Complex Coupling Effects Research Articles

A dual-scale elasto-viscoplastic constitutive model of metallic materials to describe thermo-mechanically coupled monotonic and cyclic deformations

Thermo-mechanical coupling effect often occurs during the deformation of the metallic materials, especially when they are subjected to cyclic loadings at a high loading rate. On one hand, the internal heat generation and accumulation originated from the energy dissipation during plastic deformation lead to the change of temperature field in the material. On the other hand, the variation of temperature field further changes the dissipation property of the material, since the stress-strain response depends on the temperature. These two factors influence with each other and result in a complex thermo-mechanical coupling effect. In this work, a dual-scale thermo-mechanically coupled elasto-viscoplastic constitutive model is developed to predict the monotonic, cyclic deformation and temperature field evolution of metallic materials under monotonic and cyclic loadings. At the mesoscopic scale, the polycrystalline representative volume element (RVE) is considered as an aggregation of individual grains. For an individual grain, a crystal plasticity model accounting for the internal heat generation is developed based on the fundamental laws of irreversible thermodynamics. A nonlinear kinematic hardening rule extended from the Ohno-Abdel-Karim model is adopted to capture the evolution of resolved shear back stress for each slip system, and the classical Bassani-Wu latent hardening rule is utilized to describe the interaction of dislocation slipping. To calculate the thermo-mechanical interactions among the grains, and obtain the overall responses of the polycrystalline RVE, a self-consistent (SC) homogenization scheme accounting for material nonlinearity and thermo-mechanical coupling effect is developed. At the macroscopic scale, the thermo-mechanical responses for the specimen are obtained by solving the equations of force balance, deformation compatibility, thermodynamic equilibrium and constitutive relationship through an approximation method. Finally, the proposed model is validated by predicting the monotonic, cyclic stress-strain responses and temperature evolution of 316L stainless steel.

Quantifying Order during Field-Driven Alignment of Colloidal Semiconductor Nanorods.

Aligning large populations of colloidal nanorods (NRs) into ordered assemblies provides a strategy for engineering macroscopic functional materials with strong optical anisotropy. The bulk optical properties of such systems depend not only on the individual NR building blocks but also on their meso- and macroscale ordering, in addition to more complex interparticle coupling effects. Here, we investigate the dynamic alignment of colloidal CdSe/CdS NRs in the presence of AC electric fields by measuring concurrent changes in optical transmission. Our work identifies two distinct scales of interaction that give rise to the field-driven optical response: (1) the spontaneous mesoscale self-assembly of colloidal NRs into structures with increased optical anisotropy and (2) the macroscopic ordering of NR assemblies along the direction of the applied AC field. By modeling the alignment of NR ensembles using directional statistics, we experimentally quantify the maximum degree of order in terms of the average deviation angle relative to the field axis. Results show a consistent improvement in alignment as a function of NR concentration─with a minimum average deviation of 36.2°─indicating that mesoscale assembly helps facilitate field-driven alignment of colloidal NRs.

Functional health prognosis approach of multi-station manufacturing system considering coupling operational factors

The core function of the manufacturing system is to ensure the quality and quantity of output products. Therefore, the performance of the manufacturing function can effectively evaluate the health state of the manufacturing system. However, the complex coupling effects caused by the correlation and interaction between multiple operational factors in the running manufacturing system will significantly affect the performance of manufacturing function, which has not been paid due attention. Therefore, a systematic functional health state prognosis approach for the manufacturing system considering coupling operational factors is given in this paper. First, based on functional performance analysis, the relationship among main coupling operational factors including manufacturing machine, production task, and produced workpiece is expounded, and the connotation of the functional health state is defined. Second, three quantitative models of the coupling effect between operational factors are constructed. Third, an integrated functional health prognosis model for the manufacturing system is established. Finally, a prognosis example of a ferrite phase shifting unit manufacturing system is provided to illustrate the effectiveness of the proposed method.

