1 There may be an appearance of force if the gradient of a gravitational field is extreme enough relative to a body's extension in the direction of the field to produce tidal stresses on the body's molecular binding energies. (The earth's ocean tides are a dramatic instance.) But this too is entirely geometric in its origin, and only manifests local variations in the intensity of the distortion of spacetime.
2 The most prominent case of hypothetical gravitational energy and its radiation is the inspiraling binary star system, where there is evidently a loss of net relative (kinetic/potential) energy between the companions due to their deteriorating orbital dynamics. In terms of gravitation as a geometric principle, the idea of a transformation of relative accelerations to force-like radiation is incongrous; the extrinsic energy corresponding to the decrease within the binary system would be interpreted instead as a purely relative increase of (kinetic/potential) energy between a binary system and the rest of the universe.
3 Like energy-bearing gravitational waves, other hypotheticals -- gravitomagnetism, dark matter, and dark energy -- can be expected to continue eluding detection, as all are based on the presumed association of gravitation with force.
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