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Number of results: 8
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Abstract

Recent investigations of micro engines have documented the problem of low efficiency of steady compression devices [2]. As a solution, the application of unsteady processes has been proposed [1, 6, 17-20]. Closer investigations have shown the applicability of pure unsteady devices for gas compression, but it is also shown that they are practically not applicable for torque generation [21]. A new concept of the wave engine has to be developed. This paper presents such a new concept and numerical investigation of the hybrid wave engine. A hybrid wave engine combines in a single machine components realizing unsteady compression, steady expansion, and mixed unsteady and steady scavenging due to the centrifugal force action. MEMS technology requires or prefers a flat geometry. Therefore, the use of a radial type of wave compression device for air compression is proposed. A numerical, two-dimensional complete model of this device was built, and several numerical simulations of engine operations were performed. The numerical model includes the simplified model of the combustion chamber closing the flow loop between the high-pressure compressed air port and the high-pressure hot exhaust gas port. The model represents the complete flow scheme of the hybrid wave engine. A special type of turbine in radial configuration with serial flow layout is used for torque generation.
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Abstract

This paper presents the results of numerical analysis of aerodynamic characteristics of a sports car equipped with movable aerodynamic elements. The effects of size, shape, position, angle of inclination of the moving flaps on the aerodynamic downforce and aerodynamic drag forces acting on the vehicle were investigated. The calculations were performed with the help of the ANSYS-Fluent CFD software. The transient flow of incompressible fluid around the car body with moving flaps, with modeled turbulence (model Spalart-Allmaras or SAS), was simulated. The paper presents examples of effective flap configuration, and the example of configuration which does not generate aerodynamic downforce. One compares the change in the forces generated at different angles of flap opening, pressure distribution, and visualization of streamlines around the body. There are shown the physical reasons for the observed abnormal characteristics of some flap configurations. The results of calculations are presented in the form of pressure contours, pathlines, and force changes in the function of the angle of flap rotation. There is also presented estimated practical suitability of particular flap configurations for controlling the high-speed car stability and performance.
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Abstract

The paper presents the experimental study of a novel unsteady-statemembrane gas separation approach for recovery of a slow-permeant component in the membrane module with periodical retentate withdrawals. The case study consisted in the separation of binary test mixtures based on the fast-permeant main component (N2O, C2H2) and the slow-permeant impurity (1%vol. of N2) using a radial countercurrent membrane module. The novel semi-batch withdrawal technique was shown to intensify the separation process and provide up to 40% increase in separation efficiency compared to a steady-state operation of the same productivity.
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Abstract

The paper deals with a non-linear problem of long water waves approaching a sloping beach. In order to describe the phenomenon we apply the Lagrange’s system of material variables. With these variables it is much easier to solve boundary conditions, especially conditions on a shoreline. The formulation is based on the fundamental assumption for long waves propagating in shallow water of constant depth that vertical material lines of fluid particles remain vertical during entire motion of the fluid. The analysis is confined to one – dimensional case of unsteady water motion within a ’triangular’ body of fluid. The partial differential equations of fluid motion, obtained by means of a variational procedure, are then substituted by a system of equations resulting from a perturbation scheme with the second order expansion with respect to a small parameter. In this way the original problem has been reduced to a system of linear partial differential equations with variable coefficients. The latter equations are, in turn, substituted by a system of difference equations, which are then integrated in a discrete time space by means of the Wilson-µ method. The procedure developed in this paper may be a convenient tool in analysing non-breaking waves propagating in coastal zones of seas. Moreover, the model can also deliver useful results for cases when breaking of waves near a shoreline may be expected.
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Abstract

The paper presents the results of the numerical analyses for the steam turbine rotor, dedicated for the newly-designed 900 MW steam unit with supercritical steam parameters (650 °C, 30.0 MPa). Basing on the design calculations, an optimal design solution was determined. Review of the available literature on materials for turbine rotors with supercritical steam parameters was done. Then the start-ups of the turbine were simulated. Thermal and strength states were analyzed. As a result, an optimal start-up characteristic was obtained.
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Abstract

