Upload
phunghanh
View
215
Download
2
Embed Size (px)
Citation preview
Loadings affecting on boats and small craftMarkku Hentinen 2016
Local loads
• Hydrostatic pressure• Hydrodynamic pressure
– Slamming-loads– Local loads due to pressure distribution on planing hulls
• Rudder loads• Keel loads• Propeller bearing support forces• Loadings due to engine/tanks/other heavy installations
and equipment• Loadings due to deck equipment (strong points for
attachments, winches, cranes)• Ice loads
Slamming-pressures on fast planing craft
• Pressure is proportional to the square of the relativevelocity between wave and hull bottom multiplied byconstant k.
• k-value is dependent on the bottom shape; the anglebetween water and hull surfaces.
• At small angles of incidence (< 3 ) the air trapped underhull makes determination of k-value difficult.
• Peaks of slamming-pressures are transient and verylocal.
• Equation used in NBS-rule:
Slamming-pressures on fast planing craft
• Equation in ISO-standards:• where ncg is dynamic loading factor coming from
accelerations at the Lcg:
• Based on methods by Fridsma&Savitsky
nk L
Bv B
B
kkv
cgwl
c
c
x
L
ar
0 07810
0 084 5012 2
, ( . )( ) g
missä = trimmikulma ( 4 )uppouma(ton)
L vesiviivapituuspalleleveys
= pohjanousu ( 30 )= iskun pitkittäisjakauman kerroin= pinta - alreduktio
= nopeus
WL
Trim angleDisplacementLength of waterlineChine breadthDeadriseLongitudinal distribution factorArea reduction factorSpeed
DESIGN PRESSURES FOR FAST PLANING BOATSMarkku Hentinen, MScTech, Gunnar Holm, MScTechVTT Manufacturing Technology, EspooWhy very high pressures can occur?• Frequent slamming "normal"• High vertical accelerations can be allowed by the crew
Measurements of bottom pressures, strains and vertical acceleration were carried out for NV 96
Calculation methods for slammingloads
The problem is connected to the reliableprediction of:• the relative speed between the water
and the hull surfaces• the coefficient k´s value as a function of
steepness of the bottom• acceleration values for the landing
phase of the boat - it is to be noted thatdue to the light displacement and highspeed the motions are highly non-linear.
min:s01:36,000 01:36,050 01:36,100
Luotsi11
Paneeli1 Paneeli2 Paneeli3 leikkaus1 leikkaus2
pystykiiht.
kPa
125
100
75
50
25
0
-25
-50
g
25,0
22,5
20,0
17,5
15,0
12,5
10,0
7,5
5,0
2,5
0,0
-2,5
Slamming pressure during a typical slamming situation calculated from bending stressesof the panel, shear stresses of the stiffeners. Vertical acceleration near the panel is also shown.
Vertical acceleration at CG
0
20
40
60
80
100
120
140
160
30 35 40
V [kn]
a [m/s ]
DnV HSLC,DSPL=4090 kgLloyd´s SSC,DSPL=4090 kgMeas. (NV96),DSPL=4090 kgDnV HSLC,DSPL=4455 kgLloyd´s SSC,DSPL=4455 kgMeas. (NV96),DSPL=4455 kgDnV HSLC,DSPL=4725 kgLloyd´s SSC,DSPL=4725 kgMeas. (NV96),DSPL=4725 kg
Comparison of the calculated and the measured acceleration values.
Global loads
Rigging loads on a 40’ sailing boat
Rudder loads in a 40’ sailing boat
Scantlings of keelfloors and bolts ina 40´ sailing boat
Additionally.grounding loads,see ISO 12215-9