Abstract: Disclosed are methods for transmitting data to a downhole tool. The methods include the option of confirming receipt and implementation of the transmitted data by the downhole tool. The disclosed methods utilize changes in RPM of the tool to convey the data through three separate changes in RPM. The changes in RPM are used to generate pulses suitable for identifying preprogrammed actions found within the memory of the downhole tool.

Abstract: A system for determining annulus fluid volume in a well bore during a drilling operation, the system having a pressure wave generator positioned at the top of a well, wherein the pressure wave generator generates a pressure wave that propagates through the annulus fluid in the well; a first pressure wave receiver positioned in the annulus of the well to receive the generated pressure wave at a first time value; a second pressure wave receiver positioned in the annulus of the well to receive the generated pressure wave at a second time value; and a controller that determines a change in annulus fluid volume based at least in part on a phase shift between the received pressure wave at the first and second time values.

Abstract: Systems and methods for active ranging-while-drilling (ARWD) for collision avoidance and/or well interception. A method for electromagnetic ranging of a target wellbore may comprise disposing a downhole measurement tool into a wellbore, wherein the downhole measurement tool may comprise receivers comprising at least one radially spaced pair of the receivers and at least one axially spaced pair of the receivers; performing field measurements with the receivers, where a first set of field measurements are from at least one radially spaced pair of the receivers, and a second set of field measurements are from at least one axially spaced pair of the receivers; and calculating at least one target well parameter of a target well from at least one of the first set of field measurements and the second set of field measurements.

Abstract: Reservoir sweep efficiency includes obtaining fluid front arrival times for streamlines in a reservoir. A wellbore is partitioned into independent production zones, and a target flowrate is allocated to each of the independent production zones based on the fluid front arrival times. Partition choke parameters complying with the target flowrates are allocated to generate a completion design, which is presented.

Abstract: A monitoring well installation comprising metallic casing (2) running down from the surface into a borehole and a sealing material plug (6) provided downhole for blocking the interior of the casing and sealing the borehole against the egress of fluid from a zone below the plug. There is an axial spacing (2A) between adjacent casing portions (2) in the region of the plug (6) such that there is an uncased length of borehole in which the material of the plug seals against the formation. There is provided a sensing tool (3) located below the plug (6) for sensing at least one parameter below the plug (6) and a communication arrangement (3, 4, 5) for use in transmitting data from the sensing tool (3) towards the surface. The communication arrangement comprises across plug communication apparatus (5) for facilitating transmission of signals carrying data across the plug (6) towards the surface.

Abstract: A distributed acoustic sensor is positioned within a wellbore of a geologic formation. Seismic waves are detected using the distributed acoustic sensor. A raw seismic profile is generated based on the detected seismic waves. Resonant noise is identified and reduced in seismic data associated with the raw seismic profile.

Abstract: A method of determining maximum stress in a well drilled in a reservoir, primarily a hydrocarbon reservoir, where there is at least one zone. Collapse regions are produced while drilling a well because the material of the wall of the well exceeds its maximum allowable stress, the material fractures and falls off, leaving a cavity. The caliper of the damaged zone is measured by devices that extend radially until coming into contact with the physical wall of the well. The disclosed method determines the maximum allowable stress based on the caliper measurements and other variables which are determinable.

Abstract: A Polycrystalline Diamond Compact (PDC) cutter for a rotary drill bit is provided with an integrated sensor and circuitry for making measurements of a property of a fluid in the borehole and/or an operating condition of the drill bit. A method of manufacture of the PDC cutter and the rotary drill bit is discussed.

Abstract: Techniques for determining geologic formation permeability include determining particular permeability values from an NMR log permeability data and particular permeability values of the core permeability measurements; determining a selected NMR permeability transform that includes inputs including the determined particular permeability values; minimizing a cost function to optimize the selected NMR permeability transform; calculating new permeability values for the wellbore between the terranean surface and a true vertical depth of the wellbore with the optimized NMR permeability transform; comparing the calculated new permeability values at particular depths between the terranean surface and the true vertical depth that match depths of the core permeability measurements; based on the comparison meeting a particular threshold, generating a user interface that renders one or more graphical representations of the optimized NMR permeability transform and the calculated new permeability values; and transmitting d

Abstract: A physical simulation test method for detecting a position of a ponding goaf in the excavation, which relates to physical detection of mines. This method includes: fabricating an experimental model of a composition similar to that of an excavating tunnel; fabricating a transient transmitting coil and receiving coil; connecting the coil to a wire and placing them in model A; connecting the coil to a transient electromagnetometer; injecting water into a trapezoidal goaf through a pre-buried plastic pipe; after the goaf is filled with water, immediately switching the transient electromagnetometer on to collect data; respectively transferring the coil to models B, C and D, injecting water and switching on the transient electromagnetometer to collect data; statistically analyzing detection and imaging results of the four models; and comparing the detection results with the actual data to determine detection accuracy and correction coefficient.

