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To address the challenges related to active power dissipation and node voltage fluctuation in the practical transformation of power grids in the field of new energy such as wind and photovoltaic power generation, an improved Dung Beetle Optimization Algorithm Based on a Hybrid Strategy of Levy Flight and Differential Evolution (LDEDBO) is proposed. This paper systematically addresses this issue from three aspects: firstly, optimizing the DBO algorithm using Chebyshev chaotic mapping, Levy flight strategy, and differential evolution algorithm; secondly, validating the algorithm's feasibility through real-time network reconfiguration at random time points within a 24-h period; and finally, applying the LDEDBO to address the dynamic reconfiguration problems of the IEEE-33 and IEEE-69 node bus. The simulation indicates that the power dissipation of the IEEE-33 node bus is decreased by 28.94% and the minimum node voltage is elevated from 0.9273 p.u to 0.9447 p.u after the reconstruction with LDEDBO. The power dissipation of the IEEE-69 node bus is reduced by 36.45%, and the minimum node voltage is increased from 0.9224 p.u to 0.9481 p.u. The LDEDBO enhances both the pace of convergence and the precision of the optimization model, leading to a superior solution for the switching combination. [ABSTRACT FROM AUTHOR]

This article aims to investigate the fatigue life prediction methodologies of composite laminates and lay the groundwork for establishing fatigue life evaluation technology for composite structures. By extending the Hashin criterion to the fatigue failure criterion, an empirical equation for the fatigue life of unidirectional laminates with various fiber orientation is simply created. In view of the influence of the stiffness reduction coefficient of the failure layer, the failure sequence of each layer in the laminate is determined under time-varying loads. On the basis of the equivalence principle of fatigue damage, the equivalent life of the failure layer to the remaining layers in laminate is determined by considering the effects of load interaction, variable loading, and load cycles on damage. In combination with equivalent life, the fatigue life prediction model for composite laminates is constructed, and the proposed model agrees will with the test data. [ABSTRACT FROM AUTHOR]

This study proposed a method for optimizing a radial distribution network by integrating wind turbine allocation, considering fluctuating load demands, through the use of a hybrid Grey Wolf Optimizer-Genetic Algorithm (HGWOGA). This approach aims to decrease the network's energy loss costs. By incorporating genetic algorithm techniques, the method enhances the Grey Wolf Optimizer's efficiency, speeding up convergence and avoiding local optima. The strategy determines the network's open lines and the placement and capacity of wind turbines, adhering to radiality and operational constraints. It categorizes load levels into residential, commercial, and industrial, providing a comprehensive analysis of energy losses and their cost implications under various scenarios, including constant and dynamic loads. The study suggests that managing time-varying demand offers a more accurate depiction of network challenges, enabling effective reconfiguration throughout different demand phases. Moreover, HGWOGA demonstrates its ability to find the global optimum efficiently, even with reduced population sizes—a feat not achievable with the Grey Wolf Optimizer alone. Comparative analyses reveal HGWOGA's effectiveness in curbing network energy loss costs better than previous methodologies. By simultaneously applying network reconfiguration and wind turbine allocation, as opposed to merely reconfiguring the network, this approach notably reduces power loss, diminishes the cost of losses, and enhances the voltage profile. This synergistic strategy leverages the dynamic allocation of wind turbines within the network, optimizing energy flow and distribution efficiency, thereby offering a substantial improvement over conventional network reconfiguration methods. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION 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.)

The limit equilibrium of a cylindrical shell with a longitudinal crack under the action of a time-varying load is considered. Dynamic coefficients of intensity of forces and moments near the tips of cracks in shells made of steel, copper, and cast iron are calculated. The influence of the mechanical characteristics of the shell material and the rate of load variation on their behavior is analyzed. [ABSTRACT FROM AUTHOR]

A crucial component of CNC machine tools is the linear precision sliding table, but how to improve the support and fatigue resistance performance of the slide table base has been a problem to be solved. In this research, a variable density method based on interpolating functions is used to topologically optimise the slide table base for better load-carrying capacity. The minimal compliance subject to a specified mass percentage constraint is formulated, and a quadratic topology optimisation by expanding the solution domain yields an innovative base structure. A comprehensive assessment of the structural performance of the new base was performed, including maximum von Mises stresses and cumulative fatigue damage for the reference load case. The fatigue resistance of the optimised slide table base in the reference condition proved to be much better than that of the original structure, while the new design also reduced the mass of the base. These findings conclusively show that the proposed topology optimisation methodology can propose novel base designs that can reduce the experimental cycle time in the design of the base. [ABSTRACT FROM AUTHOR]

