Marine energy as one of the least utilized renewable energy resource requires more attention in t... more Marine energy as one of the least utilized renewable energy resource requires more attention in the scientific and professional sense. This paper summarizes the energy potential, different types and operating principles of devices for the exploitation of wave energy in which the largest amount of untapped energy potential still resides.
A recent systematic experimental characterisation of technological thin films, based on elaborate... more A recent systematic experimental characterisation of technological thin films, based on elaborated design of experiments as well as probe calibration and correction procedures, allowed for the first time the determination of nanoscale friction under the concurrent influence of several process parameters, comprising normal forces, sliding velocities, and temperature, thus providing an indication of the intricate correlations induced by their interactions and mutual effects. This created the preconditions to undertake in this work an effort to model friction in the nanometric domain with the goal of overcoming the limitations of currently available models in ascertaining the effects of the physicochemical processes and phenomena involved in nanoscale contacts. Due to the stochastic nature of nanoscale friction and the relatively sparse available experimental data, meta-modelling tools fail, however, at predicting the factual behaviour. Based on the acquired experimental data, data min...
Friction and wear are recognized as one of the most puzzling problems, not only in many engineeri... more Friction and wear are recognized as one of the most puzzling problems, not only in many engineering and manufacturing applications, but also in a fun
Friction is one of the most challenging problems in microand nanosystems’ technologies. While fri... more Friction is one of the most challenging problems in microand nanosystems’ technologies. While frictional phenomena on the macroand meso-scales are well described and can generally be efficiently compensated via proper control typologies, in the nanometric domain friction is still a matter of persistent studies. Our ongoing work aims at providing a contribution to the study of friction by characterising the parameters influencing its value at the nanometric scale. The dependence of friction on material types, surface topography, loading conditions, velocity of motion, temperature and lubrication will thus be investigated via SPM measurements. Due to the large number of monitored influences, the number and type of measurements will be determined by using novel metamodeling techniques of arranging the measurement campaigns. Preliminary results aimed at a systematic engineering approach to the conduction of a finite set of methodical experiments characterising nanometric friction are th...
In this paper, an analysis of heat transfer and fluid flow in a wavy fin-and-tube heat exchanger ... more In this paper, an analysis of heat transfer and fluid flow in a wavy fin-and-tube heat exchanger has been performed followed with a comparative study of different algorithms used for the heat exchanger optimization. Three- dimensional (3D) numerical simulation results of a circular tube heat exchanger were used in multivariate optimization that included geometrical parameters that, as predicted, significantly influence thermodynamic and hydrodynamic behavior of the heat exchanger system. A nonlinear regression model (polynomial function) was derived for two developed objective functions. Several algorithms for the optimization of heat exchanger have been used: two evolutionary algorithms (Genetic Algorithm and Simulated Annealing) and Pattern Search algorithm. The influences of inlet air velocity, as well as fin pitch and wavy angle on heat transfer and pressure drop conditions have been studied. The comparison of results has been made along with the analysis and conclusions.
The main limitation in modelling nanoscale friction is the variety of physicochemical processes a... more The main limitation in modelling nanoscale friction is the variety of physicochemical processes and their interactions in nanoscale contacts that depend on the materials and on the conditions relating to sliding velocity, normal forces, temperature etc. To assess the value of the nanoscale friction coefficients, in this work an experimental methodology using a scanning probe microscope (SPM) in the lateral force microscopy (LFM) mode is hence used on various thin film samples. The measurements are designed by employing the centroidal Voronoi tessellation technique with 50 sample points. By using Support Vector Machine-based machine learning, the trends of the values of the friction coefficients can thus be established despite the marked stochastic contributions, creating therefore the preconditions for obtaining a multi-dimensional model relating the value of nanometric friction to its influencing parameters.
Friction is a ubiquitous phenomenon of great research interest in engineering practice. Fundament... more Friction is a ubiquitous phenomenon of great research interest in engineering practice. Fundamental frictional features of two solids in contact and in relative motion are governed by microscopic single asperity contacts at their interface. A structured multidisciplinary approach to the experimental determination of friction in the nanometric domain is presented in this work. The dependence of nanoscale friction on process parameters comprising the materials in relative motion, normal forces, sliding velocities and the temperature conditions is studied experimentally by employing scanning probe microscopy. The data hence attained from multidimensional experimental measurements on thin-film samples is used for the development of machine learning-based models. In fact, due to the stochastic nature of the considered phenomena, conventional regression methods yield poor predictive performances, prompting thus the usage of the machine learning numerical paradigm. Such an approach enables...
