Abstract:
Viewing enhancing apparatus for visibility impaired fluid, such as turbid water or a smoke-filled room, includes a fluid-permeable sidewall and a housing defining a confluence cavity having an axis extending between first and second housing ends. The housing ends are connected by the sidewall. The second housing end is open. The sidewall has a proximal end towards the first housing end and a distal end towards the second housing end. The housing defines a supply cavity surrounding the sidewall and coupleable to a source of viewing fluid, typically clear water when operating in a turbid water environment. The sidewall provides a resistance to flow of the viewing fluid therethrough, the resistance varying according to the position on the sidewall. The viewing fluid passes through the confluence cavity and exits the second housing end. This creates a chosen velocity profile for the viewing fluid exiting the second housing end.

Description:
CROSS-REFERENCE TO OTHER APPLICATIONS  
       [0001]     This application claims the benefit of provisional patent application No. 60/399,051 filed 26 Jul. 2002. 
     
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     None.  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates to underwater viewing systems used to allow, for example, a diver or video system to see through muddy or otherwise turbid water. The invention may also find utility for use in other visibility impaired fluids, such as smoke, oils and foaming liquids.  
         [0004]     In turbid water a viewing system typically sees nothing but a brown haze of silt, oil or mud. If the turbidity is heavy or concentrated enough, then no illumination can get through either, a condition which the diving community calls black water (BW). BW can be ubiquitous in such places as a sea floor experiencing storm action, the roiling bottom of the Mississippi River, industrial vats or working conduits transferring opaque liquid, opaque slurries, smoke or other visibility impaired gasses, foaming or sudsy liquids, etc. BW can also be caused simply by a diver&#39;s movement or a remotely operated vehicle&#39;s churning up the silted sea bottom in the normal course of doing work on the bottom. For the diver, his or her only other input is the sense of touch which leaves a lot to be desired when wearing gloves in cold or contaminated water. The quality of work may suffer and production may be slowed. For a system such as a remotely operated vehicle (ROV), which relies solely on a video camera, there is no alternative sense but SONAR which does not have the color sense and the close-up resolution of video.  
         [0005]     The simplest method of seeing through turbidity is to use a transparent hydraulic system to displace the turbidity with an illuminated free jet stream of clear water through which, for example, a diver or video system can view the work.  
         [0006]     However, one must be careful how the jet is designed because a simple jet stream played into a stationary fluid will break up into turbulence almost immediately. Turbulence is a very efficient mixing regime so the clear water jet would almost immediately be mixed with the surrounding black water, thus destroying the clear column.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     A first aspect of the invention is directed to viewing enhancing apparatus for visibility impaired fluid, such as turbid water or smoke in a smoke-filled room. The apparatus includes a fluid-permeable sidewall and a housing defining a confluence cavity having an axis extending between first and second housing ends. The housing ends are connected by the sidewall. The second housing end is open. The sidewall has a proximal end towards the first housing end and a distal end towards the second housing end. The housing defines a supply cavity surrounding the sidewall. The supply cavity is coupleable to a source of viewing fluid, typically clear water when operating in a turbid water environment. The sidewall provides a resistance to flow of the viewing fluid therethrough, the resistance varying according to the position on the sidewall. The viewing fluid enters the supply cavity, passes through the sidewall, passes through the confluence cavity and exits the second housing end. This creates a chosen velocity profile for the viewing fluid exiting the second housing end.  
         [0008]     A second aspect of the invention is directed to method for viewing through visibility impaired fluid. A viewing enhancing apparatus is coupled to a source of viewing fluid rate. The apparatus comprises a fluid-permeable sidewall; a housing defining a confluence cavity having an axis extending between first and second housing ends, the housing ends connected by the sidewall, the first housing end being light-transmissible, the second housing end being open; the sidewall having a proximal end towards the first housing end and a distal end towards the second housing end; and the housing defining a supply cavity surrounding the sidewall, the supply cavity coupled to the source of viewing fluid. Viewing fluid, such as clear water, is flowed into the supply cavity, through the sidewall, through the confluence cavity and out through the second housing end. A variable resistance to the flow of the viewing fluid through the sidewall is provided. The resistance varies according to the position on the sidewall to create a chosen velocity profile of the viewing fluid when the viewing fluid has exited the second housing end.  
