Análise e modelagem do escoamento transitório de fluidos de perfuração

Drilling fluids present a thixotropic behavior and they usually gel when at rest. The sol-gel transition is fundamental to prevent the deposit of rock fragments, generated by drilling the well, over the drill bit during eventual stops. Under those conditions, high pressures are then required in order to break-up the gel when circulation is resumed. Moreover, very high pressures can damage the rock formation at the bottom of the well. Thus, a better understanding of thixotropy and the behavior of thixotropic materials becomes increasingly important for process control. The mechanisms that control thixotropy are not yet well defined and modeling is still a challenge. The objective of this work is to develop a mathematical model to study the pressure transmission in drilling fluids. This work presents a review of thixotropy and of different mathematical models found in the literature that are used to predict such characteristic. It also shows a review of transient flows of compressible fluids. The problem is modeled as the flow between the drillpipe and the annular region (space between the wall and the external part of the drillpipe). The equations that describe the problem (mass conservation, momentum balance, constitutive and state) are then discretized and numerically solved by using a computational algorithm in Fortran. The model is validated with experimental and numerical data obtained from the literature. Comparisons between experimental data obtained from Petrobras and calculated by three viscoplastic and one pseudoplastic models are conducted. The viscoplastic fluids, due to the yield stress, do not fully transmit the pressure to the outlet of the annular space. Sensibility analyses are then conducted in order to evaluate the thixotropic effect in pressure transmission.

Modelagem eletroquímica e do distúrbio ácido-básico em atletas de karatê participantes do campeonato mundial WKO 2014

The objective of this study was to analyze the electrochemical and acid-base disorders in high performance athletes during the World Karate Championship hosted by the WKO (World Karate Organization) in 2014. In this study 19 male athletes were analyzed (age 34 ± 8), black belts and with over 5 years of experience in the sport. Capillary blood samples from the digital pulp of the finger were collected in three stages: rest, 5 minutes after and 10 minutes after fighting (kumite). The sample was analyzed using blood gas analyzer GEM Premier 3000, using the parameters pH, Na+, K+, Ca2+, lactate e HCO3−. The values related to acid-base disturbance presented statistical differences (p <0.05) in most of the collected moments. The lactate levels found were 2.77 ± 0.97mmol / L in rest, 6.57 ± 2.1 for 5 minutes after and 4.06 ± 1.55 for 10 minutes after combat. The samples collected for the electrolytic markers showed no statistical differences in their values (p <0.05). Through the data collected, we conjecture that the sport can be characterized as a high-intensity exercise and with a predominance of the glycolytic system. The analysis of acid-base disturbance is an efficient method to assist in the control of training loads.

Simulação numérica da convecção mista em cavidade preenchida com meio poroso heterogêneo e homogêneo

In this work is presented mixed convection heat transfer inside a lid-driven cavity heated from below and filled with heterogeneous and homogeneous porous medium. In the heterogeneous approach, the solid domain is represented by heat conductive equally spaced blocks; the fluid phase surrounds the blocks being limited by the cavity walls. The homogeneous or pore-continuum approach is characterized by the cavity porosity and permeability. Generalized mass, momentum and energy conservation equations are obtained in dimensionless form to represent both the continuum and the pore-continuum models. The numerical solution is obtained via the finite volume method. QUICK interpolation scheme is set for numerical treatment of the advection terms and SIMPLE algorithm is applied for pressure-velocity coupling. Aiming the laminar regime, the flow parameters are kept in the range of 102≤Re≤103 and 103≤Ra≤106 for both the heterogeneous and homogeneous approaches. In the tested configurations for the continuous model, 9, 16, 36, and 64 blocks are considered for each combination of Re and Ra being the microscopic porosity set as constant φ=0,64 . For the pore-continuum model the Darcy number (Da) is set according to the number of blocks in the heterogeneous cavity and the φ. Numerical results of the comparative study between the microscopic and macroscopic approaches are presented. As a result, average Nusselt number equations for the continuum and the pore continuum models as a function of Ra and Re are obtained.