In this paper, the homotopy analysis method (HAM) is used to give series solutions of self-exited oscillation systems governed by two Van der Pol equations, which are coupled by a linear and a cubic term. The frequency and amplitude of all possible periodic solutions are investigated. It is found that there exist either in-phase or out-of-phase periodic solutions only. Besides, the in-phase periodic oscillations are decoupled, whose periods and amplitudes have nothing to do with the linear and cubic coupled terms. However, the out-of-phase periodic oscillations are strongly coupled, whose period and amplitude can be controlled by the linear and cubic coupled terms.

Plates are common structural elements of most engineering structures, including aerospace, automotive, and civil engineering structures. The study of plates from theoretical perspective as well as experimental viewpoint is fundamental to understanding of the behavior of such structures. The dynamic characteristics of plates, such as natural vibrations, transient responses for the external forces and so on, are especially of importance in actual environments. In this paper, we consider natural vibrations of an elastic plate and the propagation of a wavepacket on it. We derive the two-dimensional equations that govern the spatial and temporal evolution of the amplitude of a wavepacket and discuss its features. We especially consider wavenumber-based nearly bichromatic waves and direction-based nearly bichromatic waves on an elastic plate. The former waves are defined by the waves that almost concentrate the energy in two wavenumbers, which are very closely approached each other. The latter waves are defined by the waves that almost concentrate the energy in two propagation directions and two propagation directions are very close each other. The fact that the solution of the governing equation for wavenumber-based nearly bichromatic waves is stable is also shown. NomenclatureA = slowly varying amplitude in space and/or time of a wavepacket CI = the function space consisting of functions f (x) which is lth differentiable at any point of x and the lth derivative of f is continuous D = plate flexural rigidity E = elastic modulus G = direction-based spectrum of a wavepacket or Green's function H = value used in boundary conditions L = linear operator defined by Equations (A.19) and (A.20) or value used in boundary conditions Al = positive integer N = positive integer O = function of order Q = function defined by Equation (A.18) or Fourier coefficient R = real space S = function used by the method of separation of variables in Equation (A.3) 88 B.T. NOHARA U = function used by the method of separation of variables in Equation (A.3) a = cos Bo b = sin Bo c = Fourier coefficient cc = complex conjugate f = function of initial condition h = plate thickness i = imaginary unit or unit vector along x axis j = unit vector along y axis k = wave number m = integer n = integer t = time u = function v = function v = velocity of envelope surface w = plane traveling waves x, y = rectangular coordinate system W = function used by the method of separation of variables in Equation (A.9) 0 = function used by the method of separation of variables in Equation (A.9) a = coefficient in Equation (A.34) ß = coefficient in Equation (A.34) -y = coefficient in Equations (A.10) and (A.11) S = Delta function e = order of time and spacial scales 0 = propagation direction A = separation constant p = separation constant v = Poisson's ratio p = mass density w = angular frequency ÖD = boundary of rectangle V4 = biharmonic operator Subscript 0 = dominant value 1, 2 = number of function or value m = number of coefficient n = number of function or coefficie...

Plates are common structural elements of most engineering structures, including aerospace, automotive, and civil engineering structures. The study of plates from theoretical perspective as well as experimental viewpoint is fundamental to understanding of the behavior of such structures. The dynamic characteristics of plates, such as natural vibrations, transient responses for the external forces and so on, are especially of importance in actual environments. In this paper, we conside the envelope surface created by the vibrations of a square plate on a weakly nonliner elastic foundation and analyze the stability of the uniform solution of the governing equation for the envelope surface. We derive the two-dimensional equation that governs the spatial and temporal evolution of the envelope surface on cubic nonlinear elastic foundation. The fact that the governing equation becomes the quintic nonlinear Schrödinger equation is shown. Also we obtain the stability condition of the uniform solution of the quintic nonlinear Schrödinger equation.

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In this paper, the author derives the modified Schrödinger equation that governs the envelope created by nearly bichromatic waves, which are defined by the waves whose energy is almost concentrated in two closely approached wavenumbers. The stability of the solution of the modified Schrödinger equation for nearly bichromatic waves on deep water is discussed and the fact that the Benjamin-Feir instability occurs in a condition is shown. Moreover, the solutions of the modified Schrödinger equation for nearly bichromatic waves on deep water are obtained and, in a special case, the solution becomes the standing wave solution is shown. NomenclatureA slowly varying amplitude in space and/or time of nearly monochromatic waves and nearly bichromatic waves K real wavenumber