Reverse Displacement Research Articles

A Non‐Iterative Wheel‐Rail Contact Geometry Determination Algorithm and Its Application

AbstractTo ensure a more accurate simulation of the wheel‐rail contact state in vehicle‐track interaction, a non‐iterative contact geometry determination algorithm is proposed. This algorithm decouples lateral movement and roll, independently calculates the minimum wheel‐rail gap on both sides, and overcomes the limitation of simultaneous wheel‐rail contact on both sides. It can be applied to single‐side and two‐side wheel‐rail separation problems. Additionally, by converting track irregularity and rail deformation into the reverse displacement of the wheel, it avoids real‐time calculation of the wheel‐rail spatial position, thereby improving calculation efficiency. The effectiveness of the algorithm is verified through Universal Mechanism software and field measurements. Subsequently, the influence of the measured wheel‐rail profile, rail cant, and rail gauge on the wheel‐rail contact characteristics is analyzed. Finally, vehicle shaking caused by track irregularity and wheel‐rail contact is examined from the perspective of wheel‐rail matching. The study demonstrates that the non‐iterative algorithm is suitable for online simulation by pre‐processing the contact geometry parameters. When the track gauge and rail cant increase, the distribution of wheel‐rail contact points becomes more concentrated. Furthermore, when the excitation frequency of wheel‐rail matching is close to the track irregularity excitation frequency, it causes vibration amplification, resulting in lateral vehicle shaking.

Investigation on tribological behaviors of a novel generation polymer-coated ceramsite particle for fracturing

During fracturing, proppant particles can create favorable pathways for shale gas production. To solve the problem of low production efficiency of shale gas, a new polymer coated particle was prepared by experiment. And its mechanical properties were tested and tribological properties were studied under different speeds, loads and medium states. The results show that the new polymer coated particles have excellent tribological and mechanical properties. The friction coefficient between proppant particles and fracture surface decreases with increasing velocity. In addition, the new proppant particles have excellent hydrophobicity under lubricating conditions, indicating that the proppant has excellent migration efficiency. When proppants just pumped into the fracture, it can reach the fracture depth quickly. In addition, the friction coefficient between proppant particles and fracture surface gradually increases with the increase of load. It is further proved that when the proppant particles enter the fracture, the friction coefficient increases due to the extrusion of the fracture, and the reverse displacement can be effectively reduced. This research has important theoretical and practical engineering application value for improving the efficiency of shale gas stimulation.

Role of preexisting faults in the structural configuration of the South Rifian Ridges, Northern Morocco: Contribution of isobase maps and gravity data

The South Rifian Ridges are located in northern Morocco, to the south of the Gibraltar Arc, and constitute a portion of the south Rifian corridor in the Rif belt front. These active fault-related folds, separated by the Volubilis piggy back basin, were structured since the Late Miocene due to the reactivation of Triassic graben fault systems in the context of the Eurasia-Africa convergence.For the first time, a combination of morphotectonic and gravity analysis coupled with field Kinematic data have been used to characterize the main structures responsible for the Late Miocene to recent evolution of the area.The morphotectonic analysis based on the dynamics of drainage network analysis allowed the isobase lineament mapping to depict a general view of the tectonic framework of the South Rifian Ridges. The interpretation of gravity data, including maps derived from the Bouguer and residual anomalies, allowed subsurface geometric features characterization and revealed buried salt diapirs to establish a new structural map. Evidenced structures confirm previously interpreted ones and support the presence of new masked faults, with the presence of compressional and extensive deformations. The main inferred structures are the NW-SE oriented buried Prerif Nappe fronts. Rooted faults related to the main ridges show reverse displacement and are expressed by high-angle reverse faults, while the NW oriented normal faults within Volubilis basin, in the field, are probably related to an active subsidence. This event is related to the current NW-SE continental collision, within a context of transition from thin to thick skinned tectonics. Our results shed light on the Miocene to Quaternary tectonics that have taken part in the closure of the South Rifain marine gateway.

