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Structural Assessment of a Diving Bell Handling System to Support In-house Capability

Introduction

Parkburn Precision Handling Systems planned to produce a triple wire load limiter designed to support the weight of a diving bell and protect the lift wires against impulse loads. To ensure the safety of the device in operating conditions, Wilde was asked to support the company’s in-house resources by carrying out a finite element analysis (FEA) of the load limiter followed by an assessment of results acceptability. This was followed by similar detailed FEA work on the swivel sheave carriage.

Company

Parkburn Precision Handling Systems is a specialist marine handling systems provider, which was rebranded in October 2002 to combine the extensive experience and complementary products of Parkburn Controls, Dowty Precision Handling Systems and Marine Project Development (MPD).

The company operates from two UK sites in Hamilton and Telford, across offshore oil and gas, HV power cable, telecommunications, seismic exploration, DSV and general marine and naval handling markets.

image-case-study-triple-wire-load-limiter
Fig. 1: Triple wire load limiter (Courtesy: Parkburn Precision Handling Systems)

Background

A load limiter comprises a pair of hydraulic cylinders, backed by pre-charged accumulators which control the operation of two specific stages. The force applied to the load limiter is supported up until the accumulator pre-charge is exceeded. Any increase to the applied force beyond this point causes the hydraulic cylinders to release pressure, thus limiting the load.

The purpose of the first stage is to manage slack-wire and is backed by an accumulator with a low pre-charge pressure. The second stage supports the suspended load during normal operational conditions and is backed by an accumulator with a high pre-charge pressure.

On a triple wire system, each individual lift wire has its own independent load limiter by incorporating three separate Parkburn standard design load limiters. Therefore, each component in the load path of each lift wire is limited to a load no greater than the lift winch design load. The control system monitors the hydraulics on a Parkburn standard design load limiter. If the control system detects any error, it must be rectified before diving operations can continue.

Challenge

Parkburn planned to produce a triple wire load limiter designed to support a suspended load (i.e. a diving bell) with all three lift wires. In normal operating conditions, the suspended load is proportioned over the three lift wires, each with an independent load limiter. In the event of one lift wire failing, the remaining two have sufficient capacity still to support the suspended load. This aspect is known as redundancy.

Parkburn has an in-house ANSYS FEA capability, supplied by Wilde. To independently verify the safety of the design in the event of component failure of any of the lift wires, Wilde was consequently asked to carry out finite element analysis (FEA) of the load limiter with two lift wires in operation, to assess whether the stress levels and deformation fell below the allowable values. This was followed by a similar request for detailed FEA and a results acceptability assessment of the swivel sheave carriage.

Solution

A static structural analysis of two load cases was carried out for the triple winch load limiter. Load Case 1 considered the swivel sheave carriage in highest position, while Load Case 2 considered the swivel sheave carriage in lowest position.

The analysis found that the stress levels within the frame for both load cases were below the allowable limits and confirmed that the deformation was within acceptable limits.

Business Benefits

Parkburn Precision Handling Systems has a long-term relationship with Wilde as a trusted supplier of ANSYS software, technical support and training services. By also utilising Wilde’s engineers for consulting services, the company is able to react quickly to major projects requiring additional skills and technical capacity. With excellent communication between the parties, results are delivered efficiently and Parkburn can keep abreast of the latest FEA techniques from Wilde’s up-to-date expertise

 

On completion of the design, Wilde, being a preferred partner of Parkburn, was enlisted to carry out independent verification. After specifying the design requirements and objectives of the analysis, Parkburn can rely on Wilde to provide reliable results in a presentable format ready for review by design approval agencies.

Parkburn Precision Handling Systems

 

 

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