Krzysztof Tesch

Arterial cannula shape optimization by means of the rotational firefly algorithm

This article presents global optimization results of arterial cannula shapes by means of the newly modified firefly algorithm. The search for the optimal arterial cannula shape is necessary in order to minimize losses and prepare the flow that leaves the circulatory support system of a ventricle (i.e. blood pump) before it reaches the heart. A modification of the standard firefly algorithm, the so-called rotational firefly algorithm, is introduced. It is shown that the rotational firefly algorithm allows for better exploration of search spaces which results in faster convergence and better solutions in comparison with its standard version. This is particularly pronounced for smaller population sizes. Furthermore, it maintains greater diversity of populations for a longer time. A small population size and a low number of iterations are necessary to keep to a minimum the computational cost of the objective function of the problem, which comes from numerical solution of the nonlinear partial differential equations. Moreover, both versions of the firefly algorithm are compared to the state of the art, namely the differential evolution and covariance matrix adaptation evolution strategies.

Determining heat transfer coefficients using evolutionary algorithms

This article presents a way of determining heat transfer calibrations for multi-objective and single-objective optimization by means of genetic algorithms. The need for optimization arises from the necessity for mathematical model validation and is very relevant to practical applications. The SPEA algorithm is used for multi-objective optimization. Scalarization of the fitness function is also addressed in combination with a small population size in order to keep the computational cost of the problem to a minimum. This is because of the time spent for a fitness function evaluation which comes from numerical solution of the nonlinear partial differential equations. The result is that a value of the heat transfer coefficient is determined that produces minimal difference between experimental results and numerical predictions.

Extended Duration Running and Impulse Loading Characteristics of an Acoustic Bearing with Enhanced Geometry

This paper presents performance during prolonged running of the acoustic bearing when PZTs are switched off and when they are switched on. The effect of active PZT on shaft’s displacements in X and Y directions is clearly demonstrated. Performance of the acoustic bearing was also assessed when an impulse force was applied to the running shaft at speed. Once again the benefits of having PZTs active are beyond doubt. The instability caused by the impulse force was rapidly mitigated as the bearing returned to its usual dynamics within around two second. In contrast, dynamics of the acoustic bearing operating with PZTs switched off was significantly disturbed and in the time of the test never returned to its status before application of the impulse force.

AN EXPERIMENTAL AND NUMERICAL STUDY ON THE PERFORMANCE OF AN INNOVATIVE VERTICAL-AXIS WIND TURBINE

This paper introduces the innovative modification of the Savonius wind turbine being able to significantly increase efficiency in comparison with the classic design. This innovative design is equipped with a stator directing the flow. The presence of the stator increases the active surface area and generates higher torques acting on a shaft. Additionally, it makes it possible to take better advantage of wind energy and compensate the effect of larger active surface area. The larger the stator angle the higher the efficiency. One of the biggest problem of the classic design, namely its relatively low efficiency, is overcome. The results of an experimental investigation, carried out in the closed return wind tunnel, are presented for various conditions and configurations. These include the most important characteristic such as the torque and power coefficient as a function of the tip speed ratio. Furthermore, a three dimensional numerical analysis of the transient phenomena occurring in the innovative turbine is investigated. Evaluation and comparison criteria are proposed in order to evaluate and compare various designs and solutions. This makes it possible to explain the increased efficiency of the innovative design.

Investigation of the aerodynamics of an innovative vertical-axis wind turbine

This paper presents a preliminary three dimensional analysis of the transient aerodynamic phenomena occurring in the innovative modification of classic Savonius wind turbine. An attempt to explain the increased efficiency of the innovative design in comparison with the traditional solution is undertaken. Several vorticity measures such as enstrophy, absolute helicity and the integral of the velocity gradient tensor second invariant are proposed in order to evaluate and compare designs. Discussed criteria are related to the vortex structures and energy dissipation. These structures are generated by the rotor and may affect the efficiency. There are also different vorticity measure taking advantage of eigenvalues of the velocity gradient tensor.