An Image Encryption Scheme Based on DNA Computing and Cellular Automata

Networks have developed very quickly, allowing the speedy transfer of image information through Internet. However, the openness of these networks poses a serious threat to the security of image information. The field of image encryption has drawn attention for this reason. In this paper, the concepts of 1-dimensional DNA cellular automata and T-DNA cellular automata are defined, and the concept of reversible T-DNA cellular automata is introduced. An efficient approach to encryption involving reversible T-DNA cellular automata as an encryption tool and natural DNA sequences as the main keys is here proposed. The results of a simulation experiment, performance analysis, and comparison to other encryption algorithms showed this algorithm to be capable of resisting brute force attacks, statistical attacks, and differential attacks. It also enlarged the key space enormously. It meets the criteria for one-time pad and resolves the problem that one-time pad is difficult to save

Nonlinear dynamic characteristic of gear system with the eccentricity

In this paper, the dynamic behavior of a spur gear system was studied with external and internal dynamic incentive. The vibration differential equations for spur gear system were expressed in equivalent discrete models of mass, damping, and spring elements using the Lagrange equation considering the effect of lateral-torsional vibration coupling on the dynamics of gears, which was solved by the Newmark method. The investigation was carried out with multi-degree of freedom system for spur gear model, which took into account gravity, gear eccentricity, backlash, dynamic transmission error and external dynamic incentive. The lateral and torsional response characteristics of geared system were analyzed by changing the value of the rotational speed, backlash and eccentricity. It was shown from the research that the jump discontinuous phenomenon occurred at lower backlash value with increasing rotational speed and the frequency amplitudes also increased, and the regions of continuous frequency became winder when the rotational speed difference was greater. Moreover, complicated combination frequency components followed a rule of increasing firstly and then decreasing with the different backlash and eccentricity. The study may contribute to a further understanding of the dynamic characteristics of such a gear rotor-bearing system

Dynamic coupled vibration analysis of a large wind turbine gearbox transmission system

A lumped-parameter coupled nonlinear dynamic model for one large multi-stage wind turbine gearbox transmission system is established comprehensively including wind varying load, mesh stiffness, dynamic transmission error, gravity, and bearing nonlinear characteristics to obtain the gearbox dynamic response. The vibration differential equations of the drive-train are deduced through the Lagrange’s equation. On the basis of that, the dynamics of wind turbine gearbox is investigated by a Runge-Kutta numerical method that includes simultaneous internal and external excitations. The results show that the dynamic response of the partial component is mainly superposed by high-frequency component caused by the internal excitation and low-frequency component caused by the external excitation. In medium-speed stage and high-speed stage, the vibration amplitude has obvious fluctuation, and the multiple frequency and random frequency components become increasingly obvious with increasing rotational speed and eccentricity at gear and bearing positions. Axial vibrations of the system also have some fluctuation. The bearing has self-variable stiffness frequency, which should be avoided in engineering design stage. The study results provide a theoretical foundation for dynamical characteristics evaluation and dynamic optimization of a large wind turbine gearbox transmission system

Nonlinear behavior of a spur gear pair transmission system with backlash

In this paper, the nonlinear vibration characteristics of spur gear-rotor system and the interactions among of gear shaft, and bearing with backlash subjected to internal/external excitation are systematically investigated. The two-degree-of-freedom purely torsional generalized lumped parameter model of the spur gear system with meshing stiffness, backlash, transmission error and external periodic excitation is established. The Newmark method is used to solve simultaneously the differential equations for analysis the vibration response characteristics as well as the effects of rotational speed, backlash and mesh damping coefficient on the dynamic characteristics of the spur gear system. The numerical results clearly reveal that the system exhibits an increase mesh damping coefficient and a decrease backlash can reduce the degree of gear nonlinearity effect, which makes the meshing state of spur gear system change from double-sided impact, single-sided impact to no impact. In addition, the rotational speed has a significant effect upon the dynamic response of the system, which shows that designing a gear system to operate at a high rotational speed should be avoided especially when the rotational speed is close to the system’s natural frequency and half of the natural frequency. The results presented in this study provide an understanding of the operating conditions under which undesirable dynamic motion takes place in a spur gear system and therefore serve as a useful source of reference for engineers in designing and controlling such systems

