Choosing functions to satisfy a system of equations (BVP including limits of ratios of derivatives)

34 Views Asked by At

I'm trying to design a trajectory for a course. I have 2 equations, $y_1$ and $y_2$ on the interval $0$ to T. I can choose any equations for these providing that I satisfy the following conditions: $y_1(0) = y_2(0) = 0$, $y_1(T) = y_2(T) = 1$, $\dot{y_1}(0) = \dot{y_2}(0) = \dot{y_1}(T) = \dot{y_2}(T) = 0$, and lastly: $\lim_{t\to0}\frac{\dot{y_2}(t)}{\dot{y_1}(t)} = \lim_{t\to T}\frac{\dot{y_2}(t)}{\dot{y_1}(t)} = 0$.

At first what I did was choose an arbitrary polynomial for $y_1$ and reason that since $lim_{x\to0}\frac{x^2}{x}$ is $0$, that my $y_2$ should have $\dot{y_2} = \dot{y_1}^2$. I could not find such a $y_1$ that would allow $y_2$ to satisfy the conditions on the bounds. So then I tried sinusoidal functions also to no avail.

Was I going down the right path with the polynomial efforts? Is there a sinusoidal function I'm missing? Should I be trying exponential functions? Is there any path or technique that could allow me to solve this? Thank you.

1

There are 1 best solutions below

1
On BEST ANSWER

If you apply L'Hôpital's rule then it follows that the only additional constraints are that $\ddot{y}_2(0) = \ddot{y}_2(T) = 0$ and $\ddot{y}_1(0) = \ddot{y}_1(T) \neq 0$.

Using this you should be able to find a solution of the form:

$$ y_1(t) = a_1\, t^2 + b_1\, t^3, $$

$$ y_2(t) = a_2\, t^3 + b_2\, t^4 + c_2\, t^5. $$