RBF-based supervisor path following control for ASV with time-varying ocean disturbance

1028-1036A robust model-free path following controller is developed for autonomous surface vehicle (ASV) with time-varying ocean disturbance. First, the geometrical relationship between ASV and virtual tracking point on the reference path is investigated. The differentiations of tracking errors are described with the relative motion method, which greatly simplified the direct differential of tracking errors. Furthermore, the control law for the desired angular velocity of the vehicle and virtual tracking point are built based on the Lyapunov theory. Second, the traditional proportional-integral-derivative (PID) controller is developed based on the desired velocities and state feedback. The radial basic function (RBF) neural network taking as inputs the desired surge velocity and yaw angular velocity is developed as the supervisor to PID controller. Besides, RBF controller tunes weights according to the output errors between the PID controller and supervisor controller, based on the gradient descent method. Hence, PID controller and RBF supervisor controller act as feedback and feed forward control of the system, respectively. Finally, comparative path following simulation for straight path and sine path illustrate the performance of the proposed supervisor control system. The PID controller term reports loss of control even in the unknown disturbance

Dimensional Analysis Theory and Molecular Dynamics Simulation of Polypropylene Melt Flow during Injection Molding Process

Flow marks are common surface defects that occur in injection-molded products. Their formation may be related to the flow process of the melt in the mold. Through dimensional analysis, we have discovered that the geometric shape of the flow field is controlled by specific dimensionless quantities. These quantities can be summarized as follows: geometric dimensionless quantities related to the shape of the mold, material dimensionless quantities related to the melt and mold materials, and physical dimensionless quantities related to the flow. When the geometric shape of the mold changes proportionally, with the melt and mold material fixed, and the initial temperature of the melt and mold fixed, the geometric shape of the flow field will be solely controlled by the Weissenberg number Wi. If Wi is kept constant, changing the injection speed, changing the relaxation time of the polypropylene melt, or scaling the mold will result in similar geometric shapes of the flow field. If the size of the mold is not changed, the geometric shape of the flow field will be the same. Since the dimensionless equation represents a similar system of all sizes, we verified the above conclusion through molecular dynamics simulations at a smaller scale. After further improvement of the micro simulation system, there is a possibility of visualizing the formation process of flow marks. This would greatly aid in the advancement of theory and the elimination of flow marks in production and experiments. This work also illustrates that the methodology of dimensional analysis plus molecular dynamics simulation may be applied to a wider range of other systems, scaling down large systems and thus significantly reducing their computational effort

Underwater dual manipulators-Part I: Hydrodynamics analysis and computation

1098-1103This paper introduces two 4-DOF underwater manipulators mounted on autonomous underwater vehicle (AUV) with grasping claws, such that the AUV can accomplish the underwater task by using dual manipulators. Mechanical design of the manipulator is briefly presented and the feature of the simple structure of dual manipulators is simulated by using Solid Works. In addition, the hydrodynamics of the manipulator is analyzed, considering drag force, added mass and buoyancy. Then, hydrodynamic simulations of the manipulator are conducted by using 3-D model with Adams software, from which the torque of each joint is calculated. This paper presents an integrated result of computed torques by combining the theoretical calculation and simulation results, which is instrumental in determining the driving torque of the manipulators

Underwater dual manipulators-Part II: Kinematics analysis and numerical simulation

1104-1112This paper introduces dual-arm underwater manipulators mounted on an autonomous underwater vehicle (AUV), which can accomplish the underwater handling task. Firstly, the mechanical structure of the dual-arm system is briefly introduced, wherein each 4-DOF manipulator has an additional grasping function. In addition, the kinematics model of the manipulator is derived by using the improved D-H method. Secondly, the working space of the underwater dual-arm system is analyzed, which is obtained by using Monte Carlo method. The cubic polynomial interpolation and the five polynomial interpolation trajectory planning methods are compared in the joint space. Finally, with the help of the Robotics Toolbox software, the numerical test is conducted to verify the functions of the underwater dual-arm manipulator system

Pilot test of a fermentation tank for producing coal methane through anaerobic fermentation

