- Introduction
- COMSOL Multiphysics
- AC/DC Module
- Acoustics Module
- Batteries and Fuel Cells Module
- CAD Import Module and LiveLink™ Products
- CFD Module
- Chemical Reaction Engineering Module
- Earth Science Module
- Heat Transfer Module
- MEMS Module
- Plasma Module
- RF Module
- Structural Mechanics Module
- LiveLink™ for MATLAB®
- The COMSOL API

COMSOL Multiphysics Version 4.1 introduces many new ideas and concepts to make it easier for you to create models. The following are the most important updates to the graphical user interface:

#### New layout:

In version 4 it is easier to organize and design models with the
intuitive structure of the *COMSOL Desktop*. The *Model Builder *displays
all the features of your model in one place.

#### Personalized desktop:

Control how you organize the *COMSOL Desktop *layout—your
preferences are saved for the next time you open COMSOL Multiphysics.

#### Sequences of operations:

You can now build custom model sequences to generate your geometry, physics, mesh, studies, and results. The sequences can be edited and changes are automatically updated across the model. Operations in the sequences can be modified by the parametric solver.

#### Geometric parameter sweeps:

With geometry sequences COMSOL can perform geometric parameter sweeps with full associativity from the user interface.

#### Material settings:

Materials are now administrated in one node in the Model Builder. You can select a material and its properties for each domain and for all physics in that domain.

#### Multiple solutions and meshes:

With the new layout, you can save and view multiple solutions and
meshes, and compare and contrast the results in the *Results*
branch.

#### Probes:

Use probes to visualize scalar quantities during computations. The quantities can be defined as integrals, max/min, the average of a field quantity, or the value at a point. This now works for time stepping and parameter sweeps.

#### Dynamic help:

The new context-dependent help enables easy browsing with extended
search functionality. The *Help Desk *provides access to the
complete documentation set in PDF and HTML formats.

#### Improved graphics:

Faster, better looking graphics.

#### Model settings:

Access to the model settings is easier and more intuitive. When you select a node in the Model Builder, a docked window containing associated settings displays at the same time.

#### Predefined selections:

Define selections of domains, boundaries, edges, and points. These predefined selections are available in the Settings windows for the physics interfaces, meshing, and when studying the results.

#### LiveLink™ family of products for integrating with CAD and MATLAB®

The new LiveLink™ for SolidWorks®, LiveLink™ for Inventor®, and LiveLink™ for Pro/ENGINEER® products connect COMSOL Multiphysics directly with these CAD programs for interactively linking parameters specified in a CAD system with simulation geometry. In addition, LiveLink for MATLAB is available for incorporating COMSOL Multiphysics models in the MATLAB technical computing and programming environment.

#### Cluster support

A floating network license for COMSOL Multiphysics can be extended at no additional cost to computational nodes for clusters on the Windows Cluster Server 2003, Windows HPC Server 2008, and Linux platforms.

Version 4 also introduces:

- New and enhanced physics interfaces and predefined multiphysics interfaces

- New parallel solvers and higher solver performance:

- A modal solver for frequency response and time domain (for structural and acoustics simulations, for example)

- The MUMPS and SPOOLES direct solvers for parallel and cluster computing

- A time discrete solver

- A fast-frequency sweep solver using AWE (asymptotic waveform evaluation) for electromagnetic waves simulations, for example

## New Functionality in Version 4.1

General COMSOL Desktop Functionality

- Undo/redo of many operations in the Model Builder and the Settings window.

- Copy-paste and duplication of selected nodes in the Model Tree, such as functions, selections, study steps, plot groups and plots, and images and data for export.
- Automatic save and recovery of models during solver operations.
- The dtang operator is a complement to the d and pd differentiation operators. dtang(f,x) computes the derivative of f with respect to x, in the tangential direction along a boundary, when f is defined only on the boundary and therefore cannot be differentiated using the d operator.
- License borrowing is now available directly in the user interface. This functionality allows floating network license users to borrow a license and run COMSOL, for example, on a laptop or a home computer that is not connected to a network.

