Publikační činnost Katedry hydromechaniky a hydraulických zařízení / Publications of Department of Hydrodynamics and Hydraulic Equipment (338)

Permanent URI for this collectionhttp://hdl.handle.net/10084/71279

Kolekce obsahuje bibliografické záznamy publikační činnosti (článků) akademických pracovníků Katedry hydromechaniky a hydraulických zařízení (338) v časopisech registrovaných ve Web of Science od roku 2003 po současnost.
Do kolekce jsou zařazeny:
a) publikace, u nichž je v originálních dokumentech jako působiště autora (adresa) uvedena Vysoká škola báňská-Technická univerzita Ostrava (VŠB-TUO),
b) publikace, u nichž v originálních dokumentech není v adrese VŠB-TUO uvedena, ale autoři prokazatelně v době jejich zpracování a uveřejnění působili na VŠB-TUO.

Bibliografické záznamy byly původně vytvořeny v kolekci Publikační činnost akademických pracovníků VŠB-TUO, která sleduje publikování akademických pracovníků od roku 1990.

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Now showing 1 - 20 out of 69 results

The effect of braid angle on hydraulic hose geometry
(MDPI, 2024) Dýrr, Filip; Bureček, Adam; Hružík, Lumír; Polášek, Tomáš; Ledvoň, Marian; Dvořák, Lukáš
Hydraulic hoses are part of most hydraulic systems, from industrial hydraulics with open loop hydraulic systems to mobile hydraulics with closed loop hydraulic systems. The design parameters of hydraulic hoses may influence the duty cycle dynamics of these systems. One of the factors that influence the behavior of a hydraulic hose under pressure loading is the steel braid angle with respect to the hydraulic hose axis. This work aims to determine the effect of the hydraulic hose braid angle on the change in its geometry. The next objective is to determine the forces that occur at the hose ends under pressure loading. The stresses occur when fluid pressure is applied to the inner wall of the hydraulic hose. Consequently, these stresses are transferred to the hose ends through the steel braid or spiral. The phenomenon of the neutral braid angle provides a balance between the stresses generated inside the hydraulic hose. Therefore, hydraulic hose manufacturers try to produce hydraulic hoses with a neutral braid angle, because the lifetime of the hydraulic hose is also related to this. As part of this research work, an experimental device was constructed in order to measuring the properties of hydraulic hoses. When the hose was loaded with fluid pressure, the change in hose geometry was measured and the angle of the hose braid was measured simultaneously. Upon the measurements, the effect of the braid angle on the hose behavior under pressure loading was determined.
Study of airfoil flow control with microcylinders using optical method
(Polska Akademia Nauk, Instytut fizyki, 2023) Gnatowska, R.; Gajewska, K.; Blejchař, Tomáš
This study aims to evaluate the effect of circular-shaped microcylinders on the flow field around an airfoil, using time-resolved particle image velocimetry. The results show that microcylinders can significantly modify the flow pattern around the NACA 0012 airfoil. The optimal configuration of microcylinder-airfoil depends on the angle of attack and the position of the microcylinder. The obtained results have practical implications for the development of more efficient and sustainable aircraft designs and wind turbine blades. The paper presents a physical analysis of flow fields using streamlines and vorticity structures to illustrate mechanisms of flow control for improving the aerodynamic properties of the airfoil. Overall, this work provides new insights into the fundamental physics of flow control using microcylinders, including general physics and optics, with potential application in various contexts, such as aerodynamics, flow control, airfoil design, optical diagnostics, and particle image velocimetry techniques.
Effect of cavitating hydraulic elements on pump characteristics
(MDPI, 2023) Jablonská, Jana; Kozubková, Milada; Drábková, Sylva; Blejchař, Tomáš
The effective and reliable performance of any pump can be significantly impacted by the piping system design. One of the essential points is the pump suction pipe. Poor design and dimension of the suction piping can lead to cavitation in the pump which affects its head and efficiency. The primary objective is to reduce the hydraulic losses of the suction piping in order to maintain a Net Positive Suction Head required by the pump. Suction piping is recommended to be short and straight, and branch connections, valves and elbows should be avoided, which is not always possible. In addition, cavitation can occur in the actual hydraulic elements installed on the pump suction. This work is focused on the investigation of cavitating hydraulic element in the suction pipe on the pump performance. A converging-diverging nozzle with a circular cross-section was used for this purpose. A straight pipe segment of constant diameter and the same length was used for comparison. Both elements were characterized by the loss coefficient and the cavitation number. Their influence on the pump head and the Net Positive Suction Head Available (NPSHA) was investigated.
