Reference no: EM133676803
Question 1:
Introduction
Tillage is an important farming operation. It involves the manipulation of soil into a desired condition by mechanical means. Suitably designed tools can achieve the desired effect (such as pulverization, cutting, or movement). Tillage is often the only way to change soil structure after it is compacted.
The purpose of this assignment question is to use real experimental data to assess and compare the design and performance of various tillage tools, and to discuss the accuracy and limitations of various measurement methods used in an agricultural engineering application. This will assist you to develop the UniSQ graduate capability to sensibly appreciate and interpret "imperfect" experimental data and results.
Specifically, this assignment question uses real measured data to compare the performance of different subsoiler configurations. This was done by measuring the cross-sectional areas of the furrows, and comparing the tillage
efficiency as expressed in kN/m2, which implies that the intention of the subsoiler is to fracture as large an area of soil as possible for the minimum tillage force. The subsoilers used were half-scale models of sub-soilers in actual commercial use (see Figure 1).
The Experimental Setup
The difference in tillage forces and their absolute value was measured using the Force Balance Frame (Figure 1), which allowed the tillage tools to be compared at the same depth and speed, and in identical soil conditions. A load cell mounted in the frame (Figure 2) was used to measure the difference in draft forces between the left and right sides of the frame (the difference in lift forces was not considered). In order to obtain the absolute value of the tillage force (in the right hand side), on the first run, no tine was placed in the left hand side (LHS), while one standard vertical tine remained in the right hand side (RHS). In subsequent runs, only the tines in the left hand side (LHS) would change so that the absolute values of the tillage forces are determined from the difference between the LHS and RHS, plus the tillage force from the first run.
All the draft force data were measured with the load cell shown in Figure 2, and recorded by a data logger.
Furrow cross sectional areas were measured by using a soil profile meter (Figure 3), and results were recorded manually. There are 32 rods across the profile meter. The distance between rods is 3 cm. The measured depth was reported in millimetres (mm).
The Experimental Procedure
The purpose of these measurements was to compare the performance between a number of different subsoiler configurations (Figures 4¬6), where different bolt holes were used for adjusting the tillage depth, and attaching the wings.
The following comparisons will be made:
(1) Curved subsoiler vs vertical subsoiler (Fig.5)
(2) Curved subsoiler with wings vs vertical subsoiler.
(3) Curved subsoiler vs vertical subsoiler with preceding tines.
The Experimental Results
The data from following experimental runs were collected (see the attached EXCEL soil profile data). The (sample) recorded force data for one run is shown in Fig.6.
Runs A and 8 (2 benchmarking run)
Left hand side: No tine.
Right hand side: One standard vertical tine.
Measured average force difference between the left and right sides: 4.5 kN
Run C (to show the possible difference between the curved tine and straight tine):
Left hand side: One curved tine.
Right hand side: One standard vertical tine.
Measured average force difference between the left and right sides: 0 kN
Run D (to show the possible effect of two small wingst
Left hand side: One curved tine with two small wings.
Right hand side: One standard vertical tine.
Measured average force difference between the left and right sides: 4.0 kN
So the final total force in the run was equal to: 4.0 + 4.5 (from Runs A and B) = 8.5 kN.
Run E (to show the possible effect of two large wings)
Left hand side: one curved tine with two large wings.
Right hand side: One standard vertical tine.
Measured average force difference between the left and right sides: 3.5 kN
Run F (to show the possible effect of two small leading tines):
Left hand side: One standard vertical tine. Right hand side: One standard vertical tine.
Two small leading tines in the LHS were added in this run.
Measured average force difference between the left and right sides: 3.5 kN.
Your tasks:
(a) Plot the recorded data in suitable software (eg EXCEL) and use this to roughly estimate the cut furrow cross sectional areas of each configuration (5-10% accuracy is acceptable. A simple and rough visual estimation of the cut furrow cross sectional areas is also acceptable. To calculate the actual cut soil areas, you will also need to deduct the depths of soil profile meter);
(b) Use the above measured (supplied) average tillage forces and cross sectional areas to compute the tillage efficiency (as expressed in kN/m2) in each run, and to compare the effect of changing tool designs on different runs;
(c) Comment on the adopted measurement methods, and also the sources of data inaccuracy, in this real experiment. Were all the results consistent with the theoretical expectations in terms of the performance between different subsoiler configurations? If not, why?
Question 2
Tillage is a farming practice that helps to prepare the soil for plant growth. Read the attached paper by Spoor and Godwin "An experimental investigation into the deep loosening of soil by rigid tines".Joumal of Agricultural Engineering Research, 1978, 23(3), pp.242-258.
Then answer the questions below in your own words. The report should be typed and written in standard format on A4 pages. Your answers should also be as concise and clear as possible (two to three A4 pages would be appropriate). In particular, the use of graphics, short sentences, tables, and bullet points are strongly encouraged. You are also allowed to copy and paste diagrams from the paper and you do not need to draw your own sketches. There is no need for referencing.
Each of the five questions will be marked out of 30.
1. Explain the concept of "critical depth" for subsoilers. Use sketches to describe the typical furrow profiles for tillage, above and below critical depth, and describe the respective modes of failure.
2. In Table II, for the conventional subsoiler, the disturbed soil area is less with tillage depth at 0.42m than at 0.35m, even though the draft is higher. How do you explain this, and what is the consequence?
3. From the data in Table II, discuss the main advantages of using a winged tine. What else do winged tines do, that represent an improvement over the action of a conventional tine?
4. Name and discuss the main factors that affect critical depth.
5. If shallow leading tines are used, how should they be set up? What recommendations would you make to a subsoiler manufacturer concerning wing geometry and placement?
Question 3
Traction is the term applied to the driving force developed by a wheel, track, or other traction device. The tyre and soil parameters can significantly influence the traction performance of farm tractors.
A 60 kW tractor of 4832 kg weight has a front wheel drive assist feature which can be either engaged or disengaged by the operator. The front tyres are 34.5 cm wide and 121 cm diameter. The rear tyres are 46.7cm wide and 165.3 cm diameter. The front to rear weight distribution is 30%/70%. The soil has the following properties: c = 15 kPa, f = 30°, kc= 50 kPa/m^-1, kf =100 kPa/m", n = 0.6 and K=6 cm.
- Determine the drawbar pull of this tractor at 11.74% wheelslip, when the front wheel drive assist mechanism is:
(a) engaged (i.e. operates as Front-Wheel¬Assist (FWA) tractor);
(b) dis-engaged (i.e. operates as a 2WD tractor).
- Show the percentage of pull force to tractor weight, for both cases.
- Comment on the relative advantages/disadvantages of these two options.
In this question, it is assumed that the tyre contact lengths is half of the overall tyre diameters.
In the case of 2WD, it is assumed that the front and rear wheels are not travelling in the same track, but the front and rear tyres will have the same rolling resistance coefficient. Soil traction is only provided by two rear tyres.
In the case of FWA, it is assumed that the front and rear wheels will be travelling in the same track. Because the front and rear tyres have different diameters, it is also assumed that the rolling resistance coefficient of the rear wheels will be 60% of their coefficient in the first-pass. Soil traction is now provided by all four tyres.