A one‐dimensional thaw consolidation model considering the density change from pore ice to pore water is established, and the model describes a special type of moving boundary problem with double moving boundaries. An analytical solution for the model under a time‐varying external load is developed using certain form of superposition principle and the similarity type of general solution. Some known solutions in literature can be recovered as special cases of the analytical solution once the density change from pore ice to pore water is neglected. If the thawing front was to cease at certain time, consolidation of thawed soil in a fixed region is then encountered, and an analytical solution for the post‐thawing consolidation problem is developed using the Green's function method. Computational examples of the analytical solutions are presented. First, comparison between our model and classical model of Morgenstern and Nixon (MN model) is conducted, showing the error caused by neglecting the density change from pore ice to pore water. The MN model overestimates the excessive pore water pressure at locations near the soil surface, while underestimates it at locations near the thawing front; the error caused by neglecting the density change becomes more pronounced with increasing ice content of frozen soil. Second, comparison between the thaw consolidation process under an instant load and that under a corresponding exponential load is made. The difference in thaw consolidation behavior between the two situations mainly displays during the early stage, when there is obvious discrepancy between the two external loads; the degree of consolidation and thaw consolidation settlement are more sensitive to the discrepancy in external load than the excessive pore water pressure is. [ABSTRACT FROM AUTHOR]

In this paper, cascaded controllers, which combine adaptive sliding mode control and recursive techniques, are presented to control quadrotor unmanned aerial vehicles with time-varying load and unknown disturbances. In the outer-loop control subsystem, an adaptive sliding mode controller, which includes adaptive laws estimating the time-varying load and unknown disturbances, is presented to control the position of the quadrotor. In the inner-loop control subsystem, an adaptive recursive sliding mode controller, which includes a self-turning law estimating the unknown inner-loop disturbances, is designed to control the attitude of the quadrotor. Moreover, a nonsingular terminal sliding mode surface is used to converge the tracking error of attitude angles to zero in finite time; and an integral sliding mode surface is designed in the adaptive recursive sliding mode controller to improve the attitude control performance of the quadrotor. Simultaneously, adaptive gain adjustment laws were applied to estimate those unknown upper bounds of the disturbances in the system. In the end, the efficiency and feasibility of the proposed control method are demonstrated by some computer simulations.

A general methodology for dynamic modeling and analysis of deep groove ball bearing used in the crank-slider mechanism of punching machine is presented in this paper. The time-varying loads applied at the inner ring of this bearing can be obtained by analyzing the planar multibody systems. The bearing joint has been modeled by introducing a nonlinear constraint force system, which takes into account the contact stiffness interaction between the rolling elements and the raceways. The four-degree-of-freedom dynamic equations for the inner and outer rings of the bearings is established by Newton's second law. By numerical calculation, the variations of the load, trajectory, FFT frequency domain response, and x direction phase trajectory and Poincare of the inner ring, and the contact force on each ball element are discussed. The results indicate that the present methodology can not only be used to analyze the overall dynamic behavior of crank-slider mechanism and the deep groove ball bearing used in punching machine, but also to obtain the dynamic loads of the inner ring and ball in bearing. Therefore, the dynamic loads on ball elements can provide a basis for the strength checking, fatigue life calculation and wear analysis of the deep groove ball bearing. [ABSTRACT FROM AUTHOR]

Digital hydraulics is a novel alternative to proportional or servovalve-controlled systems in fluid power engineering, providing hydraulic systems with high-energy efficiency, good controllability, and insensitivity to contamination. Switched inertance hydraulic converters (SIHCs) are new digital hydraulic devices that can adjust flow and pressure by digital switching instead of throttling the flow. In this paper, an efficient closed-loop control system is proposed for SIHCs subject to time-varying loading conditions in which the load pressure and/or flow varies with time. The control system is designed to operate SIHCs at optimized switching frequencies and ratios that maximize system efficiency when the load varies. With the proposed controller, the SIHC can effectively adapt to the time-varying load and has achieved up to 10% efficiency improvement and up to 65% pressure ripple reduction without affecting the system's dynamic responses, compared with using a nonoptimized controller. The work shows the feasibility and advantages of simultaneously controlling the switching ratio and switching frequency of SIHCs with a time-varying load. As time-varying loading conditions are commonly found in hydraulic applications, the research outcomes constitute an important aspect in the design and development of highly efficient SIHCs and their practical use in hydraulic machinery. [ABSTRACT FROM AUTHOR]