Experimental and numerical analysis of flow force acting on the spool of proportional directional valve
(MDPI, 2023) Ledvoň, Marian; Hružík, Lumír; Bureček, Adam; Polášek, Tomáš; Dýrr, Filip; Kolář, David
This paper deals with the experimental and numerical analysis of the flow force acting on the spool of a proportional directional valve. The flow force arises due to the fluid flow through the flow path of the proportional directional valve and significantly influences the dynamics of the valve spool. The valve under investigation is a three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The dependence of the valve spool flow force on the volumetric flow rate is measured as part of the experiment. The measurements are performed for different spool displacements. The measured data will be used to verify the numerical simulations. The proportional directional valve was modified so that a force sensor could be included on the spool axis to realize the experiment. Firstly, the flow force is measured as the fluid passes through the two flow paths of the valve (PB and AT). Subsequently, the experimental setup is modified to determine the flow force when the fluid passes through each flow path separately. The measurements are compared. Simulations of the flow through the proportional directional valve are performed using Ansys Fluent 2022 R2 software to determine the flow forces acting on the valve spool. Simulations are performed for the selected spool positions of the proportional directional valve. Finally, the results of the simulation and the experiment are compared. The contribution of this study is a CFD model of the flow paths of the proportional directional valve verified by experiment. The CFD model will allow the flow force analysis for different flow path geometries of the investigated valve. Experimental analysis of flow force is performed over the entire spool stroke at different volumetric flow rates. The flow forces are measured for each flow path separately and for both flow paths simultaneously.
Effect of geometry and surface distribution of holes on sound and light absorption properties of 3D-printed PETG materials
(MM Science, 2023) Nevřela, Martin; Vašina, Martin; Hrbáček, Pavel; Dekýš, Vladimír
Noise and lighting are significant factors that have an impact on our health, environment, production quality, etc. The purpose of this paper is to investigate sound and light absorption properties of 3D-printed polyethylene terephthalate glycol (PETG) material specimens that were manufactured with two types of holes, namely with circular and square-shaped holes. In addition, the holes were printed with different dimensions, depths, shapes, and surface spacings. Different factors influencing the material´s ability to absorb sound and light were evaluated in this paper. It was found in this study that the type of holes, their spacing and depth have a big influence on sound and light absorption properties of the investigated samples compared to the smooth PETG material.
Study of mechanical properties of epoxy/graphene and epoxy/halloysite nanocomposites
(De Gruyter, 2023) Lapčík, Lubomír; Sepetcioğlu, Harun; Murtaja, Yousef; Lapčíková, Barbora; Vašina, Martin; Ovsík, Martin; Staněk, Michal; Gautam, Shweta
This article aimed to compare various mechanical properties of epoxy/graphene and epoxy/halloysite nanocomposites. Graphene nanoplatelets (GnPs) and halloysite nanotubes (HNTs) were used as fillers at different concentrations. The studied fillers were dispersed in the epoxy resin matrices. Elastic–plastic mechanical behavior modulation was observed utilizing the fillers’ nanoparticles and carboxyl-terminated butadiene–acrylonitrile copolymer rubber-modified epoxy resin. The hypothesis of the possible preceding inter-particle gliding of the individual GnPs in the complex resin nanocomposite matrix during mechanical testings was also confirmed. Increased ductility (elongation at break increased from 0.33 mm [neat matrix] to 0.46 mm [1 wt% GnPs] [39% increase]) and plasticity of the GnP nanocomposite samples were observed. In contrast, the decreasing mechanical stiffness as reflected in the decreased Young’s modulus of elasticity (from 3.4 to 2.7 GPa [20% decrease]) was found for the epoxy/HNT nanocomposites. The obtained dynamic stiffness of the investigated nanocomposites confirmed the complexity of the mechanical response of the studied material systems as a combination of the ductile and brittle phenomena.
