ABSTRACT "Laser Droplet Welding" is an innovative joining technology. The weldi... more ABSTRACT "Laser Droplet Welding" is an innovative joining technology. The welding is realised by a laser generated liquid metal droplet which is deposited onto the parts to be joined. The raw material is a metal wire. In conventional laser welding a gap between the parts worsens the quality of the laser welded joint substantially. Contrarily a droplet offers sufficient material to bridge gaps. Even different gap sizes can be bridged by a suitable selection of the droplet size. A further advantage is the controllable heat transfer, only given by the heat content of a single drop that is sufficient to produce a high-temperature weld. The droplet heating provides the opportunity to weld small devices, thin coatings and even heat sensitive components without negative influence on their mechanical and electrical function. It is also possible to interconnect different materials by the addition of material supplied in form of drops. With the Laser Droplet Weld it is furthermore possible to join high reflective materials. This article describes the process and the system technology as well as achieved results. It will mainly focus on the droplet detachment which influences the complete process, e.g. the heat quantity or weld splashes.
ABSTRACT This paper presents results of the influence of cryogenic machining on the process stabi... more ABSTRACT This paper presents results of the influence of cryogenic machining on the process stability. The stability diagrams are obtained experimentally using the coarse-grained entropy rate estimator for chatter detection from measured cutting forces. In comparison with conventional machining, enlarged stability windows are observed for the case of cryogenic machining. Based on the defined specific force models in turning operations, it is shown that a higher machining stability is achievable in cryogenic machining due to the reduction of specific cutting force components, in comparison with dry machining.
Analysis and short-term forecasting of traffic flow data for several locations of the Slovenia hi... more Analysis and short-term forecasting of traffic flow data for several locations of the Slovenia highway network are presented. Daily and weekly seasonal components of the data are analysed and several features are extracted to support the forecasting. Various short-term forecasting models are developed for one hour ahead forecasting of the traffic flow. Models include benchmark models (random walk, seasonal random walk, naive model), AR and ARMA models, and various configuration of feedforward neural networks. Results show that the best forecasting results (correlation coefficient R > 0.99) are obtained by a feedforward neural network and a selected set of inputs but this sophisticated model surprisingly only slightly surpasses the accuracy of a simple naive model.
Potential and current fluctuations spontaneously generated by corrosion reactions are known as el... more Potential and current fluctuations spontaneously generated by corrosion reactions are known as electrochemical noise. In certain cases, good correlation can be obtained between the results of the spectral analysis of electrochemical noise and corrosion rate and type. However, because of the chaotic nature of corrosion processes, a special mathematical treatment may be needed. In the present study, the electrochemical noise measured on various metals was treated by methods known from the theory of chaos, and the results were compared with the results of spectral analysis. It has been shown that the chaotic characteristics of electrochemical noise are related to corrosion type, whereas the rate of corrosion has no influence on the fractal dimensions of the noise.
Stochastic fluctuations of the corrosion potential and the current generated by corrosion reactio... more Stochastic fluctuations of the corrosion potential and the current generated by corrosion reactions are known as electrochemical noise. These fluctuations can be measured in freely corroding systems, therefore the characteristics of electrochemical noise are influenced only by the type and rate of corrosion. The classical spectral analysis of electrochemical noise in the frequency domain achieve good correlation to corrosion rate and type; however, the chaotic nature of corrosion processes requires different mathematical treatment. In this paper self-similarity and fractal dimensions of electrochemical noise are examined in order to explain its mechanism and improve the corrosion monitoring system. Capacity and correlation fractal dimensions of voltage and current-noise, measured on various metals, are calculated and compared to the results of the classical spectral analysis. Relations between different rates and types of corrosion (passivation, local, uniform) and the fractal characteristics of electrochemical noise are established. The analysis of spontaneous electrochemical voltage and current fluctuations is confirmed as a rich source of information in corrosion processes.
