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Mohammadi, Y., Polajžer, B., Leborgne, R. C. & Khodadad, D. (2024). Most influential feature form for supervised learning in voltage sag source localization. Engineering applications of artificial intelligence, 133(Part D), Article ID 108331.
Open this publication in new window or tab >>Most influential feature form for supervised learning in voltage sag source localization
2024 (English)In: Engineering applications of artificial intelligence, ISSN 0952-1976, E-ISSN 1873-6769, Vol. 133, no Part D, article id 108331Article in journal (Refereed) Published
Abstract [en]

The paper investigates the application of machine learning (ML) for voltage sag source localization (VSSL) in electrical power systems. To overcome feature-selection challenges for traditional ML methods and provide more meaningful sequential features for deep learning methods, the paper proposes three time-sample-based feature forms, and evaluates an existing feature form. The effectiveness of these feature forms is assessed using k-means clustering with k = 2 referred to as downstream and upstream classes, according to the direction of voltage sag origins. Through extensive voltage sag simulations, including noises in a regional electrical power network, k-means identifies a sequence involving the multiplication of positive-sequence current magnitude with the sine of its angle as the most prominent feature form. The study develops further traditional ML methods such as decision trees (DT), support vector machine (SVM), random forest (RF), k-nearest neighbor (KNN), an ensemble learning (EL), and a designed one-dimensional convolutional neural network (1D-CNN). The results found that the combination of 1D-CNN or SVM with the most prominent feature achieved the highest accuracies of 99.37% and 99.13%, respectively, with acceptable/fast prediction times, enhancing VSSL. The exceptional performance of the CNN was also approved by field measurements in a real power network. However, selecting the best ML methods for deployment requires a trade-off between accuracy and real-time implementation requirements. The research findings benefit network operators, large factory owners, and renewable energy park producers. They enable preventive maintenance, reduce equipment downtime/damage in industry and electrical power systems, mitigate financial losses, and facilitate the assignment of power-quality penalties to responsible parties.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Voltage sag (dip), Source localization, Supervised and unsupervised learning, Convolutional neural network, Time-sample-based features
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:umu:diva-223198 (URN)10.1016/j.engappai.2024.108331 (DOI)2-s2.0-85189522853 (Scopus ID)
Funder
The Kempe Foundations, JCK22-0025
Available from: 2024-04-11 Created: 2024-04-11 Last updated: 2024-04-15Bibliographically approved
Mohammadi, Y., Polajžer, B., Leborgne, R. C. & Khodadad, D. (2024). Quantifying power system frequency quality and extracting typical patterns within short time scales below one hour. Sustainable Energy, Grids and Networks, 38, Article ID 101359.
Open this publication in new window or tab >>Quantifying power system frequency quality and extracting typical patterns within short time scales below one hour
2024 (English)In: Sustainable Energy, Grids and Networks, E-ISSN 2352-4677, Vol. 38, article id 101359Article in journal (Refereed) Published
Abstract [en]

