Low Safety Factor Research Articles

Non-disruptive error field measurement in DIII-D low safety factor plasmas and projection to ITER

Abstract Previous experiments in DIII-D (Paz-Soldan et al 2022 Nucl. Fusion 62 126007) introduced a method to identify intrinsic error fields (EFs) in tokamaks with minimal disruption risk by promptly healing driven magnetic islands during the conventional ‘compass scan’. This paper presents recent experimental and numerical advancements in extending this approach to low q 95 plasmas, and projects its applicability to ITER. Non-disruptive EF measurement is achieved at q 95 = 4.5 and 3.9 without any initial EF correction (EFC) by reducing the time between the occurrence of the locked mode (LM) and control action to 10 ms and increasing the density 50%–100%. However, 50% correction of the intrinsic EF is required to achieve island healing at q 95 = 3.2 with 10 ms delay for the control action. Nonlinear two-fluid modeling with the TM1 code reproduces the DIII-D experimental observations, indicating that promptly turning off the 3D coil current reduces both magnetic island width and electromagnetic force, while raising the density increases plasma viscosity, facilitating magnetic island healing. The simulations show that for scenarios with q 95 = 3.2, lowering the control action time to 5 ms will lead to island healing without EFC. TM1 simulations are extended to future ITER scenarios with 5 MA and 7.5 MA plasma currents, predicting the dependence of required density rise on action time and EF amplitude. These simulations indicate that, benefiting from the much longer resistive time, island healing can be successfully achieved in ITER when taking control action 100–500 ms after a LM occurrence.

Performance of Combined Woven Roving and Mat Glass-Fiber Reinforced Polymer Composites Under Absorption Tower Lifting Loads.

This study investigates the structural integrity of a glass-fiber reinforced polymer absorption tower during lifting operations, evaluating factors of safety and stress distribution for both horizontal and vertical scenarios. A key focus is the comparative analysis of surface and volumetric meshing techniques in finite element modeling. Results demonstrate that surface models achieve comparable stress predictions to computationally intensive volumetric models, significantly reducing computational demands without compromising accuracy. For instance, stress at the flange edge with holes was accurately captured using a surface model with 5675 elements (12.79 MPa), yielding similar results to a volumetric model requiring over 94,000 elements (13.37 MPa). Similar computational efficiency and agreement between modeling approaches were observed at the packing support ring-shell joint. Finite element analysis employing Hashin's failure criterion, informed by industry-standard experimental data, revealed safety factors ranging from 1.9 to 2.5 for horizontal lifting and four for vertical lifting. These safety factors indicate sufficient margins for safe operation. While these findings support the feasibility of both lifting methods, further investigation is recommended to address the lower safety factors observed in specific horizontal lifting scenarios. A comprehensive assessment incorporating industry standards, dynamic load effects, and potential mitigation strategies is crucial to ensure the long-term structural integrity of the GFRP absorption tower.

Application of limit equilibrium and shear strength reduction techniques for stability assessment of slope cuts- A case study of Khalid-Dijo dam project, Southern Ethiopia

Dam failure can occur due to foundation instability, downstream and upstream slopes instabilities. This study assesses the stability of upstream and downstream slope cuts at Khalid-Dijo irrigation dam project, which is located in Southern Ethiopia, 3km south of Werabe town. Limit equilibrium and finite element shear strength reduction methods are adopted. Validation of results and comparisons between those methods are carried out. The analysis considers anticipated site conditions, including static dry, static saturated, dynamic dry and dynamic saturated conditions. Slope material properties are measured from insitu, laboratory tests and used as input parameters for the analysis to obtain factor of safety and critical strength reduction factors. The properties considered in the analysis include unit weight, cohesion, angle of internal friction, poison’s ratio, dilation angle and Young’s modulus. The analysis indicates that the factor of safety values for limit equilibrium methods and the critical strength reduction factor for finite element method are very similar across the three slope cuts under all anticipated conditions. The lowest factor of safety and critical strength reduction factor is 1.56 and 2.07 respectively. Generally, the proposed dam project is safe against upstream and downstream slope failures. These studies suggest that maintained the average safety factor values of both methods during the design stage are crucial to avoid unnecessary risk.

