Moored elastic sheets under the action of nonlinear waves and current

This study is concerned with the interaction between nonlinear water waves and uniform current with moored, floating elastic sheets, resembling floating solar panels, floating airports, tunnels and bridges, and floating energy systems. The Green-Naghdi theory is applied for the nonlinear wave-current motion, the thin plate theory is used to determine the deformations of the elastic sheet and Hooke’s law defines the effect of the mooring lines. The horizontal displacement of the floating sheet is determined by substituting the forces induced by the fluid flow and the tensions generated in the mooring lines into the equations of motion of the floating body. The resulting governing equations, boundary and matching conditions are solved in two dimensions with a finite-difference technique. The results are compared with the available numerical data. Overall, very good agreement is observed. In the model developed here, the sheet is allowed to drift due to the wave-current impact, and hence the mooring lines partially restrict both deformation and the horizontal motions of the sheet. The influence of the mooring lines on the dynamics of the floating sheet is assessed in terms of wave- and current-induced elastic deformations and surge movements of the sheet. It is demonstrated that the mooring lines attached to the leading and trailing edges of the sheet can be highly effective in mitigating the horizontal oscillations and vertical elastic deformations of the floating sheet subjected to the wave and current actions. Special attention is given to the horizontal periodic motions of the sheet, which are analysed by use of a Fourier transform technique. It is shown that the moored elastic sheet can oscillate at a frequency different from its exciting frequency as a result of restoring forces from the mooring lines, exciting resonance when both frequencies meet. Extensive study in a broad range of sheet parameters, mooring stiffnesses and wave-current conditions established the location of resonant regimes of different configurations of the moored systems. Analysis of wave reflection and transmission coefficient revealed that mooring lines of increasing stiffness intensify the wave reflection and, consequently, result in smaller energy transformation downwave

Development of the Engineering Procedure for the Thermotechnical Calculation of a Building Envelope with Air Chambers and a Heat­reflecting Coating

The study has addressed the development of the engineering procedure for the thermotechnical calculation of a building envelope with thermal insulation in which air chambers with a heat-reflecting coating are formed.The engineering procedure implied determining the average RSI-value of the building envelope based on the calculation of a temperature field in it. To find the temperature field, a one-dimensional heat conduction problem in a multilayer building envelope was considered. The thermotechnical heterogeneities caused by the presence of alternating air chambers and dividers of insulation material were taken into account in the mathematical model using the effective thermal conductivity of a corresponding layer. This coefficient takes into consideration the convective and radiant components of heat transfer through air chambers. An expression was obtained for determining its value depending on the temperature at the junction of corresponding layers with adjacent building envelope layers. The iterative procedure was proposed that makes it possible to use this expression for determining the temperature fields in the building envelope under consideration. The geometric and thermophysical characteristics of building envelope elements, as well as the values of indoor and outdoor temperature and heat transfer coefficients of the corresponding surfaces, were used as initial data.The engineering procedure was verified by comparison with the results of three-dimensional CFD simulation, which takes into detailed account the free-convective motion in air chambers and the radiation heat exchange between thermally inhomogeneous walls of the air chamber. It was shown that the use of a one-dimensional mathematical model instead of a detailed three-dimensional one leads to errors not exceeding 2.5 %.As a result of our comparative analysis, the effectiveness of the proposed thermal insulation material having air chambers with a heat-reflecting coating was shown in comparison with the conventional approaches to building envelope thermal insulation. Calculations were performed for the case of the coldest five-day period in the climatic zone of Shymkent (Republic of Kazakhstan

APPLICATION OF JMODELICA.ORG TO TEACHING THE FUNDAMENTALS OF DYNAMICS OF FOUCAULT PENDULUM-LIKE GUIDED SYSTEMS TO ENGINEERING STUDENTS

The present educational research is focused on the solution of didactic problem of an engineering-friendly description and explanation of the dynamics and control of Foucault pendulum-like systems, which have arisen from practical problems of boom crane dynamics in lifting-and-handling machinery and transport. An educational actuality of the present research is grounded on the absence of a proper description and explanation of this topic in available textbooks and scientific articles in the fields of classical mechanics, control engineering, transport, lifting-and-handling machinery, engineering education, mechanical engineering education, and classical mechanics education. Among learning tools this article uses the following educational techniques: Modelica-assisted simulation with acausal equation-based freeware computer system JModelica.org with Optimica extension, physical simulation techniques, allegoric fairy tale analogy, didactic transposition method and a complex of individual Modelica-enhanced students’ computational assignments. The proposed educational approach provides a broadening of students’ ideas concerning the applicability of abstract physical concepts to the theory and practice of freeware-assisted mechanical engineering education of undergraduate and graduate students majoring in dynamics and control of guided lifting-and-handling machinery. Research finding, concepts and ideas of this research have found a practical educational application through the formulation of practical computational problems of term design works, planning of MSc degree students’ works, and freeware-enhanced curriculum of Donbass State Engineering Academy, Kramatorsk, Ukraine