Sepideh Harajchi
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5 records found
1
Interpretation of Ground-penetrating radar (GPR) data in railway environments is complicated by strong scattering generated by the heterogeneous ballast layer, which obscures reflections from sleepers, reinforcement, and deeper interfaces. To quantify the individual electromagnetic contributions of these components, this study applies a controlled finite-difference time-domain (FDTD) modelling framework incorporating realistic ballast-stone geometry. Three configurations—a ballast-sand baseline, a concrete sleeper, and a reinforced concrete sleeper—were simulated at 1 GHz and 400 MHz. Time-windowed RMS energy and Hilbert-envelope attributes were extracted from A-scans, and differential B-scan imaging was used to isolate incremental scattering effects.
The concrete sleeper produces only a weak dielectric response, detectable mainly at 1 GHz, whereas the reinforced sleeper generates a strong, coherent early-time reflection at both frequencies. Attribute trends show a symmetric central amplitude enhancement associated with the reinforcement, and differential B-scans clearly separate the sleeper and rebar signatures despite realistic ballast scattering. These results demonstrate that combining attribute-based analysis with differential imaging can provide a robust means of disentangling overlapping GPR responses and improving the interpretability of data. The ability to distinguish the signature of each structural element has potential for developing focused suppression or filtering approaches that facilitate deeper-layer and embankment monitoring. ...
The concrete sleeper produces only a weak dielectric response, detectable mainly at 1 GHz, whereas the reinforced sleeper generates a strong, coherent early-time reflection at both frequencies. Attribute trends show a symmetric central amplitude enhancement associated with the reinforcement, and differential B-scans clearly separate the sleeper and rebar signatures despite realistic ballast scattering. These results demonstrate that combining attribute-based analysis with differential imaging can provide a robust means of disentangling overlapping GPR responses and improving the interpretability of data. The ability to distinguish the signature of each structural element has potential for developing focused suppression or filtering approaches that facilitate deeper-layer and embankment monitoring. ...
Interpretation of Ground-penetrating radar (GPR) data in railway environments is complicated by strong scattering generated by the heterogeneous ballast layer, which obscures reflections from sleepers, reinforcement, and deeper interfaces. To quantify the individual electromagnetic contributions of these components, this study applies a controlled finite-difference time-domain (FDTD) modelling framework incorporating realistic ballast-stone geometry. Three configurations—a ballast-sand baseline, a concrete sleeper, and a reinforced concrete sleeper—were simulated at 1 GHz and 400 MHz. Time-windowed RMS energy and Hilbert-envelope attributes were extracted from A-scans, and differential B-scan imaging was used to isolate incremental scattering effects.
The concrete sleeper produces only a weak dielectric response, detectable mainly at 1 GHz, whereas the reinforced sleeper generates a strong, coherent early-time reflection at both frequencies. Attribute trends show a symmetric central amplitude enhancement associated with the reinforcement, and differential B-scans clearly separate the sleeper and rebar signatures despite realistic ballast scattering. These results demonstrate that combining attribute-based analysis with differential imaging can provide a robust means of disentangling overlapping GPR responses and improving the interpretability of data. The ability to distinguish the signature of each structural element has potential for developing focused suppression or filtering approaches that facilitate deeper-layer and embankment monitoring.
The concrete sleeper produces only a weak dielectric response, detectable mainly at 1 GHz, whereas the reinforced sleeper generates a strong, coherent early-time reflection at both frequencies. Attribute trends show a symmetric central amplitude enhancement associated with the reinforcement, and differential B-scans clearly separate the sleeper and rebar signatures despite realistic ballast scattering. These results demonstrate that combining attribute-based analysis with differential imaging can provide a robust means of disentangling overlapping GPR responses and improving the interpretability of data. The ability to distinguish the signature of each structural element has potential for developing focused suppression or filtering approaches that facilitate deeper-layer and embankment monitoring.
