# CM2 FEM® Engines /release 4.4.0

- 4.4.0 RC3
- April, 2019
- All CM2 FEM® Engines
- Major release of the CM2 FEM® Engines
- Due to changes in the API, client applications must be recompiled against the new headers

### /caveats

- Lib names suffix is
`_44`

for this series. - New GCC 7 and GCC 8 builds (Linux 32/64).
- Solvers are now OMP-parallelized on macOS.
- Now requires run-time type information (RTTI), i.e. option /GR on Visual Studio.
- Visual Studio < 2010 and GCC < 4.8 are no longer supported (minimum versions raised to Visual Studio 2010 and GCC 4.8).
- macOS < 10.9 is no longer supported (minimum deployment target raised to 10.9 Mavericks).
- Windows XP is deprecated and will be no longer supported in future versions.

### /new features

#### Elasto-plasticity

- New elasto-plastic laws (only Prandtl-Reuss types based on Von-Mises criterion and isotropic hardening so far):
- Scalar laws:
`fem::law_scalar_ep_perfect`

,`fem::law_scalar_ep_piecewise_linear`

,`fem::law_scalar_ep_power`

and`fem::law_scalar_ep_RambergOsgood`

. - 1-D laws:
`fem::law_spring_ep_perfect`

,`fem::law_spring_ep_piecewise_linear`

,`fem::law_spring_ep_power`

and`fem::law_spring_ep_RambergOsgood`

. - 3-D laws (also used in plane-strains and axi-3d models):
`fem::law_solid_ep_perfect`

,`fem::law_solid_ep_piecewise_linear`

,`fem::law_solid_ep_power`

and`fem::law_solid_ep_RambergOsgood`

.

- Scalar laws:
- All solvers now manage elasto-plastic states, both from an initial state and to an output state (through the new
`fem::FEM_states`

class, see below).

→ Caveat: at present elasto-plastic laws are not thread-safe. You shouldn’t run concurrently several solvers (`fem::solver_static_Newton`

) that change plastic states in shared laws (or duplicate the laws). - Cumulative plasticity and plastic strains can also be computed on an element-by-element basis with
`fem::elementary_server`

. - New
`fem::FEM_states`

to gather DOF-indexed solutions (similar to`fem::FEM_matrix`

), thermal stress managers and internal states (historic plasticity parameters at integration points) required to reproduce (usually equilibrated) FEM states.

Because`fem::FEM_states`

publicly inherit from`fem::FEM_matrix`

(and has a conversion constructor), instances of this new class can almost be used anywhere a`fem::FEM_matrix`

used to be required.

#### Thermal static analysis

- New thermal models
`fem::model_heat_conduction_1d`

,`fem::model_heat_conduction_2d`

and`fem::model_heat_conduction_3d`

(scalar isotropic Fourier models).

These new physics models should be associated to the new`fem::numerical_model_heat_conduction`

and, just like the mechanical model counterparts, to a mesh connectivity matrix (all element types are supported). - New user-defined thermal matrices:
`fem::thermal_diag`

and`fem::thermal_sym`

. - New
`fem::solver_thermal_static_linear`

to solve static linear thermal problems. - Heat flows can be post-processed on nodes with the new class
`fem::solver_least_squares`

generalizing the former`fem::solver_stress_nodal`

class (see below). `fem::elementary_server`

has been updated to computes elementary thermal matrices, vectors, temperatures and flows.`fem::solver_condensation_static`

can now condense also thermal models.

For that purpose the new field`fem::solver_condensation_static::settings_type::physics_kind`

should be set to`FEM_DOFS_TEMPERATURE`

(default`FEM_DOFS_STIFFNESS`

).`elementary_load`

now accepts also`TEMPERATURE`

and`HEAT_FLOW`

field types and works with`fem::loads_mgr`

on both Dirichlet conditions (`TEMPERATURE`

) and Neumann conditions (`HEAT_FLOW`

).

#### solver_least_squares

- Supersedes the deprecated
`fem::solver_stress_nodal`

to post-process data on nodes.

This new class smooths stresses as before but now also cumulative plasticity, plastic strains, total strains, Von-Mises stress and heat flows.

#### law_shell_skyline

- New
`fem::law_shell_skyline`

for full (skyline profile) user-defined plate/shell elasticity law.

#### law_solid_skyline

- New
`fem::law_solid_skyline`

for full (skyline profile) user-defined solid elasticity law.

#### post_processor_1d

`fem::post_processor_1d`

can now work on non-linear beam/rod models.

Note that diagrams are not exact in these cases, especially when the elements are subjected to large displacement/deformations (exact only for 2-node linear thin, non-tapered beams/rods).

