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[Objective] Clearance between motion pairs is commonly observed in mechanisms due to manufacturing errors in components, assembly requirements, and wear of the mechanisms. When the mechanism operates at high speeds with large loads and small cross-sectional areas, components are susceptible to elastic deformation. This elastic deformation, combined with the clearance in motion pairs, significantly restricts the motion accuracy of the entire mechanism, leading to chaotic behavior and ultimately reducing its stability and reliability. Therefore, it is essential to investigate the influence of the coupling effect between the clearance of the motion pair and the flexible component on the motion state of the mechanism. [Methods] This paper proposes a chaos identification method for a rigid-flexible coupling experimental teaching platform with revolute clearance joints. First, a revolute clearance joint model was established based on the three-state model of "contact-separation-collision." In addition, a flexible beam element model was created using the absolute node coordinate method. Following this, a dynamic model of the rigid-flexible coupling six-link experimental platform with revolute clearance joints was established using the Lagrange multiplier method. Finally, both qualitative and quantitative identifications of chaotic phenomena in the six-link experimental platform were conducted using phase diagrams, Poincaré maps, and maximum Lyapunov exponents. The nonlinear characteristics of the rigid experimental platform with clearance and the rigid-flexible coupling experimental platform with clearance were compared and analyzed. Additionally, the effects of different clearance values, driving speeds, and friction coefficients on the nonlinear characteristics of the experimental teaching platform were studied. [Results] The results obtained using methods such as phase diagrams, Poincaré maps, and maximum Lyapunov exponents indicate that compared with the rigid experimental teaching platform mechanism with revolute clearance, the vibration frequency of the rigid-flexible coupling experimental teaching platform mechanism with revolute clearance is higher, leading to reduced stability and more pronounced chaotic phenomena. The chaotic behavior at the clearance of the revolute pair intensifies with an increase in clearance size and driving speed, whereas it weakens as the friction coefficient increases. [Conclusions] The coupling effect between the clearance of the motion pair and the flexibility of the component reduces the stability of the mechanism, leading to the emergence of chaos. The chaos identification method based on the experimental teaching of rigid-flexible coupling with revolute clearance proposed in this article can effectively distinguish the motion states of the mechanism. This method provides a systematic and comprehensive theoretical foundation for the study of nonlinear dynamics in high-precision, high-performance multilink mechanisms. This not only enhances students' ability to analyze and practice the nonlinear characteristics of mechanisms but also increases the diversity, intuitiveness, and engagement of the teaching process, ultimately improving the quality of education. [ABSTRACT FROM AUTHOR]

In the context of rapid advancement in automation and increasing global warming, understanding the impact of artificial intelligence (AI) on carbon emissions (CES) is a cutting-edge research topic. However, there is limited focus in existing research on the nonlinear carbon reduction effect (CRE) of AI. This paper first theoretically elaborates the dual impact mechanisms of AI on CES and illuminates the nonlinear carbon reduction mechanisms of AI. Then, this study employs panel data encompassing 30 Chinese provinces between 1997 and 2019 to empirically test the net effect of AI on CES and the nonlinear carbon reduction effect of AI through econometric models. The results are as follows: first, although AI can both reduce and increase CES, AI primarily helps decrease CES. This conclusion holds true even after considering robustness, endogeneity, and spatial heterogeneity. Secondly, relative to the central and western regions, AI has significant achievement in reducing carbon intensity and per capita CES in the eastern region. However, there is still room for improvement in terms of reducing the total CES in the eastern region. Thirdly, improving the AI development level (AIDL) can magnify the marginal CRE of AI and lead to a nonlinear CRE of AI. Lastly, even if the AIDL remains constant, improving the level of marketization, human capital, digital infrastructure, economic development, openness, and government intervention can also amplify the marginal CRE of AI and lead to a nonlinear CRE of AI. To fully harness the potential of AI for green development, concerted efforts should be directed towards enhancing the innovation and application of AI technologies with carbon reduction potential. [ABSTRACT FROM AUTHOR]

Reservoir rocks have an obvious initial nonlinear crack-closure stage during geothermal energy exploration using enhanced geothermal systems (EGSs). Therefore, the purpose of this research is to establish a quantitative model considering the influence of initial nonlinear characteristics on geothermal reservoirs. According to effective medium theory (EMT), deformation of reservoir rocks after thermal shocks can be divided into rock frame and void sections, and the effect of microcracks is considered in the establishment of the proposed model. Compressive tests conducted on Suizhou granite specimens after cyclic water cooling were used to validate this model. Furthermore, the influence of microcracks on initial crack closure part of Suizhou granite specimens after thermal shocks was revealed by scanning electron microscope (SEM) observation. There is a negative exponential relationship between the axial stress–strain in void section of specimens after cyclic water cooling. The crack closure stage in the stress–strain relation of Suizhou granite after thermal shocks is more apparent with heating temperature and cyclic time. The proposed model well characterizes the crack closure part in the stress–strain curves of specimens after cyclic water cooling. The proposed model describes the initial nonlinear stage of surrounding geothermal reservoir granite and provides theoretical support for the evaluation of stability in EGS engineering design. [ABSTRACT FROM AUTHOR]

