Transition Section Research Articles

Evaluating the Impact of Mudstone Swelling on Railway Heave of Ballastless Tracks in the Transition Section Using the DEM-FDM Coupling Method

Evaluating the Impact of Mudstone Swelling on Railway Heave of Ballastless Tracks in the Transition Section Using the DEM-FDM Coupling Method

Welding 304 SS/Al2O3 ceramic joints by the transition section process

Welding 304 SS/Al2O3 ceramic joints by the transition section process

Fatigue performance of Q420C high-strength steel at room and low temperatures

Steel structures are frequently exposed to the environment with variable temperature, where the fatigue failure of steel is difficult to be predicted. In this paper, the standard Q420C high-strength steel specimens were tested to explore their fatigue performance at room (25°C) and low temperatures (0°C, −15°C and −30°C). Before fatigue tests, the tensile tests have been done, and the results indicate that the yield and ultimate strengths of Q420C steel significantly grew when the temperature decreased. The fatigue behavior of Q420C steel was discussed from different perspectives, including the crack initiation, crack growth, fracture mode and fatigue life. The fatigue failure was observed mainly near the arc transition section of specimen, with the fatigue crack initiated from the surface and internal discontinuity defects. Furthermore, the test fatigue life was compared with the recommended S-N curves provided by specifications from various countries. These comparison results suggest that recommended S-N curves were excessively conservative to evaluate the steel fatigue life at low temperature, leading to a potential economic cost for the steel structures at extremely cold conditions. To avoid needless loss, a calculation method of steel fatigue life considering the effect of low-temperature, stress range and yield strength was proposed.

Physical and numerical tests on adjustable–height structures of high–speed railway transition section

The disparity in stiffness and differential settlement between the subgrade and rigid structures can lead to track irregularities within transition sections, resulting in significant train vibrations and impacts. This study proposes an adjustable–height subgrade structure for transition sections by introducing a raft slab to divide the subgrade into upper and lower parts. When settlement occurs in the subgrade, the raft slab can be elevated using height–adjustment techniques to compensate for the settlement. To this end, large–scale physical model tests are conducted under train loading to verify the design's rationality and to elucidate the influence of settlement magnitude and train speed on the stress and deformation of the slab. The experimental results indicate that the maximum principal stress and maximum shear stress of the slab generally increase with settlement magnitude and train speed, and the area near the abutment end is the most unfavorable position for the deformation of the slab. However, it is still lower than the design compressive strength of the C40 concrete structure. Thus, the designed adjustable–height structure meets the load–bearing requirements under train loading. Additionally, a numerical simulation model of the adjustable–height structure is developed to investigate the recovery capabilities and stress distribution of the settled raft slab. The results indicated that whether the lifting operation employed linear load or equal load methods, the raft slab primarily endured compressive stress, and there is stress concentration at the lifting points. For the same lifting displacement, the linear load method proved to be more reasonable than the equal load method. These findings have significant practical and theoretical implications for ensuring the safe and smooth operation of high–speed railways, effectively addressing the post–construction settlement deformation control challenges in ballastless track transition sections.

Переходные участки бесстыкового пути, примыкающие к стрелочным переводам

Purpose: consider the problem of interaction between turnouts and adjacent sections of a seamless railway track. Methods: statistical data analysis. Results: an analysis of the results of domestic and foreign studies has been carried out, which show that in such areas there is a jump with subsequent extrusion of material of less rigidity and an increase in the slope of the elastic unevenness, i. e., an undesirable phenomenon occurs — a shock wave. The impact force depends on the mass of the rolling stock and the speed of movement, the geometric evenness of the rail track and the chosen approaches to designing the transition zone as a whole. Jump and mainly occurs due to compression and pushing out of structural layers and materials of lower rigidity in the under-rail area. The impact force depends on the mass of the rolling stock and the speed of movement, the geometric evenness of the rail track and the chosen approaches to designing the transition zone as a whole. Jump and mainly occurs due to compression and pushing out of structural layers and materials of lower rigidity in the under-rail area. Shock waves caused by uneven rigidity of sections have negative consequences (the appearance of deviations in level, subsidence, distortions, increased intensity of rail wear, the appearance of rail defects), which increase the cost of maintenance of the railway track. An analysis of the accumulation of residual deformations has been carried out, which shows the systematic formation of geometric irregularities in adjacent areas in the turnout area. Practical importance: from the point of view of the design of the transition zone, the expected advantage will be the differentiation of structural materials and elements and their influence on achieving the optimal gradation of railway track rigidity in the vertical and horizontal (transverse, longitudinal directions), selection of the optimal ratio of the mechanical properties of individual elements of the superstructure structure. It should also be noted that it is necessary to conduct an additional feasibility study of the feasibility of constructing transition sections in the area where the track and switches meet, taking into account the operational features of individual railway lines.

