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There has been an increased interest in the field of electric power aircraft propulsion systems in recent years mostly due to the technological improvements in power electronics, energy storage and permanent magnet electric motors. This is not unusual since these systems can provide a large increase in efficiency and reliability while decreasing the carbon footprint. In most small and medium size UAVs the fully electric propulsion system is implemented. To obtain a propulsion system with an overall high efficiency one must take into consideration the efficiencies of all individual components as well as their matching meaning that the individual characteristics of all components have to be considered when designing the propulsion system. In this paper a propeller design methodology for a fully electric propulsion system is presented. The electric components were represented via simplified mathematical models while the propeller design was performed by the blade momentum theory with vortex wake deflection including corrections for the tip losses. The airfoil aerodynamic characteristics for different Reynolds numbers were determined by XFOIL and corrected for Mach number and post stall effects due to rotation. An off-design point analysis of the designed propeller was then performed and discussed. It was shown that an efficient fully electric propulsion system for initial design purposes can be created with the methodology. Some recommendations regarding the limitations and the possible improvements are also given in the paper.

In this paper is analyzed turbulent swirling flow generated by axial fans. Three cases will be presented. The first one is the axial fan impeller in-built in the pipe 27.74D long, where D = 0.4 m is pipe inner diameter. The second case is study of the turbulent swirling flow in the free jet generated by the axial fan impeller with casing. The third case is conical diffuser with the inlet diameter D = 0.4 m and total divergence angle of 8.6°, studied in the test chamber followed by the flow meter. Axial fan, even in the case of the same impeller geometry, had various duty points in all these installations. All regimes were adjusted by the continuous fan rotation speed regulation, as well as with the impeller blade angles. Only in the case of the installation with diffuser, additional regulating valve and booster fan were sometimes applied. In all these cases was used laser Doppler anemometry (LDA), one- and three-component systems. All generated flows are extremely turbulent and in the case of the pipe and diffuser occur reverse flows in the central flow region. In the paper will be discussed calculated integral values, such as average circulation or swirl number. Time-averaged circumferential velocity profiles revealed Rankine vortex type in pipe, while in the diffuser is generated, with the different type of impeller, solid body profile. Turbulence levels and their distributions are analyzed. In addition, statistical moments of the higher order, like skewness and flatness factors are discussed.

The past few decades have been marked by an immense interest of the scientific community in making better use of renewable energy resources, particularly wind energy. One of the suggestions is to increase the number of small-scale vertical-axis wind turbines (VAWTs) in densely populated areas. Given that VAWTs primarily operate in adverse conditions (irregular wind speeds, Earth’s boundary layer, vortex trail of surrounding objects), it is necessary to pay special attention to the numerical and experimental estimation of their aerodynamic performances. The conceptual design of small-scale wind turbines usually begins with detailed simulations of the encompassing flow field. There are three categories of most often employed computational methods for Darrieus-type VAWTs: i) quasi 1D momentum models frequently upgraded by blade element theory, ii) vortex models and iii) computational fluid dynamics (CFD) approach that enables modeling the complete flow field. Each of these methods is founded on a particular set of assumptions, has its advantages and disadvantages and can provide different numerical results, although engineers are usually mostly interested in accurately estimating power coefficient curves. This paper describes and references some of the realized and tested small-scale VAWTs. It also accentuates modeling possibilities as well as several dilemmas, challenges and errors that may appear while performing complex, unsteady aerodynamic analyses of fluid flows encompassing VAWTs. The main goal of the paper is to provide useful guidelines for successful design of small-scale VAWTs for urban environments.

Hot water boilers are most commonly used devices in thermal and industrial plants for heat production. Boilers elements are exposed to high pressures and temperatures during boiler operation. Non-stationary working regimes of boiler may lead to breakdowns and fatigue of boiler elements. There are numerous cases of breakdowns of such units, which lead to reduced reliability and safety of the plant. In order to avoid this state, certain investigation should be made that would examine the influence of different regimes on the boiler structure. Lack of available data concerning the temperature as well as stress-strain field in boiler elements led us to perform such kind of experiment. This paper presents results of numerical analysis performed on the modelled boiler. Validation of the numerical model was performed based on experimental results obtained using DIC (Digital Image Correlation) method by using Aramis system. The character of parameters change, such as strain and stress, occurring in the critical zones of boiler elements can be verified both by experimental and numerical results. In this paper the novel approach of experimental and numerical analysis is presented. The method can be used and conducted in similar units for testing on different loads or working regimes, as well as to improve the safety and reliability of similar pressure vessel units.

Both sustainable development and corporate social responsibility (CSR) have received particular attention recently, hence becoming increasingly important in the business world as a model in building equilibrium between economic benefits and growth on the one side, and the society and the environment on the other side. CSR is a strategic business concern that indicates responsiveness towards economic and environmental issues striving for a favorable influence on the development of society, and consequently sustainable development. Along with the trend of incorporation CSR initiatives into every-day business operations, the demand for more transparency on companies’ activities in these areas has been expanding. As companies appear to increasingly engage in disclosure of information related to their environmental and social impacts, this study explores voluntary disclosure of data related to these two groups of concerns, particularly on companies’ websites. The goal of the paper is to contribute to the understanding the reporting and disclosure of sustainability data. The study particular investigates the extent to which German freight shipping companies use websites as channels for presenting their social and environmental information to the public. The research included 82 freight shipping companies, members of the German ship-owners’ association. For each company, the study measured the level of compatibility with the Global Reporting Initiative environmental and social reporting standards. The results indicate that companies seated in Hamburg, companies with group affiliation and companies with large fleets outperform those located in other German provinces, nonaffiliated shipping companies and modest-sized fleets.