Abstract: The invention discloses a retrievable sand consolidation anchor head prestressed anchor rod, an anchoring jack and an application method thereof, and belongs to the technical field of geotechnical engineering. The retrievable sand-consolidated anchor head pre-stressed anchor includes a bolt body 6, a rigid frame 5, a load member 1, a sand column 2, a pressure receiving member 4, a cut-off member 3, and an anchor pier 8. The anchoring jack includes a force transmitting frame 12, a first guiding plate 25, a second guiding plate 28, and a housing 13. The application method includes an anchoring method using the retrievable sand-consolidated anchor head prestressed anchor rod and a method of recovering the retrievable sand-consolidated anchor head pre-stressed anchor rod. After the anchoring of the reclaimed sand-consolidated anchor head pre-stressed anchor rod, the bolt body can be recovered and reused, and the operation is simpler and more environmentally friendly.

Abstract: A process for repairing an aircraft engine component includes receiving a plurality of component measurements of a damaged component, comparing the plurality of component measurements of the damaged component to a finite element model of an ideal component, generating a finite element model of the damaged component based at least partially on the comparison, determining a corrective material removal operation based at least in part on the finite element model of the damaged component, and removing material from the damaged component according to the corrective material removal operation, thereby creating a repaired component.

Abstract: An axial flow turbomachine (102) for producing thrust to propel an aircraft is shown. The turbomachine has an inner duct (202) and an outer duct (204), both of which are annular and concentric with one another. An inner fan (206) is located in the inner duct, and is configured to produce a primary pressurised flow (P). An outer fan (207) is located in an outer duct, and is configured to produce a secondary pressurised flow (S). The outer fan has a hollow hub (208) through which the inner duct passes. The inner fan is configured to have, in operation, a rate of rotation of from 3 to 8 times that of the outer fan.

Abstract: The disclosure provides a blade with an airfoil including: a root region at a first radial end; a tip region at a second radial end opposite the first radial end; and a midspan region between the root region and the tip region and at least one endwall connected with the root region or the tip region of the airfoil along the suction side, the pressure side, the trailing edge and the leading edge, wherein the midspan region includes a reduced axial width relative to an axial width of the root region and an axial width of the tip region, and a reduced opening-to-pitch ratio at the midspan region relative to the root and tip regions.

Abstract: A gas turbine engine according to an example of the present disclosure includes, among other things, a fan section having a fan including a rotor hub rotatable about an engine longitudinal axis and an array of fan blades, a geared architecture, a compressor section including a low pressure compressor and a high pressure compressor, a turbine section including a low pressure turbine and a high pressure turbine. The low pressure turbine drives the fan through the geared architecture. Each fan blade of the array of fan blades includes pressure and suction sides and extending in a radial direction from a 0% span position at an inner flow path location to a 100% span position at an airfoil tip, and facing pressure and suction sides of adjacent fan blades define a channel in a chordwise direction having a width between the facing pressure and suction sides at a given span position of the adjacent fan blades.

Abstract: A system is provided, including an airfoil. The airfoil includes a first suction portion of a nominal airfoil profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of a suction side as set forth in TABLE I to a maximum of three decimal places, wherein the X and Y values of the suction side are coordinate values that couple together to define suction side sections of the first suction portion of the nominal airfoil profile at each Z coordinate value, the suction side sections of the first suction portion of the nominal airfoil profile are coupled together to define the first suction portion, the airfoil includes an airfoil length along a Z axis, the first suction portion comprises a first portion length along the Z axis, the first portion length is less than or equal to the airfoil length, and the Cartesian coordinate values of X, Y, and Z are non-dimensional values convertible to dimensional distances.