This paper addresses the lack of consideration of short time scales, below one hour, such as sub-15-min and sub-1-hr, in grid codes for frequency quality analysis. These time scales are becoming increasingly important due to the flexible market-based operation of power systems as well as the rising penetration of renewable energy sources and battery energy storage systems. For this, firstly, a set of frequency-quality indices is considered, complementing established statistical indices commonly used in power-quality standards. These indices provide valuable insights for quantifying variations, events, fluctuations, and outliers specific to the discussed time scales. Among all the implemented indices, the proposed indices are based on over/under frequency events (6 indices), fast frequency rise/drop events (6 indices), and summation of positive and negative peaks (1 index), of which the 5 with the lowest thresholds are identified as the most dominant. Secondly, k-means and k-medoids clustering methods in a learning scheme are employed to identify typical patterns within the discussed time windows, in which the number of clusters is determined based on prior knowledge linked to reality. In order to clarify the frequency variations and patterns, three frequency case studies are analyzed: case 1 (sub-15-min scale, 10-s values, 6 months), case 2 (sub-1-hr scale, 10-s values, 6 months), and case 3 (sub-1-hr, 3-min values, the year 2021). Results obtained from the indices and learning methods demonstrate a full picture of the information within the windows. The maximum value of the highest frequency value minus the lowest one over the windows is about 0.35 Hz for cases 1 and 2 and 0.25 Hz for case 3. Over-frequency values (with a typical 0.1% threshold) slightly dominates under-frequency values in cases 1 and 2, while the opposite is observed in case 3. Medium fluctuations occur in 35% of windows for cases 1 and 2 and 41% for case 3. Outlier values are detected using the quartile method in 70% of windows for case 2, surpassing the other two cases. About six or seven typical patterns are also extracted using the presented learning scheme, revealing the frequency trends within the short time windows. The proposed approaches offer a simpler alternative than tracking frequency single values and also capture more comprehensive information than existing approaches that analyze the aggregated frequency values at the end of the specific time windows without considering the frequency trends. In this way, the network operators have the possibility to monitor the frequency quality and trends within short time scales using the most dominant indices and typical patterns.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Quantifying power system frequency quality, Statistical indices, Pattern extracting, Machine learning, Short time scales, Renewable energy sources
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:umu:diva-222928 (URN)10.1016/j.segan.2024.101359 (DOI)2-s2.0-85189032641 (Scopus ID)
Funder
The Kempe Foundations, JCK22–0025The Kempe Foundations, JCK22–0025
Available from: 2024-04-03 Created: 2024-04-03 Last updated: 2024-04-15Bibliographically approved
Saremi, A. & Khodadad, D. (2024). The timing of the cochlear wave propagation: a comparative study of computational models. Paper presented at 14th Mechanics of Hearing conference, Helsingør, Denmark, July 24-29, 2022. AIP Conference Proceedings, 3062(1), Article ID 020009.
Open this publication in new window or tab >>The timing of the cochlear wave propagation: a comparative study of computational models
2024 (English)In: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 3062, no 1, article id 020009Article in journal (Refereed) Published
Abstract [en]

It is believed that the phase of the cochlear wave propagation might play a crucial role in binaural perceptionand sound localization by generating cochlear disparities. Experimental data demonstrate that, while a tone is being played,an excitation pattern is formed extending from the base to the apex of the cochlea. The phase of the excitation patterndecays along the cochlear length until the slope of the phase curve (i.e. group delay) reaches its maximum at a locationwith the characteristic frequency (CF) that matches the frequency of the input tone. Thereafter, the phase stays almostconstant (group delay equals zero) until the apex. Computational models have been devised to simulate the cochlearresponses and thereby illuminate the underlying electromechanics of the human inner ear. These computational models canbe divided, according to their topology, into two groups: Parallel filterbanks that model the cochlea as several independentdecoupled filters versus cascade filterbanks (including transmission lines) which assume that the filters are coupled inseries. Due to their modeling principles, cascade filterbanks intrinsically include the longitudinal traveling wavepropagation whereas the parallel filterbank models lack this intrinsic feature since there is no longitudinal relation betweenthe filter stages in these models. The objective of this study is to verify if cascade filterbanks are actually more successfulin simulating the phase responses than parallel filterbanks. The excitation patterns generated by seven cochlear models(four parallel filterbanks, two cascade filterbanks and a transmission-line model) in response to 4 and 9 kHz tones wereestimated using an impulse, and the results were compared with corresponding experimental data recorded at comparablelengths in living mammalian cochleae. The accuracy of the model predictions was reported in mean absolute error (MAE)relative to the experimental data. The results show that cascade filterbank models are remarkably more successful withCARFAC and VERHULST models reproducing the experimental data most closely. However, DRNL model (a parallelfilterbank) also produces outcomes that are comparable in accuracy with those generated by cascade filterbank models.Further investigations showed that this specific parallel filterbank model externally incorporated correct phase delays inthe impulse responses of its filter stages. The results indicate that, if parallel filterbanks incorporate the phase delays intheir impulse responses according to the proposed method, they could successfully simulate the timing of the longitudinalwave propagation along the cochlea within the same accuracy range as cascade filterbank models do.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2024
Keywords
auditory models; cochlea; cochlear amplifier; cochlear wave propagation
National Category
Other Medical Engineering
Research subject
Physiology
Identifiers
urn:nbn:se:umu:diva-222718 (URN)10.1063/5.0189538 (DOI)2-s2.0-85187563936 (Scopus ID)
Conference
14th Mechanics of Hearing conference, Helsingør, Denmark, July 24-29, 2022
Available from: 2024-03-26 Created: 2024-03-26 Last updated: 2024-03-27Bibliographically approved
Khodadad, D. (2023). Advancing road safety assessment with digital holography: a study on skid resistance of asphalt pavements. In: Thilo Erbertseder; Nektarios Chrysoulakis; Ying Zhang (Ed.), Proceedings of SPIE - The International Society for Optical Engineering: . Paper presented at SPIE remote sensing; Remote Sensing Technologies and Applications in Urban Environments VIII, Amsterdam, Netherlands, September 3-7, 2023. SPIE - The International Society for Optics and Photonics, Article ID 1273507.
Open this publication in new window or tab >>Advancing road safety assessment with digital holography: a study on skid resistance of asphalt pavements
2023 (English)In: Proceedings of SPIE - The International Society for Optical Engineering / [ed] Thilo Erbertseder; Nektarios Chrysoulakis; Ying Zhang, SPIE - The International Society for Optics and Photonics, 2023, article id 1273507Conference paper, Published paper (Refereed)
Abstract [en]

