Please Fill in All the Yellow boxes , and please this time do it nicely ,as i got bad grades for my last coursework
DSGN215 – Engineering Design
Coursework A – Rudder Shaft Design
The deadline for this 10 credit assignment is 23.55 on 17th December 2014.You must submit your coursework electronically via DSGN215 Moodle site. This is an individual assignment, so must be all your own work – University plagiarism regulations apply.
You should give due consideration to your personal time management to ensure that coursework is submitted in plenty of time prior to the deadline. Coursework can be submitted at any time ahead of the deadline; however, the Faculty cannot take any responsibility for late submission due to uploading errors, etc. Please note University policy on penalties for work submitted after the published deadline without valid extenuating circumstances (see University student handbook on the portal for details). PLEASE REMEMBER – IF YOU RESUBMIT COURSEWORK AFTER THE DEADLINE IT WILL BE RECORDED AS LATE.
Intended outcomes – By the end of this assignment, you should be able to:
Apply appropriate theory to estimate loads in a real engineering structure as follows:
Present your calculations in spreadsheet form
Carry out a Finite Element Analysis (FEA) of the structure and compare results with calculations
Use a spreadsheet for a parametric design task, optimising a structure for a specific design condition (aided by the use of material/manufacturing process selection software).
Look at a simple structure (the rudder shaft in this case) and work out how it is are supported and loaded.
Produce relevant Free Body Diagram(s) of the structure.
Use relevant theory to calculate stresses in the structure.
READ ALL OF THIS ASSIGNMENT BRIEF CAREFULLY BEFORE STARTING THE WORK!
2. Task definition
A sailing vessel is normally steered by means of a rudder, controlled by either a steering wheel or (as in the case of this assignment) a tiller. Fig. 1 shows the assumed steering components for the sailing vessel to be considered. Note in particular the coordinate system to be used in this assignment; Y is the vertical (upwards positive) direction, X is the longitudinal (aft positive) direction and Z is the transverse (port positive) direction. The coordinate system origin (0,0,0) is on the shaft axis, on the interface between the shaft flange face and the top face of the rudder.
You will be looking at the design of the rudder shaft. You will develop a spreadsheet (based on a template provided) to determine the stresses in the shaft and to optimise the shaft for a specific product requirement. You will also carry out a Finite Element Analysis (FEA) of the shaft.
Figure 1 – Sailing vessel steering components
The rudder is designed to generate a sideforce to steer the boat (and also to complement the lift developed by the keel while the boat is sailing in a straight line, to prevent the boat slipping sideways under the action of a sidewind). Keen sailors will know that when a boat becomes overpowered in a strong gust of wind, the sideforce required to stop the boat making an unwanted turn to windward can be considerable, and the helmsman must pull hard on the tiller to generate that sideforce and keep the boat sailing in a straight line. A pulling force is required on the tiller because the sideforce tends to act on the rudder blade at a point aft (i.e. further back) of the rudder shaft axis. The sideforce can be assumed to act at a single point on the rudder blade. Fig. 2 below shows the defining dimensions of the steering assembly, including the assumed position at which the rudder sideforce acts.
Figure 2 – Definition of Dimensions
In Fig. 2, the crosshair on the tiller represents the force that the helmsman is applying to the tiller, and may be assumed to be acting in the positive Z direction (i.e. out of the page, towards the reader). The crosshair on the rudder represents the force that the water is imparting to the rudder, and may also be assumed to be acting in the positive Z direction (i.e. out of the page, towards the reader).
You have been given a set of input parameters that are unique to you – each student will work on a slightly different set of figures, so you will each get different results. To find out which parameters to use, open the parameters spreadsheet, and find the column with your name at the top. Marks will be lost for using the wrong inputs.
The input parameters that are provided are:
Rudder Sideforce (in +ve Z direction)
Distance of sideforce action below flange
Distance of sideforce action behind Shaft Axis
Height of lower bearing above Flange
Height of Upper Bearing above Flange
Height of Tiller above flange
Total length of shaft
Shaft Outer Diameter
Shaft Wall Thickness (= OD/2 if shaft is solid)
Mateial Yield Stress
Material Carbon Footprint
Optimisation task (Minimum weight/cost/CO2)
You must open and save your own copy of the calculations template spreadsheet, enter your input parameters and then fill in all of the yellow boxes to calculate loads, stresses, Factor of Safety, etc.
Make sure you follow all of the following guidelines:
You should rename your saved copy of the template with your own surname and first name, so the file name format should be, for example, “DSGN215_CWA_2014_Bloggs_Joe.xlsx”.
