diff --git a/docs/winch.md b/docs/winch.md index 06f70b8..fc7732c 100644 --- a/docs/winch.md +++ b/docs/winch.md @@ -2,17 +2,17 @@ First, we calculate the acceleration of the tether at the ground station. It can be calculated as -$$a_{t,o} = \frac{1}{I_w} \frac{r}{n} (\tau_g + \tau_d - \tau_f)$$ +$$a_\mathrm{t,o} = \frac{1}{I_w} \frac{r}{n} (\tau_\mathrm{g} + \tau_\mathrm{d} - \tau_\mathrm{f})$$ where $I_w$ is the winch inertia as seen from the generator, $r$ the drum radius $n$ the gearbox ratio, $\tau_g$ the generator torque, $\tau_d$ the torque exerted by the drum on the generator and $\tau_f$ the friction torque. The torque exerted by the drum depends on the tether force $F$ as follows: -$$ \tau_d = \frac{r}{n}~F$$ +$$ \tau_\mathrm{d} = \frac{r}{n}~F$$ The friction is modelled as the combination of a viscous friction component with the friction coefficient $c_f$ and the static friction $\tau_s$ -$$ \tau_f = c_f v_{t,o} + \tau_s~\mathrm{sign}(v_{t,o})$$ +$$ \tau_f = c_\mathrm{f}~v_\mathrm{t,o} + \tau_s~\mathrm{sign}(v_\mathrm{t,o})$$ ### Torque controlled winch If the winch uses a generator with Direct Torque Control (DTC) it is possible to calculate $a_{t,o}$ as function of $\tau_g$, $F$ and $v_{t,o}$. @@ -20,7 +20,7 @@ If the winch uses a generator with Direct Torque Control (DTC) it is possible to ### Test case We assume an ideal kite that pulls with the force: -$$ F=(v_w~\mathrm{cos}~\beta)^2 K$$ +$$ F=(v_\mathrm{w}~\mathrm{cos}~\beta)^2 K$$ with $K=328~Ns/m$ and the elevation angle $\beta = 26^o$. Furthermore we assume the following wind speed: