The shape and drag of bodies with small stiffness may change during the airflow. This problem refers to such bodies as flags, bands, banners, flapping sails as well as blades and cables which vibrate due to the flow.
Laboratory tests carried out to point out the aerodynamic drag coefficient of a flag are discussed in this article. The laboratory tests were carried out in an aerodynamic tunnel at different airflow velocities for flags with different dimensions made of fabrics of different roughness and stiffness. The drag coefficient value decreases with the increasing airflow velocity. The drag coefficient is higher for materials with higher roughness. The drag coefficient value is also influenced by the fabric stiffness and kind of edge.
Great engineering importance to the stability of a structure (e.g. a flag mast) and the safety of nearby persons and buildings are attached to the analysed problem.
The vortex particle method is an easy and attractive tool to analyze flow phenomena by investigating vorticity fields and the generation of vorticity at solid walls. The vorticity generation at the walls and its introduction to the flow is of fundamental significance for understanding such phenomena as transition to turbulence, boundary layer separation in an eruptive way, and vortex structures regeneration. In the present study the vortex-in-cell usefulness of the method has been tested using a variety of simple test problems: the Poiseuille flow, the second Stokes problem, the cavity, the backward step flow, the vortex dipole interaction with the wall, and the flow past a square cylinder in the vicinity of a wall in order to illustrate the correctness and usefulness of the vortex particle method.
The structure of each part of a diagonal compressor directly affects its overall performance and internal flow. We introduce the Reynolds-averaged Navier-Stokes flow simulation for unit calculation on the whole system including a diagonal impeller, a vaneless diffuser and a volute. By analyzing different flow chromatograms of specific sections, we can compare the configuration of three types of diffusers and volutes and the meridian flow status of the corresponding diagonal compressors which serves as a basis for the impeller flow path as well as for its matching designs. Considering the interference between the rotor and the upstream and downstream stillness body, this thesis analyzes how the vaneless diffuser meridian flow path, the volute flow path and its section secondary flow affect the upstream rotor flow. Both the calculation and experimental data on the rotor outlet are compared, as well as the calculated numerical value of the meridian plane streamline distribution and the diffuser velocity distribution, upstream and downstream, coincides with the designed numerical value. Without changing the conventional quasi-three-dimensional design system, the thesis applies the annulus wall boundary layer theory and the velocity distribution diagram to sweep and skew the leading edge of the airfoil. A performance test shows that the leading edge skewed-swept diagonal rotor can better improve the stall characteristic in a low flow rate area and expand the surge margin, compared with conventional diagonal rotor. It can also efficiently restrain the low-momentum fluid conglomeration near the wall region and reduce the secondary flow loss by sweeping and skewing the blade properly. The purpose of the thesis is to make a contribution to optimizing the overall structure design of diagonal compressors and to study further the complex internal flow between the leading edge skewed-swept diagonal rotor and the cover.
In this paper we review Godunov-type numerical methods for one- and two-component magnetohydrodynamic equations. Solving these equations numerically is a formidable task as a result of the internal complexity of these equations and the requirements of ∇⋅B=0. We present several results of advanced numerical simulations for complex systems. These results prove that the numerical codes which are based on Godunov-type methods, cope with all problems very well.
Numerical methods for standing fast magnetoacoustic kink waves in an isothermal solar coronal slab with a field aligned flow are considered. Such waves are triggered impulsively by a velocity pulse that is initially launched in an ambient medium. The spatial and temporal signatures of these waves are determined by solving two-dimensional, ideal magnetohydrodynamic equations numerically. The Ramses code which resolves complex spatial structures by adopting an adaptive mesh refinement technique and shock-capturing capabilities is used. The numerical results show that spatial and temporal wave signatures are reminiscent to the recent observational findings.
K^{+}@C_{60} endohedral fullerenes inside armchair, zigzag and chiral nanotubes were simulated using the MD technique. The structure of the endohedral fullerene sample was estimated by calculating the radial distribution function. The angular and translational velocity autocorrelation functions and their Fourier transforms were also calculated. The frequency dependence of potassium ion vibrations in different nanotubes at room temperature was observed and discussed. A dependency between the angular motion of endo-fullerenes and the nanotube chirality was found.
A set of elastic constants was calculated and a parametrization of the potential was derived for simple cubic tungsten trioxide based on an analytical bond-order scheme. It was shown that the obtained parametrization provided a good description of interatomic forces and such properties as the lattice constant, the bulk modulus and the elastic constants.
A magnetic field applied to a crystalline solid causes the electron states on the Fermi surface to circulate along the orbits located on the planes normal to the applied field. For a sufficiently weak field the separate orbits can cover the whole closed Fermi surface. A suitable parameterization of the states on the orbits should be done in a different way than a conventional parameterization applied for the electron states by Bloch. This new kind of parameterization becomes quite simple when the magnetic field is assumed to be directed parallel to one of the crystallographic axes. Computationally, a new description of the electron states on the Fermi surface becomes on many occasions more flexible in its use than the Blochâ€™s one. The simplifications concern mainly an examination of the curvature parameters of the Fermi surface and extremal properties of the electron observables, for example that of electron velocity. Solely the states in the cubic crystal lattices were considered as examples.
In order to check the validity of parameterization of electron states on the Fermi surface developed in the preceding paper, this parameterization is applied to the calculation of some definite crystal properties. The first property is the density of electron states versus energy in simple cubic and body-centered cubic crystal lattices, examined formerly on the basis of the Bloch parameterization of electron states by Jelitto; the other property is the length of some special arcs extended on the surfaces. The parameterizations of both approaches, that of the present paper and that developed on the basis of the Bloch states, are found to give results remaining in remarkable agreement.
An approximate analytical solution of a two dimensional problem for stationary Navier-Stokes, continuity and Fourier-Kirchhoff equations describing a free convective heat transfer from an isothermal cone is presented. The problem formulation is based on assumptions typical for natural convection: non-compressibility and the Boussinesq approximation. The solution is based on Frobenius expansions at the vicinities of two points: the initial point and the singular point of the boundary layer equation. Numerical matching of the expansions and Nusselt number evaluations are traced.
A model of electro-magneto-thermo-mechanics for electroconducting polarized nonferromagnetic medium is proposed which takes into account the local mass displacement in addition to the local electric charge displacement. The corresponding key set of equations is written. Using the isothermal approximation, the model is applied to describe the interface inhomogeneity of a stressed state, the polarization and coupled electric charge in thin dielectric films. An anomalous dependence of the electric capacity on the thickness of a thin dielectric film, observed experimentally by Mead, is also studied and is shown to be well captured by the present approach.
Body impact-contact dynamics is a classical subject in mechanics. Most of the papers on the subject are based on a kinematical or impulse-exchange approach. In this paper a different approach has been adopted. It consists in assigning a constitutive description for the contact forces between the boundaries of bodies which get close to each other. In particular, a field of short range forces has been used to model the interaction between an affine body and the planar surface of a fixed rigid support. These forces are able to describe the impact, friction and adhesion allowing the body to have complex motions which look rather realistic. By an affine body we mean a body which undergoes affine, or homogeneous, deformations. Depending on the material, such a body can show very different behavior, from a quite rigid motion to a motion characterized by very large deformations. A soft body is assumed to be made of a viscous incompressible Mooney-Rivlin material. Though a microscopic model of surface interaction could be used in a multiscale approach, the description provided here is macroscopic only.
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