Loss characteristics and optimization method of a compressed air energy storage radial turbine with nozzle governing

During the operation of the compressed air energy storage (CAES) system, a discrepancy exists between the air storage pressure and the turbine inlet pressure. At the same time, to ensure that the turbine operates efficiently when the system load varies, the turbine needs to be regulated reasonably. In this paper, the influence of three nozzle governing (NG) parameters on turbine performance during the NG process is investigated: the inlet pressure of the NG region, the area of the NG region, and the base pressure. The flow characteristics and loss mechanisms under partial admission conditions and NG conditions are also analyzed. Furthermore, the NG process is optimized by using a transition section. The results show that the loss under the NG condition with low inlet pressure at the NG region is similar to the partial admission loss, both of which are mainly affected by the area of the NG region. In both working conditions, vortex structures appear at the stator outlet of the NG region. At the same time, the mixing of different airflows and the flow separation phenomenon within the rotor leads to a significant increase in entropy production rate. The transition section can attenuate the leakage and reduce the entropy production rate in the radial gap between the stator and rotor, increasing turbine efficiency by up to 1.1 % at maximum when using the transition section.

Experimental Evaluation of Geometric and Environmental Effects on Mechanically Fastened Non-Crimp Fabric Composites.

Corresponding to marine environmental regulations is important in shipbuilding and marine industries. The application of lightweight composite materials on ships is an effective approach to reducing the emission of greenhouse gases. The mechanical fastening method is a good candidate to assemble composites and conventional metals. The joint geometric and environmental effects are two important factors in mechanically fastened ship and marine structures. In this study, we evaluated the W/D (hole diameter to width ratio) and environmental effects on the bearing strength and failure mode of a mechanically fastened non-crimp fabric (NCF) composite material. To consider the effect of joint geometry, wherein hole diameters of 5, 6, 8, and 10 mm were machined. Further, by selecting three environmental conditions (UV, saltwater and low temperature), we evaluated environmental effects on bearing strength and failure modes of NCF composite specimens. The bearing strength increased as W/D decreased, and the bearing strength of the specimen exposed to low temperature and UV environments increased, while that of the specimen exposed to saltwater remained the same. From the failure mode analysis, the specimen that was exposed to salt fog showed the same failure mode as the unaged specimen. It was observed that the changes in the transition section and new failure mode in the xenon arc and low-temperature specimens.

Thermal enhancement of targeted cooling thermosyphon array applied to the embankment–bridge transition section of the Qinghai–Tibet railway in warm permafrost

Permafrost degradation in the embankment–bridge transition section (EBTS) along the Qinghai–Tibet Railway has led to extensive damage to bridge structures, posing a serious threat to railway safety. With the ongoing global warming, reinforcing the affected EBTS to ensure long-term stability remains a pressing challenge. To address this issue, this study proposes a targeted cooling thermosyphon array (TCTA) approach utilising variable inclination evaporator (VIE) thermosyphons. The effectiveness of the VIE thermosyphon was evaluated through an in-situ test. Meanwhile, a three-dimensional numerical model was employed to analyse the overall cooling effect, long-term performance and thermal enhancement provided by the TCTA approach. The findings indicated that the VIE thermosyphon exhibited excellent cooling performance and maintained uniform wall temperature, with the lowest wall temperature reaching −15 °C. Within one year of implementation, a cold core of −2 °C formed at the centre of the foundation, and the permafrost table was uplifted by approximately 3 m, showcasing its potential to rapidly enhance the thermal stability of in-service EBTS in permafrost. With prolonged operation, the cold accumulative effect of this approach gradually becomes apparent, and the range of the low-temperature cores expands. This method effectively reinforces the thermal stability of in-service EBTS and is well-suited for future railway construction in warm permafrost amidst the challenges of climate change.