Experimental verification of pneumatic elements mathematical models in Matlab-Simulink Simscape
(MM Science, 2023) Dvořák, Lukáš; Fojtášek, Kamil; Dýrr, Filip
The paper deal with a mathematical model of a pneumatic system and simulation of its behaviour. In the Matlab-Simulink Simscape program, there are models of basic elements from which it is possible to build a model of the entire system. The article describes the gradual testing of pneumatic elements mathematical models on the base of comparison with experimental data.
Leakage characteristics of proportional directional valve
(MDPI, 2023) Ledvoň, Marian; Hružík, Lumír; Bureček, Adam; Dýrr, Filip; Polášek, Tomáš
This paper deals with the analysis of leakage characteristics of the proportional directional valve. These characteristics distinguish a real directional valve from an ideal one. The ideal directional valve is characterized by zero leakage due to its perfect geometry. The investigated element is the three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The spool position is measured by the inductive position sensor and processed by external electronics. Internal leakage occurs due to axial and radial clearances between the spool and the sleeve. The magnitude of axial clearances that occur at throttle edges and their effect on the directional valve leakage is the subject of research. The blocked-line pressure sensitivity curve, the leakage flow curve and the center flow curve are determined by experiment. Individual characteristics are determined for different working fluid temperatures and different supply pressures. The flow through internal leaks in the center position of the valve spool is determined by analytical calculations. The flow through internal leaks is also simulated using the Ansys Fluent software. Subsequently, the geometry of the flow simulation model is modified to take into account manufacturing tolerances. From simulation results, the effect of the manufacturing tolerance magnitude on the internal leakage of the directional valve is evaluated. Finally, simulated dependencies are compared with experimentally determined characteristics.
Acoustic and mechanical testing of commercial cocoa powders
(Taylor & Francis, 2022) Lapčík, Lubomír; Lapčíková, Barbora; Gautam, Shweta; Vašina, Martin; Valenta, Tomáš; Řepka, David; Čépe, Klára; Rudolf, Ondřej
In the present study, commercial cocoa powders with different cocoa fat contents were studied. It was found that the cocoa powders' flow patterns were of a cohesive to highly cohesive characters. It was demonstrated, that the powders of higher crystalline structure were less flowable compared to the ones with the more amorphous ones. It was observed by SEM that the studied cocoa powders of higher cocoa fat content and the ones with the dietary fibers content (sample 2) exhibited more amorphous structure. The predominantly smooth surface structure of the higher fat content cocoa powder allowed its higher dense packing, triggering the decreased sound absorption typical for non-porous materials as quantified by NRC of 0.289 (sample 1, 100 mm material height) and 0.227 (sample 3) to 0.182 (sample 2). The latter conclusions were also supported by the observed increase of the structural mechanical stiffness of the freely poured powder bed of high cocoa fat amorphous powders, as resulting in the increasing magnitude of the K-l of 12.83 MPa (sample 1, 100 mm material height) and 19.29 MPa (sample 3) to 37.82 MPa (sample 2). Melting temperatures of the samples were determined by DSC. Results were directly corresponded to the cocoa butter content. The highest enthalpy of fusion (Delta H (m)) of (23.32 +/- 0.21) J/g was obtained for the highest cocoa butter containing sample 2 (of 20-22 wt. %). Obtained values of Delta H (m) for samples 1 and 2 were of (12.38 +/- 0.20) J/g and (10.27 +/- 0.17) J/g. T-p (melt) for reversing heat flow was ranging from (30.16 +/- 0.10) degrees C to (32.28 +/- 0.10) degrees C indicating the melting of stable beta polymorph. The melting peaks observed at distinct temperatures in the non-reversing heat flow patterns were indicating melting of the unstable alpha and metastable beta' and stable beta cocoa butter polymorphic forms.