Transportation Research Part C-emerging Technologies, Nov 1, 2013
ABSTRACT This paper considers the dynamics of traffic on a ring road-based transportation network... more ABSTRACT This paper considers the dynamics of traffic on a ring road-based transportation network around a major city, via traffic flow time series analysis and characterization. In particular, three traffic flow time series are examined. Two of the time series are acquired from measurement stations located on highways, while one is from a station on the ring road around Ljubljana city. For the analysis and characterization of time series the novel test called 0–1 test for chaos is applied. Based on the outputs of the test it is concluded that the observed traffic dynamics is inherently chaotic. Additionally, a more detailed characterization of traffic dynamics is carried out on Lyapunov spectrum basis, which reveals that traffic dynamics on the highway is quantitatively quite different from the traffic dynamics on the ring road.
In the laser droplet generation process three different dripping regimes are experimentally obser... more In the laser droplet generation process three different dripping regimes are experimentally observed in dependence on the detachment pulse power. Besides being nonlinear, the process is also inherently nonstationary. In order to consistently analyze all the dripping scenarios based on an experimental time series, time-frequency analysis by means of instantaneous frequency is used. For the calculation of instantaneous frequency, the most recent developments of the Hilbert–Huang transform are applied, i.e. ensemble empirical mode decomposition, empirical amplitude/frequency modulation decomposition, and direct quadrature. In time-frequency spectra specific patterns are associated with corresponding dripping regimes. By means of a detailed inspection of patterns, the influence of the detachment pulse power on dripping dynamics is characterized.
Global Attractors of High-Speed Milling: Analyses, Numerics and Experiments. [ASME Conference Pro... more Global Attractors of High-Speed Milling: Analyses, Numerics and Experiments. [ASME Conference Proceedings 2003, 2231 (2003)]. Gabor Stepan, Robert Szalai, Brian P. Mann, Philip V. Bayly, Tamas Insperger, Janez Gradisek, Edvard Govekar. Abstract. ...
ABSTRACT "Laser Droplet Welding" is an innovative joining technology. The weldi... more ABSTRACT "Laser Droplet Welding" is an innovative joining technology. The welding is realised by a laser generated liquid metal droplet which is deposited onto the parts to be joined. The raw material is a metal wire. In conventional laser welding a gap between the parts worsens the quality of the laser welded joint substantially. Contrarily a droplet offers sufficient material to bridge gaps. Even different gap sizes can be bridged by a suitable selection of the droplet size. A further advantage is the controllable heat transfer, only given by the heat content of a single drop that is sufficient to produce a high-temperature weld. The droplet heating provides the opportunity to weld small devices, thin coatings and even heat sensitive components without negative influence on their mechanical and electrical function. It is also possible to interconnect different materials by the addition of material supplied in form of drops. With the Laser Droplet Weld it is furthermore possible to join high reflective materials. This article describes the process and the system technology as well as achieved results. It will mainly focus on the droplet detachment which influences the complete process, e.g. the heat quantity or weld splashes.
ABSTRACT This paper presents results of the influence of cryogenic machining on the process stabi... more ABSTRACT This paper presents results of the influence of cryogenic machining on the process stability. The stability diagrams are obtained experimentally using the coarse-grained entropy rate estimator for chatter detection from measured cutting forces. In comparison with conventional machining, enlarged stability windows are observed for the case of cryogenic machining. Based on the defined specific force models in turning operations, it is shown that a higher machining stability is achievable in cryogenic machining due to the reduction of specific cutting force components, in comparison with dry machining.
Analysis and short-term forecasting of traffic flow data for several locations of the Slovenia hi... more Analysis and short-term forecasting of traffic flow data for several locations of the Slovenia highway network are presented. Daily and weekly seasonal components of the data are analysed and several features are extracted to support the forecasting. Various short-term forecasting models are developed for one hour ahead forecasting of the traffic flow. Models include benchmark models (random walk, seasonal random walk, naive model), AR and ARMA models, and various configuration of feedforward neural networks. Results show that the best forecasting results (correlation coefficient R > 0.99) are obtained by a feedforward neural network and a selected set of inputs but this sophisticated model surprisingly only slightly surpasses the accuracy of a simple naive model.