In this paper a comparative study of several algorithms for the optimization of heat exchanger wi... more In this paper a comparative study of several algorithms for the optimization of heat exchanger with microchannel coil has been done. Multivariate optimizations included three geometrical parameters of heat exchanger which, as predicted, significantly influence hydrodynamic behaviour of the system. Data set used for the optimization has been numerically acquired and experimentally validated. The air/water side numerical model of heat exchanger composed of flat tubes with rectangular shapes has been used. Objective function that combines the heat transfer rate and the pressure drops of air and water has been developed and employed for an optimization procedure. Two evolutionary algorithms have been used (Genetic Algorithm and Simulated Annealing) and compared with Pattern Search algorithm. The comparison of results has been made along with the analysis and final conclusions.
This paper provides a brief overview of the use of solar energy in Croatia, especially in coastal... more This paper provides a brief overview of the use of solar energy in Croatia, especially in coastal areas. The current state of exploitation of solar energy and the future outlook for using this renewable energy source is also presented.
A recent systematic experimental characterisation of technological thin films, based on elaborate... more A recent systematic experimental characterisation of technological thin films, based on elaborated design of experiments as well as probe calibration and correction procedures, allowed for the first time the determination of nanoscale friction under the concurrent influence of several process parameters, comprising normal forces, sliding velocities, and temperature, thus providing an indication of the intricate correlations induced by their interactions and mutual effects. This created the preconditions to undertake in this work an effort to model friction in the nanometric domain with the goal of overcoming the limitations of currently available models in ascertaining the effects of the physicochemical processes and phenomena involved in nanoscale contacts. Due to the stochastic nature of nanoscale friction and the relatively sparse available experimental data, meta-modelling tools fail, however, at predicting the factual behaviour. Based on the acquired experimental data, data min...
In this paper a comparative study of several algorithms for the optimization of heat exchanger wi... more In this paper a comparative study of several algorithms for the optimization of heat exchanger with microchannel coil has been done. Multivariate optimizations have included three geometrical parameters of heat exchanger which, as predicted, significantly influence hydrodynamic behavior of the system. Data set used for the optimizations have been numerically acquired and experimentally validated. The air/water side numerical model of heat exchanger composed of flat tubes with rectangular shapes has been used. Objective function that combines the heat transfer rate and the pressure drops of air and water has been developed and employed for the optimization procedures. The optimization has been performed by means of two evolutionary algorithms (Genetic Algorithm and Simulated Annealing) and Pattern Search Algorithm. The comparison of obtained results has been accomplished along with the results analysis and final conclusions.
Thin films are widely used as coatings in MEMS and NEMS as well as in precision devices, where th... more Thin films are widely used as coatings in MEMS and NEMS as well as in precision devices, where they are often subjected to contact stresses and friction. Their frictional characteristics are hence of outmost importance. On the other hand, recently an original structured experimental methodology was developed and successfully implemented in determining the correlation between multiple process parameters and the resulting nanoscale friction, where an elaborated design of experiments approach is used, whereas the obtained measurements are analysed via advanced predictive machine learning algorithms. The same methodology is used in this work to characterise the meso-scale friction of an Al2O3 film, extending thus the value ranges of the most important influencing parameters beyond those achievable via scanning probe microscopy studies. A state-of-the-art nanoindentation device is hence used. The friction force is determined from nanoscratch experiments resulting from using the Berkovich...
The renewable energy market has seen a rapid increase in recent years in Croatia. An improved fee... more The renewable energy market has seen a rapid increase in recent years in Croatia. An improved feed-in tariff system which made investing in renewable energy more attractive to entrepreneurs or financiers boosted both the installed capacity and the generated electricity from renewable energy. At present, under the Croatian feed-in tariff system, the installed capacity of about 400 MW is capable of producing about 800 GWh of renewable electricity per year. This generated renewable electricity represents only 5.2% of the annual final electricity consumption in Croatia. Ranked by installed power capacity, the number one renewable energy source in Croatia is wind energy with 354 MW, followed by biomass and biogas with 17 MW, cogeneration with 12 MW, solar photovoltaics with 7 MW and small hydro with 3 MW. To keep up with the running expenditures within the feed-in tariff system, the incentive fee for renewable electricity generation increased fivefold in 2013. At the moment, end consumer...
Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain... more Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain. Measurements are performed on nickel-titanium archwires without and with different coatings as well as subjected for four weeks to an artificial saliva solution with different pH values (4.8 and 6.6). Since surface properties can have a meaningful influence on friction, corrosion or plaque accumulation, surface texture of the wires is measured by employing atomic force microscopy. On the other hand, with the aim of determining Young’s modulus and the hardness, nanoindentation tests are performed for different peak load values. It is hence established that there is no statistically relevant deterioration of the surfaces after their exposure to saliva. Rh coating leads, in turn, to an increase of surface roughness. Young’s moduli and hardness values tend to increase with increasing indentation depths, while they are not meaningfully affected by the coating or the corrosion in saliva.
