New Models and Apps in the Application Gallery in Version 5.2a Several Acoustics Module models have been added to the Application Gallery (www.comsol.com/models/acoustics-module): Acoustic Streaming in a Microchannel Cross Section Recent advances in the fabrication of microfluidic systems require handling of live cells and other microparticles as well as mixing. This can, for example, be achieved using acoustic radiation forces and the viscous drag from the streaming flow. • Streaming flow: Due to the nonlinear terms in the Navier-Stokes equations, harmonic perturbation of the flow will lead to a net time-averaged flow called acoustic streaming. Acoustic streaming is a second-order (nonlinear) acoustic effect. The effect can be simulated in two ways: direct simulation solving the nonlinear Navier-Stokes equations, or by the separation of time scales, as shown here. • Radiation force: Due to nonlinear terms in the governing equations, momentum can be transferred from an acoustic field to particles. This results in a net force acting on the particles — the acoustic radiation force. The trajectory of particles in devices will be governed by the balance between the viscous drag force (from the streaming flow) and the acoustic radiation force. This model shows how to include and model both using COMSOL Multiphysics. Poroelastic Waves with Thermal and Viscous Losses (Biot-Allard Model) In applications where pressure waves and elastic waves propagate in porous materials filled with air, both thermal and viscous losses are important. This is typically the case in insulation materials for room acoustics or lining materials in car cabins. Another example is porous materials in mufflers in the automotive industry. In many cases, these materials can be modeled using the poroacoustic models (equivalent fluid models) implemented in Pressure Acoustics. The poroacoustic models do not capture all effects, so sometimes it is also necessary to include the elastic waves in the porous matrix. This is covered by the so-called Biot-Allard theory for modeling poroelastic waves. The present model shows how the Poroelastic Waves interface, relatively simply, can be tailored to include the thermal and viscous effects as described by the Biot-Allard theory. Sonic Crystal Phononic and sonic crystals have generated rising scientific interest for very diverse technological applications. These crystals are made of periodic distributions of scatterers embedded in a matrix. Under certain conditions, acoustic band gaps can form. These are spectral bands where propagation of waves is forbidden. This model first analyzes a sonic crystal and determines its band structure. Secondly, the transmission loss through a finite-sized crystal is analyzed and the results are compared to the band structure. Acoustic-Structure Interaction and Air Flow in Violins One model applies acoustic-structure interaction to study how the air mode resonance is affected by the coupled vibrations in the violin body. The other uses a potential flow approximation to find out how the air flow through the sound holes relates to their shape. Energy Conservation with Thermoviscous Acoustics This tutorial model studies energy conservation in a small conceptual test setup. The model has an inlet and outlet and a Helmholtz resonator with a very narrow neck. The acoustics in the narrow neck are modeled with the Thermoacoustic interface for a detailed analysis of the thermal and viscous losses. To study and verify energy conservation, the model compares the total dissipated energy in the acoustic boundary layer to the total input minus the output power of the system. Subcomponent Lumping in Acoustics Using the Impedance Boundary Condition This application illustrates a modeling approach for deriving physically consistent simplified models in the Acoustics Module. The approach consists of converting complex subcomponents to an impedance boundary condition and otherwise using simple acoustics throughout the COMSOL Multiphysics model.