Potential and current fluctuations spontaneously generated by corrosion reactions are known as el... more Potential and current fluctuations spontaneously generated by corrosion reactions are known as electrochemical noise. In certain cases, good correlation can be obtained between the results of the spectral analysis of electrochemical noise and corrosion rate and type. However, because of the chaotic nature of corrosion processes, a special mathematical treatment may be needed. In the present study, the electrochemical noise measured on various metals was treated by methods known from the theory of chaos, and the results were compared with the results of spectral analysis. It has been shown that the chaotic characteristics of electrochemical noise are related to corrosion type, whereas the rate of corrosion has no influence on the fractal dimensions of the noise.
Stochastic fluctuations of the corrosion potential and the current generated by corrosion reactio... more Stochastic fluctuations of the corrosion potential and the current generated by corrosion reactions are known as electrochemical noise. These fluctuations can be measured in freely corroding systems, therefore the characteristics of electrochemical noise are influenced only by the type and rate of corrosion. The classical spectral analysis of electrochemical noise in the frequency domain achieve good correlation to corrosion rate and type; however, the chaotic nature of corrosion processes requires different mathematical treatment. In this paper self-similarity and fractal dimensions of electrochemical noise are examined in order to explain its mechanism and improve the corrosion monitoring system. Capacity and correlation fractal dimensions of voltage and current-noise, measured on various metals, are calculated and compared to the results of the classical spectral analysis. Relations between different rates and types of corrosion (passivation, local, uniform) and the fractal characteristics of electrochemical noise are established. The analysis of spontaneous electrochemical voltage and current fluctuations is confirmed as a rich source of information in corrosion processes.
Transportation Research Part C-emerging Technologies, Nov 1, 2013
ABSTRACT This paper considers the dynamics of traffic on a ring road-based transportation network... more ABSTRACT This paper considers the dynamics of traffic on a ring road-based transportation network around a major city, via traffic flow time series analysis and characterization. In particular, three traffic flow time series are examined. Two of the time series are acquired from measurement stations located on highways, while one is from a station on the ring road around Ljubljana city. For the analysis and characterization of time series the novel test called 0–1 test for chaos is applied. Based on the outputs of the test it is concluded that the observed traffic dynamics is inherently chaotic. Additionally, a more detailed characterization of traffic dynamics is carried out on Lyapunov spectrum basis, which reveals that traffic dynamics on the highway is quantitatively quite different from the traffic dynamics on the ring road.
In the laser droplet generation process three different dripping regimes are experimentally obser... more In the laser droplet generation process three different dripping regimes are experimentally observed in dependence on the detachment pulse power. Besides being nonlinear, the process is also inherently nonstationary. In order to consistently analyze all the dripping scenarios based on an experimental time series, time-frequency analysis by means of instantaneous frequency is used. For the calculation of instantaneous frequency, the most recent developments of the Hilbert–Huang transform are applied, i.e. ensemble empirical mode decomposition, empirical amplitude/frequency modulation decomposition, and direct quadrature. In time-frequency spectra specific patterns are associated with corresponding dripping regimes. By means of a detailed inspection of patterns, the influence of the detachment pulse power on dripping dynamics is characterized.
Global Attractors of High-Speed Milling: Analyses, Numerics and Experiments. [ASME Conference Pro... more Global Attractors of High-Speed Milling: Analyses, Numerics and Experiments. [ASME Conference Proceedings 2003, 2231 (2003)]. Gabor Stepan, Robert Szalai, Brian P. Mann, Philip V. Bayly, Tamas Insperger, Janez Gradisek, Edvard Govekar. Abstract. ...
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