Organizational growth and development are spurred by changes that arise as a result of business development. These organizational changes are most often explained in theory as a reaction to the resulting crisis, which ends in a transition from one to the other stage of organizational development. While in theory this topic is significantly explored within the traditional organizational forms, the changes that arise in the process of development of new technology startups are insufficiently researched. In the process of reaching business success in a highly turbulent environment, these temporary organizations are looking for a repeatable and scalable business model that will continuously deliver value to a large number of customers. In the process of development of new technology startups, there is a need for continuous changes and alignment within the organizational elements in order to achieve their goals. This paper is focused on the key changes that happen in the early stages of developing technology startups, with the aim of elaborating the most important elements of these changes that should lead to the successful development of technology startups.

The capabilities of UAVs for civil and military operations are being largely improved by the advances made in UAV technology hence allowing UAVs to become a wide spread tool for a wide range of possible applications. This spread increases the need for more efficient and accurate navigation and positioning which means that improvement of existing and innovative new solutions for this challenge is going to remain of high interest to researchers. In this paper some of the most usual positioning and navigation methodologies are presented and comparisons between their advantages and disadvantages are given.

Medical textile plays an important role in the technical textiles sector as one of the most rapidly growing sectors in the technical textile market. The textile materials should have some adequate mechanical properties to be useful as medical textile. Tensile strength presents one of the basic mechanical properties used to describe textile specimens. Standardized tensile testing procedures on textile specimens were commonly used in the past. The aim of this paper was to measure in-plane strain field on the tensile medical textile specimen using 2D Digital Image Correlation method (2D-DIC). 2D-DIC is a non-contact optical method for accurate displacement and strain full-field measurement. In this study, two medical cotton textiles, with density 120 and 130 g/m2, were used to create three specimens for each material. Each specimen was placed in the tensile testing machine and measured until the break. During the tensile testing, camera was automatically recording full-field displacement in X and Y directions. Textile 1 and Textile 2 showed significant differences in point distance values, despite the small deviation in densities (less than 10%). Mean value of the elongation for Textile 1 is more than a double than the elongation for Textile 2, although the difference for mean value of Maximum force if negligible. Also, it has been showed that 2D-DIC can play significant role for measurement in textile mechanical properties measurement.

This work presents total fatigue life prediction methodology of aircraft structural components under general load spectrum. Here is presented an effective computation procedure, that combines the finite element method (FEM) and strain-life methods to predict fatigue crack initiation life and fatigue crack growth model based on the strain energy density (SED) method. To validate computation procedure in this paper has been experimental tested specimens with a central hole under load spectrum in form of blocks. Total fatigue life of these specimens, defined as sum of crack initiation and crack growth life, was experimentally determined. Crack initiation life was computed using the theory of low cycle fatigue. Computation of crack initiation life was realized using Palmgreen-Miner’s linear rule of damage accumulation, applied on Morrow’s curves of low cycle fatigue. Crack growth life was computed using strain energy density (SED) method. The same low cyclic material properties of quenched and tempered steel 13H11N2V2MF, used for crack initiation life computation, were used for crack growth life computation. Residual life estimation of cracked duraluminum aircraft wing skin/plate 2219-T851 under multiple overload/underload load spectrum was considered too. Presented computation results were compared with own and available experimentally obtained results.

Additive manufacturing technology helped many organizations to save money in the product design process by reducing prototype costs, and also by providing a means for early evaluation and decision making. The idea of this paper is to design an electronics enclosure for an intelligent industrial pressure transmitter, using the additive technology. All enclosure elements are made on a 3D printer WANHAO duplicator i3 plus, using PLA materials. The enclosure realization, from CAD drawings to the finished model, enables a designer to correct existing errors, or make certain modifications as required by end-users. A process is described that enables designers to review their decisions at any stage of product realization, thus providing much more freedom in rapid prototyping. In this example, the advantages and disadvantages of additive manufacturing over conventional manufacturing are outlined. Some deficiencies have also been observed, such as mechanical damage to surfaces, burning of surfaces, tearing of prints, and surface roughness. To mitigate such irregularities, both mechanical and chemical finishing methods were used. The example confirmed that the finishing methods can affect the final enclosure dimensions and shape. Further prototype development should focus more on print quality, which depends on the shape of surfaces, the accuracy of the geometry, the uniformity of structure and shape, material density, and the resolution of details.

Subsonic ramjets, due to its simplicity, nowadays could be very attractive for expendable unmanned applications. However, due to very low efficiency at low Mach numbers, practically there isn’t any important application at subsonic speed. In 50’s subsonic ramjet was used for tip jet applications. Later in 70’s there was a study of Fan Augmented Ramjet (FARJ) where a fan was in-tended to be powered by a piston engine, both in subsonic and supersonic regimes. Almost at the same time it was analyzed ejector augmented subsonic ramjet. Both of these studies did not find real application of such engines. Finally, there was an attempt for the use of an Electric Ducted Fan, used in RC models, with a combustor but exit fan pressure was almost at atmospheric pressure which results in very low efficiency. This paper presents a study of propulsion system which consists of a pitot intake, electrically powered compressor/fan, combustor and nozzle (Electrically Fan Augmented Ram Jet, EFARJ). The electric motor connection to the compressor/fan is direct, without gearbox, which implies usage of a high-speed brushless motor. Such propulsion system is compared to pure ramjet and finally it is compared to performances of small expendable turbojet. Comparison is made regarding costs, weight and thrust/consumption. The study shows that the proposed propulsion system could be competitive for expendable, low speed and short duration applications.