ADsk: correction to disk average velocity equations #1205

Job	Run time
build-all-debug	7m 29s
build-all-debug-single	3m 35s
build-drivers-release	5m 16s
build-postlib-release	13m 3s
build-test-uadriver-debug	1m 26s
rtest-module-drivers	4m 35s
rtest-modules-debug	10m 45s
build-interfaces-release	4m 52s
build-fastfarm-release	13m 3s
build-openfast-release	5m 22s
rtest-interfaces	3m 33s
rtest-OF-5MW_OC4Semi_WSt_WavesWN	1m 34s
rtest-OF-5MW_Land_BD_DLL_WTurb	2m 12s
rtest-OF	15m 35s
rtest-OF-5MW_Land_AeroMap	1m 15s
rtest-OF-5MW_OC3Mnpl_DLL_WTurb_WavesIrr	2m 18s
rtest-OF-5MW_OC3Trpd_DLL_WSt_WavesReg	5m 5s
rtest-OF-5MW_OC4Jckt_DLL_WTurb_WavesIrr_MGrowth	2m 27s
rtest-OF-linearization	4m 35s
rtest-OF-simulink	11m 24s
rtest-FF	2m 58s
	2h 2m 22s

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