Purpose: The electromechanical planetary transmission system has the advantages of high transmission power and fast running speed, which is one of the important development directions in the future. However, during the operation of the electromechanical planetary transmission system, friction and other factors will lead to an increase in gear temperature and thermal deformation, which will affect the transmission performance of the system, and it is of great significance to study the influence of the temperature effect on the nonlinear dynamics of the electromechanical planetary system. Design/methodology/approach: The effects of temperature change, motor speed, time-varying meshing stiffness, meshing damping ratio and error amplitude on the nonlinear dynamic characteristics of electromechanical planetary systems are studied by using bifurcation diagrams, time-domain diagrams, phase diagrams, Poincaré cross-sectional diagrams, spectra, etc. Findings: The results show that when the temperature rise is less than 70 °C, the system will exhibit chaotic motion. When the motor speed is greater than 900r/min, the system enters a chaotic state. The changes in time-varying meshing stiffness, meshing damping ratio, and error amplitude will also make the system exhibit abundant bifurcation characteristics. Originality/value: Based on the principle of thermal deformation, taking into account the temperature effect and nonlinear parameters, including time-varying meshing stiffness and tooth side clearance as well as comprehensive errors, a dynamic model of the electromechanical planetary gear system was established. [ABSTRACT FROM AUTHOR]

Soft dielectric elastomer actuators (SDEAs) have manifested tremendous potentials in the field of soft robots. However, the tracking control of the SDEA still confronts enormous challenges because of its complicated nonlinear characteristics. In this paper, a nonlinear proportional-integral-derivative (NPID) controller is devised to fulfil the tracking control of the SDEA. A dynamic model of the SDEA is established, and then applied to construct a simulation system to coarsely tune the parameters of the NPID controller based on the iterative optimisation algorithm. Subsequently, according to the results of the coarse tuning, the parameters of the NPID controller are finely tuned in practical experiments. Finally, the NPID controller of the SDEA is proved to be effective via several tracking control experiments with different reference trajectories. [ABSTRACT FROM AUTHOR]

This study identified time-varying harmonic characteristics in a high-density plasma (HDP) chemical vapor deposition (CVD) chamber by depositing low-k oxide (SiOF). The characteristics of harmonics are caused by the nonlinear Lorentz force and the nonlinear nature of the sheath. In this study, a noninvasive directional coupler was used to collect harmonic power in the forward and reverse directions, which were low frequency (LF) and high bias radio frequency (RF). The intensity of the 2nd and 3rd harmonics responded to the LF power, pressure, and gas flow rate introduced for plasma generation. Meanwhile, the intensity of the 6th harmonic responded to the oxygen fraction in the transition step. The intensity of the 7th (forward) and 10th (in reverse) harmonic of the bias RF power depended on the underlying layers (silicon rich oxide (SRO) and undoped silicate glass (USG)) and the deposition of the SiOF layer. In particular, the 10th (reverse) harmonic of the bias RF power was identified using electrodynamics in a double capacitor model of the plasma sheath and the deposited dielectric material. The plasma-induced electronic charging effect on the deposited film resulted in the time-varying characteristic of the 10th harmonic (in reverse) of the bias RF power. The wafer-to-wafer consistency and stability of the time-varying characteristic were investigated. The findings of this study can be applied to in situ diagnosis of SiOF thin film deposition and optimization of the deposition process. [ABSTRACT FROM AUTHOR]

Numerical investigations were performed on an opposed-fired boiler to better understand the formation of the asymmetric phenomenon and its effects on the combustion characteristics. It is revealed that with the increasing of the inlet Reynolds numbers, the in-furnace flow and temperature fields evolve from symmetry to asymmetry under the symmetric combustion conditions. Nonlinearity was elaborated to explain this phenomenon. Three asymmetric combustion modes were proposed to optimize the deflected flowfield. The final optimal combustion pattern was established via comprehensive consideration of the general air stoichiometric ratio and reduction zone heights. Compared to the original symmetric combustion mode, asymmetric air disturbance creates better internal flowfield recirculation and improves the combustion performance, which obtains a significant NOx reduction from 369.16 mg/Nm3 to 216.16 mg/Nm3 and lowers the carbon content in fly ash from 3.465% to 2.07%, respectively. [ABSTRACT FROM AUTHOR]

