MBD Simulation on a Piston Assembly
AIM
The aim of this challenge to model the parts of the piston and crank assembly ie; (the piston head, wrist pin, connecting rod, end cap, crank) and to assemble them in the right way to do the motion analysis and fetch the required results in form of plots with the different wrist pin offset given and also as simulations.
INTRODUCTION
Each and every part of the assembly is modeled as per the given dimensions and also the constrains to make those sketches to be fully defined on, after which they are bought to assembly and they are set up in a way that each and every part is its position with respect to the other one so that the simulation and the motion study works fine in order to the get the results as expected.
MODELING PROCESS:
Part 1 - Piston head
As the first step, the sketch for the piston head is created on the front plane then the sketch is revolved, then to create the fins a rectangular shape is drawn on the same plane of revolve sketch and it is made to cut through revolve cut option, the cut extruded part is linearly patterned with 3 instances, now to position the wrist pin a cut extrusion is done on the front plane on both sides, then the side cut extrusion is done and to hold the wrist pin on the position the bush is created using extrude option and to have it on both sides it is mirrored. After which the required fillets are given.
https://drive.google.com/file/d/1z1wo47usl9i9Fyk5EdASJXf6VAT8qNQ2/view?usp=sharing
Part 2 - Wrist pin
To create the wrist pin a circular sketch is made on the front plane and extruded from midplane up to required distance then the edge of the pin is chamfered with chamfer option where its chosen the distance and angle option to chamfer those edges.
https://drive.google.com/file/d/1u-063lxWa732PJUS_wt1Rdmjt502jYEs/view?usp=sharing
Part 3 - Connecting rod
The front plane is selected to create the sketch of the connecting rod and then the sketch is extruded by midplane extrusion up to the given dimensions, then the flat face of the connecting rod is selected to create a sketch for the bolts or the positioning of the end cap with the connecting rod, then the sketch is also extruded with the given dimension. Then a cut extrude is provided on the same sketch now the connecting rod is modeled and finally, the fillets are provided with the specific radii.
https://drive.google.com/file/d/1QKJqr8S3OE1xNGQtPKjD_RC8AVPAfa1D/view?usp=sharing
Part 4 - Endcap
To create the endcap first the sketch is drawn on the front plane according to the dimensions of the connecting rod and it is extruded up to certain distance then as the same in connecting rod the secondary extrusion is created on the plane face of the extrusion, then again a cut extrusion is provided at the last boss extruded part then the fillets are applied within the given radii.
https://drive.google.com/file/d/1vAZn10DqAe6nUylM8lVn75LONtmc1k_B/view?usp=sharing
Part 5 - Crank
The sketch starts with the front plane where the main sketch of the crank is drawn with the given dimensions and constraints to make them fully defined and then extruded with specified dimensions, now the other face of this extruded boss is selected to create a new sketch which is then extruded to the given dimension, similarly, the front face of the crank is selected and a sketch similar to previous one is made and then extruded. Now the cut extrusion process is made one by one since it cannot be done at the same time, so the upper part is cut off first and followed by the lower part. Now one side of our crank is perfectly made and the only thing we need to do is to mirror the parts that are made till now.
https://drive.google.com/file/d/1UNJF9UfMT59KJyo91YQWPBX_VkSqe8Il/view?usp=sharing
ASSEMBLY PROCESS:
The first part that is in the assembly is the crank since it is the one that has to be defined in such a way that it only rotates at the specified axis, so the mates are provided to the crank with respect to the assemblies planes so that the part rotates in that axis, now the second part is connecting rod and the end cap, they both are perfectly mated so that it looks like a complete connecting rod, then the mated are provided with the connecting rod and the crank so this connecting rod will follow the crank rotation. And finally, the piston head and the wrist pin are on the assembly where first the wrist pin is connected to the piston head after which the connecting rod is connected with specific mate provided, now the assembly is partially set, so in order to finish it perfectly the piston needs to have only linear motion where the mate is given with the assembly plane. Now the assembly is done and ready for motion study.
https://drive.google.com/file/d/1Ijmbaiqw8IDV-ZnpsK07981w2V-Ub5Ow/view?usp=sharing
The above mentioned is the link for the assembly part file.
MOTION STUDY SETUP:
The term motion study is referred to as the study of the behavioral aspects of any mechanism or machinery with respect to the inputs given the inputs can vary with respect to project or part, and also the analysis of the output is done at the same time it can be got as a plot from the entities we provide or from the outputs generated.