For the quadrotor unmanned aerial vehicle (UAV) system with time-varying load,the compound finite-time control strategy was proposed in the presence of unknown external disturbances and unknown drag coefficients.Firstly,a complete mathematical model of quadrotor UAV was established by Newton-Euler method .An adaptive trajectory tracking controller with unknown drag coefficient was designed by combining the adaptive parameter correction method of position loop with backstepping control to estimate load.Then,a finite-time sliding mode controller and Lyapunov stability theory were used so that the position loop and the attitude loop were proved to be asymptotically stable and finite-time stable,respectively.Finally,it was verified by numerical simulation.The results show that the proposed controller improves the system convergence rate,and reduces the influence of outside disturbance to the system.This method overcomes the limitations of known drag coefficients and load in the existing research,improves the anti-interference ability of the system,and has certain reference value for enhancing the practical application of the quadrotor UAV.

The current research on wind turbine gearboxes (WTG) considering multiple-factors influence mainly focuses on dynamic response. However, load sharing performance (LSP) is also extremely important for gear transmission system reliability. In this paper, considering the comprehensive effects of manufacturing errors, assembly errors, clearance floating between stages, mesh stiffness and time-varying load, a coupled translation-torsion dynamic model for WTG was developed to study the LSP. Based on the amplitude variations of time-varying mesh stiffness caused by tooth crack, an approach is provided to introduce the tooth crack into the dynamic model. The results indicate the LSP is mostly sensitive to multiple-errors and severe tooth crack, followed by the time-varying load. The LSP of a system is periodically affected by tooth crack, and the fluctuation ranges increase with the crack growth. Furthermore, the crack of sun gear has greater influence on LSP than that of planet and ring gear. [ABSTRACT FROM AUTHOR]

The engineering application of cylindrical heat source usually influences the characteristics of the surrounding soil and induces significant coupling responses of temperature, seepage and stress fields. This paper presents a numerical investigation into the thermo-hydraulic-mechanical (THM) coupling behavior of layered soils surrounding a cylindrical heat source by combining the analytical layer element method (ALEM) and the finite element method (FEM). The FEM is utilized to analyze the soil-cylindrical heat source interaction and the ALEM is used to obtain the fundamental solution of the layered soil. Then the THM coupling solution between the heat source and the soil is obtained by the simplified FEM-ALEM coupling method. Detailed validation against experimental result, and verifications against semi-analytical solution and numerical results by Comsol Multiphysics are performed to confirm the robustness of the present method, followed by extensive parametric studies to examine the effects of decaying half-life and type of the time-varying heat source, and the soil layered characteristics on the behavior of soils. It’s evident that the present method is accessible and can be implemented via common programming language, e.g. Fortran.

When the power transmission line inspection robots(PTLIRs)cross obstacles, the phenomenon of control overshoot and vibration will appear due to the influence of time-varying loads. A method for analyzing the dynamic performance of PTLIRs in obstacle crossing state is studied considering the time-varying characteristics of load inertia. The dynamics equations of the slewing mechanism of the dual-arm PTLIR are established with the two-inertia-system, and further the kinematics and dynamics modeling are carried out based on the modified D-H method and Lagrangian mechanics, including assigning coordinate system, solving Lagrange’s equation, using inertia matrix to calculate the load moment of inertia, etc. The controller parameters are designed by selecting appropriate damping coefficient, and the changes of the damping coefficient and the natural angular frequency are used to analyze the dynamic performance of the PTLIR. The research results are helpful to analyze the dynamic performance of the dual-arm PTLIR affected by the time-varying load inertia when crossing obstacles, and can be used to debug the servo parameters of the robot. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hebei University of Science & Technology is the property of Hebei University of Science & Technology, Journal of Hebei University of Science & Technology 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.)