Soil tends to have nonlinear compression characteristics, and the consolidation laws of soil are different under different compression characteristics. Considering the nonlinear characteristics of soil, variable load and continuous drainage boundary conditions, a one-dimensional consolidation equation is established. Its solutions are obtained by using the unconditionally stable finite difference method and semi-analytical method, and the reliability of the two methods is verified by the degradation of continuous drainage boundary condition and the comparison of the two solutions. Based on the solution of finite difference method, the influences of interface parameter, load parameters and nonlinear parameter on soil consolidation are analyzed in detail. The results show that, the larger the interface parameter of continuous drainage boundary, the greater the dissipation rate of excess pore water and the settlement rate of soil, while the interface parameter has no effect on the final settlement. The excess pore water pressure gradually increases at the loading stage and dissipates at the constant loading stage. With the increase of loading rate, both the peak value of excess pore water pressure and soil consolidation rate increase, indicating that extending the construction period is conducive to reducing the influence of excess pore water pressure. It is difficult to accurately predict the consolidation rate of soil in engineering. The accuracy of soil model, boundary conditions and soil calculation parameters should be ensured when the consolidation theory is used.

This study identified time-varying harmonic characteristics in a high-density plasma (HDP) chemical vapor deposition (CVD) chamber by depositing low-k oxide (SiOF). The characteristics of harmonics are caused by the nonlinear Lorentz force and the nonlinear nature of the sheath. In this study, a noninvasive directional coupler was used to collect harmonic power in the forward and reverse directions, which were low frequency (LF) and high bias radio frequency (RF). The intensity of the 2nd and 3rd harmonics responded to the LF power, pressure, and gas flow rate introduced for plasma generation. Meanwhile, the intensity of the 6th harmonic responded to the oxygen fraction in the transition step. The intensity of the 7th (forward) and 10th (in reverse) harmonic of the bias RF power depended on the underlying layers (silicon rich oxide (SRO) and undoped silicate glass (USG)) and the deposition of the SiOF layer. In particular, the 10th (reverse) harmonic of the bias RF power was identified using electrodynamics in a double capacitor model of the plasma sheath and the deposited dielectric material. The plasma-induced electronic charging effect on the deposited film resulted in the time-varying characteristic of the 10th harmonic (in reverse) of the bias RF power. The wafer-to-wafer consistency and stability of the time-varying characteristic were investigated. The findings of this study can be applied to in situ diagnosis of SiOF thin film deposition and optimization of the deposition process.

Different lubrication states seriously affect the stability and safety of the aviation power transmission system. This study investigates how time-varying friction coefficients impact the stability of an aviation spline-rotor system using a spline-rotor model that considers uneven stress distribution on the tooth surface. Experimental tests with a high-frequency friction and wear test machine yield time-varying friction coefficients for splines with different lubrication, surface roughness, and materials. A sharp change of friction coefficient for the sample occurs under wear debris lubrication. The average friction coefficient for the sample with roughness 1.6 is lower than those with roughness 0.8 and 3.2. Under the same lubrication conditions, the friction coefficient of Resin matrix composites is smaller than that of metallic materials. Dynamic simulation of the spline-rotor model considering time-varying friction coefficients shows rich self-excited vibration behaviors influenced by lubrication, surface roughness, and materials. • Wear debris lubrication causes a sudden peak value in the friction coefficient. • Low roughness doesn't guarantee low friction in long periods of operation. • Spline self-vibration leads system to quasi-periodic state. • The resin-based materials can control the self-excited vibration of the spline. [ABSTRACT FROM AUTHOR]

Summary: The mobile welding robot based on a hybrid power drive system is a system with complex control characteristics such as nonlinearity, strong coupling, and disturbance of working environment. These characteristics have different effects on the control performance. In order to improve control characteristics of the mobile welding robot, it is necessary to study an effective evaluation method to explore the influence of these parameters on the control performance of the mobile welding robot. In the process of seam tracking, the operation indexes of welding robot system are determined by comprehensive evaluation. On the premise of ensuring tracking accuracy and stability, the energy distribution of hybrid power system is optimized to improve results of continuous power supply time. Therefore, a comprehensive evaluation of the welding robot is established, which is combined information entropy and Kernel Principal Component Analysis (KPCA). The evaluation parameters are divided into the first‐level evaluation index and the second‐level evaluation index. The evaluation model is established by using information entropy, and the data are linearized and dimensionally reduced by using the KPCA. The results show that the method can well deal with and analyze the nonlinear relationship between various indexes. At the same time, the numerical relationship between performance indexes can be established. On this basis, a comprehensive performance evaluation theory based on information entropy, and nuclear principal components is established. Finally, the comprehensive evaluation results are brought into the energy management optimization strategy. The experimental results show that this method not only improves the accuracy of weld tracking, but also ensures the stability of the robot and reduces energy consumption. [ABSTRACT FROM AUTHOR]