#### solver_z_impedance

`fem::solver_z_impedance`

: now accepts Dirichlet boundary conditions.

Just as Neumann boundary conditions (force & momentum loads), Dirichlet boundary conditions are considered as periodic with pulsation`omega`

(i.e. forced vibrations).

#### solver_static_Newton

- New
`data_type::output_steps`

giving the number of equilibrated solutions in the`outputs`

solutions.

The last converged solution is at column`outputs.col(output_steps - 1)`

and`output_steps < outputs.cols()`

in case of convergence error.

Note that`output_steps == pseudo_times.size()`

.

#### context

- New
`fem::context::get_max_threads`

and`fem::context::get_LLC_size`

members.

### /improvements

#### All solvers

- Minor speed-ups in the computation of external load works.
- Use of OMP
`ordered`

clauses for numerical reproductibility of the assemblies (factorizations and resolutions are still affected by parallel noise).

#### solver_static_linear

- Speed-ups with Dirichlet-only boundary conditions on unfixed DOFs (unfixed DOFs with prescribed values are now eliminated just like fixed DOFs).
- Minor speed-ups within the conjugate-gradient solver (called only with multiple load cases + mixed Dirichlet/Neumann conditions).

#### solver_modal, solver_modal_ldrv, solver_modal_gyroscopic, solver_buckling_Euler

- Minor speed-ups.

### /fixes

#### All solvers

- Some crashes in multi-threaded resolutions when out-of-core (OOC) management is activated (i.e. for big models exceeding the value set in
`fem::context::memory_management`

). - The quadrature schemes were inaccurate with W6, PY5, TH10, W18 and P14 elements (mass and stiffness).

For instance, we now use 5 points for TH10 stiffness (instead of 4), 12 points for W6 mass (instead of 6), 21 points for W18 mass (instead of 18). This can lead to slight increases in computation times.

The quadrature schemes for P5 and P14 are also more accurate now (with unchanged number of points). - Reproducibility issues.

#### solver_modal

- Serious performance issue with
`settings.mass_matrix_kind = cm2::FEM_LUMPED_MATRIX`

and activated out-of-core (OOC) management.

#### solver_stress_1d

`fem::solver_stress_1d`

didn’t take external loads into account. This led to inaccurate results.

#### post_processor_1d

- Crashed with 3-node beam elements and hard offsets.

#### solver_Newmark, solver_static_Newton

- Bug when a problem had multiple load cases and different prescribed DOFs on these load cases.

As stated in the API, only the first load case should have been taken into account.

This wasn’t true. The next load cases could clobber this first one leading to erratic results.

#### solver_static_Newton

- Could erroneously declare convergence.

#### solver_static_linear

- Any convergence error of the conjugate-gradient solver (called only with multiple load cases + mixed Dirichlet/Neumann conditions) was silently discarded leading to unwarned wrong solutions.

#### solver_condensation_static

- Error on
`data_type::Fc`

(usually wrong sign).

#### numerical_models_mgr

- With
`fem::numerical_models_mgr::get_NM`

, the returned numerical model lost track of its underlying mechanical model if any (i.e. the`fem::numerical_model_base::get_mechanical_model()`

failed).

Note that`fem::numerical_model_base::get_mechanical_model()`

is deprecated and renamed`fem::numerical_model_base::get_physics_model()`

. See below.

#### context

- Fix physical core count for some CPUs (Intel) and LLC size (AMD).

### /breaking changes

#### All solvers

- The output solutions is now a
`fem::FEM_states`

instead of`fem::FEM_matrix`

.

A conversion constructor is provided in`fem::FEM_states`

to conveniently convert the latter into the former.

However using the new class is recommended wherever needed. - For solvers with initial solution (almost all solvers) the initial thermal stresses field is removed and is now included in the field
`data_type::initial`

of class`fem::FEM_states`

. - The input solution fields are renamed
`data_type::inputs`

and`data_type::input_IDs`

.

Former name`data_type::sols`

and`data_type::sols_IDs`

are still valid but deprecated. - The output solution fields are renamed
`data_type::outputs`

,`data_type::S_outputs`

,`data_type::D_outputs`

or`data_type::B_outputs`

.

Former names`data_type::sols`

,`data_type::stresses`

,`data_type::reactions`

,`data_type::S_modes`

,`data_type::D_modes`

and`data_type::B_modes`

are still valid but deprecated. - The output data
`data_type::sols_requested_memory`

,`data_type::S_modes_requested_memory`

,`data_type::D_modes_requested_memory`

and`data_type::B_modes_requested_memory`

are deprecated.

