Understanding Acoustic Excitations and Loads in Ansys Mechanical

Introduction: Acoustic Simulations

Acoustic simulations in Ansys Mechanical allow engineers to predict how sound interacts with structures and fluids. When preparing an acoustic analysis in Mechanical it can be difficult to determine which acoustic excitations and/or loads are appropriate for the problem at hand. This blog post will cover all the excitations and loads available for an acoustic analysis and provide some common applications for each. Readers are also encouraged to reference this previous blog post which describes foundational concepts of acoustic analysis in Ansys Mechanical.

Acoustic Excitations

Acoustic excitations define how sound energy, in the form of pressure waves in a fluid, enters the system. Depending on the source characteristics, you can choose from several options:

Mass Source

• Introduces sound by applying a volumetric mass flow rate.
• Creates pressure fluctuations by locally changing density—similar to air blowing through a small hole or a loudspeaker diaphragm.
• These pressure fluctuations radiate outward uniformly from the source.
• Ideal for internal sound sources within a fluid region.
• This is a common way to introduce pressure fluctuations without explicitly modeling the vibrating surfaces

Surface Velocity

• Represents sound generated by a vibrating surface (contrasted with a mass source which uses mass flow)
• Users can specify the directionality of the wave propagation.
• Common for speaker cones or structural panels radiating noise.

Diffuse Sound Field

• Idealized condition where sound energy is uniformly distributed.
• Commonly used for random vibration and acoustic fatigue.
• Example: A room with perfectly reflective walls and a sound source inside, in time the energy becomes evenly spread out and omnidirectional.

Incident Wave Source

• Represents far-field sound sources entering the domain, such as an external speaker or environmental noise.
• User specifies direction and frequency.
• Example: A plane wave hitting a wall from the environment.

Port in Duct

• Models acoustic radiation from a duct or port object.
• Users can specify duct characteristics, which affects how the energy is injected into the acoustic domain
• A simplification that eliminates the need to explicitly model the duct geometry
• Common in HVAC systems, exhaust pipes, and speaker ports.

Transient Variants

• Mass Source Rate (Transient): Time-dependent mass flow excitation.
• Surface Acceleration (Transient): Time-dependent surface motion for dynamic acoustic radiation.

Acoustic Loads

Acoustic loads modify the boundary conditions or properties of the acoustic domain:

Temperature

• Accounts for temperature influence on acoustic properties (e.g., speed of sound).
• Used in high-temperature ducts or engine environments.

Impedance Sheet

• Represents a surface with a specific acoustic impedance.
• Common in acoustic liners, sound-absorbing panels, and perforated sheets.

Static Pressure

• Applies a constant pressure to bodies in the acoustic fluid region.
• Used for pressurized environments under steady-state conditions.

Summary Table

Type	Purpose	Typical Applications
Mass Source	Internal sound source via mass flow	Loudspeakers, internal noise sources
Surface Velocity	Sound from vibrating surfaces	Speaker cones, structural panels
Diffuse Sound Field	Uniform sound energy distribution	Acoustic fatigue, random vibration
Incident Wave Source	External far-field sound	Environmental noise on structures
Port in Duct	Acoustic radiation from ducts	HVAC systems, exhaust pipes, speaker ports
Temperature Load	Adjusts acoustic properties for temperature	High-temperature ducts, engine environments
Impedance Sheet	Defines absorption/reflection characteristics	Acoustic liners, sound-absorbing panels
Static Pressure	Applies constant pressure	Pressurized environments

Acoustic Excitations & Loads Key Takeaways

• Excitations define how sound enters the system—choose based on source type (internal, external, vibrating surface, diffuse field).
• Loads define boundary conditions and material behavior—critical for realistic acoustic performance.
• Combining the right excitation and load ensures accurate simulation of real-world acoustic phenomena.