Effects of Reverse Fault Dislocation Application Method for Tunnelling Through Active Faults

Active faults seriously threaten the structural integrity of mountain tunnels in seismic zones, and reverse faults are the most hazardous. A tunnel project in the western region was used as a reference to analyze the damage mechanism of tunnels under different modes of reverse fault displacement. The ABAQUS finite element analysis software was employed for the numerical simulation, and a quasi-static method was adopted to analyze the displacement and stress response patterns of the tunnel structure traversing the fault under three typical modes of reverse fault displacement. This led to deriving the tunnel structure’s longitudinal damage modes and impact zones based on reverse fault displacement. The study revealed that the damage modes of the tunnel under different fault displacement modes varied, which was reflected in the different degrees of shear and compression. Regardless of the fault displacement mode, the tunnel structure located within the fault fracture zone was severely damaged, with the most severe damage occurring at the interface between the fixed plate and the fault displacement section. Therefore, in the design, special attention should be paid to the displacement resistance performance of the dangerous sections of the tunnel. The research results provide significant reference and guidance for similar projects.

Quantitative characterization of crude oil mobilization in microscopic pores during forward and reverse flooding in tight sandstone reservoirs using various fracturing fluid systems

In the transition from conventional to unconventional oil and gas exploration, the focus on tight sandstone reservoirs has grown due to their complex microscopic pore structures, narrow pore throats, and high capillary pressures. These characteristics often lead to the retention of fracturing fluids post-fracturing, hindering fluid recovery and reducing crude oil extraction efficiency. To address these issues, this study employed a combination of microscopic displacement experiments and nuclear magnetic resonance (NMR) analyses to investigate oil displacement mechanisms at the microscale in tight sandstone reservoirs. The experimental setup involved testing three core samples using distinct fracturing fluid systems: a guar gum-based system (System I), an EM30+ + guar gum water-based system (System II), and a CNI (Carbon Nanotechnologies Inc) nano variable-viscosity slick water-based system (System III). The study aimed to assess the impact of these different fracturing fluid systems on oil displacement efficiency in both forward and reverse directions. Results revealed that forward oil displacement efficiencies for Systems I to III were 26.86%, 33.3%, and 33.43%, respectively. In contrast, reverse displacement efficiencies were slightly higher at 28.9%, 37.5%, and 38.34%. Overall, Systems II and III outperformed System I in terms of oil displacement efficiency. The study also found that in cores with large pores, forward displacement predominantly mobilized crude oil, while reverse displacement was more effective in smaller pores. This trend was consistent in cores exhibiting bimodal pore distributions. However, in unimodal cores, small pores were significantly impacted in both directions. Notably, System III demonstrated a remarkable efficiency in mobilizing crude oil within smaller pores.

Biosensor-based multiple cross displacement amplification platform for visual and rapid identification of hepatitis C virus.

Hepatitis C remains a global health problem, especially in poverty-stricken areas. A rapid and sensitive point-of-care (POC) diagnostic tool is critical for the early detection and timely treatment of hepatitis C virus (HCV) infection. Here, for the first time, we reported a novel molecular diagnostic assay, termed reverse transcription multiple cross displacement amplification integrated with a gold-nanoparticle-based lateral flow biosensor (RT-MCDA-AuNPs-LFB), which was developed for rapid, sensitive, specific, and visual identification of HCV. HCV-RT-MCDA induced rapid isothermal amplification through a specific primer set targeting the 5'untranslated region gene from the major HCV genotypes 1b, 2a, 3b, 6a, and 3a that are prevalent in China. The optimal reaction temperature and time for RT-MCDA-AuNPs-LFB were 68°C and 25 min, respectively. The limit of detection of the assay was 10 copies per test, and the specificity was 100% for the experimental strains. The whole detection procedure, including crude nucleic acid isolation (~5 min), RT-MCDA (68°C, 25 min), and visual AuNPs-LFB result confirmation (less than 2 min), was performed within 35 min. The preliminary results indicated that the HCV-RT-MCDA-AuNPs-LFB assay could be a valuable tool for sensitive, specific, visual, cost-saving, and rapid detection of HCV and has potential as a POC diagnostic platform for field screening and early clinical detection of HCV infection.

