Abstract: Static and dynamic characteristics of an induction motor (IM) under frequency vector control are reviewed. Limiting static characteristics enabling to determine the limits of an automatic electric drive, as well as regions of short-term and admissible continuous performance of an induction motor under frequency vector control are presented. Recommendations on the choice of maximum phase voltage of an inverter, DC link voltage of a frequency converter and supply voltage of an induction motor as well as possible ways to reach maximum angular velocity of an induction motor under frequency vector control are suggested.
Keywords: induction motor; frequency control; vector control; three-phase inverter; limiting characteristics
Abstract: Graph-search algorithms belong to the set of basic problem-solving algorithms in Artificial Intelligence. There are systematic graphs search algorithms and also heuristic ones. Depending on the aim, e.g., to find any solution, all solutions, the best solution, one can choose an appropriate algorithm. The best-first algorithm is apt to find the best solution if a good heuristic is provided. Even, the obtained solution itself is the cheapest one, the way to obtain it may contain several useless branches. In this paper, a modified approach is shown which finds a solution having the minimal number of useless branches (depending also on the used heuristic). For the new algorithm, called minimum total cost search, the concept of the heuristic function is also changed: instead of predicting the cost of the closest goal state a kind of directed heuristic function is used: providing an estimation to the closest goal state from the given state to the given direction.
Keywords: Artificial Intelligence; problem solving; graph-search algorithms; cheapest way to obtain solution; minimum total cost search; best-first search; backtracking; heuristic search
Abstract: The most pressing requirement currently faced by the automotive industry is the speed at which a certain product can be offered to the market. The present paper discusses the applicability of the Rapid Prototyping method in the automotive industry, illustrated as a development approach of a potential solution to the early evaluation phase of a system. The offered method advances an implementation of a pilot approach in the context of the final product. The functioning of the prototype is measured in different test scenarios, the results being increasingly encouraging towards the industrial adoption of this technique from a technical as well as an economic point of view.
Keywords: Automotive; Engine Control Unit; External Rapid Prototyping; Performance
Abstract: This article presents a new robust LiDAR processing method. This method fits a regression plane to a point cloud in any horizontal position by fitting a disc (with R radius) on it, which contains a specified portion (q) of points under the disc plane in all three sectors of the disc. This method can be used to create digital elevation models even without any filtering process. This article also describes an analysis, which compares the results of the fitting disc method using different parameters in processing of digital elevation models.
Keywords: LiDAR; Point Cloud; Digital Elevation Model
Abstract: Today, with the increasing popularity of JSON-LD on the Web, there is a need for transformation and extraction of such structured data. In this paper, the authors propose extensions of the JSON-LD Framing specification which are able to create a tree layout based on recursive application of prioritized inverse relationships defined in a frame. The extensions include recursive application of reverse framing, a new @priority keyword which prioritizes reverse properties, a new embedding rule defined with the @first keyword, and the new @reverseRoots keyword used for filtering the result hierarchies of full-length. The proposed Extended Framing Algorithm, together with an extended frame, can be applied on arbitrary JSON-LD input files regardless of the length of its reverse hierarchy chains present in the frame. The proposed solution was tested on JSON-LD documents containing the ENTSO-E CIM Profiles. The two test scenarios were selected because of their complexity and size, each of them containing the ENTSO-E CIM Profiles expressed in CIM RDF Schema and OWL 2 Schema, respectively.
Keywords: Common Information Model; ENTSO-E; Framing; JSON-LD; RDF; Semantic Web
Abstract: The present paper is dedicated to introducing an accurate, generally applicable and minimum requirement demanding quasi steady-state CFD simulation method for investigating the effect of an aircraft propeller within the framework of the ESPOSA project. The simplest solution has been looked for in low Mach number flow regime, thus instead of direct discretization or using source terms, the Actuator Disk Method (ADM) has been applied with two different boundary condition settings: applying induced velocities or total pressure. Formerly, the Rotating Domain Model (RDM) has been validated, thus its output can be used as the reference solution. The results of the three models have been investigated both qualitatively and quantitatively. The most problematic part was the engine nacelle and propeller interaction, which has a strong influence on propeller efficiency. The investigation has shown that the ADM with total pressure boundary condition settings can provide acceptably close results to the reference RDM: within 5% amongst the investigated parameters.
Keywords: Actuator Disk Model; Schmitz method; Rotating Domain Model; Reynolds-Averaged Navier-Stokes Simulation; propeller-body interaction
Abstract: The evaluation of the visual quality of digital images is most commonly performed with various objective and subjective quality assessment methods. To calculate and analyse these methods, usually one of predefined image databases, e.g. TID2008 or TID2013, is used to compare an unmanipulated image with a manipulated one. When comparing quality assessment parameters to the communication value of images, a different, hi-resolution and more detail-oriented image database is required; therefore, a novel database for the evaluation of digital images was developed. Using detail coverage and color difference calculations, the research team designed a series of 30 color images with 28 manipulations that can be successfully used for determining the correlations among various quality assessment parameters, metrics and the communication value (ability to communicate) of digital images. The parameters that were used to manipulate images include sharpness, contrast, noise, compression, resizing and lightness (all were chosen based on real-life photography usage). Using RMSE (root mean square error), PSNR (peak signal to noise ratio) and SSIM index (structural similarity index) assessment methods, the influence of image details on quality parameters was calculated. The calculations demonstrate the importance of each parameter and its influence on the image visual quality. The results show a new way of understanding quality parameters and predicting which quality parameter is more important when the image is more or less complex. Complexity as a mathematical value is closely correlated to the content of an image. Hence, understanding the results of this research can help photographers and editors choose a more suitable digital image for publication. The benefits are not only theoretical, but can be applied instantly in real-life use.
