Abstract: Various embodiments disclosed relate to a fracture network model for simulating treatment of subterranean formations. In various embodiments, the present invention provides a method of simulating treatment of a subterranean formation. The method includes flowing a proppant slurry composition including proppant into each of one or more inlets of a fracture network model. The fracture network model includes a solid medium including a channel network, the one or more inlets, and one or more outlets. The channel network is free of fluidic connections leading outside of the solid medium other than the one or more inlets and the one or more outlets. The channel network includes a primary channel fluidly connected to each of the one or more inlets. The channel network also includes at least one secondary channel and fluidly connected to the primary channel, with the primary channel having a channel cross-section with a greater area than an area of a channel cross-section of the secondary channel.

Abstract: A downhole fluid separation apparatus can include multiple sections connected together with connectors, the connectors providing fluid communication between annuli in adjacent ones of the sections, and between inner conduits in adjacent ones of the sections. Each connector can include at least one flow passage providing communication between an inner conduit of each of the connected sections, and another flow passage providing communication between an annulus of each of the connected sections. A bypass valve can be included that opens in response to a predetermined differential pressure between an exterior of the apparatus and the inner conduits.

Abstract: A method of detecting a fault in an oil and gas apparatus controlled by a controller is provided. The method includes collecting a test set of data using a sensor proximate to an oil and gas apparatus during the operation of the oil and gas apparatus under test operating conditions, the test set of data being associated with an operating parameter of the controller, determining a percentage of the test set of data that falls outside a normal operation region of the oil and gas apparatus, and configuring the controller in response to the percentage being between a fault-free percentage threshold and a fault percentage threshold.

Abstract: A disclosed vibration monitoring method includes: processing sensor information downhole to detect one or more vibration modes; responsively updating a vibration mode state machine; communicating a current machine state to an uphole module; deriving from said current machine state at least a primary vibration mode and associated severity; and modifying at least one drilling parameter if the severity exceeds a threshold. A disclosed drilling system implementation includes: a drill string; a rig or other deployment device that conveys the drill string into a borehole using at least one controllable drilling parameter; one or more downhole sensors providing vibration-related signals; a downhole processor that operates on the vibration-related signals to detect one or more vibration modes and responsively updates a vibration mode state machine; and an uphole module that receives the current state from the downhole processor and derives from the current state at least a primary vibration mode and severity.

Abstract: A method of estimating properties of wellbore cement by penetrating the cement, and monitoring the amount of energy or power required for penetrating the cement. Penetrators include a drill bit that bores into the cement, and probes or pins that are forced into the cement. The energy or power monitored can be current and/or voltage supplied to a motor that drives the drill bit or probe. Comparing the monitored energy or power with that required to penetrate a reference cement sample of known properties can yield information about the cement being sampled. When the wellbore is lined with multiple coaxially disposed strings of casing with cement between adjacent strings and on the outer surface of the outer string; the method further includes obtaining core samples from portions of each string, each layer of cement, and formation adjacent the wellbore.

Abstract: A sensor system includes interconnected and axially spaced apart sensor devices deployed along an outer surface of a downhole tool string. The sensor devices including a sensor disposed with a protective housing and control electronics located remote from the sensor devices and operationally connected to the sensors.

Abstract: A method and apparatus that includes positioning a completion string that has an internal passageway and that has an external surface that at least partially defines an external region within a wellbore; isolating a zone of the external region from a wellbore hydrostatic pressure; measuring a pressure within the external region of the isolated zone; determining whether the pressure within the external region of the isolated zone is within a predetermined pressure range; and operating a valve that controls a flow of a fluid through a flow path from the internal region to the external region of the isolated zone when the pressure within the external region is outside of the predetermined pressure range.

Abstract: A technique facilitates placement of a pumping system, e.g. an electric submersible pumping system, in a borehole. The pumping system is deployed downhole into the borehole via a conveyance which may be in the form of an electric power cable for providing electric power to the pumping system. A measuring device is disposed between the conveyance and the pumping system and connects the pumping system to the conveyance. The measuring device detects engagement of the pumping system with downhole equipment by monitoring a selected property, e.g. load on the conveyance.

