Resumo em Inglês:

The developing region of an axially symmetric laminar flow from a reservoir to a sharp-edged tube is numerically simulated with a primitive-variables solver of the Navier-Stokes equations, using a plenum upstream of the tube inlet in order to avoid arbitrary specification of the profile at the inlet. Development region lengths, velocity profiles and head losses for varying Reynolds numbers are obtained. Results are compared to available experimental and theoretical results.

Resumo em Inglês:

This paper presents the results and methodology used to calibrate the thermal power of the TRIGA Mark I IPR-R1 Research Reactor at the Nuclear Technology Development Centre (CDTN), in Belo Horizonte, Brazil. The TRIGA Mark I is a pool type reactor, cooled by water natural convection. The method used in the calibration consisted in the steady-state energy balance of the primary cooling loop of the reactor. For this balance, the inlet and outlet temperatures and the water flow in this primary cooling loop were measured. The heat transferred through the primary loop was added to the heat leakage from the reactor pool. The thermal losses from the primary loop were not evaluated since the inlet and outlet temperatures were measured just above the water surface of the reactor pool. The temperature of the water in the reactor pool as well as the reactor room temperature were set as close as possible to the soil temperature to minimize heat leakages. These leakages are mainly due to the conduction through the concrete and metal walls and also due to the evaporation and convection through the water surface of the reactor pool.

Resumo em Inglês:

Aeroelastic instabilities may occur in aircraft surfaces, leading then to failure. Flutter is an aeroelastic instability that results in a self-sustained oscillatory behaviour of the structure. A two-degree-of-freedom flutter can occur with coupling of bending and torsion modes. A flexible mount system has been developed for flutter tests in wind tunnels. This apparatus must provide a well-defined 2DOF system on which rigid wings encounter flutter. Simulations and Experimental Tests are performed during the design period. The dimensions of the system are determined by Finite Element analysis and verified with an Aeroelastic Model. The system is modified until first bending and torsion modes become the first and second modes and other modes become higher than these. After this, a Modal Analysis is performed. An identification algorithm, ERA, is used to determine modes shape and frequencies from experimental data. Detailed results are presented for first bending and torsion modes, which are involved in flutter. The flutter mechanism is demonstrated by Frequency Response Functions obtained in several wind tunnel velocities until flutter achievement and by a V-g-f plot obtained from an identification process performed with an extended ERA. Mode coupling, damping behaviour and the self-sustained oscillatory behaviour are verified characterising flutter.

Resumo em Inglês:

A numerical method based on the vortex methodology is presented in order to obtain unsteady solution of the aerodynamic coefficients of a thin airfoil in either compressible subsonic or supersonic flows. The numerical model is created through the profile discretization in uniform segments and the compressible flow vortex singularity is used. The results of the proposed model are presented as the lift and the pressure coefficient along the profile chord as a function of time. The indicial response for the unit step change of angle of attack and unit sharp-edged gust response of the profile are also obtained numerically. The results yielded by the present methodology are also compared with solutions available in the literature.

Resumo em Inglês:

In this work a discussion on the particularities of the pressure drop equations being used in the design of natural gas pipelines will be carried out. Several versions are presented according to the different flow regimes under consideration and through the presentation of these equations the basic physical support for each one is discussed as well as their feasibility.

Resumo em Inglês:

This work analyses a real time orbit estimator using the raw navigation solution provided by GPS receivers. The estimation algorithm considers a Kalman filter with a rather simple orbit dynamic model and random walk modeling of the receiver clock bias and drift. Using the Topex/Poseidon satellite as test bed, characteristics of model truncation, sampling rates and degradation of the GPS receiver (Selective Availability) were analysed.

Resumo em Inglês:

This paper presents specific cutting energy measurements as a function of the cutting speed and tool cutting edge geometry. The experimental work was carried out on a vertical CNC machining center with 7,500 rpm spindle rotation and 7.5 kW power. Hardened steels ASTM H13 (50 HRC) were machined at conventional cutting speed and high-speed cutting (HSC). TiN coated carbides with seven different geometries of chip breaker were applied on dry tests. A special milling tool holder with only one cutting edge was developed and the machining forces needed to calculate the specific cutting energy were recorded using a piezoelectric 4-component dynamometer. Workpiece roughness and chip formation process were also evaluated. The results showed that the specific cutting energy decreased 15.5% when cutting speed was increased up to 700%. An increase of 1º in tool chip breaker chamfer angle lead to a reduction in the specific cutting energy about 13.7% and 28.6% when machining at HSC and conventional cutting speed respectively. Furthermore the workpiece roughness values evaluated in all test conditions were very low, closer to those of typical grinding operations (~0.20 mm). Probable adiabatic shear occurred on chip segmentation at HSC.

Resumo em Inglês:

Predictive models are required to provide the bending set point for bending for the flatness control devices at rolling stands of finishing mill of Hot Strip Mill (HSM). A simple model for roll stack deflection at the finishing mill has been illustrated where a modified Misaka’s equation has been used to obtain mean flow-stress. Investigation has been performed to understand the effect of width of roll on roll stack deflection. The bending on the deflection has been found to have a positive effect to reduce the amount of the stack deflection. The results from the sensitivity analysis of the roll width on roll deflection are also described.

