Structural-Acoustic Simulation

Structural-acoustic interaction covers diverse application areas including noise transmission, radiation, acoustic attenuation or amplification. Abaqus integrates noise simulation within the finite element solver, allowing fully coupled structural-acoustic simulations to be performed within familiar Abaqus workflows.

: Acoustic-Mechanical Simulation of Engine Cover - Color coding of acoustic pressure generated at various excitation frequencies.

Fast, advanced linear dynamics capability for acoustic and solid media
Acoustic finite elements and materials
Nonreflecting impedance and infinite elements for exterior and radiation problems
Boolean tools for meshing acoustic cavities
Fully coupled and uncoupled eigenanalysis
Fully coupled frequency response
Transient and time-harmonic (steady-state) analysis
Surface-based fluid-solid coupling
Acoustics in moving fluids
Adaptive acoustic meshes for large-deformation enclosures (tires, seals)

Examples:

Underwater Explosion Simulation

Simulations are increasingly supplanting expensive live-fire explosive testing in the design and analysis of ships and offshore structures. Simulating the effects of underwater explosions on ship and offshore structures presents several challenges: accurate application of loading from distant explosions, strong coupling effects between the water and the ship, the effects of cavitation, and often modeling the explosion itself. In Abaqus, underwater explosion simulation capability is provided by native functionality in Abaqus/Explicit.

Far-field explosion modeling:
- Finite elements for acoustic and solid media
- Incident wave loading with surface and bottom reflections
- Fast pressure-based cavitation models
- ALE-based fluid models for coupling to structures with large deformations
- Surface-based fluid-solid coupling
- Interior fluid volumes
- Infinite elements and nonreflecting boundary conditions
- Analytical underwater explosion bubble modeling
Near-field explosion modeling

Examples:

Twin-hulled surface ship: Abaqus coupled structural-acoustics used for shock analysis of surface naval vehicle. The example shows a catamaran (double-hull boat) subjected to a shock due to an underwater explosion. Abaqus allows including free-surface and cavitation effects in the model. The total acoustic pressure animation is shown here along with the deformation of the boat. The cavitation is shown using a light gray color in the water region.
Bow section of a submarine: Underwater shock analysis of a submarine using the coupled structural-acoustics capability of Abaqus. The submarine is modeled with structural details including the free-flood compartments and torpedo tubes subjected to a shock due to an underwater explosion. The total acoustic pressure plots in the water filling the compartments along with the deformation of the structure is shown here.
Dynamic deformations of a stiffened submarine pressure hull: this model uses the coupled acoustic-shell capability in Abaqus/Explicit. The fluid exterior is modeled using tetrahedral elements (not shown), coupled to the nonconforming quadrilateral shell elements on the hull surface. The displacement response of the hull to an incident pressure wave is shown in the animations.
Free-surface cavitation: The fast pressure-based cavitation model and the nonreflecting boundary conditions are demonstrated in these two movies. The difference between the cavitating and non-cavitating solution is evident, as is the effectiveness of the nonreflecting boundary conditions in Abaqus.

Acoustic Resonance of the Tire-Air Cavity

The coupled vibration of the tire-air system is an important factor in automotive N&V. Spindle forces, and therefore noise and vibration, are observed at the resonances of the tire-air system.

Tire rotation has a significant effect on the behavior of the tire-air modes. For a stationary tire, the fundamental acoustic cavity resonance consists of two acoustic modes; the fore/aft acoustic mode and the vertical acoustic mode. For a tire with no load, all these modes occur at the same frequency. For a tire under footprint loading, the difference in frequency depends primarily on the tire construction and the load magnitude.

When a tire undergoes rotation, the air inside a tire rotates with the same velocity as the tire. This rotation gives rise to two rotating modes, one rotating with the tire and one rotating against the tire. The difference in frequency of these modes is approximately equal to twice the rotational frequency of the tire; the mode that rotates with the tire increases in frequency while the one that rotates against the tire decreases in frequency.

This behavior is illustrated by simulating a tire-wheel-air cavity model in Abaqus/Standard. The cross-section of this model is shown to the right. The tire is inflated with a prescribed inflation pressure. For simplicity, no footprint load is applied to the tire. For the stationary case, both the fore/aft and vertical modes of the tire are observed at 241 Hz. An animation showing the pressure distribution in the cavity for these modes is given below.

The tire is analyzed under two different rotational velocities, corresponding roughly to ground speeds of 40 km/h and 100 km/h. A mixed Eulerian-Lagrangian scheme is used in Abaqus to analyze the steady state rotation of the tire. The modes of the cavity for the 40 km/h case are located around 235 Hz and 247 Hz. For the 100 km/h case, the modes are located around 226 Hz and 255 Hz. The pressure distribution for the rotating modes is shown in the following animation.

A frequency response analysis, conducted for all three cases, illustrates the effect of these modes on the spindle forces. A vertical excitation in the form of a concentrated load is applied to the bottom of the tread. The effect of the mode-split can be observed on the spindle forces.

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