CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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Czechoslovakia/Czech Republic as a leader in polymer technologies in Central Europe: from contact lenses to 3D printing
Get PDFThe Czech Republic prides itself on a long-standing tradition in the scientific field of polymer studies and technologies. Seen in this light, the following article seeks to single out this particular tradition and to highlight some of the facts concerning practical applications that have been significantly enhanced by Czech experts such as Otto Wichterle in the latter half of the 20th century. Otto Wichterle, a prominent Czech chemist, revolutionised the field of ophthalmology with his invention of soft contact lenses. Despite the restrictive regime of Communist Czechoslovakia, Wichterle’s innovative work in organic chemistry, plastics, and biomaterials led to the development of hydrophilic soft contact lenses. His home-based experimental setup, which included a children construction set, a bicycle light battery, a phonograph motor, and homemade glass tubing and moulds, resulted in the creation of a transparent and absorbent gel suitable for eye implants. Wichterle’s pioneering work has had a profound global impact, with his invention now used by over 100 million people worldwide. His research has also paved the way for the development of “smart” biomaterials used in various medical devices
Parameters of back filling material prepared from mine tailing, fly ash, and mine water
Get PDFThe article investigates the influence of mine tailing, fly ash, and mine water on strength parameters as mine paste filling material performing the strength tests on different recipes of mortar mixes with individual types of fillers and wastewater from extraction of mine tailings. Recipe is prepared in proportions corresponding to the standard mortar and compared with a reference recipe according to the fresh mortar consistency test using a shaking table according to ČSN EN 1015-3. Resulting measured values on 40 × 40 × 160 mm solids samples for which the evaluation of the volume weight was carried out in the range of 2, 7, 14, 28, 56 and 90 days according to EN 1015-10 (722400). The results showed that that it is possible to prepare relatively fluid mixtures with extremely low binder dosage. And not only the water coefficient but also the granulometry of the raw material plays an important role in the long-term strengths of samples
EVALUATING FISH PASSAGE EFFICIENCY IN VERTICAL SLOT FISHWAYS USING THE ANALYTIC HIERARCHY PROCESS
Get PDFBased on the Analytic Hierarchy Process (AHP), a comprehensive evaluation system has been developed to assess the performance of vertical slot fishways. This system incorporates 30 factors related to fish passing efficiency, thereby facilitating a detailed analysis of hydraulic characteristics, engineering layout, operation management, and monitoring. For its practical application, the vertical slot fishway at the Laolongkou Hydro-junction project’s comprehensive evaluation was assessed and consequently rated as "Operating Excellently". This rating accurately reflects the fishway’s operational status. The case study demonstrates that the established index system and the model calculation method are capable of thoroughly considering the operational conditions of fishways and the applicability of the model. Moreover, the methodology offers valuable experiences and guidance for creating evaluation systems in various other water conservancy project sectors
Simulation of switching arcs in climate-neutral 420 kV earthing switches and disconnectors filled with Clean Air
Get PDFThe investigation of various SF6-alternatives is even more in the focus of current research and development efforts. In this context, gas-insulated switchgear with Clean Air (80% N2 and 20% O2) insulation and the use of vacuum switching technology for the circuit breaker can represent an environment-friendly (GWP = 0) and highly performant SF6-free solution for future high-voltage switchgear applications. Within this framework, this contribution focusses on the modelling and simulation of switching arcs in the active back parts of a Clean Air-filled gas-insulated switchgear, namely the earthing switch and disconnector. The presented arc model uses an alternative 2D axisymmetric simulation approach where the arc attachment size is conserved by means of a scaling of the arc current. In contrast to the conventional 2D axisymmetric approach based on the assumption of the conservation of electrical current, the presented alternative approach allows the electrical arc simulation away from the geometrical symmetry axis. The simulation results are in good agreement to the measurements in a real earthing switch configuration validating the new simulation approach
The importance of using active thermal protection following restoration work on old buildings
