Posted: May 2nd, 2015

Computational Fluid Dynamic

Computational Fluid Dynamic

Answer ALL parts

1.    Domains and Meshes (10 Marks)

A domain has dimensions of 18m by 12m by 9m in the x, y and z directions, respectively, write appropriate lines of code for each of the following:

a.    Please draw a figure to show the original point of your coordinate system and the domain in your coordinate system. Using a single mesh, specify a uniform cell size of 0.1m using FDS instructions. How many cells does the mesh contain? (2 marks)

b.    Split the domain into 3 meshes along the x axis. Specify a uniform cell size of 0.1m for the central mesh. Specify a cell size of 0.2m in the x and y direction and 0.1m in the z direction for the two neighbouring meshes. Meshes should be given approximately equal physical dimensions. How many cells does each mesh and the domain contain? (4 marks)

c.    Discuss the importance of cell size in CFD. How to do cell sensitivity analysis? (2 marks) Please list other parameters in FDS simulations you think may need sensitivity analysis. (2 marks)

2.    Design fires (10 Marks)

For each of the following, select an appropriate design fire, provide any assumptions made and justify your selection with reference to suitable documents. In addition, write the appropriate lines of code.

a.    A sprinkler controlled shop fire specified by heat release rate and TAU_Q. (2 marks)

b.    An office fire grows continuously from 0s to 900s, starting from a point. (3 marks)

c.    A fire reproducing the following HRR v Time graph. Comment how heat release rate density affects the input lines of code.
(5 marks)

3.    Effect of fuel and mesh size (30 Marks)

Create a simple single mesh model of a room fire scenario (guide: use room height 2.7m, horizontal dimensions between 4m to 10m); output temperature slices and visibility distance slices at 2m above floor level and across the centre of the fire; use FDS5 or FDS6. Assume a medium growing fire capped at 2.0MW. Investigate the following:

a.    The difference in output of 3 fuels of significantly different soot yields
(i.e. 3 models)

b.    The effect cell size on the output using the following uniform cell sizes of 0.4m, 0.2m and 0.1m and a single fuel. (i.e. 3 models)

Provide a brief write up of the modelling performed including: A brief description of the modelling; A visual representation of key data obtained; Analysis, comparison and discussion of the results obtained; Conclusions.

Provide the FDS Input file for each model in an appendix (Note: These do not count to document word count)

4.    Detailed modelling (50 Marks)

A building contains an atrium of 16m in length, 18m in width, and 9m height. There are 1.8m wide walkways around the atrium at 3m and 6m high levels. Assuming a medium growing fire of 2.5MW peak heat release rate is started on the atrium base and the centre of the fire is 1.8m away from the atrium wall, please make assumptions as necessary and build a model to simulate the smoke movement in the atrium. Please provide a smoke extraction fan at the ceiling level to extract smoke and appropriate fresh air inlet at low level; chose an extraction flow rate between 2 m3/s to 4.5m3/s; start the extraction (both the fan and the inlet vents) either by a timer or a smoke detector. Please determine the ASET at each level of atrium.

Your write up should include: An introduction to the model; values of the parameters you assumed and why; acceptance criteria you used to determine the ASET (temperature, visibility, thermal radiation, toxicity, air velocity, and etc.); a visual representation of key data obtained; analysis, and discussion of the results obtained; Limitations; Conclusions.

Provide the FDS Input file for each model in an appendix (Note: These do not count to document word count)

Total maximum mark for this assignment 100

•    Submit all drawings and calculations with your answers.
•    Reasonable data of student’s own choice should be used in cases where assignment does not provide sufficient information. The choice should be explained.

The word limit is 3,000 per assessment – indicative only (+/-10%). This excludes footnotes but includes quotations. The word count must be printed on the top right hand corner of your work.

Remember:

•    You must answer the questions set
•    You must demonstrate that you have met the learning outcomes
•    As you construct and present your answers, consider the assessment criteria

Presentation Instructions

It is your responsibility to ensure that your work is neatly and accurately presented.

The work must be:
•    Word-processed
•    Single sided
•    1.5 or double line spaced
•    Ariel 12 point font
•    Justified
•    Page numbered
•    On A4 paper
•    Margins left and right 3cm
•    Attached to a cover sheet.

Reference :
Use the Harvard system of referencing within your text. This will take the form: surname, year of publication, page number, and is enclosed within brackets, for example (Bradley 1998, 277). At the end of your essay you should provide an alphabetical list of all the works you cite