The corrosion behavior of HR230 and 740 H alloys in CO2 with 7% H2O environment at 1000 ℃ were investigated. Some TiO2 oxides and Al2O3 internal oxides were observed on the surface and in the matrix ...of 740 alloy respectively, which caused the weight gain of 740 H alloy was higher than that of HR230 alloy. The chemical adsorption capacity of H2O molecules on the surfaces of both alloys was stronger than that of CO2 molecules. The H2O molecule preferentially reacted with both alloys to form a Cr2O3 oxide layer, while the delayed CO2 molecule caused the internal oxidation of Al.
•The corrosion behavior of HR230 and 740 H alloys in CO2 with 7% H2O at 1000 ℃ were investigated.•TiO2 oxides and Al2O3 internal oxides were formed on the surface and in the matrix of 740 alloy respectively.•The volatile CrO2(OH)2 oxides were formed on the surface of Cr2O3 oxide layer.•The adsorption capacity of H2O molecules on the surfaces of both alloys was stronger than that of CO2 molecules.•The internal oxidation behavior of Al was mainly caused by CO2 molecules.
The dynamics of a hyperelastic splitter plate interacting with the laminar wake flow of a circular cylinder is investigated numerically at a Reynolds number of 80. By decreasing the plate’s ...stiffness, four regimes of flow-induced vibrations are identified: two regimes of periodic oscillation about a symmetric position, separated by a regime of periodic oscillation about asymmetric positions, and finally a regime of quasi-periodic oscillation occurring at very low stiffness and characterized by two fundamental (high and low) frequencies. A linear fully coupled fluid–solid analysis is then performed and reveals the destabilization of a steady symmetry-breaking mode, two high-frequency unsteady modes and one low-frequency unsteady mode, when varying the plate’s stiffness. These unstable eigenmodes explain the emergence of the nonlinear self-sustained oscillating states and provide a good prediction of the oscillation frequencies. A comparison with nonlinear calculations is provided to show the limits of the linear approach. Finally, two simplified analyses, based on the quiescent-fluid or quasi-static assumption, are proposed to further identify the linear mechanisms at play in the destabilization of the fully coupled modes. The quasi-static static analysis allows an understanding of the behaviour of the symmetry-breaking and low-frequency modes. The quiescent-fluid stability analysis provides a good prediction of the high-frequency vibrations, unlike the bending modes of the splitter plate in vacuum, as a result of the fluid added-mass correction. The emergence of the high-frequency periodic oscillations can thus be predicted based on a resonance condition between the frequencies of the hydrodynamic vortex-shedding mode and of the quiescent-fluid solid modes.
In this paper, the problem of minimizing the weighted sum of age of information (AoI) and total energy consumption of Internet of Things (IoT) devices is studied. In the considered model, each IoT ...device monitors a physical process that follows nonlinear dynamics. As the dynamics of the physical process vary over time, each device should find an optimal sampling frequency to sample the real-time dynamics of the physical system and send sampled information to a base station (BS). Due to limited wireless resources, the BS can only select a subset of devices to transmit their sampled information. Thus, edge devices can cooperatively sample their monitored dynamics based on the local observations and the BS will collect the sampled information from the devices immediately, hence avoiding the additional time and energy used for sampling and information transmission. To this end, it is necessary to jointly optimize the sampling policy of each device and the device selection scheme of the BS so as to accurately monitor the dynamics of the physical process using minimum energy. This problem is formulated as an optimization problem whose goal is to minimize the weighted sum of AoI cost and energy consumption. To solve this problem, we propose a novel distributed reinforcement learning (RL) approach for the sampling policy optimization. The proposed algorithm enables edge devices to cooperatively find the global optimal sampling policy using their own local observations. Given the sampling policy, the device selection scheme can be optimized thus minimizing the weighted sum of AoI and energy consumption of all devices. Simulations with real PM 2.5 pollution data show that the proposed algorithm can reduce the sum of AoI by up to 17.8% and 33.9%, respectively, and the total energy consumption by up to 13.2% and 35.1%, respectively, compared to a conventional deep Q network method and a uniform sampling policy.
The objective of this work is to verify the accuracy of indirect pressure measurement from particle image velocimetry in water entry problems. The pressure is evaluated by solving the incompressible ...Navier–Stokes equations, whose kinematic components are estimated from particle image velocimetry. We focus on the water entry of a rigid wedge, for which we explore variations of the entry velocity. Experimental results are verified through comparison with well-established analytical formulations based on potential flow theory. Our findings demonstrate the feasibility of accurately reconstructing the hydrodynamic pressure field over the entire duration of the impact. Along with a thorough experimental validation of the method, we also offer insight into experimentally relevant factors, such as the maximum resolved fluid velocity and the required spatial integration area.