Marine energy as one of the least utilized renewable energy resource requires more attention in t... more Marine energy as one of the least utilized renewable energy resource requires more attention in the scientific and professional sense. This paper summarizes the energy potential, different types and operating principles of devices for the exploitation of wave energy in which the largest amount of untapped energy potential still resides.
A recent systematic experimental characterisation of technological thin films, based on elaborate... more A recent systematic experimental characterisation of technological thin films, based on elaborated design of experiments as well as probe calibration and correction procedures, allowed for the first time the determination of nanoscale friction under the concurrent influence of several process parameters, comprising normal forces, sliding velocities, and temperature, thus providing an indication of the intricate correlations induced by their interactions and mutual effects. This created the preconditions to undertake in this work an effort to model friction in the nanometric domain with the goal of overcoming the limitations of currently available models in ascertaining the effects of the physicochemical processes and phenomena involved in nanoscale contacts. Due to the stochastic nature of nanoscale friction and the relatively sparse available experimental data, meta-modelling tools fail, however, at predicting the factual behaviour. Based on the acquired experimental data, data min...
Friction and wear are recognized as one of the most puzzling problems, not only in many engineeri... more Friction and wear are recognized as one of the most puzzling problems, not only in many engineering and manufacturing applications, but also in a fun
Friction is one of the most challenging problems in microand nanosystems’ technologies. While fri... more Friction is one of the most challenging problems in microand nanosystems’ technologies. While frictional phenomena on the macroand meso-scales are well described and can generally be efficiently compensated via proper control typologies, in the nanometric domain friction is still a matter of persistent studies. Our ongoing work aims at providing a contribution to the study of friction by characterising the parameters influencing its value at the nanometric scale. The dependence of friction on material types, surface topography, loading conditions, velocity of motion, temperature and lubrication will thus be investigated via SPM measurements. Due to the large number of monitored influences, the number and type of measurements will be determined by using novel metamodeling techniques of arranging the measurement campaigns. Preliminary results aimed at a systematic engineering approach to the conduction of a finite set of methodical experiments characterising nanometric friction are th...
In this paper, an analysis of heat transfer and fluid flow in a wavy fin-and-tube heat exchanger ... more In this paper, an analysis of heat transfer and fluid flow in a wavy fin-and-tube heat exchanger has been performed followed with a comparative study of different algorithms used for the heat exchanger optimization. Three- dimensional (3D) numerical simulation results of a circular tube heat exchanger were used in multivariate optimization that included geometrical parameters that, as predicted, significantly influence thermodynamic and hydrodynamic behavior of the heat exchanger system. A nonlinear regression model (polynomial function) was derived for two developed objective functions. Several algorithms for the optimization of heat exchanger have been used: two evolutionary algorithms (Genetic Algorithm and Simulated Annealing) and Pattern Search algorithm. The influences of inlet air velocity, as well as fin pitch and wavy angle on heat transfer and pressure drop conditions have been studied. The comparison of results has been made along with the analysis and conclusions.
The main limitation in modelling nanoscale friction is the variety of physicochemical processes a... more The main limitation in modelling nanoscale friction is the variety of physicochemical processes and their interactions in nanoscale contacts that depend on the materials and on the conditions relating to sliding velocity, normal forces, temperature etc. To assess the value of the nanoscale friction coefficients, in this work an experimental methodology using a scanning probe microscope (SPM) in the lateral force microscopy (LFM) mode is hence used on various thin film samples. The measurements are designed by employing the centroidal Voronoi tessellation technique with 50 sample points. By using Support Vector Machine-based machine learning, the trends of the values of the friction coefficients can thus be established despite the marked stochastic contributions, creating therefore the preconditions for obtaining a multi-dimensional model relating the value of nanometric friction to its influencing parameters.
Friction is a ubiquitous phenomenon of great research interest in engineering practice. Fundament... more Friction is a ubiquitous phenomenon of great research interest in engineering practice. Fundamental frictional features of two solids in contact and in relative motion are governed by microscopic single asperity contacts at their interface. A structured multidisciplinary approach to the experimental determination of friction in the nanometric domain is presented in this work. The dependence of nanoscale friction on process parameters comprising the materials in relative motion, normal forces, sliding velocities and the temperature conditions is studied experimentally by employing scanning probe microscopy. The data hence attained from multidimensional experimental measurements on thin-film samples is used for the development of machine learning-based models. In fact, due to the stochastic nature of the considered phenomena, conventional regression methods yield poor predictive performances, prompting thus the usage of the machine learning numerical paradigm. Such an approach enables...
