Vilnius Gediminas Technical University
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Rapeseed-based polyols and paper production waste sludge in polyurethane foam: Physical properties and their prediction models
No full textIntervention into the present building industry is the main strategy of the European Commission in order to achieve one of its planned aims regarding the reduction of greenhouse gas emissions up to 20% up by 2020 and
up to 80% by 2050. Therefore, it is necessary to develop not only energetically efficient but also more environmentally friendly materials. This work presents bio-based propylene glycol and paper waste sludge particles modified polyurethane foams, their physical properties and their prediction models. The conducted research has revealed that paper waste sludge particles negatively affect dimensional changes. In order to eliminate the negative impact of paper waste sludge, bio-based propylene glycol is used. The obtained results have shown that this raw material allows development of dimensionally and structurally stable polyurethane foams used as a thermal insulating layer having the following properties: density in the range of 40–50 kg/m3
, compressive strength in the range of 193–243 kPa, thermal conductivity in the range of 0.0349–0.0359 W/(m·K), long-term water absorption in the range of 6–11 vol.% and water vapour transmission factor in the range of 26.2–40.9. On the basis of the results, prediction models are suggested for the most important physi
Control of the Electromagnetic Fields by Metamaterials
No full textMetamaterials are engineered composites. Much of the effort in the electrical engineering,
material science, physics, and optics communities emphasized constructing efficient metamaterials and using
them for potentially novel applications in antenna and radar design, subwavelength imaging, and invisibility
cloak design. The purpose of this chapter is to provide a detailed introduction to the basic metamaterial
modelling approaches and an overview of innovative phenomena enabled by metamaterials. While high
tunability of the electromagnetic properties might be provided by metamaterial structures and metasurfaces,
the former option has not yet been used to solve this problem. By means of the freedom of design provided by
metamaterials, we propose the ways to redirect electromagnetic fields and demonstrate a design strategy.This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Single Cylinder-Type Piezoelectric Actuator with Two Active Kinematic Pairs
Get PDFThere is an ever-increasing demand for small-size, low-cost, and high-precision positioning systems. Therefore, investigation in this field is performed to search for various solutions that can meet technical requirements of precise multi-degree-of-freedom (DOF) positioning systems. This paper presents a new design of a piezoelectric cylindrical actuator with two active kinematic pairs. This means that a single actuator is used to create vibrations that are transformed into the rotation of the sphere located on the top of the cylinder and at the same time ensure movement of the piezoelectric cylinder on the plane. Numerical and experimental investigations of the piezoelectric cylinder have been performed. A mathematical model of contacting force control was developed to solve the problem of positioning of the rotor when it needs to be rotated or moved according to a specific motion trajectory. The numerical simulation included harmonic response analysis of the actuator to analyze the trajectories of the contact points motion. A prototype actuator has been manufactured and tested. Obtained results confirmed that such a device is suitable for both positioning and movement of the actuator in the plane.This article belongs to the Special Issue Piezoelectric Transducers: Materials, Devices and ApplicationsThis research was funded by the European Regional Development Fund according to the
supported activity No. 01.2.2-LMT-K-718 under the project No. DOTSUT-234
Analysis of Steel Wire Rope Diagnostic Data Applying Multi-Criteria Methods
No full textSteel ropes are complex flexible structures used in many technical applications, such as elevators, cable cars, and funicular cabs. Due to the specific design and critical safety requirements, diagnostics of ropes remains an important issue. Broken wire number in the steel ropes is limited by safety standards when they are used in the human lifting and carrying installations. There are some practical issues on loose wires—firstly, it shows end of lifetime of the entire rope, independently of wear, lubrication or wrong winding on the drums or through pulleys; and, secondly, it can stick in the tight pulley—support gaps and cause deterioration of rope structure up to birdcage formations. Normal rope operation should not generate broken wires, so increasing of their number shows a need for rope installation maintenance. This paper presents a methodology of steel rope diagnostics and the results of analysis using multi-criteria analysis methods. The experimental part of the research was performed using an original test bench to detect broken wires on the rope surface by its vibrations. Diagnostics was performed in the range of frequencies from 60 to 560 Hz with a pitch of 50 Hz. The obtained amplitudes of the broken rope wire vibrations, different from the entire rope surface vibration parameters, was the significant outcome. Later analysis of the obtained experimental results revealed the most significant values of the diagnostic parameters. The evaluation of the power of the diagnostics was implemented by using multi-criteria decision-making (MCDM) methods. Various decision-making methods are necessary due to unknown efficiencies with respect to the physical phenomena of the evaluated processes. The significance of the methods was evaluated using objective methods from the structure of the presented data. Some of these methods were proposed by authors of this paper. Implementation of MCDM in diagnostic data analysis and definition of the diagnostic parameters significance offers meaningful results
Urban (Un)Sustainability: Cases of Vilnius’s Informal and Illegal Settings
