CYLINDER AIR WATER IMPEDANCE BOUNDARY 3 D FEM

CYLINDER AIR WATER IMPEDANCE BOUNDARY 3 D FEM Monopole Source Water Air and Cylinder

geometry water air UNITS m: kg: s: N: Pa

FIELD POINT LOCATION Position where SPL is measured FIELD POINT NID 5374

Mesh 0. 25 m

Mesh lengths RADIAL AXIAL

Mesh 0. 25 Cylinder Air Water

Runt time 1. 024 s STEP 1 TIME DOMAIN ANALYSIS Step 1 Time Domain Analysis Step 2 Frequency Domain Analysis Maximum solid element length 0. 25 m (AXIAL) Maximum solid element length 0. 09 m (RADIAL) V= d/t or c=l*f c: speed sound l: wavelength f: frequency WATER c=1500 m/s want f=500 hz hence l=1500/500 l=3 m AIR c=340 m/s hence l=340/500 l=0. 68 m AIR element size <(1/6)*0. 68 = 0. 113 m (maximum length must not be greater) Largest Element size = 0. 25 m > 0. 113 m STEP 2 FREQUENCY DOMAIN ANALYSIS

BOUNDARY CONDITION – Impedance surface BOUNDARY CONDITION - Velocity by TRANSIENT ANALYSIS FREQUENCY DOMAIN ANALYSIS

Impedance WATER =1000*1500 kg/(m^2*s)

SCENARIO CWA Mesh length (z direction) 0. 25 Cylinder diameter(m) Cylinder length(m) Cylinder thickness(m) End plate thickness(m) 1 10 0. 005 Mesh length

Simulated Monopole Source

Mesh length MESH 1 0. 25 m Monopole Source Element Volume 7. 1144 e-05

Monopole Source Simulation Displacement

Max MS volume (expanded) Neutral MS Volume Min MS volume (compressed) Frequency 10 hz expanded Neutral position compressed

Mesh 0. 25 m Monopole Source

PLOT INTERVAL VERSUS TIME (DATABSE_D 3 PLOT)

Boundary Acoustic Impedance Surface on the Water External Surface External Water Boundary Condition elements point away from the water

Water WATER AIR Air Solid elements where pressure extracted

Monopole Source

SCENARIO CWA Mesh length (z direction) 0. 25 Cylinder diameter(m) Cylinder length(m) Cylinder thickness(m) End Plate thickness(m) 1 10 0. 005 Cylinder Air Water

MESH 0. 25 m CWA 10 HZ AIR WATER

Transient Analysis 1 s or 2 s duration

Monopole Source Excitation Frequency 10 hz 20 hz 50 hz 100 hz