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Abstract. We describe a large-scale geodynamo model based on hypothesis about 6-cells convection in the Earth's core. This hypothesis suggests indirect data of inhomogeneities in the density of the Earth?s core. The convection pattern is associated with a spherical harmonic Y 2 4 which defines the basic poloidal component of velocity. The model takes into account the feedback effect of the magnetic field on convection. It was ascertained that the model contains stable regimes of field generation with reversals. The velocity of convection and the dipole component of the magnetic field are similar to the observed ones.

We study some fractal properties of the hereditary αω-dynamo model in the two-mode approximation. The phase variables of the model describe the temporal dynamics of the toroidal and poloidal components of the magnetic field. The hereditary operator of the quenching the α-effect by field helicity in numerical simulation is determined using the Riemann–Liouville fractional differentiation operator. The model also includes a stochastic term. The structure of this term corresponds to the effect of coherent structures from small-scale magnetic field and velocity modes. A difference scheme and a program code for numerical simulation have been developed and verified. A series of computational experiments with the model has been carried out. The Hausdorff dimension of the polarity scale in the model and the distribution of polarity intervals are calculated. It is shown that the Hausdorff dimension of the polarity scale is less than 1, i.e., this scale is a fractal. The numerical value of the dimension for some values of the control parameters is 0.87, which is consistent with the dimension of the real geomagnetic polarity scale. The distribution histogram of polarity intervals in the model has a pronounced power-law tail, which also agrees with the properties of real polarity scales.

The paper describes the developed by authors technique for construct-ing complex shell models of turbulence. The compilation of the equa-tions of this model and its exactly solution are implemented using by computer algebra system. The technique allows one to vary the sizes of nonlocality of nonlinear interaction in the space of scales, expressions for shell analogues of conservation laws, and the nature of stationary solutions with different power distribution.

Одним из популярных классов моделей мелкомасштабной турбулентности является класс каскадных моделей. В этих моделях поля турбулентной системы представляются зависящими от времени коллективными переменными (вещественными или комплексными), которые осмысливаются как интенсивность поля в заданном диапазоне пространственных масштабов. Сама модель является некоторой системой квадратично нелинейной обыкновенных дифференциальных уравнений для коллективных переменных. Составление новой каскадной модели требует достаточно сложных аналитических преобразований. Это связано с тем, что система уравнений модели при отсутствии диссипации должна иметь некоторые квадратичные инварианты и сохранять фазовый объем. Кроме того, есть ограничения, связанные с невозможностью нелинейного взаимодействия взаимодействия некоторых диапазонов масштабов. Все это накладывает ограничения на коэффициенты нелинейных членов модели. Ограничения образуют систему уравнений с параметрами. Сложность этой системы резко возрастает для нелокальных моделей, когда описывается взаимодействие не только близких диапазонов масштабов и при использовании комплексных коллективных переменных. В работе предложена вычислительная технология, позволяющая автоматизировать процесс построения каскадных моделей. Она позволяет легко комбинировать различные инварианты и значение нелокальности. Технология основана на методах компьютерной алгебры. Автоматизирован процесс построения уравнений для неизвестных коэффициентов и их решения. В результате получаются параметрические классы каскадных моделей, обладающих нужными аналитическими свойствами. One popular class of small-scale turbulence models is the class of shell models. In these models, the fields of a turbulent system are represented by time-dependent collective variables (real or complex), which are understood as the field intensity meassure in a given range of spatial scales. The model itself is a certain system of quadratically nonlinear ordinary differential equations for collective variables. Construction a new shell model requires rather complex analytical transformations. This is due to the fact that the system of model equations in the absence of dissipation must have some quadratic invariants and phase-space volume is unchanged. In addition, there are limitations associated with the impossibility of non-linear interaction of some scales ranges. All this imposes limitations on the coefficients of the nonlinear terms of the model. Constraints form a system of equations with parameters. The complexity of this system increases sharply for non-local models, when the interaction is described not only close ranges of scales and when complex collective variables are used. The paper proposes a computational technology that allows automating the process of building shell models. It makes it easy to combine different invariants and the meassure of nonlocality. The technology is based on computer algebra methods. The process of constructing equations for unknown coefficients and their solution has been automated. As a result, parametric classes of cascade models are obtained that have the required analytical properties.