A priori estimates for solutions to nonlinear elliptic equations

Communicated by P. H. Rabinowitz     

A priori estimates for excitable models

An integro-differential operator $\mathcal{L}$ which models several phenomena in viscoelasticity, biology and superconductivity is considered. The initial-boundary problems with Neumann, Dirichlet and mixed boundary conditions are analyzed and results on existence, uniqueness and a priori estimates are achieved. As example of equivalence among $\mathcal{L}$ and various p.d.e. systems, the FitzHugh-Nagumo model is considered and results are applied both in the linear case and in the non linear one.     

An unconditionally stable time integration method with controllable dissipation for second-order nonlinear dynamics

Nonlinear Dynamics - This paper proposes a two-sub-step time integration method with controllable dissipation to solve nonlinear dynamic problems. The proposed method has second-order accuracy,...     

Closed set of the uniqueness conditions and bifurcation criteria in generalized coupled thermoplasticity for small deformations

This paper reports the results of a study into global and local conditions of uniqueness and the criteria excluding the possibility of bifurcation of the equilibrium state for small strains. The conditions and criteria are derived on the basis of an analysis of the problem of uniqueness of a solution involving the basic incremental boundary problem of coupled generalized thermo-elasto-plasticity. This work forms a follow-up of previous research (?loderbach in Bifurcations criteria for equilibrium states in generalized thermoplasticity, IFTR Reports, 1980, Arch Mech 3(35):337–349, 351–367, 1983), but contains a new derivation of global and local criteria excluding a possibility of bifurcation of an equilibrium state regarding a comparison body dependent on the admissible fields of stress rate. The thermal elasto-plastic coupling effects, non-associated laws of plastic flow and influence of plastic strains on thermoplastic properties of a body were taken into account in this work. Thus, the mathematical problem considered here is not a self-conjugated problem.     

Highly computationally efficient parameter estimation algorithms for a class of nonlinear multivariable systems by utilizing the state estimates

This paper investigates the parameter estimation issue for an input nonlinear multivariable state-space system. First, the canonical form of the input nonlinear multivariable state-space system is obtained through the linear transformation and the over-parameterization identification model of the considered system is derived. Second, by cutting down the redundant parameter estimates and extracting the unique parameter estimates from the parameter estimation vector in the least-squares identification method, we present an over-parameterization-based partially coupled average recursive extended least-squares parameter estimation algorithm to estimate the parameters. As for the unknown states in the parameter estimation algorithm, a new state estimator is designed to generate the state estimates. Third, in order to improve the computational efficiency of the parameter estimation algorithm, an over-parameterization-based multi-stage partially coupled average recursive extended least-squares algorithm is proposed. Finally, the computational efficiency analysis and the simulation examples are given to verify the effectiveness of the proposed algorithms.

     

单步Newmark预测-校正算法无条件稳定的充分必要条件的论证

应用判别差分方程稳定性的Schur－Cohn准则，研究用于一般耦合系统动力响应分析的单步Newmark预测－校正算法的稳定性问题；给出了算法无条件稳定的充分必要条件的严格理论证明。     

A criterion for the stability of motion of nonlinear system

As to an autonomous nonlinear system, the stability of the equilibrium state in a sufficiently small neighborhood of the equilibrium state can be determined by eigenvalues of the linear part of the nonlinear system provided that the eigenvalues are not in a critical case. Many methods may be used to detect the stability for a linear system. A lot of researches for determining the stability of a nonlinear system are completed by mathematicians and mechanicians but most of them are methods for the special forms of nonlinear systems. Till now, none of these methods can be conveniently applied to all nonlinear systems. The method introduced by this paper gives the necessary and sufficient conditions of the stability of a nonlinear system. The familiar Krasovski's method is a special case of this method.     

A comparison of three algorithms for tracing nonlinear equilibrium paths of structural systems

The relative efficiencies of the Riks/Wempner, Crisfield, and normal flow solution algorithms for tracking nonlinear equilibrium paths of structural systems are compared. It is argued that the normal flow algorithm may be both more computationally efficient and more robust compared to the other two algorithms when tracing the path through severe nonlinearities such as those associated with structural collapse. This is demonstrated qualitatively by comparing the relative behaviors of each algorithm in the vicinity of a severe nonlinearity. Quantitative results are presented for the collapse a blade stiffened panel.     

分段线性耦合动力系统的周期解及稳定性分析

以某货车的主副钢板弹簧悬架为模型建立两自由度分段线性和轮胎非线性耦合动力学方程,采用打靶法求耦舍系统的周期解;将所得结果与近似解析法分析的结果进行比较,并利用Floquet理论判断周期解的稳定性。研究结果表明：当激励频率在等效固有频率附近时系统的周期解不稳定,其Floquet乘数的模大于1,系统振动剧烈,KBM法得到的周期解将产生较大误差;当路面工况突然发生改变或路面工况不变而载重发生较大变化时都有可能发生舅毡跃现象,造成系统的不稳定;周期解的长期时域图和Floquet理论验证了这一现象;     

A truly self-starting implicit family of integration algorithms with dissipation control for nonlinear dynamics

Nonlinear Dynamics - In this paper, a novel implicit family of composite two sub-step algorithms with controllable dissipations is developed to effectively solve nonlinear structural dynamic...     

A data-driven quadratic stability condition and its application for stabilizing unknown nonlinear systems

This paper proposes a data-driven stability criterion for quadratic stabilization of unknown nonlinear discrete-time systems. The novelty of this quadratic stability criterion lies in the direct use of the time series of system states, instead of using mathematical models. The data-driven stability criterion is utilized to design a control for stabilizing unknown nonlinear systems using online black-box system identification. The effectiveness and the adaptability of the proposed approach are compared with those of adaptive feedback linearization method with an example of stabilizing a nonlinear aeroelastic system.