         [0009]     Various features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is an overall view of a clear water viewer made according to the invention mounted to a diving helmet.  
         [0011]      FIG. 2  is a cross sectional view taken along line  2 - 2  of  FIG. 3 .  
         [0012]      FIG. 3  as a cross sectional view taken along line  3 - 3  of  FIG. 2 .  
         [0013]      FIG. 4  is a cross sectional view taken along line  4 - 4  of  FIG. 2  and illustrating the creation of a clear water path with a generally conical velocity profile.  
         [0014]      FIG. 5  illustrates the flow of water through the variable resistance diffuser ring.  
         [0015]      FIG. 6  illustrates the use of flow straightening honeycomb.  
         [0016]      FIG. 7  illustrates biasing the fluid flow to one side by compressing one side of the diffuser ring.  
         [0017]      FIG. 8  illustrates alternative method of biasing the fluid flow to the use of a cross current vane.  
         [0018]      FIG. 9  illustrates an alternative embodiment comprising two different variable resistance diffuser rings.  
         [0019]      FIG. 10  illustrates an alternative embodiment used with a video application.  
         [0020]      FIG. 10   a  is a cross sectional view taken along line  10   a - 10   a.    
         [0021]      FIG. 11  illustrates the effects of the change in the radius of curvature of a variable resistance diffuser ring having an elliptical cross sectional shape.  
         [0022]      FIGS. 11   a  and  11   b  are exploded cross sectional views, respectively taken along lines  11   a - 11   a  and  11   b - 11   b  of  FIG. 11 , illustrating the different numbers of layers of flow resistance cloth at different circumferential locations.  
         [0023]      FIG. 11   c  is a view similar to  FIG. 11   a  but illustrating the creation of a variable resistance to flow by placing bands of flow inhibiting or flow preventing material on the diffuser ring. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     The hydraulic shear stress at the interface between a jet stream and the surrounding stationary fluid seems to cause the onset of turbulence. So, the initial stress which breaks the laminarity can be written as
 
 T =μ( ∇×v )  (1)
 
 where T is the shear stress, μ is the absolute viscosity, v is the local jet speed and the vector ∇×v is the velocity gradient or shear rate. A term “velocity profile” is used to describe the local velocity of the jet stream across the radius of the jet. The shear rate is the slope of that profile. If you drew a picture of the initial velocity profile at the orifice of a standard laminar jet it would have a generally radially uniform velocity profile; that is it would look like a top hat where the rim represents the stationary ambience outside the interface and the “stove pipe” represents the speed of the jet stream. (S. C. Crow, et.al.,  Orderly Structure In Jet Turbulence , J. Fluid Mech., v. 48, pp. 547-591, 1971.) It is readily apparent that since the slope ∇×v at the interface is very large, a top hat profile has an enormously destructive shear at the interface. See  FIG. 1  of Crow,et al. The natural viscosity μ of the intermixing fluids is simply not great enough to damp out the vortices responsible for the mixing. 
 
         [0026]     One aspect of the invention is the recognition that to prevent jet stream mixing, the shear rate ∇×v must be reduced in order to give the viscosity μ a chance to damp out the vortices. This means the jet must have a gradual coaxial increase in speed from the jet periphery all the way inward to the jet centerline just like a laminar flow inside a pipe. The more gradual the profile, the lower the shear rate anywhere on the radius and the farther the jet survives. Pictorially, the velocity profile preferably has an inwardly tapering, generally conical or parabolic profile, that is it should look like a conical “derby hat”. That way the slope ∇×v is always finite.  
         [0027]     There are two strong markets for black water viewing, the diving helmet market and the underwater minicam market. One embodiment is patterned after a prototype to be mounted on a Kirby Morgan type SL27 diving helmet (Diving Systems International, Santa Barbara, Calif.).  FIGS. 1-4 . A second embodiment notes a hydraulic enclosure around an underwater mini-camera, capable of, for example, a 3300 foot immersion depth, which is to be mounted on an ROV or to be handheld by a diver. See  FIG. 10 .  