Abstract: A system is provided, including an airfoil. The airfoil includes a first suction portion of a nominal airfoil profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of a suction side as set forth in TABLE I to a maximum of three decimal places, wherein the X and Y values of the suction side are coordinate values that couple together to define suction side sections of the first suction portion of the nominal airfoil profile at each Z coordinate value, the suction side sections of the first suction portion of the nominal airfoil profile are coupled together to define the first suction portion, the airfoil includes an airfoil length along a Z axis, the first suction portion comprises a first portion length along the Z axis, the first portion length is less than or equal to the airfoil length, and the Cartesian coordinate values of X, Y, and Z are non-dimensional values convertible to dimensional distances.

Abstract: A system is provided, including an airfoil. The airfoil includes a first suction portion of a nominal airfoil profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of a suction side as set forth in TABLE I to a maximum of three decimal places, wherein the X and Y values of the suction side are coordinate values that couple together to define suction side sections of the first suction portion of the nominal airfoil profile at each Z coordinate value, the suction side sections of the first suction portion of the nominal airfoil profile are coupled together to define the first suction portion, the airfoil includes an airfoil length along a Z axis, the first suction portion comprises a first portion length along the Z axis, the first portion length is less than or equal to the airfoil length, and the Cartesian coordinate values of X, Y, and Z are non-dimensional values convertible to dimensional distances.

Abstract: A turbine machine blade has an aerodynamic surface that is made of organic matrix composite material reinforced by fibers and metal structural reinforcement that is adhesively bonded by an epoxy adhesive bond on the leading edge, which is of matching shape, and that presents along its entire height a section that is substantially V-shaped with a base extended by two lateral flanks of respective profiles that become thinner at free ends going towards the trailing edge. In order to increase the toughness of the epoxy adhesive bond in the event of the epoxy adhesive bond cracking, the epoxy adhesive bond includes a reinforcing sheet of elastomeric polymer enabling the reinforcing sheet to be torn into two portions, the elastomeric polymer having the following properties at 23° C.: Young's modulus E?10 MPa; stress at rupture ?r>10 MPa; strain at rupture ?r>80%.

Abstract: An edge guard apparatus for an airfoil includes: a body having a nose section with spaced-apart first and second sidewalls extending therefrom, the body defining a cavity between the first and second sidewalls; and internal bracing disposed in the cavity, the internal bracing including at least one cross-member extending between the first and second sidewalls.

Abstract: A turbine blade is provided. The turbine blade may include a blade body including a leading edge, a trailing edge, a suction side, a pressure side, and a tip region, a squealer tip extending upward from the tip region of the blade body, a winglet extending outward from the squealer tip on the suction side of the blade body, and a cooling hole obliquely formed through the winglet to communicate with an inner cavity of the blade body.

Abstract: An airfoil for a gas turbine engine is provided that includes a first portion formed from a first plurality of plies of a ceramic matrix composite material and defining an inner surface of the airfoil, as well as a second portion formed from a second plurality of plies of a ceramic matrix composite material and defining an outer surface of the airfoil. The first portion and the second portion define a non-line of sight cooling aperture extending from the inner surface to the outer surface of the airfoil. In one embodiment, a surface angle that is less than 45° is defined between a second aperture and the outer surface. A method for forming an airfoil for a gas turbine engine also is provided.

Abstract: A platform for an airfoil of a gas turbine engine having an axis extending from a front of the gas turbine engine to a rear of the gas turbine engine. The platform includes a leading edge configured to face towards the front of the gas turbine engine. The platform further includes a trailing edge opposite the leading edge. The platform further includes a radially outer surface that defines a pocket for receiving a cooling airflow. The platform further includes a cover coupled to the radially outer surface to at least partially enclose the pocket and defining a plurality of air inlet holes configured to port at least a portion of the cooling airflow into the pocket.

Abstract: A blade body of a turbine blade, which defines an interior cavity fluidly communicative with coolant, is provided. The blade body includes an interior surface and one or more pins extending from the interior surface. The interior surface and the one or more pins are disposable to thermally interact with the coolant. At least one of the one or more pins includes a first section and a second section interposed between the first section and the interior surface. The first section has a larger cross-sectional area than the second section.

Abstract: A turbine blade is provided. The turbine blade may include: a cooling passage configured to be defined by a partition wall which partitions an internal area of the turbine blade; and an inlet passage extending from a root part of the turbine blade toward a platform part of the turbine blade and configured to supply cooling air into the cooling passage, wherein an inclined part having a diameter reduced from the root part toward the platform part is formed in the inlet passage.