Resumo em Inglês:

This work presents an automated and dedicated system aiming at the measurement of straightness errors of mechanical components, using an industrial robot. A multi-probe error separation technique was used to make measurements independent from the coordinate system of the robot. A mathematical model that takes into account the readings from three sensors was specifically designed for the proposed measurements and produces inspection results by means of the solution of a system of linear equations, in only one operation. Also in this work, a new approach was developed to minimize the influence of the zero-adjustment errors of the sensors, which represent the major source of errors in the separation process. Experimental tests applied to the measurement of straightness errors of mechanical components were accomplished, which demonstrated the effectiveness of the employed methodology.

Resumo em Inglês:

In this paper, we report on numerical simulations of incompressible MagnetoHydroDdynamic flows by a two dimensional finite difference scheme associated to an appropriate projection method performed to characterize velocity-pressure formulations along the specified MHD duct by solving the set of differential equations of magnetohydrodynamics. In the present calculation, a working electrolytic solution is considered in order to bring up the application of the magnetohydrodynamic micropump. Numerical results show the characteristics of flow velocity, pressure distribution and their convergence tests. The computations aim to optimize the flow rate of a given MHD micropump regarding to its geometrical dimensions and the external electromagnetic excitation.

Resumo em Inglês:

Airlift pumps are finding increasing use where pump reliability and low maintenance are required, where corrosive, abrasive, or radioactive fluids must be handled and when a compressor is readily available. The objective of the present study is to evaluate the performance of a pump under predetermined operating conditions and to optimize the related parameters The effects of design parameters viz. mass flow rate of air, immersion ratio, diameter of rising main etc. on the performance of airlift pump are presented. The larger diameter of rising main is found to be suitable for high flow rate of water. The injecting device used in the system has considerable effect on the performance of the pump. The paper is focused on the general mathematical expression to determine the effective diameter of nozzle applicable to air lift pump installations in the diameter range of 25.4 mm < d < 101.6 mm. The various types of flows are visualized in the rising main of a pump and the corresponding airlift pump performance is analyzed. It is observed that the slug flow is more predominant for improving the performance of the pump.

Resumo em Inglês:

High speed cutting (HSC) offers the opportunity to significantly reduce machining times as well as to minimize manual rework for complex free form surfaces in the die and mould making industry. To achieve the best results it is also necessary to apply HSC-suitable machining strategies to perform optimal high speed milling operations. This paper presents a method to use free form features to improve the automatic generation of high speed machining information for specific geometric areas to create HSC free form manufacturing features. By examining the geometrical and topological information of the work piece’s virtual model, the feature elements can be extracted and joined with the required information. This covers several important high speed cutting aspects in the CAM system, like optimal technology and strategy suggestion, machining safety requirements and process stability of different strategies. Using this approach the programming time to produce HSC appropriate tool paths is reduced significantly, while it is quality is secured.

Resumo em Inglês:

This paper concerns the numerical simulation of internal recirculating flows encompassing a two-dimensional viscous incompressible flow generated inside a regularized square driven cavity and over a backward-facing step. For this purpose, the simulation is performed by using the projection method combined with a Chebyshev collocation spectral method. The incompressible Navier-Stokes equations are formulated in terms of the primitive variables, velocity and pressure. The time integration of the spectrally discretized, incompressible Navier-Stokes equations is performed by a second-order mixed explicit/implicit time integration scheme. This scheme is a combination of the Crank-Nicolson scheme operating on the diffusive terms and a second-order Adams-Bashforth scheme acting on the advective terms. The projection method is used to split the solution of the incompressible Navier-Stokes equations in two decoupled problems: the Burgers equation to predict an intermediate velocity field and the Poisson equation for the pressure, which is used to correct the intermediate velocity field and satisfy the continuity equation. Numerical simulations for flows inside a two-dimensional regularized square driven cavity for Reynolds numbers up to 10000 and over a backward-facing step for Reynolds numbers up to 875 are presented and compared with numerical results previously published, where good agreement is demonstrated.

Resumo em Inglês:

Gas-phase transient effects during the combustion of an infinite linear array of droplets are studied in the limit of infinite Damköler number and in the absence of surrounding convective effects. The present study stems from the quantification of truncation-distance effects on the droplet mass vaporization rate, flame position and flame shape in quasi-steady numerical simulations. The solution domain is initially split into near and far-field subdomains. Within each subdomain, analytical grid generation techniques are applied allowing the development of appropriate finite-difference expressions, the control of grid point distribution and the treatment of outflow boundary conditions. The interdroplet distance effect is studied and results for the droplet mass vaporization rate and flame behavior are presented. The results show the existence of different flame regimes ranging from isolated to merged flame conditions and similar vaporization rate evolution for different interdroplet distances.