Attenuation Law Research Articles

The IRX–β relation in kpc-sized star-forming regions in nearby galaxies

ABSTRACT The effect of dust attenuation on a galaxy’s light depends on a number of physical properties, such as geometry and dust composition, both of which can vary across the faces of galaxies. To investigate this variation, we continue analysis on star-forming regions in 29 galaxies studied previously. We analyse these regions using Swift/UV Optical Telescope and Wide-field Infrared Survey Explorer images, as well as Sloan Digital Sky Survey/Mapping Nearby Galaxies at Apache Point Observatory emission line maps to constrain the relationship between the infrared excess (IRX) and the ultraviolet spectral index, β, for each star-forming region. This relationship can be used to constrain which dust attenuation law is appropriate for the region. We find that the value of Dn(4000) for a region is correlated with both IRX and β, and that the gas-phase metallicity is strongly correlated with the IRX. This correlation between metallicity and IRX suggests that regardless of aperture, metal-rich regions have steeper attenuation curves. We also find that integrated galactic light follows nearly the same IRX–β relationship as that found for kpc-sized star-forming regions. This similarity may suggest that the attenuation law followed by the galaxy is essentially the same as that followed by the regions, although the relatively large size of our star-forming regions complicates this interpretation because optical opacity and attenuation curves have been observed to vary within individual galaxies.

Skid-resistance durability and wear/polish-resistance behaviors of ultra-thin friction course designed based on the differential polishing of aggregates

To improve the skid-resistance durability of asphalt pavements in a cost-effective manner, this study introduced a differential-polishing principle based on blending various aggregates. SMA-5 ultra-thin friction courses (UTFC) were prepared using mineral aggregates consisting of 88# calcined bauxite and limestone blended in six proportions. Long-term simulated traffic polishing tests were performed on six types of UTFC surfaces in the laboratory. Direct skid-resistance indexes, BPN20 and μ80, were used to evaluate skid resistance at low and high velocities after different polishing cycles, respectively. Surface texture evolution during long-term polishing was analyzed using bearing area ratio, mean profile depth, and fractal dimension D. Additionally, an attenuation prediction model for skid resistance was developed. Aggregate mechanical properties affecting skid-resistance durability of UTFC were investigated through grey correlation analysis. The results show that a significant differential-polishing effect was generated during long-term polishing due to large differences in the two aggregates’ wear/polish resistance, which can effectively reduce the attenuation rate of skid resistance of UTFC and improve skid-resistance durability by decreasing wear loss of UTFC surface aggregate and forming texture structure difference between aggregates to maintain rough surface texture. The reasonable blending proportion of 88# calcined bauxite was determined to be 40%–60% of the mineral aggregate mass. It was also found that the developed predictive model can reflect the attenuation law of skid resistance, and PSV and LAA loss of aggregates are well correlated with the skid-resistance durability of UTFC.

Study on fatigue damage evolution and model prediction of asphalt pavement in the end-stage of service

Through the use of the material test system (MTS), bending fatigue tests are conducted in this work in order to investigate the attenuation law of fatigue performance of asphalt pavement in the end-stage of service. Response surface methodology (RSM) is used to analyze the effects of strain, frequency, and temperature on the asphalt surface layer's initial stiffness, fatigue life, phase angle, and cumulative dissipated energy when there is a 50 % reduction in the initial stiffness. Through multi-factor coupling analysis, the optimal combination is found and verified by the MTS-810 test system. Based on this, the data of the initial stiffness declining to 20 % was used for analysis on the AC-13C asphalt surface mixture of the APT full-size test road in the laboratory. At 15 °C and 10 Hz, the evolution law of the flexural stiffness, the residual stiffness, phase angle, and cumulative dissipated energy of the asphalt mixture was investigated. Analysis of the asphalt mixture's damage evolution under the single stage of loading and various strain levels revealed changes in the fatigue cracking crack. Beam specimens were made from asphalt mixture field test beams of AC-13C (laboratory accelerated pavement test road), AC-20C, and AC-25C (Ji-Qing expressway) to conduct four-point bending fatigue test (4PB). According to the constant strain fatigue prediction equation, and the residual fatigue life of prediction localized model was established. The results show that the influence of frequency and temperature on the initial stiffness and phase angle is more significant than strain, and the influence of strain on number of fatigue is more significant. The flexural stiffness of the asphalt mixture shows an obvious S-curve, and larger the tensile strain at the bottom of the asphalt layer, shorter the time needed to reach the termination condition, that is, the faster the fatigue failure occurs. When the damage termination condition is reached, under the strain level of 200–300 με, 60 % of the number of loading produce about 35–40 % damage, and the remaining 20 % of the number of loading lead to 10–20 % damage.

