Incipient sliding of adhesive contacts

A model is proposed herein to investigate the incipient sliding of contacts in the presence of both friction and adhesion, where the interfacial response is modeled based on traction-separation laws. A Maugis-like parameter is defined to characterize the response in the tangential direction. Subsequently, the model is used to investigate the contact between a smooth cylinder and a flat body, where adhesion-friction interactions are strong. A range of behaviors are observed when a tangential displacement is imposed: When the parameter is low, the contact pressure exhibits a relatively constant profile; when it is high, a pressure spike is observed at the edge of the contact. This difference is caused by a significant interface compliance in the former case, which limits the amount of slip. The results for the mid-range values of the Maugis-like parameter can qualitatively replicate various experiments performed using polydimethylsiloxane (PDMS) balls.

Experiments in Shock-Vortex Interactions

Studies of shock-vortex interactions in the past have predominantly been numerical, with a number of idealizations such as assuming an isolated vortex and a plane shock wave. In the present case the vortex is generated from flow separation at a corner. A shear layer results which wraps up into a spiral vortex. The flow is impulsively initiated by the diffraction of a shock wave over the edge. The strength of the shock determines the nature of the flow at the corner and that induced behind the diffracted wave. A wide variety of cases are considered using different experimental arrangements such as having two independent shock waves arriving at the corner at different times, to reflecting the diffracting wave off different surfaces back into the vortex, and to examining the flow around bends where the reflection off the far wall reflects back onto the vortex. The majority of studies have shown that the vortex normally retains its integrity after shock transit. Some studies with curved shock waves and numerous traverses have shown evidence of vortex breakup and the development of turbulent patches in the flow, as well as significant vortex stretching. Depending on the direction of approach of the shock wave it refracts through the shear layer thereby changing the strength and direction of both. Of particular note is that the two diffracted waves which emerge from the vortex as the incident wave passes through interact with each other resulting in a pressure spike of considerable magnitude. An additional spike is also identified.

The pressure spike mystery

An intuitive understanding of the pressure spike appearing in the elastohydrodynamic pressure distribution is presented. This comes from my personal memories of Professor Dowson from my first encounter with his book to my final conversation with him.

Resonance attenuation in fluid transmission through channels without the use of accumulator systems

Accumulators are often effective in reducing noise from hydraulic systems due to their pressure spike dampening effect. Their use is feasible in most cases where replacements are easy. However, certain conditions like harsh environments or sub-sea fishing make accumulator replacements extremely difficult. In line dampeners provide a very easy solution but have never been designed to cater for the resonance dampening as such. Commercially developed inline dampeners also have nitrogen filled bladders or act like and behave as accumulators, posing the same risk of rupture and replacements. This paper addresses a simplistic approach for such channels replacing the need for a bladder/bladder-less accumulator for moderate pressure high rate flow of a non-Newtonian fluid for reduced resonance. Test results show minimal back pressure from the usage of the device. The paper only addresses the resonance factor and not the usual pressure spike control that hydraulic lines suffer from where accumulators work best. Proprietary material and innovation used in the design of the dampener is not discussed here. Sound attenuation for various input levels are compared between the device made and a traditional accumulator and test results were later used in the complete development of an inline bladder-less nitrogen free resonance attenuation device that performs better than having an accumulator in the system.

