In order to overcome the shortcomings of the dolphin algorithm, which is prone to falling into local optimum and premature convergence, an improved dolphin swarm algorithm, based on the standard dolphin algorithm, was proposed. As a measure of uncertainty, information entropy was used to measure the search stage in the dolphin swarm algorithm. Adaptive step size parameters and dynamic balance factors were introduced to correlate the search step size with the number of iterations and fitness, and to perform adaptive adjustment of the algorithm. Simulation experiments show that, comparing with the basic algorithm and other algorithms, the improved dolphin swarm algorithm is feasible and effective.
Aluminum alloys are widely used today in plastic injection molds in the automotive and aerospace industries due to their high strength and weight ratio, good corrosion and fatigue resistance as well as high feed rates. The 5754 aluminum alloy has high corrosion resistance and a structure suitable for cold forming. In this study, an AA 5754-H111 tempered aluminum alloy with the dimensions of 80×80×30 mm was used, and some of the materials were cryogenically heat treated. For the milling operations, ϕ12 mm diameter 76 mm height uncoated as well as TiCN and TiAlN coated end mills were used. Different levels of cutting depth (1.25, 2.0, 2.5 mm), cutting speed (50, 80, 100 m/ min), feed rate (265, 425, 530 m/ min) and machining pattern (concentric, back and forth and inward helical) were used. The number of experiments was reduced from 486 to 54 using the Taguchi L54 orthogonal array. The values obtained at the end of the experiments were evaluated using the signal-to-noise ratio, ANOVA, three-dimensional graphs and the regression method. Based on the result of the verification experiments, the processing accuracy for surface roughness was improved from 3.20 μm to 0.90 μm, with performance increase of 71.88%.
In the present study, a titanium cellular lattice structure with a mathematical designed porosity gradient was successfully fabricated using the selective laser melting method. The samples with smooth gradient transition of porosity of between 60% and 80% were received for different elementary cell geometries. Elementary cells belong to the triply periodic minimal surfaces family (G, D, I2Y, IWP). Each sample was subjected to a comprehensive analysis including: dimensional metrology and assessment of material defects (X-ray micro-tomography), surface morphology tests (scanning electron microscopy) and mechanical properties (universal testing machine). It has been shown that a cellular lattice with high dimensional accuracy (+0.16/–0.08 mm) and full dense struts can be obtained. According to the assumption, the gradient increases the strength of the cellular lattice samples. The highest increase in plateau stress between the samples with and without gradient was found for the I2Y series (about 185%). Furthermore, it was found that the stress-strain response of the samples depends not only on total porosity, but also on the 3D geometry of the cellular lattice. The stress-strain curves for G, IWP and I2Y samples are smooth and exhibit three characteristic regions: linear elasticity, plateau region and densification region. The size of regions depends on the geometric features of the cellular lattice. For series D, in the plateau region, the fluctuations in stress value are clearly visible. The smoothest stress-strain curve can be noted for the G series, which combined with good mechanical properties (the plateau stress and energy absorbed, at respectively 25.5 and 43.2 MPa, and 46.3J and 59.5J for Gyr_80 and Gyr_6080, which corresponds to a strain of almost 65% and 50%) positively affects the applicability of cellular structures with such geometry.
The study attempts to investigate the influence of severe plastic deformation (SPD in the hydrostatic extrusion (HE) process on the anisotropy of the structure and mechanical properties of the AA 6060 alloy. Material in isotropic condition was subjected to a single round of hydrostatic extrusion with three different degrees of deformation (ε = 1.23, 1.57, 2.28). They allowed the grain size to be fragmented to the nanocrystalline level. Mechanical properties of the AA 6060 alloy, examined on mini-samples, showed an increase in ultimate tensile strength (UTS) and yield strength (YS) as compared to the initial material. Significant strengthening of the material results from high grain refinement in transverse section, from »220 μm in the initial material to »300 nm following the HE process. The material was characterized by the occurrence of structure anisotropy, which may determine the potential use of the material. Static tensile tests of mini-samples showed »10% anisotropy of properties between longitudinal and transverse cross-sections. In the AA6060 alloy, impact anisotropy was found depending on the direction of its testing. Higher impact toughness was observed in the cross-section parallel to the HE direction. The results obtained allow to analyze the characteristic structure created during the HE process and result in more efficient use of the AA 6060 alloy in applications.