Maintenance management in wind energy industry has great impact on the overall wind power cost. Maintenance services are either supported by wind turbine manufacturers within warranty period, or managed by wind farm owners. With condition-based maintenance (CBM) strategy, maintenance activities are scheduled based on the predicted health conditions of wind turbine components, and accurate prognostics methods are critical for effective CBM. The reported studies on integrated health prognostics considered the uncertainty in crack initiation time (CIT) uncertainty, but did not incorporate time-varying loading conditions, which could also have a significant impact on future health condition and remaining useful life (RUL) prediction. Constant loads were generally used to approximate the actual time-varying loading conditions. In this paper, an integrated prognostics method is proposed for wind turbine gearboxes considering both time-varying loading conditions and CIT uncertainty. As new condition monitoring observations are available, the distributions of both material model parameter and CIT are updated via Bayesian inference, and the failure time prediction is updated accordingly. An example is provided to demonstrate that the proposed time-varying load approach presents more benefits considering the uncertainty of CIT, with significant accuracy improvement comparing to the constant-load approach. [ABSTRACT FROM AUTHOR]

This paper proposes an effective network reconfiguration (NR) method in the presence of distributed generations (DGs) for energy loss. The proposed method uses average load and average power of DGs instead of the load and DGs' generation curves. For finding the optimal network configuration, pathfinder algorithm (PFA) is used to solve the NR problem. The effectiveness of the proposed method has been validated on two distribution network systems without and with DGs placement. The obtained results show that the proposed method has a good ability to determine the optimal configuration similar to the method based on the graphs of loads and DGs with much shorter calculated time and PFA can reach optimal solution with a much higher success rate and better obtained solution compared with particle swarm optimization and sunflower optimization algorithms. As a result, the proposed method is an effective and reliable method for solving the NR problem for energy loss reduction considering time-varying condition of loads and DGs. [ABSTRACT FROM AUTHOR]

Crack monitoring for damage-prone structural area, named hot-spot, is one of the most interesting concerned technologies for aircraft structural health monitoring. This paper proposes an efficient technique based on Fuzzy c-means (FCM) clustering algorithm to monitor the crack growth under time-varying load condition. The proposed method first extracts damage indexes from the collected signals to construct the baseline model as well as the online FCM model. Migration index of the online model is calculated by Kullback-Liebler Divergence (KLD) and Bhattacharyya Distance (BD), respectively. By comparing with the Gaussian mixture model (GMM), experimental results show that the proposed FCM algorithm has less computation time and its migration index curve is smoother when the crack size is small. Furthermore, KLD achieves a higher sensitivity than BD as crack grows.

This paper presents a new data-driven voltage control approach for distribution networks based on kernel methods. Voltage control becomes more and more challenging due to the increased penetration of Distributed Generation (DG), bidirectional power flow and faster voltage dynamics. State-of-art strategies for voltage control rely on physics model-based Optimal Power Flow (OPF) solutions, which can be implemented in a centralized or distributed manner. Nevertheless, such strategies require a detailed model of the network, and often lack scalability due to the large number of nodes and the limited communication infrastructure in distribution networks. In order to achieve real-time voltage control in distribution networks of meshed and radial topology, this paper presents a data-driven approach, which relies on local or regional measurements and does not require accurate models of the grid or an advanced communication infrastructure. Specifically, the proposed data-driven approach uses functional stochastic gradient descent in Reproducing Kernel Hilbert Spaces (RKHSs), to learn the control strategies for Distributed Generation (DG) units in real-time that lead to near-optimal operation costs, while maintaining adequate voltage profiles in the network and alleviating congestions for time-varying load and generation conditions.

Aiming at the structural strength of the valve adjusting structure of the marine gas turbine ejector under fluid-solid-thermal coupling, the three-dimensional flow field of the ejector and the structural model of the valve plate were established. The steady-state and transient simulation analysis of the flow field were carried out by using the computational fluid dynamics ( CFD) method. Taking the transient simulation results as the boundary conditions of the finite element model, the sequential unidirectional fluid-solid-thermal coupling analysis including thermal, aerodynamic and centrifugal loads was carried out. The result showed that compared with the steady-state simulation, the trend of transient simulation results is similar, but the pressure difference is larger. The steady-state solution of the time-varying load may lead to underestimation of strength. For the valve adjusting structure, the thermal load plays a major role in the deformation and stress of the valve plate. The bending stress caused by the aerodynamic load can offset part of the bending stress caused by the thermal load, while the centrifugal load has little effect on the structure, which can be ignored. The analysis method can be used for the structural design and optimization of such typical motion adjusting structures as ejector valve adjusting structure. [ABSTRACT FROM AUTHOR]

