase shale oil developed in the Lucaogou Formation of the Jimsar region has great exploration potential, and the first national terrestrial shale oil demonstration region was built in China (Kuang et al., 2012; Li et al., 2021; Wang et al., 2020; Li et al., 2021). The shale oil formation conditions in the Lucaogou Formation of the Jimsar region are complex, the reservoir is non-homogeneous, the field has a poor ability to sustain stable production, and the economic benefits of preliminary development are poor (Shen et al., 2021; Xie et al., 2020; Zhang et al., 2020; Wu et al., 2019).
Engine fault diagnosis based on abnormal sound signal analysis is a non-contact fault diagnosis methods, It has advantages that judge fault fastly and accuratly, convenient operation, high degree of automation. Based on this background. This paper research on the transform domain feature extraction of the engine abnormal sound signal and recognition problems. Mainly using the homomorphism analysis method to extract cepstrum features of different sound channel signal, using linear spectrum pairs analysis method to establish full pole model to the different sound channel, using the template matching method to the simulation results, that shows in this paper the cepstrum and the characteristic parameter can effectively identify various abnormal sound signal.
An experimental study on initial cracking criterion has been carried out by using four-point shearing beams with three different crack-depth ratios.The maximum loads,the initial loads and crack initiation angles were measured in the experiment.Based on the initial loads measured in the test,the corresponding KⅠ and KⅡ can be calculated using finite element method.Besides,a more rational load distribution under four-point shearing condition was obtained.Finally,a crack initial cracking criterion for I-II mixed mode crack was proposed,which is different from the cracking criterion by using maximum loads,and its crack-depth ratio effect,crack-depth ratio effect on the crack initiation angles,KⅠ /KⅡ were also discussed.The result shows that when crack-depth ratio in the range from 0.3 to 0.4,it has important effect on crack initial cracking criterion for I-II mixed mode crack,while the crack-depth ratio in the range from 0.4 to 0.5,it has little impact.The test results also show that the crack initiation angles increase with the increase of crack-depth ratio.While for KⅠ/KⅡ,it decreases along with the increase of the crack-depth ratio.
We demonstrate the double-Brillouin-frequency spaced multiwavelength generation at room temperature by using a simple ring Brillouin-erbium fiber laser. The Brillouin pump is pre-amplified before entering the single-mode fiber, the odd Stokes and even Stokes are amplified in two opposite directions. All amplification provided by a home-made bi-directional operation erbium-doped fiber may achieve high intensity of Brillouin Stokes that leads to the homogenous gain saturation. Twelve even Stokes and thirteen odd Stokes with a wavelength spacing of 0.172 nm (20 GHz) are simultaneously obtained for 6 dBm Brillouin pump power and 120 mW pump power at 980 nm. The influence of different Brillouin and erbium-doped-fiber pump powers on multiwavelength and tuning range are investigated in detail.
The performance of low-cost smart terminals is limited by the performance of their low-cost Global Navigation Satellite System (GNSS) hardware and chips, as well as by the impact of complex urban environments, which affect the positioning accuracy and stability of GNSS services. To this end, this paper proposes a robust adaptive Kalman filter for different environments that can be applied after data preprocessing. Based on the Kalman filter algorithm, a robust estimation approach is introduced into real-time kinematic (RTK) positioning to make judgments on the abnormal observation values of low-cost smart terminals, which amplifies the variance and covariance of the outlier observation equation, and reduces the impact of outliers on positioning performance. The Institute of Geodesy and Geophysics III (IGG III) function is used for regulation purposes, where prior information is modified and refreshed using the equivalent weight matrix and adaptive factors, thus reducing the impact of system model errors on system state estimation results. In addition, a robust factor is defined to adjust positioning deviation weighting between the pre- and post-test robust estimates. The experimental results show that after robust RTK positioning in the static experiments, the overall improvement in positioning accuracies of the Xiaomi 8, Huawei P40, Huawei mate40, and low-cost M8 receiver reached 29.6%, 31.3%, 32.1%, and 30.7%, respectively. Similarly, after applying the proposed robust method in the dynamic experiments, the overall positioning accuracies of the Xiaomi 8, Huawei P40, Huawei mate40, and the low-cost M8 receiver improved by 28.3%, 32.9%, 35.4%, and 26.2%, respectively. The experimental results reveal that an excellent positioning effect of a smartphone is positively correlated with robust RTK positioning performance. However, it is worth noting that when the positioning accuracy reaches a high level, such as the positioning results achieved using low-cost receivers, the robustness performance shows a relatively decreasing trend. This finding suggests that under the condition of high positioning accuracy, the sensitivity of specific positioning equipment to interference sources may increase, resulting in a decline in the effect of robust RTK positioning.
We propose a despeckling method based on dual-tree complex wavelet transform (DTCWT) for SAR image. The Gaussian model is used to model the non-logarithmic additive noise of the local isotropic region. Shrinkage function is obtained with maximum a posteriori estimation.
Biomass gasification, especially distribution to power generation, is considered as a promising way to tackle global energy and environmental challenges. However, previous researches on integrated analysis of the greenhouse gases (GHG) abatement potentials associated with biomass electrification are sparse and few have taken the freshwater utilization into account within a coherent framework, though both energy and water scarcity are lying in the central concerns in China's environmental policy. This study employs a Life cycle assessment (LCA) model to analyse the actual performance combined with water footprint (WF) assessment methods. The inextricable trade-offs between three representative energy-producing technologies are explored based on three categories of non-food crops (maize, sorghum and hybrid pennisetum) cultivated in marginal arable land. WF results demonstrate that the Hybrid pennisetum system has the largest impact on the water resources whereas the other two technology options exhibit the characteristics of environmental sustainability. The large variances in contribution ratio between the four sub-processes in terms of total impacts are reflected by the LCA results. The Anaerobic Digestion process is found to be the main contributor whereas the Digestate management process is shown to be able to effectively mitigate the negative environmental impacts with an absolute share. Sensitivity analysis is implemented to detect the impacts of loss ratios variation, as silage mass and methane, on final results. The methane loss has the largest influence on the Hybrid pennisetum system, followed by the Maize system. Above all, the Sorghum system demonstrates the best performance amongst the considered assessment categories. Our study builds a pilot reference for further driving large-scale project of bioenergy production and conversion. The synergy of combined WF-LCA method allows us to conduct a comprehensive assessment and to provide insights into environmental and resource management.
This article analyzed the cause and harm of excessive circulating current in the single core cable metal sheath due to the moist intermediate insulation in the 110～220 kV transmission cable,introduced the procedure and application of dehumidifying process for connector,and demonstrated the feasibility of the connector dehumidifying process to solve its metal sheath grounded circulating current problem.
Anti-slip pile's columns are the important supports between the upper hull and the lower hull of a mobile submersible drilling unit,which have an important effect on structural stability of the mat and the upper hull shell of the drilling unit.By means of visual and thickness examinations,corrosion reason analysis and finite element simulation calculation for the mobile submersible drilling unit with the service life near 30 years,the anti-slip pile's columns of the unit were renewed.This paper presents a detailed description of examining and renewing the columns of the unit,which offers experience for similar drilling units.
