Search results for "drilling"
showing 10 items of 88 documents
Stable isotopic composition of three foraminifera species in ODP Hole 160-963D
2020
Carbon-rich layers exist at both sides of the Mediterranean Sea sedimentary record and are called sapropels and organic rich layers (ORLs), respectively in the eastern and western basins. They have different levels of organic carbon accumulation and seafloor oxygen deprivation. The most recent sapropel and ORL deposition have a different timing, 10.8-6.1 and 14.5-9.0 ka respectively. Here we investigate oxygen isotopic records of three foraminifera species that occupy different habitats within the Sicily Channel water column since ~ 12.0 ka, thus in the sill between the eastern and western Mediterranean basins. These data are ice volume-corrected, to get information on water masses density …
Adaptive control of a drilling system with unknown time-delay and disturbance
2016
In this paper, we address adaptive predictor feedback design for a simplified drilling system in the presence of disturbance and time-delay. The main objective is to stabilize the bottomhole pressure at a critical depth at a desired set-point directly. The stabilization of the dynamic system and the asymptotic tracking are demonstrated by the proposed adaptive control, where the adaptation employs Lyapunov update law design with normalization. The proposed method is evaluated using a high fidelity drilling simulator and cases from a North Sea drilling operation are simulated. The results show that the proposed predictor controller is effective to stabilize the bottom hole pressure within th…
Drilling dimension effects in early stages of osseointegration and implant stability in a canine model
2015
Background: This study histologically evaluated two implant designs: a classic thread design versus another specifically designed for healing chamber formation placed with two drilling protocols. Material and Methods: Forty dental implants (4.1 mm diameter) with two different macrogeometries were inserted in the tibia of 10 Beagle dogs, and maximum insertion torque was recorded. Drilling techniques were: until 3.75 mm (regular-group); and until 4.0 mm diameter (overdrilling-group) for both implant designs. At 2 and 4 weeks, samples were retrieved and processed for histomorphometric analysis. For torque and BIC (bone-to-implant contact) and BAFO (bone area fraction occupied), a general-linea…
Biomechanical evaluation of oversized drilling technique on primary implant stability measured by insertion torque and resonance frequency analysis
2015
Background This study evaluated the influence of implant site preparation depth on primary stability measured by insertion torque and resonance frequency analysis (RFA). Material and Methods Thirty-two implant sites were prepared in eight veal rib blocks. Sixteen sites were prepared using the conventional drilling sequence recommended by the manufacturer to a working depth of 10mm. The remaining 16 sites were prepared using an oversize drilling technique (overpreparation) to a working depth of 12mm. Bone density was determined using cone beam computerized tomography (CBCT). The implants were placed and primary stability was measured by two methods: insertion torque (Ncm), and RFA (implant s…
The Shielding Effect of Drilling Fluids on MWD Downhole Compasses: The Effect of Drilling Fluid Composition, Contaminants and Rheology
2014
Materials such as added clays, weight materials, drill solids and metalic wear products in the drilling fluid are known to distort the geomagnetic field at the location of the Measurement While Drilling (MWD) tool magnetometers that are used to measure the direction of well path. This distortion contributes to substantial errors in determination of azimuth while drilling deviated wells. These errors may result in missing the target of a long deviated 12 ¼″ section in the range of 1–200m; representing a significant cost to be mitigated. The error becomes even more pronounced if drilling occurs in arctic regions close to the magnetic North Pole (or South Pole). The effect on the magnetometer …
The Shielding Effect of Drilling Fluids on Measurement While Drilling Tool Downhole Compasses—The Effect of Drilling Fluid Composition, Contaminants,…
2016
Materials such as added clays, weight materials, drill solids, and metallic wear products in the drilling fluid are known to distort the geomagnetic field at the location of the measurement while drilling (MWD) tool magnetometers that are used to measure the direction of well path. This distortion contributes to substantial errors in determination of azimuth while drilling deviated wells. These errors may result in missing the target of a long deviated 12 ¼ in. section in the range of 1–200 m, representing a significant cost to be mitigated. The error becomes even more pronounced if drilling occurs in arctic regions close to the magnetic north pole (or south pole). The effect on the magneto…
Effects of the indentation process on fatigue life of drilled specimens: optimization of the distance between adjacent holes
2016
The generation of permanent compressive stresses around the holes is recognized as a valuable mean to delay the onset and propagation of the defects and to extend the fatigue life of the mechanical components. In the work, a bilateral indentation process, performed on each side of the component, is widely used in order to create a residual circumferential stress field around the area to be drilled and that persists after the drilling operation. In order to evaluate the process parameters and to identify optimal geometric solutions, several static and fatigue tests are conducted on AW 6082-T6 aluminum alloy specimen where two holes are created. In particular, experimental tests on only drill…
Orthogonal and Oblique Cutting Mechanics
2008
This chapter provides the engineering knowledge and modelling techniques applied in description of the material behaviour in the cutting zone resulting in chip formation and its separation from the bulk material. Geometrical and kinematical characteristics of orthogonal and oblique cutting models are classified and specified. Forces acting on the cutting tools and their measurement methods for several machining operations, such as turning, milling, drilling, boring and grooving, are presented. Moreover, forces acting in the cutting zone and their resolution on the shear plane and the rake and flank faces, along with stress distributions, are presented. The chapter highlights how components …
Holocene climate variability of the Western Mediterranean: Surface water dynamics inferred from calcareous plankton assemblages
2020
A high-resolution study (centennial scale) has been performed on the calcareous plankton assemblage of the Holocene portion of the Ocean Drilling Program Site 976 (Alboran Sea) with the aim to identify the main changes in the surface water dynamic. The dataset also provided a seasonal foraminiferal sea surface water temperatures (SSTs), estimated using the modern analog technique SIMMAX 28, and it was compared with available geochemical and pollen data at the site. Three main climate shifts were identified as (1) the increase in abundance of Syracosphaera spp. and Turborotalita quinqueloba marks the early Holocene humid phase, during maximum summer insolation and enhanced river runoff. It i…
Drilling predation on Gryphus vitreus (Brachiopoda) off the French Mediterranean coasts
2004
Abstract A total of 145 valves of Gryphus vitreus with naticid drillholes have been recorded from samples during 21 cruises in the Northwestern Mediterranean, out of about 30,000 empty valves. Drilling was lower than 1% in all stations, except in one station where it reached up to 25.5%. Selectivity of drillhole site by the naticid Euspirella pulchella seems to apply in G. vitreus as drillholes are mainly concentrated in the relatively meaty distal half of the shell, which is also the thickest part of the valve (about 0.6–2 mm). Attacks occur generally on the ventral valve (86.2%) according to the life position of Gryphus. The predation pressure on G. vitreus by drilling appears exceptional…