Measuring the Dust Attenuation Curves of SINGS/KINGFISH Galaxies Using Swift/UVOT Photometry

We present Swift/Ultraviolet Optical Telescope (UVOT) integrated light photometry of the Spitzer Infrared Nearby Galaxies Survey (SINGS) and the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH) samples of nearby galaxies. Combining the Swift/UVOT data with archival photometry, we investigate a variety of dust attenuation curves derived using MCSED, a flexible spectral energy distribution (SED) fitting code. We fit the panchromatic data using three different star formation history (SFH) parameterizations: a decaying exponential, a double power law, and a piecewise function with breaks at physically motivated ages. We find that the average attenuation law of the sample changes slightly based on the SFH assumed. Specifically, the exponential SFH leads to the shallowest attenuation curves. Using simulated data, we also find the exponential SFH fails to outperform the more complex SFHs. Finally, we find a systematic offset in the derived bump strength between SED fits with and without UVOT data, where the inclusion of UVOT data leads to smaller bump strengths, highlighting the importance of the UVOT data. This discrepancy is not seen in fits to mock photometry. Understanding dust attenuation in the local universe is key to understanding high-redshift objects where rest-frame far-infrared data are unavailable.

An isoparametric element permutation method for railway tunnel–soil interaction modeling in train–track–tunnel–soil dynamic analysis

For evaluating the ground vibration involving metro tunnel operation, it is of necessity to extend the train-track-tunnel near-filed vibration to the train-track-tunnel-soil far-filed vibration in viewpoint of numerical analysis. It therefore becomes a key technology to achieve the tunnel-soil coupling simulation. In this work, a isoparametric element permutation method is proposed, where the 6-node triangular prismatic elements and 8-node spatial isoperimetric elements have been effectively integrated to achieve the finite elemental modelling of the soil system with the tunnel penetrating. The tunnel and soil subsystems are coupled by the spring-dashpot elements. Once the tunnel satisfies symmetrical property in geometry, the proposed method can be applied to build the tunnel-soil interaction by parametric finite element modelling. Through a combination of this proposed tunnel-soil interaction model and the train-track-tunnel dynamic model, a unified model for characterizing the train–track–tunnel–soil dynamic interaction analysis is constructed within the finite element framework. By comparing the simulation results to the measurements in site, the effectiveness of this model is validated, through which track, tunnel, and ground vibrations can be assessed in an entirely coupled way. Through the numerical studies, it is known that both the number of tunnel lines and the number of trains in operation and their running modes hold significant influence and show different vibration attenuation law on ground vibrations, and quantitative analysis can be achieved through this present work.