Railway ballast is essential for maintaining track stability, ensuring proper drainage, and efficiently distributing loads across the track bed. Regular monitoring of ballast conditions is crucial for the safety and durability of railway infrastructure. Ground Penetrating Radar is commonly employed to assess ballast conditions; however, its signals can be significantly affected by structural elements such as sleepers, which may distort signal propagation due to their material properties. Specifically, reinforced concrete sleepers with embedded metal reinforcement contribute to additional attenuation and scattering, complicating signal interpretation. Numerical simulations using the Finite-Difference Time-Domain method were conducted to model wave propagation in three configurations: no sleeper, pure concrete sleeper, and reinforced concrete sleeper. Simulations at 1 GHz and 400 MHz frequencies reveal that reinforced concrete sleepers significantly enhance signal reflections and introduce complex scattering, particularly at higher frequencies. These results exhibit frequency-dependent behavior, where higher frequencies provide better resolution but also more signal distortion caused by the sleeper material. The study offers valuable insights into optimizing GPR signal interpretation in railway ballast inspections and emphasizes the importance of considering sleeper type and frequency selection in data acquisition and processing.
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Railway ballast is essential for maintaining track stability, ensuring proper drainage, and efficiently distributing loads across the track bed. Regular monitoring of ballast conditions is crucial for the safety and durability of railway infrastructure. Ground Penetrating Radar is commonly employed to assess ballast conditions; however, its signals can be significantly affected by structural elements such as sleepers, which may distort signal propagation due to their material properties. Specifically, reinforced concrete sleepers with embedded metal reinforcement contribute to additional attenuation and scattering, complicating signal interpretation. Numerical simulations using the Finite-Difference Time-Domain method were conducted to model wave propagation in three configurations: no sleeper, pure concrete sleeper, and reinforced concrete sleeper. Simulations at 1 GHz and 400 MHz frequencies reveal that reinforced concrete sleepers significantly enhance signal reflections and introduce complex scattering, particularly at higher frequencies. These results exhibit frequency-dependent behavior, where higher frequencies provide better resolution but also more signal distortion caused by the sleeper material. The study offers valuable insights into optimizing GPR signal interpretation in railway ballast inspections and emphasizes the importance of considering sleeper type and frequency selection in data acquisition and processing.
Accurate monitoring of railway ballast and embankments is critical for ensuring stability and safety in railway operations. Ground Penetrating Radar has emerged as a powerful non-destructive tool for characterizing ballast and underlying layers, particularly in estimating layer thickness. The ballast layer is modeled as a heterogeneous layer with pieces of rock and as a homogenized layer represented by a single relative permittivity value using the complex refractive index model. Numerical simulations were performed to evaluate the effects of ballast heterogeneity, layer composition, and thickness on expected reflection data. The results indicate that while homogeneous models are computationally efficient, they fail to capture the intrinsic scattering and attenuation effects of realistic ballast geometries, particularly under variable substructure configurations. The results suggest that laboratory measurements can be performed to understand the quality of the current state of the numerical models.
...
Accurate monitoring of railway ballast and embankments is critical for ensuring stability and safety in railway operations. Ground Penetrating Radar has emerged as a powerful non-destructive tool for characterizing ballast and underlying layers, particularly in estimating layer thickness. The ballast layer is modeled as a heterogeneous layer with pieces of rock and as a homogenized layer represented by a single relative permittivity value using the complex refractive index model. Numerical simulations were performed to evaluate the effects of ballast heterogeneity, layer composition, and thickness on expected reflection data. The results indicate that while homogeneous models are computationally efficient, they fail to capture the intrinsic scattering and attenuation effects of realistic ballast geometries, particularly under variable substructure configurations. The results suggest that laboratory measurements can be performed to understand the quality of the current state of the numerical models.