         [heading-0028]     Specifications, Diving Helmet Application  
         [0029]     See  FIG. 1 . Beginning with diving helmet  64  and its attendant air supply valves, auxiliary valve  14  and steady flow valve  16  which controls supply line  18 . Helmet  12  is held in place by base lock  20 . Supply line  18  feeds a demand regulator  22 . A viewing glass  24  is fastened to the helmet bolting ring  32 .  
         [0030]     A clear water viewer  10  is fastened to a welding shield  26  and the shield is hinged and fastened to the brass bolting ring  32  by hinge  28 . The viewer  10  can then be flipped up so the diver can better see his or her footing when, for example, on board a tender barge. The viewer is fitted with a 1½″ corrugated hose  30  which lays over the back of the diver to a control valve  36  fastened to the diver&#39;s waist. The valve  36  is fed by a ¾″ hose  38 , the hose is taped to the diver&#39;s umbilical air hose package (not shown) supplied by the tender barge (not shown). The hose  38  is fastened to a clear water pump and filter  34 . The corrugated supply hose  30  is fastened to the viewer  10  at input manifold  46 . Orifice  44  of viewer  10  provides a dual-purpose hydraulic output and viewing port while the diver (not shown) looks through a transparent plexiglass backing plate  56  along an optical or viewing centerline  42 . Front cover  48  is held in place by Velcro® hook and loop fastener straps  50 .  
         [0031]     Refer to  FIGS. 2 and 3 . Water supply hose  30  is attached to input manifold  46 , the manifold being an integral part of fiberglass, or equivalent, case  40 . Manifold  46  has an elbow. At the intersection of manifold  46  and case  40  is an internal preliminary diffuser  66 . Contained inside the case  40  is an annular space  72  formed by the inner surface of said case and the outer surface of ring diffuser  86   a . The annular space  72  is divided into six semi compartments by a series of scoop vanes  78 . Two of the vanes  76  and  84  are stationary and divide the annular space into two halves. The remaining four vanes  78  are adjustable catcher vanes, each pivoting at points  82  and are adjustably positioned by adjusting screws  80 . Fitted snuggly inside of, but not attached to, pivot points  82  is the diffuser ring  86   a . Fit just inside diffuser ring  86   a  is a hollow, truncated, conical diffuser ring  86   b . Both rings are the same length and are held in place by a slight compression force caused by being wedged between backing plate  108  and front cover  48 . Both diffuser rings  86   a  and  86   b  may be, for example, constructed from Scotch Brite®, or equivalent, scouring pads (fine) that can be purchased at most hardware stores. The pads are comprised of a random maze of fibers. Distally, the large diameter of cone  86   b  is located adjacent to the cover plate  48 . Glued to the small, proximal, small diameter end of cone  86   b  is a {fraction (1/16)} th  inch thick flexible washer  106  with an outer diameter no larger than the distal end. The purpose of the ring is to prevent the thin proximal end from collapsing under pressure. The reason there are two diffuser rings is simply the ease of cutting out a taper inside the cylindrical maze while maintaining right cylindrical surfaces on the inner and outer ring surfaces; the outer surface fits snuggly within the pivots  82 , the inner surface to facilitate a proper hydrodynamic flow into confluence cavity  90 . Cover  48  has a large central hole cut out of the center and is just large enough to expose the entire inner surface of diffuser cone  86   b . The result is orifice  44 , as seen in  FIGS. 1, 3 , and  4 .  
         [0032]     Backing plate  108  has a central part cut out and fitted with a viewing glass  56 . The viewing glass has two holes cut into it, the upper hole to act as a bubble relief  54 , the lower hole is threaded to accept a focused light assembly  52 . Viewer  10  is held to a welding shield  26  by Velcro® strips  50  placed between shield  26  and backing plate  108 . Shield  26  is fastened to diver&#39;s helmet by a hinge  28  which is bolted to a brass helmet ring  32  built into helmet  12 ; the same ring also permanently holds helmet viewing port  24  in place. Finally, a porous ring  104  is fastened to backing plate  108  so that when welding shield is lowered into working position, shown in  FIG. 4 , the ring  104  just touches the viewing port  24 .  