Enhancing road safety through improved skid resistance is a critical endeavor in preventing accidents and promoting secure driving conditions. This study delves into the investigation of skid resistance in asphalt pavements using digital holography, focusing on macro and microtexture attributes. By employing off-axis digital holography, the paper presents a novel method to accurately measure surface profiles and assess friction properties. The experimental setup leverages single-shot dual-wavelength holography, providing precise 3D topographic information. The study demonstrates how the obtained phase information aids in deriving surface profiles and subsequently determining friction coefficients. The approach overcomes limitations of conventional methods, offering micron-level accuracy for surface roughness measurements. Through experimental results, the versatility of adjusting measurement accuracy and range based on requirements is showcased. The paper concludes by highlighting the interplay between surface features and friction characteristics, paving the way for improved road safety assessment.

Place, publisher, year, edition, pages
SPIE - The International Society for Optics and Photonics, 2023
Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 12735
Keywords
asphalt, digital holography, friction coefficient, road safety assessment, Skid resistance, surface profiling
National Category
Applied Mechanics Infrastructure Engineering
Identifiers
urn:nbn:se:umu:diva-218674 (URN)10.1117/12.2688297 (DOI)2-s2.0-85180011664 (Scopus ID)9781510666993 (ISBN)
Conference
SPIE remote sensing; Remote Sensing Technologies and Applications in Urban Environments VIII, Amsterdam, Netherlands, September 3-7, 2023
Available from: 2023-12-27 Created: 2023-12-27 Last updated: 2023-12-27Bibliographically approved
Khodadad, D. (2023). Creating a supportive and effective learning environment for engineering students: Pedagogical strategies, engagement, and enhanced outcomes. International Journal of Engineering Pedagogy, 13(8), 33-50
Open this publication in new window or tab >>Creating a supportive and effective learning environment for engineering students: Pedagogical strategies, engagement, and enhanced outcomes
2023 (English)In: International Journal of Engineering Pedagogy, ISSN 2192-4880, Vol. 13, no 8, p. 33-50Article in journal (Refereed) Published
Abstract [en]

Engineering education requires a strong emphasis on problem-solving, critical thinking, and practical application of knowledge. To achieve the highest quality of teaching, educators must create a trusting environment that allows students to feel comfortable asking questions and performing to the best of their abilities. This paper outlines the teaching philosophy and prac-tices of an engineering lecturer who has adapted his pedagogical approach across several universities in Sweden and abroad. The author emphasizes the importance of being flexible and responsive to student needs, offering early and constructive feedback, and providing students a safe and supportive learning environment with opportunities to develop program-ming skills. The paper also includes comments from students that reflect the author’s effec-tiveness as an educator in creating a supportive and challenging learning environment for engineering students.

