Water screens and projection

Water screens and projection

Image geometry, hydraulic facilities, projector placement and evaluation of display quality

The water curtain creates a moving and semi-transparent surface to display the image. In the night performance, parts of the image can appear in the dark and combine with the movement of water, light and music. This feature makes the water curtain attractive for urban narratives, cultural programs and special shows.

The quality of the result depends on the coordination of several factors: the uniformity of the water surface, the size of the image, the ambient light, the position of the projector, the image content and the location of the audience. The choice of nozzle or projector alone does not determine the final quality of the display.

In this chapter, a hypothetical example is examined to explain the design process. The numbers are educational inputs and are not specifications of an actual GSO product or project. The relationship between curtain dimensions, flow rate and pressure should be confirmed with the manufacturer's data and test of the selected equipment before purchase.

50–1. Defining the function of the water curtain in the project

Before determining the dimensions, the role of the water curtain should be determined in the program. The curtain may be the scene of a short urban narrative, appear as part of a musical fountain, or be used for special events.

For the example of this chapter, the goal is defined as:

A nightly presentation of short video content, accompanied by music, for the audience located in a certain area in front of the pond.

The main content will consist of large forms, featured images and short texts. The use of a water curtain to display a table, long text or fine details should be tested with a real sample before the design is approved.

On the GSO site, the Waterscreen nozzle has been introduced to create a water curtain and display multimedia content. The information of the selected model, including the dimensions of the effect and the hydraulic conditions, should be fixed in the documents of the same project. Introduction of GSO water screen nozzle ^[327]

50–2. Select the type of blue surface

The title "water curtain" can refer to several different mechanisms:

In this study, the fan curtain is selected.

Aquatique Show also differentiates between the inflatable curtain and the waterfall wall, and for the inflatable curtain, the show from the back is the main approach. The company emphasizes the sensitivity of the water surface to the wind and the concentration of more detailed content in the central area. Aquatique Show water curtain technical questions ^[328]

Choosing the type of curtain should be done before designing the structure and facilities; Changing it in the final stages can change the location of the equipment, the path of the pipes and the geometry of the image.

50–3. Educational sample specifications

The dimensions of 18 x 6 meters are the basic geometric cover of the curtain; The usable image surface does not necessarily cover this entire range.

The location of the projector must also be determined along with the pond and viewing area. Adequate distance for image formation, service access and light path control all affect placement.

Figure note from the source manuscript

Fig. 50-1: Equipment deployment plan

The water curtain, reception basin, audience area, projector booth and light path should be shown. The projector should be placed behind the curtain and its service path should be separated from the general circulation. Subtitle: "Conceptual plan; The placement angle and height should be finalized with the selected lens and the evaluation of the light path.

50–4. Determine usable image size

For a 16 by 9 image with a width of eight meters:

$H_{image}=8\times \frac{9}{16}=4.5m$

Image area:

$A_{image}=8\times 4.5=36m^2$

With the lower edge at a height of 0.5 meters, the upper edge will be at a height of five meters.

For a basic geometric control, we assume the curtain is semi-elliptical:

$\frac{x^2}{9^2}+\frac{y^2}{6^2}=1y\ge 0$

This relationship is a training model of the curtain shape and is not a substitute for the actual spray curve.

The upper corner of the image is at a horizontal distance of four meters from the axis. Hypothetical cover height at this point:

$y=6\sqrt{1-\frac{4^2}{9^2}}\approx 5.37m$

Because the top edge of the image is at a height of five meters, the proposed rectangle fits in this geometrical envelope.

However, being in the water cover does not mean the same image quality in all places. The useful area should be determined by experimental pattern and actual observation.

Figure note from the source manuscript

Figure 50-2: Front view of the curtain

Draw a hypothetical half-elliptical cover of 18 x 6 meters and an image rectangle of 8 x 4.5 meters, with a distance of half a meter from the base. Highlight the main content area in the center. Subtitle: "Basic geometric control; "The actual boundary of the useful image is determined after the test."

50–5. Projector distance and lens selection

Throw Ratio, in a common approximation, is obtained by dividing the throw distance by the width of the image:

$TR=\frac{D}{W}$

For the present example:

$TR=\frac{16}{8}=2.0$

Therefore, the combination of projector and lens should be able to create an image with this ratio in the desired geometry.

