Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering ConferenceShanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

A Study on Structural Optimization of Leg Mating Unit
Lisi He1,2, Jinju Cui1,2*, Deyu Wang1,2, Li Chen1,2
1. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China
2. Institute of Marine Equipment, Shanghai Jiao tong University, Shanghai, China

study on the mechanical performance of a LMU. By changing thequantities of rubber rings, adjusting the rubber’s inner and outer
diameters and increasing the specific sandbox, an optimized design of
the LMU is eventually proposed. The comprehensive optimization
process is expected to provide references for the practical LMU
designing of modern engineering applications.

ABSTRACT
Leg mating unit (LMU) plays a cushioning role when installing thesuperstructure of large offshore platforms. In the present study, wecarried out nonlinear FEM structural analysis of a large scale LMU,
using a quasi-steady approach of ABAQUS software. Based on thenumerical results, the structural optimization of LMU was conducted
via increasing the sand box and changing the quantity and the diameter
ratio of the rubber rings. The results of this study are of reference value
for designing and optimizing the LMU device.

STRUCTURE OF LEG MATING UNIT
Structural Form
As shown in Fig.1 a LMU structure includes typically a upper structure,
a lower structure, an outer sleeve. And the outer sleeve is composed of
the receptor cone, the vertical elastomer unit, the horizontal elastomer
unit, the rib plate, the support structure, and so forth.

Key Word: Leg Mating Unit, Nonlinear FEM analysis, Quasi-Staticanalysis, Optimization.

INTRODUCTION
With the rapid development of the ocean engineering, more and morelarge structures have been employed for offshore oil and gas
exploitation. As a popular install method, the float-over method has
been increasingly used in the large structure installation. And the leg
mating unit (LMU), which plays the role of buffering and controllingthe vertical displacement of the upper structure of the platform, is a key
equipment of a for the whole installing process.
Indeed, the float-over installation and the performance of LMU havebeen widely investigated in recent years. For example, Han and Lee(2017-2020) studied the local structural strength of the LMU andconducted the corresponding design optimization. Chaitanya (2013)
designed the LMU structure and proposed a stiffness selection criterion
based on the load-displacement relationship. Sun (2012) compared Twomethods of hydrodynamic calculation of float-over installation arediscussed. Jung (2009) analyzed the stress of each part of a structure in
the process of the float over. Li et al. (2021) proposed a novel type ofinverted leg coupling buffer.

Figure 1 Typical LMU structure
Among them, 1- Cone receiver, 2- Cone receiver stiffener plate, 3-outersleeve, 4-horizontal rubber, 5-bracket, 6-pressure washer, 7-verticalrubber rings, 8-pressure washer, 9- - Sand, 10- Reinforcing rib plate,11- Inner sleeve, 12- Inner guide cylinder, 13- Piston, 14- Round plate,15- Bottom plate.

Although these investigations provide useful information for designingand optimizing the LMU device, most of them are limit to discuss aspecific component of the LMU structure. To make a comprehensive
exposition of the LMU device, present study carried out systematicallyWorking Principle
The leg mating unit is a docking device, which is used for to connecting

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