### Geometry

- 3D Helix predefined geometric primitive.

- Parametric curves in 2D and 3D. Curves can now be described as functions of a parameters.
- Geometry sweep, in 3D, based on parametric curves.
- Polygon nodes for easily creating polygons from coordinate data.
- Rendering of work planes in 3D.
- COMSOL geometries can now be converted to the Parasolid format in the CAD Import Module. This allows for the parameterization of geometries that combine imported parts from CAD files and parts created using COMSOL geometry operations.
- Export to the Parasolid file format using the CAD Import Module is now supported for most COMSOL geometries, including objects created by extrude and revolve. You can then access geometries created in COMSOL in your CAD software.

### Mesh

- Physics-controlled meshing, which automatically creates meshes that are adapted to the physics in the model. This is for example utilized by the Fluid Flow interfaces that create a somewhat finer mesh than the default and in addition create boundary layer meshes on no-slip boundaries.
- Improved and more robust boundary layer meshing. The boundary-layer mesher can now handle cases where interior boundaries intercept the boundary layer.
- A deformed mesh can now be used as a geometry. Using the Moving Mesh interface, you are able to manually remesh in order to keep a high quality mesh as the geometry deforms.

For more information on how to use physics-controlled meshing for fluid flows, see *“Physics-Controlled Meshing” *in the COMSOL Multiphysics User’s Guide.

### Physics Interfaces

- Display of equations in physics interfaces, which gives a compact and precise description of your physics settings.
- Support for additional element types in the PDE interfaces: Argyris, bubble, curl, divergence, discontinuous, Hermite, and Gauss point data elements.
- The PDE interfaces now support setting the field name and dependent variables independently. You can create a vector field, under one name, that encompasses several dependent variables.
- Additional functionality in the physics interfaces for each module, see the module sections in these release notes.

### Studies and Solvers

#### Improved usability in the Study branch:

- Settings in the study steps and the corresponding settings in the solvers are synchronized by default.
- The relative tolerance for the time-dependent solver can now be set in the study step.
- The Time discrete solver is now enabled by adding a Time Discrete study step. This solver gives you full control of the time discretization and can be used, for example, in the projection method for fluid flow. To use this method for fluid flow, you also have to select the memory efficient form option in a Fluid Flow interface.
- A computation is easily resumed by right-clicking on the study or solver nodes and selecting Continue.
- Computations can also be started from any solver step by selecting Compute From Selected in the solver sequence.
- Time-dependent simulations can be segregated for one-way coupled multiphysics models. The solver picks the value of the variable not solved at every time step during the solution of a second variable. This is available by selecting the All option for the variables not solved for in the Dependent Variables settings.
- Show default solver creates a new active solver if the current solver has been edited. The old solver is kept in the tree but it is no longer active. If the study step or the physics have been changed, but the current solver has not been edited, the current solver is refreshed with the settings from the study step and physics. If a solver setting has been changed manually, an edit overlay is displayed on the corresponding solver.
- Scaling of eigenvectors can be done using mass scaling and maximum values, in addition to the root mean square (RMS). The mass scaling gives eigenvectors that can exchange with other software in a standard fashion. The scaling with maximum values visualize eigenmodes using the same range (max = 1).
- Mass participation factors are computed for eigenvalue/eigenfrequency studies. A mass participation factor for an eigenmode gives an estimate of how much vibrational energy is dissipated through an eigenmode in each direction.
- Linearized frequency-domain problems can be solved about a general stationary bias solution. This bias solution can be the solution to a nonlinear problem. A perturbation operator allows you to specify the load that should be applied in the frequency domain. In Results, you are able to visualize the load and the response to the load in the frequency domain as well as the bias solution and combinations of the bias solution and the frequency response.
- The AMG preconditioner now support complex-valued problems. This allows for the use of memory efficient iterative solvers for problems solved in the frequency domain.
- The choice of damping factor in the automatic damped Newton method is improved. This yields a more robust solution process for nonlinear problems.
- Automatic and manual scaling can now be mixed for more robust solution of multiphysics problems.
- Explicit time stepping solver using the Runge-Kutta method is now available. This solution method may give a higher performance for problems that require very small time steps.