         [0033]     Refer to  FIG. 6 . The truncated cone  86   b  is shown in half view to expose a honeycomb flow straightener  116  fastened in the distal end of confluence cavity  90  (orifice  44 ). A viewing slot  128  is cut out of the honeycomb for viewing purposes. The use of flow straightener  116  is discussed below.  
         [0034]     Refer to  FIG. 7 . The flow  92  is skewed off axis from centerline  42  by compressing one side of the cone  86   b  with a push rod  136 . Stabilizer rings  152  are glued inside of cone  86   b  to prevent wall thickening during compression. This increases the fiber density and thus the resistivity of that portion of the cone. The resulting clockwise or azmuthal assymetry causes the high speed flow to overwhelm the diametrically opposite flow. This causes the core  92  to angle away from the centerline. If the honeycomb of  FIG. 6  is added, the flow is again made generally parallel to the centerline but now the flow is shifted off center. This causes the flow  92  to ‘lean’ into the crossflow to reduce side stream errosion.  
         [0035]     Refer to  FIG. 8 . Truncated cone  86   b  is moveable about pivot  112 . The cone is caused to pivot by a cross-current vane  126  which is located outside the case  40  in order to sense any cross flow currents. The cone can then “float” around the pivot point. To prevent water inside confluence cavity  90  from passing into the proximal end of the cone, a viewing port  132 , typically made of Plexiglas® or other suitable material, is fastened to the proximal end of the cone, thus all the flux inside cavity  90  is forced to leave through orifice  44  at an angle with respect to the centerline  42 . The jet stream  92  and its attendant off-center hydraulic centerline  62  is driven back in a curve due to the cross-flow  124  pushing the jet sideways as the jet progresses outward to meet the optical centerline  42 . This allows the diver&#39;s eye  58  to see farther to the target  120 —like throwing a ball upward as well as horizontally to gain a greater distance. Diffuser  86   c  bleeds a small amount of clear water into rotating space  134  inside orifice  44  to keep out the turbidity  100 .  
         [0036]     Refer to  FIG. 9 . Flow profile  122  can be changed by the diver on site by simply shifting lever  142  in or out. The “in” position closes a gate valve  138  to annular cavity  72   b . This causes all the flow  68  to enter annular area  72   a . The flow then enters truncated cone  86 A which then fills confluence cavity  90   a . The flow distribution is designed to cause the velocity profile  122   a  to be radially uniform across the orifice  44 . This could be used for short viewing distances with a wide view. When lever  142  is pulled out the gate valve  138  closes off  72   a  and opens  72   b . This floods confluence cavity  90   b . Cavities  90   a  and  90   b  are mounted tandemly and are separated by a non-porous membrane  140 , which has a hole in the center to couple  90   a  with  90   b . The resulting velocity profile is more derby hat (profile  122   b ) for long distance viewing. If desired, truncated cone  86   a  could be configured to create a turbulent stream. This would allow the user to, for example, initially place gate valve  138  in the solid line position and use the turbulent jet to excavate the muddy site; the user would then move gate valve  138  to the dashed line position to permit viewing of the excavated area. This excavate-then-view system may eliminate the need for a separate hose of pressurized water for excavation purposes.  
         [0037]     If a top hat velocity profile is ever used, as in severe crossflow where a slow peripheral boundary layer  92   b  may be blown away, then to prevent turbulent break-up, the diver could inject a 1% solution of a pseudoplastic into the supply stream  68  of input line  30 . A Pseudoplastic changes its viscosity μ according to the shear rate ∇×v; Newtonian fluids such as water do not. So a non-Newtonian use of a stir-thinning pseudoplastic such as the Bingham plastic Carbopol, manufactured by Goodyear, could be used as a very effective anti-turbulent stabilizer even with a top hat profile. With a 1% pseudoplastic injected in a jet stream issuing into a Newtonian environment., a non mixing, laminar jet stream has been measured out, to 30 to 50 orifice diameters. The diver would need a supply tank somewhere on his suit or it could be supplied at the clear water pump  34 .  
