Adaptive region tracking control for underwater vehicles with large initial deviation and general uncertainty

A region tracking control system is developed for underwater vehicles with large initial deviation and general uncertainty. The developed system is a nonlinear cascaded system, consisting of two subsystems in series. The fixed-gain controller of the first subsystem is designed to compensate for the region tracking error caused by the large initial deviation. In the second subsystem, the radial basis function neural network is adopted to approximate the general uncertainty along with the external disturbance and modelling uncertainty. According to the Lyapunov theory, the control law of the two subsystems and adaptive law of the second subsystem are derived to ensure the region tracking errors asymptotically converge to zero. The validity of the control system is verified by a series of comparisons on simulation results.

Influence of Temperature on the Bolt Loads and Variation in a Bolted Flange for Subsea Pipeline Connection

This article proposed an analytic and finite element-combined modelling method for the investigation of temperature effects on bolt loads and variation in a bolted flange for subsea pipeline connection. With this method, the preloads of bolt in the bolted flange assembly were investigated under different medium liquid temperatures in the pipeline. The simulation results illustrate that the deviation of bolt loads can be increased due to the medium liquid temperature increasing. The final bolt load deviation increases along with the increasing of the initial deviation of bolt preloads in a constant medium liquid temperature. The final distribution of bolt loads can be affected by the initial condition of the bolts. When bolt preloads are staggered, the variance of the final bolt loads is minimized; when the bolt preloads are axisymmetric, the final bolt load variance is the maximum.

Design of Robotic Motion Platform utilising Continuous Contact Skating

The continuous contact-based skating technique utilises the sideways movement of the two skates while changing the orientation of the two skates simultaneously. The skates remain in contact with the surface. A mathematical model mimicking a continuous skating technique is developed to analyse the kinematic behaviour of the platform. Kinematic and dynamic equations of motion are derived for the impending non-holonomic constraints. Heuristic-based motion primitives are defined to steer the robotic platform. For the lateral movement of the platform, a creeping based motion primitive is proposed. A prototype of the robotic platform is developed with three actuated degrees of freedom – orientation of two skates and distance between them. A multibody model of the platform is also developed in MATLAB. Analytical expressions are verified to be useful using the simulation and experimental results. The robotic platform follows the desired motion profiles. However, the initial deviation has been observed in both the simulations and experiments due to the slipping of the roller skate at the contact point with the surface. The platform can be effectively used in a structured environment autonomously.

Bilateral combined resection-recession of the same rectus muscle versus Fadenoperation for treatment of purely tonic esotropias

Purpose: To compare the efficiency of bilateral combined resection-recession surgery of the medial rectus muscle versus using a modified Fadenoperation for surgical management of esotropias that totally resolve under general anesthesia, which we called “purely tonic” esotropias. Methods: We included 65 unselected consecutive cases of patients with purely tonic esotropias who underwent surgery between October 2017 and 2018. Patients were divided into group I, who underwent a combined resection and recession of medial recti muscles, and group II, who underwent a bilateral medial rectus Fadenoperation using posterior strapping. A satisfactory outcome was defined as deviation ⩽10 prism diopters (PD), at near and distance fixation, between 3 and 6 months postoperatively. Results: Mean initial deviation was in group I, 19.6 PD and 32.0 PD, in group II, 23.6 PD and 33.5 PD, at distance and near fixation respectively. Postoperatively, in group I, 31 patients (91.2%) showed satisfactory alignment at near and distance fixation. Post-operatively, in group II, 25 patients (80.6%) showed satisfactory alignment at near and distance fixation. Conclusion: Our results suggest both techniques are good options to treat purely tonic esotropias.

ON OSCILLATIONS DESCRIBING A GENERALIZED DIFFERENTIAL RELAY EQUATION

The motion of an oscillatory system with one degree of freedom, described by the generalized Rayleigh differential equation, is considered. The generalization is achieved by replacing the cubic term, which expresses the dissipative strength of the equation of motion, by a power term with an arbitrary positive exponent. To study the oscillatory process involved the method of energy balance. Using it, an approximate differential equation of the envelope of the graph of the oscillatory process is compiled and its analytical solution is constructed from which it follows that quasilinear frictional self-oscillations are possible only when the exponent is greater than unity. The value of the amplitude of the self-oscillations in the steady state also depends on the value of the indicator. A compact formula for calculating this amplitude is derived. In the general case, the calculation involves the use of a gamma function table. In the case when the exponent is three, the amplitude turned out to be the same as in the asymptotic solution of the Rayleigh equation that Stoker constructed. The amplitude is independent of the initial conditions. Self-oscillations are impossible if the exponent is less than or equal to unity, since depending on the initial deviation of the system, oscillations either sway (instability of the movement is manifested) or the range decreases to zero with a limited number of cycles, which is usually observed with free oscillations of the oscillator with dry friction. These properties of the oscillatory system are also confirmed by numerical computer integration of the differential equation of motion for specific initial data. In the Maple environment, the oscillator trajectories are constructed for various values of the nonlinearity index in the expression of the viscous resistance force and a corresponding comparative analysis is carried out, which confirms the adequacy of approximate analytical solutions.

