The goal of this work is to provide accurate dynamical models of oscillations in the flow past a rectangular cavity, for the purpose of bifurcation analysis and control. We have performed an extensive set of direct numerical simulations which provide the data used to derive and evaluate the models. Based on the method of Proper Orthogonal Decomposition (POD) and Galerkin projection, we obtain low-order models (from 6 to 60 states) which capture the dynamics very accurately over a few periods of oscillation, but deviate for long time.

Self-sustained oscillations in the flow past an open cavity

Modeling oscillation modal interaction in a hydroelectric generating system

Effect mechanism of cavitation on the hump characteristic of a pump-turbine

Utility of CFD in the design and performance analysis of hydraulic turbines — A review

Diabetes is a disease resulting from the impaired mechanism of insulin secretion from the pancreas, which prevents glucose from entering the cells and being utilized and leads to wide swings of blood sugar and many complications such as heart disease and stroke, kidney disease and amputations. In order to prevent these complications and achieve a better quality of life for diabetic patients, effective regulation of blood glucose is essential. This study aims to achieve a better blood glucose control profile by incorporating the time-dependent uncertainties in diabetic patient parameters into formulations of optimal control using a novel approach which originates from finance literature. The time-dependent uncertainties are represented using stochastic processes called Ito processes and the mathematical formulation for this problem is presented. The usefulness of this approach is shown using experimental data from a diabetic patient and stochastic and deterministic optimal control profiles are computed. The stochastic profile results in fewer variations in blood glucose from the reference value of 4.5 mmol/L as compared to the deterministic profile in the presence of parametric uncertainty. This method holds a lot of promise in reducing the wide swings of blood glucose observed in diabetic patients and preventing possible complications of diabetes.

Blood glucose regulation with stochastic optimal control for insulin-dependent diabetic patients

Numerical research of cavitation on Francis turbine runners

The objective of this work is to develop a closed-loop controlled insulin pump to keep the blood glucose level of Type 1 diabetes mellitus (T1DM) patients in the desired range. In contrast to the existing artificial pancreas systems with syringe pumps, an energy-efficient, valveless piezoelectric pump is designed and simulated with different types of controllers and glucose-insulin models. COMSOL Multiphysics is used for piezoelectric-fluid-structural coupled 3D finite element simulations of the pump. Then, a reduced-order model (ROM) is simulated in MATLAB/Simulink together with optimal and proportional-integral-derivative (PID) controllers and glucose–insulin models of Ackerman, Bergman, and Sorensen. Divergence angle, nozzle/diffuser diameters, lengths, chamber height, excitation voltage, and frequency are optimized with dimensional constraints to achieve a high net flow rate and low power consumption. A prototype is manufactured and experimented with different excitation frequencies. It is shown that the proposed system successfully controls the delivered insulin for all three glucose–insulin models.

A Novel Artificial Pancreas: Energy Efficient Valveless Piezoelectric Actuated Closed-Loop Insulin Pump for T1DM

Particle swarm optimization (PSO) is a popular method to solve the optimization problems. However, calculations for each particle will be excessive when the number of particles and complexity of the problem increases. As a result, the execution speed will be too slow to achieve the optimized solution. Thus, this paper proposes an automated design and optimization method for rotary MRF brakes and similar multi-physics problems. A modified PSO algorithm is developed for solving multi-physics engineering optimization problems. The difference between the proposed method and the conventional PSO is to split up the original single population into several subpopulations according to the division of labor. The distribution of tasks and the transfer of information to the next party have been inspired by behaviors of a hunting party. Simulation results show that the proposed modified PSO algorithm can overcome the problem of heavy computational burden of multi-physics problems while improving the accuracy. Wire type, MR fluid type, magnetic core material, and ideal current inputs have been determined by the optimization process. To the best of the authors’ knowledge, this multi-physics approach is novel for optimizing rotary MRF brakes and the developed PSO algorithm is capable of solving other multi-physics engineering optimization problems. The proposed method has showed both better performance compared to the conventional PSO and also has provided small, lightweight, high impedance rotary MRF brake designs.

Design and multi-physics optimization of rotary MRF brakes

Every single turbine is custom-designed specifically to meet the requirements of a hydroelectric power plant. Performance of a designed turbine is validated, to some extent, by computational fluid ...

https://journals.sagepub.com/doi/pdf/10.1177/0020294017702284

Model Testing of Francis-Type Hydraulic Turbines:

This article presents a novel rotary magnetorheological fluid device with inherently low off-state torque. The working principle of the device is similar to peristaltic pumps except the fluid remains inside the device and circulates continuously. Unlike other continuous rotation magnetorheological fluid devices, which operate in shear mode, the proposed device works in pressure driven flow mode. A proof of concept prototype with arbitrary dimensions is built and experimentally evaluated. Measured off-state torque is as low as 20 N.mm. Analytical model of the resistant torque and finite element simulations of the magnetic circuit are presented and validated with the experimental results. Using these models, an optimal device with similar off-state characteristics can be designed to fulfill specific requirements of size, weight, power and on-state torque. The proposed concept is promising especially for use in high precision haptic interfaces that require stability and transparency at the lower end of force spectrum.

Yigit Tascioglu

Papers

Numerical research of cavitation on Francis turbine runners

A Novel Artificial Pancreas: Energy Efficient Valveless Piezoelectric Actuated Closed-Loop Insulin Pump for T1DM

Design and multi-physics optimization of rotary MRF brakes

Model Testing of Francis-Type Hydraulic Turbines:

Modeling and experimental evaluation of a rotary peristaltic magnetorheological fluid device with low off-state torque for haptic interfaces