Companies always search for alternative solutions for designing mechatronic systems in more efficient ways to cope with the high-performance standards, competitive market, and design time reduction. ...In this article, we present a complete multiphysical approach to design and validate an electronic throttle body (ETB) system in a concurrent way. Our goal is to reduce the modeling and test efforts by using an enriched multiphysical model in the preliminary phase. This model is the main stone that connects different fields and ensures efficient collaboration. This article is the result of a close collaboration between laboratories and industrials in the automotive field and aims at developing a methodology that takes into account collaboration constraints during design. Thanks to this approach, industrial requirements of the ETB are achieved at an early stage. An experimental test bench is presented to validate the simulation results.
The need for higher efficiency motors is becoming more relevant due to recent policies adopted in most advanced economies, which are adopting new minimum energy performance standards. A great effort ...to optimize several parts of rotating electric machines is being done to fulfill that requirement. Recent studies focus on stator winding optimization, because of its high loss share. In this paper, a general multilayer winding configuration is proposed for winding design optimization for multiphase symmetrical machines, by combining multilayer integer-slot, fractional-slot, and fractional-slot concentrated windings. The constrained minimization of the airgap magnetomotive force harmonic distortion and winding resistance is solved by the hybridization of differential evolution with a non-dominating sorting algorithm. A framework is provided for replication purposes. An experimental application example of standard and optimized windings is included for performance assessment. The optimized winding leads to a significant motor efficiency gain, while reducing the amount of copper needed for manufacturing.
Solar power forecasting improvements are mainly evaluated by statistical and economic metrics, and the practical reliability benefits of these forecasting enhancements have not yet been well ...quantified. This paper aims to quantify reliability benefits from solar power forecasting improvements. To systematically analyze the relationship between solar power forecasting improvements and reliability performance in power system operations, an expected synthetic reliability (ESR) metric is proposed to integrate multiple state-of-the-art independent reliability metrics. The absolute value and standard deviation of area control errors (ACEs), and the North American Electric Reliability Corporation Control Performance Standard 2 (CPS2) score are calculated through a multi-timescale scheduling simulation, including the day-ahead unit commitment, real-time unit commitment, real-time economic dispatch, and automatic generation control sub-models. The absolute ACE in energy, CPS2 violations, CPS2 score, and standard deviation of the raw ACE are all calculated and combined as the ESR metric. Numerical simulations show that the reliability benefits of multi-timescale power system operations are significantly increased due to the improved solar power forecasts.
The determination of the exact rheological properties, in fundamental units, of cementitious materials has become gradually a necessary step in the domain of concrete science. Several types of ...rheometers and their corresponding transformation equations are described in the literature. In this paper, the Reiner–Riwlin transformation equation, valid for coaxial cylinders rheometers, is developed for the modified Bingham model, which is an extension of the Bingham model with a second order term in the shear rate. The established transformation is shown to be compatible with the Reiner–Riwlin equation for the Bingham and Herschel–Bulkley models. Its validation is further proven by means of numerical simulations applied on experimental data. The yield stress values for the three rheological models (applied on the same experimental data) are compared with the yield stress calculated by means of slump flow values. Results showed that the modified Bingham model results in the most stable yield stress values, which are independent of the non-linear behaviour.
The major environmental impact of concrete is caused by CO2-emissions during cement production. Great potential for reducing the impact is seen especially for concretes with normal strength. The use ...of superplasticizers and highly reactive cements as well as optimization of particle-size distribution and reduction in water content allows a significant reduction in Portland cement clinker in the concrete. Essential is the addition of mineral fillers (e.g. limestone powder) to provide an optimal paste volume. In addition, the already practicable substitution of secondary raw materials like fly-ash or furnace-slag for cement clinker is an appropriate option which is however limited by the availability of these resources.
In several test series the fresh and hardened concrete properties of concretes with reduced water and cement contents were investigated, especially their workability, strength development, design-relevant mechanical properties as well as durability aspects such as carbonation. It was shown that concretes with cement clinker and slag contents as low as 150kg/m3 were able to meet the usual requirements of workability, compressive strength (approx. 40N/mm2) and mechanical properties. The carbonation depth of concretes with 150-175kg/m3 clinker and slag was equal or lower than the depth of conventional reference concretes for exterior structures. The ecological advantages were identified, using environmental performance evaluation. A reduction of up to 35% in environmental impact was calculated compared with conventional concrete and of more than 60% with granulated blast-furnace slag. Practical application was verified by means of full-scale tests in a precast and ready-mix concrete plant.