Clearance exists in mechanical equipment, which aggravates the friction and wear in moving pairs and reduces the use accuracy of mechanism. So as to reduce the impact of clearance on industrial equipment, lubricating oil is usually added to the clearance of moving pair. The lubricating oil can effectively reduce the collision and vibration between components and reduce noise. Previous studies mainly concentrated on the research of dry clearance joints, but less on clearance lubrication. At the same time, there is little research on nonlinear characteristic of lubrication clearance. For the sake of studying the impact of lubrication clearance with multiple revolute joints on mechanical system, the dynamic response and nonlinear characteristic of planar six-bar linkage are analyzed. The movement model of lubrication clearance is developed, and lubrication force of lubrication clearance is modeled by modified Pinkus–Sternlicht model. Dynamical model of lubrication clearance of planar six-bar linkage is established by Lagrange multiplier method. The impacts of lubrication, viscosity coefficient, clearance value and driving speed on dynamic of mechanism with lubrication clearance are explored. By drawing bifurcation diagram, phase trajectory diagram and Poincare map, the nonlinear characteristic of mechanism with lubrication clearance is studied. [ABSTRACT FROM AUTHOR]

Studying the energy evolution characteristics of coal in a deep underground engineering environment will help people to understand the evolution process and induced mechanism of geological disaster and risk. To explore the influence mechanism of gas pressure on coal deformation, failure, and energy evolution, triaxial compression tests of coal under different gas pressure conditions were conducted in this study. Based on the test data, the mechanical properties, acoustic emission (AE) energy characteristics, and nonlinear characteristics of the energy evolution of coal containing gas were obtained. A theoretical formula for analyzing energy evolution is introduced. After this theoretical formula is verified by test data, the evolution characteristics of three energy rates (derivative of energy to stress) of coal are obtained based on this formula. It is found that energy rate can be used as a new effective mechanical parameter to analyze and predict the damage and failure characteristics of coal. The energy dissipation characteristics before the peak can be divided into two types: high dissipative energy rate type (HDERT) and low dissipative energy rate type (LDERT), which indicates different failure modes (plastic failure and brittle failure). On this basis, the ratio of dissipative energy rate and input energy rate is further defined to effectively distinguish the two types of dissipative energy rates of coal mass. The research results are helpful to explore the fracturing evolution and energy driving mechanism of coal, and then play a guiding role in rock instability prediction and support and reinforcement measures selection. [ABSTRACT FROM AUTHOR]

The nonlinear dynamics of functionally graded graphene nanoplatelets (GPLs) reinforced composite plates are studied based on the first-order shear deformation theory (FSDT). The ordinary differential equation of the plate is derived by Hamilton principle and Galerkin method. The multi-scale method is used to analyze the jump forces. The effects of GPL distribution pattern, weight fraction, total number of layers and plate size on the resonance peak under sweep excitations, the maximal amplitude and attenuation time under impact loads, the jump force under harmonic excitations are quantitatively studied. The highest nonlinearity is found for the plate with uniform GPL distribution. The change of the number of layers has no effect on the nonlinearity but affects the natural frequency. The size of the plate and weight fraction of GPL both influence the natural frequency and nonlinearity, thereby influencing the dynamic characteristics. [ABSTRACT FROM AUTHOR]

This paper presents a new basic nonlinear track model consisting of an infinite Euler-Bernoulli beam (rail) resting on continuous foundation with two elastic layers (rail pad and ballast bed) and intermediate inertial layer (sleepers). The two elastic layers have bilinear elastic characteristic obtained from the load-displacement characteristic of the rail pad and ballast. A time-varying load with two components - time-constant one and harmonic other, representing the wheel/rail contact force is considered as the track model input. Rail deflection due to the time-constant component of the load is obtained solving the nonlinear equations of the balance position. Subsequently, the structure of the nonhomogeneous foundation is determined. Dynamic response of the rail in terms of receptance due to the harmonic component of the load is calculated using the linearised track model with nonhomogeneous elastic characteristic. Influence of the time-constant component and the reflected waves due to the nonhomogeneous foundation are presented. [ABSTRACT FROM AUTHOR]

The permanent magnet sodium flowmeter (PMSF) without the bluff body installed on the large-diameter pipe in the fast reactors to measure the sodium coolant flow rate has to be calibrated in situ owing to the degradation of the magnetic field. Since the length of the magnetic field of the PMSF is limited in practical engineering applications, the characteristic between the cross correlation flow rate (CCFR) and the standard flow rate is nonlinear in in situ calibration based on the cross correlation method. Moreover, the nonlinear characteristic has a large repeatability error, which is difficult to apply to in situ calibration. In order to realize the in situ calibration, an “M-type” mean velocity profile in the pipe is obtained by analyzing the influence of the magnetic field on the fluid field. The distribution of the CCFR of the signal at each frequency is analyzed by using the phase-frequency characteristic of the cross-power spectral density (CPSD) of the two signals, and a physical model of the turbulence distribution in the pipe cross section is obtained combining with the “M-type” mean velocity profile. A nonlinearity correction method based on signal frequency band selection is proposed according to the physical model. The in situ calibration experiments of DN150 PMSF without the bluff body are carried out at the sodium temperatures of 400 °C. The signals within 11–20 and 18–35 Hz are used to calculate the CCFR for correcting the nonlinear characteristic, and sodium flow rate measurement accuracy is ±3.0%. [ABSTRACT FROM AUTHOR]