Seismic Safety Evaluation of Mechanically Stabilized Earth (MSE) Wall for Highway Construction

The usage of Mechanically Stabilized Earth (MSE) Walls has grown in popularity over the last few decades and has been widely used in many countries for highway construction, including Indonesia. As a country with a high risk against seismic hazards, a considerable stability analysis against earthquakes for construction must be conducted. This paper is directed to evaluate the static and seismic stability of MSE wall by adopting design criteria from SNI 8460:2017 using the pseudo-static approach with Limit Equilibrium Method (LEM) which modelling earthquake as a seismic coefficient, a one-way constant load and dynamic response approach with Finite Element Method (FEM) which modelling earthquake as ground motion, a fluctuating load which varies in time. The stability analysis is performed by considering three failure mechanisms that mostly occurred in MSE Walls; base sliding, tensile overstress, and slope failure. The earthquake load is modelled based 1000-year return period earthquake. Based on the analysis result, the most potential failure mechanism that may occur in the MSE wall is tensile overstress, while the least potential failure is base sliding. The analysis result also shows that the finite element method obtained higher safety factors compared to limit equilibrium, while on the other hand, the remaining two failure mechanisms shows the different result, with the finite element method obtaining lower safety factors than limit equilibrium. Modelling seismic load as an accelerogram indicates that earthquakes have higher impacts on structure stability compared to seismic coefficient, based on seismic safety factor reduction of each method. Although show differences in the value of the safety factor, the minimum safety factor required still complies with both methods.

The stability of natural and man-made unsaturated slopes influenced by different rainfall patterns.

Many slope failures have been recorded in Malaysia in recent times, particularly during the rainy season. An irregular rainfall is a change in rainfall patterns that is found to affect the slope stability with the infiltration of rainfall. The objective of this research is to investigate variations in the pattern of rainfall and their effect on the stability of natural and man-made unsaturated slopes in two separate site locations. Case A is located near a student's hall in Universiti Kebangsaan Malaysia (UKM), and another is located at the main entrance of UKM. Both cases are simulated with current and projected rainfall. The behaviour of the slopes with applied rainfall is analyzed with generated pore-water pressure, displacement and factor of safety. The first case was conducted by including the rainfall records from January 2011 to January 2021 and future-oriented data in January 2050. The software package used for this case is Plaxis2D. The results indicate that the highest factor of safety captured for 2021 was 1.156, while the lowest factor of safety was 1.11. It is observed that the obtained safety factor decreased with increasing rainfall intensity. Moreover, the displacement obtained was 0.1761m. In Case B, the capillary barrier system was used consisting of two layers of soil with different hydraulic properties as slope cover. A parametric study was performed to investigate the effect of several variables, including the hydraulic conductivity of soil and the rate of infiltration. By using SEEP/W from the GeoStudio, the results obtained show that the pore-water pressure in the initial slope is higher than the slope with the capillary barrier system. In addition, the factor of safety was calculated in SLOPE/W, indicating that the slope with a capillary barrier system has a high factor of safety than the original slope. The capillary barrier system was seen to improve slope stability by reducing the rainwater infiltration. These two cases were investigated in regard to the behaviour of unsaturated slopes within the changing rainfall and the unsaturated soil conditions.

Exploring the physics of a high-performance H-mode scenario with small ELMs at low collisionality in JET with Be/W wall

A new H-mode regime at low density and low edge safety factor (q 95 = 3.2, with Ip = 3 MA) that combines high energy confinement, stationary conditions for density and radiation and small Edge Localized Modes (ELMs) have been found in JET with Be/W wall. Such a regime is achieved by operating without external gas puffing, leading to a decrease in the edge density and a substantial increase in rotation and ion temperature in both the pedestal and the core region. Transport modelling shows a reduction of the turbulence, which starts in the pedestal region and extends into the plasma core, and outward impurity convection, consistent with the improved energy confinement and the lack of W accumulation observed in those conditions. In addition, large type I ELMs, typically found in gas-fuelled plasmas, are replaced by smaller and more frequent ELMs, whose appearance is correlated with a substantial reduction of the pedestal density and its gradient. Pedestals in this operating regime are stable to peeling–ballooning modes, consistent with the lack of large ELMs. This is in contrast to results in unfuelled JET-C plasmas that typically operated at higher pedestal densities and developed low frequency, large type I ELMs, thus pointing to the low density as one of the critical parameters for accessing this small ELMs regime in JET. This small ELMs regime exhibits the same low pedestal collisionality ( νe,ped∗∼0.1 ) expected in ITER and operates at low q 95, thus making it different from other small ELMs regimes that are typically obtained at higher q 95 and higher pedestal collisionality. These features make this newly developed H-mode regime in JET with Be/W wall a valuable tool for exploring the underlying transport, the different mechanisms of turbulence stabilization, as well as the physics associated with the appearance of small ELMs in high-temperature plasmas at ITER relevant pedestal collisionality.