In this paper, a novel dynamic model of coupling translation joints with subsidence for time-varying load in a planar mechanical system is established. One translational joint has four working scenarios, which are free motion, one corner rub-impact, two adjacent corners rub-impact and two opposite corners rub-impact. However, the rub-impact of double coupling translation joints are not a simple superposition of these scenarios, but rather a more complex rub-impact configuration that should be considered in this model. An adaptive fourth-order Runge–Kutta method is utilized to solve the dynamic differential equations. After that, we discuss the dynamic behavior of the rub-impact coupling by taking a triplex member of the crosshead slider, piston rod and piston slider as an example in the reciprocating compressor system. The results show that the double coupling translation joints experience free motion, continuous contact motion and rub-impact motion. The difference is that, in the rub-impact motion, for the crosshead slider there only appears one single corner and two adjacent corners impacting the guide, while the coupling piston slider experiences multiple rub-impact situations including one single corner, two adjacent corners and two opposite corners impacting the guide. Moreover, the results reveal that the subsidence has a significant influence on the rub-impact behavior of the coupling translation joints, and the greater the subsidence, the more severe the vibration response of the slider impacting the guide. Finally, in this rub-impact coupling system, the existence of chaotic behavior is confirmed by the Poincaré section and the largest Lyapunov exponent approaches. [ABSTRACT FROM AUTHOR]

To study the vibration characteristics of deep-groove ball bearing, considering the influence of sliding, the dynamic model of the DGB 6205 system is established in this paper. The DGB 6205 system model includes the movement of the bearing inner ring in the X and Y directions, the rotation of the cage, the rotation movement of each ball, the revolution movement of each ball and the movement along the radial direction of each ball. Based on the system model, the differential equations of motion of the system are established, and the correctness of the model is verified by experiment. The slip characteristics of the DGB 6205 system are studied by numerical simulation. At the same time, the influence of time-varying load on the vibration characteristics of the system is studied. Then, the sensitivity of system parameters is analyzed. The results show that the sliding speed between the ball and the inner raceway is greater than that between the ball and the outer raceway. The radial vibration response of DGB 6205 system under time-varying load is less than that under constant load. The increase of radial clearance will increase the vibration response of DGB 6205 system.

Considering the problems of internal and external disturbances, i.e. time-varying load, inaccurate system model and external uncertainties etc., a compound control strategy based on model predictive control (MPC) and non-linear extended state observer (ESO) are proposed to attenuate the output voltage fluctuation under continuous conduction mode (CCM) mode of the buck circuits. In addition, a non-linear ESO is used to observe all kinds of uncertainties caused by internal and external disturbances and to eliminate their effects by compensating these disturbances in the feed-forward channel. Compared with the pure MPC control, the simulation results show that the proposed composite control method has the better disturbance suppression effect and also can effectively improve the stability of the buck circuit.

• The controller can handle actuator capability, load variation, and road disturbance. • A piecewise suspension model and a PQLF-based design method are employed. • The controller can exert different damping properties for different load conditions. Magnetorheological (MR) dampers enable wide-range adjustment of damping and are considered as promising actuators for suspension performance optimization. However, MR dampers also exhibit complex nonlinearities, including hysteresis and bi-viscosity. Moreover, in addition to handling road irregularities, the suspension system needs to adjust its performance according to variations in vehicle load. The above nonlinearities and requirements both bring challenges to the design of semi-active suspension controllers. In this paper, the nonlinearities of MR dampers are handled with a piecewise modeling method, and the vibration attenuation is realized by designing a static piecewise-affine (PWA) H ∞ controller. Furthermore, to deal with the time-varying load and to fully utilize the capability of MR dampers, a parameter-dependent piecewise-quadratic Lyapunov function (PDPQLF) is employed, which results in a load-dependent PWA (LDPWA) H ∞ controller. Simulation and experimental results under random, bumpy and sinusoidal excitations show that the proposed controller can achieve enhancements on both comfort and handling performance. Above all, the proposed method enables effective high-frequency vibration suppression for underload conditions, while for overload conditions, the low-frequency performance is more significantly improved. [ABSTRACT FROM AUTHOR]

In order to study the dynamic characteristics of cutting head and cantilever system, a nonlinear dynamic model with a 13 degrees of freedom (13-DOF) lateral torsional coupled cutting head-rotor-bearing system (CHRBS) is established. The nonlinear coupled factors of spline clearance and bearing contact force are mainly considered, the dynamic analysis of CHRBS under time-varying load is carried out. The results show that there is no positive correlation between the cutting rock thickness and the states of chaotic motion and quasiperiodic motion. The system is in the two states mentioned above when in low speed region. With the increase of rotational speed, the chaotic motion becomes periodic motion. When the hardness of rock is lower, increasing rotational speed can reduce the vibration of the system, and the cutting thickness can be increased to improve the productivity and lump rock rate. As the hardness of rocks increases, the coupled system shows complex dynamic characteristics when the rotational speed changes from low to high, and the vibration increased. When cutting hard rock, the cutting speed should be increased. However, when the speed is too high, the cutting torque of system becomes smaller. In the case of cutting hard rock, reasonable rotational speed should be chosen between improving stability and increasing cutting force. The dynamic analysis results provide strong support for the vibration reduction and dynamic design of roadheader. [ABSTRACT FROM AUTHOR]