On the Behavior of the Generalized Alignment Index (GALI) Method for Regular Motion in Multidimensional Hamiltonian Systems

We investigate the behavior of the Generalized Alignment Index of order k (GALIk ) for regular orbits of multidimensional Hamiltonian systems. The GALIk is an efficient chaos indicator, which asymptotically attains positive values for regular motion when 2≤k ≤N, with N being the dimension (D) of the torus on which the motion occurs. By considering several regular orbits in the neighborhood of two typical simple, stable periodic orbits of the Fermi-Pasta-Ulam-Tsingou (FPUT) β model for various values of the system's degrees of freedom, we show that the asymptotic GALIk values decrease when the order k of the index increases and when the orbit's energy approaches the periodic orbit's destabilization energy where the stability island vanishes, while they increase when the considered regular orbit moves further away from the periodic one for a fixed energy. In addition, by performing extensive numerical simulations we show that the behavior of the index does not depend on the choice of the initial deviation vectors needed for its evaluation.

Trajectory Planning and Tracking for Carrier Aircraft-Tractor System Based on Autonomous and Cooperative Movement

The solution of how to plan out the cooperative moving trajectory autonomously and control the motion of carrier-based aircraft timely and accurately is the key to helping improve the overall deck operation efficiency. The main problem discussed in this article is coordinated trajectory planning strategy for multicarrier aircraft and cooperative control between tractor and carrier aircraft. First, the kinematic model and three-degree-of-freedom dynamics model of the towbarless traction system are established. Then, a coevolution mechanism for aircraft systems is proposed to ensure coordinated trajectory planning among multiple aircraft and a trajectory adapted to the tractor-aircraft system is generated based on the hybrid RRT∗ algorithm. Next, a double-layer closed-loop controller is designed for the trajectory tracking of the tractor-aircraft system on the deck under the constraints of incomplete constraints and various physical conditions. It includes an outer model predictive controller which effectively controls the cooperative motion between the carrier aircraft and tractor and an inner torque control strategy based on adaptive fuzzy PID control which strictly ensures the stability of the system. Simulation results demonstrate that the controller is more rapid, more accurate, and more robust in tracking line trajectory with initial deviation, sine curve with large curvature, and complex trajectories on decks compared with backstepping control and LQR algorithm.

Effect of the Magnetic Force on Ferrite Pendulum Oscillation Parameters: Parametric Analysis on Ferrite Pendulum

The magnitude of the damping force of the mathematical pendulum swinging on a medium is usually proportional to the speed of the pendulum. In this research, the pendulum oscillation parameters oscillating on an air medium under the influence of a magnetic field of 1.8 G will be investigated. In the initial stage, the effect of the magnetic force on the damping coefficient of ferrite pendulum oscillations with an initial deviation of 15 degrees observed. Furthermore, the study continued with varying the angle of deviation from 5 degrees to 25 degrees. The results of the data fitting amplitude (xi) at various swing times (ti) are using to analyze the effect of the angle of deviation on the maximum amplitude. The results showed that for the deviation angle of 15o the coefficient of damping of the medium affected by the magnetic force was 0,0022 greater than the coefficient of air damping 0,00006. It affects the amplitude, which decreases faster than the pendulum amplitude without the influence of magnetic force. Variation in the angle of deviation also affects the amplitude of the pendulum. In the deviation angle below 10, the pendulum motion is more influenced by the magnetic force, whereas in the deviation above 10, the pendulum motion is more dominated by gravity.

Retrieval dynamics of recognition and rejection

Recognition memory is often viewed as the end-product of discrete cognitive events, involving the combination of latent operations such as the assessment of memory strength, the decision time, and the memory judgement. Recently, researchers have begun using the physical dynamics of memory retrieval to provide insight into the dynamic, possibly non-discrete, processes that underlie memory decisions. In this study, the underlying distributional properties of targets and lures were manipulated by populating lists with items drawn from either homogeneous or heterogeneous word frequency and context variability ranges. In all conditions, participants’ x-, y-mouse coordinates were recorded as they processed test items, allowing estimates of response dynamics (e.g., initial deviation and area under the curve [AUC]), and eventual old/new responses. The stimulus manipulations affected the distribution shapes and, to a greater degree, the placements of subjective confidence thresholds. We observed tight correspondences between confidence and AUC for both hits and correct rejections. We interpret these results within dynamic models of recognition memory.