Features of distribution of electric field strength and current density in the reactor during treatment of liquid media with high-voltage pulse discharges

Purpose. Development and use of a mathematical model of the stages of formation of high-voltage pulse discharges in gas bubbles in the discharge gap «rod-plane» to identify the features of the electric field intensity distribution in the reactor and determine the current density in the load during disinfection and purification of liquid media by high-voltage pulse discharges and find the most rational treatment. Methodology. To achieve this goal, we used computer modeling using the finite element method as a method of numerical analysis. An experimental reactor model was created that takes into account the dynamics of discharges in gas bubbles in water. The equations describing the system include the generalized Ampere equation, the Poisson equation and the electric displacement equation, taking into account the corresponding initial and boundary conditions, as well as the properties of materials. The dependence of the potential of a high-voltage electrode on time has the form of a damped sinusoid, and the specific electrical conductivity in a gas bubble is a function of time. Processes occurring at the front of the voltage pulse from 0 to 20 ns are considered. Results. It is shown that with an increase in conductivity and high-voltage potential to amplitude values in a gas bubble, the electric field strength in the water layer in the reactor reaches 70 kV/cm, and it is in the water layer that there is a strong electric field. The calculations show that already by 19th ns the density of conduction currents in water prevails over that of displacement currents. At the same time, additional inclusions in the water significantly affect the distribution of electric field strength and current density, creating a significant difference in their values at the boundaries of the interface between the bubble, conductive element and water. Originality. A simulation of the dynamics of transient discharge processes in a gas bubble and a layer of water with impurities was carried out, including an analysis of the distribution of the electric field strength and current density in a system with rod-plane electrodes in the phase transition section of a gas bubble-water. This approach allows us to reveal the features of processes in reactors and to investigate the influence of phase transitions on the distribution of electrophysical quantities. Practical value. Computer simulations confirm the prospect of using nanosecond discharges generated in gas bubbles within a volume of water for widespread industrial use and are of great interest for further experimental and theoretical research. References 25, figures 9.

Fabrication and testing of the transition section between modules of a wakefield accelerator

The fabrication process is presented for a typical transition section located between each cylindrical corrugated waveguide structure comprising the wakefield accelerator module. The transition section includes couplers for extracting the 180 GHz TM01 accelerating mode and separate couplers for extracting the 190 GHz HE11 dipole mode, both modes induced by the electron bunch traversing the cylindrical corrugated waveguide structure. Extraction of the high-power accelerating mode reduces the heat load due to the subterahertz wave power dissipation within the corrugated accelerating structure. Extraction of the low-power dipole mode serves the purpose of detecting the electron bunch transverse oscillations within the wakefield accelerator and identifying the onset of beam breakup instability. Comprehensive testing of the fully functional transition section with an electron beam was done at the Accelerator Test Facility in Brookhaven National Laboratory which verified the functionality of the transition section. Published by the American Physical Society 2024

Modeling and analyzing the complex deformation of thermoplastic polymers

Existing constitutive models rarely considered the effect of transition point from the strain-softening phase to the strain-hardening phase. In this paper, a new phenomenological model is proposed. The model introduces a transition optimization factor to take the effect of the transition point into consideration. The tensile and compressive deformations under different loading conditions are analyzed separately and compared with the results of the DSGZ (Duan-Saigal-Greif-Zimmerman) model. The results indicate that the proposed model is more accurate than the DSGZ model in analyzing the post-yield deformation that possesses a significant transition section. Based on the new stress-strain updating algorithm, a VUMAT subroutine was written for cyclic compression simulations. Comparing with the simulation data of DSGZ model, the proposed model effectively describes the hysteresis loop in the cyclic process. This indicates that the proposed model is more capable of analyzing complex deformations of thermoplastic polymers. Meanwhile, compared with the primal algorithm, the new stress-strain updating algorithm improves the analytical accuracy of the proposed model for the unloading and reloading phases.

A physically-informed machine learning model for freeform bending

AbstractThis work aims at a fast computational process model of the free-form bending process. It proposes a novel physically-informed machine learning model, which is trained with experimental data of bending constant radii and utilizes additional physical bending knowledge by integrating Timoshenko’s beam theory. The model is able to predict the resulting plastic deformation of the tube after exiting the die by computing an elastic representation of the tube’s deformation with beam theory at each time step. This elastic representation serves as input for a regression model similar to a partially connected neural network. This physically-informed machine learning model generalizes the constant training radii to complex bend geometries consisting of transitional sections and true spline geometries. It is compared to a benchmark finite element simulation and has an improved prediction quality for complex kinematics while reducing the computation time by four orders of magnitude.