Creep behavior is an inevitable problem for viscoelastic layered structures and needs to be predicted for long-term service situations. In this study, a new technique to obtain analytical solutions for three-dimensional (3D) viscoelastic equations for layered rectangular plates under time-varying loads is developed to predict bending creep behavior. In the analytical model, all the constituent materials of the plate, including the laminar layers and interlayers, exhibit viscoelastic properties, which are simulated by the Burgers model. The slip effect between neighboring laminar layers due to a relatively soft interlayer is considered. The stresses and displacements of each laminar layer in the layered plates are described by 3D elasticity theory combined with the Boltzmann superposition principle. The viscoelastic analytical solutions are obtained by means of series expansions and the Laplace transformation method. The present solution has good accuracy and agrees with the finite element (FE) solution. The influence of various parameters, such as the modulus degradation pattern, modulus ratio and viscoelastic constants, on the creep of the plate are studied. [ABSTRACT FROM AUTHOR]

Frame saw machine is one of machine tools that is used to process dimension stone. The velocity fluctuation of traditional feed drive system (FDS) lead to excessive wear of diamond particles. The dynamic performance of the FDS has time-varying characteristics during the processing of stone with a large material removal rate. In this paper, a novel FDS was proposed. Firstly, the dynamic modeling of FDS was set up on account of lumped parameter method (LPM). Then the speed of the new FDS was compared with that of the traditional FDS. Finally, the frequency response characteristics of the system were solved by Lagrange and state space method. Results showed that the new FDS has a faster response feed and less velocity fluctuation. The natural frequency and the amplitude of acceleration increase with decreasing load. With the time-varying load, the range of the second-order natural frequency increased by 50 Hz, which was larger than that of the first-order. The modal test verified that the first two natural frequencies of the saw blade are within the range of the natural frequencies of FDS. The proposed FDS can guide for design, reduce the wear of diamond, and improve processing quality.

Wind power is a significant clean energy source. Operation & maintenance (O&M) costs account for about 25% of the cost of wind power, and it is critical to improve the reliability of wind power generators to reduce the overall cost and increase wind power competitiveness comparing to other power sources. Wind turbines are subject to instantaneously varying load due to wind turbulence, which challenges the prognostic study for predicting equipment future health conditions and remaining useful lives. With existing prognostics methods, the average constant load is typically used to approximate the varying external load. In this paper, an integrated varying-load approach is proposed for predicting wind turbine gearbox remaining useful life by specifically considering instantaneously varying external load, which is more realistic. Fatigue crack damage is focused on. The method integrates gear physical models and available health condition data, and the distribution of uncertain material parameter modeled in crack degradation process is updated via Bayesian inference once new health condition data become available. Examples are provided to demonstrate the effectiveness of the proposed varying-load approach. A comparative study is conducted between the proposed approach and existing constant-load approximation method, and the results show that the proposed varying-load approach can provide more accurate prediction. [ABSTRACT FROM AUTHOR]

A nonlinear dynamic model of nose landing gear (NLG) shimmy considering the coupling of time-varying load and Coulomb friction is proposed, and the effects of Coulomb friction on the shimmy stability under constant load, time-varying load and vertical motion are investigated. The results indicate that the anti-shimmy effect of the Coulomb friction is weakened under time-varying load. The coupling mechanism between time-varying load and Coulomb friction is mainly reflected in the change of Coulomb friction caused by vertical motion. Finally, the influence parameters of Coulomb friction are analyzed, which can provide guidance for the design of Coulomb friction of NLG under time-varying load. The above is of great benefit to the development of new and more robust shimmy suppression strategies. [ABSTRACT FROM AUTHOR]