Non-linear MHD investigations of high-confinement regimes without type-I ELMs in ASDEX Upgrade and JT-60SA

Large edge localised modes (ELMs) would cause an unacceptable reduction of material lifetime in future large tokamaks due to the significant amount of energy expelled from the magnetically confined region towards the plasma facing components. Thoroughly validated modelling of regimes devoid of large ELMs is crucial as it may then provide predictive insights prior to tokamak operation and design. This paper describes recent efforts pursued with the non-linear extended MHD code JOREK in the modelling of three scenarios without large ELMs: quiescent H-mode (QH-mode), quasi-continuous exhaust regime (QCE regime), and the enhanced D-alpha H-mode (EDA H-mode). For each of these regimes, the non-linear dynamics observed in the simulations are detailed and compared to experimental observations of the underlying instabilities of each regime (edge harmonic oscillation for QH-mode, small ELMs for QCE regime, and quasi-coherent mode for EDA H-mode). For QH-mode, the kink-peeling mode is found to govern the dynamics and a transition to a large ELM is obtained above the same density threshold as in the modelled experiment. For the QCE regime and EDA H-mode, resistive peeling–ballooning modes dominate and pedestal fluctuation frequencies correspond well to experimental observations. The dominant mechanisms for the excitation and suppression of these instabilities are presented and their influence on simulation dynamics is shown. Finally, predictive simulations of edge instabilities at different values of plasma resistivity in a 4.60 MA scenario with low edge safety factor in JT-60SA are presented.

Optimizing biomass allocation for optimum balance of seed yield and lodging resistance in rapeseed

ContextDense planting can boost achievable yields in rapeseed (Brassica napus L.). But it aggravates the lodging risk that is often associated with high–yielding cropping systems. ObjectivesThis research aimed to assess the agronomic performance of rapeseed in terms of yield and lodging related attributes under various planting densities. Meanwhile, the effectiveness of electrical measurements i.e., root capacitance (EC) and impedance (EI) for predicting root morphology and lodging resistance was also evaluated. MethodsThis study comprised two rapeseed varieties (Qinyou7: a lodging susceptible; Shanyou28: a lodging resistant) which were grown in four planting densities (15, 30, 45 and 60 plants m–2) across four site-year environments. Data on various agronomic parameters were recorded including seed yield, root and stem morphology and lodging resistance. Results and conclusionsWith an increase in planting density from 15 to 60 plants m–2, the seed yields of variety Qinyou7 and Shanyou28 were increased by 67 % and 56 %, respectively. However, a tradeoff of seed yield with lodging resistance was evidenced in lodging susceptible variety Qinyou7. It tended to invest more biomass in the siliques to maximize seed yield, which led to reduced stem bending strength (Ss) and weaker root anchorage strength (Sr), thus making plants more prone to lodging (in terms of lower safety factor, SF). Conversely, the lodging resistant Shanyou28 allocated a greater amount of photosynthates to the stems and roots to enhance its lodging resistance by maintaining higher Ss and Sr, thus compromising on a part of its seed yield. Large diameter of the root–soil cone and robust roots can be considered as critical traits for selecting lodging resistant varieties due to their strong correlation with Sr, and other lodging associated root morphological traits. Both EC and EI measurements were closely linked with seed yield, root–related traits, and SF. ImplicationsWe strongly recommend exploiting these electrical measurements as a quick, low–cost, non-destructive, and efficient technique for predicting seed yield and lodging susceptibility of rapeseed.