You must ensure that your spreadsheet is fully parametric – so use Excel formulae such that if any inputs change, calculations automatically update. You will lose marks if they do not. (Note – in Row 86, it is OK to type a value rather than calculate it).
Work your way through the spreadsheet step by step, and make sure you follow all the instructions carefully.
Don’t change the structure of the spreadsheet (i.e. don’t add rows/columns or put additional calculations in cells outside the specified yellow boxes). If you change the structure, my automatic calculation checks won’t work and you will lose marks.
Fill in yellow boxes in the Formula column, writing formulae using the nomenclature I have given, not Excel cell references. This helps you to check your work, and allows me to give you credit for using the right formula, even if you made a calculation error.
Fill in the yellow boxes in the Comments/Working column to show HOW you worked out your answer – again so I can give credit for the method even if the answer is wrong. A simple explanation (e.g. “used Pythagoras to calculate length of the hypotenuse”) or a line or two of working would be ample.
Change the colour of the cells in the Value column as you have done in the class exercises – so any typed in input value cell is green and any calculated value cell (i.e. containing a formula) is red.
About half of the marks for this assignment are for your calculations, and half are for your answers to the 7 questions (including the optimisation task). So make sure you answer all 7 questions carefully.
If you have followed the instructions on the spreadsheet correctly, you should end up with two worksheets (plus a worksheet for FEA inputs) in your final spreadsheet:
o Basic Calculations containing all your calculations based on the inputs assigned to you, with all seven questions answered.
o Optimised containing calculations revised for your optimised material property and diameter inputs (without answers in the 7 question cells). Make sure you have optimised for the parameter that you have been allocated – either minimum weight, minimum material cost or minimum material carbon footprint.
You calculations must assume the following:
Neglect self-weight of the shaft (and weight of attached components) in your load calculations.
Assume that the tiller is aligned with the centreline of the boat and that the sideforce you have been allocated represents the maximum hydrodynamic force that the rudder will experience. Also, you don’t need to consider drag force on the rudder, just sideforce.
Assume that your shaft is some type of stainless steel, with a Young’s Modulus of 207 GPa.
Ignore fatigue in your calculations. (In reality, this would be an important design consideration – we will learn more about this later in DSGN215 lectures).
Assume that the only shear stress is that due to the torque that the shaft is carrying – neglect shear due to direct forces & reactions.
Assume that the tiller is firmly bonded to the shaft, and there are no stress concentrations on the shaft associated with the connection to the tiller. In reality, there would probably be a key and keyway transmitting torque between tiller and shaft, so there would be a stress concentration associated with this.
Assume that the rudder is firmly bonded to the shaft flange face, and that all loads are transferred purely through this bond. This means that you don’t need to account for the way that the flange bolts would load the flange in reality.
Assume that the greatest stresses in the shaft occurs at the lower bearing, so you don’t need to calculate stresses at the flange, tiller or upper bearing. In reality, you would probably calculate stresses throughout the shaft to show this is a valid assumption.
Assume that the radial stress (i.e. the stress pushing into the surface of the shaft) because of interference pressure of bearings press fitted onto the shaft is negligible.
Assume that the shaft has constant inner and outer diameters along its entire length. In reality it would probably have some steps for bearings to be pressed up against.
4. FEA Instructions
You will need to run an FEA simulation of your shaft. A SolidWorks model of a shaft has been created for you, but you will have to update this model so that the dimensions match your allocated parameters. To do this:
Open the SolidWorks model from Coursework A Files on the module site and save your own copy, renaming it as per your spreadsheet (e.g. “DSGN215_CWA_2014_Bloggs_Joe.sldprt”.
Select the Configurations tab, expand Tables then right click on Design Table in the model tree and select Edit Table
You should see the Design Table open over the graphics window. Overtype the default values with your allocated values for YT (Y_Tiller@Sketch1), OD (OD@Sketch1), W (Wall Thickness@Sketch1), YL (Y_Lower@Sketch3) and YU (Y_Upper@Sketch3). Note that all dimensions must be in mm. Then click away from the table, elsewhere in the graphics window to close the table and update the part.
You can now run your FEA simulation (defining material, mesh, fixtures and loads as you have learned in lectures). You should see that your part contains the right split lines on the shaft surface so that you can apply loads and fixtures in the right places, and so that you can extract the relevant stress information on split lines using the List Selected tool under Plot Tools.
Note that when using the List Selected tool, you will have to select 7 edges (see below), press Update, then click on the Y(mm) tab in the results table to plot results in ascending order of Y value. You can then click the Save button under Report Options to send the results to an Excel compatible .csv file.
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