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18.5kW Boost Blower Platform, Frequency Response Analysis

Using a preliminary design from our client, MDA designed this platform to European specifications for use in Romania. Our design and analysis led to a 35% weight reduction over the preliminary design significantly decreasing material and construction costs. The platform will be mounted to an existing skid and supports two 18.5 [ kW ] boost blowers operating at 49.08 [ Hz ]. The finite element model (FEM) was cnstructed using beam elements possessing the S235JR EN 10025-2 (Euronorm) steel material model. The figure (below left) shows the loads and boundary conditions. Nodal masses representing the motor/blower weight, located at the motor/blower center of gravity, are connected to the platform using rigid massless beam elements. Shaking forces and forcing frequencies are applied to the nodal masses. For clarity, grating is not shown in the figures below.

Modal analysis revealed seven modes in the 45-55 [ Hz ] frequency range. A frequency sweep was performed over the seven natural frequencies and the operating frequency considering two different load cases: y-direction (transverse) shaking forces, and z-direction (vertical) shaking forces, resulting in a total of 16 load cases. Displacement magnitude (visually scaled 200x) at 49.08 [ Hz ] is shown in the lower right figure. For clarity, grating is not shown. Comparing the displacements and deformed shape below to the 49.07 [ Hz ] mode, it's obvious the mode is slightly activated in the braces. Read more on our Mechanical Design and Modal Analysis pages.

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375kW Vacuum Pump Baseplate, Frequency Response Analysis

MDA designed and structurally substantiated this foundation mounted baseplate to support a 375 [ kW ] motor and vacuum pump operating at 16.6 [ Hz ]. Nodal masses representing the motor and pump weights, located at the motor and pump centers of gravity, are connected to the baseplate using rigid massless beam elements. Shaking forces and forcing frequencies are applied to the nodal masses. The figure below left shows Von-Mises stresses resulting from the shaking forces. The figure below right shows the internal axial loads on the beam elements used to represent the hold-down bolts. In application, the baseplate rests on a foundation; a flat surface. However, for analysis purposes, the baseplate is constrained using the beam elements as pinned connections. This modeling technique has negligible effect on the natural frequencies and structural response, and provides a more conservative analysis as opposed to constraining the baseplate to a flat plane. Additionally, the foundation loads we supplied to our client were easily calculated using beam element forces. Read more about this analysis on our Linear Static page.

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350HP Vacuum Pump Baseplate, Frequency Response Analysis

MDA designed and structurally substantiated this platform mounted baseplate to support a 350 [ HP ] motor and vacuum pump operating at 11.9 [ Hz ]. Nodal masses representing the motor and pump weights, located at the motor and pump centers of gravity, are connected to the baseplate using rigid massless beam elements. Shaking forces and forcing frequencies are applied to the nodal masses. The pump operates at a frequency of 11.9 [ Hz ], but as the pump loads up, its speed may drop such that it operates at a slightly lower frequency. For this reason, our client requested a frequency sweep be carried out over the range 10.0 - 12.0 [ Hz ]. Read more about this analysis on our Linear Static and Modal pages.

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350HP Vacuum Pump Platform, Frequency Response Analysis

MDA designed and structurally substantiated this platform used to mount three 350 [ HP ] motors and vacuum pumps operating at 11.9 [ Hz ]. The analysis included the baseplates and rotating equipment weights. Frequency ranges for the analysis were established based on system natural frequencies obtained from the modal analysis and the pump operating frequency. Load cases were based on the shaking forces generated by the rotating equipment. Nodal masses representing the motor and pump weights, located at the motor and pump centers of gravity, are connected to the baseplate using rigid massless beam elements. Shaking forces and forcing frequencies are applied to the nodal masses. The figure below shows the displacement magnitude for the response at a frequency of 10.39 [ Hz ]; the only significant structural mode close to the operating frequency of 11.9 [ Hz ]. Read more about this analysis on our Linear Static and Modal pages.

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Diesel Engine Radiator, Frequency Response Analysis

MDA completed modal, frequency response, and stress analysis on this diesel engine radiator and bracket system. Our client provided the engine torque vs frequency curve, CAD data, material data, and system mass properties. The modal analysis was performed for the frequency range 0-200 [ Hz ] to capture adequate modes for the frequency analysis. The frequency sweep was performed over the frequency range 0.1- 130.1 [ Hz ] at 0.025 [ Hz ] intervals. We provided our client with the first 21 normal modes and frequency data as well as worst case stresses in each component and the corresponding forcing frequencies.

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Industrial Fan, Frequency Response Analysis

MDA performed linear static, modal, and frequency response analyses on this industrial fan because the customer was experiencing premature fatigue failures in the spider near one of the rivets. The operating frequency of the fan is 8.33 [ Hz ] and the lowest structural mode determined by the modal analysis was 9.55 [ Hz ]. Because the operating frequency is so close to a natural frequency, the reversed bending stresses induced in the spider over time are decreasing the fatigue life of the spider. Our client implemented design changes we recommended and validated with an additional frequency response analysis. Our recommendations led to a design resulting in decreased stresses and a theoretical infinite fatigue life. Read more about this analysis on our Modal page.

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About Frequency Response Analysis

Frequency response analysis is used to compute structural response to steady-state oscillatory excitation. Examples of oscillatory excitation include rotating machinery, vehicle engine components, and helicopter blades. In frequency response analysis, the excitation is explicitly defined in the frequency domain. Excitations can be in the form of applied forces and enforced motions (accelerations). The direct frequency response method solves the coupled equations of motion in terms of forcing frequency. As the second part of the analysis, structural response (stress and displacement) of the modal frequencies and any other frequencies of importance to the design requirements are determined. These stresses and displacements can be compared to the design requirements to make certain the structure will perform satisfactorily.

MDA and Frequency Response Analyses

MDA has performed dozens of frequency response analyses. A brief list is shown below:

  • Skid mounted generator sets
  • Skid mounted pumps
  • Industrial fans
  • Robotic components
  • Industrial coolers
  • Platforms, stacks, & derricks
  • Floors of buildings
  • Diesel truck chassis and engine components
  • Heavy machinery
  • Component parts
  • Complex assemblies

In some projects, the frequency response analysis identifies stresses and displacements which exceed the design requirements. In such instances, when requested, MDA works with our client to improve the design so it complies with requirements. Clients leverage our skills and experience for their structural substantiation needs. Read more on our Modal page. Click here to view an example of an analysis report we provide.

Our FEA Capabilities
  • Linear
  • Static stress & deflection
  • Dynamic stress & deflection
  • Critical buckling load
  • Nonlinear
  • Thermal
  • Topology optimization
  • Size optimization
  • Geometric
  • Material
  • Contact
  • Postbuckling (Riks)
  • Mechanical event simulation
  • Dynamic stress & deflection
  • Dynamic
  • Modal analysis
  • Frequency response
  • Time response
  • Response spectrum
  • Random vibration
  • Transient stress
  • Explicit & implicit
  • Drop and direct impact events
  • Rotor dynamics
  • Shock and seismic
  • Power train vibration analysis
  • Fatigue life & durability