Band 29, Heft 3

An approach based on projection of a vector onto a pointed convex polyhedral cone is proposed for solving the quadratic programming problem with a positive definite matrix of the quadratic form. It is proved that this method has polynomial complexity. A method is said to be of polynomial computational complexity if the solution to the problem can be obtained in N 1 = O(n α ) elementary operations, where α is some positive number, in contrast with a method of exponential computational complexity whose implementation requires N 2 = exp(O(n)) operations.

A difference scheme on unstructured grids is constructed for the system of equations of large scale ocean dynamics. The properties of the grid problem and grid operators are studied, in particular, a series of a priori estimates and the theorem on existence and uniqueness of the solution are proved.

A new derivation of completely nonlinear weakly-dispersive shallow water equations is given without assumption of flow potentiality. Boussinesq type equations are derived for weakly nonlinear waves above a moving bottom. It is established that the total energy balance condition holds for all nonlinear dispersion models obtained here.

A finite-volume numerical method for studying shallow water flows over an arbitrary bed profile in the presence of external force has been proposed in [33]. This method uses the quasi-two-layer model of hydrodynamic flows over a stepwise boundary with advanced consideration of the flow features near the step. A distinctive feature of the suggested model is a separation of the studied flow into two layers in calculating the flow quantities near each step, and improving by this means the approximation of depth-averaged solutions of the initial three-dimensional Euler equations. We are solving the shallow-water equations for one layer, introducing the fictitious lower layer only as an auxiliary structure in setting up the appropriate Riemann problems for the upper layer. Besides, the quasi-two-layer approach leads to the appearance of additional terms in the one-layer finite-difference representation of balance equations. Numerical simulations are performed based on the proposed in [33] algorithm of various physical phenomena, such as breakdown of the rectangular fluid column over an inclined plane, large-scale motion of fluid in the gravity field in the presence of Coriolis force over amounted obstacle on the underlying surface. Computations are made for the two-dimensional dam-break problem on a slope precisely conform to laboratory experiments. The interaction of the Tsunami wave with the shore line including an obstacle has been simulated to demonstrate the efficiency of the developed algorithm in domains, including partly flooded and dry regions.

The problem of modelling the movement of a nonlinear conformational perturbation (i.e., kink) along a DNA molecule is considered taking into account the dissipation. The study of movement peculiarities is performed using a homogeneous sequence of nucleotides and a heterogeneous one consisting of two homogeneous parts separated by a boundary. Using analytic and numerical methods, it is shown that the effect of dissipation leads to a decrease of the energy of kink E, its velocity v, and the mass M. It is also shown that the consideration of the dissipation near the boundary leads to a smoothing of kink motion trajectories in the plane {z, t} in comparison with trajectories calculated without taking into account the dissipation and characterized by a sharp bend on the boundary caused by effects of reflection from the boundary or by a passage through the boundary with an increase or decrease of motion velocity.