This study develops a gear diagnostic procedure for the detection of multi- and concurrent degradation processes evolving under time-varying loads. Instead of a conventional comparison between a descriptor and an alarm level, this procedure bases its detection strategy on a descriptor evolution tracking; a lasting descriptor increase denotes the presence of ongoing degradation mechanisms. The procedure works from time domain residual signals prepared in the frequency domain, and accepts any gear conditions as reference signature. To extract the load fluctuation repercussions, the procedure integrates a scaling factor. The investigation first examines a simplification assuming a linear connection between the load and the dynamic response amplitudes. However, while generally valuable, the precision losses associated with large load variations may mask the contribution of tiny flaws. To better reflect the real non-linear relation, the paper reformulates the scaling factor; a power law with an exponent value of 0.85 produces noticeable improvements of the load effect extraction. To reduce the consequences of remaining oscillations, the procedure also includes a filtering phase. During the validation program, a synthetic wear progression assuming a commensurate relation between the wear depth and friction assured controlled evolutions of the surface degradation influence, whereas the fillet crack growth remained entirely determined by the operation conditions. Globally, the tested conditions attest that the final strategy provides accurate monitoring of coexisting isolated damages and general surface deterioration, and that its tracking-detection capacities are unaffected by severe time variations of external loads. The procedure promptly detects the presence of evolving abnormal phenomena. The tests show that the descriptor curve shapes virtually describe the constant wear progression superimposed on the crack length evolution. At the tooth fracture, the mean values of the residual signal evince strong perturbations, while after this episode, the monitoring curves continue signaling the ongoing wear process. [ABSTRACT FROM AUTHOR]

The engineering application of cylindrical heat source usually influences the characteristics of the surrounding soil and induces significant coupling responses of temperature, seepage and stress fields. This paper presents a numerical investigation into the thermo-hydraulic-mechanical (THM) coupling behavior of layered soils surrounding a cylindrical heat source by combining the analytical layer element method (ALEM) and the finite element method (FEM). The FEM is utilized to analyze the soil-cylindrical heat source interaction and the ALEM is used to obtain the fundamental solution of the layered soil. Then the THM coupling solution between the heat source and the soil is obtained by the simplified FEM-ALEM coupling method. Detailed validation against experimental result, and verifications against semi-analytical solution and numerical results by Comsol Multiphysics are performed to confirm the robustness of the present method, followed by extensive parametric studies to examine the effects of decaying half-life and type of the time-varying heat source, and the soil layered characteristics on the behavior of soils. It's evident that the present method is accessible and can be implemented via common programming language, e.g. Fortran. [ABSTRACT FROM AUTHOR]

• This paper establishes a multi-objective optimization model for the dynamic reconfiguration of the distribution network. • Aiming at the time-varying load, considering the switching constraints, a dynamic optimal period division function and optimal function threshold are proposed. • An improved SMA is proposed, called MFSMA. It is used to solve the dynamic reconfiguration of distribution network problem for the first time. This paper suggests a multi-period dynamic reconfiguration method for the distribution network. The reconfiguration period is preliminarily divided based on the load monotonicity and amplitude change with taking the length of the actual load as the reconfiguration time section. A multi-objective dynamic reconfiguration is modeled based on the time-varying load distribution network considering network active power loss, static voltage stability, and load balance. The optimal period partition function is dynamically adjusted by the time-division method under the constraint of switching actions. The paper also proposes a multi-group flight slime mould algorithm (MFSMA) by applying a multi-group optimization strategy and adaptive Levy flight for the dynamic distribution network reconfiguration problem. Through experiments on IEEE-33 and IEEE-118 bus distribution networks, the experimental results show that the MFSMA for the multi-period dynamic reconfiguration effectively simulates the actual reconfiguration of the distribution network and provides a new scheme for the economic, stable, and safe operation of the distribution network. [ABSTRACT FROM AUTHOR]

Abstract: Fault detection and diagnosis in mechanical systems during their time-varying nonstationary operation is one of the most challenging issues. In the last two decades or so researches have noticed that machines work in nonstationary load/speed conditions during their normal operation. Diagnostic features for gearboxes were found to be load dependent. This was experimentally confirmed by a smearing effect in the spectrum. In order to better understand the involved phenomena and to ensure agreement between simulation and experimental results, two models of gearboxes (a fixed-axis two-stage gearbox and a planetary gearbox) operating under varying load conditions are proposed. The models are based on two mechanical systems used in the mining industry, i.e. the belt conveyor and the bucket wheel excavator. An original transmission error function expressing changes in technical condition and load variation is presented. Energy based parameters (the signal RMS value or the arithmetic sum of the amplitudes of spectral gearmesh components) are adopted as the diagnostic features. Simulation results show a strong correlation between load values, changes in condition and the diagnostic features. The findings are key to condition monitoring. Thanks to the use of the models one can better understand the phenomena identified through an analysis of vibration signals captured from real machines. [Copyright &y& Elsevier]