Computational fluid dynamics could enable individualized surgical treatment of nasal obstruction (a preliminary study)
(MDPI, 2022) Plášek, Marek; Masárová, Michaela; Bojko, Marian; Komínek, Pavel; Matoušek, Petr; Formánek, Martin
Passage of nasal airflow during breathing is crucial in achieving accurate diagnosis and optimal therapy for patients with nasal disorders. Computational fluid dynamics (CFD) is the dominant method for simulating and studying airflow. The present study aimed to create a CFD nasal airflow model to determine the major routes of airflow through the nasal cavity and thus help with individualization of surgical treatment of nasal disorders. The three-dimensional nasal cavity model was based on computed tomography scans of the nasal cavity of an adult patient without nasal breathing problems. The model showed the main routes of airflow in the inferior meatus and inferior part of the common meatus, but also surprisingly in the middle meatus and in the middle part of the common nasal meatus. It indicates that the lower meatus and the lower part of the common meatus should not be the only consideration in case of surgery for nasal obstruction in our patient. CFD surgical planning could enable individualized precise surgical treatment of nasal disorders. It could be beneficial mainly in challenging cases such as patients with persistent nasal obstruction after surgery, patients with empty nose syndrome, and patients with a significant discrepancy between the clinical findings and subjective complaints.
The impact of different hydrocolloids on the viscoelastic properties and microstructure of processed cheese manufactured without emulsifying salts in relation to storage time
(MDPI, 2022) Kratochvílová, Alena; Salek, Richardos Nikolaos; Vašina, Martin; Lorencová, Eva; Kůrová, Vendula; Lazárková, Zuzana; Dostálová, Jolana; Šenkýřová, Jana
The current study was conducted to evaluate the effect of the addition of selected hydrocolloids [agar (AG), kappa-carrageenan (KC), or gelatin (PG); as a total replacement for emulsifying salts] on the viscoelastic properties and microstructure of processed cheese (PC) samples during a storage period of 60 days (at 6 +/- 2 degrees C). In general, PC viscoelastic properties and microstructure were affected by the addition of hydrocolloids and the length of storage time. The evaluated PC reported a more elastic behavior (G' > G '') over the viscous one. The highest values of viscoelastic moduli (G'; G*) were recorded for PC samples manufactured with KC addition, followed by those prepared with AG and PG. The control sample presented values of viscoelastic moduli similar to those of the PG sample. All PC samples tested had fat globule size values lower than 1 mu m. Moreover, PC with AG and KG addition presented similar microstructures and sizes of fat globules.
Effect of machining conditions on temperature and Vickers microhardness of chips during planing
(MDPI, 2022) Monka, Peter Pavol; Monková, Katarína; Vašina, Martin; Kubišová, Milena; Korol, Martin; Sekeráková, Adriana
For the machining of long and narrow surfaces and when processing multiple pieces, planing technology is used, the productivity of which can be higher than that of milling, although it is relatively slow machining. The article aims to study the degree of influence of the geometry of the tool (the angle of cutting-edge inclination and the angle of the tool-orthogonal rake), as well as the cutting conditions (cutting depth and cutting speed) on the chip characteristics (temperature and microhardness) in orthogonal and oblique slow-rate machining of steel 1.0503 (EN C45). The experiments were carried out on specially prepared workpieces designed for immediate stopping of machining. The results of the experiments were statistically processed, and behavioural models were created for temperature and Vickers microhardness of chips for individual combinations of factors. The obtained dependencies revealed how the geometry of the cutting tool and the cutting conditions affect the temperature and microhardness in the cutting area and at the same time allowed the best conditions for both orthogonal and oblique machining to be set up.
Experimental analysis of fluidic muscles
(MM Science, 2022) Dýrr, Filip; Dvořák, Lukáš; Fojtášek, Kamil; Brzezina, Petr; Hružík, Lumír; Bureček, Adam
Fluidic muscles have been the subject of research since the 1930s to the present day. McKibben's muscle is one of the most common ones. This type is the basis for fluidic muscles already being used commercially. The power-to-weight ratio is one of their main advantages. The disadvantage is difficult handling. The article describes experimental verification of static characteristics of fluidic muscles. During muscle contraction, a tensile force is developed which changes as the length of the muscle changes. This dependence is experimentally verified. A measuring equipment for testing fluidic muscles of various lengths and diameters is designed and assembled. The device consists of a pneumatic circuit, where the output drive is a loaded fluidic muscle. The load of muscle is generated by a hydraulic cylinder. The results will be further applicable to fluidic muscle simulations.
