Two-level preconditioners with projectors for unstructured grids

An ingot gripper assembly for use in gripping an ingot which is substantially cylindrical in shape and having a base with an upwardly and downwardly inclined surface and being provided with an opening which extends to the inclined surface. First and second spaced apart pairs of spaced apart pins are carried by the base and extend upwardly from the inclined surface. A ball is disposed between the first and second pairs of pins and is movable upwardly from the inclined surface and inwardly and outwardly between the first and second pairs of pins. The first and second pairs of pins face each other with the first pair being spaced farther from the cylindrical surface than the second pair. The first pair of pins are inclined sideways in an upward direction. The size of the ball and the spacing between the pins of the second pair being such that when the ball is resting upon the inclined surface, the ball extends into a region defined by an imaginary cylindrical surface coincident with the first named cylindrical surface. The spacing between the first pair of pins is such that when an ingot is disposed in said opening, said ball engages said ingot and engages said first pair of pins. The ingot is free to move upwardly through the opening but is restrained in downward movement by the ball engaging the ingot and frictionally engaging the same to prevent substantial downward movement of the ingot.