The unexpected success of China's PV industry in technology catch-up has been noted. However, existing research has overlooked the multidimensional nonlinear complexities in its underlying mechanisms. This study introduces the "Seven-Element Diamond Model" theoretical framework and employs machine learning (ML) methods to address this. Using observed data from 84 listed China's PV companies from 2000 to 2021, we systematically examine the intricate mechanisms of technology catch-up in China's PV industry. Key findings include: 1) The self-enhancing mechanism stemming from R&D effort, government subsidies, and domestic demand is pivotal for the successful technology catch-up of China's PV industry. 2) Key regulatory directions are identified from R&D effort to market competition, technology spillover, productivity, and government subsidies. 3) R&D effort forms the underlying logic of China's PV industry technology catch-up, and domestic market demand is an extremely important driver for China's PV technology catch-up. Government subsidies exhibit a "blowout" incentive effect, and the synergistic coupling between key variables is also significant in driving China's PV technology catch-up. This study offers valuable insights into the catch-up of clean energy or sustainable technologies in China and other emerging economies. [Display omitted] • Constructed the theoretical framework of the Seven-Element Diamond Model. • The self-reinforcing mechanism among R&D efforts, government subsidies, and domestic demand are investigated. • Key regulatory directions from R&D efforts to market competitiveness, technology spillovers, productivity, and government subsidies are identified. • R&D efforts are the underlying logic of China's photovoltaic industry technology catch-up. [ABSTRACT FROM AUTHOR]

The structure and the cavity surface hardened steel mold of automobile cover is very complex. In the stamping process, the local structure bears higher extrusion stress than the type surface, which often causes local wear and even cracking. The process of multi-hardness splicing joint is applied to ensure the service life of the die according to the features of each part of the mold. The impact load caused by the repeatedly cutting in which always leads to the unevenness of cutting force in the whole process. The machining quality of the mold surface is reduced. Aiming at the ball-end milling process in mold splicing area, first, the impact behavior of tool workpiece cutting contact is analyzed. A prediction model for ball-end milling force in the splicing area is established by establishing the transient chip thickness model which considering the impact factors. Second, the experiment of cutting force measurement for Cr12MoV mold steel ball-end milling which is based on single hardness and multi-hardness are carried out to verify the model. Cross-correlation analysis based on data of milling force signal and machined surface roughness is carried out for getting the relevance of them in different processing states. Finally, the ApEn is used to analyze the nonlinear characteristics of the milling force signal at the multi-hardness splicing state. This explores the influence of the milling force on the machining quality. The experimental and analytical results show that the milling force signal exhibits more obvious chaotic characteristics in the multi-hardness stitching area than that in the single hardness region. This provides a basis for improving workpiece surface quality and improving cutting efficiency. [ABSTRACT FROM AUTHOR]

To overcome the non-structure-preserving drawbacks in traditional numerical simulation of transmission-line nonlinear vibration responses, the Noether symmetry and conserved quantity of transmission lines’ 2-way galloping under ice and wind excitation were studied. Firstly, in view of the nonlinearity of the aerodynamic force and the line geometry, a 2-DOF galloping model of vertical and torsional vibrations was established based on the analytical mechanics method. Secondly, the group analysis theory was introduced, and the condition and the conserved quantity of the Noether symmetry were given according to the invariance principle. Finally, a conserved quantity-preserving discrete numerical algorithm was constructed. The dynamic characteristics of the nonlinear mechanical structure were studied with the Noether symmetry theory. The results show that, the proposed novel method is structure-preserving in a wide range of application, and is reliable and accurate. [ABSTRACT FROM AUTHOR]

A well-founded class of dependences, based on the theory of nonlinear electrical circuits, is proposed for the formal approximation of static characteristics for various electronic devices. The dependences are simple fractionally linear and fractionally quadratic expressions (a particular case of rational functions), convenient for engineering calculations. However, these expressions represent projective transformations in the sense of projective geometry. The projective transformations preserve an invariant in the form of a cross ratio (double proportion) of four samples of variable mode parameters (currents, resistances, voltage). The mutual reduction of measurement errors is an attractive practice property of the cross ratio. This leads to the direct formulas for recalculating the mode parameters that have group properties. An example of the approximation of the magnetization characteristic and relative magnetic permeability of the Nickel Steel Carpenter 49 is considered; invariants for the magnetic flux density and absolute permeability are established. The results are applicable in various fields of electronics and spintronics. [ABSTRACT FROM AUTHOR]