Study of factors influencing vibro- isolating properties of materials for passive elastic bearing of machines
(MM Science, 2022) Vašina, Martin; Pöschl, Marek; Hružík, Lumír; Bureček, Adam; Kotrasová, Kamila; Kormaníková, Eva
Machinery or instruments are subjected to external forces from a base in many cases. It can have a negative influence on manufacturing accuracy, tightness, wear of machine parts, work safety etc. Therefore, it is necessary to perform suitable passive elastic bearings of machinery to eliminate external vibration from the base. An application of suitable vibro-isolating materials is one way of the vibration elimination. The aim of the paper is to study vibration damping properties of different materials by means of a non-destructive method of forced mechanical oscillations. Different factors influencing transfer damping of mechanical vibration were investigated in this work, e.g., material type and its thickness, excitation frequency of mechanical oscillations, size of mass load and effect of material composition. These factors were subsequently evaluated. Finally, suitable recommendations for passive damping of mechanical vibration were described.
Intelligent high-tech coating of natural biopolymer layers
(Elsevier, 2022) Murtaja, Yousef; Lapčík, Lubomír; Lapčíková, Barbora; Gautam, Shweta; Vašina, Martin; Spanhel, Lubomir; Vlček, Jakub
Polymeric materials play a vital role in our daily life, but the growing concern for the environment demands economical and natural biopolymers that can be cross-linked to create technologically innovative lightweight materials. Their cellular matrix with extreme flexibility makes them highly acceptable for application prospects in material science, engineering, and biomedical applications. Furthermore, their biocompatibility, mechanical properties, and structural diversity provide a gateway to research them to form technologically important materials. In the light of the same, the review covers cellulose derivatives. The first section of the study covers the general properties and applications of cellulose and its derivatives. Then, the biopolymers are characterised based on their dielectric properties, crystallinity, rheology, and mechanical properties. An in-depth analysis of the diffuse process of swelling and dissolution followed by a brief discussion on diffusion and diffusion of crosslinking has been done. The review also covers a section on swelling and swelling kinetics of carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC). The examination of all the aforementioned parameters gives an insight into the future aspects of the biopolymers. Lastly, the study briefly covers some preferred choices of cross-linking agents and their effect on the biopolymers.
Effect of 3D-printed PLA structure on sound reflection properties
(MDPI, 2022) Monková, Katarína; Vašina, Martin; Monka, Peter Pavol; Vanca, Ján; Kozak, Dražan
3D printing technique is currently one of the promising emerging technologies. It is used in many areas of human activity, including acoustic applications. This paper focuses on studying the sound reflection behavior of four different types of 3D-printed open-porous polylactic acid (PLA) material structures, namely cartesian, octagonal, rhomboid and starlit structures. Sound reflection properties were evaluated by means of the normal incidence sound reflection coefficient based on the transfer function method using an acoustic impedance tube. In this study, various factors affecting the sound reflection performance of the investigated PLA samples were evaluated. It can be concluded that the sound reflection behavior of the tested PLA specimens was strongly affected by different factors. It was influenced, not only by the type of 3D-printed open-porous material structure, but also by the excitation frequency, the total volume porosity, the specimen thickness, and the air gap size behind the tested specimen inside the acoustic impedance tube.
Methods of CFD modelling of twin-screw pumps for non-newtonian materials
(MM Science, 2021) Bojko, Marian; Hertl, Lukáš; Drábková, Sylva
The twin-screw pump is designed for pumping highly viscous materials in the food industry. Rheological characteristics of materials are important in the specification of design parameters of screw pumps. Analysis of flow in the twin-screw pumps with definition of non-newtonian materials can be made by numerical modelling. CFD generally oriented software ANSYS Fluent and ANSYS Polyflow has been used for modelling. In this study those software's (ANSYS Fluent and ANSYS Polyflow) were defined for solution of flow in the twin-screw pumps. Results were compared for the same boundary conditions on the inlet and outlet of the 3D model. For definition of the viscosity were used the Nonnewtonian power law. Parameters as consistency coefficient and flow exponent for Nonnewtonian power law were analysed by software ANSYS Fluent and ANSYS Polyflow. Postprocessing form ANSYS Fluent and ANSYS Polyflow were made by contours of field and by graphs.