Parameter Sensitivity Analysis for Machining Operation of Autofrettaged Cylinder Using Taguchi Method

This study investigates the impact of material parameters such as yield strength (Sy), Young’s modulus (E), and tangent modulus (T) on the safety factor (SF) of autofrettaged cylinders under 400 MPa working pressure, considering the three scenarios: no machining, internal machining, and external machining. Finite element (FE) simulations were conducted based on the Taguchi experimental design and converted into signal-to-noise (S/N) ratios to determine the optimal settings. ANOVA was utilized to evaluate the significance and percentage contributions of each factor. The analysis indicated that Sy is the most influential parameter on SF, contributing approximately 98.20% across all scenarios, including no machining, internal machining, and external machining. The contributions of E and T were minimal, but T had a slightly greater effect than E. The analytical validation of the FE model showed good agreement, with a maximum deviation of 4.37% for no machining, 4.75% for internal machining, and 5.20% for external machining. Regression analysis further confirmed the high prediction capability of the model, validated using AISI 4340 steel. The study concludes that internal machining results in higher residual stress loss compared to external machining. Overall, the analytical method tends to provide lower SF values than the numerical method, highlighting its conservative nature.

Assessment of runaway electron beam termination and impact in ITER

The vertical motion and shrinking of the cold plasma column after a tokamak disruption leads to a natural decrease in the edge safety factor when most of the current is carried by runaway electrons (REs). Reaching a low edge safety factor can potentially cause a strong plasma instability. We present magnetohydrodynamic simulations of the termination of a post-disruption plateau-phase RE beam in ITER when the edge safety factor falls close to two. Growth of instabilities is observed to result in stochastization of the magnetic field and a prompt loss of REs. As RE impact must be mitigated in ITER, the effect of parameters that influence the final termination have been assessed. Higher background plasma resistivity is seen to cause larger mode magnitudes and stronger stochastization, leading to less remnant REs after the termination event. Lower ion-densities also project a qualitatively similar behavior although weaker in effect. Using computations from a wall collision model, the ensuing load distribution on the first-wall is also presented.

Fracture risk analysis of a stylet-driven lead for left bundle branch area pacing using a human beating heart model

Abstract Background Left bundle branch area pacing (LBBAP) has emerged as a promising approach to cardiac physiologic pacing. However, the mechanical stress and fracture risk has not been studied for stylet-driven leads implanted in the left bundle branch area (LBBA). Purpose The main purpose of this study was to evaluate the change in curvature during a cardiac cycle when a stylet-driven lead with a rigid distal end was implanted in LBBA and to identify any increased risk of conductor fracture for the LBBAP lead compared to those implanted at the His bundle (HB), traditional right atrium (RA) and right ventricle (RV) locations. Methods A high-resolution, four-dimensional human beating heart model was utilized for simulating the stress on the lead. The bending stiffness of lead body segments was measured with 3-pts bending test and the values were assigned to the finite element model. The curvature change of lead body during one cardiac cycle was measured. The safety factor of lead conductors was calculated using the curvature measurements, the conductor’s endurance limit, and the ultimate stress of the material (MP35N). A higher safety factor indicates better lead durability and lower risk of fracture. A parametric study was also performed to investigate how additional implant factors impact the safety factor of LBBAP leads: lead insertion angle, implant depth, degree of slack, and implant location (Figure 1). Results A total of 8 implant scenarios for LBBAP were defined and tested using the combination of the implant factors described above. Two RV implanted locations were tested: RV apex and RV apical septum. One HBP and one RA implant location were tested. The region with maximum change in curvature for LBBAP lead was at 0-10 mm proximal to the ring electrode (Figure 2A). The maximum change in curvature on the lead body for LBBAP, HBP, RV, and RA implants were: 0.022±0.005 (n=8), 0.033 (n=1), 0.036±0.002 (n=2), and 0.024 mm-1 (n=1), respectively (Figure 2B). The safety factor for the lead conductors for LBBAP, HBP, RV, and RA implants were 5.57±1.35 (n=8), 3.48 (n=1), 4.62±0.04 (n=2), and 4.65 (n=1), respectively (Figure 2C). The highest safety factor among all implant locations was 7.63, corresponding to a LBBAP implant scenario with mid-septum location, a 45 degree lead insertion angle towards apex, 7.5 mm lead depth in the septum, and low lead slack. HBP had the lowest safety factor among all implant locations. Conclusion The stylet-driven lead with a rigid distal end implanted at the left bundle branch area does not introduce any further risk of fracture compared to the HBP or traditional RA/RV implant locations in this computational modeling study.Fig 1: LBBAP implants testedFig 2: Lead curvature and safety factor

