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Coursework Brief:

The aim of this coursework is to model the following structure as lumped mass model with single or three degree of freedom system.

The triple split drilling configuration are installed to drill three wells in vicinity to each other at the offshore location. The depth of the sea at the location is 30m. Each of the well is connected to the topside weighing 10,00kg via six concentric steel tubes. Each pair of the concentric tube are cemented at various depth below seabed. All dimensions, weights and material specifications for triple split well are shown in Figure 1 and 2.

 

 

 

 

 Figure 1: The representative cross section sketch of the pipes at MSL (Mean sea level).

Since risers are exposed to environmental loads (waves) in the offshore locations, they will oscillate at low frequency. The transverse oscillation is not considered but axial oscillation are required to be analysed. To design safe structure, it is important to know its natural frequency.

As a part of coursework,

(i) You are required to model a triple split well drilling structure (Figure 1 and 2) as single and three degree of freedom system. You may have to find equivalent stiffness of each structural components such as pipes and topside.

 

(ii) Calculate the natural frequency of the modelled system considering a single and three of freedom. State difference in the value of natural frequencies, if system is modelled as single or three degree of freedom.

 

(iii) The model should only capture length of each pipe equivalent to 6 x OD of the conductor pipe below mudline.

 

(iv) Stiffness of the topside can be assumed to be 10 time that of the conductor pipe. Inside mud or seawater is not required to be considered.

 

 

Figure 2: A side view of three splitter well installations (not to scale)

Your task is to prepare a report analysing the proposed model and its suitability for this application.

Your report should include:

 . An overview of a method of calculating the stiffness and mass values for a single or three degree of freedom model.

 . Show calculation for equivalent stiffness and masses.

 . A justification for choice of discretising structural mass and stiffness. Please also discuss suitability of the discretising method, making reference, where it is relevant and appropriate.

 . Discuss the difference or similarity in value of natural frequencies, if system is modelled as single or three degree of freedom. Explain the reason behind the difference or similarity in values of natural frequencies.

 . Your report should be no more than 2000 words long. Number of words for the references section, figure/table captions, tables, contents page, abstract and appendices (if used) will not be counted towards 2000 words limit.

 

Report Guidelines

You are expected to produce a professionally written report which is split into sections with clear headings (and subheadings if necessary). The calculations should be carried out using MathCad or Matlab. Please clearly describe the step of calculations with comments next to each equation in MathCad or Matlab. Submit the report and a MathCad and Matlab sheet through Dropbox on Campusmoodle. This coursework is related to dynamics part of the module. The report should: Include a coursework cover sheet and on MathCad or Matlab

code (Name, Number).

 

 

. Include a brief introduction stating what the calculations are about.

. Include methods employed for system analysis.

 . Include a discussion of your understanding of your results and findings.

. Include a comment of most steps of your solution in Mathcad sheet.

. Include a clear explanation of each use of a value that is not given or that is to be selected from a references.

 . Include well annotated scaled plots (title, axis labels, units, legend), if necessary. If you use the figure, table, equations, plot, use caption and cross reference them in the discussion. For example: “As seen in Figure 1, the strength of material decreases with the temperature”

 . Include any source codes used in your calculations. You are allowed to use Matlab or Mathcad to calculate.

 . Show the numerical answers as three significant digits (i.e. 1.14, 2.25 x 10-3, or 6.85 x 104).

 . Show the physical units of every numerical answer (i.e. MJ, kg/m3, m/s, W/m2, unitless, etc…).

 

Additionally, it is recommended to limit the number the equations in the main text.

 

 

 

 

 

 

 

Assessment Criteria

The criteria used to assess the report and weighting allocated to each criterion are detailed in the table below.