Study of load-bearing timber-wall elements using experimental testing and mathematical modelling

We present the experimental-numerical analysis of the influence of temperature on mechanical properties of structural high-strength steel class S690QL. Since the steel S690QL belongs to a group of steels with good mechanical properties, the aim of this paper is to determine the highest temperatures at which these good characteristics are kept. Experimental tensile testings of the specimens were performed at five different temperatures in the range from 20 to 550°C. Beside experimental testing, strengthening curves were calculated and numerical analysis using finite element method was performed. Both the experimental and numerical results have shown that decrease of mecahanical properties occurs at approximately 450°C.

MEMS thruster with blended propellant was fabricated and experimentally tested in order to improve specific impulse of micro scale monopropellant thruster and to improve stability of thrust to be better. 90 wt. % H2O2 blended with 25 O/F ratio ethanol was used as propellant of thruster and platinum on alumina support was used as catalyst for decomposition of propellant. Thruster was made by five layers of photosensitive glasses. Four layers were integrated by thermal bonding method and catalyst was directly inserted into chamber before UV bonding process for the last layer bonding. Results of experimental tests showed ethanol blended hydrogen peroxide had higher specific impulse than unblended hydrogen peroxide. Expected improvement of thrust stability due to the blended propellant was found only in the transient state of thrust. Also, unlike the thrust instability of vertical type thruster of previous research, improvement of thrust stability was found owe to horizontal type thruster pattern on glass, despite aspect ratio limitation of glass fabrication with wet etching process. During the experimental test, combustion phenomena of ethanol with decomposed hydrogen peroxide were observed through glass layer and it made fracture on structure of thruster.

A liquid metal microfluidic metasurface is demonstrated for the continuous and simultaneous reconfiguration of electromagnetic properties, including phase, resonance frequency, and reflection amplitude. The metasurface, constructed from each split-ring cell with a variable cross-section, is fabricated using a polydimethylsiloxane array microchannel molding process. The designed subarray (5 × 3 units) of the metasurface enables continuous, independent, and differential regulation by bistable liquid metal microfluidics. A continuous state coding method for electromagnetic reconfiguration is proposed and validated through both simulations and experimental tests. The resonant frequency and reflection amplitude are experimentally tested by a 30 cm × 30 cm liquid metal metasurface, demonstrating a frequency reconfiguration range from 2.1 to 5.1 GHz and a continuous reflection amplitude regulation of up to 10 dB within the 2.5 to 6.5 GHz range. The relative bandwidth and absolute bandwidth are up to 88.89% and 4 GHz, respectively. Therefore, this technique provides an effective approach for broadband continuous reconfiguration and multi-bit coding of electromagnetic responses with low-power consumption.

In the last century, the refrigerant R744 (carbon dioxide) has become an environmentally friendly solution in commercial refrigeration despite its particular issues related to the low critical temperature. The use of transcritical cycles in warm and hot countries reveals the necessity of adopting different configurations and technologies to improve this specific cycle. Among these, subcooling methods are well-known techniques to enhance the cooling capacity and the Coefficient of Performance (COP) of the cycle. In this work, an R600a dedicated mechanical subcooling system has been experimentally tested in an R744 transcritical system at different operating conditions. The results have been compared with those obtained using a suction-to-liquid heat exchanger (IHX) to determine the degree of improvement of the mechanical subcooling system. Using the experimental tests, a computational model has been developed and validated to predict the optimal subcooling degree and the cubic capacity of the mechanical subcooling compressor. Finally, the model has been used to analyze the effect of using different refrigerants in the mechanical subcooling unit finding that the hydrocarbon R290 and the HFC R152a are the most suitable fluids.

A low-cost high-efficiency high power-density electronic ballast for 35 W automotive high intensity discharge (HID) is presented along with the results of theoretical computations and experimental tests. The ballast circuits is based on a 100 kHz resonant inverter, a half-wave rectifier and a 400 Hz operated square-wave inverter. The converter operates at zero turn on losses, nearly zero turn off losses, and at a reduced electromagnetic interference level. The ballast circuit is designed to prevent inappropriate operations due to the acoustic resonances. The lamp voltage waveform has limited dv/dt and no DC component contributing to a long operating life of the lamp. A breadboard of the electronic ballast was designed and experimentally tested on a 35 W lamp, for a DC input voltage ranging from 9 V to 16 V. The electronic ballast performs all the features required to turn-on, warm-up and drive at the steady state a 35 W HID lamp and operates at a maximum steady state efficiency /spl eta/=84%,.