Time-dependent soil–structure interaction analysis using a macro-element foundation model

The delayed settlement of foundations due to soil consolidation, creep or particle breakage can alter the internal load distribution and differential settlements in a superstructure through soil–structure interaction (SSI). The study introduces a novel methodology to simulate time-dependent SSI that overcomes the complexity of incorporating the time-dependent behaviour of foundations into routine SSI analysis. The proposed approach represents the superstructure as a condensed stiffness matrix, and replaces the foundations and underlying soils with macro-element foundation models that encapsulate the foundation–soil interaction into load–displacement relationships derived from constitutive models. To examine the performance of the proposed method, a macro-element model for time-dependent analysis of shallow foundations on sand was integrated with structural analysis to simulate two tests performed in a geotechnical centrifuge on a 3D-printed aluminium framed structure supported by footings on sand. The simulated responses of the superstructure and foundations were found to agree well with those observed in the centrifuge tests. Parametric analyses were conducted to investigate the effect of loading history, load level on the superstructure, and creep tendency of soil on post-construction load redistribution and differential settlements. The findings suggest that creep of foundations on sand facilitates load redistribution in the structure from heavily loaded sections to lightly loaded sections. Moreover, post-construction load redistribution depends on the differential creep between footings and should be considered for structures that are quickly constructed or at high levels of strength mobilisation (low factor of safety). Overall, the study highlights the potential of the proposed methodology in analysing the time-dependent SSI and its applicability in practical SSI analysis.

ANALYSIS OF SLOPE STABILITY DUE TO ILLEGAL GOLD MINING IN BENGKAYANG REGENCY

Illegal gold mining is extracting gold without a formal license from the government or competent authority. It presents a significant environmental and geological challenge in Bengkayang Regency, Indonesia. This practice, carried out without proper authorization or adherence to safety regulations, is recognized as a significant cause of slope instability in the area.This study analyzes slope stability from unlicensed gold mining in Kinande Village, Bengkayang Regency. It uses manual Fellenius calculations and Geo Studio/Geo Slope 2023 software to determine the Safety Factor (SF) for potential landslides, assuming circular landslide planes are unaffected by earthquakes.Laboratory tests revealed varying soil types and properties at these points, impacting shear strength and slope stability. Loamy soils exhibit high cohesion but low internal friction, making them susceptible to instability. Sandy soils lack cohesion and rely on particle friction. Shear strength parameters like cohesion (c) and internal friction angle (φ) are critical in assessing slope stability. The study employed the Fellenius method and Geo Studio 2023 software to analyze slope stability, with safety factor (SF) results indicating potential hazards. Mining in plain areas showed favorable SF values (>1.5), suggesting activity safety. Conversely, mining in mountainous and watercourse areas exhibited lower SF values (<1.5), indicating instability and safety risks. Recommendations include stratified mining practices to maintain stable slopes and ensure miner safety. This research contributes to understanding geohazards and proposes measures for enhanced safety, environmental sustainability, and regulatory governance in mining areas. Understanding and analyzing these factors are crucial for the stability and safety of geotechnical projects, ensuring balanced shear stress and shear strength for slope stability.

Water reservoirs influenced by slow moving landslides

AbstractWater storages for energy production in mountain valleys or snow retention basins on mountain slopes or mountain ridges are common buildings in Alpine regions. When such water reservoirs are situated on or nearby of a large slow‐moving landslide, low factors of safety and ongoing deformation of the reservoir structure – or parts of it – need to be handled in some cases. Questions about the justification but also the reliability of reservoirs influenced by such landslides need to be discussed. Verification procedures which proof a save operation of the reservoir over time but also an estimation of the behaviour of the reservoir influenced by the landslide for exceptional load cases need to be investigated. In this paper main issues and problems related to such questions are discussed for reservoirs in the design as well as in the operation state which are influenced by such slow moving landslides.

