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DEVELOPMENT OF HIGH-REACH PANTOGRAPHS FOR HIGH-SPEED RAILWAYS
Get PDFThe pantograph’s purpose is to transfer electrical power from the overhead contact line to the train’s electric propulsion unit. To perform its function adequately, it is necessary to maintain the static contact force between the pantograph and the contact line within the values prescribed by appropriate standards for the entire extension range of the pantograph. The requirement to reach high contact lines complicates the kinematic scheme because the deviation of the trajectory of the pantograph’s collector head from vertical is also prescribed by standards. Further, the structural design of the pantograph is challenging because the greater slenderness ratio of the structure makes it difficult to meet the requirements in terms of stiffness and resistance to vibrations. While at low speeds aerodynamic forces are usually neglected, in high-speed pantographs, they have a significant impact and it is necessary to compensate for them. An aggravating circumstance is the
requirement that the pantograph should work in both knuckle-downstream and knuckle-upstream directions. This paper aims to present the development of a high-speed high–reach pantograph that is developed through the cooperation of company Minel General Electric and the University of Belgrade – Faculty of Mechanical Engineering as well as to present innovative designs of
gravitational and aerodynamical compensations that enabled the satisfaction of requested requirements in terms of geometric and static performance
WMLES of flows around small-scale propellers - estimating aerodynamic performance and wake visualization
Get PDFWall-modeled large-eddy simulation (WMLES) is an advanced mathematical model for turbulent flows which solves for the low-pass filtered numerical solution. A subgrid-scale (SGS) model is used to account for the effects of unresolved small-scale turbulent structures on the resolved scales (i.e. for the dissipation of the smaller scales), while the flow behavior near the walls is modeled by wall functions (thus reducing the requirements for mesh fineness/quality). This paper investigates the possibilities of applying WMLES in the estimation of aerodynamic performance of small-scale propellers, as well as in the analysis of the wake forming downstream. Induced flows around two propellers designed for unmanned air vehicles (approximately 25 cm and 75 cm in diameter) in hover are considered unsteady and turbulent (incompressible or compressible, respectively). Difficulties in computing such flows mainly originate from the relatively low values of Reynolds numbers (several tens to several hundreds of thousands) when transition and other flow phenomena may be present. The choice of the employed numerical model is substantiated by comparisons of resulting numerical with available experimental data. Whereas global quantities, such as thrust and power (coefficients), can be predicted with satisfactory accuracy (up-to several percents), distinguishing the predominant flow features remains challenging (and requires additional computational effort). Here, wakes forming aft of the propeller rotors are visualized and analyzed. These two benchmark examples provide useful guidelines for further numerical and experimental studies of small-scale propellers
Initial development of tandem wing UAV aerodynamic configuration
No full textPurpose: Unmanned aerial vehicles (UAV) with remote and/or automated flight and mission controls have replaced airplanes with pilots in many important roles. This study aims to deal with computational fluid dynamics (CFD) analysis and development of the aerodynamic configuration of a multi-purpose UAV for low and medium altitudes. The main aerodynamic requirement was the application of the tandem wing (TW) concept, where both wings generate a positive lift and act as primary lifting devices. Design/methodology/approach: Initial design analyses of the UAV’s aerodynamic configuration were performed using ANSYS Fluent. In previous work in Fluent, the authors established a calculation model that has been verified by experiments and, with minor adjustments, could be applied for subsonic, transonic and supersonic flow analyses. Findings: The design evolved through eight development configurations, where the latest V8 satisfied all the posted longitudinal aerodynamic requirements. Both wings generate a substantial amount of positive lift, whereas the initial stall occurs first on the front wing, generating a natural nose-down stall recovery tendency. In the cruising flight regime, this configuration has the desired range of longitudinal static stability and its centre of pressure is in close proximity to the centre of gravity. Practical implications: The intermediate development version V8 with proper longitudinal aerodynamic characteristics presents a good starting point for future development steps that will involve the optimization of lateral-directional aerodynamics. Originality/value: Using contemporary CFD tools, a novel and original TW aerodynamic configuration have evolved within eight development stages, not being based on or derived from any existing designs
The Results of Common Fixed Points in b-Metric Spaces
Get PDFIn this paper, we present some results on the existence and uniqueness of common fixed points on ������∗-complete topological spaces. Our results generalize and improve upon earlier results in the literature. Finally, we give some examples in ������������ spaces, (������∈(0,1)), where we use the obtained results
Influence of ventilation system effectiveness on the safety of hydrogen storage and transportation
Get PDFIn this paper influence of ventilation system availability and effectiveness is evaluated by applying standardized analytical methods for classification of areas of explosive atmospheres with the aim to obtain high dilution for non-hazardous zone or to reduce Zone 2 area within hydrogen storage room and transportation pipeline corridors in industrial applications
Izvori ispuštanja i zone opasnosti vodoničnih instalacija
Get PDFУ раду је дат преглед Српских прописа који дефинишу услове за безбедно држање, складиштење, транспорт и употребу водоника, као и преглед дефиниција зона опасности и сигурносних растојања око извора испуштања на водоничним инсталацијама који се уобичајено користе у нашој индустрији. У другом делу су дате зоне опасности дефинисане истим изворима испуштања израчунате према хармонизованом SRPS EN 60079-10-1:2017 и америчком NFPA 55:2020 стандарду. Наведени су и услови за држање водоника у лабораторијама, дефинисани NFPA 45:2020 стандардом.
