Marine engineering students wanted for computer modelling for solar electric boats

Marine engineering students wanted for computer modeling for solar electric boats

I am looking to encourage the development of a computer modelling program for calculating the optimal array size, hull configuration, length and beam, Cp and electric drive power for photovoltaic powered vessels with specific load and speed requirements. I don't know if this has already been done, but it should be very straight forward mathematically.

 

There is a small paper on the hydrodynamics of solar-powered vessels at:
www.cyberiad.net\multihulls.htm

It is not a simple mathematical task.

Regards,
Leo.

 

Anything by Leo has lots of credibility. Unfortunately, Leo, your link doesn't work. Perhaps if you leave in http:// ...? Could the slash be in the wrong direction?

Try http://www.cyberiad.net/multihulls.htm

 

Sure Leo, I read all your stuff a long time ago. Very useful in a limited way since it is for a very limited set of rules of the specific race that the work seems to have been done for.

I have noticed however that there are size crossover points where according to the length, beam, and solar array size that certain loaded displacement weights are tolerated better than with smaller or narrower boats that cannot support a sufficiently large array. A cat is certainly the way to maximize the platform footprint for mounting photovoltaics. It also seems to be nearly as efficient as the best monohull configurations at least with constrained speeds. It appears to me that with a solar boat, the longer and wider the design, the greater a load may be supported at a given hull speed. For example, if I start with a 16 meter by 6 meter array (on the roof of a power cat) and increase each dimension by 10% I get more than a 10% increase in the output of the array. So the larger the footprint of the boat the greater the power to size ratio. The greater the size, the greater the displacement and load capability. Or am I missing something?

 

Hi Jonathan!
You are right that my paper is of limited use because it depends so much on the constraints imposed by the competition rules.

I don't know if I can help much unless I know what your constraints you are working with? I would have thought that a very wide array would need considerable bracing to prevent breaking. Eventually the weight of the structure would be a limiting factor.

Leo.

 

No constraints. This is a process of discovery as to where the sweet spots (dimensionally) are for solar powered twin hulls.

I think this could almost be put together in a spreadsheet. The key is to have a formula that in a catamaran, relates the length and beam of the demihull, The Cp, the hull speed, the length and beam of the twin hull platform and the power output of the array in daily KwHrs. This can yield the amount of thrust available from an electric drive of a given efficiency. I may be dreaming here, but since a higher L/B ratio gives a higher hull speed in a displacement mode, the longer the demihulls, the less power required to drive a given unit of displacement. At the same time, the longer the demihulls and wider the spacing, the bigger the power/displacement ratio (because the arrays are bigger per unit of displacement). Assuming of course that there is sufficient displacement to support the array (should be no problem, photovoltaics are lightweight), the widest section of the demihull is 2/3 aft and you have the best possible Cp. At some point you must have an awesome power/displacement ratio. Then you start using hydrofoils and you might have one hell of a boat.

As far as structure to support the array, since the roof deck can be supported by as may vertical posts as required, the array size itself should have no limitations except the platform under it which spans the deminhulls. That, of course, needs to be strong truss/triangulated construction.

 

I am not sure if it can be done straight forward as the process is iterative. Most boat design use the Design Spiral method to arrive at the optimum.

1.First, i will lay down the basic parameters such as length, speed, and range.

2.Next i will calculate the displacement by listing down arbitrary weights that will go into the boat including the weight of the hull, motor, Ect. This will give me a target displacement.

3.Then I will use michlet to find the optimum hull shape and spacing for a given displacement and speed. This will give me the Lengt overall and Width overall and consequently give me the approximate surface area for the photovoltaic cells and batteries needed.

4.The next procedure would be to design the hull in order to approximate the hull weight.

5. Back to number 2 again, or jump to 3 if the area is not enough to power the motor at a given speed or range.

6. I will repeat the iteration several times until the design spiral is tight and satisfies the ever changing constraint.

Mine is a personal approach to the subject. maybe the others have a different way of tackling it.

 

RXCOMPOSITE, No 2 will come first before you can calculate No 1 ?