There are many competing theories to model concrete exposed to freezing temperatures but few of them provide comprehensive quantitative predictions of the mechanical behavior, while accounting for ...the multi-scale physics of the confined crystallization of ice. When a part of the liquid in the pores solidifies, a pressure build up is generated, and excess liquid is expelled from the freezing sites towards the remaining part of the porous network. In turn, with increasing cooling a cryo-suction process drives the liquid towards the frozen sites. Unsaturated poroelasticity theory provides new perspectives on the computation of stresses and strains developed in such a complex mechanism. The formulation includes the deformation of all the phases during the freezing process. Special attention is given to the influence of entrained air-voids on the frost resistance of the porous material. The analysis indicates that the air voids act both as expansion reservoirs and efficient cryo-pumps whose respective effects are quantitatively assessed. The theory also allows for the estimation of the critical spacing factor. Numerical simulations are conducted to study the effect of pore size distribution on the critical spacing factor and on the internal pressurization within the porous material as it freezes.
AbstractThe use of supplementary cementitious materials as partial replacements of the cement in concrete will play a significant role with respect to the environmental control of greenhouse effects ...and global temperature reduction. The development of geopolymer concrete (GPC), in which all of the portland cement is replaced with fly ash (in combination with sodium hydroxide and sodium silicate solutions), offers a promising alternative to ordinary portland cement concrete. This paper evaluates the durability characteristics of low-calcium fly ash–based geopolymer concrete that was subjected to a corrosive marine environment. A series of GPC beams, which contained fly ash with 8- and 14-M concentrations of NaOH and SiO2/Na2O solutions, respectively, and were centrally reinforced with a 13-mm rebar, were tested for accelerated corrosion exposure with wet and dry cycling in artificial seawater and an induced current. A sudden rise in the current intensity that is attributable to specimen cracking was indicative of durability. The test results indicated excellent resistance of the geopolymer concrete to chloride attack, with a longer time to corrosion cracking relative to ordinary portland cement concrete.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this paper, mortars and pastes containing large replacement of pozzolan were studied by mechanical strength, thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), mercury ...intrusion porosimetry (MIP) and electrical impedance spectroscopy (EIS). The effect of metakaolin (35%) and fly ash (60%) was evaluated and compared with an inert mineral addition (andalusite). The portlandite content was measured, finding that the pozzolanic reaction produced cementing systems with all portlandite fixed. The EIS measurements were analyzed by the equivalent electrical circuit (EEC) method. An EEC with three branches in parallel was applied. The dc resistance was related to the degree of hydration and allowed us to characterize plain and blended mortars. A constant phase element (CPE) quantified the electrical properties of the hydration products located in the solid–solution interface and was useful to distinguish the role of inert and pozzolanic admixtures present in the cement matrix.
An experimental research is performed on the complete compressive stress–strain relationship for concrete after heating to temperatures of 100–800 °C. All concrete specimens are ϕ15 cm
×
30 cm ...standard cylinders, made with siliceous aggregate. The heated specimens are tested at 1 month after they are cooled to room temperature. From the results of 108 specimens with two original unheated strengths, a single equation for the complete stress–strain curves of heated concrete is developed to consider the shape varying with temperature. Through the regression analysis, the relationships of the mechanical properties with temperature are proposed to fit the test results, including the residual compressive strength, peak strain and elastic modulus. Compared with the experimental curves, the proposed equation is shown to be applicable to unheated and heated concrete for different temperatures. In addition, the split-cylinder tests of 54 specimens are also carried out to study the relationship of splitting tensile strength with temperature.
In this report, we assessed the importance of internal microstructure on TiO2-containing cement-based mortars during the degradation of NOx gases through a photocatalytic oxidation process. Six ...samples of mortar containing the same amount of cement (14%) and TiO2 (1%) were prepared by changing the amount and type of sand used in their formulation, as well as the water/cement ratio, thus yielding mortars with different overall porosities and pore size distributions. The particle size distribution of the raw materials had a strong influence on the final microstructure of the hardened products. The volume of macropores (in this study, pores with diameter larger than 80 nm), which appeared according to the size of particle used in the mortar preparation and the extent of the hydration reaction of the cementitious compounds, was related to the presence of active sites accessible to the photocatalytic oxidation (PCO) process. Samples with large macropore volume and lower amount of hydration products exhibited the highest PCO efficiency. Taking into account the low weight-percent of TiO2, the PCO performance was found to be outstanding, with NO conversion values generally larger than 20%. Moreover, the microstructure was related to the amount of TiO2 present in the mortar surface.
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•NOx photocatalytic degradation is enhanced by regulating the microstructure of mortars.•The highest macropores population yielded outstanding values of NOx degradation.•Good pollutant degradation is obtained with very low amount of TiO2 in mortars.
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