Abstract: A portable locator and method for establishing the location of the cable line in a region which includes at least one generally straight electrically conductive cable line extending across the region from which cable line a locating signal includes a first arrangement for measuring a local flux intensity of the locating signal at a first above ground point within the region with the portable locator in a particular orientation at the first above ground point. A second arrangement uses the local flux intensity to establish a cable line angular orientation which limits the possible directions to the cable line relative to the particular orientation of the portable locator at the above ground point. A third arrangement uses the measured local flux intensity to establish an actual direction of the cable line that is selected from the possible directions based on certain characteristics of the locating signal.

Abstract: A method and apparatus for downhole data transmission. The method comprising monitoring electrical impedance properties of a downhole formation by applying an electrical signal between a first portion and a second portion of a drill string that are electrically insulated from each other by an insulating portion, selecting a frequency for transmitting data by electromagnetic telemetry based at least in part on the monitored electrical impedance and transmitting the data by encoding the data in a waveform having the selected frequency and applying the waveform between the first portion and the second portion of the drill string.

Abstract: A method for selecting a drilling fluid pressure pulse transmission frequency in a downhole telemetry tool comprises: emitting a frequency sweep wave in a drilling fluid that comprises pressure pulses over a range of frequencies and over a period of time; measuring a pressure of the drilling fluid at the telemetry tool while the frequency sweep wave is being emitted; determining a signal strength at each frequency in the range of frequencies from the measured pressure of the drilling fluid; and selecting at least one frequency in the range of frequencies that meets a selected signal strength threshold as a telemetry signal transmission frequency for the telemetry tool.

Abstract: Examples of techniques for determining robustness of a discrete fracture network (DFN) permeability estimate are disclosed. In one example implementation according to aspects of the present disclosure, a method may include: receiving a DFN of an earth formation of interest, the DFN comprising a plurality of connected fractures; determining a directional equivalent permeability of the plurality of connected fractures of the DFN using a numerical upscaling method; and determining the robustness of the directional equivalent permeability.

Abstract: A system and method calibrate efficiency of a gas extraction system in extracting hydrocarbons from mud flowing in a drilling operation. A background reading of a hydrocarbon is extracted from the mud flowing in the drilling operation with the gas extraction system and is checked for stability. An injection operation injects a known concentration of the hydrocarbon into mud, and a subject reading of the hydrocarbon is obtained with the gas extraction system during the injection operation. A correction factor of the hydrocarbon is determined for the gas extraction system by comparing the subject reading against its corresponding known concentration. Then, at least one operational reading of the hydrocarbon extracted from the mud with the gas extraction system can be corrected using the determined correction factor.

Abstract: A bit assembly includes a base block and a bit holder having a forward body portion and a shank. The bit holder includes a diametrically expanding retainer circumferentially disposed around a shank of the bit holder adapted to maintain the interference contact between the bit holder and the base block as the diameter of a bore of the base block increases from use. The bit assembly also includes a sealing gasket that forms a force fit between a washer disposed about the shank of the bit holder and the base block.

Abstract: Methods and equipment have been developed that combine the use of continuous miners, flexible conveyor trains, and longwall mining techniques to provide flexible and efficient removal of resources from subterranean formations. Some systems include: a main gate; and a tailgate connected to the maingate by an active mine face; wherein the active mine face extends at an angle between 95° and 135° relative to the maingate.

Abstract: There is provided an excavation assembly for use in an excavator, wherein the excavation assembly is removably coupled to an arm at a pair of spaced shaft-receiving portions defined therein, wherein the excavation assembly performs an excavation operation into a ground or a rock, wherein the excavation assembly comprises: a body removably coupled at one end thereof to the pair of spaced shaft-receiving portions; a driving mechanism configured to generate at least one of a linear driving force, a rotational driving force, and a striking force; an excavation tool coupled to the driving mechanism and configured to be driven by at least one of the linear driving force, the rotational driving force, and the striking force transmitted from the driving mechanism, thereby to perform the excavating operation, wherein a direction of the excavation operation by the excavation tool varies depending on coupling positions between the pair of spaced shaft-receiving portions and the body.

Abstract: A roller bracket having a base, a raising and lowering mechanism, a platform, and horizontal and vertical rollers. The base is attached to the vertical face of a starter wall at a level to provide a desired height for a concrete ceiling. With the platform in the raised position, the bottom edge of a tunnel form is lowered between the vertical roller and the starter wall onto the horizontal rollers. A wedge is driven between the vertical roller and the tunnel form to seal the tunnel form against the starter wall. After concrete has been poured, retained by the seal, and cured to form the concrete walls and ceiling, the mechanism can lower the platform to strip the tunnel form from the tunnel. The tunnel form can then be rolled away on the horizontal rollers while being retained on the horizontal rollers by the vertical roller and the starter wall.

