Stressed Skin Design for High-Voltage Direct Current Topside
Authors: Adhikary Biplab Ranjan , Majumdar Ananya , Rajalu Bhaskar G. 
Published: April 2024

The primary objective of this research is to investigate the application of stressed skin design principles to HVDC topside structures. This encompasses an in-depth examination of structural geometric configurations, and load-bearing mechanisms to optimize the structural performance. The scope extends to assessing the potential benefits of this approach in terms of cost-efficiency, reliability, and resilience in offshore environments.

The study compares conventional open-frame topside designs versus the proposed stressed skin design technique using a multidisciplinary approach, combining cutting-edge structural analytic tools, finite element simulations, and Python coding. It builds a thorough finite-element model of the HVDC topside structure using ANSYS software suit and several load situations. Substructure analysis, which reduces the system matrices to smaller set of DOFs, replicates boundary conditions and loading situations. Submodelling analysis focuses on specific regions of interest, while defeaturing removes the unwanted geometries. Shell elements with 1st order shear deformation consideration properly depicts the stressed skin design's intricate geometry and thin-walled sections.

The results indicate that the stressed skin design significantly improves the structural integrity of HVDC topsides, while reducing the overall weight by 30% compared to the traditional open-frame design approach. It demonstrates superior resistance to buckling and dynamic loads, reduced vulnerability to fatigue, enhanced load distribution and reduced localized stress characteristics. Furthermore, the stressed skin design exhibits reduced maintenance requirements, contributing to overall lifecycle cost savings. Additionally, the stressed skin design allows for a more compact and streamlined topside configuration, potentially reducing the environmental footprint of offshore converter stations.

Stressed skin design is capable to address the real-life geometries like stiffened panels, corrugated plates, or perforated plates, along with the non-linear behaviour of the structures, like initial imperfection or welding distortion. The present numerical work shows a maximum difference between simulation and experimental measurement within 3%, indicating good consistency, and confirms the accuracy and reliability of the modelling.

Impact: The implementation of stressed skin design in HVDC topsides has the potential to revolutionize the offshore power transmission industry. The improved structural performance and reduced maintenance requirements will lead to increased system uptime and reduced operational costs. Additionally, the reduced environmental impact through a more compact design aligns with sustainability goals, making it a promising solution for future offshore converter stations.

The novelty of the present work is in demonstrating a completely new design philosophy, implementing it in real-life scenario covering a wide range of analysis and modelling in terms of size and complexity of the structure, automation along with various environmental loads.