Water Rocket Computer Model Problems

Here is the fourth Water Rocket Computer Model Problem.

The screen shot below is from the 3D optimisation of the default 2 litreRight Click and Zoom In to see better or Left Click to show full screen. water rocket.

Again I have included the file details so that you can reproduce it yourself to investigate the peculiar maxima displayed in the screen shot on the right.

It is a plot of Flight Time as the output variable with Pressure in Vessel (18psi to 131psi) on the Y axis and Mass of Water (212g to 1487g) on the X axis with a post-thrust integration interval of 10ms and a model time limit of 1 second.

The graph shows a number of lines that run all of the way across the display.

Water Rocket Computer Model Problem 04    
Mass of Rocket Empty 120   g
Capacity of Pressure Vessel 2050   cm3
Rocket Diameter 9.5   cm
Rocket Coeff of Drag 0.56    
Nozzle Diameter 21.5   mm
Constant K for nozzle 0.16    
[ ] Launch Tube in use Not Used    
Duration of air impulse 50   ms
[ ] Parachute in use Not Used    
Launch Tube
Length 20   cm
External Diameter 21   mm
[X] Hollow Launch Tube Used    
Wall Thickness 2   mm
Length of Tube Empty 25   cm
Distance of Vent from End 0   cm
[ ] T-Nozzle in use Not Used    
T-Nozzle Diameter 4.75   mm
Diameter opened out flat 1.2   m
Parachute Coeff of Drag 0.9    
Deploy () Apogee.( ) Timer 4   s
Delay in opening 5   m
Mass of Water 850   g
Pressure in Vessel 75   psi
Height 1.5   feet
Angle of Elevation 88  
Speed at Angle of Elevation 0   m/s
Temperature 10   C
Gamma of Gas in Rocket 1.402    
Density of Gas in Rocket 1.293   kg/m3
Density of Liquid in Rocket 998   kg/m3
Acceleration due to Gravity 9.81   m/s2
Atmospheric Pressure 1013   mBar
Density of Air at STP 1.293   kg/m3

The problem here is . . .
1. to find an explanation for the curiously shaped lines.

The variables are in the table on the left...

If you give up or you think you know what is going on, look at the answers.

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