A CLOSED-FORM APPROXIMATE SOLUTION FOR COUPLED VIBRATIONS OF COMPOSITE THIN-WALLED BEAMS WITH MID-PLANE SYMMETRY
Original scientific paper The purpose of this paper is to develop and present an approximate analysis procedure to estimate the natural frequencies and mode shapes of thin-walled beams with arbitrary open cross-section, made of laminates with mid-plane symmetry. Theory of thin-walled composite beams is based on assumptions consistent with the Vlasov's beam theory and classical lamination theory. The equations of motion for coupled bending-torsional vibrations are derived from the principle of virtual displacements. In the case of simply supported thin-walled beam the frequency equation, given in determinant form, is expanded in an explicit analytical form, which gives the natural frequencies of free harmonic vibrations. For verification, the analytical study by other researchers and the FEM analysis using ANSYS are compared with the current results.
On triply coupled vibrations of thin-walled beams with arbitrary cross-section
The purpose of this paper is to analyze triply coupled vibrations of thin-walled beams with arbitrary open cross-section. Starting from the Vlasov's theory, the governing differential equations for coupled bending and torsional vibrations were performed using the principle of virtual displacements. In the case of a simply supported thin-walled beam, a closed-form solution for the natural frequencies of free harmonic vibrations was derived. The significance of neglecting cross-sectional warping and rotary inertia on the accuracy of results was analyzed. A recent paper on the same subject is discussed, with a critical review of it.
The microscale obstacle-resolving meteorological model MITRAS v2.0: model theory
Abstract. This paper describes the developing theory and underlying
processes of the microscale obstacle-resolving model MITRAS version 2. MITRAS
calculates wind, temperature, humidity, and precipitation fields, as well as
transport within the obstacle layer using Reynolds averaging. It explicitly
resolves obstacles, including buildings and overhanging obstacles, to
consider their aerodynamic and thermodynamic effects. Buildings are
represented by impermeable grid cells at the building positions so that the
wind speed vanishes in these grid cells. Wall functions are used to calculate
appropriate turbulent fluxes. Most exchange processes at the obstacle
surfaces are considered in MITRAS, including turbulent and radiative
processes, in order to obtain an accurate surface temperature. MITRAS is also
able to simulate the effect of wind turbines. They are parameterized using
the actuator-disk concept to account for the reduction in wind speed. The
turbulence generation in the wake of a wind turbine is parameterized by
adding an additional part to the turbulence mechanical production term in the
turbulent kinetic energy equation. Effects of trees are considered
explicitly, including the wind speed reduction, turbulence production, and
dissipation due to drag forces from plant foliage elements, as well as the
radiation absorption and shading. The paper provides not only
documentation of the model dynamics and numerical framework but also a solid
foundation for future microscale model extensions.