Abstract: A new approach to the prediction of the reliability of electrical systems is presented. In this approach a graph trace based reliability analysis of electric transmission and/or distribution systems is used. The systems are modeled using containers with iterators, where the iterators manage graph edges and are used to process through the topology of the graph. The analysis provides a means of computationally handling dependent failure rates and cascading failures. The effects of weather, time-varying loads, equipment age, wetness, and dependent failures associated with repaired components are considered. A sequential Monte Carlo simulation is used to evaluate the reliability changes for different system configurations, including distributed generation and transmission lines. Historical weather records and loading are used to update the component failure rates on-the-fly. Simulation results are compared against historical reliability field measurements. [Copyright &y& Elsevier]

Aiming at the problem of the gear mesh was affected by time varying loads which lead to gear surface fatigue damage and shock, the dynamic characteristics of gear and modification were carried out. The coupled model of rigid and flexible was built by ADAMS, and then the different time-varying loads were obtained based on different modification methods. Finally, modal analysis and dynamic stress behavior were carried out by ANSYS Workbench. The results indicate that the long parabolic modification is better than that of short arc modification in the process of alternating two and three pairs of teeth meshing of helical gear, which can provide the effective basis for gear dynamics analysis. [ABSTRACT FROM AUTHOR]

To study the vibration characteristics of deep-groove ball bearing, considering the influence of sliding, the dynamic model of the DGB 6205 system is established in this paper. The DGB 6205 system model includes the movement of the bearing inner ring in the X and Y directions, the rotation of the cage, the rotation movement of each ball, the revolution movement of each ball and the movement along the radial direction of each ball. Based on the system model, the differential equations of motion of the system are established, and the correctness of the model is verified by experiment. The slip characteristics of the DGB 6205 system are studied by numerical simulation. At the same time, the influence of time-varying load on the vibration characteristics of the system is studied. Then, the sensitivity of system parameters is analyzed. The results show that the sliding speed between the ball and the inner raceway is greater than that between the ball and the outer raceway. The radial vibration response of DGB 6205 system under time-varying load is less than that under constant load. The increase of radial clearance will increase the vibration response of DGB 6205 system. [ABSTRACT FROM AUTHOR]

A one-dimensional thawing process of frozen soil under a uniform initial temperature and a step increase of boundary temperature is investigated. The classical thaw consolidation model developed by Morgenstern and Nixon is extended by including unfrozen water in frozen soil and time-varying loads under two types of drainage boundaries. It is proven that the thawing front advances in proportion to the square root of time even with the unfrozen water effect included. It is also indicated that a certain form of superposition principle is applicable to the consolidation process even with the presence of a moving interface. An analytical solution for the external load in the form of a power function is developed using the similarity transformation technique, and this solution can be applied to construct the analytical solution for an arbitrary external load using the superposition principle. A numerical solution for the problem is also developed. Computational examples are presented. First, the correctness of the analytical solution and the numerical solution is verified. Second, thaw consolidation processes under an instant load and a corresponding exponential load are compared and discussed. Third, the effects of unfrozen water and drainage types on the thaw consolidation behavior are investigated. [ABSTRACT FROM AUTHOR]

• This paper presents a new analytical method to optimal siting and sizing of DERs. • This method is based on a minimizing the total daily power losses. • In the formulation, the new factor in order to consider time-varying DG defined. • This paper is considered several types of time-varying load and DG model. • This method identifies optimal buses to be placed on DERs and sizes of this units. In the most studies related to allocation of distributed generation the load model assumed in constant. Such assumptions may lead to inconsistent and misleading results in the reduction of energy losses, improve system stability, etc. However, this paper is considered several different types of time-varying to allocation of units. In this study, Optimal Sizing and Siting of Distribution Generation units (Consisting of dispatchable, nondispatchable and photovoltaic) Problem are provided at the same time with considering the role of demand response and time-varying voltage-dependent load models (Consisting of commercial, industrial and residential). This method first identifies a set of buses to be placed of DG units. The optimal sizes of DG units at the identified buses are then evaluated by minimizing Multiobjective Index (Consisting of active, reactive power losses). The proposed method has been tested and validated on 33-buses test distribution system. The results show that demand response and different load models have a significant impact on the planning of Distribution Generation units in radial distribution network. [ABSTRACT FROM AUTHOR]