Abstract: A method for efficiently treating spontaneous ignition of the remaining coal in a large area goaf of a shallow-buried coal bed, which method integrates leaking stoppage, airflow control and fast inerting and cooling so as to efficiently prevent and treat the spontaneous ignition of the remaining coal in the large area goaf of the shallow-buried coal bed.

Abstract: A method for measuring load performance of a positive displacement motor (PDM) test coupon. The test coupon comprises a partial length of a PDM stage and is received inside a sealable test chamber. In some embodiments, the test coupon may be cut from a failed PDM stage. The test chamber is filled with test fluid. In some embodiments, the test fluid may be drilling fluid sampled from a live well. Rotation of the rotor on the test coupon actuates rotation of the stator. A braking torque is applied to the stator rotation, enabling evaluation of, for example, fatigue load performance of test coupon. Additional embodiments comprise the rotor axis and the stator axis being offset in order to simulate rotor/stator eccentricity in a full size PDM stage.

Abstract: Scroll fluid machine (1) in which the dislodgement of a slide bush (56) and a spring (61), which are provided in an eccentric bush (36), is prevented. Provided in receiving hole (58) of eccentric bush (36) are slide bush (56), which is movable in the direction of eccentricity, and spring (61), which biases slide bush (56) in a moving direction. A spring holding section (56b) and engagement projections (56a) are formed on slide bush (56). After slide bush (56) is placed in the receiving hole (58), engagement projections (56a) engage with eccentric bush (36) in a state in which slide bush (56) has been moved by the biasing force of spring (61), thus preventing slide bush (56) from falling off the receiving hole (58), and the spring holding section (56b) prevents the spring (61) from falling off the receiving hole (58).

Abstract: A system and method of energy conversion using a mixture of a compressible gas and an incompressible liquid. Systems found in prior art do not convert all of the potential energy. Novel features of the system increase the conversion of the potential energy with a nozzle and turbine in the area where a mixture of incompressible liquid and compressed gas are separated. A turbine is at the exit of the nozzle, where the mixture contacts that turbine. A compressed gas displaces an incompressible liquid below the exit of the nozzle and location of the turbine. Another turbine can be prior to the nozzle to further increase conversion. A novel feature of the method combines waste heat with a compressed gas to increase potential output during expansion which includes driving a liquid pump that moves the incompressible liquid. External energy in waste heat or electricity is captured, converted, or stored.

Abstract: The present disclosure is directed to a system and method for preventing damage to one or more components of the gas turbine engine during a repair procedure. The method includes locating one or more gaps of one or more components of the gas turbine engine in the vicinity of the defect. Further, the method includes filling the one or more gaps with a filler material so as to prevent arcing over the gaps during repair. Thus, the method also includes applying an electrical discharge to the defect.

Abstract: According to a feature, the present invention comprises: a housing having a power generator provided therein; a rotating body coupled to the housing so as to rotate; rotary support bars coupled to the outer peripheral surface of the rotating body so as to rotate integrally with the rotating body around the housing; resistance plates formed in a plate shape, generating resistance by means of gas or fluid, and having fixing grooves formed to be recessed inwards from one side surface thereof such that the rotary support bars are rotatably inserted therein; and an angle restricting part for rotatably coupling the resistance plates to the rotary support bars such that the range of a rotational angle of the resistance plates is restricted, the resistance plates are in a vertical state so as to generate resistance in a forward direction in which the gas or fluid moves and the resistance plates are in a horizontal state so as to prevent the resistance from being generated in a reverse direction, wherein the rotating

Abstract: A method of manufacturing a gas turbine engine component (10) and the component so formed. The method includes: stacking a plurality of CMC layers (16) along a metal core (30) to form a stack of disconnected CMC layers, wherein adjacent edge faces (46) of the layers define a surface (44); additively depositing ceramic material (14) to only selected portions of the surface (44) to bond together at least some of the layers at their respective edge faces; and selecting locations for the depositing of the ceramic material to achieve a predetermined mechanical characteristic of the resulting component.

