Michael Valášek

The transition toward sustainable aviation fuels (SAF) represents one of the most promising and immediate pathways to reduce greenhouse gas emissions and improve environmental performance in regional aviation. As global air traffic continues to grow, especially in short- and medium-haul operations where turboprop aircraft are widely used, the adoption of alternative fuels becomes increasingly critical. This study presents a comprehensive performance analysis of an advanced turboprop engine operating with three different fuel types: conventional Jet-A1 kerosene, neat SAF, and a representative SAF blend. The evaluation focuses on a detailed assessment of key engine performance parameters, including specific fuel consumption and power output, as well as the associated gaseous emissions profile. Comparative results highlight measurable differences in both performance behavior and emissions characteristics depending on the selected fuel type. Beyond the quantitative comparison, the analysis also investigates potential operational impacts related to fuel composition, combustion stability, and compatibility with existing engine architectures. Findings show that while SAF and SAF blends may introduce only minor variations in traditional performance metrics relative to Jet-A1, they offer significant advantages in terms of lifecycle carbon footprint reduction, particulate matter emissions, and alignment with long-term decarbonization strategies. Overall, this work contributes to a deeper understanding of the technical implications of SAF utilization in turboprop propulsion systems. It also provides valuable insights for future engine development, certification activities, and policy measures supporting sustainable fuel adoption in aviation.

The long-term success of interventions in cardiovascular medicine can be enhanced by the computer-assisted planning of these procedures. However, the reliability of all computational simulations depends significantly on the input parameters. One of the most important is the constitutive model for the biological tissue and for the implant material. While the last few decades have brought great advances in modelling the mechanical properties of the arterial wall, synthetic grafts have not received as much attention. The primary goal of our research is to contribute to filling this gap. Our study is focused on determining a constitutive model for ePTFE vascular grafts. Uniaxial tensile experiments with strips cut from tubular vascular grafts SA1802 (Gore-Tex Stretch Vascular Graft – Large diameter) in the circumferential and longitudinal direction, and pressurization experiments with intact graft tubes V06010L (Gore-Tex Vascular Graft – Standard-walled) were carried out. A nonlinearly elastic anisotropic model was used to describe the mechanical response observed in these experiments. The four-fiber hyperelastic model based on the exponential function combined with the neo-Hookean term was able to fit the data observed in both the uniaxial tensile and inflation-extension experiments with one single set of parameters. Thus, the resulting model is suitable to be used in numerical simulations studying surgical procedures involving ePTFE vascular grafts in the mechanical states of uniaxial as well as multiaxial stress.

Vortices belong to the most important phenomena in fluid dynamics and play an essential role in many engineering applications. They can act detrimentally by harnessing the flow energy and reducing the efficiency of an aerodynamic device, whereas in other cases, their presence can be exploited to achieve targeted flow conditions. The control of the vortex parameters is desirable in both cases. In this paper, we introduce an optimization strategy for the control of vortices in the wake of a bluff body. Flow modelling is based on RANS and DES computations, validated by experimental data. The algorithm for vortex identification and characterization is based on the triple decomposition of motion. It produces a quantitative measure of vortex strength which is used to define the objective function in the optimization procedure. It is shown how the shape of an aerodynamic device can be altered to achieve the desired characteristics of vortices in its wake. The studied case is closely related to flame holders for combustion applications, but the conceptual approach has a general applicability to vortex control.

This work deals with the control of flexible structures as underactuated systems. The invariant control method performs the control of a flexible robot as a representative of an underactuated system with zero dynamics. The control input is separated into two parts. The arbitrary part of the control input is designed to control the directly actuated part of the dynamic system. The invariant part of the control is selected to steer the system zero dynamics in the desired way. The harmonic functions create the base for the invariant part of the control function. The residual vibration cancellation is the target of the presented invariant control strategy. The harmonic function frequencies are overtaken from the so-called natural motion, amplitudes are the results of the optimization process. The main target of this paper is to show the invariant control approach and its application to the system with flexible elements.

The paper deals with the overview of software tools for the design of mechatronic vehicles based on the approach of design through modelling and simulation. This design methodology is based on the assembly of the simulation model and the following control synthesis and/or parameter optimisation within design iterations by simulation runs. Therefore the software tools are mainly covering the simulation systems. The key problem is the way how to assemble the simulation model of the complete mechatronic system. Two approaches are described and analysed: interfacing of specialised simulation tools for particular components and uniform modelling by uniform language of the complete system. The main result of this study is the overview (certainly being uncomplete) of software tools which enable to create the simulation model of the complete mechatronic vehicle either by interconnecting or uniform modelling.

An interesting concept of wave-based control(WBC) has been around for about two decades now. Its core objective is to control the end-point motions of 1-D lumped mass flexible chains using one single base actuator and a motion sensor from the immediately adjacent mass. This severely underactuated mechanism is shown to achieve a benchmark point-to-point motion without (or with considerably attenuated) residual oscillations. WBC strategy is based on a set of hypothetical motion waves (in forward and backward directions) as the decomposition of physical motion of the masses. This paper revisits the concept in order to rectify several misconceptions, especially the earlier claim that such a control strategy can be created without any prior knowledge on the system dynamics. In particular the stability of the controlled system is revisited. Furthermore we offer one well-defined step-by-step procedures for formulating a WBC law and suggest vast opportunities for future explorations. An example parametric optimization pathway is also presented.