Developments in the Analysis and Design of Marine Structures

Proceedings of the 8th International Conference on Marine Structures (MARSTRUCT 2021, 7-9 June 2021, Trondheim, Norway)

Jorgen Amdahl, C. Guedes Soares, Jorgen Amdahl, C. Guedes Soares

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000533835
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Military Science & Technology
• Index: Technology & Engineering

Developments in the Analysis and Design of Marine Structures is a collection of papers presented at MARSTRUCT 2021, the 8th International Conference on Marine Structures (by remote transmission, 7-9 June 2021, organised by the Department of Marine Technology of the Norwegian University of Science and Technology, Trondheim, Norway), and is essential reading for academics, engineers and professionals involved in the design of marine and offshore structures.

The MARSTRUCT Conference series deals with Ship and Offshore Structures, addressing topics in the fields of:

- Methods and Tools for Loads and Load Effects;

- Methods and Tools for Strength Assessment;

- Experimental Analysis of Structures;

- Materials and Fabrication of Structures;

- Methods and Tools for Structural Design and Optimisation; and

- Structural Reliability, Safety and Environmental Protection.

The MARSTRUCT conferences series of started in Glasgow, UK in 2007, the second event of the series took place in Lisbon, Portugal in March 2009, the third in Hamburg, Germany in March 2011, the fourth in Espoo, Finland in March 2013, the fifth in Southampton, UK in March 2015, the sixth in Lisbon, Portugal in May 2017, and the seventh in Drubovnik, Croatia in May 2019.

The 'Proceedings in Marine Technology and Ocean Engineering' series is dedicated to the publication of proceedings of peer-reviewed international conferences dealing with various aspects of 'Marine Technology and Ocean Engineering'. The Series includes the proceedings of the following conferences: the International Maritime Association of the Mediterranean (IMAM) conferences, the Marine Structures (MARSTRUCT) conferences, the Renewable Energies Offshore (RENEW) conferences and the Maritime Technology (MARTECH) conferences. The 'Marine Technology and Ocean Engineering' series is also open to new conferences that cover topics on the sustainable exploration and exploitation of marine resources in various fields, such as maritime transport and ports, usage of the ocean including coastal areas, nautical activities, the exploration and exploitation of mineral resources, the protection of the marine environment and its resources, and risk analysis, safety and reliability. The aim of the series is to stimulate advanced education and training through the wide dissemination of the results of scientific research.

Collision and grounding

Design against ship collisions in accordance with the new DNV RP C204

J. Amdahl & Z.L. Yu

Centre for Autonomous Marine Operations and Systems (AMOS), Norwegian University of Science and Technology (NTNU), Norway

Department of Marine Technology, Norwegian University of Science and Technology (NTNU), Norway

DOI: 10.1201/9781003230373-20

ABSTRACT: A new version of the DNV RP C204 standard for the design of offshore steel structures against accidental loads was released in 2019. The updated recommended practice made considerable changes on the design against ship collisions. The changes addressed the challenge of increasing ship sizes and collision energy and new structural designs. This paper discussed several aspects of the changes in the revised DNV RP C204, including updated design collision energy and force-displacement curves of the standard supply vessel, ship installation interactions, compactness criterion of offshore tubulars and external dynamic models. Examples are given to demonstrate application of the new standards. Potential impact of the new standard on structural design is discussed.

1 Introduction

The DNV RP C204 standard is a recommended practice released by DNV for the design of offshore structures against accidental loads. Accidental loads mainly include ship collisions, explosions, and fire. The overall goal in the design of a structure against accidental loads is to prevent an incident to develop into an accident disproportional to the original cause. This means that the main safety functions should not be impaired by failure in the structure due to the design accidental loads.

In the design against ship collisions, the size and speed of the vessel shall be determined by a risk analysis according to NORSOK N003 standard (NORSOK-N003, 2017), where the best estimate of a design impact event should not exceed an annual probability of occurrence of 10⁻⁴. The standard collision event that has been used for the past several decades (DNV, 1981) is the impact from a supply vessel of 5000-ton displacement and a speed of 2 m/s. This gives a kinetic energy of 11 MJ and 14 MJ for bow/stern collisions and broad side impacts, respectively considering the added mass effects. Over the years, significant changes have taken place with noticeably larger ship sizes, increasing ship speeds and new structural designs (bulbous bows, X-bows, ice strengthen vessels, etc). Kvitrud (2011) summarized ship collision events on the Norwegian Continental Shelf in the period of 2001-2010 and highlighted six most severe cases, the collisions energies of which are in the range of 20-70 MJ. This exceeds significantly the standard collision energy in the old RP (DNV-RP-C204, 2010). In the revision of the NORSOK N-003 standard, the requirements to ship impacts were reassessed and updated based on statistics on supply vessel sizes and collision energies (Moan et al., 2017). The new NORSOK-N003 (2017) increased the standard design collision energy significantly to around 50 MJ. In consistent with the new NORSOK N003 standard, a revision of the DNV RP C204 standard (DNV-RP-C204, 2019) was released in 2019, where the design standards for ship collisions were rewritten. This paper discusses several new features of the new DNV RP C204 standard (DNV-RP-C204, 2019) for the design against ship collisions. Examples are given to demonstrate the application of the new standards. Potential impact of the new standard on the structural design is discussed.

2 Updated Design Energy And Force Displacement Curves

The latest NORSOK N003 (NORSOK-N003, 2017) standard requires that ‘if no operational restrictions on allowable visiting vessel size are implemented, the displacement of supply ships should not be selected less than 10 000 tons from risk assessment. The corresponding speed in head-on collisions shall be set to 0.5 m/s and 3.0 m/s for ULS and ALS design checks, respectively. In sideways and stern impacts, the speed should not be less than 0.5 m/s and 2.0 m/s for ULS and ALS design checks, respectively. A hydrodynamic (added) mass of 40 % for sideways and 10 % for bow and stern impact can be assumed’. This yields a design collision energy of around 50 MJ, which represents a substantial increase from 11MJ and 14 MJ in the old recommended practice.

Design against ship collision is generally categorized into three regimes that depend on the relative strength. To dissipate a design energy of 11 MJ and 14 MJ following the old recommended practice, ductile design is often aimed for, where the bow or side of the striking ship is considered virtually rigid, such that most of the kinetic energy is dissipated by the impacted installation. However, an increase of the design collision energy to 50 MJ in the new RP places much heavier demands on the resistance and/or ductility of the offshore structure. It becomes difficult for the installation to absorb the energy alone without damaging structural integrity. It is therefore favorable that the striking ship also deforms and absorbs considerab...