Abstract: An airfoil having a radial direction extending away from an engine axis is provided. The airfoil includes an airfoil wall having an airfoil outer surface and an airfoil inner surface, with the airfoil extending radially from a first end to a second end. The airfoil defines a cooling channel interior to the inner surface with a thickness being defined between the airfoil outer surface and the airfoil inner surface. The thickness varies in the radial direction from the first end to the second end along at least one radial cross-section of the airfoil. A turbine nozzle of a turbine engine is also provided, which may include an outer band, an inner band, and the airfoil.

Abstract: An apparatus and method relating to a film hole of a component of a turbine engine comprising including forming the hole in the component and applying a coating to the component such that the coating fills in portions of the film hole.

Abstract: A turbine blade for a turbomachine having a turbine blade wall and a fluid channel having inlet channel section on the end region leading to the cold side, outlet channel section on the end region leading to the hot side, and central channel section therebetween having a circular cross-section constant along the length. The turbine blade forms an acute angle with the surface of the turbine blade wall over which hot gas flows, and has an intermediate channel section between the inlet and central channel sections, the intermediate channel section having a larger cross-sectional area than the central channel section. The central channel section connects to the intermediate channel section forming a shoulder surface formed on a wall region of the fluid channel and, on the opposing wall region, the intermediate and central channel sections merge with one another in a linear manner with a reduced shoulder height.

Abstract: An airfoil (10) for a gas turbine engine in which the airfoil (10) includes an internal cooling system (14) with one or more internal cavities having an insert (18) contained within an aft cooling cavity (76) to form nearwall cooling channels having enhanced flow patterns is disclosed. The flow of cooling fluids in the nearwall cooling channels may be controlled via a plurality of cooling fluid flow controllers (22) extending from the outer wall (24) forming the generally hollow elongated airfoil (26). The cooling fluid flow controllers (22) may be collected into spanwise extending rows. In at least one embodiment, the cooling fluid flow controllers (22) may be positioned within a pressure side nearwall cooling channel (48) and a suction side nearwall cooling channel (50) that are both in fluid communication with a trailing edge channel (30). The trailing edge channel (30) may also include cooling fluid flow controllers (22) extending between the outer walls (12, 13) forming the pressure and suction sides.

Abstract: An airfoil includes: an airfoil body having convex and concave sides extending between a leading edge and a trailing edge, the airfoil body including primary and secondary regions having differing physical properties; and at least one metallic cladding element attached to the airfoil body.

Abstract: A steam turbine rotor blade for forming a turbine rotor cascade of a steam turbine includes a rotor blade main body having a blade portion, a blade base portion and a first coupling portion, which has first facing surfaces, provided on opposite end sides of the blade portion, and a second coupling portion provided in an intermediate portion of the blade portion and having second facing surfaces. The steam turbine rotor blade also includes a coating layer which is made of a Co-based alloy having a single composition on a surface of at least one of the first and facing surfaces with a diffusion layer having a thickness of 10 ?m or less provided between the coating layer and the surface.

Abstract: A disc of a gas turbine engine system with particular retaining ring placement and engagement implementation are provided. For example, the disc includes a disc bore including, a groove formed on an axially extending surface of the disc bore, wherein the groove includes a forward surface that extends radially into the disc bore to a groove floor that is cut into the disc bore, and wherein the groove extends axially to an aft surface that extends radially outward to at least the axially extending surface of the disc bore, and a disc web that extends radially outward from the disc bore, relative to an axis of rotation of the gas turbine engine.

Abstract: A disc of a gas turbine engine system with particular retaining ring placement and engagement implementation are provided. For example, the disc includes a disc bore including, a groove formed on an axially extending surface of the disc bore, wherein the groove includes a forward surface that extends radially into the disc bore to a groove floor that is cut into the disc bore and extends axially to an aft surface that extends radially outward to at least the axially extending surface of the disc bore, and a scallop formed along at least one surface of the groove, wherein the scallop is configured to provide a flow path, and a disc web that extends radially outward from the disc bore, relative to an axis of rotation of the gas turbine engine.