Fault‐tolerant control of an aerial manipulator with guaranteed tracking performance

AbstractIn this article, a fault‐tolerant control (FTC) scheme of an aerial manipulator is proposed, which can guarantee the transient and steady‐state tracking performance under actuator faults. A novel performance function (NPF) with simple form and explicit terminal time is designed to constrain the tracking errors. First, backstepping technique combined with the NPF is adopted as control framework to guarantee the asymptotic stability. Then, adaptive nonsingular terminal sliding mode with estimated actuator faults is used as the robust controller to deal with actuator fault. Finally, extended state observer is used to estimate and compensate complex coupling effects between the main‐body UAV and loading manipulator, and external disturbance. The stability of the aerial manipulator system with actuator faults and external disturbance is proved by Lyapunov analysis. Besides, the effect of the turbulent wind field on the body of the vehicle is analyzed. Several comparative simulations are carried out to show the effectiveness of the proposed FTC scheme.

Research on modeling and parameter sensitivity of flow and heat transfer process in typical rectangular microchannels: From a data-driven perspective

With the miniaturized and high-powered development of power equipment and electronic devices, the microchannel heat sink is becoming an important device widely used in the modern cooling field. The heat transfer performance of the microchannel heat sink is affected by many influence factors, and amongst them there exists a complex coupling effect. So far, the mechanism of the microchannel heat sink has not been clearly elucidated. To figure out the dominant characteristics that affect the heat transfer performance of the microchannel heat sink and the interaction mechanism between relevant characteristics, this work carried out numerical simulations and parameter sensitivity analysis to investigate the key factors of the fluid flow and heat transfer performance in rectangular microchannels, and considered variables included key physical parameters of the fluids and dimensional parameters of the microchannels. To satisfy the enormous amount requirement of sample size in the parameter sensitivity analysis, a machine learning model, Gradient Boosting Tree (GBT), was constructed based on computational fluid dynamics (CFD) simulation results; then, the Sobel sensitivity analysis algorithm was coupled in to analyze the multi-parameter contribution of each input parameter. Results show that the number of channels N and Reynolds number Re have a greater impact on heat transfer performance under low Re conditions, and the cross-sectional area A and aspect ratio α have a much higher effect on the pumping power rather than Nusselt numbers Nu; N and A have a positive second-order interaction on Nu. When moving to the conditions with a higher Re, the number of channels N became the dominant factor that influenced both heat transfer and flow performance of the microchannel heat sink. This work also provides effective guidance for the design and optimization of high-efficiency microchannel heat sinks.

Investigating the impact of route topography on real driving emission tests based on large data sample at data window level

Route topography is an important boundary condition for the regulated real driving emission (RDE) test. However, accurately and comprehensively evaluating the influence of route topography on the RDE test is difficult, because the effect cannot be easily separated from those of other test boundaries. We selected two light-duty gasoline vehicles to complete two rounds of RDE tests on four different test routes, and conducted the correlation analysis between pollutant emissions and route topography quantified by the cumulative positive altitude gains of the test routes based on the moving averaging window method. Since the small number of sample data at the total trip and road section level were not sufficiently representative of the population, we proposed to use the pollutant emission data of the data windows to analyze the complex coupling effect of the cumulative positive altitude gains and trip dynamic parameters of v·apos[95] on the RDE tests. At data window level, thousands of data windows were treated as the road section subsets of the RDE test, and the sample space of road section emission data was expanded by several orders of magnitude. With the help of the large data sample space, the influence mechanism of the random test boundaries on the RDE tests was demonstrated.