### Results

- Labels have been added to contour plots.
- You can now display several plot windows that visualize a plot group. (The Plot In option in 4.0a only allowed several plot windows with snapshots of the graphics window.)
- Polar plots that displays graphs in polar coordinates specified by radius and angle.
- Frequency-domain transformation using FFT for computing frequency spectra from time-dependent simulations.
- Data sets for visualization of results on surfaces and edges.
- Data series operations for computing the maximum, minimum, average, or integral of, for example, the values of a quantity in a point over time for a time-dependent model.
- Export of table data to file.
- Syntax for special characters (Greek letters, mathematical symbols, and others) are now enabled in plots. Unicode characters can also be used and will then be printed with the current font. Special characters always use our symbol font.
- Transparency has been improved to correctly show several overlapping faces. This works for OpenGL rendering and software rendering.

### Backward Compatibility vs. Version 3.5a

#### Deformed Geometry Interface

The Parameterized Geometry application mode in versions 3.5a, which is limited to 2D, is replaced with the Deformed Geometry interface in version 4.1. This interface is available in 2D and 3D. The Deformed Geometry interface deforms the mesh using an arbitrary Lagrangian-Eulerian (ALE) method and is not the parameterized geometry using geometric parameter sweeps (see above), which is new functionality in version 4.1.

In the version 4.1 interface, the Linear Displacement and Similarity Transform boundary conditions are not yet available as preset conditions. Those boundary conditions are planned for version 4.2.

In version 4.1, you can create the corresponding conditions by manually entering variables.

#### Pairs Boundary Conditions

Pairs are used to connect boundaries between domains that are separated by an assembly boundary (boundary between different parts in an assembly). To create an assembly, you have to either import it from a CAD package or actively form an assembly as a final step in the COMSOL geometry sequence.

Pair boundary conditions are available as general conditions for all application modes in versions 3.5a. Most pair boundary conditions that were available in COMSOL 3.5a can be found in the physics interfaces in version 4.1. Exceptions from this are listed under backward compatibility for each product.

### Periodic PAIR Boundary Conditions

Periodic boundary conditions are used to model repetitive structures, where one boundary in a domain is identical to another boundary in the same domain.

Periodic boundary conditions are available as general conditions for all application modes in version 3.5a. In version 4.1, this functionality is a tailored condition for each physics interface.

However, some physics interfaces may lack periodic boundary conditions in version 4.1; see the Backwards Compatibility section for the modules below.

Note that all physics interfaces will include periodic boundary conditions in the future.

### Axisymmetric Models

In version 3.5a equations in axisymmetric application modes use the independent variable for the radius, r, to account for axisymmetry. In version 4.1, the equations are compensated by using the factor 2πr.

If you have manually multiplied expressions by 2π for a version 3.5a model, please note that these may be incorrect when the model is opened in version 4.1.

### Report Generator

The report generator is not yet implemented in version 4.1. A report generator is planned for 4.2.

### Backward Compatibility for pre-3.5a models

COMSOL 4.1 can load models saved from version 3.5a. For loading models from earlier COMSOL versions than 3.5a you need to load them in COMSOL 3.5a and then save them. For simplifying this task a utility is available where you can convert all files in a directory from versions 3.0–3.5 to version 3.5a. See the section *“COMSOL Convertpre35a Command” on page 51* for Windows, section *“COMSOL Convertpre35a Command” on page 85* for Linux, section *“COMSOL Convertpre35a Command” on page 112* for the Mac in the COMSOL Installation and Operations Guide for more information.