Get PDFThe paper deals with the issue of humidity and the unhealthy environment of old buildings. Humidity is a very widespread problem not only in historical buildings, but also in newer buildings. This problem can be observed in various parts of the world and thus it can be said that it is a global problem. Humidity in these buildings causes an unhealthy environment, which has a negative effect on individual building constructions, but also on people’s health. Humidity is also associated with the form of disruption of the individual layers of the construction and the disruption of the thermal resistance of these constructions. Buildings such as these subsequently have an unhealthy environment. After a part of the description of the known issue, the contribution follows on from this part by indicating possible remedial interventions and analyses the systems of additional thermal insulation (ETICS, ATP), ensuring the improvement of the internal environment. Finally, the article presents possible connections and extensions of this research and its application directly in practice. The results of the proposed research will significantly contribute to the approach to rehabilitated older buildings and their long-term sustainability from an economic point of view, as well as the possible use of them
Self-compacting concrete with reduced formwork pressures
Get PDFSelf-compacting concrete (SCC) is normally characterized with high pressures exerted on the formwork during casting. The pressures can easily exceed bearing capacity of a regular formwork when casting a high structural member in one step. The contribution shows new ways of reducing the pressures using mineral additives based on calcinated clay minerals and clay nanoparticles whose addition together with interrupted casting process leads to a substantial reduction of the formwork pressures. Short interruptions in the casting lead to microstructural changes and flocculation, thixotropy and early strength evolution. The positive effects are studied systematically in microstructural studies performed on modified cement pastes using microscopy and viscosimetry. Rheological behavior of standard SCCs is improved towards thixotropy of the mixture by using the mineral additives. The newly developed recipes are tested on SCCs used on real construction sites. Examples of their practical utilization and on-site measurements show on up to 50 % pressure reductions in enriched SCCs compared to ordinary SCCs
Analysis of the effect of hydration heat resulting in the formation of cracks on the experimental block of the spillway at Orlik reservoir
Get PDFThis article concentrates on the numerical analysis of hydration heat resulting in formation of cracks on the experimental block of the spillway at Orlik Reservoir and its verification with the experimental measurement. In order to eliminate the maximum of critical factors which could lead to appearance of early age cracking and faulty execution of the spillway, an experimental block was concreted. It served as a trial block for all steps of the execution process as well as a validating temperature measurement during cement hydration to confirm with the preliminary numerical analysis
Assessment of local mechanical properties of laser powder bed fused aluminium alloy by non-destructive testing based on FIMEC indentation
Get PDFLaser powder bed fusion process is a versatile metal additive manufacturing process. Although significant progress has been made so far, there is still limited large-scale adoption of this technique by the industry. The main problems are repeatability and lack of proper knowledge. In this work, an innovative and non-destructive testing methodology, based on flat-top cylinder indentation, was used to define the mechanical properties of laser powder bed fused aluminium alloy to highlight any variations induced by the combination of process parameters, for global characterization, and by the building direction, for local characterization. Results show similar or improved global mechanical properties of the laser powder bed fused specimens when compared to traditional die-casted ones. Indentation tests highlight a local dependence of properties along the building direction in favor of the upper part of the samples
Design of the testing procedure for investigation of Eryx conicus dermal armour characteristics
Get PDFThe aim of this work is to develop an experimental method suitable for the mechanical testing of highly non-standard biological samples such as snake skin with osteoderms. The objective of the method is to determine, whether the osteoderms provide a protective function for the animal in its natural environment. For this purpose, a simulation of rodents biting the skin based on uni-axial compressive loading using a synthetic tooth as a penetrator was developed with an emphasis on integration with X-ray scanners to facilitate in-situ testing. To identify and characterise the structure of snake skin and to prove the protective function of osteoderms, all samples were subjected to high resolution X-ray computed tomography. The results of the experiments are presented in the form of stress-strain curves and a map of the tangent modulus