Impact of high-speed rail operation on urban economic resilience: Evidence from local and spillover perspectives in China

Based on the panel data of 280 prefecture-level cities in China from 2004 to 2019, this paper provides an empirical investigation of the mechanism and the impact of high-speed rails (HSRs) on urban economic resilience. The economic resilience evaluation has been constructed from three levels: risk resistance ability, organization and adjustment ability, as well as renewal and development ability. The difference-in-differences (DID) model and spatial difference-in-differences (SDID) model are adopted to analyze the impact of the HSR service intensity on the urban economic resilience. Results imply that the HSR has significantly improved the urban economic resilience along the lines. Further analysis shows that HSR mainly increases the economic resilience through potential effect of human resources, dynamic effect of new economic sectors and vitality effect of innovation output. From a spatial spillover perspective, HSR not only improves the local economic resilience, but also improves that of neighboring cities. The spatial spillover effect of HSR conforms to the law of geographic distance attenuation with spillover coefficient changes. Moreover, the study documents a series of heterogeneity analysis concerning HSR effects across Chinese cities. Particularly, HSRs promote the development of talents, new economic sectors, as well as innovation output, and help resource-based cities unlock their over-reliance on resource industries, thereby improving their economic resilience. This paper introduces the concept of urban economic resilience into the analysis framework of HSR effect, and measures the geographical boundary and effective scope of the HSR's spillover effect. It provides a new lens for the sustainable development of transportation-regional social economy.

Numerical investigation of seismic wavefield characteristics induced by a tensile source in a heterogeneous mining environment

Mining-induced tremors serve as the main dynamic stress source of coal bursts which represent one type of the most critical mining disasters in underground coal mines. To evaluate coal burst risks and comprehend the response of the coal-rock mass to seismic waves, microseismic monitoring stands as the principal method. By inferring the zones with elevated coal burst risks based on the seismic event clusters, valuable insights can be gained. However, because of limited seismic monitoring results generated from an individual seismic event, the recognition of the corresponding dynamic disturbance process remains ambiguous. The dynamic disturbance process presents immense complexity due to the focal mechanism and heterogeneous medium, particularly under the effect of structural heterogeneity induced by large-scale mining operations. In this study, forward numerical modelling was employed to gain the comprehension of seismic wave propagation affected by extraction zones. The findings revealed heightened intricacy of the wavefields and increased displacement concentrations around the working face. The characteristics of peak particle velocity (PPV) and displacement spectra were investigated in the near- and far-field zones, respectively. Owing to the existence of the extraction zone, both a significant amplification effect and the redistribution of PPV were observed around the near-field zone. The intricate wavefield caused by the focal mechanism and extraction zones resulted in more scattered distributions of the low-frequency spectral level, which can potentially cause an overestimation of source intensity. However, the impact of the complex wavefield on the corner frequency was limited. Through the analysis of the PPV attenuation law, as well as the distribution of both seismic moment and source radius, this study offered valuable insights for seismic risk assessment. The forward modelling approach facilitated the identification of high-risk potential areas resulting from seismic events, which deepened our comprehension of the dynamic disturbance process in the complex underground mine environment.

The attenuation of macroseismic intensity in the volcanic island of Ischia (Gulf of Naples, Italy): comparison between deterministic and probabilistic models and application to seismic scenarios

In this paper, we tackle the problem of the intensity attenuation at Ischia, a critical parameter in a high seismic risk area such as this volcanic island. Starting from the new revised catalogue of local earthquakes, we select a dataset of 118 macroseismic observations related to the four main historical events and analyse the characteristics of the intensity attenuation according to both the deterministic and probabilistic approaches, under the assumption of a point seismic source and isotropic decay (circular spreading). In the deterministic analysis, we derive the attenuation law through an empirical model fitting the average values of ΔI (the difference between epicentral intensity I0 and intensities observed at a site IS) versus the epicentral distances by the least-square method. In the probabilistic approach, the distribution of IS conditioned on the epicentre-site distance is given through a binomial-beta model for each class of I0. In the Bayesian framework, the model parameter p is considered as a random variable to which we assign a Beta probability distribution on the basis of our prior belief derived from investigations on the attenuation in Italy. The mode of the binomial distribution is taken as the intensity expected at that site (Iexp). The entire calculation procedure has been implemented in a python plugin for QGIS® software that, given location and I0 (or magnitude) of the earthquake to be simulated, generates a probabilistic seismic scenario according to the deterministic or probabilistic models of attenuation. This tool may be applied in seismic risk analyses at a local scale or in the seismic surveillance to produce real-time intensity shake-maps for this volcanic area.

