# FEM, FEA structural analysis

We provide structural FEM numerical simulations (FEM strucrural analysis) of rotating and nonrotating machinery in the ANSYS Mechanical environment. We specialize in dynamic modal and harmonic analysis related to rotating machinery vibrations. We often perform also standard strength calculations.

Based on 3D CAD model provided by customer we develop a mathematical simulation model. We also have internal design capacities. So if necessary, we are ready to create 3D CAD models based on provided drawings or we can provide 3D scanning of existing parts and translation into CAD.

“Thanks to experience from industrial practice, when solving FEM calculations, we do not focus on generating “color images “, but on solving a technical problems with engineering approach of appropriate (generally as low as possible) complexity. An integral part of each out project is close cooperation with the client, finding and designing a solution corresponding to his technological and implementation possibilities.”

## Typical applications for FEM calculation

• Turbomachinery and its components (compressors, turbines, fans, pumps)
• Electric motors and generators
• Mechanical gearboxes
• Cabinets and base frames of rotary machines
• Vehicle frames and components
• Aircraft engine components

## Dynamic calculations (Dynamic FEM structural analysis)

RotMach specializes in FEM in dynamic analysis of rotor systems and complete machines, including damping. Dynamic analysis makes it possible to identify and solve vibration-related problems during early product development phase, but also during the entire product life cycle.
A typical output of the dynamic FEM structural analysis is a design recommendation for reinforcement or modification of the structure so that the resonant frequencies are retuned outside the working area of the device or damped out.

When calculating complete machines, we are able to consider housings, foundation frames, dynamic properties of bearings, the influence of the flowing medium (Alfords forces), etc. Based on years of experience, we are also able to approximate dynamic matrices of rolling and hydrodynamics bearings.

## Modal analysis

Modal analysis is an effective tool in solving machinery problems associated with vibration. Modal analysis makes it possible to find eigenmodes and “problematic” resonant frequencies of systems without the need for knowledge of damping or excitation effects.

The modal analysis includes in particular:

• determination of frequencies of natural frequencies (Campbell diagram) and shapes of oscillations
• evaluation of the relative damping of individual eigenmodes

## Harmonic analysis

Harmonic analysis provides a more comprehensive insight into vibration calculations. The result of the harmonic analysis is the knowledge of the magnitude of vibrations in the dimensional quantity (mm/s, mm/s2 or the magnitude of the Pk-Pk oscillation). The values ​​calculated in this way can be directly compared with the vibration values ​​measured on the actual equipment in operation or on the test bench.

• Based on information from the customer about the excitation, or our knowledge of effects such as component residual imbalance etc., we introduce into the mathematical model one or a combination of several excitations sources (represented by amplitude & frequency).
• The amount of damping introduced into the calculation is also based on our experience or consultation with the customer based on his requirements and available input data.
• The output of the harmonic analysis is, in addition to the identification of problematic resonances, also frequency-amplitude characteristics (Bode diagram) across the operating spectrum of the device.

## Strength calculations (Static FEM structural analysis)

Static strength calculations allow the identification of highly loaded areas with stress concentrations and the risk of damage and deformation of parts and assemblies. We perform static calculations considering linear (elastic region – below the yield strength) and nonlinear material models (plastic region – above the yield strength). If necessary, we include nonlinear contacts with friction in the computational model.

## Examples of solved tasks can be, for example:

• Strength calculation of stresses and deformations of all types of machine parts and structures
• Deformation of complex and inhomogeneous rotors and shaft, including complex matrices of bearing stiffness
• Calculations of thermal deformations and stresses from inhomogeneous temperature field (thermally stressed parts such as turbomachinery housings, components of  internal combustion engines, heat exchangers, etc.)
• Strength calculation of impellers, blades, rotating parts, etc. also in plastic material regions (for example for overspeed test conditions)
• Calculations of mechanisms with friction (kinematics mechanisms, turning of blades of axial blade machines etc.)
• Fatigue strength, evaluation of finite life
• Permissible load on the pipe necks of vane machines (e.g. according to API 617), stress on the piping supports etc.