Place, publisher, year, edition, pages
International Association of Online Engineering, 2023
Keywords
supportive learning, engineering education, constructive feedback, problem solving, video solution, self-directed learning, flexibility, pedagogy, trusting environment
National Category
Mechanical Engineering Learning Pedagogy
Identifiers
urn:nbn:se:umu:diva-219762 (URN)10.3991/ijep.v13i8.41755 (DOI)001126694600002 ()2-s2.0-85183091699 (Scopus ID)
Available from: 2024-01-18 Created: 2024-01-18 Last updated: 2024-02-13Bibliographically approved
Khodadad, D. (2023). Digital holography for temperature investigations in space and transparent media. In: Proceedings of SPIE - The International Society for Optical Engineering: . Paper presented at SPIE Remote Sensing, Amsterdam, Netherlands, September 3-6, 2023. SPIE
Open this publication in new window or tab >>Digital holography for temperature investigations in space and transparent media
2023 (English)In: Proceedings of SPIE - The International Society for Optical Engineering, SPIE , 2023Conference paper, Published paper (Refereed)
Abstract [en]

The paper presents a method for investigating temperature fields in space and transparent media using off-axis digital holographic interferometry. This interferometric technique is particularly well-suited for measuring dynamically changing temperature fields due to its capability to automatically evaluate temperature from a single interferogram. The experimental validation of this technique involved measuring temperature variations within a burning candle's flame. To establish a reference point, an initial hologram was captured without a burning candle, followed by subsequent holograms during the burning process. This allowed the observation of changing refractive index gradient states in the surrounding air. The reconstruction of the complex amplitude facilitated the calculation of the distribution of phase changes. By establishing a relationship between phase changes, thermal coefficients of the air's refractive index, and temperature fluctuations, temperature measurements were achieved at these distinct states. The accuracy of the measurement was estimated to be less than 1 °C in our experimental setup, showing the high precision achievable with this technique. In summary, the paper offers analysis of digital holographic interferometry as a tool for temperature measurements in transparent media. Its potential applications extend to combustion studies, space exploration, atmospheric research, and various other scientific disciplines.

Place, publisher, year, edition, pages
SPIE, 2023
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:umu:diva-215979 (URN)10.1117/12.2688295 (DOI)2-s2.0-85180012543 (Scopus ID)
Conference
SPIE Remote Sensing, Amsterdam, Netherlands, September 3-6, 2023
Available from: 2023-10-30 Created: 2023-10-30 Last updated: 2023-12-28Bibliographically approved
Mohammadi, Y., Palstev, A., Polajžer, B., Miraftabzadeh, S. M. & Khodadad, D. (2023). Investigating Winter Temperatures in Sweden and Norway: Potential Relationships with Climatic Indices and Effects on Electrical Power and Energy Systems. Energies, 16(14), Article ID 5575.
Open this publication in new window or tab >>Investigating Winter Temperatures in Sweden and Norway: Potential Relationships with Climatic Indices and Effects on Electrical Power and Energy Systems
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2023 (English)In: Energies, E-ISSN 1996-1073, Vol. 16, no 14, article id 5575Article in journal (Refereed) Published
Abstract [en]