In this paper a comparative study of several algorithms for the optimization of heat exchanger wi... more In this paper a comparative study of several algorithms for the optimization of heat exchanger with microchannel coil has been done. Multivariate optimizations included three geometrical parameters of heat exchanger which, as predicted, significantly influence hydrodynamic behaviour of the system. Data set used for the optimization has been numerically acquired and experimentally validated. The air/water side numerical model of heat exchanger composed of flat tubes with rectangular shapes has been used. Objective function that combines the heat transfer rate and the pressure drops of air and water has been developed and employed for an optimization procedure. Two evolutionary algorithms have been used (Genetic Algorithm and Simulated Annealing) and compared with Pattern Search algorithm. The comparison of results has been made along with the analysis and final conclusions.
This paper provides a brief overview of the use of solar energy in Croatia, especially in coastal... more This paper provides a brief overview of the use of solar energy in Croatia, especially in coastal areas. The current state of exploitation of solar energy and the future outlook for using this renewable energy source is also presented.
A recent systematic experimental characterisation of technological thin films, based on elaborate... more A recent systematic experimental characterisation of technological thin films, based on elaborated design of experiments as well as probe calibration and correction procedures, allowed for the first time the determination of nanoscale friction under the concurrent influence of several process parameters, comprising normal forces, sliding velocities, and temperature, thus providing an indication of the intricate correlations induced by their interactions and mutual effects. This created the preconditions to undertake in this work an effort to model friction in the nanometric domain with the goal of overcoming the limitations of currently available models in ascertaining the effects of the physicochemical processes and phenomena involved in nanoscale contacts. Due to the stochastic nature of nanoscale friction and the relatively sparse available experimental data, meta-modelling tools fail, however, at predicting the factual behaviour. Based on the acquired experimental data, data min...
In this paper a comparative study of several algorithms for the optimization of heat exchanger wi... more In this paper a comparative study of several algorithms for the optimization of heat exchanger with microchannel coil has been done. Multivariate optimizations have included three geometrical parameters of heat exchanger which, as predicted, significantly influence hydrodynamic behavior of the system. Data set used for the optimizations have been numerically acquired and experimentally validated. The air/water side numerical model of heat exchanger composed of flat tubes with rectangular shapes has been used. Objective function that combines the heat transfer rate and the pressure drops of air and water has been developed and employed for the optimization procedures. The optimization has been performed by means of two evolutionary algorithms (Genetic Algorithm and Simulated Annealing) and Pattern Search Algorithm. The comparison of obtained results has been accomplished along with the results analysis and final conclusions.
Thin films are widely used as coatings in MEMS and NEMS as well as in precision devices, where th... more Thin films are widely used as coatings in MEMS and NEMS as well as in precision devices, where they are often subjected to contact stresses and friction. Their frictional characteristics are hence of outmost importance. On the other hand, recently an original structured experimental methodology was developed and successfully implemented in determining the correlation between multiple process parameters and the resulting nanoscale friction, where an elaborated design of experiments approach is used, whereas the obtained measurements are analysed via advanced predictive machine learning algorithms. The same methodology is used in this work to characterise the meso-scale friction of an Al2O3 film, extending thus the value ranges of the most important influencing parameters beyond those achievable via scanning probe microscopy studies. A state-of-the-art nanoindentation device is hence used. The friction force is determined from nanoscratch experiments resulting from using the Berkovich...
The renewable energy market has seen a rapid increase in recent years in Croatia. An improved fee... more The renewable energy market has seen a rapid increase in recent years in Croatia. An improved feed-in tariff system which made investing in renewable energy more attractive to entrepreneurs or financiers boosted both the installed capacity and the generated electricity from renewable energy. At present, under the Croatian feed-in tariff system, the installed capacity of about 400 MW is capable of producing about 800 GWh of renewable electricity per year. This generated renewable electricity represents only 5.2% of the annual final electricity consumption in Croatia. Ranked by installed power capacity, the number one renewable energy source in Croatia is wind energy with 354 MW, followed by biomass and biogas with 17 MW, cogeneration with 12 MW, solar photovoltaics with 7 MW and small hydro with 3 MW. To keep up with the running expenditures within the feed-in tariff system, the incentive fee for renewable electricity generation increased fivefold in 2013. At the moment, end consumer...
Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain... more Mechanical properties of orthodontic archwires are studied in this work in the micrometric domain. Measurements are performed on nickel-titanium archwires without and with different coatings as well as subjected for four weeks to an artificial saliva solution with different pH values (4.8 and 6.6). Since surface properties can have a meaningful influence on friction, corrosion or plaque accumulation, surface texture of the wires is measured by employing atomic force microscopy. On the other hand, with the aim of determining Young’s modulus and the hardness, nanoindentation tests are performed for different peak load values. It is hence established that there is no statistically relevant deterioration of the surfaces after their exposure to saliva. Rh coating leads, in turn, to an increase of surface roughness. Young’s moduli and hardness values tend to increase with increasing indentation depths, while they are not meaningfully affected by the coating or the corrosion in saliva.
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