Nonlinear modelling and optimal control via Takagi-Sugeno fuzzy techniques: A quadrotor stabilization

Using the principles of Takagi-Sugeno fuzzy modelling allows the integration of flexible fuzzy approaches and rigorous mathematical tools of linear system theory into one common framework. The rule-based T-S fuzzy model splits a nonlinear system into several linear subsystems. Parallel Distributed Compensation (PDC) controller synthesis uses these T-S fuzzy model rules. The resulting fuzzy controller is nonlinear, based on fuzzy aggregation of state controllers of individual linear subsystems. The system is optimized by the linear quadratic control (LQC) method, its stability is analysed using the Lyapunov method. Stability conditions are guaranteed by a system of linear matrix inequalities (LMIs) formulated and solved for the closed loop system with the proposed PDC controller. The additional GA optimization procedure is introduced, and a new type of its fitness function is proposed to improve the closed-loop system performance.Web of Science71110

On multidimensional linear modelling including real uncertainty

The theoretical background for abstract formalization of vague phenomenon of complex systems is fuzzy set theory. In the paper are defined vague data as specialized fuzzy sets - fuzzy numbers and there is described a fuzzy linear regression model as a fuzzy function with fuzzy numbers as vague regression parameters. To identify the fuzzy coefficients of model the genetic algorithm is used. The linear approximation of vague function together with its possibility area are analytically and graphically expressed. The suitable numerical experiments are performed namely in the task of two-dimensional fuzzy function modelling and the time series fuzzy regression analysis as well

Time series analysis by fuzzy linear regression

Fuzzy set theory constitutes the theoretical background for abstractly formalizing the vague phenomenon of complex systems. Vague data are defined herein as specialized fuzzy sets, i.e., fuzzy numbers, and a fuzzy linear regression model is described as a fuzzy function with such numbers as vague parameters. We applied a generic algorithm to identify the associated coefficients of the model, and provide both analytically and graphically, a linear approximation of the vague function, together with description of its potential application. We also provide an example of the fuzzy linear regression model being employed in a time series with economic indicators, namely the evolution of the unemployment, agricultural production, and construction between 2009 and 2011 in the Czech Republic. We selected this period since it represents the period when the financial and economic crisis started, and a certain degree of uncertainty existed in the evolution of economic indicators. Results take the form of fuzzy regression models in relation to variables of the time-specific series. For the period 2009-2011, analysis confirmed assumptions held by the authors on the seasonal behaviour of such variables and connections between them. In 2010, the system behaved in a fuzzier manner; hence, relationships between variables were vaguer than otherwise, brought about by factors such as difference in the elasticity of demand, state interventions, globalization, and transnational impacts.Web of Science321

Effect of Solution Annealing on Fatigue Crack Propagation in the AISI 304L TRIP Steel

Fatigue crack propagation in near-threshold regime was studied in the 304L austenitic stainless steel in two microstructural states: as-received (AR) with finer microstructure and low susceptibility to the transformation-induced plasticity (TRIP) effect, and solution-annealed (SA) with coarser microstructure and higher susceptibility to TRIP. At the load ratio R = 0.1 the threshold was higher in the SA state than in the AR state due to coarser grains and possibly the TRIP effect. In order to clarify the role of crack closure, experiments at R = 0.7 were done. The threshold in the SA state was still higher by 1 MPa center dot m(0.5). This effect was identified as crack tip shielding induced by phase transformation, an example of a non-closure shielding effect. Higher resistance to crack growth in the SA state was attributed to promoted martensitic transformation in non-favorable oriented grain families rather than thicker martensite layers in the crack path area. The conclusions were verified by experiments at R = 0.7 and temperature 150 degrees C > M-s which did not reveal any notable difference in thresholds. However, the threshold values were affected by the load-shedding gradient C = -d Delta K/da, which had to be equalized in both experimental setups inside and outside the furnace

Case study comparing Fiala-based thermophysiological model and PHS Index with experimental data to predict heat strain in normal and protective clothing