Prediction of Sound Scattering from Deep-Sea Targets Based on Equivalence of Directional Point Sources

A fast prediction method is proposed for calculating the sound scattering of targets in the deep-sea acoustic channel by equating the sound scattering field of a complex elastic target to the acoustic field excited by a directional point source. In deep-sea conditions, the effects of the sea surface on the impedance characteristics of the elastic target surface can be ignored. Through the finite element simulation of the acoustic scattering of the target in the free field, the sound scattering field is equated to the radiation field of a directional point source. Subsequently, the point source is placed in the channel, and the acoustic ray method is used to calculate the distribution of the scattering field. On the basis of theoretical modelling, the method of obtaining the directional point source and the influence of the sea surface on the impedance of the scattering field are analysed. Subsequently, the proposed method is compared with the finite element method in terms of computational efficiency. The result shows that the method considers the multiple complex coupling effects between the elastic structure and marine environment. The influence of the boundary is approximately negligible when the distance from the ocean boundary to the elastic structure is equal to the wavelength. The method only performs finite element coupling calculation in the free field; the amount of mesh size is greatly reduced and the calculation efficiency is significantly improved when compared with the finite element calculation in the entire channel, the. The calculation time in the example can be reduced by more than one order of magnitude. This method organically combines the near-field calculation with acoustic ray theory and it can realise the rapid calculation of the large-scale acoustic scattering field in complex marine environments.

Comprehensive analysis for influence of complex coupling effect and controllable suspension time delay on hub-driving electric vehicle performance

For in-wheel driving vehicle electric vehicles (EVs), mechanical electromagnetic coupling effect caused by the air gap deformation in permanent magnet synchronous hub motor and intensified by the road excitation deteriorates the EVs performance. In this paper, after studying the numerical method for multi-field coupling problems of hub-driving vehicle under the coupled action of electromagnetic field and mechanical field. The experimental validation is investigated. The results indicate that the multi-field coupling effect in hub-driving motor worsens the dynamics performance of the vehicle. To enhance the vehicle performance, suppress mechanical electromagnetic coupling effect and, at same time, reduce the influence of controllable suspension time delay, a delay-dependent H∞ controller is designed based on Lyapunov theory. By applying the particle swarm optimization (PSO) algorithm and the linear matrix inequality theory, the desired output controller gain is derived. Numerical simulations reflect that the active suspension controller considering control time delay not only achieves the favorable riding comfort performance and restrains the coupling effect in hub driving motor but also ensures the suspension deflection and the safety performance requirement. Moreover, it maintains the closed-loop asymptotically stability regardless of t the variation on the sprung mass and control time delay.

A micromechanics-based model for deformation-induced damage and failure in elastomeric media

In order to predict damage and failure in elastomeric media, a new physically-based model based upon a multiscale approach is proposed. The behavior of polymer chains is described by means of statistic mechanics, in which the stretchability and detachability of the internal bonds are introduced to account for the enthalpy contribution to chain elasticity and the time-dependent stochastic process of chain scission, respectively. The complex but inevitable coupling effect between the chain conformation change and the bond length change is addressed in a rigorous approach, and the bond rupture is treated as an energy activation process that is related to the thermal oscillation and stimulated by the chain stretch. The micro-macro transition is realized with a non-affine microsphere-based strategy where the length variability of polymer chains is considered statistically, as well as its evolution with the loading histories. The model is firstly used to discuss some history-dependent features (Mullins effect and monotonic biaxial failure) of rubbers in relation to damage accumulation due to progressive chain scission events. The efficiency of the model is then critically discussed by comparisons with a few illustrative experiments of different rubbery media under high thermal environmental and thermal aging effects. To illustrate further the predictive capability of the model, the failure of rubbers is finally treated under a wide range of biaxial loading conditions.

Influence of complex coupled factors in BZ reaction

In this paper, the influence of the complex coupling factors on the oscillation taking place in the (Belousov–Zhabotinsky) BZ reaction has been studied. By analyzing the oscillation process of the BZ reaction from both the non-equilibrium thermodynamic and dynamic methods, it is found that if the complex coupling effects in the entire reaction system are strong enough, the steady state of the system will lose its stability; obviously, in this case, the dissipative structure is more likely to appear in the system, and the larger the complex coupling effects are, the easier the steady state of the system is to lose its stability, so it can be concluded that the complex couple factors make their most important contributions to the oscillation phenomena of the BZ reaction. Furthermore, it is also found that one of the complex coupling factors is related to the strength of this self-catalyst reaction.