In existing studies, external factors, such as hydrologic, hydraulic, and decision-making uncertainties, have been widely recognized as major risk source in reservoir flood routing. There are few researches focused on the intrinsic uncertainties which rooted in the reservoir flood routing modeling, for instance, the sensitivity of the water level to the initial condition in the passage of flood routing. The governing equation of the reservoir flooding routing is a first-order Ordinary Differential Equation, which can be simplified as a water balance equation. A deterministic mathematical model can be set up by combining the governing equation with the flood operating rules and the water level-storage relationship functions of reservoirs. As far as the deterministic model is concerned, nonlinear behaviors and their characteristics in different stages of flood routing were discussed for the reservoir with multistage operating rule by simulations in this paper. The results showed that the state variables (i.e., water level and discharge rate) of the system are not sensitive to initial small perturbations in the free overflow stage. However, in the confined outflow stage, which usually appears in segmented flood operating rules designed for multi-purpose flood control, a small initial disturbance can grow gradually over time with the evolution of the system, as a result, a large deviation of the water level and discharge rate of the reservoir could developed at the end of the simulation. Additionally, some case studies were conducted in this paper to demonstrate this nonlinear response of flood routing to the initial disturbance. Although the nonlinear behaviors in reservoir flood routing are still subject to further study, once again, it proves that uncertainties appear there indeed in a deterministic system according to this research. The results of this paper indicate that the nonlinear responses and the corresponding uncertainties rooted in it may have to be considered deliberately in different stages of flood routing, because this could has potential impacts not only on reservoir flood control but also on the reliability of the risk assessment. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we present an improved method for analyzing the stability of the nonlinear hybrid dynamical systems (NHDSs) using a monodromy matrix. We define an n‐dimensional NHDS and focus on an orbit whose initial values exist near the periodic orbit. Because the system has nonlinearity, the circuit equation cannot be expressed in the form of a linear ordinary differential equation, meaning that the existing monodromy‐matrix‐based stability analysis method cannot be used because it requires a matrix exponential. Therefore, we propose a general theory for calculating orbital perturbations during Poincaré observation. Perturbation through switching events is expressed by a state‐transition matrix, which we refer to as the saltation matrix. By computing the perturbations, we obtain the monodromy matrix, whose characteristic multipliers denote the stability of the periodic orbit. We apply the proposed algorithm to an interrupted electric circuit with a nonlinear characteristic to confirm its validity. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sc 2 O 3 modified Bi 2 O 3 -ZnO films varistors with different doping ratios were prepared by Sol-gel method. The result indicated that doping of Sc 2 O 3 significantly enhance the nonlinear current-voltage ( I-V) characteristics of Bi 2 O 3 -ZnO films. The highest non-linearity was obtained for 0.4mol% Sc content with the nonlinear coefficient α = 3.7 and 301 μA in leakage current. The grain size of ZnO phase firstly increased with Sc 2 O 3 doping when the content of Sc 2 O 3 is no more than 0.2 mol%. Upon the much more doping of Sc 2 O 3 , the growth of ZnO crystal was inhibited, leading to smaller grain size. The threshold voltage V T was inversely proportional with grain size of ZnO phase. Doping oxides gathered in the grain boundary significant impact on threshold voltage and leakage current. [ABSTRACT FROM AUTHOR]

The topology image is constructed from the 2D matrix (XY directions) of heights Z captured from the force-feedback loop controller. For small height variations, nonlinear effects such as hysteresis or creep of the PZT-driven Z nano scanner can be neglected and its calibration is quite straightforward. For large height variations, the linear approximation of the PZT-driven Z nano scanner fail and nonlinear behaviors must be considered because this would cause inaccuracies in the measurement image. In order to avoid such inaccuracies, an additional strain gauge sensor is used to directly measure displacement of the PZT-driven Z nano scanner. However, this approach also has a disadvantage in its relatively low precision. In order to obtain high precision data with good linearity, we propose a method of overcoming the low precision problem of the strain gauge while its feature of good linearity is maintained. We expect that the topology image obtained from the strain gauge sensor showing significant noise at high frequencies. On the other hand, the topology image obtained from the controller output showing low noise at high frequencies. If the low and high frequency signals are separable from both topology images, the image can be constructed so that it is represented with high accuracy and low noise. In order to separate the low frequencies from high frequencies, a 2D Haar wavelet transform is used. Our proposed method use the 2D wavelet transform for obtaining good linearity from strain gauge sensor and good precision from controller output. The advantages of the proposed method are experimentally validated by using topology images. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi Journal of Physics is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Different power amplifier (PA) models have their own effects on PA linearization. In this paper, the nonlinear characteristic of the radio frequency power amplifier (RF PA) is simulated based on the two models combining predistortion technology, and the nonlinear effects of the two models are analyzed, respectively. The simulation results show that Power Series model normalized mean square error (NMSE) is −37.8 dB, which is less than Power Series model −30.4 dB before loading predistortion technology. NMSE of the two systems are −23.4 dB and −26.0 dB respectively, while Saleh model compensates better than the Power Series model combing predistortion technology. The error vector magnitude (EVM) of Power Series model is only 6.75%, whereas the Saleh model EVM is 9.99%, indicating that Power Series model can better describe the nonlinear characteristic of PA. It will have a positive effect on improving the power utilization of wireless communication system. [ABSTRACT FROM AUTHOR]