Abstract: A disc of a gas turbine engine system is provided. The disc includes a disc bore including, an interstage coupling disposed on an axially extending surface at a peripheral edge of the disc bore that includes a protrusion that extends axially beyond an outer surface of the disc bore, and a groove formed on the axially extending surface of the disc bore wherein an aft surface of the groove is also a forward surface of the interstage coupling, wherein the groove includes a forward surface that extends radially into the disc bore to a groove floor that is cut into the disc bore and extends axially to the aft surface that extends radially outward to at least the axially extending surface of the disc bore, and a disc web that extends radially outward from the disc bore, relative to an axis of rotation of the gas turbine engine.

Abstract: According to one or more embodiments, a cover plate for a gas turbine engine is provided. The cover plate includes a cover plate body that extends from a disc blade attachment radially along an outside surface of a disc web to a disc bore of a disc creating a cavity between the cover plate body and the disc web of the disc, and an attachment protrusion extending from the inner most end of the cover plate body toward the disc bore, and wherein the attachment protrusion is configured to engage with a retention ring.

Abstract: A transition duct support apparatus and a method to support an exit frame in a transition duct in a gas turbine engine are provided. A stiffener (24) may be arranged to provide support to an outer edge (27) of an exit frame (12) in a transition duct (14). Stiffener (24) may be configured to circumferentially extend between mutually opposed corners (30) of the exit frame of the transition duct. A brace (26) may be connected to a centrally-disposed section (20) and may extend to support respective end portions (32) of the stiffener. The support apparatus is effective to provide a respective tuned level of stiffness support with respect to one or more axes of the exit frame in the transition duct. The apparatus and method may be effective for distributing mechanical stresses on the exit frame of the transition duct and/or neighboring regions in the transition duct.

Abstract: A guide vane (10, 10?) according to the invention for a guide vane ring of a turbomachine has a vane element as well as a guide vane plate (12) for its support on an inner ring (20). The guide vane plate has a cover surface (14) facing the vane element, a base surface (17) lying opposite to the cover surface, and an edge surface (15) joining the cover and base surfaces. In a first region (B1), the edge surface forms a chamfer (16) of the vane plate, and in a second region (B2), which forms the edge of a sector of the guide vane plate that is different from that of the first region (B1), the edge surface runs along a cylindrical surface. A method comprises inserting a plurality of guide vanes (10, 10?) according to the invention into respective uptakes (21) in an inner ring (20).

Abstract: A vane retainer for a gas turbine engine includes a retainer body, an inner surface of the retainer body to engage complimentary threads of a mating component, and a plurality of castellations located at an end of the retainer body for engagement with complementary installation tool features during installation of the vane retainer to the mating component. A gas turbine engine includes a combustor and a plurality of vane assemblies in fluid communication with the combustor. Each vane assembly includes a vane having an airfoil portion and a vane stem extending from the airfoil portion. The vane stem is inserted into a bushing. A vane retainer is engaged with the bushing and includes a retainer body, an inner surface of the retainer body to engage complimentary threads of the bushing, and a plurality of castellations located at an end of the retainer body for engagement with complementary installation tool features.

Abstract: An airfoil (10) for a gas turbine engine in which the airfoil (10) includes an internal cooling system (14) with one or more internal cavities (16) having an insert (18) contained therein that forms nearwall cooling channels (20) having enhanced flow patterns is disclosed. The flow of cooling fluids in the nearwall cooling channels (20) may be controlled via a plurality of cooling fluid flow controllers (22) extending from the outer wall (24) forming the generally hollow elongated airfoil (26). The cooling fluid flow controllers (22) may be collected into spanwise extending rows (28), and the internal cooling system (14) may include one or more bypass flow reducers (30) extending from the insert (18) toward the outer wall (24) to direct the cooling fluids through the channels (20) created by the cooling fluid flow controllers (22), thereby increasing the effectiveness of the internal cooling system (14).

Abstract: An ingestion restricting device is provided, which is particularly useful in a turbine engine. The ingestion restricting device can include a first component defining a first edge and including a plurality of ceramic matrix composite (CMC) plies forming outer, inner, and intermediate layers. The ingestion restricting device can also include a second component adjacent to the first component and defining a second edge. The first edge of the first component is opposite the second edge of the second component and defines a gap therebetween. Also, at least one ply of the plurality of CMC plies in the outer layer of the first component comprises an integral protrusion extending from the first edge a distance sufficient to traverse the gap and to overlap the second edge of the second component.