Use`data_type::outputs_requested_memory`

,`data_type::S_outputs_requested_memory`

,`data_type::D_outputs_requested_memory`

and`data_type::B_outputs_requested_memory`

instead.

#### solver_stress_nodal

- Deprecated. Please use now
`fem::solver_least_squares`

.

#### law_plane_strain, law_axi3d_stiff, law_axi_torsion_stiff

`law_plane_strain`

,`law_axi3d_stiff`

and`law_axi_torsion_stiff`

are removed.

You must now use directly the`fem::law_solid_stiff`

instead wherever the former laws was required (plane-strain, axi3d and axi-torsion mechanical model constructors and initializers).

#### stiffness_sym

- Former class
`stiffness_sym`

is now split into two classes:`fem::stiffness_sym`

for linear unmodifiable models (loosing the callback handler) and`fem::stiffness_sym_nl`

for non-linear matrix modifiable through a call-back handler (`fem::stiffness_sym_nl::stiff_callback_handler_type`

).

This latter class gains two additional handlers (`fem::stiffness_sym_nl::get_state_callback_handler_type`

and`fem::stiffness_sym_nl::set_state_callback_handler_type`

) to allow users to manage internal states of elasto-plastic constitutive laws. - The stiffness handler can now be called with
`code_KFE = 0`

(i.e. none of the stiffness matrix, internal work vector or elastic energy is requested). In these cases, the`stiffness_sym_nl`

object should consider the current solution`U_loc`

as balanced (i.e. no longer virtual) and save internally its current (plastic) state. This happens at each Newton and Newmark step.

#### contact_plane, contact_cyliner, contact_sphere

- To help convergence of the Newton-Raphson algorithm, the stiffness law is now based on a Hill-sigmoid function instead of the former (not derivable) Heaviside march function.

The new parameter`lambda`

controls the slope near the`e = 0`

point (the larger, the stiffer the slope).

The default (`lambda = DBL_MAX`

) reduces the sigmoid to the former Heaviside function. - The
`lambda`

parameter can be negative. This has the effect of reversing the direction of contact (but only positive`radius`

are now accepted).

#### damping_Rayleigh

- Renamed
`fem::damping_Rayleigh`

.

#### solver_condensation_static

- Field
`fem::solver_condensation_static::data_type::Fc`

is now a`cm2::DoubleMat`

(to be consistent with`fem::solver_condensation_static::data_type::Kc`

).

Used to be a`fem::FEM_matrix`

.

#### DOF stride

- The DOF stride is now 9 instead of 6.

This change shouldn’t have any impact if you use the`fem::DOFs_mgr::DOF_STRIDE()`

member as required (note however that this member is now deprecated, use`fem::DOFs_mgr::stride()`

instead).

#### numerical_models_base

`fem::numerical_model_base::get_mechanical_model()`

renamed`fem::numerical_model_base::get_physics_model()`

.

`fem::numerical_model_base::get_mechanical_model()`

is left for compatibility but deprecated.

#### context

`fe::context::set_default_penalty_factor`

(resp.`get_default_penalty_factor`

) renamed`fem::context::set_min_penalty_factor`

(resp.`get_min_penalty_factor`

).

And the behaviour changed.

The default penalty factor was used whenever the regular penalty factor (product of the raw penalty factor with the model’s characteristic stiffness) was 0.

This happened when the model had no sub-models associated to a mesh (only springs, links, punctual masses for instance).

Now, the minimum penalty factor is used as a lower bound for the regular penalty factor (even when this regular penalty factor is not 0).

The default value for this minimum penalty factor is still`1E12`

(like the default value for the former default penalty factor).

#### File names

- New files in the API and changes in old filenames.

These changes shouldn’t have any impact if you include the main file`cm2_fem.h`

as required.

#### physics_type

- Changes in
`physics_type`

enums (used in`fem::elementary_server`

and new`fem::solver_least_squares`

):- New
`FEM_NODES_STRAINS`

,`FEM_NODES_ELASTIC_STRAINS`

,`FEM_NODES_PLASTIC_STRAINS`

,`FEM_NODES_STRESSES`

,`FEM_NODES_PLASTICITY`

,`FEM_NODES_VON_MISES`

. - New
`FEM_DOFS_TEMPERATURE`

,`FEM_NODES_HEAT_FLOW`

. - Former
`FEM_NODES_STIFFNESS`

replaced with`FEM_NODES_UNIT_MASS`

.

- New

#### error_type, warning_type

- Changes in values of enums in
`error_type`

and`warning_type`

.

#### Miscellaneous

- Now built on Windows with
`UNICODE`

encoding setting (used to be`MBCS`

).

This may impact functions taking a filename as argument (such as`context::memory_management`

).