Lateral Flow Biosensor for On-Site Multiplex Detection of Viruses Based on One-Step Reverse Transcription and Strand Displacement Amplification.

Respiratory pathogens pose a huge threat to public health, especially the highly mutant RNA viruses. Therefore, reliable, on-site, rapid diagnosis of such pathogens is an urgent need. Traditional assays such as nucleic acid amplification tests (NAATs) have good sensitivity and specificity, but these assays require complex sample pre-treatment and a long test time. Herein, we present an on-site biosensor for rapid and multiplex detection of RNA pathogens. Samples with viruses are first lysed in a lysis buffer containing carrier RNA to release the target RNAs. Then, the lysate is used for amplification by one-step reverse transcription and single-direction isothermal strand displacement amplification (SDA). The yield single-strand DNAs (ssDNAs) are visually detected by a lateral flow biosensor. With a secondary signal amplification system, as low as 20 copies/μL of virus can be detected in this study. This assay avoids the process of nucleic acid purification, making it equipment-independent and easier to operate, so it is more suitable for on-site molecular diagnostic applications.

La agricultura del maíz y el sorgo en el Bajío mexicano: Revolución verde, sequías y expansión forrajera, 1940-2021

The article analyzes maize and sorghum agriculture from 1940 to 2021 in the agricultural region of central Mexico known as the Mexican Basin or Bajío. The paper discusses the linear approach of scholars in observing the displacement of maize by sorghum under the Green Revolution paradigm that dominated the second half of the twentieth century. Analysis of surface data, agricultural production, and meteorological records shows how interactions between innovation, environment, and agro-industry, along with shifts in the Mexican government’s political economy concerning agriculture have influenced a reverse displacement since the 1990s. This displacement is also reflected in the global decline of sorghum as a forage crop, which has been replaced by soybeans and other legumes as well as maize. The relevance of maize as animal feed and a food industry input has increased greatly over the last forty years.

Mitigation of reverse faulting in foundation soils using geosynthetic-encased granular columns

In this study, a series of reduced model tests was conducted on soil foundations reinforced by Geosynthetic-Encased Granular Columns (GECs) placed across a reverse fault. These tests aimed at evaluating the effectiveness, reinforcing mechanism and optimal GEC horizontal spacing to mitigate the ground surface deformation associated with reverse faulting. For comparison, reduced model tests were also performed on unreinforced and Geosynthetic-Reinforced Soil (GRS) foundations. The reduced model tests were conducted to simulate a prototype 3-m-thick foundation layer subjected to a reverse fault displacement of 0.9 m. Digital Image Analysis (DIA) techniques were adopted to determine the surface displacement profile, angular distortion and shear rupture propagation considering various reverse fault offsets. Test results revealed that the GEC foundation can considerably reduce the fault-induced angular distortion at the ground surface. A reduction of 23.3% on the maximum angular distortion at the ground surface was observed as the fault displacement reached 30% of the foundation height (S/H = 30%), indicating the GEC foundation can mitigate the risk of surface fault hazards associated with large reverse fault movement. Two mechanisms, shear rupture diffusion and diversion effects, were identified for the GEC foundation, depending on the magnitude of the fault displacement and the system stiffness of the GEC foundation. Because of complex mechanisms between diversion and diffusion of the shear rupture in the GEC foundations, an optimal GEC spacing of Sh/dc = 3.3 was observed, which exhibited the most significant reduction in βmax at large fault offsets.