This Review illustrates the evaluation of permeability of lipid membranes from molecular dynamics (MD) simulation primarily using water and oxygen as examples. Membrane entrance, translocation, and ...exit of these simple permeants (one hydrophilic and one hydrophobic) can be simulated by conventional MD, and permeabilities can be evaluated directly by Fick’s First Law, transition rates, and a global Bayesian analysis of the inhomogeneous solubility-diffusion model. The assorted results, many of which are applicable to simulations of nonbiological membranes, highlight the limitations of the homogeneous solubility diffusion model; support the utility of inhomogeneous solubility diffusion and compartmental models; underscore the need for comparison with experiment for both simple solvent systems (such as water/hexadecane) and well-characterized membranes; and demonstrate the need for microsecond simulations for even simple permeants like water and oxygen. Undulations, subdiffusion, fractional viscosity dependence, periodic boundary conditions, and recent developments in the field are also discussed. Last, while enhanced sampling methods and increasingly sophisticated treatments of diffusion add substantially to the repertoire of simulation-based approaches, they do not address directly the critical need for force fields with polarizability and multipoles, and constant pH methods.
The revolute pair and translational pair are the two most important kinematic pairs in planar mechanism. Their clearances directly affect the accuracy of planar mechanism. In addition, flexible ...components will also lead to a certain degree of vibration and shaking of the mechanism, which will seriously affect the stability. In this paper, considering the coupling effect of revolute clearance pair, translational clearance pair and elastic deformation of components, an accurate dynamic modeling method of rigid-flexible coupling multi-link mechanism (MLM) considering revolute clearance and translational clearance is proposed to accurately predict the nonlinear behavior. Clearance models of revolute pair and translational pair are established, the flexible element model is established based on the absolute node coordinate formulation (ANCF), and the nonlinear dynamic equation of rigid-flexible coupling six-bar mechanism considering the clearance of revolute pair and translational pair is built by Lagrange multiplier method (LMD). Dynamic response and chaos identification are researched. Chaos identification is determined qualitatively and quantitatively by phase diagram, Poincaré map and largest Lyapunov exponent. Influences of different clearance values and driving speeds on nonlinear dynamic behavior of mechanism are discussed. Bifurcation diagrams varying with clearance size and driving velocity are studied, respectively. Dynamic modeling method is compared and verified by ADAMS. The experimental platform of six-bar mechanism is built to further verify the correctness of theoretical model.
The paper aims to establish a general framework for robust output synchronization of a group of networked agents. The agents under investigation have nonlinear, uncertain and heterogeneous dynamics. ...Output synchronization denotes that all agents, through collaborative control, achieve output agreement and follow a desired pattern. In particular, the agreed trajectory is not defined by nor known to any agent in advance. Collaborative control is achieved using only output information from neighboring agents. Two concurrent actions are revealed in the proposed synchronization framework. This framework involves design strategies for both perturbed consensus and perturbed regulation problems, subject to a class of small gain conditions. The success of the framework is verified by constructive proof and numerical simulation.
•A unified dynamic model of eccentric curve-face gear system was established.•Dynamic equation was derived through Lagrange bond diagram.•The dynamic response of the system is a highly nonlinear ...process•The gear eccentricity can modulate both amplitude and frequency.•Frequency components and amplitudes of different tooth profiles were different.
This paper establishes a dynamic model and a Lagrange bond diagram model for the eccentric curve-face gear transmission system. The dynamic model includes a gear meshing model, a lumped-parameter supporting model, a drive and a load, etc. Considering the impact of cam effect and inertia force caused by gear eccentricity, the dynamic equations are established based on the Lagrange bond diagram model. Moreover, the parameters of the model are analyzed deeply, the effects of gear eccentricity, helical angle, tooth profile of gear pairs, and input velocity on the vibration response in time and frequency domain are studied. It is found that the dynamic response of the eccentric curve-face gear transmission system is a highly nonlinear process. The gear eccentricity can modulate both amplitude and frequency. Introducing a force-locking spring in the eccentric curve-face gear transmission system with helical-teeth will negatively affect the system, resulting in the increase of vibration amplitude. The time-varying helical angle of the eccentric curve-face gear transmission system with circle-arc teeth will also have a negative effect on the dynamic characteristics and cause more small pulses. The axial dynamic response, bending dynamic response, and torsion dynamic response are more sensitive than the radical dynamic response to the change of helical angle. Finally, the correctness of numerical analysis was verified through experimental studies.
The elastic hydraulic isolator is a novel liquid-gas mixture isolator applied to floating slab track structure. The dynamic parameters of isolators are the key to the attenuation effect of ground ...vibration. Therefore, a nonlinear dynamic model and parameter identification method for vibration isolation supports of floating slab track structure is proposed. The changes in stiffness and damping parameters of the elastic hydraulic isolator are studied by changing its damping components and comparing them with those of the steel spring isolator and rubber isolator. The results indicate that the accuracy of the nonlinear dynamic model is verified by comparing the experimental curve with the reconstructed curve. The dynamic parameters of the elastic hydraulic isolator are dependent on the excitation frequency and amplitude and are influenced by the liquid viscosity and the damping plate. The stiffness and damping parameters of the elastic hydraulic isolator are similar to those of the rubber isolator, but the variation law with excitation frequency is different.
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