Experimental and modelling investigation on chloride transport and flexural behaviour of RC beams subjected to simultaneous deteriorating factors of carbonation, FT cycles and multi-type sustained stress

Reinforced concrete (RC) structures are often exposed to coinstantaneous deterioration effects such as carbonation, chloride corrosion, freeze–thaw cycles and external loads which causing deterioration of concrete and reinforcement. This paper discussed the effects of carbonation, freeze–thaw cycles and sustained loads on chloride ion transport and proposed a chloride ion transport model taking porosity as the main coupling variate. The attenuation law of the corroded beams under coupling corrosion factors was studied. Through chloride immersion tests, it was found that applying freezing and thawing cycles and sustained tensile stress can enhance chloride transport capacity by coarsening the pores; Carbonation and low compressive stress can repress the chloride ion transport by densifying concrete, but the compressive stress beyond about 0.7 times the compressive strength and tensile stress would enhance the penetrating capacity due to the damage of the internal microstructure of concrete. Then, a comprehensive and unified theoretical model of chloride ion transport considering the coupling of carbonation, freeze–thaw cycle, sustained loading and other factors was proposed and verified by taking porosity as the main coupling variable quantity. This model could essentially explain the effects of various factors on chloride ion transport and has good consistency with the test results. Finally, the flexural bearing capacity of the corroded beams was tested, and the failure characteristics, crack characteristics, ultimate bearing capacity, load–displacement relationship and strain distribution of the corroded beams under different corrosion conditions were researched. The results show that the flexural capacity of the corroded beams suffered the coupling effects of multiple corrosion factors degrades, and the bearing capacity decreases with the increase of the corrosion degree of carbonation-freezing thawing cycles; The continuous tensile stress applied to the test beams in the corrosion process intensifying the degradation of bending bearing capacity and ductility, the continuous compressive stress increases the flexural capacity and improves the ductility slightly, but excessive compressive stress significantly degrades the flexural capacity; When chloride ions are used as the third kind of corrosive substance for coupling corrosion, the tensioned or without-load corroded beams have obvious degradation in bending bearing capacity, while the corrosion beams bearing continuous compressive stress have no obvious degradation in bending bearing capacity.

Experimental and numerical study on ground shock propagation in calcareous sand

Surface explosion tests were conducted on calcareous sands to study the ground shock propagation in this medium. In the tests, ground shock at scaled distances between 0.33 m/kg1/3 and 1.46 m/kg1/3 was measured. After each explosion, the surface craters were observed and measured. The propagation and attenuation law of the peak pressure was derived according to the experimental measurement. The shock wave velocity and rise time were derived based on the pressure time-history curves. The empirical formula for pressure time-history curve of direct ground shock in calcareous sand induced by surface explosion was derived, and the predicted impulses showed good agreement with the experimental impulses. The indirect ground shock induced by air shock compression effect on the soil was discussed. Based on the field blast test results, validated numerical models were established to investigate the propagation of direct and indirect ground shock in calcareous sand. The attenuation law of peak pressure of indirect ground shock was then derived according to the numerical simulation results. Besides the surface explosion scenario, the contained burst cases were also modelled. The critical scaled depth of burial was derived as 1.3 m/kg1/3 in calcareous sand based on the surface crater and shock impulse.

The influence of the number of free surfaces on the energy distribution and attenuation law of blasting vibration signals from peripheral holes: field experiment and simulation

Tunnels are commonly excavated using drilling and blasting methods, and the surrounding rock is greatly affected by the vibration of surrounding hole blasting. To study the influence of the number of free surfaces on the energy distribution and attenuation law of surrounding hole blasting vibration signals, on-site experiments and numerical simulation experiments were conducted. The research results indicate that the higher the number of free surfaces, the smaller the peak vibration velocity. The longitudinal Fourier main frequency decreases with the distance from the monitoring point. The more free surface, the greater the centroid frequency and zero crossing frequency. In addition, numerical simulation shows that the degree of rock fragmentation after blasting increases with the increase of the number of free surface of rock.