This work depicts the effects of deep cryogenically treated high-speed steel on machining. In recent research, cryogenic treatment has been acknowledged for improving the life or performance of tool materials. Hence, tool materials such as the molybdenum-based high-speed tool steel are frequently used in the industry at present. Therefore, it is necessary to observe the tool performance in machining; the present research used medium carbon steel (AISI 1045) under dry turning based on the L9 orthogonal array. The effect of untreated and deep cryogenically treated tools on the turning of medium carbon steel is analyzed using the multi-input-multi-output fuzzy inference system with the Taguchi approach. The cutting speed, feed rate and depth of cut were the selected process parameters with an effect on surface roughness and the cutting tool edge temperature was also observed. The results reveal that surface roughness decreases and cutting tool edge temperature increases on increasing the cutting speed. This is followed by the feed rate and depth of cut. The deep cryogenically treated tool caused a reduction in surface roughness of about 11% while the cutting tool edge temperature reduction was about 23.76% higher than for an untreated tool. It was thus proved that the deep cryogenically treated tool achieved better performance on selected levels of the turning parameters.
In this paper we study the dynamical behavior of linear discrete-time fractional systems. The first main result is that the norm of the difference of two different solutions of a time-varying discrete-time Caputo equation tends to zero not faster than polynomially. The second main result is a complete description of the decay to zero of the trajectories of one-dimensional time-invariant stable Caputo and Riemann-Liouville equations. Moreover, we present Volterra convolution equations, that are equivalent to Caputo and Riemann-Liouvile equations and we also show an explicit formula for the solution of systems of time-invariant Caputo equations.
The stability of positive linear continuous-time and discrete-time systems is analyzed by the use of the decomposition of the state matrices into symmetrical and antisymmetrical parts. It is shown that: 1) The state Metzler matrix of positive continuous-time linear system is Hurwitz if and only if its symmetrical part is Hurwitz; 2) The state matrix of positive linear discrete-time system is Schur if and only if its symmetrical part is Hurwitz. These results are extended to inverse matrices of the state matrices of the positive linear systems.
In this paper, an energy coordination control method based on intelligent multi-agent systems (MAS) is proposed for energy management and voltage control of a DC microgrid. The structure of the DC microgrid is designed to realize the mathematical modeling of photovoltaic cells, fuel cells and batteries. A two-layer intelligent MAS is designed for energy coordination control: grid-connection and islanding of a DC microgrid is combined with energy management of PV cells, fuel cells, loads and batteries. In the hidden layer and the output layer of the proposed neural network there are 17 and 8 neurons, respectively, and the “logsig” activation function is used for the neurons in the network. Eight kinds of feature quantities and 13 different actions are taken as the input and output parameters of the neural network from the micro-source and the load, and the as the control center agent’s decision-makers. The feasibility of the proposed intelligent multi-agent energy coordination control strategy is verified by MATLAB/Simulink simulation, and three types of examples are analyzed after increasing the load. The simulation results show that the proposed scheme exhibits better performance than the traditional approaches.
The artificial neural network method (ANN) is widely used in both modeling and optimization of manufacturing processes. Determination of optimum processing parameters plays a key role as far as both cost and time are concerned within the manufacturing sector. The burnishing process is simple, easy and cost-effective, and thus it is more common to replace other surface finishing processes in the manufacturing sector. This study investigates the effect of burnishing parameters such as the number of passes, burnishing force, burnishing speed and feed rate on the surface roughness and microhardness of an AZ91D magnesium alloy using different artificial neural network models (i.e. the function fitting neural network (FITNET), generalized regression neural network (GRNN), cascade-forward neural network (CFNN) and feed-forward neural network (FFNN). A total of 1440 different estimates were made by means of ANN methods using different parameters. The best average performance results for surface roughness and microhardness are obtained by the FITNET model (i.e. mean square error (MSE): 0.00060608, mean absolute error (MAE): 0.01556013, multiple correlation coefficient (R): 0.99944545), using the Bayesian regularization process (trainbr)). The FITNET model is followed by the FFNN (i.e. MAE: 0.01707086, MSE: 0.00072907, R: 0.99932069) and CFNN (i.e. MAE: 0.01759166, MSE: 0.00080154, R: 0.99924845) models with very small differences, respectively. The GRNN model has noted worse estimation results (i.e. MSE: 0.00198232, MAE: 0.02973829, R: 0.99900783) as compared with the other models. As a result, MSE, MAE and R values show that it is possible to predict the surface roughness and microhardness results of the burnishing process with high accuracy using ANN models.