The development and utilization of clean energy has long been a focus of research. In the coal bed methane field, most coal bed biogenic methane experiments are small static sample tests in which the initial conditions are set and the process cannot be batch-fed elements and microbial strains, and the gas cannot be collected in batches. Although significant results have been achieved in the coal-to-biogenic methane conversion in China, findings are restricted to the laboratory scale. No successful commercialization of coal bed biogenic methane production has been achieved yet. This study used a large-capacity fermentation tank (5 L) to conduct biogenic methane experiments. Results were compared to those from the traditional laboratory test. The gas production rate and gas concentration were higher when the 250 mL methane test volume was increased to a 5 L fermentation volume, increasing by 20.9% and 2.3%, respectively. The inhibition effect of the liquid phase products was reduced in the large fermentation tank, and the microbial activity was extended by batch feeding trace elements (iron and nickel) and methane strains and by semi-continuous collection of the gas. However, the gas conversion rate can be increased by retaining the H2 and CO2 in the intermediate gas products in the fermentation tank. The gas production rate was increased from 17.9 to 24.6 mL/g, increasing by 37.4%. The simulation pilot test can lay a foundation for the transition from a coal bed biogenic methane laboratory static small sample test to a dynamic pilot test, optimizing the process parameters to improve the reaction efficiency and move forward to commercialization test

On stochastic dynamic analysis and assessment of bistable structures

This paper investigates some basic issues on the stochastic dynamic analysis and assessment of bistable structures from an applications perspective, illustrated with a classical spring–mass–rod structure. A complete Lagrangian-description-based Monte Carlo simulation and an Eulerian-description-based Fokker–Planck equation analysis are implemented, respectively, to capture the evolution process of the physical response probability density function, with special focus on the dynamics under the statistical steady state condition. A comparison of these two methods outlines their capabilities. As a representative example, quantitative counting and statistical analysis of the number and amplitudes of snapping-through of the structure indicate that physical quantities for structural assessment may show certain statistical regularities under the statistical steady state condition, which can be utilized efficiently to reduce the efforts of structural assessment without loss of precision

Density Functional Theory of Molecular Structure and Properties of Fatty Acid Collectors

This is an article in the field of mineral processing engineering. Fatty acid collectors are widely used in the flotation of oxidized ores, and the molecular structure is an important factor affecting the flotation performance. To reveal the effect of the structural change of fatty acid collector on its reaction activity from the microscopic point of view, the relationship between electronic structure and properties of fatty acid collectors was studied by the density functional theory. The research results show that the oxygen atom in oleic acid molecule and oleate ion has strong reaction activity, which is the bonding atom of oleic acid interaction with oxidized minerals. The two oxygen atoms of oleate ion have similar chemical activity, and the density of states at Fermi level is higher than that of oleic acid molecule, which makes the activity of oleate ion much stronger than that of oleic acid molecule. The length of the carbon chain and the unsaturation of the alkyl have almost no effect on the density of states of the oxygen atoms in fatty acids, their effect on the properties of fatty acids is not through the action of carboxyl groups. The interaction energy between fatty acids and common metal cations is consistent with the decrease of their solubility product constants, and there is a good corresponding relationship between them. The research has certain theoretical significance and reference value for understanding the relationship between the structure and performance of fatty acid collectors and developing new fatty acid collectors

Correlative study on retinal microvascular changes and sex hormones in male patients with central serous chorioretinopathy

Central serous chorioretinopathy (CSC) is a disease in which the outer retinal barrier is damaged with high incidence in young adult males. We aimed to analyze the correlations between retinal microvascular changes and sex hormone levels. The vascular density of the superficial retinal capillary plexus (SCP), deep retinal capillary plexus (DCP), foveal avascular zone (FAZ) area, choriocapillary blood flow area, and the subfoveal choroidal thickness (SCT) were investigated by optical coherence tomography angiography (OCTA). We also determined the levels of sex hormones (adrenaline (AD), norepinephrine (NE), dopamine (DA), corticosteroids (Cor), aldosterone (ALD), estradiol (E2) and total testosterone (TT)). The relationship between sex hormone levels and OCTA parameters was then determined. We detected significantly higher levels of NE, Cor and TT in serum from the observation group than in the control group (p < 0.05). Significant correlations were identified between SCT and choriocapillary blood flow area in the affected eyes, contralateral eyes and healthy eyes in the control group (p < 0.05). SCT levels of both eyes in the observation group were higher and the choriocapillary blood flow area was smaller than in the control group. The SCT in affected eyes from the observation group were higher than the contralateral eyes (p < 0.05). The choriocapillary blood flow area was significantly smaller than in the contralateral eyes (p < 0.05). Correlation analysis unveiled that NE, Cor and TT levels were positively correlated with SCT in CSC patients and negatively correlated with choriocapillary blood flow area (p < 0.05). The serum levels of sex hormone levels in male CSC patients were different from those in healthy men of the same age. Our findings suggest that the serum levels of NE, Cor and TT levels may influence the pathogenesis of CSC by affecting SCT thickness and choriocapillary blood flow