         [0038]     The problem with injectants of this type is that they contaminate the environment, and there is a limited supply of injectant. Viscous Newtonians such as glycerine or honey could also be used but the injection point would have to be close to the orifice otherwise the high viscosity dramatically slows pumping speeds.  
         [0039]     The elliptical orifices shown are one example of how they can be shaped. If the viewer  10  is mounted on an ROV inside a conduit and the orifice  44  were a rectangular slit with a width-to-height aspect ratio of 10 or 20, then a video system could scan in the width X direction (curvature of the conduit) while the viewer  10  was physically transported by the ROV in the height Y direction (along the conduit length), much like a side scan SONAR records the sea bottom. A monitor could then record the entire surface of the conduit in a minimum of time. If time were very short, several viewers could ring the ROV so that one pass records the entire circumference and length of the conduit in optical acuity and in color.  
         [0040]     If a crack is found and one was interested if it was leaking, an ink injection system could be placed at the edge of the orifice, right in the image, and opaque ink around the crack would indicate if fluid was leaking in or out by the character of the ink flow. This would give an indication of the condition outside the conduit as well. The shape our slant of the crack would give the survey engineer an idea of the type of stress the conduit is undergoing. This could be done even though the conduit is full of working fluid.  
         [0041]     Another use of a shaped orifice would be to mount the viewer on a shovel or broom, or scraper so the archaeologist can view the dig in real time. This would provide an intelligent, real time excavation, important when working in a time dependent weather window and when one is digging around very fragile ruins or electrical cables. Also, one could attach a video viewer to his or her wrist for a look-and-feel exploration in archaeological research or search and rescue operations.  
         [0042]     In a circular orifice where the curvature K of the periphery is uniform all around, the flow  96  enters the confluence cavity  90  in a radial direction and then turns axially as an azmuthally uniform or symmetrical jet stream  92 . But in an elliptical orifice, the curvature K is greater at the major axis (elliptical end) than at the minor axis or mid section,  FIG. 11 . The radius of curvature r=1/K is therefore smaller in that region and even though the control supply area,  1   c , of the fiber ring  86   a  may be the same (in this drawing) the subtended area rc is smaller at the elliptical ends than in the center. This can cause the end flow to be more intense than the mid-ellipse flow and may cause a top hat profile at the elliptical ends. To prevent this the elliptical ends (a) of fiber matrix ring  86   a  may be masked with more layers of resistance cloth  154  than at the center of the ellipse (b) as shown in  FIG. 11   a  and  11   b  respectively. Instead of multiple layers of uniform resistance cloth, a doppled paint or glue pattern to achieve the proper resistance profile. The fiber backing  86  averages out the dot irregularities. One can also use a wound opacity tape, see  FIG. 11   c , closely wound at the high impedance (distal) end, and open wound at the proximal end. Other bands of flow inhibiting or flow preventing material may also be used.  
         [heading-0043]     Specifications, Video Application  
         [0044]     Refer to  FIG. 10 . A video application is shown as a black water video viewer  10 . Inlet hose  30  is attached to the proximal end of case  40 . At the distal end of case  40  is a truncated cone  86  having a hollow center. The proximal side of the center is blocked off by a camera system, the distal end is open and is orifice  44 . The interior is confluence cavity  90 . The camera system comprises a video camera  142 , such as an Outland Tech Mini, model 400 color, or equivalent (Outland Technology, Slidell, La.) with lens  144 . Attached to the camera is a video cable  148  for power-in and signal-out. The camera lens  144  is focused on target  120  (see  FIG. 4 ) along hydraulic centerline  62 . The hydraulic centerline is also the optical centerline  42 . An illumination source  52  is focused along the same centerlines  42  and  62 . A split beam mirror encased in a glass cube  146 , such as the Edmund 25 millimeter, non polarizing cube, allows a light source  52  to be located perpendicular and off the optical axis  42 . The cube is protected from rough handling by a disk, typically made of Lexan® polycarbonate or other suitable material, at the proximal end of confluence cavity  90 . The incoming flow  68  through pipe  30  enters axially so the spider system  78  is not needed.  FIG. 10   a  shows a uniform azmuthal geometry used to supply video diffuser cone  86 .  
