Angle of attack dependence of flow past cactus-inspired cylinders with a low number of ribs

The aerodynamic coefficients and the Strouhal number of cylinders with three and four ribs, inspired by succulents Euphorbia trigona and Euphorbia Abyssinica are investigated using 2D Unsteady Reynolds-Averaged Navier-Stokes simulations at Reynolds number 20,000. Both configurations show a significant dependence of the studied characteristics on the angle of attack. The obtained results are compared to the smooth circular cylinder, previous results for cylinders with 24 ribs based on the Saguaro cactus, and cylinders with triangular and square cross-sections. Relative to the circular cylinder, the mean drag coefficient is lowered only for the four-rib case at high angles of attack. However, at some angular positions, the ability to reduce unsteady force fluctuations exceeds Saguaro-inspired cylinders. For both shapes studied, the Strouhal number at most angles of attack is lower compared to both the circular cylinder and cylinders with 24 ribs at the same Reynolds number. The minimum values of the aerodynamic coefficients for both configurations are related to the angular orientation. For the four-rib case a critical angle of αcr ≈ 40◦ is observed, at which the mean drag coefficient and the fluctuating lift coefficient attain their minima. The mean lift coefficient reaches at this angle its maximum value before a sudden drop for higher angles of attack. Therefore, for cactus-shaped cylinders with four ribs high angles of attack give the optimum orientation relative to prevailing winds

Wind influence on plants: ecophysiological, biomechanical, and aerodynamic aspects

Wind has a wide range of effects on plants: from wind-induced damage in the form of lodging to an increased rate of photosynthesis. Climate models predict that plants will be exposed to elevated wind conditions in many regions around the world due to global warming. To be able to attenuate the negative impact of changing wind patterns on plants, it is necessary to expand our understanding of wind-plant interaction. In this thesis two different aspects of wind-plant interaction are investigated. In the first part, the acclimation response of a model plant, Arabidopsis thaliana, to mechanical stress in the form of continuous wind of a constant speed is explored. A bespoke wind tunnel, suitable for continuous growth of plants, was developed. For the mechanical characterisation of Arabidopsis stems a new multiple resonant frequency method was devised and validated. As a result of the wind treatment, the plants exhibited a positive anemotropic response. This response was documented for the first time in any plant system. Overall, the wind-induced thigmomorphogenetic changes and alterations in the mechanical properties of the primary inflorescence stem were considered to be adaptive to this type of mechanical stress. The mechanical properties can be related to modification in the anatomical tissue organisation and ion content, providing possible sources of the observed changes. In many experiments reported in the literature, wind is mimicked by brushing treatments. In this project, the validity of this approach was investigated by conducting a comparison of the response of Arabidopsis to uni- and bidirectional brushing treatments with the wind-induced changes. While some of the changes to Arabidopsis morphology can be reproduced by matching the vectorial influence of wind and brushing treatments, the changes in the mechanical properties occurred in opposite directions. The unidirectional brushing treatment also evoked a positive tropic response, which can be considered thigmotropic and has been demonstrated for the first time in Arabidopsis shoot. The second part of this thesis explores the aerodynamics of succulent-inspired cylinders using numerical and experimental techniques. Succulents and cacti are, probably, the most well-known examples of convergent evolution in plants, where two different species have independently developed similar traits and features in similar environments but in different parts of the Earth. Investigations inspired by the Saguaro cactus reported in the literature, showed that the presence of ribs on its trunk, among other functions, helps to reduce the aerodynamic forces and decreases unsteady force fluctuations. In contrast to Saguaro, which can have up to 30 ribs, succulents tend to have a considerably lower number of ribs, with only three and four ribs found in many species. This work investigates whether succulent-inspired bluff bodies with a low number of ribs show similar aerodynamic benefits as cactus-shaped cylinders with many ribs. 2D URANS simulations were carried out for two cylinders with three and four ribs, which resemble the succulents Euphorbia trigona and Euphorbia abyssinica, respectively, at Reynolds number 20,000. The succulent-inspired cylinder with four ribs was also investigated using wind tunnel tests with Reynolds numbers ranging from 50,000 to 150,000. For both studied cylinders, a strong angle of attack dependence of all aerodynamic properties was found. For the four-ribbed cylinder no Reynolds number dependence of these properties was observed within the tested range. Overall, succulent-inspired cylinders with a low number of ribs show some aerodynamic advantages in terms of reduction of the mean drag coefficient and the Strouhal number, albeit over a limited range of angles of attack