This paper presents a comprehensive study of winter temperatures in Norway and northern Sweden, covering a period of 50 to 70 years. The analysis utilizes Singular Spectrum Analysis (SSA) to investigate temperature trends at six selected locations. The results demonstrate an overall long-term rise in temperatures, which can be attributed to global warming. However, when investigating variations in highest, lowest, and average temperatures for December, January, and February, 50% of the cases exhibit a significant decrease in recent years, indicating colder winters, especially in December. The study also explores the variations in Atlantic Meridional Overturning Circulation (AMOC) variations as a crucial climate factor over the last 15 years, estimating a possible 20% decrease/slowdown within the first half of the 21st century. Subsequently, the study investigates potential similarities between winter AMOC and winter temperatures in the mid to high latitudes over the chosen locations. Additionally, the study examines another important climatic index, the North Atlantic Oscillation (NAO), and explores possible similarities between the winter NAO index and winter temperatures. The findings reveal a moderate observed lagged correlation for AMOC-smoothed temperatures, particularly in December, along the coastal areas of Norway. Conversely, a stronger lagged correlation is observed between the winter NAO index and temperatures in northwest Sweden and coastal areas of Norway. Thus, NAO may influence both AMOC and winter temperatures (NAO drives both AMOC and temperatures). Furthermore, the paper investigates the impact of colder winters, whether caused by AMOC, NAO, or other factors like winds or sea ice changes, on electrical power and energy systems, highlighting potential challenges such as reduced electricity generation, increased electricity consumption, and the vulnerability of power grids to winter storms. The study concludes by emphasizing the importance of enhancing the knowledge of electrical engineering researchers regarding important climate indices, AMOC and NAO, the possible associations between them and winter temperatures, and addressing the challenges posed by the likelihood of colder winters in power systems.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
Atlantic Meridional Overturning Circulation (AMOC), electrical power and energy systems, North Atlantic Oscillation (NAO), Singular Spectrum Analysis (SSA), weakening, winter temperatures
National Category
Climate Research
Identifiers
urn:nbn:se:umu:diva-212753 (URN)10.3390/en16145575 (DOI)001036043700001 ()2-s2.0-85166299968 (Scopus ID)
Funder
The Kempe Foundations, JCK22-0025
Available from: 2023-08-11 Created: 2023-08-11 Last updated: 2023-08-28Bibliographically approved
Moradi, M., Karamimoghadam, M., Meiabadi, S., Casalino, G., Ghaleeh, M., Baby, B., . . . Khodadad, D. (2023). Mathematical modelling of fused deposition modeling (FDM) 3D printing of poly vinyl alcohol parts through statistical design of experiments approach. Mathematics, 11(13), Article ID 3022.
Open this publication in new window or tab >>Mathematical modelling of fused deposition modeling (FDM) 3D printing of poly vinyl alcohol parts through statistical design of experiments approach
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2023 (English)In: Mathematics, E-ISSN 2227-7390, Vol. 11, no 13, article id 3022Article in journal (Refereed) Published
Abstract [en]

This paper explores the 3D printing of poly vinyl alcohol (PVA) using the fused deposition modeling (FDM) process by conducting statistical modeling and optimization. This study focuses on varying the infill percentage (10–50%) and patterns (Cubic, Gyroid, tri-hexagon and triangle, Grid) as input parameters for the response surface methodology (DOE) while measuring modulus, elongation at break, and weight as experimental responses. To determine the optimal parameters, a regression equation analysis was conducted to identify the most significant parameters. The results indicate that both input parameters significantly impact the output responses. The Design Expert software was utilized to create surface and residual plots, and the interaction between the two input parameters shows that increasing the infill percentage (IP) leads to printing heavier samples, while the patterns do not affect the weight of the parts due to close printing structures. On the contrary, the discrepancy between the predicted and actual responses for the optimal samples is below 15%. This level of error is deemed acceptable for the DOE experiments.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
3D printing, additive manufacturing, fused deposition modeling, infill percentage, optimization
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:umu:diva-212308 (URN)10.3390/math11133022 (DOI)2-s2.0-85164962701 (Scopus ID)
Available from: 2023-07-25 Created: 2023-07-25 Last updated: 2023-07-25Bibliographically approved
Khodadad, D., Tayebi, B., Saremi, A. & Paul, S. (2023). Temperature Sensing in Space and Transparent Media: Advancements in Off-Axis Digital Holography and the Temperature Coefficient of Refractive Index. Applied Sciences, 13(14), Article ID 8423.
Open this publication in new window or tab >>Temperature Sensing in Space and Transparent Media: Advancements in Off-Axis Digital Holography and the Temperature Coefficient of Refractive Index
2023 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 13, no 14, article id 8423Article in journal (Refereed) Published
Abstract [en]

