In one embodiment, a method for reducing drag includes forming a smooth surface on a first portion of a physical object. The method also includes forming periodic riblets on a second portion of the physical object. The second portion of the physical object is adjacent to the first portion of the physical object. Each riblet of the periodic riblets of the second portion of the physical object is depressed below a plane of the smooth surface of the first portion of the physical object. The method further includes generating a flow over the periodic riblets of the second portion of the physical object and over the smooth surface of the first portion of the physical object. A length of each riblet of the periodic riblets runs parallel to a direction of the flow.

Provided is a filtering apparatus configured to interact with objects of interest within a medium. The properties of the filtering apparatus can be configured to modify the trajectory of individual objects of interest which interact with the filtering apparatus within several orders of magnitude of the mean free path of objects of interest. Surfaces of a filtering apparatus can be constructed to preferentially redirect objects of interest in a desired direction, such as a direction substantially parallel to a surface, or substantially along the length of a channel connecting two reservoirs. This can modify the net diffusion of objects of interest relative to the surface, which can modify the bulk fluid flow velocity magnitude along the surface. This can be employed to reduce the viscous drag on a surface moving relative to a fluid, or to generate thrust, or to convert thermal energy of a fluid into useful work.

Provided is a filtering apparatus configured to interact with objects of interest within a medium. The properties of the filtering apparatus can be configured to modify the trajectory of individual objects of interest which interact with the filtering apparatus within several orders of magnitude of the mean free path of objects of interest. Surfaces of a filtering apparatus can be constructed to preferentially redirect objects of interest in a desired direction, such as a direction substantially parallel to a surface, or substantially along the length of a channel connecting two reservoirs. This can modify the net diffusion of objects of interest relative to the surface, which can modify the bulk fluid flow velocity magnitude along the surface. This can be employed to reduce the viscous drag on a surface moving relative to a fluid, or to generate thrust, or to convert thermal energy of a fluid into useful work.

A viscous-drag-reducing cladding for a ship's hull whereby the wetted area of the hull is reduced by interspersing air between the hull surface and the water. A substantial portion of the submerged area of the ship's hull comprises densely packed air pockets. The dimension of the air pocket is less than twice the capillary length of water. Each air pocket is supplied with pressurised gas by means of a restrictor. The pressurised air is supplied to each air pocket by means of a network of corrugated channels.

A viscous-drag-reducing cladding for a ship's hull whereby the wetted area of the hull is reduced by interspersing air between the hull surface and the water. A substantial portion of the submerged area of the ship's hull comprises densely packed air pockets. The dimension of the air pocket is less than twice the capillary length of water. Each air pocket is supplied with pressurised gas by means of a restrictor. The pressurised air is supplied to each air pocket by means of a network of corrugated channels.

A watercraft system including one or more air passageways and/or one or more water passageways is provided. The air passageways may extend from an upper surface of the watercraft, through the body of the watercraft, to an underneath surface of the watercraft. The water passageways may extend from an underneath forward or side portion on the watercraft, through the body of the watercraft, to a rear portion of the watercraft. The air and/or water passageways may be constricting from the inlets to the outlets so that the air and/or water is accelerated through the passageways during use of the craft. In this way, the release of the accelerated air and/or water decreases the craft's drag and provides the craft a forward thrust.

A watercraft system including one or more air passageways and/or one or more water passageways is provided. The air passageways may extend from an upper surface of the watercraft, through the body of the watercraft, to an underneath surface of the watercraft. The water passageways may extend from an underneath forward or side portion on the watercraft, through the body of the watercraft, to a rear portion of the watercraft. The air and/or water passageways may be constricting from the inlets to the outlets so that the air and/or water is accelerated through the passageways during use of the craft. In this way, the release of the accelerated air and/or water decreases the craft's drag and provides the craft a forward thrust.

In the absence of inventive practice, the hydrodynamic flows on both sides of a vertically oriented bluff body (e.g., cylinder) traveling through water tend to hug the bluff body proximate its curved back surface and to converge behind the bluff body, resulting in lateral sway of the bluff body. Exemplary inventive practice provides for attachment of a pair of waterjet-streaming devices at opposite axial ends of a bluff body such as a cylinder. The waterjet streams discharged by the two inventive devices, which adjoin the vertical bluff body, deflect the hydrodynamic flows on both curved side surfaces of the bluff body. The inventive apparatus thereby encourages a continued approximate parallelity of the hydrodynamic flows behind the bluff body, resulting in significantly greater stability of the bluff body. Some exemplary embodiments of the present invention provide for attachment of a single waterjet-streaming device at one axial end of the bluff body.

In the absence of inventive practice, the hydrodynamic flows on both sides of a vertically oriented bluff body (e.g., cylinder) traveling through water tend to hug the bluff body proximate its curved back surface and to converge behind the bluff body, resulting in lateral sway of the bluff body. Exemplary inventive practice provides for attachment of a pair of waterjet-streaming devices at opposite axial ends of a bluff body such as a cylinder. The waterjet streams discharged by the two inventive devices, which adjoin the vertical bluff body, deflect the hydrodynamic flows on both curved side surfaces of the bluff body. The inventive apparatus thereby encourages a continued approximate parallelity of the hydrodynamic flows behind the bluff body, resulting in significantly greater stability of the bluff body. Some exemplary embodiments of the present invention provide for attachment of a single waterjet-streaming device at one axial end of the bluff body.

An element comprising a non-stick surface for substantially cleanly removing a product which is arranged against said non-stick surface. The element comprises a first layer of an pervious material, which is configured to allow a fluid to flow there through. An outer surface of said first layer provides the non-stick surface. The element comprises a second layer of an impervious material, which is configured to substantially block a flow of fluid there through. The second layer is arranged at a side of said first layer opposite to the outer surface. The element comprises ducts or chambers which are arranged in said first layer or in between said first and second layer. Said ducts or chambers are arranged in fluid connection with said pervious material and are configured for feeding a pressurized fluid to the pervious material. At least the first layer is formed using a three-dimensional printing tool.