         [heading-0045]     Operation. Diver Application  
         [0046]     See  FIG. 1 . Clear water  68  is pumped from a clear water source by pump  34 . The flow is controlled by a valve at the diver&#39;s waist  36  because there are simply too many valves already at the typical control site. Also, if there is any air in line  38  the line might buck when first turned on and that motion should not be transferred to the diver&#39;s helmet.  
         [0047]     See  FIGS. 2 and 3 . Flow  68  then enters manifold  46 . Because the line approaches the helmet from behind the diver&#39;s back, flow  68  enters  46  at an angle. This is not recommended because it puts too much dynamic pressure on the forward (distal) end of viewer  10 . So an elbow  64  deflects flow  68  back toward the center of the manifold as back flow  70 . The average flow between  68  and  70  is mixed and partially smoothed by a preliminary diffuser  66  so that the flow enters case  40  as perpendicular flow  74 . Flow  74  is then distributed azimuthally around annular spaces  72 . Scoop vanes  78  can be adjusted by screws  80  so that the distribution is equal all around. As the flow  74  enters outer diffuser ring  86   a , the pressure of the diffuser on the screws  82  prevent any leak-by from one semi-compartment or quadrant to another; the quadrants being created by the space between adjacent scoop vanes  78 . Thus, each scoop vane has full control over the portion of the flow  74  entering its quadrant.  
         [0048]     See  FIGS. 2, 3 , and  4 . There are several reasons for using a fiber diffuser ring  86 . Beside being a very low pressure device (1-2 psi) and inexpensive to manufacture, a nested fiber ring set  86   a  and  86   b  can eliminate micro vortices by the simple damping action of viscous water passing through a fine fibril maze. (Dryden, et.al., Growth And Delay Of Vortex Motion, pp. 212-218, chapter 3.4 , Hydrodynamics , Dover Publications, 1956.) In a laminar, non mixing jet it is essential that as little vortical flow exists in the output in order to eliminate unwanted turbulence downstream.  
         [0049]     Another use of the fiber ring is that the pre flow  74  does not have to enter perpendicularly the outer surfaces of rings  86   a  and  86   b  in order for an effusing flow  114  and  96  respectively to leave perpendicularly. This is described in Irmay&#39;s Law of Refractive Flow through a Porous Medium Interface between two adjacent porous materials. (Bear, Discontinuity In Permeability, pp. 263-269, chapter 7.1.10 , Dynamics Of Fluids A Porous Medium , Dover Publications, 1972.) So, all around the inside of diffuser  86   b , the effusion  96  is flowing radially and non-rotationally inward toward hydrodynamic centerline  62  centrally located inside confluence cavity  90 .  
         [0050]     See  FIG. 5 . Because of the viscosity of water, additional vortical damping can occur as flow  96  converges toward the center as long as the critical Reynolds Number is not exceeded, as mentioned in the next paragraph. This convergence phenomenon can be called Vortical Pinch Effect.  
         [0051]     The outer shape of diffuser  86   b  is conical in shape in order to cause the proximal flow, as seen in  FIG. 5 , to effuse faster than the distal flow. Since the flow  96  into the confluence cavity  90  is perpendicular to the surface of the pot, the local velocity can be written as
 
 V   96   =Δp/Zυ   (2)
 
where,  Z=RT   (3)
 
         [0052]     Here, V 96  is the radially inward perpendicular flow, Δp is the local pressure differential between intermediate cavity  94  and confluence cavity  90 , R the resistivity of the porous material of  86   b , and T the local thickness and υ is the kinetic viscosity. Flow  96  effuses radially inward toward the centerline  62  and then, because it has nowhere else to go, turns along the centerline to become axial flow  92 . Since the streamlines do not cross, the high speed proximal flow  96   p  turns to become high speed axial core  92   c . The low speed distal flow  96   d  turns to become low speed axial shroud or boundary layer  92   b  which surrounds the high speed core  92   c  and protects  92   c  from the surrounding turbidity  100 . The shear rate ∇×v from (1) should be continuous along the radius of the jet stream so that a derby hat profile is maintained.  