Improving dynamic characteristics for IGBTs by using interleaved trench gate

A novel trench insulated gate bipolar transistor (IGBT) with improved dynamic characteristics is proposed and investigated. The poly gate and poly emitter of the proposed IGBT are arranged alternately along the trench. A self-biased p-MOSFET is formed on the emitter side. Owing to this unique three-dimensional (3D) trench architecture, both the turn-off characteristic and the turn-on characteristic can be greatly improved. At the turn-off moment, the maximum electric field and impact ionization rate of the proposed IGBT decrease and the dynamic avalanche (DA) is suppressed. Comparing with the carrier-stored trench gate bipolar transistor (CSTBT), the turn-off loss (E off) of the proposed IGBT also decreases by 31% at the same ON-state voltage. At the turn-on moment, the built-in p-MOSFET reduces the reverse displacement current (I G_dis), which is conducive to lowing dI C/dt. As a result, compared with the CSTBT with the same turn-on loss (E on), at I C = 20 A/cm2, the proposed IGBT decreases by 35% of collector surge current (I surge) and 52% of dI C/dt.

Highly sensitive and rapid identification of coxsackievirus A16 based on reverse transcription multiple cross displacement amplification combined with nanoparticle-based lateral flow biosensor assay.

One of the main pathogens responsible for human hand, foot, and mouth disease (HFMD), coxsackievirus A16, has put young children's health at danger, especially in countries in the Asia-Pacific region. Early quick identification is essential for the avoidance and control of the disorder since there are no vaccinations or antiviral medications available to prevent and manage CVA16 infection. Here, we describe the creation of an easy, speedy, and accurate CVA16 infection detection approach using lateral flow biosensors (LFB) and reverse transcriptionmultiple cross displacement amplification (RT-MCDA). A group of 10 primers was developed for the RT-MCDA system in order to amplify the genes in an isothermal amplification device while targeting the highly conserved region of the CVA16 VP1 gene. Then, without requiring any extra tools, RT-MCDA amplification reaction products might well be detected by visual detection reagent (VDR) and LFB. The outcomes showed that 64°C within 40 min was the ideal reaction setting for the CVA16-MCDA test. Target sequences with <40 copies might be found using the CVA16-MCDA. There was no cross-reaction among CVA16 strains and other strains. The findings demonstrated that the CVA16-MCDA test could promptly and successfully identify all of the CVA16-positive (46/220) samples identified by the traditional real-time quantitative polymerase chain reaction (qRT-PCR) assays for 220 clinical anal swab samples. The whole process, such as the processing of the sample (15 min), the MCDA reaction (40 min), and the documenting of the results (2 min), could be finished in 1 h. The CVA16-MCDA-LFB assay, which targeted the VP1 gene, was an efficient, simple, and highly specific examination that might be used extensively in rural regions' basic healthcare institutions and point-of-care settings.

Reverse Circulation Displacement of Miscible Fluids for Primary Cementing

AbstractPrimary cementing is the well construction operation where drilling fluid is displaced from the annular space behind the casing string, and replaced by a cement slurry. The annular cement sheath is a critical barrier element that should provide zonal isolation along the well and prevent uncontrolled flow of formation fluids to the environment. We present a combined experimental and computational study of reverse circulation displacement of the annulus, corresponding to operations where cementing fluids are pumped down the annulus from the surface. We focus on iso-viscous displacements in a vertical and concentric annulus, and vary the density hierarchy among the fluids to study both stable and density-unstable displacement conditions. While the interface between the two fluids is advected according to the laminar annular velocity profile for density-stable and iso-dense displacements, considerable secondary flows and fluid mixing is observed for density-unstable cases. Increasing the imposed velocity from the top is seen to provide a certain stabilizing effect by suppressing backflow of the lighter fluid and reduce the magnitude of azimuthal fluctuations. Computational results are in qualitative agreement with the experiments, and support the categorization of the displacement flows as either inertial or diffusive, in accordance with previous work on buoyant pipe displacements.

