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Fin Type Propulsive Devices with Varying Working Area of Vibrating Tail
No full textThe object of the study is a fin type propulsive device of robotic fish moving inside water. The aim of the study is to find out optimal control law for variation of additional area of vibrating tail, which ensures maximal positive impulse of motive forces acting on tail. The problem has been solved using the maximum principle of Pontryagin. It is shown that optimal control action corresponds to the case of bound values of area limits. The proposed method makes it possible to increase effective surface area of the fin within motion cycles, when useful tractive force is formed. But within cycles, when fin motion is hindered by water resistance forces, effective surface area is decreased. Thanks to this energy losses are minimized, and operation of fin propulsive device becomes more effective. Examples on synthesis of real mechatronic systems are given
Control System for a Diesel Generator and UPS Based Microgrid
No full textIn this paper a microgrid composed of a diesel generator and two uninterruptible power supply systems with separate battery banks is introduced. The microgrid located in three academic buildings of Tallinn University of Technology. A three-level control and monitoring system for the microgrid based on the EtherNet/IP communication network is developed. In addition, a control strategy of the microgrid in the grid-connected and stand-alone mode of operation is propose
Mathematical Modelling of Induction Motor Transient Processes during Stator Winding Interruption
No full textThis research presents induction motor mathematical model in coordinate axis’s , which allows to learn transient processes in rotor and stator circuits in the conditions of stator windings opening. Such kind of researches is nowadays actual due to impossibility of main calculated values measuring directly, but only on the stator terminals. Induction motor mathematical model forms Park-Gorev equations in coordinate axis. It is preferable to use this coordinate system because it allows comparing the results of mathematical modeling in one of the phases with experimental data without transformations
Current-Fed Step-up DC/DC Converter for Fuel Cell Applications with Active Overvoltage Clamping
No full textIn order to use hydrogen fuel cells in domestic applications either as main power supply or backup source, their low DC output voltage has to be matched to the level and frequency of the utility grid AC voltage. Such power converter systems usually consist of a DC-DC converter and a DC-AC inverter. A double inductor step-up push-pull converter is investigated in this paper, presenting simulation and experimental results for passive and active overvoltage clamping. The prototype of the investigated converter is elaborated for 1200 W power to match the rated power of the proton exchange membrane (PEM) fuel cell located in hydrogen fuel cell research laboratory
Īpašības aprakstošo jēdzienu saistība ar citiem jēdzieniem konceptu kartēs
No full textZināšanu novērtēšana norāda, cik veiksmīgs ir bijis apmācības process. Šim nolūkam var izmantot konceptu kartes. Konceptu karte ir grafs, kura virsotnes apzīmē jēdzienus, bet loki starp tām — attiecības starp šiem jēdzieniem. Literatūrā ir minētas sešas pamatattiecības, kādas var tikt izmantotas jēdzienu sasaistei konceptu kartēs. Tās ir: “ir daļa”, “ir veids”, “ir apakškopa”, “ir īpašība”, “ir vērtība” un “ir piemērs”. Tomēr svarīga ir ne tikai saistība starp diviem atsevišķiem jēdzieniem, bet arī tas, kā šis fragments iekļaujas konceptu kartē kopumā. Cilvēki savas zināšanas strukturē dažādi, tāpēc, lai varētu automatizēt apmācāmā un pasniedzēja konceptu kartes salīdzināšanu, ir nepieciešams noskaidrot visas atļautās un aizliegtās attiecību kombinācijas. Šajā rakstā apskatītas attiecības “ir īpašība” kombinācijas ar pārējām pamatattiecībām konceptu kartē
Thin Sheet Metal Stamping with Elastic Media
No full textThe article covers a part of the PhD research on sheet metal stamping with elastic media. Calculations have confirmed that stamping with elastic media is much cheaper than traditional punching technology. Nevertheless the weak point of the stamping with elastic media is the relatively large technological wastage size deriving from the need to support forces to hold technological bridges. The metrological achievements allow for the creation of a 3D surface roughness model for the working surfaces of the stamp. In its turn, this 3D surface roughness model can help reduce technological wastages. By knowing the surface friction dependence between sheet material, base plate and elastic area, it is possible to calculate the precise minimal size of the technological bridge
Психическая надёжность спортсменов и свойства личности
No full textВ работе исследовано влияние свойств личности на показатели психической надёжности.
Выявлены основные личностные комплексы по критерию их взаимосвязи с такими компонентами психической надёжности, как стабильность и помехоустойчивость, соревновательная эмоциональная устойчивость, саморегуляция, мотивация и суммарный показатель надёжности.
Показано относительно равномерное распределение типов стрессоров. При этом наиболее характерны высокие показатели суммарной чувствительности и стрессорам.
Определены ведущие компоненты психической надёжности спортсменов – соревновательная эмоциональная устойчивость и саморегуляция.
Выявлены наиболее характерные личностные типы для спортсменов-боксёров: «спокойный, нетревожный, эмоционально открытый», а также «активный, нетревожный, контролируемый».
Обнаружено заметное уменьшение тесноты корреляционных связей в зависимости от спортивного мастерства. Подчеркивается, что с ростом спортивного уровня уменьшается влияние свойств личности на проявление психической надёжности.
Предлагается учитывать определённые компоненты психической надёжности и отдельные свойства личности, направленные на нейтрализацию соревновательных стрессовых факторов, что значительно повысит эффективность выступления спортсменов на ответственных соревнованиях
Helical Pile Behaviour and Load Transfer Mechanism in Different Soils
No full textThis article explores the system of helical piles and its behavior in compression. Three calculation methods have been examined: Latvian building code LBN 214-03 “Geotechnics. Pile foundations and footings” (СНиП 2.02-03-85), the calculation method proposed by the company “A.B.CHANCE”, and the large load-bearing capacity screw piles calculation methods developed by Canadian building engineers, which are used for the determination of helical pile load-bearing capacity. The construction methods of screw pile foundations have been compared and the advantages and disadvantages have been described. The article analyzes helical screw piles in compression with a different number of capacitive plates in four different soils – fine sand, floating loam, sandy loam and hard loam. The capacity of screw pile was obtained using the method developed by the American company “A.B.CHANCE”. Factors causing incapability have been determined. As none of the methods mentioned above describes the deformation of screw piles and does not provide any calculation or evaluation principles, the finite element calculation model by computer soft-ware “Lira 9.2” was used for the simulation. The deformation of a screw pile with one or two capacitive plates was examined in four different soils. The model also showed the interaction between the screw pile and the soils. The stresses in the soil massif have been calculated. Further research should be directed towards the development of the calculation method for deformation, as well as towards the verification of the calculation model of finite elements, and the modification to take into account the soils plasticity
Towards Narrowing a Conceptual Gap between IT Industry and University
No full textThe situation when the number of the students and the popularity of the engineering education in general and IT education in particular is not increasing dramatically due to the fact that there exists an opinion that engineering education is complex and time-consuming from one side and that the graduates are not sufficiently prepared for the industry from another, requires the University to perform a series of actions that can improve the current situation. One of the areas for improvement is the quality of the study programs in the sense of their suitability to ‘customers’, namely Students and Industry. Previous research shows that the knowledge requirements monitoring system and the processes behind it can improve the quality of the study programs, e.g. the results of the Value Network Analysis demonstrate that the Monitoring System can give additional value to both the University and the Industry. Developing a monitoring system prototype requires narrowing the gap between industry and university and introduces new ways of industry-university cooperation