Now let's go into the procedure to do the motion study setup, Here we are going to perform this motion study on the Piston-crank assembly for which firstly the motion addon is selected from Solidworks add-in's and then in the bottom bar we go to new motion study and select the motion analysis from the dropdown, then we proceed on, firstly the motor with required RPM is set on the crank by selecting its temporary axis and after which the contacts are given one by one, at first the contact is made between the crank and the end cap, secondly between the end cap and the connecting rod, after which the contact is between the connecting rod and the wrist pin and followed by wrist pin and piston rod.
In order to get the result in the form of simulation, we need to click the calculate button after which we'll be able to see the simulation, and the plots are got by going on to the results option and selecting the required category such as displacement, velocity, etc and the required part. Then the plots are exported to the spreadsheet to have the graphs and the values corresponding to them, and which can b used for further research.
CONDITION - 1
- "0" mm Offset
According to the given challenge, the wrist pin is in zero offset.
PLOT:
The below mentioned are the plots from the results of motion study for condition 1;
The linear displacement of the Piston Head
The above plot is obtained from the motion study of Piston-crank assembly where after the simulation of the working the results are made to be a plot with given specifications ie
-Displacement/velocity/acceleration
-linear displacement
-Magnitude
and so we get the above plot where the axis is defined as
Y-axis(Linear displacement in mm), X-axis(Time in sec)
OBSERVATION AND RESULT
At the (0 mm offset) the plots are normal and they form a possible sinusoidal waveform of the plot, where this is due to the movement of the piston head from one point to another, ie from one distance(mm) to other, and also here the graphs are evenly spaced and do not have any distortions, and the distance is probably from max(302) and min(202) observed from plots.
CONDITION - 2
- 10 mm Positive Offset
According to the second case of challenge, the wrist pin is in 10 mm positive offset when compared to the one in the video, this is made by giving an additional dimension on the sketch of the piston head at the cut extrude.
And also the mate is coinciding with both the axis.
PLOT:
The below mentioned are the plots from the results of motion study for condition 2;
The linear displacement of the Piston Head
The above plot is obtained from the motion study of Piston-crank assembly provided with 10 mm positive offset, where after the simulation of the working the results are made to be a plot with given specifications ie
-Displacement/velocity/acceleration
-linear displacement
-Magnitude
and so we get the above plot where the axis is defined as
Y-axis(Linear displacement in mm), X-axis(Time in sec)
OBSERVATION AND RESULT
At the (10 mm positive offset) the plots are normal and they form a possible sinusoidal waveform of the plot with the higher time span or in other words, the width of the curve is very large when compared to the 0mm offset, where this is due to the movement of the piston head from one point to another, ie from one distance(mm) to other provided with the offset in the wrist pin in the piston head, and also here the graphs are evenly spaced and do not have any distortions, and the distance is probably from max(302) and min(202) observed from plots.
CONDITION - 3
- 10 mm Negative Offset
According to the third case of challenge, the wrist pin is in 10 mm negative offset when compared to the one in the video, this is made by giving an additional dimension on the sketch of the piston head at the cut extrude as did for positive 10 mm case but this time it is in other direction or in the opposite direction.
And also the mate is coinciding with both the axis.
PLOT:
The below mentioned are the plots from the results of motion study for condition 3;
The linear displacement of the Piston Head
The above plot is obtained from the motion study of Piston-crank assembly provided with 10 mm negative offset, where after the simulation of the working the results are made to be a plot with given specifications ie
-Displacement/velocity/acceleration
-linear displacement
-Magnitude
and so we get the above plot where the axis is defined as
Y-axis(Linear displacement in mm), X-axis(Time in sec)
OBSERVATION AND RESULT
At the (10 mm negative offset) the plots are normal and they form a possible sinusoidal waveform of the plot with the medium time span or in other words, the width of the curve is in between when compared to other curves, where this is due to the movement of the piston head from one point to another, ie from one distance(mm) to other provided with the negative offset in the wrist pin in the piston head, and also here the graphs are evenly spaced and do not have any distortions, and the distance is probably from max(302) and min(202) observed from plots.
Superimposed all three graphs into a single graph
OBSERVATION AND RESULT
As we can see in the above given superimposed plots, the 0 offsets and the negative 10 mm offsets are clearly superimposed at its higher and lower values but not so during the transition line so the two lines are visible at that path when we compare the positive offset with the other two, this varied drastically as seen from the graph it doesn't get impose with either of the graphs and it is clearly visible throughout the graph, which is due to the positive offset provided. Even the start points of all the three vary with one another at a given distance.
so in order to understand it clearly the separate plots are provided below;
From the above separate graphs, it is clearly known that which are the graphs that superimposed and which doesn't and the reason behind it.(the width of time span)