Offshore wind turbine generator

1. A floating offshore wind turbine generator comprising:

a nacelle that rotatably supports a rotor head;

a column that supports the nacelle and yaws integrally with the nacelle;

a ballast that is mounted to a lower portion of the column; and

a cable that is configured to connect the ballast to a sea floor, wherein

the column has a structure portion that bears a strength of the column and that has a higher strength against a load in a direction included in a plane having a rotation axis of the rotor head and an extending direction of the column than a strength of the structure portion against a load in a direction included in other planes including the extending direction of the column, and

the structure portion extends from a position of 50 to 80% of a height from a sea level to the nacelle to a position of 50 to 80% of a depth from the sea level to the ballast.

2. The floating offshore wind turbine generator according to claim 1 , wherein

the structure portion is a cylinder made of metal, and

a length of a cross section intersecting, at right angle, the extending direction of the column in a direction of a plane including a rotation axis of the rotor head and the extending direction of the column is longer than a length of another direction of the cross section.

3. The floating offshore wind turbine generator according to claim 2 , further comprising at least one disk-shaped or doughnut-shaped reinforcing member that has an outer peripheral portion connected to an inner peripheral portion of the structure portion and is provided in an inner space of the structure portion.

4. The floating offshore wind turbine generator according to claim 1 , wherein the structure portion is a cylinder made of metal, and includes a plurality of divided members divided in a circumferential direction of the structure portion,

a strength of the divided member intersecting, at right angle, a plane including the rotation axis of the rotor head and the extending direction of the column is higher than a strength of the divided member intersecting other planes including the extending direction of the column at right angle.

5. The floating offshore wind turbine generator according to claim 4 , wherein the strengths of the divided members are changeable by using materials of the divided member having different strengths.

6. The floating offshore wind turbine generator according to claim 4 , wherein the strength of the divided member is changeable by changing a thickness of material of the divided member.

7. The floating offshore wind turbine generator according to claim 4 , further comprising at least one disk-shaped or doughnut-shaped reinforcing member that has an outer peripheral portion connected to an inner peripheral portion of the structure portion and is provided in an inner space of the structure portion.

8. The floating offshore wind turbine generator according to claim 1 , wherein at least a portion of the structure portion is made of concrete.

9. The floating offshore wind turbine generator according to claim 1 , wherein

the structure portion has a truss structure, and

the length of the structure portion in a direction of a plane including the rotation axis of the rotor head and the extending direction of the column in a cross section intersecting the extending direction of the column at right angle is longer than the length thereof in another direction of the cross section.

10. The floating offshore wind turbine generator according to claim 1 , wherein an outer surface or an inner surface of the structure portion includes at least one reinforcing member extending on a plane that is in parallel to a plane including the rotation axis of the rotor head and the extending direction of the column.

11. The floating offshore wind turbine generator according to claim 1 , wherein

the structure portion includes a plurality of divided members divided in a circumferential direction of the structure portion,

the plurality of divided members have a first member, a second member and a third member connected together, the second member being arranged between the first member and the third member, and

a thickness of the second member is greater than that of the first member and less than that of the third member.

12. A floating offshore wind turbine generator comprising:

a nacelle that rotatably supports a rotor head;

a column that supports the nacelle and yaws integrally with the nacelle;

a ballast that is mounted to a lower portion of the column; and

a cable that is configured to connect the ballast to a sea floor, wherein

the column has a structure portion that bears a strength of the column and that has a higher strength against a load in a direction included in a plane having a rotation axis of the rotor head and an extending direction of the column than a strength of the structure portion against a load in a direction included in other planes including the extending direction of the column,

the structure portion is a cylinder made of metal, and includes a plurality of divided members divided in a circumferential direction of the structure portion,

a strength of the divided member intersecting, at right angle, a plane including the rotation axis of the rotor head and the extending direction of the column is higher than a strength of the divided member intersecting other planes including the extending direction of the column at right angle, and

the floating offshore wind turbine generator further includes at least one disk-shaped or doughnut-shaped reinforcing member that has an outer peripheral portion connected to an inner peripheral portion of the structure portion and is provided in an inner space of the structure portion.