Study on propagation mechanism and attenuation law of acoustic emission waves for damage of prestressed steel strands

The study of acoustic emission waves propagation mechanism and attenuation laws for damage of prestressed steel strands is the theoretical basis for acoustic emission health monitoring of prestressed steel strands such as stay cables, slings, suspenders, and concrete structures. Firstly, the propagation mechanism of acoustic emission waves in prestressed steel strands is studied using numerical simulation methods. Secondly, the amplitude and energy attenuation laws of acoustic emission waves caused by damage of prestressed steel strands are analyzed by experimental research, and the amplitude and energy attenuation models of the influence of prestress level are constructed. Finally, the constructed acoustic emission attenuation models are analyzed in combination with practical engineering. The results show that numerical simulation visualizes the propagation path of acoustic emission waves in prestressed steel strands; With the increase of prestress levels, the acoustic emission frequency distribution of prestressed steel strands damage ranges from 100 to 200 kHz, with a dominant frequency of 160 kHz, the acoustic emission amplitude and energy attenuation coefficients decrease, and the amplitude attenuation is slower than the energy attenuation; The acoustic emission amplitude attenuation of prestressed steel strands damage in prestressed hollow slab beams is 5 times faster than that of steel strands without surrounding media.

The ionizing photon production efficiency at z ∼ 6 for Lyman-alpha emitters using JEMS and MUSE

ABSTRACT We study the ionizing photon production efficiency at the end of the Epoch of Reionization (z ∼ 5.4 − 6.6) for a sample of 30 Ly α emitters. This is a crucial quantity to infer the ionizing photon budget of the universe. These objects were selected to have reliable spectroscopic redshifts, assigned based on the profile of their Ly α emission line, detected in the MUSE deep fields. We exploit medium-band observations from the JWST Extragalactic Medium-band Survey (JEMS) to find the flux excess corresponding to the redshifted Hα emission line. We estimate the ultraviolet (UV) luminosity by fitting the full JEMS photometry, along with several HST photometric points, with Prospector. We find a median UV continuum slope of $\beta = -2.09^{+0.23}_{-0.21}$, indicating young stellar populations with little-to-no dust attenuation. Supported by this, we derive ξion,0 with no dust attenuation and find a median value of log$\frac{\xi _{ion,0}}{\text{Hz erg}^{-1}} = 25.44^{+0.21}_{-0.15}$. If we perform dust attenuation corrections and assume a Calzetti attenuation law, our values are lowered by ∼0.1 dex. Our results suggest Ly α emitters at the Epoch of Reionization have slightly enhanced ξion,0 compared to previous estimations from literature, in particular, when compared to the non-Ly α emitting population. This initial study provides a promising outlook on the characterization of ionizing photon production in the early universe. In the future, a more extensive study will be performed on the entire data set provided by the JWST Advanced Deep Extragalactic Survey (JADES). Thus, for the first time, allowing us to place constraints on the wider galaxy populations driving reionization.

Experimental and mesoscale analysis on wave propagation induced by impact in dry silica sand

When investigating the propagation of stress waves in sand-like materials, the materials are generally modeled as homogeneous parts despite their complex structures comprising numerous particles of varying sizes and shapes. However, this approach fails to consider the non-continuum nature of sand-like materials. To address this issue, a mesoscale numerical model of silica sand particles with random shapes and three sizes is employed in this study to numerically analyze wave propagation. Experimental data from an upgraded split Hopkinson pressure bar test are utilized to validate the accuracy of the numerical model. Using the validated numerical model, we investigate the impact of relative densities, incident wavelengths, and wave amplitudes on stress wave attenuation in dry silica sand. Empirical equations are derived from summarizing the stress wave attenuation law induced by impact loading. The study shows that relative density and wavelength are critical factors affecting the residual peak stress ratio in silica sand, while the effect of loading wave amplitude is limited.