A specialised wind tunnel for investigation of ecophysiological response of plants to wind

No abstract available

Influence of ridge spacing, ridge width, and Reynolds number on secondary currents in turbulent channel flow over triangular ridges

This dataset contains velocity data discussed in the associated article

LES and PIV investigation of the flow past a cactus-shaped cylinder with four ribs

This data set contains mean and fluctuating aerodynamic coefficients, Strouhal number, wake width, recirculation region length, and eigenvalue spectrum for all considered angles of attack discussed in the paper

Effect of Wind on Morphology and Mechanical Properties of Arabidopsis Thaliana

No abstract available

Reduction operators and exact solutions of generalized Burgers equations

Reduction operators of generalized Burgers equations are studied. A connection between these equations and potential fast diffusion equations with power nonlinearity -1 via reduction operators is established. Exact solutions of generalized Burgers equations are constructed using this connection and known solutions of the constant-coefficient potential fast diffusion equation.Comment: 7 page

Анализ исследования тонкой структуры холоднодеформированной стали 20 до и после предрекристаллизационной термической обработки

Дубовой, А. Н. Анализ исследования тонкой структуры холоднодеформированной стали 20 до и после предрекристаллизационной термической обработки = Analysis of the study of the fine structure of the cold-deformed 20 steel before and after the pre-recrystallizational heat treatment / А. Н. Дубовой, А. В. Чечель, А. А. Жданов // Зб. наук. пр. НУК. – Миколаїв : НУК, 2015. – № 1 (457). – С. 34–39.Наведено результати досліджень тонкої структури холоднодеформованої маловуглецевої сталі 20 до і після передрекристалізаційної термічної обробки за допомогою електронної металографії і рентгеноструктурного аналізу. Показано, що після передрекристалізаційної термічної обробки холоднодеформованої сталі 20 відбувається подрібнення субзерен, зниження рівня мікронапружень і щільності дислокацій, що забезпечує підвищення фізико-механічних властивостей.The article deals with the influence of the prerecrystallization heat treatment on the fine structure of colddeformed mild steel 20 by the help of metallography and X-ray structure analysis. It was determined experimentally that the prerecrystallization heat treatment of the plastically deformed by 60 % steel 20 at 500 °С for 1.5 minutes leads to the grinding of the blocks sizes (with the CSR reduced from 139 nm after deformation to 87 nm after the prerecrystallization heat treatment). At that, the reduction of the level of the internal stresses by 20 % occurs. The prerecrystallization heat treatment of steel 20 does not result in complete removal of the long-range stress fields formed in the structure during the plastic deformation. The sources of the long-range stress fields are boundaries and junctions of grain and subgrain boundaries. The dislocation density is reduced by 57 % due to the restructuring and ordering of the substructure, and relaxation processes which occur when heating the plastically deformed steel. It was determined that the prerecrystallization heat treatment at 500°C with a 1.5 minute hold enables grinding the plastically deformed substructure (by 60 %) of the steel 20 by ordering defects, forming dislocation networks and subgrains with low-angle boundaries, providing the enhancement of the physical and mechanical properties.Приведены результаты исследований тонкой структуры холоднодеформированной малоуглеродистой стали 20 до и после предрекристаллизационной термической обработки при помощи электронной металлографии и рентгеноструктурного анализа. Показано, что после предрекристаллизационной термической обработки холоднодеформированной стали 20 происходит измельчение субзерен, снижение уровня микронапряжений и плотности дислокаций, обеспечивающих повышение физико-механических свойств

Reduction operators of Burgers equation

The solution of the problem on reduction operators and nonclassical reductions of the Burgers equation is systematically treated and completed. A new proof of the theorem on the special "no-go" case of regular reduction operators is presented, and the representation of the coefficients of operators in terms of solutions of the initial equation is constructed for this case. All possible nonclassical reductions of the Burgers equation to single ordinary differential equations are exhaustively described. Any Lie reduction of the Burgers equation proves to be equivalent via the Hopf-Cole transformation to a parameterized family of Lie reductions of the linear heat equation.Comment: 11 pages, minor correction