Flow of oil and water through the nozzle and cavitation
(MDPI, 2021) Jablonská, Jana; Kozubková, Milada; Bojko, Marian
Today, the correct understanding of the issue of oil and water cavitation is important due to the growing demands on working conditions in hydraulic systems (pressure and flow rate). This article deals with the measurement and subsequent mathematical modeling of cavitation in a convergent-divergent nozzle of circular cross-section. Cavitation depends on the physical properties of the flowing medium as a function of temperature. Usually, cavitation in water is defined by a two-phase flow of water and vapor, but the air contained in the water significantly affects cavitation. There is usually no vapor cavitation in the oil. Far more often, cavitation in oil is caused by the air it contains. For comparison, cavitation in water and oil was generated in experiments with an identical nozzle. The measurement was used to define boundary conditions in mathematical models and to verify simulations. The problem of cavitation was solved by three variants of multiphase flow, single-phase flow (water, oil), two-phase flow (water-vapor, oil-air) and three-phase flow (water-vapor-air, oil-vapor-air). A turbulent model with cavitation was used for all variants. The verification of simulations shows that for water cavitation it is necessary to use a three-phase model (water, vapor, air) and for oil cavitation a two-phase model (oil, air) is sufficient. The measurement results confirm the importance of the air phase in modeling cavitation in both water and oil.
Inquiry into the temperature changes of rock massif used in energy production in relation to season
(MDPI, 2021) Klempa, Martin; Látal, Jan; Grafová, Barbora; Matloch Porzer, Michal; Vrtek, Mojmír; Kunz, Antonín; Šiška, Petr
This research was undertaken to perform and evaluate the temperature measurement in the ground utilized as an energy source with the goal to determine whether significant temperature variations occur in the subsurface during the heating season. The research infrastructure situated on our University campus was used to assess any variations. The observations were made at the so called "Small Research Polygon " that consists of 8 monitoring boreholes (Borehole Heat Exchangers) situated around a borehole used as an energy source. During the heating season, a series of monthly measurements are made in the monitoring boreholes using a distributed temperature system (DTS). Raman back-scattered light is analysed using Optical Frequency Time Domain Reflectometry (OTDR). Our results indicate that no noticeable changes in temperature occur during the heating season. We have observed an influence of long-term variations of the atmospheric conditions up to the depth of a conventional BHE (& AP;100 m). The resulting uncertainty in related design input parameters (ground thermal conductivity) was evaluated by using a heat production simulation. Production data during one heating season at our research facilities were evaluated against the design of the system. It is possible to construct smaller geothermal installations with appropriate BHE design that will have a minimal impact on the temperature of the surrounding rock mass and the system performance.
Study of the mechanical, sound absorption and thermal properties of cellular rubber composites filled with a silica nanofiller
(MDPI, 2021) Pöschl, Marek; Vašina, Martin
This paper deals with the study of cellular rubbers, which were filled with silica nanofiller in order to optimize the rubber properties for given purposes. The rubber composites were produced with different concentrations of silica nanofiller at the same blowing agent concentration. The mechanical, sound absorption and thermal properties of the investigated rubber composites were evaluated. It was found that the concentration of silica filler had a significant effect on the above-mentioned properties. It was detected that a higher concentration of silica nanofiller generally led to an increase in mechanical stiffness and thermal conductivity. Conversely, sound absorption and thermal degradation of the investigated rubber composites decreased with an increase in the filler concentration. It can be also concluded that the rubber composites containing higher concentrations of silica filler showed a higher stiffness to weight ratio, which is one of the great advantages of these materials. Based on the experimental data, it was possible to find a correlation between mechanical stiffness of the tested rubber specimens evaluated using conventional and vibroacoustic measurement techniques. In addition, this paper presents a new methodology to optimize the blowing and vulcanization processes of rubber samples during their production.

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