Hip Surveillance and Management of Hip Displacement in Children with Cerebral Palsy: Clinical and Ethical Dilemmas

Hip displacement is the second most common musculoskeletal deformity in children with cerebral palsy. Hip surveillance programs have been implemented in many countries to detect hip displacement early when it is usually asymptomatic. The aim of hip surveillance is to monitor hip development to offer management options to slow or reverse hip displacement, and to provide the best opportunity for good hip health at skeletal maturity. The long-term goal is to avoid the sequelae of late hip dislocation which may include pain, fixed deformity, loss of function and impaired quality of life. The focus of this review is on areas of disagreement, areas where evidence is lacking, ethical dilemmas and areas for future research. There is already broad agreement on how to conduct hip surveillance, using a combination of standardised physical examination measures and radiographic examination of the hips. The frequency is dictated by the risk of hip displacement according to the child's ambulatory status. Management of both early and late hip displacement is more controversial and the evidence base in key areas is relatively weak. In this review, we summarise the recent literature on hip surveillance and highlight the management dilemmas and controversies. Better understanding of the causes of hip displacement may lead to interventions which target the pathophysiology of hip displacement and the pathological anatomy of the hip in children with cerebral palsy. We have identified the need for more effective and integrated management from early childhood to skeletal maturity. Areas for future research are highlighted and a range of ethical and management dilemmas are discussed.

Deformation analysis of buried subsea pipeline under different pressure-reverse​ fault displacement loading paths

The combined action of subsea seismic faults and pressure loads can cause pipelines to reach the limit state. Consequently, various failure modes, such as global buckling and system collapse, can occur. In this study, the deformation of a buried subsea pipeline under different pressure-reverse fault displacement loading paths is investigated using the nonlinear vector form intrinsic finite element (VFIFE). To quantify the damage to the pipeline and identify its failure modes under accidental reverse fault displacement, the loading path ‘fault displacement → internal/external pressure’ was analysed first. The post-earthquake resumption and reconditioning of unpressurised and pressurised pipelines, respectively, are evaluated based on the performance criteria in terms of strain and deformation. The corresponding loading paths are simplified as ‘ambient hydrostatic pressure → fault displacement → operation pressure’ and ‘operation pressure → fault displacement → external over pressure’. Moreover, the residual bearing capacity, weak position, and possible failure behaviour of the pipeline are comprehensively analysed for all subsequent external overpressures. The results show that the loading paths have a significant effect on structural responses, particularly on the elasto-plastic deformation. The two yield bends of a deformed pipeline under fault displacement are dangerous regions. Their inadequate relative residual strength leads to several successive local collapses and determines the occurrence and direction of buckling propagation during the subsequent external overpressure. The previous internal pressure has a significant influence on the residual capacity and failure modes of the pipeline, particularly the strain hardening effects with the influence of large seismic faults. The critical points of the first local collapse have specific characteristics, and the minimum residual resistance to external over pressure occurs when the maximum flattening parameter is 15% under initial fault displacement. The results of this study can guide the development of seismic design methodologies and engineering practice for buried subsea pipelines.

A novel, ultrafast, ultrasensitive diagnosis platform for the detection of SARS-COV-2 using restriction endonuclease-mediated reverse transcription multiple cross displacement amplification.

Coronavirus disease 2019 (COVID-19) is a highly infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-COV-2). Though many methods have been used for detecting SARS-COV-2, development of an ultrafast and highly sensitive detection strategy to screen and/or diagnose suspected cases in the population, especially early-stage patients with low viral load, is significant for the prevention and treatment of COVID-19. In this study, a novel restriction endonuclease-mediated reverse transcription multiple cross displacement amplification (MCDA) combined with real-time fluorescence analysis (rRT-MCDA) was successfully established and performed to diagnose COVID-19 infection (COVID-19 rRT-MCDA). Two sets of specific SARS-COV-2 rRT-MCDA primers targeting opening reading frame 1a/b (ORF1ab) and nucleoprotein (NP) genes were designed and modified according to the reaction mechanism. The SARS-COV-2 rRT-MCDA test was optimized and evaluated using various pathogens and clinical samples. The optimal reaction condition of SARS-COV-2 rRT-MCDA assay was 65°C for 36 min. The SARS-COV-2 rRT-MCDA limit of detection (LoD) was 6.8 copies per reaction. Meanwhile, the specificity of SARS-COV-2 rRT-MCDA assay was 100%, and there was no cross-reaction with nucleic acids of other pathogens. In addition, the whole detection process of SARS-COV-2 rRT-MCDA, containing the RNA template processing (15 min) and real-time amplification (36 min), can be accomplished within 1 h. The SARS-COV-2 rRT-MCDA test established in the current report is a novel, ultrafast, ultrasensitive, and highly specific detection method, which can be performed as a valuable screening and/or diagnostic tool for COVID-19 in clinical application.