Numerical study of detonation propagation under the action of supersonic pulsating flow in expanding combustor

In this study, the effect of a velocity-pulsating stoichiometric hydrogen-oxygen mixture entering an expanding combustion chamber on the detonation wave is investigated. The hybrid sixth-order weighted essentially non-oscillatory centered difference scheme was used to solve the Navier–Stokes equations with a one-step two species chemistry model. The results verify that the induction zone is extended under the influence of pulsating flow. The discontinuous structure is formed in the flow field. A lot of unburned jets between the wavefront and the reaction zone were generated, which resulted in insufficient energy release. Coupled with the weakening of the wave strength by the Prandtl–Meyer (P-M) expansion fan, the detonation wave show different degrees of attenuation. The decay of the detonation wave shows different patterns at different amplitudes and periods. When the velocity amplitude is 0.3VCJ, the decay rate of detonation wave increases with the increase of the disturbance period. This attenuation law is different from the amplitude of 0.1VCJ and 0.2VCJ. This is because the discontinuous structure area formed by high-amplitude disturbance is large. Therefore, the longer its existence time is, the more serious the detonation wave attenuation is.

Mapping function model representing the relationship between explosion shock wave pressure and wavefront temperature

The evaluation of ammunition damage power and guidance for ammunition design heavily relies on the shock wave pressure and wavefront temperature produced by an ammunition explosion. However, temperature test results are often inaccurate and unreliable. Therefore, this study utilized Autodyn explicit dynamics simulation software to conduct finite element numerical simulations of explosion shock wave pressure, wavefront temperature propagation, and distribution for trinitrotoluene explosives weighing 10, 20, 50, and 100 kg. The shock wave pressure and wavefront temperature were measured at different measuring points. The cloud maps of wavefront propagation evolution obtained at different explosion times were analyzed to determine the attenuation laws of pressure and temperature propagation in the near field and far field. Based on the similarity law of explosions and the dimensional analysis method, a mapping function model was established to represent the relationship between a shock wave’s peak pressure and peak temperature. The parameters of the model include explosive mass (w), measuring point radius (r), specific heat capacity in the air (c), and the peak pressure of an explosion shock wave (p). The model’s accuracy in calculating the explosion shock wavefront temperature exceeds 89.75%, effectively resolving the issue of low accuracy in the results of explosion field temperature tests and calculations. Therefore, this study provides data and theoretical support for testing and evaluating the damage power of ammunition explosives, and the proposed model has high applicability in the engineering field.

Study on Overpressure Explosion of Oil and Gas Pipelines and Risk Prevention & Control Measures

In view of the flammable and explosive characteristics of oil and gas pipeline transportation medium, once it leaks, production safety accidents are easy to occur. This study uses explosions with severe consequences caused by natural gas pipeline leakage as an example. The risk factors and accident modes of oil and gas storage and transportation pipelines are analyzed; the explosion load is calculated by a scaling explosion prediction model with the TNO multi-energy method; the relationship between overpressure load and combustible gas cloud radius is studied. The methane-air explosion volume fraction of 9.5% is taken as another example, with which the overpressure attenuation law of explosion wave is obtained. Based on the above research, safety risk prevention and control measures are proposed. The research results can provide technical support for daily management and risk prevention and control of oil and gas storage and transportation pipelines.

