Time series variability blog

How do different aspects of the input metocean data affect Mermaid results?

There are a range of sources of variability when it comes to putting together a Mermaid analysis, and they can all affect the output statistics to various degrees.  It could be subtle changes such as weather thresholds, task durations or the level of suspendability; or more strategic changes such as vessel and port choice.  But that’s what Mermaid is designed for, for you to be able to tweak and optimise your operation to minimise the weather risk. Read more >

Comparison of using Mermaid metocean data against a higher quality dataset

With the recent addition of access to a 10-year hindcast dataset within Mermaid we thought it would be a good idea to provide some handy guidance and advice on how it should be used.

The general aim of this dataset is to allow users to generate some ‘headline’ average duration statistics that will be useful for things such as writing or reviewing bids and operation overviews.

The key things to be aware of with this dataset are threefold:

  1. The duration of the dataset is ten years (January 2006 to December 2015)
  2. The time step of the wind data is three hours whereas it is six hours for the wave data
  3. The horizontal grid resolution is 0.25°, i.e.
Read more >

Vessel Utilisation – Part 5: The analysis of results outside Mermaid

Introduction

In the last part we looked at how we can use Mermaid outputs to perform a bespoke analysis and discussed the process of writing a script to extract additional information.  This example is reasonably simple, but the timestep by timestep nature of the results allows substantial detail to be considered.

In this post we’ll take a look at the results we generated by running this script on our cases, considering only simulations starting in June.  We’ll also consider the process we have undertaken and the impact that this type of analysis can have on the success of a project. Read more >

Vessel Utilisation – Part 4: An overview of bespoke post processing

Introduction

So far in this series we have prepared and run a number of simulations and considered the results in Mermaid, all with the aim of answering the question:

“When should we take the trenching vessel on hire, relative to the installation vessel?”

We saw in the last post that our base case offset (32 days) is a fairly good position, however, we think there might be opportunity to improve on this.  The issue we have is that our post-processing requirement is outside the type of charts and tables offered by Mermaid.  Read more >

Vessel Utilisation – Part 3: The analysis of results using Mermaid

Introduction

Last time we finished the setup of the analysis by preparing the flow diagram.  We considered a number of options for modelling these tasks, ultimately selecting a clean, simple and easy to maintain approach.  We also performed a number of simulations.

In this post we will take a look at the results we have generated and will consider the impact these can have on our decision making.  Finally, we’ll make some decisions regarding the next steps we should take.

Box Whisker Charts

In this post we are going to analyse our results using Mermaid’s “Duration Box Whisker Charts”, here’s a quick overview of the data represented by different elements of these. Read more >

Vessel Utilisation – Part 2: The simulation of cable lay operations

Introduction

Last time we outlined the analysis of cable installation operations for a hypothetical operation at WaveHub.  We looked at the map and the shelter characteristics of the vessels we intend to use and outlined the main objective of the analysis, which is:

“When should we take the trenching vessel on hire, relative to the installation vessel?”

In addition we sketched out our operations, at quite a high level, ahead of putting them in to Mermaid, this sketch is shown below:

Overview Flow Diagram

In this post we are going to look at how we can model these operations in Mermaid and consider, in a little more detail, how we vary the length of the lay and trench operations. Read more >

Vessel Utilisation – Part 1: The analysis of on hire times

Introduction

Marine operations often require multiple vessels which are assigned specific tasks to perform.  Often the tasks performed by the vessels are independent of each other (i.e. the vessels work alone) but are linked in such a way that one vessel is dependent on the other completing work.  In this series of posts we are going to consider cable lay and trenching operations using two assets.  We’ll also look at the consideration of the simulation results both in Mermaid and as part of a bespoke analysis outside Mermaid. Read more >

Analysing Wind Farm Foundation Installation – Part 7: Two Vessels – The Division of Labour

In the last post we arrived at a strategy which we like, this being:

  • Start our operations sometime in March.
  • Use two vessels, unfortunately we can get the two we’d like though, so we’re using a slight cheaper, slightly less capable vessel as our second.
  • Modify the capable vessel so it can carry more foundation units per trip (3).

However, we saw that the division of labour we’d set wasn’t optimal and that we off hired one of our vessels early and lost some of the advantage gained by this strategy. Read more >

Analysing Wind Farm Foundation Installation – Part 6: Work Faster – Two Vessels On Hire

As we’ve moved through this analysis process and applied Mermaid to the consideration of how we can baseline and improve our performance two main objectives have repeatedly arisen:

  • Work entirely in the spring and summer to reduce winter downtime.
  • Maximise the time spent performing offshore operations when favourable conditions occur by reducing the number of transits required.

Here we are going to perform two simulations which it is hope will improve our performance.

The Simulations

There are two scenarios under consideration here:

  • Two vessels operating, both vessels can carry a set of foundations at a time, one vessel is from the base case, the other is a different, slightly less capable vessel (i.e.
Read more >