Saturday, September 8, 2012

Wave Sculpture Elements

Just as a graphical scene can be built up from primitive graphical elements and other structural elements such as transformations, superpositions, etc., so it is also possible to build up a wave sculpture by combining various primitive and compositional elements.

An Example Wave Sculpture
This can all be understood fairly intuitively by considering a sculpture such as that shown below...

Figure 1.  An Example Wave Sculpture 15m x 30m

The basic shape is a promontory of approximately the same extent as the typical distance between wave crests at the beach.  The choice of scale is such that different features of the sculpture are engaged in succession as the wave approaches the shore.  We believe that an ideal choice in this regard is one where the promontory is somewhat less than the distance between incoming crests.  This would afford a period of rest between each cycle of activity on the sculpture.

Next note that the promontory is wider at the base so that the sides are somewhat oblique to the incoming waves.  This is to minimize the effect of one cavity "shadowing" another behind it.  Each cavity, or cell, in the structure should intercept a relatively fresh and energetic section of the incoming wave.

Now note the location of the cavities:  their placement dictates a certain rhythm of activation.  For this design, cells a and b would act together as the wave first engages the promontory,  These cells might be blow-hole cells to give the effect of smoke coming from a dragon's nose.  After this cells, c, d, e, f, g, and h would act in sequence on alternate sides of the sculpture.  An effective choreography would be for these cells to be jets, designed to arch over to the cell on the opposite side that is about to shoot.  The overall sequence would a back-and-forth jumping motion with the arching trajectories creating a sort of arbor way as the wave comes in.

Finally, cells i and j will act together, and cells k and l at the end.  i and j might produce large forward- or outward-directed jets, and k and l might be a pair of ram tubes feeding a jet aimed straight into the air.  Alternatively, i and j might be scoops that fill the top level of a cascade that drains for a while until the next wave comes.

Composite Shapes
The example of figure 1 illustrates relative positioning of cells for timing, juxtaposition of cells for symmetry or sequence, and the use of different cell types to support an overall theme or dramatic effect.

Note that changing tides, and especially storm surges, can be used to effect a complete change in artistic effect.  Some cells might be buried and thus inactive at high tide and others might be out of the water and thus inactive at low tide.  Careful planning and simulation can take advantage of this effect to great advantage.
Figure 2.  A Composite Wave Sculpture

Figure 2 illustrates another composite shape consisting of two promontories similar to that of Figure 1.  These could be matched for symmetry or differentiated for variety.  It may at first appear that this configuration is simply 
two separate wave sculptures, but in fact it is three.  The space between the two promontories has been shaped to be a large converging channel designed to produce a variety of effects or one huge central effect.  For instance the central effect might be a scoop that fills a descending fountain as in figure 3, or it might be a spectacular jet that is only active during high tides and severe weather.
Figure 3.  A scoop feeding a trough with cascading falls

Some Basic Cells
The vocabulary of interesting wave-shaping cells is infinite, but many interesting effects can be obtained from four basic shapes and their simple variants.
Figure 4.  Four basic wave-shaping cell types

Jet - fig. 4a
The jet is designed to convert the forward momentum of a breaking wave into pulse of high pressure that shoots out a jet of water at high velocity.

Scoop - fig. 4b
The scoop is a non-turbulent effect.  In its simplest form, it is designed to shape a wave to run up a slope without ever breaking over.  The water just runs up the slope and back down.  However this shape can be combined with a converging outer channel to deliver a high volume of water to an elevated feature such as the top pool of a cascading fountain as in fig. 3a.

Blow hole - fig. 4c
The blow hole is similar to the jet in that its best effect is produced with high impact pressure, but in this case the configuration is designed to trap air that is then expelled in a swirling blast of air and spray.

Cannon - fig 4d
The cannon is similar to the jet, except that it is designed to shoot a small slug of water at an even higher velocity.  One can think of the jet as a gun, with the entire gun barrel full of water.  While a high impact pressure may shoot the water quite far, the mass in the barrel is large, and therefore resistant to acceleration.  The cannon is shaped so that, when idle, there is pool of water in the exit barrel, but the chamber is mostly full of air.  When a wave impacts the chamber, its first effect is to compress the air and shoot the pooled water out the barrel.

Almost all interesting wave shapes derive their impressive effects from some degree of convergence or focus of the incoming wave.  Focus increases velocity, which increases momentum and impact pressure.  Almost every cell can benefit from a converging shape at its entrance, but huge converging shapes are also possible as illustrated in the overall design of Figure 2.  Here the two promontories, in addition to being active wave sculptures themselves, serve to focus the entire wave volume between them on a narrow space at the shore, affording a great concentration of wave volume and momentum.

A ram constrains moving water to impact a barrier generating high instantaneous pressures.  The simplest version of this feature is a pipe leading to an active cell.  Because the pipe is closed, the momentum of all the water in the pipe will act in creating a pulse of high pressure at the end.  A ram pipe may also be somewhat convergent to increase velocity toward the end.

Help Wanted
Artists:  I'm in the process of building up a credible presentation to fund a real wave sculpture.  I would love to work with an artist to produce a few motivating images of an actual wave sculpture in action.  Can you see my sketches as real life?

Computational Fluid Dynamicists:  At the same time, I would like to work with people who are capable of simulating some of these effects so that we can understand how to improve them and combine them to best effect.  I don't think we can expect any patron to support a wave sculpture installation without a credible simulation of its action.

Environmental Artists:  There are all sorts of challenges involved in funding and permitting environmental art.  If you know people with experience in this area, please put me in touch.

No comments:

Post a Comment