boundary of the frequency region in which the bispectrum can be calculated for the data 
sampled by interval At . 
Figure 11.2 is an example of the bispectrum of the rolling of an actual ship on the 
sea, reported by Y. Yamanouchi and K. Ohtsu.’*:’° The bispectrum in Fig. 11.2 shows 
higher values along a similarly shaped segment ABCD in Fig. 11.1 with w, at the fre- 
quency at which the linear spectrum, drawn down the side of the w, axis, shows the peak 
value, that implies the nonlinear interference is higher along these shaped segment lines, 
as ABCD. 
ROLLING BISPECTRUM 
@2 (1/SEC 
SEIUN MARU (modulus) 
DATA NO. 751 
SKEWNESS 0.22185 
PEAKEDNESS 2.79025 
LOG SCALE 
0.5 
DEG®/(CPS) 
3p fe sr NS 22 
= Din ws (Bal 
DO) 
TI4 1 |y5) 34mm vu O te BO Be BO 26) 18 
Alyy 
29a 2/@) pel won i-\2s so\ 2 28 23 \.is ae: 
rs 
POWER SPECTRUM 
/\ 18) 277 33—341N ip) \ B47 37 ee 28) 3!=S29) (27) (28 2g 1s) o6 
————————s s -——_~ 
05 AA) 4.5 @; (1/SEC) 
50 \ / THE NUMBERS GIVE THE CONTRIBUTION TO THE 
MEAN CUBED RECORD IN DEG? PER (CPS)? 
DEG?/CPS 
100 
ROLLING BISPECTRUM SEIUN MARU (modulus) 
@2 (1/SEC) EXAMPLE: 45! = 0.45 X 10’ RAD 
fora 15'43' © eS? Sa’ 20/54! 14'20' 47/5732 76°40 17'S0' 9'ZT' 46 $9 75°44! 46 S'S 38 EC 1B 
4°26'ser Sa 1a‘ 14! tal '13933'46'25'56'77 e9'25" 36‘ 58.4797! 44! GF 29' 10'S3' GO GO'SY 38 56! BOSS 4a'a3 0) 
236 45 25 375 55‘! 45' Sa 26993713! 5e'az' 39'38%1f 17°40'sd e2'27'37'22'25'10' 18 39'26 9F°3f T72'39 
's0'ss'38'46's0 53’ 32'40'a7'39! 09138 a9 56 $0'$0'48! $7 67120 38/3021! 17'34' 4) <8 47 48! 45' $0 46 49' 526.35 <5'48 
0.5 1.0 1.5. @, (1/SEC) 
ROLLING BISPECTRUM 
SEIUN MARU 
(ARGUMENT) 
ROLLING BISPECTRUM SEIUN MARU (Argument) 
Fig. 11.2. An example of bispectrum of rolling of a ship on the sea. 
(From Yamanouchi and Ohtsu, 78:79 (1972).) 
301 