Differential Fiber Grating Vector Flow Velocity Sensor Based on Strain Amplifying Cantilever Beam Structure

A vector flow velocity sensor with a stainless steel equal-strength cantilever beam as the elastic element and dual fiber-optic gratings as the sensitive element has been proposed and experimentally demonstrated. And it uses differential measurement to eliminate the effect of temperature. To improve the sensitivity and stress transfer efficiency, we focus on the structural design of the cantilever beam through theoretical derivation and simulation. The cantilever beam structure combines two lug bosses on both sides, a rectangular beam, and an enlarged thrust surface. Three sensors A–C with cantilever beams that are 0.3, 0.4, and 0.4 mm thick with double size, are selected for experiments. The displacement sensitivities of the three sensors at static stress tests are 1.4405, 1.6455, and 0.6662 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , respectively. For practical measurements of underwater velocity, the quadratic term coefficients of the flow velocity sensitivity fitting curves as 210.2, 48.9, and 354.6, the linear term coefficients as −6.67, +5.05, and −19.76, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}}$ </tex-math></inline-formula> as 0.9963, 0.9887, and 0.9981, have been calculated respectively. The error between the forward and reverse displacement sensitivities of sensor C is 0.404%, and its average error between the forward and reverse flow velocity measurements is 4.98%. Temperature-controlled experiments are further conducted and verify that the sensors can resist the effect of temperature. Experiments show that the sensor with large size and small thickness of cantilever beam has better velocity sensitivity. And experiment results prove that the sensors have application prospects in 3-D ocean current measurements.

Electrical Properties of Cadmium Telluride Films and the Al/CdTe Based Schottky Barrier

It is shown that with an increase in the thickness of cadmium telluride films from 0.4 to 1 μm, the resistivity decreases from 8·108 to 8,1·107 Ohm·cm. It is equivalent to an increase in conductivity from 1,25·10-9 to 1,23·10-8 Ohm-1· cm-1. The resistivity and conductivity change only slightly at thicknesses above 1 μm.&#x0D; One broad maximum is observed on the X-ray diffraction pattern at film thicknesses D=0.4 μm. This indicates the imperfection of the crystallites. As the thickness increases to 1 μm, a number of clear reflections with increasing intensity appear on the X-ray diffraction pattern, which is associated with the improvement of the crystal structure of the films.&#x0D; The current-voltage characteristic of the Schottky diode is obtained. It is shown that with an increase in the forward displacement, a significant increase in the forward current is observed, as well as a noticeable increase in the reverse current with a reverse displacement. The initial section of the forward characteristic at voltages up to 10 V is linear, which is inherent in Schottky barriers. However, the characteristic becomes non-linear at high voltages.&#x0D; The nonlinearity of the current-voltage characteristic of the Schottky barrier in a fairly wide range of applied voltage is related to the grain boundary effect in polycrystalline films. Namely, as the applied voltage increases to a certain value, the density of trap states in the region of the crystallite boundary decreases; holes begin to fill, which is usually observed in semiconductors containing conductive particles in a non-conductive matrix. We used this effect when studying the possibility of manufacturing nuclear radiation detectors with a metal — semiconductor — metal structure.