The focus of research works on cavitation has changed since the 1960s; the behaviour of a single bubble is no more the area of interest for most scientists. Its place was taken by the cavitating flow considered as a whole. Many numerical models of cavitating flows came into being within the space of the last fifty years. They can be divided into two groups: multifluid and homogeneous (i.e., single-fluid) models. The group of homogenous models contains two subgroups: models based on transport equation and pressure based models. Several works tried to order particular approaches and presented short reviews of selected studies. However, these classifications are too rough to be treated as sufficiently accurate. The aim of this paper is to present the development paths of numerical investigations of cavitating flows with the use of homogeneous approach in order of publication year and with relatively detailed description. Each of the presented model is accompanied by examples of the application area. This review focuses not only on the list of the most significant existing models to predict sheet and cloud cavitation, but also on presenting their advantages and disadvantages. Moreover, it shows the reasons which inspired present authors to look for new ways of more accurate numerical predictions and dimensions of cavitation. The article includes also the division of source terms of presented models based on the transport equation with the use of standardized symbols.
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Abstract

The central theme of this work was to analyze high aspect ratio structure having structural nonlinearity in low subsonic flow and to model nonlinear stiffness by finite element-modal approach. Total stiffness of high aspect ratio wing can be decomposed to linear and nonlinear stiffnesses. Linear stiffness is modeled by its eigenvalues and eigenvectors, while nonlinear stiffness is calculated by the method of combined Finite Element-Modal approach. The nonlinear modal stiffness is calculated by defining nonlinear static load cases first. The nonlinear stiffness in the present work is modeled in two ways, i.e., based on bending modes only and based on bending and torsion modes both. Doublet lattice method (DLM) is used for dynamic analysis which accounts for the dependency of aerodynamic forces and moments on the frequency content of dynamic motion. Minimum state rational fraction approximation (RFA) of the aerodynamic influence coefficient (AIC) matrix is used to formulate full aeroelastic state-space time domain equation. Time domain dynamics analyses show that structure behavior becomes exponentially growing at speed above the flutter speed when linear stiffness is considered, however, Limit Cycle Oscillations (LCO) is observed when linear stiffness along with nonlinear stiffness, modeled by FE-Modal approach is considered. The amplitude of LCO increases with the increase in the speed. This method is based on cantilevered configuration. Nonlinear static tests are generated while wing root chord is fixed in all degrees of freedom and it needs modification if one requires considering full aircraft. It uses dedicated commercial finite element package in conjunction with commercial aeroelastic package making the method very attractive for quick nonlinear aeroelastic analysis. It is the extension of M.Y. Harmin and J.E. Cooper method in which they used the same equations of motion and modeled geometrical nonlinearity in bending modes only. In the current work, geometrical nonlinearities in bending and in torsion modes have been considered.
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Abstract

The paper describes the behavior of the liquid in a container that moves with a constant speed along a track consisting of three arcs. Such a complicated track shape generates complex form of inertia forces acting on the liquid and generates the sloshing effect. The behavior of the tank container vehicle is affected by the time-dependent inertia forces associated with the transient sloshing motion of the liquid in the non-inertial frame. These internal excitations, acting on a tank construction, can cause a loss of stability of the vehicle. For that reason, the authors analyze the dynamic loads acting on the walls of the tank truck container. The variation of the position of the liquid cargo gravity center, that depends on the filling level of the container, is also analyzed. The simulations were performed according to the varying fill level, which was 20%, 50% and 80% of a liquid in the whole tank volume. The simulations were carried out for a one-compartment container. Another aim of this study was the investigation of the influence of container division (tank with one, two and three compartments) on behavior of the liquid. These simulations considered only the half-filled container which was treated as a dangerous configuration prohibited by the law regulations for one-compartment tank. The results of simulation are presented in the form of visualization of temporary liquid free surface shape, variation of forces and moments, as well as frequency analysis. The results of simulation were analyzed, and some general conclusion were derived, providing the material for future investigation and modifications of the law regulations.
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