The increasing demand for modular and reusable steel structures has driven the development of demountable connections that preserve the integrity of structural components. This study investigated the structural performance of beam-to-column connections using clamp-based fastening systems, operating strictly within the elastic regime and targeting applications in temporary systems and industrial platforms. Two triangular steel frame configurations (180 mm and 260 mm), differing in clamp capacity and hole arrangement, were experimentally tested and numerically modeled to assess their influence on load-bearing capacity, displacements, and stress distribution. Experimental tests were conducted with controlled bolt pretension and progressive vertical loading, continuously monitoring displacements and applied forces. The finite element model (FEM), validated with high correlation (>97%) to the experimental data, confirmed that all configurations remained within the elastic domain. Results showed that increasing the number of clamps significantly enhanced both stiffness and load capacity, with gains of up to 27.3% depending on the configuration, while reductions exhibited a nonlinear performance loss. Stress concentrations were observed in clamp contact regions without plasticization. Overall, clamp-based connections demonstrated efficient structural performance and alignment with design-for-deconstruction and circular economy principles, proving to be technically feasible for systems requiring reusability and adaptability.

ABSTRACTThe corrugated paper fiberboard (CPF) includes the medium and liner papers, which are elastic–plastic materials with numerous mechanical parameters and can be modelled by the MAT274 paper constitutive model in LS‐DYNA. Li's simplified formula and Garbowski's modified empirical formula for calculating the edge crush strength (ECS) of CPF also need some known mechanical parameters of base papers. The methodology is proposed to determine these paper mechanical parameters through the tensile and ring crush tests. To realize the simulation of the ECS test of CPF, the finite element (FE) model with contacts having failure criteria is created using ANSYS/Workbench and LS‐PREPOST. Meanwhile, the compressive force–displacement curves, compression deformation modes and ECS values of CPFs were obtained through experimental tests and theoretical formulas. The agreement between the simulated, experimentally tested and theoretically calculated results verifies the reliability of the FE model. A specific sensitivity analysis is conducted on the primary mechanical parameters of liner and medium papers, which offers a brief assessment of how changes in these mechanical parameters influence the ECS values. This study provides important reference and guidance for the digital design and reliable application of CPFs.

Thermal analysis of novel minichannel-based solar flat-plate collector

Optimized Prototype of Instrumented Knee Implant: Experimental Validation

Thousands of infants are born every year with cardiac defects leaving them with only one functioning ventricle. As a result of these defects, these infants undergo strenuous palliative procedures to create what is known as a Fontan physiology and still are left facing numerous complications including congestive heart failure, thrombosis, arrhythmias and more. Treatment and management costs for these Fontan patients exceeds $1 billion every year, and the available donor supply is too small to be considered a feasible solution. The available blood pumps and ventricular assist devices, while they have been implemented successfully in some cases, were not specifically designed for these single ventricle patients and thus have several shortcomings. The size of these pumps in addition to rigid design leads to irregular flow dynamics, insufficient performance and blood damage. It is suggested that only 1-5 mmHg would be sufficient to alleviate the many complications associated with single ventricle physiology, making a purposely designed blood pump a viable solution as a bridge therapy to heart transplantation. Using computational means and experimental testing, this study investigated the use of a minimally invasive axial flow blood pump with a cage and impeller to support the Fontan physiology until a donor heart becomes available. Prior research focused on cage filament direction and impeller angle separately, making the focus of this thesis determining an optimal combination of cage and impeller design. Design geometries were rapid prototyped to be experimentally tested and Solidworks models were used in ANSYS CFX to run computational simulations. Geometries varied in the number of filaments, cross-sectional shape of the filament and the impeller blade angle of twist. Pressure generation, capacity range, estimated shear stresses and blood damage levels were examined. Both the simulations and experiments demonstrated that the new cage designs were within the desired pressure rise and hemodynamic ranges, but qualitatively some designs were able to outperform others. A resulting combination of the 5-filament cage design with the 350°impeller angle was determined as optimal, thus furthering the support in the development of an axial flow blood pump for a failing Fontan physiology.

