Vessel/Stinger/Pipeline Fully Coupled Analysis for Pipelaying Operation

During pipelaying operations, dynamic performance of the stinger due to vessel motion has a strong impact on the stinger capacity estimation. However, the conventional stinger structural design is based on the maximum load on the roller boxes corresponding to a target top tension value. In addition, the installation analysis uses the uncoupled vessel motion Response Amplitude Operators (RAOs) to calculate the motion induced loads on the stinger and the pipeline. Since the maximum loads on the stinger are conservatively estimated by linearly superimposing maximum forces from different loading conditions, the conventional design and analysis approach leads to either over-design of the stinger structure or underestimation of the stinger capacity. To improve conventional pipelaying design and analysis methodologies, a time domain vessel/stinger/pipeline Fully Coupled Analysis (FCA) is presented in this study. The new analysis procedure significantly improved the stinger operation limit compared to the conventional design and analysis procedure.

Stinger Structural Analysis Using Fully Coupled Model for Pipelay Operations

With the growing demands and increasing challenges in deep-water pipeline installation, it is increasingly important to optimize stinger capacity assessment procedure for higher level of accuracy and cost-efficiency as compared to the traditional approach which is highly conservative. The traditional approach combines maximum stresses from three different analyses for environmental loads, vessel motions and pipeline forces to calculate the dynamic performance of a stinger. This approach ignores the coupled behavior between stinger, vessel and pipeline leading to conservative results and over-design which significantly underestimates the operational limits of the stinger structure. The main objective of this study is to develop a simple yet optimized and accurate stinger design and analysis procedure by considering the combined effect of vessel motion, pipeline forces and environmental loading on stinger structure. This is achieved by performing a Fully Coupled Analysis (FCA) in time domain, with capability to capture the impact of stiffness and hydro-elastic properties of stinger and pipeline. The fully coupled model also allows inclusion of hydrodynamic loads on installation vessel as compared to use of vessel motion RAOs in the traditional approach. Forces from this time-history analysis are extracted and mapped onto the structural model to check for structural strength using API and AISC codes. This paper presents a comparison between structural analysis results obtained from Fully Coupled Analysis (FCA) and traditional approach. Results from the FCA procedure have shown significant improvement in the operational limits of stinger.

A Mistuned Forced Response Analysis of an Embedded Compressor Blisk Using a Reduced-Order Model

Accuracy when assessing mistuned forced response analyses is still a major concern. Since a fully coupled analysis is still very computational expensive, several simplifications and reduced-order models (ROMs) are carried out. The use of a reduction method, the assumptions and simplifications, generate different uncertainties that challenge the accuracy of the results. Experimental data are needed for validation and also to understand the propagation of these uncertainties. This paper shows a detailed mistuned forced response analysis of a compressor blisk. The blisk belongs to the Purdue Three-Stage (P3S) Compressor Research Facility. Two different stator–rotor–stator configurations of 38 and 44 upstream stator vanes are taken into consideration. Several loading conditions are analyzed at three different speed lines. A ROM known as subset nominal mode (SNM), has been used for all the analyses. This reduction takes as a basis a set of modes within a selected frequency spectrum. It can consider a complete family of modes to study the disk–blade modal interaction. A detailed comparison between the predicted and measured results has been performed, showing a good agreement for the high loading (HL) conditions.