Christie's guide also states the relationship between image width and throw ratio to estimate distance, and references the lens information for the exact selection. Christie installation and launch distance calculation guide ^[329]

In the final design, in addition to the distance, these items should be controlled:

• focus range in selected image size;

• The possibility of optically moving the image with the lens;

• Installation height and angle;

• The effect of the protective window of the chamber;

• Rear projection limitations;

• Ability to adjust without changing the geometry of the image.

Digital distortion correction can be useful for limited tuning, but it doesn't compensate for poor placement without costing in image quality and usability.

50–6. Image brightness and lumen calculation limits

For preliminary analysis, we assume the nominal luminous flux of the projector to be 20,000 lumens. We also assume that in the white test mode, after path drops and settings, 55% of this flux will reach the image range:

${\Phi }_{effective}=20000\times 0.55=11000lm$

Average theoretical brightness on the image reference screen:

$E_{average}=\frac{{\Phi }_{effective}}{A}$

$E_{average}=\frac{11000}{36}\approx 306lux$

This number does not specify the brightness perceived by the viewer or the contrast of the image. Light transmission and scattering in droplets, viewing angle and background light must be evaluated separately.

If the width and height of the image are both increased by 20%, the area becomes 1.44 times:

$E_{new}=\frac{306}{1.44}\approx 212lux$

So enlarging the image with constant luminous flux reduces the average brightness. This example is independent of geometry control; A larger image may no longer fit in the useful area of ​​the screen.

The number of lumens is one of the selection inputs; The final criterion is the visible quality in the actual conditions of the project.

50–7. Water circuit and pump power estimation

The conceptual arrangement of the circuit includes water withdrawal from the pond, inlet protection, pump, transmission line, regulating equipment and curtain nozzle. The splashed water returns to the pond.

For example, the flow rate is 120 cubic meters per hour and the total head is assumed to be 25 meters. The hypothetical components of the head are:

This table is not the real data. The achievement of the 18 x 6 m curtain with this work point must be confirmed by the manufacturer.

With a hypothetical total return of 0.65:

$P_{electric}=\frac{\rho gQH}{\eta }$

$P_{electric}=\frac{1000\times 9.81\times (120/3600)\times 25}{0.65}\approx 12577W$

Therefore, the estimated input power:

$P_{electric}\approx 12.58kW$

The motor rating and pump operating range should be determined by the actual curve, suction conditions and circuit setting conditions.

50–8. Pressure stability and water level quality

The screen needs a relatively stable surface. Pressure fluctuation can change the curtain border, water density and image uniformity.

To check a line with an assumed internal diameter of 125 mm:

$v=\frac{Q}{A}$

$v=\frac{120/3600}{\pi (0.125{)}^2/4}\approx 2.72m/s$

This number is only the result of speed calculation and does not confirm the final diameter. Pressure drop, noise, transient conditions and pump characteristics should still be checked.

In this example, the circuit of the curtain should be designed in such a way that turning on and off other fountain effects does not disturb its pressure. If a common source is used, pressure stability must be demonstrated in all permitted display combinations.

Increasing the pressure does not necessarily improve the quality of the image; The criterion for adjustment is the shape and continuity of the curtain at the valid working point of the nozzle.

50–9. Water intake and management basin

The dimensions of the pool should not be chosen just equal to the nominal width of the curtain. Water landing, wind, surface wave and secondary spray should be considered in determining the receiving area.

Aquatique Show also introduces a water curtain installation, receiving basin or installation on a floating structure. The selection of each arrangement depends on the location and dimensions of the effect. Aquatique Show water curtain deployment methods ^[330]

In this project, the pond design must specify the following:

• The actual scope of receiving water in the permitted wind conditions;

• exploitation balance and return water acceptance capacity;

• Spillway and authorized discharge route;

• cleaning access and sediment collection;

• Water quality management circuit;

• Prevent public entry into the equipment area.

The flow rate is 120 cubic meters per hour, circulation flow. Fresh water consumption should be calculated from the balance of evaporation, splashing, washing, leakage and inventory change.