Active fault-tolerant control scheme of aerial manipulators with actuator faults

In this paper, an active fault-tolerant control (FTC) strategy of aerial manipulators based on non-singular terminal sliding mode (NTSM) and extended state observer (ESO) is proposed. Firstly, back-stepping technology is adopted as the control framework to ensure the global asymptotic stability of the closed-loop system. Next, the NTSM with estimated parameters of actuator faults is used as main robustness controller to deal with actuator faults. Then, the ESO is utilized to estimate and compensate the complex coupling effects and external disturbances. The Lyapunov stability theory can guarantee the asymptotic stability of aerial manipulators system with actuator faults and external disturbances. The proposed FTC scheme considers both actuator fault and modelling errors, combined with the adaptive law of actuator fault, which has better performance than traditional FTC scheme, such as NTSM. Finally, several comparative simulations are conducted to illustrate the effectiveness of the proposed FTC scheme.

Effects of bed longitudinal inflexion and sediment porosity on basal entrainment mechanism: insights from laboratory debris flows

Channel morphology and bed sediment erodibility are two crucial factors that significantly affect debris flow entrainment processes. Current debris flow entrainment models mostly hypothesize the erodible beds are infinite with uniform slopes. In this study, a series of small-scale flume experiments were conducted to investigate the effects of bed longitudinal inflexion and sediment porosity on basal entrainment characteristics. Experimental observations revealed that sediment entrainment is negligible at early stages and accelerates rapidly as several erosion points appear. Continual evolution of flow-bed interfaces changes interactions between debris flows and bed sediments, rendering the interfacial shear action involved into a mixed shear and frontal collisional action. Lower bed sediment porosity will change the spatial arrangement and orientation of particle mixture, strengthen the interlocking and anti-slide forces of adjacent sediment particles, and promote the formation of particle clusters, all of which will increase bed sediment resistance to erosion. By examining the post-experimental bed morphology, the slope-cutting amounts and topographic reliefs are determined to positively correlate with longitudinal transition angles. These high topographic reliefs may indicate the propensity of triangular slab erosion, rather than strip-shaped slab erosion, in non-uniform channels with relatively steep erodible beds. Empirical formulas are obtained that denote the relationships among bed sediment strength, channel curvature radius, and sediment porosity through a multi-parameter regression analysis. This study may aid in clarifying the complex coupling effects of spatial variations in debris flow dynamics as well as sediment erodibility and bed morphology in non-uniform channels with abundant seismic loose material.

Undrained Seismic Compression of Unsaturated Sand

Unsaturated soils in engineered geostructures like embankments or retaining walls may experience seismic compression during earthquakes due to particle rearrangement associated with large-strain cyclic shearing. Although previous studies have investigated volume changes during drained cyclic shearing of unsaturated soils, undrained cyclic shearing presents a more complex situation. During undrained cyclic shearing, changes in total volume, matric suction, degree of saturation, effective stress, shear modulus, and damping ratio may occur that have complex coupling effects that affect seismic compression. To better understand these coupling effects, this study performed a series of undrained cyclic simple shear tests on unsaturated sand specimens. Contractile volumetric strain after 200 cycles in these tests was found to vary nonlinearly with degree of saturation. The largest volumetric contraction occurred at a degree of saturation of 0.4 and coincided with the largest decrease in mean effective stress. The sand specimens followed a wetting-path scanning curve during shearing, with small changes in matric suction. The decrease in mean effective stress during cyclic shearing for all specimens followed the same linear relation with the accumulation of volumetric strain.

