L5: Tidal Energy Flashcards
Technically, what is the tide?
A forced wave caused by the sun and moon - unlike ‘free waves’ caused by the wind as it must be driven by a force all the time
What are the names of tidal currents flowing in and out?
In: flood current
Out: ebb current
When do the strongest ebb and flood currents occur?
Near time of/before high and low tides
Why is the moon more influential over the tides than the sun?
The distance is to the power of 3 in the gravity equation. The sun has a far larger mass but is much further away
What forces cause the moon to orbit Earth?
Combined effect of gravity and inertia (tendency of moving objects to move in a straight line)
What is the combined result on the sea of the inertial forces from Earth’s motion and the gravitational attraction to the moon?
Two bulges of water, roughly opposite each other with one facing the moon
What do the Earth and moon both rotate about?
The system’s centre of mass, which lies within the Earth but offset from the centre towards the moon
Why are two bulges of water formed?
When near the moon gravitational forces are stronger than inertial forces. On the other side of the planet, it’s further away from the system’s centre of mass so inertial forces are stronger
What is a neap tide?
A neap tide is the tide when the moon, earth and the sun forms a right angle. They are smaller than average
What is a spring tide?
A spring tide is the tide when the Sun, Earth and moon align. The gravitational effects of the sun and the moon are superimposed onto each other, creating a large tide
When do spring and neap tides occur?
In two week intervals - spring with every new and full moon, then neap tides arrive one week after the spring tide
What causes the different tidal patterns across Earth?
Land masses interfere with tidal flow
What are the three types of tidal cycles?
- Diurnal (one high tide per day)
- Semidiurnal (two high tides of approx same size)
- Mixed semidiurnal (two high tides of different size)
What dictates current flow direction?
In open water, it depends on the direction of the tidal wave. In channels/straits, current is constrained to flow up and down the channel
Why is no yaw mechanism needed for tidal turbines?
The ebb and flow currents simply flow opposite to each other every day, will only be slightly off-axis