Analysis of Water Migration and Spoil Slope Stability under the Coupled Effects of Rainfall and Root Reinforcement Based on the Unsaturated Soil Theory

Root reinforcement is an effective slope protection measure due to root water absorption and soil suction. However, the coupled effect of rainfall and root reinforcement remains unclear, resulting in a challenge to evaluate slope stability in complex environments. This paper regards the root–soil composite as a natural fiber composite and quantifies its reinforcement effect using direct shear tests. The unsaturated soil seepage–stress theory was employed to simulate the effect of rainfall on water migration and the stability of spoil, overburden, and vegetated slopes. Field measurements and pore water pressure tests verified the simulation results. Furthermore, the influences of the slope angle, rainfall parameters, and vegetation cover thickness on slope stability were analyzed. The results showed the following: (1) The root reinforcement enhanced the soil’s ability to resist shear deformation, substantially improving soil shear strength. The cohesion of the root–soil composite (crs = 33.25 kPa) was 177% higher than that of the engineering spoil (ces = 12 kPa) and 32.21% higher than that of the overburden soil (cos = 25.15 kPa). (2) The overburden and vegetated slopes had lower permeability coefficients and a higher shear strength than the spoil slope, and the effect was more pronounced for the latter, resulting in lower landslide risks. The water migration trend of the vegetated slope was characterized by substantial runoff and a low sediment yield. The safety factors of the spoil slope, overburden slope, and vegetated slope were 1.741, 1.763, and 1.784 before rainfall and 1.687, 1.720, and 1.763 after rainfall, respectively, indicating a significantly higher safety factor of the vegetated slope after rainfall. (3) The slope angle significantly affected slope stability, with lower safety factors observed for higher rainfall intensities and durations. Under these conditions, the slope angle should be less than 30°, and the soil thickness should be 0.5 m for herbaceous vegetation and shrubs and 1.0 m for trees.

Comparative Analysis of Piston Rings Made with Aluminum Titanium Carbide (AlTiC-75-2) and Carbon Cast Steel (AISI 1540) Materials Using Numerical Method

Aim: The main purpose of this study is to perform a comparative analysis of piston rings made with aluminum titanium carbide (AlTiC-75-2) and carbon cast steel (AISI 1540) materials using numerical method. Study Design: Numerical methods. Materials and Methods: The 3D piston rings were modelled with SOLIDWORDS version 2019 and imported to ANSYS 2020 RI environment for simulation and analysis. Results: The study revealed that AISI 1540 and AlTiC-75-2 had maximum deformations of 1.0356 mm and 1.0773 mm, respectively. Also, when the equivalent elastic strains of the piston rings were compared, it was revealed that, the maximum and minimum elastic strain of the AlTiC-75-2 piston was 4.8826e-3 and 2.2581e-5, respectively, whiles the maximum and minimum elastic strain of AISI 1540 was 2.1878e-5 and 2.1878e-5 respectively. Numerical results further showed that AISI 1540 piston suffered the least elastic strain while the AlTiC piston ring endured more elastic strain. Furthermore, results showed that the maximum Von Mises stresses induced in AlTiC-75-2 and AISI 1540 piston rings were 915.2 MPa and 911.27 MPa, respectively, which implies that stresses induced in both rings were beneath the compressive yield strengths of the individual materials, therefore both rings could withstand the load imposed. Conclusion: Result shows that the AISI 1540 ring has high minimum value than AlTiC which makes it more suitable material in terms of failure as against AlTiC-75-2 with a low minimum safety factor of 0.094187 as against 0.10182 for carbon cast steel. The study therefore recommends that AlTiC-75-2 should be considered as one of the most suitable materials for piston ring design.