Performance study of multi-source driving yaw system for aiding yaw control of wind turbines

Multi-source driving (MSD) yaw system is widely used in large-scale wind turbines. However, due to the complex coupling effect of mechanical, electrical, and hydraulic, there is a knowledge gap on the dynamic process of the MSD yaw system. To fill this gap, a dynamic coupling model of the MSD yaw system is established. In this model, multi-way power source subsystems, transmission gearbox subsystems, and hydraulic brake subsystems are established, and the coupling of multi-way yaw subsystems are realized. Based on this model, different yaw angle control modes are studied, including comparison control and servo control. To further reflect the dynamic process in-service condition, the MSD yaw system model is integrated into a wind turbine model. An approximate solution for calculating yaw load is also presented. Through this study, the results show the established MSD yaw system model can work effectively. The difference of gear meshing gaps directly affects the distribution of yaw load. The dynamic response of the yaw system, including yaw position, yaw speed, and yaw acceleration, is affected by the changing amplitude and frequency of yaw load, but the large inertia of yaw system can restrain the fluctuation of yaw dynamic response to some extent.

A practical time-delay control scheme for aerial manipulators

In recent years, aerial manipulators consist of unmanned aerial vehicles and robotic manipulators have been widely utilized in aerial operations. The complex dynamic coupling effects between unmanned aerial vehicles and robotic manipulators will bring some issues to the motion control. Therefore, the article proposes a new control scheme for aerial manipulators. The proposed method includes three elements, that is, time-delay estimation, backstepping design, and nonsingular terminal sliding mode. The time-delay estimation technique is adopted to estimate the complex system dynamics and to bring a model-free feature of the system. With the backstepping design, the proposed control strategy can ensure the asymptotic stability of the closed-loop system by recursive procedure. To deal with the unmodelling dynamics and disturbances, and to assure finite-time convergence of the system states, the nonsingular terminal sliding mode is adopted. By combining three elements, the tracking performance of aerial manipulators is improved under unmodelling dynamics and disturbances. Global stability of closed-loop control system is analyzed using Lyapunov stability theory. Finally, comparative simulations are conducted, and the results show that the proposed controller has better performance than a conventional proportional–derivative controller or a nonsingular terminal sliding mode controller.

Interactive and individual effects of multi-factor controls on water use efficiency in Central Asian ecosystems

Water use efficiency (WUE) characterizes the relationship between water dissipation and carbon sequestration. Knowledge of WUE dynamics and its responses to complex climate controls are prerequisites for addressing the challenges of future climate change and human disturbance of wild lands. Owing to a lack of experimental observations and the complexity of quantifying the individual and interactive effects of different environmental factors, the mechanism of WUE dynamics and the spatiotemporal characteristics of WUE in Central Asian ecosystems remain unclear. Here, a specific Arid Ecosystem Model was used to assess WUE dynamics under environmental stresses, specifically isolating and identifying proprietary features from complex coupling effects, across different ecosystems in Central Asia from 1980 to 2014. WUE declined in southern Xinjiang but exhibited an upward trend in the Tianshan Mountains and northern Kazakhstan. Precipitation and CO2 controlled WUE of 39% and 54% of Central Asia, respectively. The factor analysis showed that the negative effects of climate change were largely compensated by the CO2 fertilization effect, and their interaction produced negative feedback to WUE. This resulted in inhibition of the CO2 fertilization effect during long droughts. The negative effects of warming included increased water stress and enhanced evapotranspiration from vegetation. Based on variations in precipitation and net primary production, we determined that southern Xinjiang and the Turgay Plateau were environmentally vulnerable areas. Our study provides guidance regarding how ecologically fragile regions in Central Asia might cope with environmental pressures under extreme climate change in the future.