50–10. Designing suitable content for the water curtain

For the present example, the visual content must be compatible with a moving and semi-transparent surface.

The guidelines for the proposed project are as follows:

• The main elements should be placed in the central area;

• The writings should be short, thick and have enough space;

Important details should not be close to the edges of the curtain;

• Each view has enough opportunity to be recognized;

• Sample content should be tested on water before full production.

A black background can help the image appear suspended, but the degree of success depends on the ambient light and the residual light of the projector.

In the hypothetical file of 1920 x 1080 pixels, the width of eight meters of the image leads to the following geometric pitch:

$p=\frac{8}{1920}\approx 0.00417m$

That's about 4.2mm per pixel on the reference screen. This value is not the actual resolution of the water curtain; Droplet movement and viewing conditions can limit detectable detail.

Figure note from the source manuscript

Figure 3–50: Example of comparable content

Two frames should be designed: first, a large emblem or form in the center with a short text; Second, the same message with fine text and many details. Subtitle: "Teaching sample for reading test; The final choice after the actual screening.”

50–11. The order of the start and end of the show

The start of the show should be done after the curtain is ready. In this example, the suggested sequence is:

1. Confirmation of permitted conditions of operation; 2. Setting up the water circuit and reaching a stable state; 3. Verification of the readiness of the video and audio chain; 4. Start of scheduled content; 5. Finishing the image and controlling the light output; 6. Controlled stop of the curtain according to the program.

The time of curtain formation should be measured. Using a fixed delay without checking the water condition is not sufficient for all conditions.

Image and music synchronization must also be adjusted after passing through all playback and processing equipment. The computer preview does not show the actual delay of the projector and audio chain.

In the image error, it must be clear that the water curtain will continue, change to a simple effect, or the display will stop.

50–12. Ambient light and wind

The lighting of the area should allow proper visibility of the image during the display and also maintain the necessary lighting of the public paths.

For this project, several lighting states are defined: normal area state, show preparation, image playback and audience exit. The effect lights that directly illuminate the curtain must be controlled in the video section, according to the program.

Wind can also move the curtain or change its density. As a result, the limited edition of the show should be anticipated from the beginning; For example, removing the visual part and continuing the effects that are of acceptable quality under the existing conditions.

The image stop threshold is not necessarily the same as the whole fountain stop threshold. The assembly may be mechanically operable, but image legibility may fall below acceptable limits.

50–13. Projector room and light path

The chamber must provide the permitted environmental conditions of the device, ventilation, service access and prevention of splashes. The window in front of the lens is also part of the optical path and should be checked for reflection, light transmission, contamination and vapor formation.

In high-power projectors, the range of access to the beam depends on the model, lens and installation conditions. Christie's guidelines also specify hazard distances and access controls for specific device and lens combinations. Christie projector installation and safety guide ^[331]

A water curtain should not be considered a reliable safety barrier for the beam. The light path should be evaluated in the absence of water.

For curtain interruption or instability, light output control shall be defined according to the method approved by the manufacturer; Showing a black frame alone should not be assumed as a protective measure.

50–14. Purchase specifications and supplier responsibilities

The query should describe the functionality of the set, not just list the equipment.

If water and imaging equipment are supplied by two suppliers, the person responsible for coordination and final quality should be specified in the contract. The separate acceptance of each device does not guarantee the quality of the set.

50–15. Image quality test at night

The test should be performed with the final geometry, the agreed ambient light and the reference content.

Viewing points should include the center and sides of the viewing area. To record a comparative image, keep the camera settings fixed; Different exposure can apparently change the quality of the two tests.

Figure note from the source manuscript

Figure 4-50: Night test from the company's archives

The grid template image and the final content should be selected from a fixed location. Test conditions, camera position and real project name should be recorded in the subtitle. The images should not be introduced as the implementation of the hypothetical project of this chapter.

50–16. Study results and final documents

Before implementation, the actual curtain curve, pump and lens selection, water intake range, light path and acceptance criteria must be completed. The final content sample should also be tested in near-operational conditions.

Delivery documents should record hydraulic settings, exact projector position, image settings, program versions, cleaning instructions, and stand-by conditions. This information allows the quality of the show to be adjusted and checked again after repair, content change or the start of a new season.