Effects of windbreak types on aerodynamics of high-speed trains traversing from flat ground to semi-cutting and semi-embankment under crosswinds

Under the operation of strong crosswinds, the aerodynamic performance of high-speed trains (HSTs) will be seriously deteriorated when the transition section of flat ground and semi-cutting and semi-embankment (FGSCSE) is traversed, and the setting of windbreaks will help to slow down the impact of strong crosswinds on the trains. In this study, a three-dimensional coupled computational fluid dynamics numerical model to assess the aerodynamic performance of train–windbreak–FGSCSE–air system is developed. A comparative assessment is carried out to identify the variations in aerodynamic performance on the train carriage: no windbreak (NW), 50% ventilation windbreak (VW), and solid windbreak (SW), and the reasons for these variations are elucidated by examining the flow field structure's evolution. Furthermore, the operational safety of the train is discussed based on the indicator of wheel unloading ratio (fΔQ). Across the three distinct conditions, significant abrupt changes in aerodynamic load coefficients (ALCs) and the shedding of vortex structures are experienced by HSTs traversing the FGSCSE transition sections. Compared to the VW condition, the NW and SW conditions result in a greater number of shedding vortices on the leeward side and the tail of the train, and the VW condition results in the smallest magnitude of ALCs fluctuation. The power spectral density peak values of the aerodynamic loads follow the order: SW > NW > VW. Upon the train fully enters the subsequent operational environment, the VW condition has the smallest standard deviation of these coefficients. The standard deviations of CFy, CFz, CMx, CMy, and CMz for the head train in the VW condition are only 57.17% (46.81%), 55.85% (54.15%), 72.74% (34.62%), 57.99% (51.92%), and 44.60% (43.82%) of the corresponding values in the NW (SW) condition, respectively. In the NW, VW, and SW conditions, the fΔQ exceeds 0.9 when the wind speeds reach 30, 40, and 35 m/s, respectively. The windbreak with a ventilation rate of 30% performs the best, providing the most effective safety and stability for train operation.

Study on the Influence of Buried Depth on the Deformation of Bridge Approach Slab

The setting of the bridgehead slab can effectively alleviate the harm caused by the bridgehead bump, but the secondary bump may occur due to the fracture and void of the slab. Given the above problems, the influence of buried depth on the deformation of the bridge approach slab is studied through theoretical analysis and numerical simulation. The results show that compared with the conventional slab, the shear force of the slab is reduced and the service life is increased when the slab is deeply buried. The deep-buried slab can help to reduce the differential settlement of the road-bridge transition section and alleviate the phenomenon of vehicle bumping at the bridgehead. And the deeper the buried depth of the slab, the more gentle the settlement change of the transition section of the bridge.

Mechanical Performance Analysis and Parametric Study of the Transition Section of a Hybrid Cable-Stayed Suspension Bridge

Mechanical Performance Analysis and Parametric Study of the Transition Section of a Hybrid Cable-Stayed Suspension Bridge

Electrochemical machining of titanium alloy blades using optimized cathode with built-in insulators

ABSTRACT The passivation characteristics of titanium alloys in electrolytes are often the main reason that impede the electrochemical reaction process. Hence, maintaining uniform electrochemical dissolution is a prerequisite for stable electrochemical machining (ECM) of titanium alloys. In this study, a novel cathode structure with built-in insulator is proposed, whichimproves machining stability of titanium alloys in ECM. Flow dynamics simulation results show that the cathodes with built-in insulator 1 or insulator 3 demonstrate more uniform flow effect. ECM experiments reveal that the optimized cathode can reduce the time of current from transition section to balance section, presenting a optimal transition time of 180 s. Compared with the original cathode, the sample surface machined using the optimized cathode is smooth without defects. Additionally, the optimal width of the non-processing stray corrosion area decreases from 603.47 μm to 214.54 μm, and 1010.47 μm to 349.25 μm. The optimal machining taper angle is 9.85°.

How Do the Eight Hypotheses in Plato’s Parmenides Come to Light? Chiasmus as a Method of Division

In this paper, I aim to explore the structure of the exercise in the second part of the Parmenides. In analyzing the transitional section, I claim that in addition to diairesis, there is another method of division, namely, cross-division, which Porphyry terms chiasmus. On this basis, I explain how Plato uses chiasmus to divide the exercise into eight hypotheses, in which the subjects of the paired hypotheses (I–VI, II–V, III–VII, and IV–VIII) are the same and those of the nonpaired hypotheses differ. In closing, I reconstruct the universal scheme of the exercise on the basis of Plato’s use of chiasmus.

