Variational modelling of wave-structure interactions with an offshore wind-turbine mast

We consider the development of a mathematical model of water waves interacting with the mast of an offshore wind turbine. A variational approach is used for which the starting point is an action functional describing a dual system comprising a potential-flow fluid, a solid structure modelled with nonlinear elasticity, and the coupling between them. We develop a linearized model of the fluid–structure or wave–mast coupling, which is a linearization of the variational principle for the fully coupled nonlinear model. Our numerical results for the linear case indicate that our variational approach yields a stable numerical discretization of a fully coupled model of water waves and an elastic beam. The energy exchange between the subsystems is seen to be in balance, yielding a total energy that shows only small and bounded oscillations amplitude of which tends to zero with the second-order convergence as the timestep approaches zero. Similar second-order convergence is observed for spatial mesh refinement. The linearized model so far developed can be extended to a nonlinear regime

Horizontal circulation and jumps in Hamiltonian wave models

We are interested in the numerical modeling of wave-current interactions around surf zones at beaches. Any model that aims to predict the onset of wave breaking at the breaker line needs to capture both the nonlinearity of the wave and its dispersion. We have therefore formulated the Hamiltonian dynamics of a new water wave model, incorporating both the shallow water and pure potential flow water wave models as limiting systems. It is based on a Hamiltonian reformulation of the variational principle derived by Cotter and Bokhove (2010) by using more convenient variables. Our new model has a three-dimensional velocity field consisting of the full three-dimensional potential velocity field plus extra horizontal velocity components. This implies that only the vertical vorticity component is nonzero. Boussinesq-type simplifications of the vertical flow profile follow directly from the new Hamiltonian formulation, such as extensions of variational Boussinesq models and Green-Naghdi equations. Since the full water wave dispersion is retained in the new model, waves can break. We therefore explore a variational approach to derive jump conditions for the new model and its Boussinesq simplifications

Political absenteeism of Russian youth

В современном российском обществе снижается политическая активность молодежи. Крайней формой политической пассивности является абсентеизм – равнодушное отношение людей к политической жизни. В связи с чем одной из важнейших задач российского государства должно стать преодоление абсентеизма молодежи.In modern Russian society political activity of youth decreases. An extreme form of political passivity is the absenteeism – the indifferent relation of people to political life. In this connection overcoming an absenteeism of youth has to become one of the most important problems of the Russian state

Topical issues of prevention of uncurious dental lesions

The article is devoted to the issues of prevention of uncarious lesions accompanied by demineralization of the hard structures of the teeth, as well as the means and methods used for remineralizing therapy in modern realities.В статье рассматриваются вопросы профилактики некариозных поражений, сопровождающихся деминерализацией твердых структур зубов, а также средства и методы, используемые для реминерализующей терапии в современных реалиях

From bore-soliton-splash to a new wave-to-wire wave-energy model

We explore extreme nonlinear water-wave amplification in a contraction or, analogously, wave amplification in crossing seas. The latter case can lead to extreme or rogue-wave formation at sea. First, amplification of a solitary-water-wave compound running into a contraction is disseminated experimentally in a wave tank. Maximum amplification in our bore–soliton–splash observed is circa tenfold. Subsequently, we summarise some nonlinear and numerical modelling approaches, validated for amplifying, contracting waves. These amplification phenomena observed have led us to develop a novel wave-energy device with wave amplification in a contraction used to enhance wave-activated buoy motion and magnetically induced energy generation. An experimental proof-of-principle shows that our wave-energy device works. Most importantly, we develop a novel wave-to-wire mathematical model of the combined wave hydrodynamics, wave-activated buoy motion and electric power generation by magnetic induction, from first principles, satisfying one grand variational principle in its conservative limit. Wave and buoy dynamics are coupled via a Lagrange multiplier, which boundary value at the waterline is in a subtle way solved explicitly by imposing incompressibility in a weak sense. Dissipative features, such as electrical wire resistance and nonlinear LED loads, are added a posteriori. New is also the intricate and compatible finite-element space–time discretisation of the linearised dynamics, guaranteeing numerical stability and the correct energy transfer between the three subsystems. Preliminary simulations of our simplified and linearised wave-energy model are encouraging and involve a first study of the resonant behaviour and parameter dependence of the device

On variational and symplectic time integrators for Hamiltonian systems

Various systems in nature have a Hamiltonian structure and therefore accurate time integrators for those systems are of great practical use. In this paper, a fi nite element method will be explored to derive symplectic time stepping schemes for (non-)autonomous systems in a systematic way. The technique used is a variational discontinuous Galerkin nite element method in time. This approach provides a uni ed framework to derive known and new symplectic time integrators. An extended analysis for the new time integrators will be provided. The analysis shows that a novel third order time integrator presented in this paper has excellent dispersion properties. These new time stepping schemes are necessary to get accurate and stable simulations of (forced) water waves and other non-autonomous variational systems, which we illustrate in our numerical results

Studying the influence of the psycho-emotional state of a human on the appearance of the deja vu phenomenon

The purpose of the study is to determine the presence or absence of a correlation between the psycho-emotional state of a person and the occurrence of the déjà vu phenomenon.Цель исследования – определить наличие или отсутствие корреляции между психоэмоциональным состоянием человека и возникновением феномена дежавю

Investigation of some hematological blood values of smokers

The purpose of the study is to identify changes in some haematological indicators and tobacco smokingЦель исследования – выявить взаимосвязь изменений некоторых гематологических показателей и курение табака