Origin of the Palos Verdes Restraining Bend and Its Implications for the 3D Geometry of the Fault and Earthquake Hazards in Los Angeles, California

ABSTRACT The Palos Verdes fault zone (PVFZ) extends across the southwestern Los Angeles basin and Inner Continental Borderland, California, and is considered capable of generating large (Mw&amp;gt;7), damaging earthquakes with short recurrence intervals. The 110 km long fault zone is composed of vertical and moderately dipping segments that accommodate oblique, right-lateral reverse displacement. Onshore, there is a counterclockwise reorientation in the PVFZ’s strike, which produces a major restraining bend that generates the Palos Verdes Peninsula. Here, we use well and seismic reflection data to develop kinematic models that show folding of the PVFZ by the Wilmington blind thrust led to formation of the restraining bend. North of the peninsula in Santa Monica Bay, debate persists over the extent, geometry, and activity of the PVFZ. Here, we analyze a dense grid of high-resolution seismic reflection data and present a new mapping of the Santa Monica Bay segment of the PVFZ, including multiple active splays (e.g., Redondo Canyon fault zone) that occur within a broad damage zone at the northern termination of the fault system. Based on these insights and prior studies, we develop a new, comprehensive 3D model of the PVFZ including its Santa Monica Bay, San Pedro Bay, and Lasuen Knoll segments. The sizes of these segments indicate that PVFZ is capable of larger events than previously reported—Mw 7.1–7.4 for single-segment ruptures and Mw 7.4–7.8 for multisegment ruptures. Based on a reported slip rate of 1.1–5.9 mm/yr, average recurrence intervals for these single- and multisegment rupture scenarios are 580–610 and 760–1170 yr, respectively.

Study on the Horizontal Bearing Characteristic of a New Type of Offshore Rubber Airbag Branch Pile

In this work, a new type of marine rubber airbag branch pile has been presented, and the influences of the exposed length L0 of the pile, size of rubber airbag branch and depth S0 of rubber airbag branch embedded in soil on the horizontal bearing capacity of the pile, have been investigated using numerical simulations. Simulation results were used to modify the eigenvalue equations of the horizontal bearing capacity. The results also showed that reverse displacement and the bending moment of the rubber airbag branch pile were lower in pipe piles with larger diameters, and the horizontal bearing capacity was more stable. At small horizontal displacements of the pile top, horizontal bearing capacities of large-diameter pipe piles were slightly higher, while for the pile’s top horizontal displacements of above 10 mm, horizontal bearing capacities of rubber airbag branch piles became significantly greater than those of the large-diameter pipe piles. Based on assumptions, the calculation equations of vacuum negative pressure and friction force between the rubber airbag branch and soil were derived. The equations for calculating the characteristic horizontal bearing capacities of rubber airbag branch piles were also derived and were modified based on simulation results. The calculation results confirmed the improvement in the accuracy of the modified equations.

A Numerical Study of Density-Unstable Reverse Circulation Displacement for Primary Cementing

Abstract Primary cementing of the casing string is the operation where the annular space behind the casing is displaced to a cement slurry. Once hardened, the cement should form a solid annular barrier and provide zonal isolation behind the casing. Reverse circulation cementing involves injecting the cement slurry directly into the annulus that is to be cemented, displacing drilling fluid down the well. This will normally represent a density-unstable situation with an increased risk of inter-mixing of fluids and slurry contamination compared to conventional circulation cementing. This study addresses the reverse circulation displacement mechanics and is based on a reverse circulation field case where the quality of the hardened cement has previously been established by characterization of two retrieved joints. We use 3D numerical simulations to study possible displacement conditions and compare findings qualitatively to the actual cement. Additional simulations indicate the importance of imposed flowrate and viscous stresses in suppressing the destabilizing effect of buoyancy. A simplified one-dimensional displacement model provides reasonable predictions of the front propagation speed in vertical, concentric annuli, and correct identification of conditions results in backflow of lighter fluid. To the best of our knowledge, this study is the first numerical study undertaken to better understand density-unstable displacements in annular geometries.