Teasing Meaning Out of a Tangle of Fracturing Data

The snarled red lines on the chart look more like a plate of spaghetti than a source of fracturing insights. It looks like a meaningless mess, which is generally how the ups and downs of difficult stages are viewed. To Adam Hoffman, a completion engineer for Chesapeake Energy, those 47-stages-worth of data look like a valuable opportunity. “We see so many stages with so many odd spikes and drops or chatter. We chop it off and say that was an odd stage. In my mind when we are looking at all those stages, we should wonder, ‘what was that pressure spike telling us,’” he said. That curiosity became a research project after Chesapeake encountered a spate of blockages in recently fractured Eagle Ford wells. The investigation into the cause of the casing damage led to a collaboration with Well Data Labs to look for connections between pressure changes and what is happening in the wells. Based on hundreds of stages of data from 19 wells fractured in the Eagle Ford, and later in the Powder River Basin, they reported finding a distinctive pressure signature that provides a reliable, but not foolproof, guide to when casing damage is likely. Well Data Labs has automated the search for those signatures as it looks for the meaning of the terabytes of fracturing data in this overwhelming number of seemingly random, squiggly lines. The oilfield data and software company is working on ways to monitor changes in the fracturing-fluid chemistry, the proppant intake into perforations, and an explanation for the pressure spikes seen before the pressure falls, said Jessica Iriarte, research manager at Well Data Labs. The troubleshooting and pressure analysis were covered in paper SPE 201484 presented at the 2020 SPE Annual Technical Conference and Exhibition (ATCE). It described how engineering trouble-shooting revealed that geological stresses were the likely source of problems in one case, and faulty pipe in the other. It followed up with data analysis, which used machine learning to identify distinctive patterns that provide an early warning of what is happening in the well faster and more objectively than a completion engineer studying the chart. Based on the troubleshooting, Chesapeake made changes that largely eliminated those costly problems. But it was also a costly learning process. In the Eagle Ford, they identified the underlying problem by investigating why multiple coiled-tubing runs were blocked while they were trying to drill out plugs after fracturing. When that happens, Hoffman said, “it can mean a week lost working past it.” Failure to drill out a plug can block access to the productive rock further down the lateral. A reliable automated treating-pressure analysis in the daily report could alert the completion team to problems while fracturing is in progress. They could then make adjustments on later stages and create a plan to limit the time lost when drilling out plugs on stages where they are likely to encounter tight sections.

Placement of dual capsular tension rings for the combined management of traumatic cyclodialysis cleft and zonular dialysis

Background To evaluate the efficacy and safety of placing dual capsular tension rings for the combined management of traumatic cyclodialysis cleft and zonular dialysis. Methods A modified capsular tension ring was inserted into the ciliary sulcus and a capsular tension ring or modified capsular tension ring was inserted into the capsular bag in 20 eyes in 20 consecutive patients showing signs of ocular hypotony and ectopia lentis. Outcome measures included intraocular pressure, best-corrected visual acuity, and postoperative complications. Results Dual capsular tension ring placement was performed in 20 patients with a mean age of 48.7 years. The cyclodialysis cleft extended over 2.9 clock hours (range 0.5–6.5). The modified capsular tension ring was successfully inserted into the ciliary sulcus and a capsular tension ring or modified capsular tension ring in the capsular bag in all eyes. At the last follow-up, the cyclodialysis cleft was closed in 16/20 (80.0%) eyes. The intraocular lens was stable in all patients postoperatively. Best-corrected visual acuity, in terms of the logarithm of the minimal angle of resolution, improved from 1.3 ± 0.8 before surgery to 0.4 ± 0.3 after surgery (P < 0.001). Intraocular pressure increased significantly from 10.6 ± 3.2 mmHg before surgery to 13.0 ± 4.8 mmHg after surgery (P = 0.040). Postoperative complications included a painful reversible intraocular pressure spike in four patients (20.0%). Logistic regression revealed no significant factors associated with successful cleft closure and a stable final intraocular pressure of ≥ 10 mmHg. Conclusions The placement of two capsular tension rings into the ciliary sulcus and the capsular bag is a safe, successful procedure combined for repairing a traumatic cyclodialysis cleft and managing zonular dialysis.

Integrity Validation of Small Diameter-Thin Wall Pipeline Susceptible to Cracking or Crack-Like Indications: A Case Study