Copyright of Ingeniería (0121-750X) is the property of Ingenieria and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vibration signal of wind turbine has the non‐linear and non‐stationary characteristic, thus it is difficult to extract the fault feature. In this study, a novel method based on variational mode decomposition (VMD) and Teager energy operator (TEO) is proposed to diagnose the bearing faults of wind turbine. First, vibration signal is decomposed into several intrinsic mode function (IMF) components by means of VMD, which is a recently proposed signal decomposition method. Then, the most sensitive IMF component is selected according to kurtosis criterion. Moreover, TEO is applied to the most sensitive IMF in order to highlight impact signal. Finally, spectrum is obtained by applying Fourier transform to Teager energy of the selected IMF, thus extracting the fault feature to diagnose bearing fault. The effectiveness of the proposed method for fault diagnosis is validated by simulation and experimental signal analysis results, and comparison studies show its advantage over empirical mode decomposition and conventional spectrum analysis for wind turbine bearing fault diagnosis. [ABSTRACT FROM AUTHOR]

Bearings based on aerostatic principle belong to the new machine elements advantageous for low- and high-speed applications, but their dynamic and stability properties are not yet sufficiently known. This paper presents a new elaborated method and gained results of theoretical investigation of dynamic properties of aerostatic bearing in general dimensionless form. It is aimed also as a supporting tool for diagnostic and identification methods used at developing of new bearings proposed by TECHLAB, Prague for industrial applications. Mathematical model expresses nonlinear and evolutive properties in the entire area of bearing clearance, contains sufficient number of free parameters in functions of restoring and damping forces and can therefore describe all types of motions occurring in gas bearings as periodic, quasi-periodic, including beats and instability, which can leads to chaotic and self-excited vibrations. The influence of non-diagonal elements of stiffness and damping matrices of linearized model on the spectral properties and the stability of system is investigated, too.

Joints in deployable structures can degrade the stiffness and the stability of spacecraft. In this study, the nonlinear stiffness of spherical joints is investigated. The traditional contact model of spherical joints based on non-conforming contact assumption is presented. A new contact model for spherical joints based on the Winkler model and geometric constraints is established to calculate the stiffness of spherical joints with small clearances. The finite element model (FEM) of spherical joints is built to evaluate the accuracy of the theoretical model. The effects of the clearance and the contact force of spherical joints on the deformation of joints are investigated. When compared with FEM results, the error of the new spherical model is smaller than that of the traditional contact model when the clearance of spherical joint is not excessively large. The new contact model for spherical joint is more accurate than the traditional contact model when the clearance of spherical joint is large.

Power amplifier (PA) is one of important components in wireless communication system. However, its non‐linear and memory characteristic cause harmful distortion, which significantly decreases the power efficiency and wastes electronic energy since the power of PA needs back off. To overcome the non‐linear and memory problems, a novel method based on distortion‐characteristic estimation algorithm is developed in this study. The main innovation of this study is manifested in two aspects: first, the authors use well designed training signals to estimate the distortion characteristic of the PA; second, a novel PA characteristic estimation algorithm is developed in order to calculate the optimal state of the ideal predistorter that behaves like the inverse characteristic of PA theoretically. Since this novel method does not require the error between original signals and feedback signals, it can avoid the significant errors caused by the time mismatch between source signals and feedback signals, and can increase the power efficiency of the PA. The simulation results validate the performance increase and the synchronisation‐error immunity over the existing simplified filter look up table method. [ABSTRACT FROM AUTHOR]

We investigated the nonlinear elastic characteristic of an in-arm hydropneumatic suspension unit (ISU) as well as the damping characteristic of the controllable vane absorber. Due to the strong nonlinear characteristic of the ISU, simplify is needed to accurately model the vehicle. Based on the theory of multibody dynamics, a virtual prototype of the tracked vehicle was built, which includes the hydraulic system, the multi-dynamics of running gears and a road surface model. The virtual prototype is validated using both a static balancing test and a stiffness characteristics test. By simulating the road impact loading of the tracked vehicle when travelling on a trapezoidal US military road, the changes of the pitch angle and the acceleration of seats and centroid of the tracked vehicle was analyzed for two different damping ratios. We also determined key ride indicators for different speeds. The stiffness and damping characteristics of the ISU were tested in a bench experiment. [ABSTRACT FROM AUTHOR]