Cumulative damage and bearing capacity attenuation law of anchorage structure interface under cyclic loading and unloading

The specimens of anchorage structures bonded by different anchoring materials are prepared to study the damage and reduced safety and reliability caused by the cyclic loading and unloading stress to the roadway anchorage structure. Using Fiber Bragg grating, acoustic emission monitoring and ANSYS, the anchorage structures’ bearing properties, interface failure characteristics, overall failure mode and internal influence mechanism are obtained under cyclic loading and unloading stress path. Results show that the cracks at the anchorage interface would develop and expand rapidly under this path, and the cumulative damage to anchorage structures is primarily caused by repeated residual deformation, periodic opening-expanding-closing of internal cracks, and impact vibration resulted from large-scale cyclic loading and unloading. Compared with the results under single pull-out stress, the ultimate loads of the anchorage structures bonded by H and S materials are reduced by 30.8% and 45.5%, respectively, and the radii of inner damage are increased by 1.64 and 1.67 times, respectively, showing a significant decrease in the bearing capacity of anchorage structures under cyclic loading and unloading. The anchorage structures bonded by these two materials have more prominent brittleness and weaker post-peak bearing capacity than those bonded by resin anchoring agent. Therefore, the balance between bonding strength and brittle-plastic extension characteristics shall be fully considered for the selection of anchoring materials. Five failure modes of anchorage structure are summarized: failure of the bolt-anchoring material interface, failure of the anchoring material-surrounding rock interface, fracture of the anchoring material, fracture of the bolt, and integral bulging of the anchorage structure. Besides, under the action of stress disturbance, the anchorage structure of bolt group can mobilize adjacent bolts to restrain the continuous damage and bearing capacity attenuation of the middle bolt, thus guaranteeing the overall safety and stability.

Impact of Evaluation of Freeze–Thaw Cycles on Collapse Zone at Entrance and Exit of Loess Tunnel

The entrance and exit of loess tunnel are easily affected by freezing and thawing, which leads to collapse in cold regions. Based on the slip line network method, this paper proposed a graphical method and analyzed the impact of evaluation of freeze–thaw cycles on the collapse zone at the entrance and exit of a loess tunnel. Firstly, the slip line network method was improved for a graphical calculation program, and the program was validated by monitoring the data of collapse evolution in an unlined loess tunnel in situ. Then, some triaxial tests of freeze–thaw cycles were carried out on loess, and the attenuation law of loess strength was summarized after freeze–thaw cycles in cold regions. Finally, the graphical calculation program was applied to evaluate the impact of freeze–thaw cycles on collapse range in the unlined loess tunnel. The results show that introducing the classic slip line field into the analysis process of a tunnel collapse zone can provide a feasible and efficient analysis method for a tunnel surrounding rock collapse arch for tunnel engineering, and the collapse zone increases with the growing number of freeze–thaw cycles. Moreover, the attenuation of loess strength which suffered from the freeze–thaw cycles would cause the collapse zone area to increase by a maximum of 16.13%.

Single-end traveling wave protection method in flexible DC transmission line based on dominant frequency attenuation characteristics

The conventional traveling wave protection (TWP) for flexible DC transmission lines suffer from low-sensitivity problem in far-end high-impedance faults. Also, they are lack of theoretical basis in threshold setting. In this paper, the initial traveling wave is analysed considering the frequency attenuation law and discrepancy between internal and external faults. Then, the frequency domain expressions of the initial traveling wave are analysed deeply. By enhancing the influence of high-frequency components in energy calculation reasonably, the initial traveling wave dominant frequency (ITWDF) is constructed, which can reflect the fault location and the attenuation characteristics of the boundary. The expressions of the ITWDF show that the ITWDF decreases with the increasing fault distance, and the ITWDF is significantly different between the internal faults and the external faults. On this basis, a single-ended TWP method based on the attenuation characteristics of the ITWDF is proposed. The method is immune to the fault impedance, and the expressions of the ITWDF provide a theoretical basis for protection threshold setting as well. The simulation results show that the proposed method can fast and correctly identify line faults, even with 1000 Ω fault impedance. The ITWDF can reflect the fault location effectively, and the threshold setting is simple. Moreover, the proposed method is high-adaptability in different network topologies.