INTRODUCTION

At the time of their operation, most of the structures experiences forced vibrations. In most of the cases, these vibrations are random in nature. In the case of random vibrations, the amplitude & nature of vibrations is varying with respect to time. The random vibration response spectrum is converted from the time domain to frequency domain using a tool called FFT (Fast Fourier Transform). The resultant data is plotted in the form of PSD (Power Spectral Density) (g2/Hz) versus Frequency (Hz). This data can be provided as input in ANSYS solver in order to perform PSD analysis for the structure.

Renowned Pump Manufacturer from India approached ANALYZER to seek assistance in evaluating the design of their newly developed pump assembly for its reliability being a nuclear power plant product.

FEA WORKFLOW

• Creation of FEA model from the provided 3D model using a preprocessing tool – Hypermesh.
• Solving the FEA model for PSD Spectrum in ANSYS APDL Solver. In order to solve the model, the solver needs to be set for PSD analysis. Here we have a tool to adjust the accuracy of the solution. The accuracy is directly proportional to solution time. Hence it is decided based on the structure’s application.
• The results of PSD analysis are mostly evaluated for the Fatigue assessment of the structure while in some specific applications like shelters, the structures are evaluated for induced stresses with increased allowable limits above static loading allowable stresses.
• Report the results for the client’s reference.

CHALLENGES

• Capturing the Mass of various components of structure assembly in FEA
• Optimize the FEA model Mesh
• Setting up the accuracy for PSD Analysis

THE SOLUTION

The shelter assembly is solve for PSD Analysis. The loading is provided by client itself based on the transportation/operating conditions of the shelter assembly. Considering the application, acceptable limit of accuracy is set for PSD analysis. The shelter assembly is evaluated for induced stresses.

The results showed that the induced stresses are much below the allowable limits. Thus the shelter assembly design was predicted to be safe even in severe operating conditions during its service life.

BENEFITS

• With the help of PSD analysis, the structure or an assembly can be evaluated for the unpredicted loading – Random vibrations in a much simpler way which is not possible by a regular analytical calculations.
• The design is ensured for its reliability under dynamic loading too.