The integrity validation of small diameter, thin wall pipelines can be challenging. In-line inspection tool limitations for diameters below approximately 4.5-inch contribute significantly to this challenge. This paper will describe experiences related to the successful integrity validation of a 3-inch vintage high vapour pressure (propane) pipeline which was susceptible to external cracking as well as crack-like indications at the seam weld (e.g. hook cracks and lack of fusion). This line pipe was manufactured in 1967 with a low frequency electric resistance welding (ERW) process. The major threat was identified to be external corrosion since external metal loss up to 70% of the wall thickness was reported by in-line inspection (ILI). The cut-out samples obtained from integrity digs following the ILI were examined by magnetic particle inspection methods. Some external features on these cut-out samples were reported as cracks. The pipeline licensee involved Skystone to complete an engineering assessment and provide a short-term and long-term integrity plan to validate the integrity of the pipeline for continued service. The cut-out samples were re-examined. This examination included cross-sectional metallography of the area suspected to contain crack-like indications. No external cracking was identified; however, crack-like indications such as lack of fusion were found on the ERW seam. A pressure-spike test was designed as an integrity validation technique and completed successfully. This paper reviews the difference between the pressure-spike test and conventional pressure tests, the technical basis for the pressure-spike test, its limitations, and practical considerations that need to be considered. The regulatory recognition of spike testing as well as available recommended practices that refer to this approach will be discussed. A long-term integrity plan was developed by establishing an interval for the next pressure-spike test using fatigue life estimation.

Use of micropulse trans-scleral cyclophotocoagulation for acute rise in intraocular pressure due to anterior segment inflammation

Purpose The aim of this study was to report the use of micropulse trans-scleral cyclophotocoagulation as an adjunct therapy for two cases of medically uncontrolled intraocular pressure spikes due to anterior segment inflammation. Case description: Case 1 had previous cataract surgery and exhibited an intraocular pressure spike due to phacoantigenic uveitis (right eye intraocular pressure = 52 mmHg). Despite medical treatment, the right eye intraocular pressure remained high (43 mmHg), thus micropulse trans-scleral cyclophotocoagulation was carried out as a rescue therapy. After micropulse trans-scleral cyclophotocoagulation, the intraocular pressure at 1 day and 3 weeks was 9 and 16 mmHg, respectively. Case 2 had a history of previous blunt ocular trauma and 180° of angle recession. Both eyes were pseudophakia and underwent right eye Nd:YAG laser capsulotomy for posterior capsular opacification. Immediately after the procedure, the right eye intraocular pressure increased to 64 mmHg. Due to poor response to medical therapy, rescue micropulse trans-scleral cyclophotocoagulation was performed. After micropulse trans-scleral cyclophotocoagulation, the intraocular pressure at 1 day and 2 months was 12 and 21 mmHg, respectively. Conclusion Micropulse trans-scleral cyclophotocoagulation successfully decreased intraocular pressure in both cases of acute rise in intraocular pressure. Micropulse trans-scleral cyclophotocoagulation can potentially be useful as a rescue procedure to safely reduce medically uncontrollable intraocular pressure spike due to anterior segment inflammation.

Early transient intraocular pressure spike after cataract surgery in highly myopic cataract eyes and associated risk factors

PurposeTo investigate the incidence of the early transient intraocular pressure (IOP) spike after cataract surgery in eyes with highly myopic cataract (HMC) and associated risk factors.MethodsConsecutive patients treated with phacoemulsification were recruited. IOP was measured before and 1 day, 3 days, 1 week and 3 months after surgery. Axial length (AL) and anterior chamber depth (ACD) were recorded, and optic disc tilt, rotation and beta-zone peripapillary atrophy (β-PPA) were measured from fundus photographs taken 1 week after surgery. Backward stepwise multiple linear regression was used to investigate the risk factors for early transient IOP spike in the HMC group.ResultsFinally, 94 eyes of 94 HMC patients and 67 eyes of 67 age-related cataract (ARC) controls were included in analysis. The incidence of early IOP spike was 10% in the ARC group and 28% in the HMC group (OR=3.277, p<0.05) at 1 day after surgery. In the HMC group with IOP spikes, more males were seen and affected eyes showed longer AL, shallower ACD, greater optic disc tilt, and larger β-PPA than those without (all p<0.05). Multivariate analysis showed that sex, AL, ACD, and area of β-PPA were significantly associated with an early transient IOP spike in HMC eyes (all p<0.05).ConclusionsHighly myopic eyes are more susceptible to early transient IOP spike after cataract surgery, and male sex, longer AL, shallower ACD, and greater β-PPA are associated risk factors.Clinical trial registration numberNCT02182921.