Abstract: A method of forming an airfoil, includes forming a hybrid skin core, a tip flag core, and a trailing edge core. The hybrid skin core, tip flag core, and trailing edge core are connected to form a first core portion. A leading edge core and a serpentine core are formed. The first core portion, the leading edge core, and the serpentine core are assembled together to form an airfoil core. An airfoil is formed around the airfoil core.

Abstract: A turbine wheel assembly adapted for use in a gas turbine engine includes turbine blades made from ceramic matric composite materials. The turbine blades are mounted to a disk and anti-rotation features block movement of the turbine blades around a circumference of the disk.

Abstract: A coated gas turbine engine part includes a substrate and a calcium-magnesium-alumino-silicate CMAS protection layer present on the substrate. The layer includes a first phase of a calcium-magnesium-alumino-silicate CMAS protection material and a second phase including particles of an anti-wetting material dispersed in the first phase.

Abstract: An assembly for use in an attritable engine includes a hub and a blade. The hub is configured to rotate about a centerline axis passing through a center of the hub and is formed with a first type of layer-by-layer additive manufacturing process. The blade is connected to and extends radially outward from the hub. The blade is formed with a second type of layer-by-layer additive manufacturing process that is different than the first layer-by-layer additive manufacturing process. The hub and the blade are integrally formed together as a single piece of material with a layer-by-layer additive manufacturing process. The blade includes a root of a first material, a platform connected to the root, an airfoil connected to and extending from the platform, and a tip connected on a distal end of the airfoil opposite from the root. The platform includes a material that is different from the first.

Abstract: An outer seal structure for a rotor assembly includes a stator structure and a non-contact seal assembly. The non-contact seal assembly is fixed relative to the stator structure and includes a plurality of seal shoes, a seal base, a plurality of spring elements, and a shoe support plate. The plurality of seal shoes are arranged about an axis in an annular array. The seal base circumscribes the annular array of the plurality of seal shoes. Each of the plurality of spring elements extend radially between a respective seal shoe of the plurality of seal shoes and the seal base. The shoe support plate is arranged about the axis and mounted to the stator structure and includes a plurality of shoe support tabs extending axially from the shoe support plate. Each shoe support tab of the plurality of shoe support tabs is disposed between each seal shoe.

Abstract: A seal arrangement may comprise a seal comprising an outer ring, a shoe, and an arm extending between the shoe and the outer ring, wherein the shoe moves relative to the outer ring via the arm, a seal ring adjacent the seal, and a support plate disposed between the seal and the seal ring, wherein the support plate moves together with the shoe in a radial direction relative to the seal ring.

Abstract: An air seal for a jet turbine engine with an upper stator, lower stator and finned turbine disk. The thermal expansion of the stators may be regulated by a control ring, which has a lower rate of thermal expansion that the stators, to prevent rubbing between the stator and fins.

Abstract: A blade outer air seal according to an exemplary aspect of the present disclosure includes, among other things, a body to be distributed circumferentially about a blade array. The body has a plurality of grooves, which can, for example, improve the aerodynamic efficiency of a turbine. A fin is between a first groove and a second groove of the plurality of grooves. The fin extends radially from the body and terminates at a radially inner fin face that provides one or more cooling outlets. A sacrificial structure for forming internal cooling passages within a blade outer air seal and a method of cooling an interface between a blade outer air seal and a rotating blade array is also disclosed.

Abstract: A gas turbine engine includes a turbine section that is configured to drive a fan through a fan shaft. The fan includes a plurality of fan blades rotatable about an axis of rotation of the gas turbine engine. A fan nacelle includes a first electrical machine component. The fan is located within the fan nacelle. A plurality of fan inlet guide vanes includes a second electrical machine component. The plurality of fan inlet guide vanes are rotatable about the axis.

Abstract: A service apparatus for use in maintaining a turbine assembly (100) includes a carriage (132, 304) configured to move through a cavity of the turbine assembly (100), a motorized system (218, 500, 600, 700, 800) coupled to the carriage (132, 304), and a maintenance device (128, 400) coupled to the motorized system (218, 500, 600, 700, 800). The motorized system (218, 500, 600, 700, 800) is configured to move the maintenance device (128, 400) relative to the carriage (132, 304). The motorized system (218, 500, 600, 700, 800) includes a first motor (710, 720, 805) configured to move the maintenance device (128, 400) in a first direction (324) and a second motor (710, 720, 805) configured to move the maintenance device (128, 400) in a second direction (324).