Experimental and Numerical Analysis of the Strength of a Drone Arm Made of Composite Material
No full textAerospace engineering, as a field in which the reduction of mass has always been one of the primary tasks of its engineers, has made significant progress as a result of numerous developments and advancements in the field of composite materials in the sense of gaining large benefits from the relatively low density that characterizes composites. In the spirit of the increasing use of composite materials on aerospace structures, in this paper we will conduct an experimental and numerical analysis of the strength of a drone arm made of a composite material. Every method of analysis, whether it is analytical, numerical, or experimental, has some advantages and disadvantages. Experimental results are easily affected by random and instrumental errors and numerical methods are highly affected by the chosen physical model. In order to obtain the most reliable analysis solution, a mixture of numerical analysis backed up by experimental data is required. In the hope of bypassing the expensive and time-consuming experiments in the future, in this paper we will conduct a numerical analysis on a drone arm made of composite materials which will then be replicated by an experiment verifying its validity
К задаче о качении тяжелого однородного шара без проскальзывания по неподвижной поверхности вращения
No full textPredavanje po pozivu na Seminaru "Механические задачи с особенностями" Instituta za mehaniku Moskovskog državnog univerziteta "Lomonosov
Analysis of Two Stage Production Technology of Defatted Soybean Flakes
No full textSoy is widely used in the production and preparation of various protein nutrients and beverages used in both human and animal nutrition. The technological process of soybean processing is more complex than the processing of other oilseeds and therefore requires more attention. Soybeans have a unique feature among oilseeds that during the growing season, three to five months, they can produce the largest amount of protein of the most favorable amino acid composition used in human and animal nutrition. This paper clearly presents one of the possible technological processes of soybean processing in industrial conditions. Soybean processing technology can be observed from three technological phases within the production plant of the factory. The first technological phase (phase 1) in soybean processing refers to the manipulation and storage of grain until processing. Within this phase, there are the following technological operations: grain reception, grain cleaning, grain drying, and grain storage. The second technological phase (phase 2) is the phase of soybean processing, within which there are technological operations that differ depending on the final product. Phase 2 produces intermediates of soybean flakes and soybean cake. The third phase refers to the final processing of intermediate products, packaging of the final product and its distribution to customers
Effects of biomass particles size and shape on combustion process in the swirl-stabilized burner reactor: CFD and machine learning approach
No full textWhen planning the development of the energy sector, significant attention is given to the energy from the renewable sources, amongst which the biomass has an important role. Computational fluid mechanics and machine learning models are the powerful and efficient tools which allow the analysis of various heat and mass transfer phenomena in energy facilities. In this study, the in-house developed CFD code and machine learning models (Random Forest, Gradient Boosting and Artificial Neural Network) for predicting the biomass trajectories, particle mass burnout and residence time in a swirl burner reactor are presented. Pulverized biomass combustion cases (fine straw, pinewood and switch grass) with various mean diameters (ranging between 60 and 650 μm) and different shape factors (within the range 0–1) are considered. The results of numerical simulations revealed a noticeably nonlinear dependence between the input values (particle types, sizes and shapes) and the output values (particle trajectories, mass burnout and residence time), mostly due to the complex swirling flow in the reactor. For particles with the mean diameters within the ranges considered, the mass burnout of particles generally decreases as the biomass particle shape factor increases. The residence time of pulverized biomass in the reactor shows in most cases a decreasing trend as the particle shape factor increases. Artificial Neural Network showed the best predictions for both particle mass burnout (RMSE = 0.083 and R2 = 0.937) and particle residence time (RMSE = 1.145 s and R2 = 0.900), providing the reliable assessment of these important indicators in the combustion process