Abstract: A magnetic seal system adapted for use between a support structure and a rotatable shaft. The seal system includes a rotating annular seal assembly surrounding the shaft and rotating therewith, which includes an annular seal, and a non-rotating biasing assembly sealingly mounted to the support structure around the shaft and axially engaging the annular seal assembly. The biasing assembly includes an annular magnet unit axially displaceable relative to the shaft and supported surrounding the shaft. The annular magnet unit exerting an attracting force on the annular seal assembly to biasingly displace the annular magnet unit towards the annular seal. A bias member unit is also provided for non-magnetically biasing the annular magnet unit axially relative to the shaft towards the annular seal. Adjacent contacting surfaces between the annular seal and the annular magnet unit biasingly contact one another to form a sealing interface therebetween.

Abstract: A seal system includes a segmented annular seal support that has carriage arc segments arranged circumferentially in circumferential carriage joints, and a segmented annular seal that includes seal arc segments arranged end-to-end in circumferential seal joints. The circumferential seal joints are circumferentially offset from the circumferential carriage joints.

Abstract: A blades outer air seal includes a seal arc segment that defines radially inner and outer sides. The radially outer side includes radially-extending sidewalls and a radially inner surface that joins the radially-extending sidewalls. The radially-extending sidewalls and the radially inner surface define a pocket. A manifold is disposed at least partially in the pocket. The manifold subdivides the pocket such that there is a manifold chamber bounded by the manifold and the radially inner surface. The manifold includes at least one inlet and a plurality of outlets.

Abstract: A gas turbine engine includes a case disposed around a central axis, a vane structure disposed radially inwards of the case, a seal carriage mounted to the case, and a seal arc segment mounted to the seal carriage. The vane structure exerts an axial load on the seal carriage. The seal carriage defines a load path that radially transmits the axial load to the case.

Abstract: A seal assembly includes a seal arc segment that defines radially inner and outer sides and first and second axial arc segment sides, a carriage that carries the seal arc segment, and a cover that defines first and second axial cover sides. The second axial cover side is adjacent the first axial arc segment side.

Abstract: A seal arc segment includes a body including a radially inner surface and a radially outer surface. The radially inner surface and the radially outer surface are located between a first circumferential end and a second circumferential end. A recessed portion defines a cavity in the radially outer surface. A notch is located in an edge of the recessed portion adjacent the first circumferential end.

Abstract: A blade outer air seal support includes, at least one arc body having a first portion and a second portion, a blade outer air seal mounting region defined at least partially between the first portion and the second portion, and an interface feature interfacing the first portion and the second portion. The interface feature is configured such that axially aligned forces are communicated between the first and second portions through the interface feature, bypassing the blade outer air seal mounting region.

Abstract: A seal assembly includes a seal arc segment defining first and second seal supports. A carriage defines first and second support members with the first support member supporting the seal arc segment in a first ramped interface and the second support member supporting the seal arc segment in a second ramped interface such that the seal arc segment is circumferentially moveable with respect to the carriage. The seal assembly includes an anti-rotation interface in which the seal arc segment and the carriage are engaged. The anti-rotation interface restricts circumferential movement of the seal arc segment.

Abstract: A seal assembly includes a seal arc segment that defines radially inner and outer sides. The radially outer side includes radially-extending sidewalls and a radially inner surface that joins the radially-extending sidewalls, with the radially-extending sidewalls and the radially inner surface defining a pocket. A rail shield has radially-extending walls that line the radially-extending sidewalls. A spring is configured to bias the rail shield radially inward.

Abstract: A seal assembly includes a seal arc segment that defines radially inner and outer sides with the radially outer side including radially-extending sidewalls. A radially inner surface joins the radially-extending sidewalls. The radially-extending sidewalls and the radially inner surface define a pocket. A rail shield has radially-extending walls lines the radially-extending sidewalls.

Abstract: A seal assembly includes a seal arc segment that defines first and second seal supports and radially inner and outer sides with the radially outer side including radially-extending sidewalls and a radially inner surface that joins the radially-extending sidewalls. The radially-extending sidewalls and the radially inner surface define a pocket. The seal assembly includes a carriage that defines first and second support members with the first support member supporting the seal arc segment in a first ramped interface and the second support member supporting the seal arc segment in a second ramped interface. The radially inner surface has a higher surface roughness than the radially extending sidewalls.