Abstract: Methods and systems for diagnosing a condition of an engine based on lubrication fluid analysis are disclosed. One embodiment of the methods comprises: receiving input data representative of a respective geometric parameter and a respective chemical composition for a plurality of particles filtered from a sample of fluid obtained from the engine; generating data representative of a mass of material of a chemical composition category in one or more of the particles; comparing the mass of material of the chemical composition category with reference data; and generating output data representative of a diagnosis of the condition of the engine.

Abstract: A blade for a propulsion apparatus that includes a body formed of a first material having opposed pressure and suction sides, and extending in span between a root and a boundary, and extending in chord between a leading edge and a trailing edge. A tip region that is formed of a second material and that is positioned such that it extends from the body and defines a tip. The tip region joins the body at the boundary. The tip region is configured to fail when a predetermined force is applied to the tip such that the tip separates from the blade and defines a fused tip.

Abstract: A blade for a propulsion apparatus. The blade includes a body having opposed pressure and suction sides. The blade extends in span between a root and a tip and the blade extends in chord between a leading edge and a trailing edge. The blade includes a fracture structure that is defined within the body and positioned such that it is spaced-away from the tip. The fracture structure includes at least one chamber. A first fracture wall is disposed between the at least one chamber and the pressure side, and a second fracture wall is disposed between the at least one chamber and the suction side. The fracture structure is configured to fail when a predetermined force is applied to the tip such that the tip separates from the remainder of the body.

Abstract: A system is presented for directing the flow of cooling fluid in a rotational machine having co-axial rotatable shafts. The system comprises a first shaft rotatable about an axis, a second shaft rotatable about the axis and having a portion axially overlapping with the first shaft, and a fluid catcher. The fluid catcher is coupled between the first shaft and the second shaft. The fluid catcher comprises a first interface region interfacing with the first shaft, a second interface region interfacing with the second shaft, a fluid retention lip at least partly defining an oil capture region; and a body. The body is coupled to the oil retention lip and defines a channel in fluid communication with the oil capture region. The channel is positioned to direct fluid to one of the first interface region or the second interface region.

Abstract: An emissions reduction system for a combined cycle power plant having a gas turbine engine and a heat recovery steam generator (HRSG) can comprise a duct defining a flow space configured to receive exhaust gas from the gas turbine and convey the exhaust gas into the HRSG, and a louver system coupled to the duct that can comprise a plurality of emission medium panels extending across the flow space, the emission medium panels configured to be moved between a first position where adjacent filter medium panels extend contiguously across the flow space of the duct and a second position where adjacent filter medium panels include spaces therebetween to provide an unobstructed flow path and an actuator to move the plurality of panels between the first position and the second position.

Abstract: An emission reduction system for a combined cycle power plant including a gas turbine and heat recovery steam generator (HRSG) can comprise a stationary emission converter in fluid communication with and disposed upstream of the HRSG, and a diversion system operably coupled to an exhaust passage of the gas turbine, the exhaust passage defining an exhaust path for exhaust gas of the gas turbine through the heat recovery steam generator, the diversion system operable to define a primary exhaust path excluding the stationary emission converter and a start-up exhaust path including the stationary emission converter.

Abstract: A system for repowering a coal fired electrical generation plant with natural gas is disclosed. The plant has having high and low pressure steam turbines that drives an electrical generator. The coal fired plant has a regenerative system comprising a plurality of feedwater heaters that supply heated feedwater to evaporators and superheaters that supply steam to the turbines. The repowering system has a gas turbine that drives a second electrical generator where the HRSG is configured to receive the exhaust from the gas turbine and which is heated by a burner so as to generate steam for driving the steam turbines. The feedwater heaters utilize condensate from the said and from steam extractions to supply heated feedwater to the superheaters that feed superheated steam to turbines such that the first generator driven by the turbines is driven at a high percentage of its rated megawatt output.