The paper addresses optimal control problem of mobile manipulators. Dynamic equations of those mechanisms are assumed herein to be uncertain. Moreover, unbounded disturbances act on the mobile manipulator whose end-effector tracks a desired (reference) trajectory given in a task (Cartesian) space. A computationally efficient class of two-stage cascaded (hierarchical) control algorithms based on both the transpose Jacobian matrix and transpose actuation matrix, has been proposed. The offered control laws involve two kinds of non-singular terminal sliding mode (TSM) manifolds, which were also introduced in the paper. The proposed class of cooperating sub-controllers is shown to be finite time stable by fulfilment of practically reasonable assumptions. The performance of the proposed control strategies is illustrated on an exemplary mobile manipulator whose end-effector tracks desired trajectory.
The paper raises the issue of controlling rural low voltage microgrids in an optimal manner. The impact of different criterion functions, related to the amount of energy exchanged with the distribution system operator network, the level of active power losses, the amount of energy generated by different energy sources and the value of financial performance measures regarding the microgrid operation, on the choice of operating points for devices suggested by the optimization algorithm has been analyzed. Both island and synchronous microgrid operation modes are being considered. We propose two variants of the optimization procedure: the first one is based on the particle swarm optimization algorithm and centralized control logic, and the second one takes advantage of the decentralized approach and Monte Carlo methods. A comparison of the simulation results for two sample rural microgrids, obtained for different objective functions, microgrid operation modes and optimization procedure variants, with the use of prepared algorithm implementations, has been provided. The results show that the proper choice of an objective function can have a crucial impact on the optimization algorithm’s behavior, the choice of operating points and, as a consequence, on microgrid behavior as well. The choice of the proper form of the objective function is the responsibility of the person in charge of both the microgrid itself and its operation. This paper can contribute towards making correct decisions in this area. Generally, slightly better results have been achieved for the centralized control mode of operation. Nevertheless, the results also suggest that in many cases the approach based on distributed logic can return results that are better or sufficiently close to the ones provided by the centralized and more sophisticated approach.
The stability and positivity of linear positive Markovian jump systems with respect to part of the variables is considered. The methodologies of stability of positive systems with known transition probabilities based on common linear copositive Lyapunov function and stability of linear systems with respect to part of the variables are combined to find sufficient conditions of the stochastic stability and positivity of Markovian jump systems with respect to part of the variables. The results are extended for a class of nonlinear positive Markovian jump systems with respect to part of the variables. An example is given to illustrate the obtained results.
The problems connected to developing inductive power transfer IPT systems in aspects of high efficiency and suppression of electromagnetic field (EMF) emission are discussed. It is shown how important it is to compensate for large leakage impedance of IPT coils (air transformer) to improve efficiency of high power transfer. Such compensation circuits operating with resonant frequencies at soft switching conditions additionally allow for reduction of switching losses in power semiconductor devices of converters. The consideration has been illustrated and verified by experimental results measured on two different test stands (50 kW with planar coils and with two 12 kW receiver coils) built in a laboratory of the Łukasiewicz Research Network – Electrotechnical Institute.
In this article, we present a comprehensive measurement system to determine the level of user emotional arousal by the analysis of electrodermal activity (EDA). A number of EDA measurements were collected, while emotions were elicited using specially selected movie sequences. Data collected from 16 participants of the experiment, in conjunction with those from personal questionnaires, were used to determine a large number of 20 features of the EDA, to assess the emotional state of a user. Feature selection was performed using signal processing and analysis methods, while considering user declarations. The suitability of the designed system for detecting the level of emotional arousal was fully confirmed, throughout the number of experiments. The average classification accuracy for two classes of the least and the most stimulating movies varies within the range of 61‒72%.
This article focuses on the finite element analysis (FEA) of the nonlinear behavior of a layered functionally graded material (FGM) plate as concerns displacement, stresses, critical buckling load and fundamental frequency. The material properties of each layer in an FGM plate are assessed according to a ceramic based simple power law distribution and the rules of mixture. The finite element model of a layered FGM plate is developed using ANSYS®15.0 software. The developed finite element model is used to study the static and dynamic responses of an FGM plate. In this paper, the effects of power law distribution, thickness ratio, aspect ratio and boundary conditions are investigated for central displacement, transverse shear stress, transverse normal stress, critical buckling load and fundamental frequency, and the obtained FEA results are in sound agreement with the literature test data results. Since the FGM is used in a high temperature environment, the FE analysis is performed for the FGM plate under a thermal field and then correlated. Finally, the FGM plate is analyzed under a thermomechanical load by using the current FE concept.