In terms of the nonlinear characteristics of hydraulic propulsion system used in 3500 m rated work-class ROV (remotely operated underwater vehicle), the paper improved the responsiveness of the hydraulic propulsion system by adding an impulse signal to the input end of the system. Because the maximum static damping moment provided from water is much larger than the dynamic damping moment, it results in large dead zone of thrust during the startup process of the hydraulic propulsion system. The dead zone of thrust caused by static damping moment can be effectively reduced by adding a specific impulse signal to the input end of the propulsion system. The results of numerical simulations and underwater experiments show that using this method, the nonlinear characteristics of the hydraulic propulsion system have been significantly improved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Through test and simulation analysis, this paper obtained the variation of electric field distribution in the oil gap in the aging oil-paper insulation model at different test temperatures. • The critical field strength/frequency calculation method of nonlinear loss factor in the pores of oil-paper insulation was proposed. The influence of insulation aging test temperature and field strength on the change of pore limiting proportion coefficient was obtained. • This paper clarified the reasons for the positive and negative nonlinear changes in the test curve of the loss factor at different excitation amplitudes. Meanwhile, considering the ion recombination process, the quantitative calculation method for the nonlinear loss factor of the aging oil-paper insulation model was proposed, and the effectiveness of the method was verified by experiments. Frequency domain dielectric response technology is widely used to detect the major insulation status of transformers. The influence of the test excitation amplitude on the nonlinear change of the dielectric characteristics of oil-paper insulation will interfere with the accuracy of the assessment results. In this paper, the electric field intensity distribution law of the oil gap in the oil-paper insulation model is obtained through test and simulation analysis. The influence of insulation aging, test temperature, and excitation frequency on the electric field distribution in the oil gap is clarified, it provides a reference for field strength for nonlinear loss calculation of oil-paper insulation. Meanwhile, based on the Garton's ion motion nonlinear response model, considering the influence of the external electric field on the ion recombination in the oil gap, the nonlinear loss calculation model of transformer oil-paper insulation is corrected. Furthermore, the mechanism of positive and negative nonlinear loss variation for the oil-paper insulation model in a wide frequency range is revealed, and the calculation method of critical frequency and critical field strength of nonlinear loss variation in the oil-paper insulation model is proposed. Finally, according to the test results of the frequency domain dielectric response of oil-paper insulation with different aging and the apparent ion mobility in transformer oil, combined with the corrected calculation method proposed in this paper, the influence of the test excitation amplitude on the nonlinear change of the loss factor of oil-paper insulation is eliminated at different temperatures. The mean square error (MSE) of the corrected loss factor is reduced by 88.03% on average compared with that before. [ABSTRACT FROM AUTHOR]

In order to grasp the nonlinear characteristic of high-speed spatial parallel mechanism, the analysis of nonlinear characteristics for spatial parallel mechanism is investigated. The nonlinear elastic dynamic equation of 4-UPS-UPU high-speed spatial parallel mechanism is derived by kineto-elastodynamics theory, the dynamic equation is solved by numerical method, the nonlinear characteristic of the parallel mechanism is analyzed by phase diagram. Numerical results show that 4-UPS-UPU high-speed spatial parallel mechanism exhibits typical nonlinear characteristic during exercise, the factors, such as the motion trajectory of parallel mechanism, the material of driving limbs, the diameter of driving limbs and the mass of moving platform, are also have effect on nonlinear characteristics of parallel mechanism. Therefore the reasonable choice of the above factors can weaken the chaos motion. This researches provide important theoretical base of the chaos suppression for spatial parallel mechanism. [ABSTRACT FROM AUTHOR]

Joints in deployable structures can degrade the stiffness and the stability of spacecraft. In this study, the nonlinear stiffness of spherical joints is investigated. The traditional contact model of spherical joints based on non-conforming contact assumption is presented. A new contact model for spherical joints based on the Winkler model and geometric constraints is established to calculate the stiffness of spherical joints with small clearances. The finite element model (FEM) of spherical joints is built to evaluate the accuracy of the theoretical model. The effects of the clearance and the contact force of spherical joints on the deformation of joints are investigated. When compared with FEM results, the error of the new spherical model is smaller than that of the traditional contact model when the clearance of spherical joint is not excessively large. The new contact model for spherical joint is more accurate than the traditional contact model when the clearance of spherical joint is large. [ABSTRACT FROM AUTHOR]

The electromagnetic transduction coefficient has a strong influence on efficiency as well as the sensorless control of linear oscillation electrical machine (LOEM). This paper presents a reciprocal LOEM method for measurement of the electromagnetic transduction coefficient, to investigate the effect of the magnet length on the characteristics of the transduction coefficient. The result shows that the transduction coefficient has two regimes, a constant regime and a nonlinear regime. As the harmonic distortion begins to appear in the induced electromotive force, the electromagnetic transduction coefficient passes from the constant regime to the nonlinear regime, and the corresponding stroke is defined as critical stroke. The range of constant regime equals the observed critical stroke, and the critical stroke is 8.81 mm and 10.78 mm when the length of the permanent magnet is 11 mm and 13 mm respectively. The relationship among the geometrical dimension of yoke and permanent magnet, the critical stroke and the stroke of the LOEM are carefully investigated. Then optimal lengths for both the yoke and the permanent magnet are suggested for the LOEM design with the rated stroke, to achieve the highest efficiency and least material cost simultaneously. [ABSTRACT FROM AUTHOR]