This research investigates the interaction between a flexible thin-walled hemisphere and the surrounding wake at ReD=2×105 acting as a simplified model of a flexible surface protuberance immersed within a turbulent boundary layer (BL). A flexible model and a rigid model, both 100 mm in diameter, are experimentally tested to observe and contrast the flow variation between a rigid structure and a freely deforming structure. Two experiments were conducted. To capture fluid flow behaviour, stereo particle image velocimetry (SPIV) was used. To capture structural deformation of the model, digital image correlation (DIC) was utilised. Experimental testing was conducted non-simultaneously. From the experimental testing, it was observed that the flexible model experienced a leading edge (LE) deformation at 29° of the altitude angle (θ), showing an average deformation of 2.11 mm. All regions of the structure experienced non-zero distortion due to the incoming wind load. This was similar to behaviour observed in previous literature. This caused a modulation in the wake region, giving a parabolic wake velocity contour to form about θ≈20°. A velocity inflection point is observed for the flexible model at an average of θ=23.39° within the wake. This inflection region extends surrounding the area of maximum structural deflection up to θ≈40°. This indicates that the deflection across the LE centreline has a direct interaction with location and size of the near wake. Turbulent kinetic energy (TKE) in the wake was observed to drop with the introduction of the flexible model, with a lower dissipation rate observable. This is indicative of energy transfer from the flow to the structure, allowing deformation. The maximum region of TKE coincides with the recirculation vortex core region, which was shown to move from z/D= 0.19 to z/D= 0.35 for the rigid and flexible models, respectively. The results indicate that, with the Reynolds number tested, the rigid behaviour is in line with previous literature trends. The flexibility of the model, therefore, highly influences the wake region, with general shape deformation causing a decrease in near wake TKE and change in wake shape and recirculation core location.

This work evaluates the technical viability of using green composites to build small boats, such as those used by riverine communities in the Amazon region. A 730 mm-long boat was constructed using a sandwich lamination technique. This miriti wood boat was coated with epoxy resin reinforced with two layers of unidirectional jute fabric on both the interior and exterior. The sandwich lamination provided benefits such as increased stiffness, impermeability, and a standardized production process. Fourteen strain gauges were installed on the boat's hull to measure strains in the key regions under various loads. The boat was experimentally tested using a bending test with bi-supported conditions. Additionally, a numerical model was developed using the finite element software ANSYS to simulate the same conditions as the experimental test. To enhance the accuracy of the numerical model, a code was developed using ANSYS Parametric Design Language to account for the anisotropic behavior of the jute composite. The numerical model was validated by comparing the experimentally measured strains with the calculated strains from the simulation.

This paper presents a complete design methodology of a Class-E inverter for capacitive wireless power transfer (CWPT) applications, focusing on the capacitance coupling influence. The CWPT has been investigated in this paper, because most of the literature refers to inductive power transfer (IWPT). However, CWPT in perspective can result in lower cost and higher reliability than IWPT, because it does not need coils and related shields. The Class-E inverter has been selected, because it is a single switch inverter with a grounded MOSFET source terminal, and this leads to low costs and a simple control strategy. The presented design procedure ensures both zero voltage switching (ZVS) and zero derivative switching (ZDS) conditions at an optimum coupling coefficient, thus enabling a high transmission and conversion efficiency. The novelties of the proposed method are that the output power is boosted higher than in previous papers available in the literature, the inverter is operated at a high conversion efficiency, and the equivalent impedance of the capacitive wireless power transfer circuit to operate in resonance is exploited. The power and the efficiency have been increased by operating the inverter at 100 kHz so that turn-off losses, as well as losses in inductor and capacitors, are reduced. The closed-form expressions for all the Class-E inverter voltage and currents waveforms are derived, and this allows for the understanding of the effects of the coupling coefficient variations on ZVS and ZDS conditions. The analytical estimations are validated through several LTSpice simulations and experimental results. The converter circuit, used for the proposed analysis, has been designed and simulated, and a laboratory prototype has been experimentally tested. The experimental prototype can transfer 83.5 W at optimal capacitive coupling with operating at 100 kHz featuring 92.5% of the efficiency, confirming that theoretical and simulation results are in good agreement with the experimental tests.