Keywords: photography; image quality assessment; digital image evaluation; image quality parameters; RMSE; PSNR; SSIM; novel image database; visual database
Abstract: Accurate design of heat treatment operations requires the knowledge of the Heat Transfer Coefficients (HTC), which quantity can be determined by performing Inverse Heat Transfer Calculations. The novel approaches for the estimation of HTC are based on heuristic optimisation methods, but the usage of these techniques raises several questions. In the case of genetic algorithms, there are not any rules of thumb for selecting the appropriate population size, mutation rate, stopping condition, and similar. The most efficient way to fine-tune these parameters is to run thousands of experimental tests and evaluate the results. However, in the case of inverse heat conduction, this has not been a viable option because of the high computational demand of fitness calculation which leads to a runtime of dozens of years. This paper presents a solution to this problem using a novel data-parallel direct heat conduction problem solver method implemented on multiple graphics accelerators. The ~100× speed-up achieved by this parallel algorithm made it possible to finish the necessary experimental tests in 15 weeks (instead of 29 years). Data gathered during these experiments are directly useful in practice. Based on these, it is possible to make recommendations for optimal genetic algorithm configuration parameters.
Keywords: inverse heat conduction problem; genetic algorithm; parameter optimisation; population size; mutation rate; stopping condition; graphics accelerators; CUDA
Abstract: The paper discusses the material compaction process under various types of stress conditions based on the simulation of the multiaxial compression process of powdered titanium sponge. The finite element model of the multiaxial compression process made it possible to apply both radial and axial pressure independently from one another. Titanium sponge subjected to reversible thermo-hydrogen processing was used as the research material. For the description of the material plasticity condition, the modified Drucker-Prager Cap plasticity model was used, implemented in Abaqus.
Keywords: stress state; multiaxial compression; titanium sponge; metal powder; modified Drucker-Prager Cap plasticity model; representative unit cell; micromechanical model; finite element simulation
Abstract: Determining a roundness value is essential for enabling fast, easy and smooth assembly of workpieces with circular fitting surfaces. In a number of cases, roundness specifications should be defined if other geometrical specifications are not sufficient for enabling reliable assembly. Various standards treat roundness as a deviation from an ideal circle, whereas, the actual cross section form is not treated at all. It seems this characteristic is not worth examining. Knowing the cross section form, however, enables determining various factors that result in undesirable deviations of workpiece cross sections from an ideal circle. This paper presents a new method which, in addition to determining roundness, can be used to determine the actual form of a circular workpiece cross section, using a coordinate measuring machine.
Keywords: Cross section actual form; roundness; CMM; V-block method
Abstract: The paper presents a novel controller and observer design methodology for nonlinear systems based on the Linear Parameter Varying (LPV) framework. The introduced techniques effectively combine the classical state feedback methodology with matrix similarity theorems. The presented solutions are analyzed in order to assess their benefits, drawbacks and limitations. The possible selection of scheduling variables is investigated and dyadic structures are used to strengthen the eigenvalue equality from a mathematical point of view. The connection between the controller and observer side is presented and a solution is given for occurring matrix invertibility issues. The method is tested for a control of nonlinear physiological system, more specifically, for the control of innate immune system. The results show that the developed complementary LPV controller and observer are able to satisfy the predefined criteria.
Keywords: Linear Parameter Varying, Control of immune system, LPV-based control technique, Physiological control
Abstract: A heuristic active fault tolerant controller is designed based on the model of elections in a two-party democratic society. The goal of the proposed controller is to modify reference trajectories to maintain the stability of the faulty spacecraft. The elections are assumed to be first order Markovian. Final state constraints are used to ensure that the angular velocities asymptotically converge to the origin. A simulation shows that the proposed method makes the origin an asymptotically stable equilibrium point for the considered spacecraft. Because of its computational efficiency, the proposed method can be effectively used on-line in real-time, an important feature of any active fault tolerant controller. The present paper shows that socio-political models have a great potential to solve complex engineering problems and opens a new window for further developments in this field.
Keywords: Active fault tolerant control, two-party democratic society, reference trajectory management, under-actuated spacecraft
Abstract: SCADA solutions are under a high flux to shift their focus from process control of a limited set of industrial plants to the control of large-scale system of systems. This is in par with the recent proliferation of ubiquitous/pervasive computing paradigm mostly embodied as Internet of Things (IoT). In a traditional setup, a whole system is only partially covered by SCADA data points; therefore, complex simulation is required to fit the missing measurements, hence, buttress decision support scenarios. This usually entails a fully integrated and centralized approach, where SCADA infrastructure needs to hold and distribute data, both collected and calculated. It leads to the increase of load on a supporting real-time database, which hosts millions of data points. It is a challenge that a traditional SCADA design (based on a shared memory database and competing processes), cannot fulfill in real-time. This paper proposes an alternative approach of an architecture and basic functionality of a SCADA system. The proposed architecture targets distributed SCADA systems that can be used to supervise and control large-scale distributed industrial or infrastructural systems. Strategic data organization and segmentation are introduced, so that the acquired data can be efficiently distributed throughout the system. The proposed architecture pushes forward a peer-to-peer node structuring scheme, where an autonomous node supervises and controls only subsets of the system. Nodes collaborate to establish a unified view of the entire system. The proof of the concept implementation has proven to be able to manage significantly more data points in a distributed fashion than a centralized variant.
Keywords: SCADA; smart city; distributed system; peer-to-peer architecture; smart grid