Nonlinear vibration behaviors of marine rotor system coupled with floating raft-airbag-displacement restrictor under ship heaving motion

To study the nonlinear vibration behaviors of rotor system coupled with floating raft-airbag-displacement restrictor under ship heaving motion, the dynamic model is established considering the effect of heaving motion, its steady-state responses are numerically obtained using Runge-Kutta method and the results are surveyed by tools such as the spectrum waterfall diagram, time-domain response, frequency-domain response, axis orbit, and Poincaré map. The effects of rotating speed, ship heaving amplitude, and its frequency on the nonlinear dynamic behavior of the system are mainly studied. The results show that the responses of the rotor and raft are of obvious nonlinear behaviors such as amplitude jumping, bifurcation, and chaos due to the effects of nonlinear oil film force and ship heaving motion. With the increase of rotating speed, the motion of rotor and raft presents quasi-periodic and chaotic vibrations. Ship heaving amplitude and its frequency all have great effect on the vibration of rotor and raft; as heaving amplitude or frequency increases, the motion state of rotor and raft changes, and the amplitude of raft increases significantly. The displacement restrictor can effectively limit the vibrating displacements of the raft when ship heaving amplitude or its frequency is large.

Introduction to the method of estimating time-domain response based on amplitude-frequency characteristics

How to use the amplitude-frequency characteristics to reconstruct the signal to obtain the time-domain response has always been a concern in the field of nuclear electromagnetic protection. So far, in practical applications, parametric modeling and non-parametric modeling have been used to solve related problems. This article summarizes the research and development of using amplitude-frequency characteristics to recover time-domain signals in the field of nuclear electromagnetic pulse protection, and briefly introduces the shortcomings of the two methods in combination with specific experiments.

Determination of Natural Frequency and Critical Velocity of Inclined Pipe Conveying Fluid under Thermal Effect by Using Integral Transform Technique

This study proposes an analytical solution of natural frequencies for an inclined fixed supported Euler-Bernoulli pipe containing the flowing fluid subjected to thermal loads. The integral transform technique is employed to obtain the spatial displacement-time domain response of the pipe-fluid system. Then, a closed-form analytical expression is presented. The effects of various geometric and system parameters on the vibration characteristics of pipe-fluid system with different flow velocities are discussed. The results illustrate that the proposed analytical solution agrees with the solutions achieved in previous works. The proposed model predicts that the pipe loses the stability by divergence with the increasing flow velocity. It is evident that the influences of inclination angle and temperature variation are dramatically increased at a higher aspect ratio. Additionally, it is demonstrated that the temperature variation becomes a more harmful effect than the internal fluid velocity on the stability of the pipe at elevated temperature.

Active impulsive disturbance rejection and oscillation control of robot manipulator, using nonclassical rod models and proportional integral derivative controller

Micro-electro-mechanical-systems scale robots are prone to impulsive disturbances during operation. Such disturbance leads to adverse oscillations of the robot manipulator. So, it is essential to mitigate and control such unwanted oscillations. On the other hand, to capture size dependencies of such robot elements, it is required to adopt nonclassical models. To address these cases, robot manipulator is modeled as a mechanical rod, comprehensive rod models are utilized, proportional integral derivative (PID) controller is designed, and the time-domain response of the system is simulated in MATLAB. Results show that adopting proper gain values of the PID controller leads to total rejection of the pulsive disturbances. However, findings conceal the importance of the nonclassical rod model such that strain gradient (SG) model shows less oscillatory amplitude than the classical theory (CT) model. While considering the nonlocal model effects (NL), such undesired vibrations are bigger than CT model. In other words, meanwhile, a simple PID controller can reject the disturbance for SG models; a stronger controller should be adopted to reject such pulsive disturbances with NL models. Eventually, it is valuable to note that to suppress unwanted oscillations in small-sized robots, PID closed-loop feedback controller is a decent choice because of the simplicity and less costs. Application of successful control design alongside the proper nonclassical theory leads to neutralizing the disturbances and increases the robot manipulator precision.

A novel and robust technique for identifying prestress forces in prestressed concrete beams using generic finite elements and simulated annealing algorithms

This work presents a novel technique for estimating the prestressing forces in simply supported beams with axial prestress force. The technique is based on the use of generic finite elements for modeling the beam and experimental time-domain response to simultaneously identify axial forces and generic parameters. Parameter updating is accomplished using a Simulated Annealing algorithm implemented for the solution of the prestress force identification problem. The effectiveness of the method was assessed in numerical simulations and was further verified on an experimental prestressed concrete beam. The results show that the inclusion of generic elements allows the identification of the force to be achieved even in the presence of errors in model parameters, thus eliminating the restraints of previous approaches.

Analysis of periodically switched nonlinear circuits and nonlinear oversampled sigma-delta modulators

This thesis proposes a new method for time domain response and sensitivity analysis of periodically switched nohnlinear circuits and nonlinear oversampled sigma-delta modulators. Using Volterra functional series and interpolating Fourier series, it extends the sampled datasimulation and two-step algorithm of linear circuits to periodically switched nonlinear circuits. The method can handle the inconsistent initial conditions encountered at switching instants. It is applied to the analysis of nonlinear oversampled sigma-delta modulators. The efficiency and accuracy of the proposed method are assessed using SPICE, brute-force, and the law of charge conservation on periodically switched nonlinear circuits, and nonlinear oversampled sigma-delta modulators. The method does not require the costly Newton-Raphson iterations. It is most efficient for analysis of circuits with mildly nonlinear characteristics and simulation over a long period of time.

Analysis of periodically switched nonlinear circuits and nonlinear oversampled sigma-delta modulators

This thesis proposes a new method for time domain response and sensitivity analysis of periodically switched nohnlinear circuits and nonlinear oversampled sigma-delta modulators. Using Volterra functional series and interpolating Fourier series, it extends the sampled datasimulation and two-step algorithm of linear circuits to periodically switched nonlinear circuits. The method can handle the inconsistent initial conditions encountered at switching instants. It is applied to the analysis of nonlinear oversampled sigma-delta modulators. The efficiency and accuracy of the proposed method are assessed using SPICE, brute-force, and the law of charge conservation on periodically switched nonlinear circuits, and nonlinear oversampled sigma-delta modulators. The method does not require the costly Newton-Raphson iterations. It is most efficient for analysis of circuits with mildly nonlinear characteristics and simulation over a long period of time.

Implementation of non-isolated three-port converter through augmented time response

<p><span lang="EN-US">The work is concerning a multi-port dc-dc converter with improved time response and steady state output. Here the converter carries bare amount of switches for managing the power with mono inductance. The inductance and along with that the switched capacitance are pre owned to bring large voltage gain. This paper put forwarded an appropriate controller for the closed loop monitored high-gain converter with three ports. Higher is that the conversion rate. This converter is also a good interface between DC-source and load that aims to progressing time response with FLC and PI controller in the closed loop system. The converter with the PI controller and FLC is look over and the fast responses are compared with time domain specifications. The simulation outcome indicates that the FLC based converter brings most excellent time domain response.</span></p>