The use of protective clothing under extreme conditions leads to heat stress with undesired consequences on human physiology. As a prevention measure, thermal indices and thermophysiological models have been developed. Based on these models and indices, it is possible to estimate the time limits for staying under risky conditions, e.g., by the predicted rectal temperature whose value is one of the most important parameters used for assessing the heat stress. This article is focused on the comparison of rectal and mean skin temperature prediction realized by the Fiala-based thermophysiological model (FMTK) and Predicted heat strain (PHS) index with results from the real experiment for normal and protective clothing. Three types of ensembles were tested and simulated as follows: Klimatex underwear, air-permeable military NBC suit M2000 (FOP), and impermeable chemical protective clothing Tychem-F. The real experiments of thermal strain were performed with one male participant (80 kg, 1.75 m) walking on the treadmill located in the climate chamber. The temperature range for neutral and hot tests was set from 25 °C to 40 °C. The rectal temperature, skin temperatures, and heart rate were measured. The results showed that PHS index is well usable for normal clothing (Klimatex underwear) and air-permeable protective clothing (FOP) under various ambient temperatures, and it is able to give results similar to FMTK model and experiment, the mean absolute error MAE for rectal temperature prediction was for all ambient temperatures lower than 0.5 °C. FMTK model demonstrated good predictability for impermeable protective clothing Tychem-F, the maximum value of MAE 0.69 °C. Whereas PHS index showed several times larger error, the maximum value higher than 1.8 °C, in the prediction for this type of clothing. The performed simulations showed that the accuracy of the prediction by the PHS index is not so strongly dependent on the value of the overall clothing resistance, but it depends on the value of the moisture permeability index (permeable vs impermeable clothing) which is connected with the water vapor partial pressure under the clothing

Measurement of airflow and pressure characteristics of a fan built in a car ventilation system

The aim of this study was to identify a set of operating points of a fan built in ventilation system of our test car. These operating points are given by the fan pressure characteristics and are defined by a pressure drop of the HVAC system (air ducts and vents) and volumetric flow rate of ventilation air. To cover a wide range of pressure drops situations, four cases of vent flaps setup were examined: (1) all vents opened, (2) only central vents closed (3) only central vents opened and (4) all vents closed. To cover a different volumetric flows, the each case was measured at least for four different speeds of fan defined by the fan voltage. It was observed that the pressure difference of the fan is proportional to the fan voltage and strongly depends on the throttling of the air distribution system by the settings of the vents flaps. In case of our test car we identified correlations between volumetric flow rate of ventilation air, fan pressure difference and fan voltage. These correlations will facilitate and reduce time costs of the following experiments with this test car

Airflow Measurement of the Car HVAC Unit Using Hot-wire Anemometry

Thermal environment in a vehicular cabin significantly influence drivers’ fatigue and passengers’ thermal comfort. This environment is traditionally managed by HVAC cabin system that distributes air and modifies its properties. In order to simulate cabin thermal behaviour, amount of the air led through car vents must be determined. The aim of this study was to develop methodology to measure airflow from the vents, and consequently calculate corresponding air distribution coefficients. Three climatic cases were selected to match European winter, summer, and spring / fall conditions. Experiments were conducted on a test vehicle in a climatic chamber. The car HVAC system was set to automatic control mode, and the measurements were executed after the system stabilisation—each case was independently measured three times. To be able to evaluate precision of the method, the airflow was determined at the system inlet (HVAC suction) and outlet (each vent), and the total airflow values were compared. The airflow was calculated by determining a mean value of the air velocity multiplied by an area of inlet / outlet cross-section. Hot-wire anemometry was involved to measure the air velocity. Regarding the summer case, total airflow entering the cabin was around 57 l s-1 with 60 % of the air entering the cabin through dashboard vents; no air was supplied to the feet compartment. The remaining cases had the same total airflow of around 42 l s-1, and the air distribution was focused mainly on feet and windows. The inlet and outlet airflow values show a good match with a maximum mass differential of 8.3 %

New calculation technique for assessment of smoke layer interface in large buildings in connection with the design of buildings in the Czech Republic

The sustainability of the indoor environment of buildings is also related to the conditions that arise in the case of fires. Fires in buildings are characterized by the formation of combustion products, which can significantly endanger the life and health of people. One of the major sources of danger is smoke. If there is no smoke exhaust into the outside environment during the development of the fire, the building is gradually filled with smoke. The important characteristic of the smoke layer is the level of the smoke layer, which changes over time. Several methods have been derived for determining the descent of the smoke layer in an enclosed area of space, which mainly differ in terms of the application area and limits of use. The methods used in the Czech Republic for the assessment of smoke layer descent in the case of fires do not have a clear rationale and in many cases lead to completely misleading results. For this reason, in connection with the standards for the assessment of the buildings in the Czech Republic, a new calculation technique (CSN) has been derived, which has been compared with the selected simple calculation techniques in large buildings. The deviations between the results have been evaluated by the percentage bias method (PBIAS), while the largest deviation, compared to the ISO standard technique, did not exceed 20%. The CSN calculation technique shows a favourable compliance with the technique presented by the ISO standard, where the deviation did not exceed 1.6%. In response to the proposed standards in the Czech Republic, the CSN calculation technique enables the assessment of safe evacuation in relation to the smoke layer interface and can be a considered perspective.Web of Science1411art. no. 644