No full textThe current analysis addresses cases of both informal and illegal settlements in Vilnius, Lithuania. By using semiotic means (specifically, semiotic squares), the author presents the Romani district (tabors), as well the Šnipiškės district, describing the circumstances of their emerging and comparing these cases. In addition to that, the philosophical questions about the dichotomies ‘formal/informal’, ‘temporal/eternal’, ‘order/chaos’, ‘legal/illegal’, ‘sustainable/unsustainable’ are discussed. On the one hand, illegal buildings serve as a signal about too high a barrier of bureaucracy, about a surfeit of law and even about the violation of certain rights. On the other hand, some urban districts can become illegal because of a changed urban vision reflected in a new General Plan. The paper also analyzes the issue of public interest. Additionally, the tendency of democratic society to turn into bureaucratic society is analyzed. The paper addresses sensitive issues related to sustainable development of cities, intercultural dialogue and equal opportunities.This article belongs to the Special Issue Urban Renewal and Built Heritage ManagementThis research carried on the Hungarian-Lithuanian joint project Conception of creative city within Central
Europe: historical images and empirical indices within the framework of a bilateral agreement of the Hungarian and
Lithuanian Academies of Sciences. The research received funding from Vilnius Gediminas Technical Universit
The impact made on project portfolio optimisation by the selection of various risk measures
No full textThis study addresses the effect of selecting an appropriate risk measure and the impact of this choice on the efficient frontier of the
project portfolio of an organisation. The appropriate choice of a firm’s project portfolio has a great impact on the organisational
success. Each portfolio manager selects the best projects with different criteria and consistent with firm’s strategic objectives. We
used the Markowitz efficient frontier method to select the best projects of the organisation. The choice of proper measures impacts
on this decision and can change the organisation’s portfolio. The standard deviation was applied, and the relevant optimisation
was made for this purpose. Then, the semi-standard deviation was used to differentiate between favourable and unfavourable
opportunities. Afterwards, Value at Risk and Expected Shortfall were applied as appropriate risk measures to make a better
estimate of the tail risks. All these risk measures were used to select the best possible projects. Managers should select the
appropriate risk measures according to their objectives, estimation of their project distribution, and characteristics of the projects.
This research studied the best measures consistent with construction projects and the effect of changes in these measures
Knowledge management process model
No full textIn the context of globalization and transformations, the knowledge potential management is an effective tool for increasing the effectiveness of organizations. The aim of the research is to study the procedural approach to the organization knowledge potential management, to distinguish the main knowledge management processes and to present suggestions on how to improve the knowledge management process model. The organization's knowledge potential in this study is defined, as the organization's resources and market opportunities, generating its knowledge potential, complexity and effective management of which create prerequisites for meeting the changing individual user needs, creating reciprocal value, uniqueness and leadership in the global marketplace. The conceptual knowledge management process model has been improved, based on the research. The first step in the model is the choice of a knowledge strategy, covering aspects of the formation and selection of strategic decision-making in knowledge potential management. The choice of an appropriate knowledge strategy brings to its implementation through a process of knowledge management cycle, consisting of knowledge acquisition, sharing, development, preservation and application of it. The knowledge management process model is completed with an evaluation of the knowledge strategy implementation
Kinematics of trunk-like robots with piezo actuators
Get PDFThis paper presents the investigation of direct and inverse kinematics for piezo robot with spherical actuators. Two different actions of spherical piezo actuators are intro-duced. Several methods to solve inverse kinematics were analyzed. A geometric approach is chosen for solving the inverse kinematics, because it has a lot of advantages in ac-cordance to other methods. A theory and a concise algo-rithm to find the solutions of the inverse kinematics using the global projections of robot links is presented
Decision-aiding evaluation of public infrastructure for electric vehicles in cities and resorts of Lithuania
No full textIn the National Communication Development of 2014–2022 Program and Guidelines of the
Development of the Public Electric Vehicle Charging Infrastructure confirmed by the Government
of the Republic of Lithuania, it is planned that, until the year of 2025, among newly registered
vehicles, electric ones should make at least 10%. Analysis of the trend of electric vehicles makes
evident that the target does not have a real chance to be achieved without targeted efforts. In order to
improve the infrastructure of electric vehicles in major cities and resorts of Lithuania, we have carried
out a comparative analysis of public infrastructure for electric vehicles in 18 Lithuanian cities and
resorts. For the quantitative analysis, we proposed eight criteria describing such an infrastructure.
As perception of the infrastructure by owners of electric cars depends on complex factors, we used
multiple criteria evaluation methods (MCDM) for evaluation of the current state of its development
by four such methods: EDAS, SAW, TOPSIS, and PROMETHEE II. Based on the evaluation results,
prominent and lagging factors were understood, and proposals for effective development of public
infrastructure of electric vehicles were proposed for improvement of the infrastructure
Control features of 3D deflector under different braking conditions
Get PDFThe purpose of this article is to accurately evaluate
the stopping distances of 3D deflector using tunable rheological
features of smart fluids. Experimental characteristics
of the chosen fluids are changed into smooth polynomial
functions in accordance to the form of experimental graph
and small total difference of ordinate values. Braking action
and motion are modeled using a stepped approximation
method, which is simple to use. This method was performed
with Microsoft Excel program