Valencia-Bravo, Joaquín M.

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    Distension mechanism of a compliant tube caused by partial downstream fluid flow obstruction
    (2019-12-10) Valencia-Bravo, Joaquín M.; Just-Agosto, Frederick A.; College of Engineering; Silva Araya, Walter F.; Acosta Costa, Felipe J.; Suárez, Luis E.; Department of Civil Engineering; Menegozzo Sperotto, Marco
    This investigation examines the distension of a silicone tube through experiments and finite element modeling. Three experiments were conducted to examine the distension of the tube. Two experimental configurations were built. In the first two experiments the tube rests on a PVC base and in the other a soft silicone material encases the tube. Collapsing a silicone tube located inside an air pressure chamber downstream increases the fluid pressure causing distension. In the first experiment the volumetric flow rate is kept constant while the air pressure inside the chamber is increased. In the second experiment, the air pressure inside the chamber is kept constant while the volumetric flow rate is increased via a flow control valve. The procedure followed in the third experiment was similar to that performed in the first experiment. In all cases, an incoming laminar flow was imposed. Experimental distensions obtained ranged from 0.851 mm, 0.483 mm and 0.784 mm in the first, second and third experiment respectively. The range in the rotameter used limited the allowable flow rate obtainable in the second experiment. Experiments were repeated ten times. A Student's t distribution was used to obtain Ninety-five percent confidence bounds of the data. Finite element modeling was performed for steady-state cases using a fluid-structure interaction method with the arbitrary Lagrangian-Eulerian formulation. Experimental geometry was replicated using the NX software and then imported to the model. When meshing, hexahedral elements were used for the fluid and silicone-tube regions, while tetrahedral elements were used for the soft body domain. Trilinear interpolation functions were used in the discretization of the fluid velocity, fluid mesh displacement and fluid pressure, while quadratic interpolation functions were used for the solid displacement and solid pressure. In all cases, the flow was modeled as an incompressible laminar flow using the continuity and momentum equations. The solid was modeled with the nearly incompressible Ogden's hyperelastic model using the momentum equation in a mixed form. For comparison, when modeling the first experiment, the solid was also modeled with a linear-elastic material model. Applying boundary and coupling conditions completed the equations for both continuums. The system of nonlinear algebraic equations was linearized first and then solved with the damped Newton's method, with the help of iterative and direct solvers in a segregated way that were available in the software. Results of the Ogden's model fell within the 95% of confidence bound and matched very well with the mean values of the experimental data.
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    On-line performance parameter estimation of SR-30 turbojet engine
    (2010-12) Valencia-Bravo, Joaquín M.; Serrano-Acevedo, David; College of Engineering; Just, Frederick; Ruiz, Orlando E.; Department of Mechanical Engineering; Lorenzo, Edgardo
    Accurate estimation of jet engines performance parameters is the key to develop reliable diagnostics systems. The development of a reliable and accurate nonlinear model of the SR-30 turbojet engine is proposed. To comply with this general objective, it was necessary to achieve specific objectives. Models of the compressor and turbine characteristic maps were required and developed. These models were constructed based on SR-30 engine’s dimensions, fundamental theory and initial conditions of operation. A nonlinear model was developed for the SR-30 engine and implemented using Simulink. Resulting model is based on nested iterations, two iterations are used for the steady state performance model and one iteration for the transient state model. The characteristic maps developed are crucial for the steady state behavior of the engine model. The nonlinear engine model was validated using experimental data obtained from actual SR-30 test runs, using the same command input, to produce the system output. Correction factors were used, before implementing the Kalman filter estimator, to improve the model results. For the tuning/fitting procedure, the dual unscented Kalman filter (DUKF) was developed. DUKF is based on two Kalman filters which work simultaneously; one of these is the state estimation filter and the other is the parameter estimation filter. DUKF uses the residual parameter vector, which is the difference between the model outputs and the measured outputs, to modify the tuners. The tuners are health parameters, such as efficiency and flow capacity which represent performance deteriorations of engine components. These tuners are used to adjust the output engine model parameters to closely match the measured values. The simulation results with the use of correction factors, were satisfactory. However, the results were improved by using the DUKF. Areas for future work are identified.