         [0053]     For an orifice Reynolds Number 4Q/πD υ greater than 10 4  the Reynolds stresses might become significant and rotation of the core might occur. Here, Q is the pumping speed, D is the orifice diameter and. To help prevent rotation a flow straightener such as honeycomb  116  might be used, see  FIG. 6 . But for relatively slow orifice flow speeds, e.g. 20 gallons per minute pumped through a 4 square inch orifice, a simple open orifice such as shown in  FIGS. 1-5  is sufficient.  
         [0054]     Computations involving empirical flow parameters in (2) shows similar derby hat profile as in  FIG. 4  and was also found in shallow ocean water tests runs. There were two types of runs. The first involved ink injections into hose  30  which would exit orifice  44  causing velocity profile  122  to be very apparent. The second type of runs included lighted through-the-core visual observations of an object in black water, just as a diver would see it. A very strong core was observed due to the linear taper described in (2) aided by the Pinch Effect.  
         [0055]     So much of the viewer&#39;s success depends on the cone  86   b . But a cone is not necessary. It can be replaced with layers of strategically placed resistance cloth  154  which, for example, can be wrapped around cylinder  86   a , thus eliminating the necessity of cone  86   b  altogether. This is discussed below with reference to  FIGS. 11-11   b . It is simply another alternative to facilitate an impedance gradient ∇Z to flow  96 . In this case confluence cavity  90  and orifice  44  would be formed by the inner surface of  86   a , cover  48 , and backing plate  108 .  FIG. 11   c  shows a modified form of impedance gradient ∇Z: a layer of resistance cloth  154  is secured to the outer surface of ring  86   a . A series of spaced apart flow barrier tapes  158  are secured to cover cloth  154 ; adjusting the distance between adjacent tapes increases or decreases the flow impedance through ring  86   a . Flow barrier tapes  158  may completely prevent fluid flow through the tapes or merely retard fluid flow through the tapes.  
         [0056]     The orifice may be elliptically shaped for two reasons: 1) the major horizontal axis accommodates the distance between the viewer&#39;s eyes, and 2) the orifice height minor axis reduces the cross sectional area of the orifice.  
         [0057]     The elliptical orifice is like that of an aerodynamic strut in a wind—the drag and thus the deflection of the jet column  92  is reduced, since the head-on cross section of the jet with an oncoming horizontal cross flow  124  is reduced. Also, a small minor axis increases the effective core speed v 92 . thus stabilizing the flow which keeps the viscosity from diffusing the jet stream too rapidly. There seems to be an optimum core speed-to-viscosity ratio that maximizes the distance the core travels before dissolution takes place. Most divers are interested in core distances of 3 feet with a minimum major diameter of 3 to 4 inches. A reduced orifice area also decreases the recovery time when a momentary cross flow deflection takes place.  
         [heading-0058]     Operation, Video Application  
         [0059]     Clear water  68  enters input hose  30  to supply intermediate manifold  46 . The annular space  72  just inside body  40  and the outside surface of a camera system forms the supply route for internal flow  114  to enter the porous cone  86 . See  FIG. 5 . As in the helmet system, cone  86  creates a non-mixing laminar core  92   c  with a low speed boundary layer  92   b ; see Operation, Diving.  
         [0060]     If inlet pipe  30  must be connected to the side of viewer case (not shown) then the pre-flow scoop vane system shown in  FIG. 2  would have to be used in order to control the azimuthal supply to the cone  86 .  
         [0061]     All modifications shown in  FIGS. 6-9  are applicable in the video system as well with one modification. If the video system were to be connected to the proximal end of the rotating cone  86   b , such that the system would be attached to the back of rotatable surface  132 , then the camera could be rotated with respect to the body  40  for scanning the inside surfaces of a conduit for instance. This is not shown, but is assumed to be understood. In this case the cross current vane  126  would be replaced by a remotely operated controller for selective viewing left and right.  
         [0062]     Other modification and variation can be made to the disclosed embodiments without departing from the subject of the invention as defined in following claims. For example, the viewing fluid is typical clear water when working in turbid water; or other fluids, such as clean air, may be used when operating in other environments, such as a smoke-filled room.  
         [0063]     Any and all patents, patent applications and printed publications referred to above are incorporated by reference.