Avoiding fusion plasma tearing instability with deep reinforcement learning

For stable and efficient fusion energy production using a tokamak reactor, it is essential to maintain a high-pressure hydrogenic plasma without plasma disruption. Therefore, it is necessary to actively control the tokamak based on the observed plasma state, to manoeuvre high-pressure plasma while avoiding tearing instability, the leading cause of disruptions. This presents an obstacle-avoidance problem for which artificial intelligence based on reinforcement learning has recently shown remarkable performance1–4. However, the obstacle here, the tearing instability, is difficult to forecast and is highly prone to terminating plasma operations, especially in the ITER baseline scenario. Previously, we developed a multimodal dynamic model that estimates the likelihood of future tearing instability based on signals from multiple diagnostics and actuators5. Here we harness this dynamic model as a training environment for reinforcement-learning artificial intelligence, facilitating automated instability prevention. We demonstrate artificial intelligence control to lower the possibility of disruptive tearing instabilities in DIII-D6, the largest magnetic fusion facility in the United States. The controller maintained the tearing likelihood under a given threshold, even under relatively unfavourable conditions of low safety factor and low torque. In particular, it allowed the plasma to actively track the stable path within the time-varying operational space while maintaining H-mode performance, which was challenging with traditional preprogrammed control. This controller paves the path to developing stable high-performance operational scenarios for future use in ITER.

Soft H-L back transitions by applying resonant magnetic perturbations in the low q 95 EAST plasmas

Controlled ‘soft’ H-L transitions with a simultaneous ramp-down of plasma density and stored energy, generated by applying resonant magnetic perturbations (n = 2 RMPs), relevant to the control of ITER terminations, are achieved in the EAST tokamak. These H-mode plasmas are run at median electron densities and a low safety factor q 95 ( q95=3.5 –4.0) under neutral beam injection (NBI) dominant heating. During a slow ramp in the RMP current the internal transport barrier for the electron density collapses at the beginning and the edge transport barrier for the electron density collapses later. Before the controlled H-L back transitions, the plasma stored energy W MHD is linearly correlated with the core line-averaged density ⟨ne⟩ . These controlled H-L back transitions ensue from the collapse of the edge transport barrier and at a similar energy confinement time τeH-L∼48 ms. These H-L transitions are not sensitive to the NBI power but are very sensitive to the fueling rate and ramp-up rate of the RMP current.

Numerical Analysis of the Effect of Crude Oil Pollution on Vertical Clay Trenches

ABSTRACT The presence of oil contamination causes changes in mechanical properties of clayey soil trenches with low liquid limits (CL) such as stress-strain behavior, rupture plain position, plastic zone, and strain energy for soil trenches compared with uncontaminated soils. These changes usually lead to a lower factor of safety against failure and expansion of the plastic zone. The effects of crude oil contamination on the soil shear strength were evaluated by direct shear and plate load tests for various clays and sandy soils. In this research, a numerical finite element modeling in ABAQUS software was used to estimate the effect of oil contamination in the range of 0 to 16% (0%–4%–8%–12%–16%) on the stability safety factor of vertical clayey trenches with heights of 3 m, 4 m, 5 m, and 6 m, and the results were compared with results of a limit state analysis. The findings of the limit equilibrium method show that adding 4% of oil contamination to a clayey trench will decrease 62% of its critical depth. Also, the numerical analysis results show that adding oil contamination in the range of 0 to 16% to the clayey soil will increase the maximum displacements of the trenches to five times their clean state.

Assessment of seismic slope stability of Rangamati Hill Tracts, Bangladesh

Slope stability is an essential aspect of geotechnical engineering. Unstable slopes or stable slopes influenced by external factors may result in a catastrophic disaster called a landslide. In seismically active areas with steep terrain, landslides commonly occur and are regarded as one of the most severe threats. Bangladesh has not suffered any destructive earthquakes in recent years but has a considerable risk of facing such earthquakes owing to its geological conditions. Although slope failures occurring in the Rangamati Hill Tracts of Bangladesh are mainly rainfall-induced, due to the seismic risk in Bangladesh, it is essential to assess earthquake-induced slope failure in vulnerable areas. In this study, the authors analyzed the seismic slope stability at three locations in the Rangamati Hill Tracts using pseudostatic approaches. The pseudostatic approach with the variation in seismic force based on the seismic coefficient was utilized to determine the critical conditions. Using Newmark’s rigid block method, the permanent displacements for various slope conditions were calculated for the Kobe earthquake. The analysis provided crucial insight into the state of the locations. One location has a low factor of safety (FS) value at a slope angle of 30° or greater, whereas the others have a risk of slope failure at a slope angle of 50° or greater. Newmark’s displacement analysis also showed that the slopes at location 3 have the highest displacement at a lower slope angle, with location 1 and location 2 showing relatively better results than location 3. Structural and bioengineered preventive measures are needed in this area to reduce the vulnerability of possible slope failure.