Sex allocation theory can provide successful predictions about how individuals allocate resources into male and female reproduction. However, in simultaneous hermaphrodites, experimental support for some fundamental aspects of sex allocation theory are, so far, limited, and many studies are conducted as correlational analyses without experimental trait manipulation. This limitation is especially true in animals, where gonads are usually internal, making it difficult to experimentally manipulate the traits of a specific sex function. Therefore in my PhD project I established and performed phenotypic engineering in the free-living simultaneous hermaphroditic flatworm Macrostomum lignano, and experimentally tested two fundamental aspects of sex allocation theory, namely a saturating male fitness gain curve and the existence of a trade-off between male and female allocation. First, in order to identify candidate genes that could be involved in sex allocation, I searched sex-specific genes based on existing gene annotations from other organisms using available gene sequence databases in M. lignano. Next, I examined gene expression patterns of such candidate genes using in situ hybridization. After confirming sex specificity, I knocked down gene expression using RNA interference (RNAi), enabling me to obtain a number of male-sterile phenotypes. In Chapter II, I report one of the identified testis-specific genes, named melav2, as an example of how to confirm sex specificity, an important aim for specific manipulation of one sex function in a simultaneous hermaphrodite. Having identified male-specific genes, I next investigated how the manipulation of sperm production using one of these genes impacts on male fitness. In sex allocation theory the shape of the fitness gain curve has an important role to predict optimal sex allocation. In many simultaneous hermaphrodites saturating male fitness gain curves are predicted, but studies experimentally testing this prediction are scarce. Therefore in Chapter III, I quantitatively manipulated sperm production using dose-dependent testis-specific RNAi knock-down of the macbol1 gene, and the results provide clear experimental evidence of a saturating male fitness gain curve in M. lignano, to my knowledge the first such evidence in copulating simultaneous hermaphrodites. Another fundamental but to date poorly supported assumption of sex allocation theory is the existence of a trade-off between male and female resource allocation. In theoretical models individuals are assumed to have a limited amount of reproductive resources, and an increase in allocation in one sex function necessarily leads to a decrease in the other sex function, imposing some constraints on the individual’s sex allocation decisions. In Chapter IV, in support of this assumption, I show that experimentally hindering spermatogenesis via testis-specific RNAi knock-down of the mac-C3H-zfn gene results in an increase in ovary size, as assumed by theory. In conclusion, my thesis provides experimental evidence for two fundamental aspects of sex allocation theory, namely a saturating male fitness gain curve and the existence of a trade-off between male and female allocation in a copulating simultaneous hermaphrodite. These two findings confirm an important theoretical prediction, namely that selection favors lower male allocation when there are diminishing male fitness returns and that freed reproductive resources can flow from the male to the female function.

The main organic carbon stocks in the predominantly boreal forests of Russia are contained in the soil pool. Quantitative estimates of soil pool carbon stocks vary considerably. This is due to the high temporal and spatial variability of the organic carbon content in soils, the lack of empirical data for a number of regions, the difference in approaches to assessing soil carbon and the density of soil horizons, the thickness of the soil layer taken into account, the inclusion of forest litter carbon stocks, the peat layer, etc. In 2020, the 1st cycle of the State Forest Inventory in Russia was completed using a selective statistical method. Forest inventory characteristics, environmental indicators and information on forest growth conditions have been obtained for 69.1 thousand permanent sample plots. The limited availability of field descriptions of soils necessitates the testing of an integrated approach to using the State Forest Inventory data in the software environment of geographic information systems in combination with open-access digital resources to assess carbon stocks in the soil pool. A methodology for quantitative assessment of carbon stocks in the forest soil pool has been developed and experimentally tested. The proposed methodology includes: 1) geo-referencing of sample plots; 2) bringing the initial data of the State Forest Inventory on soil types to a standard classification; 3) using the digital resources of the World Data Center for Soils (SoilGrids) to obtain reference average carbon stocks on the network of sample plots surveyed during the State Forest Inventory; 4) calculating the total carbon stock in the soil pool of forest lands based on the average carbon stocks of SoilGrids and areas of standard soil types based on the data of the State Forest Inventory. The experimental testing has been carried out using the Republic of Karelia as an example. The sample size has been 667 permanent sample plots. According to the results of the study, the predominant complex of soil types – illuvial-ferruginous and illuvial-humus podzols (without division), illuvial low- and high-humus podzols – covers an area of 7.28 mln ha. The total carbon stock in the 0–30 cm soil layer for the forest lands of the Republic of Karelia is estimated at 773.9 Mt C with an average of 79.1 t C/ha.