 

For step 4, is there a formula for determining approximate hull weight based on material used, material thickness, reinforcement bulkhead spacing, L/B, and Cp?

D'Artois may be correct. Perhaps target displacement is the first step. Or at least maximum displacement since that together with L,B, and Cp should determine how much hull surface is below the water line.

 

Technically you are correct but when you first start "dreaming about" the boat you want, you lay down your goal then start calculating # 2 to see if what you have in mind tallies up with what the numbers are showing.

I am revising my program on multihull design and will post it soon. It runs on excell and needs only seven inputs. Other parameters such as Cp, Cb, etc. are automatically calculated. I am still working on hull population that will fit the input parameters as no single hull will fit. It is nice to see at a glance what population of hulls will fit then make the decision afterwards.

It is not a boat design, only a hull optimization program. An intelligent base to run the design spiral.

 

rxcomposite, you are a man of action! Maybe you should call it a design double helix, since it appears that you have to go through multiple iterations to zero in on the target (no offense to my Japanese friends!)

I am going to try to find out if there is a program that can calculate hull weight based on materials used, dimensions and design parameters (L, B, Cp, etc).

 

Jonathan,
Have finished it. Just writing the instructions and validating the program. I am also trying to get a tight fit on the low end of the spectrum as the formula on skin friction needs to be modified.

This should make cat design very easy. For your specific need, the program outputs a boundary area or roof area so that you will be able to tell quickly how much energy you can squeeze out of the "real state available on the roof".

I think you should couple this to a power management spreadsheet. that is, given a surface area, you would be able to divide the available power for storage, propulsion, navigation, and amenities.

Rx

 

And yes. It is based on the "sweet spot" or the optimum Froude # for a given hull to length spacing. It runs parrallel also to another set of set of formulas that defines optimum hull (least resistance for a given Froude number).

 

When a catamaran moves through water, the waves created by one hull interferes with the wave created by the other hull. Hull spacing is associated with interference effect between the component hull. The wider the hull spacing the less interference effect. But how wide is wide without necessarily creating an ungainly wide boat that will turn out to be heavier than needed?

Tasaki has published a chart based on mathematical hull form showing the interference effect between the two hulls in relation to the hull spacing plotted against Froude number. The graph shows that there are two bands (sweet band) where the waves cancels each other and is considered “beneficial”.

I have prepared a program that searches this sweet band with a given hull spacing, length, and speed. Purist call this a spreadsheet as it lacks the macro or structured program to run it but I will leave it that way so that others may be free to modify or improve on it.

The hulls are analyzed separately using parametric design lanes published by Saunders. The hull design is guided by a narrow band of workable parameters plotted against Froude/Taylors numbers. These parameters coincide with form coefficients by Lindblad and Todd.

The program does the finger walking on the tables and is designed to trap errors when the inputs are out of range.

The master program defines the general hull coefficients while the hull population sheet evaluates a set of hulls that will fit the constraint. This is the “what if scenario” wherein slight variations of breadth, draft, and maximum cross section area will give an output of deck surface area or total resistance. It is also possible to exceed the constraint to check if other variation maybe missed out.

The work was inspired by Mike D, a former member of this forum when he posted several widely used formulas. Other formulas are standard NA’s formulas.

The formulas have been validated against sea trial report of boats that have been built and works out close. Be cautioned though that the ehp is a bare hull resistance and the shaft hp has only 40% loss. In actual practice, appendage resistance may go up to 20% on bare hull resistance and propeller may attain only up to 67% efficiency in open water.

The simple resistance formula as suggested is accurate only up to S/L ratio of 1.1. The Metric value of f in resistance formula was fitted to the English f as it is more accurate.

The program will only guide the user into tight design parameters. As Leo has said, if you want to be accurate, go mathematical. Michlet will give a dead on result.

Attached is the program and instructions.

 

P.S.
I unprotected the sheet before sending. for the user, please click protection on the excell menu before using it. The entry cells and buttons are already unlocked.
Thanks