Seismic interferometry (SI) retrieves seismic responses by, for example, cross-correlating observations at different receiver locations, offering a new data for subsurface imaging. Monitoring soil conditions along railway embankments is essential for ensuring the stability and safety of rail infrastructure. This study explores the use of active and passive seismic sources, combined with SI technique, to enhance subsurface imaging.Active seismic sources produce high-resolution reflections and surface-wave data, critical for identifying and monitoring key soil properties. These controlled sources provide superior signal-to-noise ratios and establish a reliable baseline for subsurface imaging. Passive seismic sources, such as train-induced vibrations, complement active-source data by providing continuous and natural excitation of the subsurface. Both active and passive sources are processed using SI technique, with adaptive subtraction applied to suppress dominant surface waves and improve imaging clarity.The integration of active- and passive-source data might help achieve better interpretation of the subsurface and monitoring for possible changes. Although this study is still under development, it demonstrates the potential to deliver a scalable, non-invasive solution for monitoring railway embankments and surrounding soils. By advancing our understanding of subsurface conditions, this approach could contribute substantially to the predictive maintenance and safety of rail infrastructure, paving the way for future innovations in geophysical monitoring.
...
Seismic interferometry (SI) retrieves seismic responses by, for example, cross-correlating observations at different receiver locations, offering a new data for subsurface imaging. Monitoring soil conditions along railway embankments is essential for ensuring the stability and safety of rail infrastructure. This study explores the use of active and passive seismic sources, combined with SI technique, to enhance subsurface imaging.Active seismic sources produce high-resolution reflections and surface-wave data, critical for identifying and monitoring key soil properties. These controlled sources provide superior signal-to-noise ratios and establish a reliable baseline for subsurface imaging. Passive seismic sources, such as train-induced vibrations, complement active-source data by providing continuous and natural excitation of the subsurface. Both active and passive sources are processed using SI technique, with adaptive subtraction applied to suppress dominant surface waves and improve imaging clarity.The integration of active- and passive-source data might help achieve better interpretation of the subsurface and monitoring for possible changes. Although this study is still under development, it demonstrates the potential to deliver a scalable, non-invasive solution for monitoring railway embankments and surrounding soils. By advancing our understanding of subsurface conditions, this approach could contribute substantially to the predictive maintenance and safety of rail infrastructure, paving the way for future innovations in geophysical monitoring.
Journal article
(2023)
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jamal Abbasi Bolaghi, S. Harajchi, Asghar Taheri, Mohammad Hosein Babaei, Masoumeh Gholami
In this research, a new Z-source inverter inspired by the quasi-inductor-switched Z-source inverter is presented. The new inverter has an acceptable boost factor, and gain voltage compared to the similar Z-source inverter. Also, in this new topology, the capacitors’ voltage stress has been decreased compared to similar inverters. In this converter, a capacitor is replaced with the side diodes of the quasi-Z-source inverter. The input current in this inverter is continuous and it is a low figure that at the moment of switching off about 54 A (V
in = 120 V). The high inrush current damages the converter components. The operation of this inverter has been checked in different modes and the voltage and current equations of all elements have been calculated. The new converter can be extended to n-cascade, and it makes to achieve a higher boost factor with a low-duty cycle. The ingredients used in the new topology are fewer than those of the switched-inductor Z-source inverter. The analysis and extraction of all voltage stress such as capacitors, diodes, switches, all currents such as inductors, dc-link average, inrush current, voltage gain and boost factor of the new topology have been done and compared with other structures. The DC-link voltage (V
i) is 148 V with an input voltage of 120, so the boost factor is 1.43.
...
In this research, a new Z-source inverter inspired by the quasi-inductor-switched Z-source inverter is presented. The new inverter has an acceptable boost factor, and gain voltage compared to the similar Z-source inverter. Also, in this new topology, the capacitors’ voltage stress has been decreased compared to similar inverters. In this converter, a capacitor is replaced with the side diodes of the quasi-Z-source inverter. The input current in this inverter is continuous and it is a low figure that at the moment of switching off about 54 A (V in = 120 V). The high inrush current damages the converter components. The operation of this inverter has been checked in different modes and the voltage and current equations of all elements have been calculated. The new converter can be extended to n-cascade, and it makes to achieve a higher boost factor with a low-duty cycle. The ingredients used in the new topology are fewer than those of the switched-inductor Z-source inverter. The analysis and extraction of all voltage stress such as capacitors, diodes, switches, all currents such as inductors, dc-link average, inrush current, voltage gain and boost factor of the new topology have been done and compared with other structures. The DC-link voltage (V i) is 148 V with an input voltage of 120, so the boost factor is 1.43.