Nonlinear behavior of a spur gear pair transmission system with backlash

In order to investigate the nonlinear characteristics of gear transmission system under the action of external and internal excitations, a dynamic model of a spur gear pair was established involving the backlash, damping, transmission error and the meshing stiffness. Based on the incremental harmonic balance method (IHBM), the general forms of the periodic solution with arbitrary precision are deduced. The vibration response obtained by IHBM compare very well with the results obtained by New-Mark method, which verifies the accuracy and electiveness of the analytical methodology (IHBM) and provide information on the dynamic characteristic of spur gear. The simulation results revealed that several types of steady-state periodic solution are identified and determined by employing the IHBM. Due to the effect of backlash, the nonlinear characteristics of jump discontinuity phenomena and multiple stable solutions coexist and the meshing impact phenomenon are obvious. In addition, the influences of the system damping, transmission error and excitation amplitude on the amplitude frequency characteristic are illustrated by a series of diagrams. The results implicate that increasing the external excitation amplitude and system damping can effectively decrease the system resonant amplitude and control the nonlinear vibration response of the gear system and the effect of hardening spring behavior becomes weaker. The transmission error excitation amplitude variation also tends to worse the degree of nonlinearity. Therefore, it presents some useful information to reduce the vibration and noise of gear system

Fractional-Order Time Delay Compensation in Deadbeat Control for Power Converters

Deadbeat control scheme is widely implemented in the control of power electronics and electrical drives, which is of simplification, rapidity and flexibility. However, owing to its sensitive to model uncertainties and unmodeled dynamics, the practical control performance is severely degraded and sometimes even unstable. Uncertain time delay is a typical case of model uncertainties, which severely deteriorates the control accuracy and dramatically reduce the system stability margin of deadbeat control. In this paper, the time delay effects on the control performance and system stability are investigated. A fractional-order Smith Predictor based solution is proposed to compensate arbitrary time delay with high accuracy, simple structure, and good robustness. The composite control scheme offers accurate time delay compensations in digital implementation and considerably enhances the robustness of the control system, which will effectively promote widespread applications of the deadbeat scheme. An application example of three-phase inverter system is explored to comprehensively illustrate the feasibility and effectiveness of the proposed scheme

Nonlinear dynamic analysis for high speed gear-rotor-bearing system of the large scale wind turbine

In this paper, an eight-degree-of-freedom (8-DOF) lumped parameter dynamic model considering the coupled lateral-torsional vibration is proposed and the coupled multi-body dynamics of the spur gear rotor bearing system is studied containing backlash, transmission error, eccentricity, gravity and time-variant mesh stiffness. Based on the dynamical equations, the coupled dynamic response of the system is investigated using the Runge-Kutta method and the effects of error fluctuation and load fluctuation on the dynamic responses are demonstrated by 3-D frequency spectrum bifurcation diagram, etc. The results show that a diverse range of nonlinear dynamic characteristics such as periodic, chaotic behaviors and impacts exhibited in the system are strongly attributed to the interaction between internal and external excitations. For gear system, the dynamic behaviors are analyzed in light, middle and high rotational speed conditions. With the increase rotational speed, the vibration amplitude increase markedly and the region of the chaotic motion become narrow gradually. At the low rotational speed, the chaos behavior turns out more easily, and the vibration intensity relatively weak. With the increase rotational speed, the vibration amplitude obvious increase, and the characteristics of the chaos strengthen and turns backward. This study may contribute to a further understanding about the spur gear bearing system with the coupled internal and external excitation