Abstract: A liquid air energy storage system, the system comprising: a liquid air storage means; an input of a first pump in fluid communication with the liquid air storage means; a first heat exchanger in fluid communication with an output of the first pump; a second heat exchanger in fluid communication first heat exchanger and configured to receive the fluid stream from the first pump and the first heat exchanger; a first expander turbine generator in fluid communication with the second heat exchanger; the first heat exchanger in fluid communication with the first expander turbine generator; a third heat exchanger in fluid communication with the first heat exchanger and configured to receive the fluid stream from the first expander turbine generator and the first heat exchanger; a second expander turbine generator in fluid communication with the third heat exchanger; the first heat exchanger in fluid communication with the second expander turbine generator; the fluid stream from second expander turbine generator and

Abstract: A rocker arm includes an outer arm and an inner arm which selectively pivots relative to the outer arm. The rocker arm also includes a lock pin which is displaced along a lock pin axis between a coupled position and a decoupled position. The rocker arm also includes a linkage and a linkage guide which guides the linkage along a linkage axis. One surface of the linkage engages an actuator while another surface of the linkage engages the lock pin such that the linkage translates motion from the actuator to motion of the lock pin.

Abstract: A cam follower device includes: a bearing holding member that has a pair of opposing side walls disposed with a space therebetween and that is arranged with respect to a cam provided on a camshaft; a support shaft inserted into insertion holes provided coaxially in each of the pair of opposing side walls; an outer ring that has the support shaft inserted therethrough, is disposed between the pair of opposing side walls, and faces the cam; an inner ring formed by an outer peripheral surface of the support shaft; and a plurality of rollers disposed in an annular gap between the outer ring and the inner ring.

Abstract: An electromagnetic valve drive device includes: a state detection unit configured to detect an on-state or an off-state of a first switch and a second switch forming a boosting circuit; a boosting control unit configured to control a boosting operation, by performing a synchronous rectification control on switching of the first switch and the second switch, depending on the state of the first switch or the second switch detected by the state detection unit; and a drive circuit configured to drive an electromagnetic valve by supplying a voltage boosted by the boosting operation to the electromagnetic valve.

Abstract: An oil distributor is provided for a lubricating and cooling system in a powertrain, comprising a housing with a first oil outlet connected to a first oil chamber and a first oil circuit and a second oil outlet connected to a second oil chamber and a second oil circuit; and a piston arranged in a cavity of the housing and movable between first and second positions and comprising: a first bore partly constituting the second oil chamber; and a second bore connecting the first bore with an outer periphery of the piston, so that when the piston is in the first position, the first oil inlet is connected to the first oil chamber and the first oil outlet, and when the piston is in the second position, the first oil inlet is connected to the second oil chamber and the second oil outlet.

Abstract: A blow-by gas treating device has an oil separator. A tubular attachment portion is disposed at a discharge port of the oil separator. A PCV valve is inserted in the attachment portion. The PCV valve includes an inflow hole, a discharge hole, a flow rate regulating portion, and a stopping portion. The stopping portion is located closer to the inflow hole than to the flow rate regulating portion. The stopping portion has a dimension greater than the inner diameter of the attachment portion in a direction perpendicular to the central axis of the attachment portion. The flow rate regulating portion is surrounded by the attachment portion. The stopping portion is arranged in the space defined by the oil separator.

Abstract: Provided is an electric valve device which is capable of improving the accuracy of detecting whether there is a gas leakage from a blow-by gas passage and capable of detecting detachment of the electric valve device from a pipe of a fresh air passage. The electric valve device includes an inflow side pipe portion, an outflow side pipe portion, a barrier which partitions off the inflow side pipe portion from the outflow side pipe portion, a valve body which opens and closes an opening arranged on the barrier by moving in the axial direction, and a solenoid which drives the valve body. The inflow side pipe portion includes a bypass path which communicates with the outflow side pipe portion through a second opening separately from a passage which communicates with the outflow side pipe portion through a first opening used as the opening.

Abstract: A muffler has a housing enclosing a plurality of chambers. A first flow path extends from an inlet to an outlet passing through a bypass chamber. A flow tube has a plurality of perforations being open to a chamber other than the bypass chamber. A second in flow path passes from the inlet to the outlet without passing through the bypass chamber and passing through the perforations. Exhaust gas is introduced into the muffler via the inlet and discharged therefrom via the outlet. A first portion of the exhaust gas flows from the inlet to the outlet along the first flow path. A second portion of the exhaust gas flows from the inlet to the outlet along the second flow path, the first and second portions mixing at least in the outlet chamber. A semi-closed tube has an open end being open to one of the chambers and a closed end.