An off-axis digital holographic interferometry technique integrated with a Mach–Zehnder interferometer based setup is demonstrated for measuring the temperature and temperature profile of a transparent medium. This technique offers several advantages: it does not require precise optomechanical adjustments or accurate definition of the frequency carrier mask, making it simple and cost-effective. Additionally, high-quality optics are not necessary. The methodology relies on measuring the phase difference between two digitally reconstructed complex wave fields and utilizing the temperature coefficient of the refractive index. In this way, we presented an equation of the temperature as a function of phase changes and the temperature coefficient of refractive index. This approach simplifies the calculation process and avoids the burden of complicated mathematical inversions, such as the inverse Abel transformation. It also eliminates the need for additional work with the Lorentz–Lorentz equation and Gladstone–Dale relation and can be extend for 3D measurements.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
digital holography, flame, measurement, space, temperature, temperature coefficient of refractive index, transparent media
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-212751 (URN)10.3390/app13148423 (DOI)001034894000001 ()2-s2.0-85166182725 (Scopus ID)
Available from: 2023-08-11 Created: 2023-08-11 Last updated: 2023-08-11Bibliographically approved
Paul, S., Turnbull, R., Khodadad, D. & Löfstrand, M. (2022). A Vibration Based Automatic Fault Detection Scheme for Drilling Process Using Type-2 Fuzzy Logic. Algorithms, 15(8), Article ID 284.
Open this publication in new window or tab >>A Vibration Based Automatic Fault Detection Scheme for Drilling Process Using Type-2 Fuzzy Logic
2022 (English)In: Algorithms, E-ISSN 1999-4893, Vol. 15, no 8, article id 284Article in journal (Refereed) Published
Abstract [en]

The fault detection system using automated concepts is a crucial aspect of the industrial process. The automated system can contribute efficiently in minimizing equipment downtime therefore improving the production process cost. This paper highlights a novel model based fault detection (FD) approach combined with an interval type-2 (IT2) Takagi–Sugeno (T–S) fuzzy system for fault detection in the drilling process. The system uncertainty is considered prevailing during the process, and type-2 fuzzy methodology is utilized to deal with these uncertainties in an effective way. Two theorems are developed; Theorem 1, which proves the stability of the fuzzy modeling, and Theorem 2, which establishes the fault detector algorithm stability. A Lyapunov stabilty analysis is implemented for validating the stability criterion for Theorem 1 and Theorem 2. In order to validate the effective implementation of the complex theoretical approach, a numerical analysis is carried out at the end. The proposed methodology can be implemented in real time to detect faults in the drilling tool maintaining the stability of the proposed fault detection estimator. This is critical for increasing the productivity and quality of the machining process, and it also helps improve the surface finish of the work piece satisfying the customer needs and expectations.

Place, publisher, year, edition, pages
MDPI, 2022
Keywords
fault detection, fuzzy logic, stability analysis, drilling operation, predictive maintenance
National Category
Control Engineering
Identifiers
urn:nbn:se:umu:diva-198686 (URN)10.3390/a15080284 (DOI)000846411300001 ()2-s2.0-85137265416 (Scopus ID)
Projects
A digital twin to support sustainable and available production as a service
Funder
Vinnova
Available from: 2022-08-18 Created: 2022-08-18 Last updated: 2023-03-29Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2960-3094

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