Dynamic Vibration Analysis of Rotating Equipment Mounted on Steel Skid Foundations
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Finite Element Analysis
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Skid Equipment Vibration Analysis
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Design and Optimization
Poisson and Youngs Engineering was tasked with the design improvement of centrifuge mounting skid. The skid is a height adjustable platform and high vibrations are observed when the centrifuge is in operation. Poisson and Youngs Engineering was tasked to perform a Dynamic FEA analysis on the skid structure and suggest the design improvements.
​Dynamic vibration analysis of rotating equipment mounted on steel skid foundations is a crucial engineering task to ensure the structural integrity and operational reliability of equipment. The analysis involves understanding how dynamic loads, particularly those induced by rotating machinery, affect both the equipment and its supporting structure. Below are key components typically addressed in such an analysis:
Rotating Equipment Dynamics
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Rotational Imbalance: Rotating machines (e.g., pumps, compressors, turbines) generate dynamic forces due to slight mass imbalances, leading to vibrations at the operating speed (1x, 2x harmonics, etc.).
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Forcing Frequencies: Critical frequencies like running speeds and blade pass frequencies must be identified, as they can cause resonance in the supporting structure.
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Torsional Vibration: Involves the twisting oscillations in shafts due to torque fluctuations, which can affect both the machinery and the skid.
Skid Foundation Dynamics
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Natural Frequencies: The skid foundation's natural frequencies should be calculated and compared with the operating frequencies of the machinery to avoid resonance.
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Modal Analysis: This helps in identifying the mode shapes and natural frequencies of the skid and equipment assembly. FEM (Finite Element Method) is commonly used for this purpose.
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Damping Characteristics: Both structural and material damping play a role in controlling vibration amplitudes. Proper damping reduces resonant peaks and prevents excessive vibration.
Load Transfer
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Dynamic Loads: The rotating machinery induces dynamic loads on the skid foundation due to forces like imbalance, misalignment, and cyclic loading.
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Support Conditions: The boundary conditions (fixed, pinned, etc.) of the skid play a significant role in its dynamic behavior. Foundation stiffness should be accurately modeled, including soil-structure interaction if applicable.
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Transmission Paths: Vibration paths from equipment to the skid, and further to the base or ground, should be considered. Isolation mounts or pads can be introduced to reduce vibration transmission
Finite Element Analysis (FEA)
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FEA is often used to simulate the structural response of the skid and equipment. It helps in calculating stress, displacement, and modal frequencies.
First mode natural frequency equals 5.3 Hz. The Z directional Mass Participation Factor is 77% of the Total Mass of the system.
Mass Participation Factor in Vibration Analysis
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In the dynamic vibration analysis of rotating equipment mounted on steel skid foundations, the mass participation factor (MPF) is an essential concept for understanding how different modes of vibration contribute to the overall response of the system. It quantifies how much of the system's mass participates in each mode of vibration.
Standards and Guidelines
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Analysis should adhere to relevant standards like ISO 10816 for vibration severity of rotating machinery or API standards for skid-mounted equipment.
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Equipment-specific guidelines, such as API 610 (for pumps) or API 617 (for compressors), may dictate vibration limits and design criteria.
Conclusion
Through Finite Element Analysis, the Natural Frequency and Mode shapes are extracted for the maximum and minimum height conditions. It was understood that the natural frequencies of the skid are within the operating range, which may cause high amplitude vibrations due to resonance. Through design iterations, the stiffness of the skid was modified by additional enforcements. And the natural frequency of optimized skid have a 10% deviation with the operating frequency range, which will avoid resonance.