Comparing various neural network methods for temperature prediction of CRTS II slab track on transition sections

Abstract Based on the meteorological measuring data, the prediction of the temperature field is worthy of thermal performance evaluation of CRTS II slab tracks in bridge-subgrade transition sections. To find the best temperature prediction method, this present study shows a comparison of internal temperature predictions in CRTS II slab track by using three typical neural network methods (ANN, CNN, LSTM) subjected to different meteorological factors. Firstly, the distribution characteristics of four meteorological factors (e.g. ambient temperature, solar radiation, wind speed, and humidity) and internal temperature for the CRTS II slab track on three different foundations are analyzed. Moreover, temperature prediction effects of track slab and base plate on three foundations under five meteorological testing cases are compared by using three neural network models, respectively. The results show that the ambient temperature ranging from 15°C and 25°C accounts for about 7% and the solar radiation during daytime mainly ranges from 100 W/m2 to 1100 W/m2. The solar radiation has more effect on the temperature gradients of the CRTS II slab track on bridge and transition zone than that of the ambient temperature, and Case 5 with five different input variables has the best prediction accuracy for three predict models among five testing cases. Although the LSTM model has the best prediction accuracy among the three prediction models with R2 values of about 0.85, it costs the longest calculation time of about 180 s. In addition, the track slab on bridge has the worst prediction accuracy for the ANN and CNN models among the three foundations with RMSE values of 4.5 and 2.5 for Case 2, and the base plate on transition zone has the best prediction accuracy both for the CNN and LSTM models among the three foundations with RMSE values of 3 for Case 5.

Study on aerodynamic and structural performance of floating offshore wind turbine with fusion winglets

ABSTRACT The surge motion of the platform affects the aerodynamic and structural performance of the floating offshore wind turbine (FOWT) with tip-fusion winglets. Hence, this paper aims to study the aerodynamic and structural performance of the wind turbine with and without tip-fusion winglets under the surge motion by ANSYS software. Comparison of the differences in the pressure distribution, flow fields, modal analysis, and stress of the wind turbines under surge motions. The results show that the tip-fusion winglets have an obvious influence on the pressure distribution and flow fields, and the influence mainly concentrates on the tip of the blade. In addition, the frequency of the wind turbine with fusion winglets is less than without winglets from the first mode to the third mode. The main vibration type of wind turbines with and without winglets is flapping. Besides, the maximum stress of the wind turbine with fusion winglets is increased by 19.91%, and there is a stress concentration phenomenon at the connection between the blade tip and the winglet, which is easy to cause fatigue damage. The location of the maximum stress appears in the transition section between the Cylinder airfoil and the DU airfoil.

Deformation causes of the Embankment-Bridge transition section in warm permafrost: The case study of a dry bridge along the Qinghai-Tibet railway

Differential embankment settlement and expansion joint failure in the embankment bridge transition section (EBTS) are two main issues endangering the safety of the Qinghai-Tibet Railway (QTR) in permafrost. A better understanding of the causes of EBTS deformation can offer valuable guidance for engineering maintenance. In this study, a comprehensive field investigation and a series of simulations were carried out to reveal the formation causes. The results revealed significant permafrost degradation beneath the EBTS after 15 years of operation, with temperatures nearing the thawing point. Despite contact between the abutment and beam end, the expansion joint exhibited continuous narrowing, particularly during the cold season. Permafrost degradation was primarily attributed to the heating effect of adjacent bridge structures. Foundation ground settlement emerged as the primary cause of embankment settlement in the transition section, contributing up to 80 % of the total settlement. Differential embankment settlement of the EBTS primarily stemmed from the uneven warming or thawing of permafrost, induced by the thermal impact of the adjacent bridge structures. The weakening of the transition section had a concentrated impact on embankment settlement within a 12-meter span behind the abutment, inducing approximately 30 % to 50 % of the embankment settlement. The backfill soils near the abutment experienced severe lateral frost heave in cold seasons. Horizontal displacement of the abutment caused by the lateral frost heave was identified as the main reason for expansion joint failure. Additional cooling measures are necessary to ensure the long-term stability of the EBTSs along the QTR, considering the faster degradation of ambient permafrost than expected. The findings offer valuable insights for the maintenance and design of railways in permafrost regions.