Deformation properties of coarse-grained sulfate saline soil under the freeze-thaw-precipitation cycle

Salt expansion deformation is the main engineering hazard of saline soil, which restricts the application of coarse-grained sulfate or sulfite soil as roadbed filling. The main factors affecting salt expansion deformation are change of salt, water and temperature. The principal research objectives of this paper is to offer a basic data reference for the structural design of coarse-grained sulfate saline soil roadbed. To investigate the deformation properties of coarse-grained sulfate saline soil under the freeze-thaw-precipitation cycles, the large-scale sample experiments under the freeze-thaw-precipitation cycles and the freeze-thaw cycles were carried out with self-designed experiment equipment. The results showed that under the same freeze-thaw-precipitation cycles experiment conditions, the minimum temperatures of these samples with 1.5% and 3.0% soluble salt contents at a depth of 20 cm were 3.32 °C and 3.56 °C, respectively. In addition, it took less time for the lower salt content (1.5%) sample to reach the same low temperature compared to the higher salt content sample (3.0%). However, after seven freeze-thaw-precipitation cycles, it was shown that deformation of the sample with 1.5% soluble salt content was 32% higher than that with 3.0% soluble salt content. The maximum deformation amount of the coarse-grained sulfate saline soil after repeated freeze-thaw-precipitation cycles experiment was approximately 1.9–9.4 times larger than that after repeated freeze-thaw cycles experiment, which indicated that precipitation had a serious impact on the deformation of the sample. However, there was almost no difference between the lower salt content and higher salt content samples in the residual deformation caused by the cumulative effect of salt expansion in each cycle. Furthermore, the results showed that under the influence of precipitation, a high-level soluble salt content did not necessarily promote expansion deformation of coarse-grained sulfate soil. Water, salt, and temperature have complex coupling effects.

Dynamics and control for in-space assembly robots with large translational and rotational maneuvers

There are two major characteristics of in-space structure assembly missions. First, in order to improve the transport efficiency of assembly robot and reduce the number of structural modules, the size of each structural module is usually designed as large as possible. Second, it is necessary for autonomous assembly robot to quickly transport such large-sized flexible structural modules to the desired locations for integration. However, the coupling effect between the deformation of structural module and large-scale maneuver of robot is inevitably involved during transportation. In this paper, a dynamics modeling method for in-space assembly (ISA) robot with large translational and rotational maneuvers was proposed. The descriptions of dual quaternions were expanded, and a general expression for the dynamics model of rigid-flex system was derived to describe motion of the assembly robot. Innovation of this method is that it considered the complex coupling effect among deformation of structural modules, translational and rotational maneuvers of the assembly robot during transportation in ISA missions. On this basis, the proportional-derivative (PD) controllers were adopted as the in-space structural module assembly method. Finally, taking the ISA of antenna as an example, successful application of the proposed dynamics model and controller to the assembly mission was verified.

Fast coherent integration method for moving target detection with random PRI variation

This Letter addresses the coherent integration problem for the moving target detection in a pulse repetition interval (PRI)-staggered radar system. Due to the random sampling, the complex coupling effects between range and azimuth will severely degrade the target parameter estimation and coherent integration performance. To deal with this issue, a fast coherent integration detection method with random azimuth sampling is proposed, where range migration is firstly compensated by applying the range-frequency reversal transform. Then, the random phase fluctuation caused by the staggered PRI can be efficiently removed by applying the non-uniform FFT technique. Finally, a moving target can be well focused. Simulated results are provided to validate the effectiveness of the proposed algorithm.

Complex coupling effects and dissipative structure in nonlinear thermodynamic systems

It is well known that a dissipative structure can only possibly turn out when the nonlinear system is far away from the equilibrium. In this paper, the instability of steady state in an ideal system with two kinds of irreversible processes has been studied. The most important factor in our discussions is that, in the nonlinear range, both the linear and nonlinear items of the generalized thermodynamic forces have been included in the functional relationship between the generalized thermodynamic flows and forces. Our results show that the complex coupling effect plays a very important role in the instability of steady state: if the coefficient related to complex coupling item is very small, the steady state of the system almost does not lose its stability. The dissipative structure is almost impossible, however, if the coefficient about the complex coupling is very large, it is possible for the steady state to lose its stability. Then a dissipative structure is possible. And, this conclusion was verified by the dynamical analyzing about a chemical monomolecular reaction system with strong complex coupling effects. So the dissipative structure can only possibly turn out in a nonlinear non-equilibrium system which is not only far away from the equilibrium but also is strongly coupled.