MAE 1351 SUICIDE EXAM 2

In the creation of solid models, computer-generated geometry was referred to as parts, features, or objects; however, the objects that make up a system are referred to as

components

In assembly modeling, the copies of a component within the system are called

instances

A ___________is a grouping of components that serves a single purpose within the overall assembly

subassembly

Why not just put multiple copies of the abutment part within the assembly? Why do you have to learn about components and instances? Why are subassemblies that are made up of instances and that are instances themselves important? The main reasons for the changes are to

improve assembly modeling efficiency and to save computer storage space

improve assembly modeling efficiency and to save computer storage space __________ means that if you change the geometry of a part, the component and all instances of it also will change by the same amount

associativity

Assembly models are easier to work with when they are organized in a logical manner. An assembly is usually thought of as a composition of several smaller subassemblies, each of which may consist of other subassemblies or individual components. The organization or structure of a system is referred to as its

hierarchy

The first thing you want to do after setting up your system hierarchy is to orient the instances so they are properly located in space relative to one another. To do that, you need to select one component to serve as the

base instance.

As with objects and features, the associations between components and subassemblies are often called

parent-child relationships

hen creating parts, you used constraints to establish geometric and dimensional relationships between 2-D entities or features. Thus, you constrained two lines to be parallel or perpendicular to each other. Or you constrained the diameter of a circle to be a specific size and its center to be located given distances from lines on the drawing or from edges on an object. In assembly modeling, you can apply ____________ between two 3-D instances so the instances maintain dimensional or geometric relationships with respect to each other within the assembly

assembly constraints

Each time you bring an instance of a component into an assembly, you introduce______________... Simultaneously, Each time you apply a constraint to the assembly, you________________________

six degrees of freedom.

Remove one or more of these degrees of freedom (DOF)

Two entities take up the same space

Coincidence

Once you assemble your system, you can create an ________________ that will essentially be an assembly drawing for the system

exploded configuration

The amount that two instances overlap is referred to as the _________. Another advantage is that you can determine _______________

interference, Clearance

___________________ is an advanced design analysis technique that has been made possible through the development of sophisticated 3-D CAD solid modeling tools

Finite Element Analysis (FEA)

Similar to the way the computer solved for the moment-of-inertia of a complex object, the FEA method is founded on dividing the part into small pieces, which are together called a

mesh

Objects that are subjected to loads experience

If you are pulling on an object, it will tend to elongate or stretch. If you are pushing on the object, it will compress or squash together. If you are applying a shear stress to the object, it will shear and become distorted. The FEA method can be used to solve for all of these types of stresses and deformations for objects subjected to various types of loads.

mechanical stresses (FEA)

This type of analysis is used to compute the airflow around airplane wings, enabling engineers to design bigger and better jets that can develop sufficient lift with bigger payloads. Air pressure fields also can be determined through this type of analysis.

could be blood cells or nano-particles in a blood vessel. By predicting and altering the way the fluid flows, or altering the geometry of the particles, a desired motion of the particles can be produced.

Fluid flow and pressure fields (FEA)

large variations in temperature can cause thermal stresses, because the warmer side expands and the colder side contracts. If the stresses are too large, permanent deformation or even fracture can result. Figure 8.21 shows a spindle motor for a disk drive that has been analyzed for its temperature distribution.

Thermal flow and temperature fields (FEA)

Electromagnetic fields are also a significant consideration in the design of antennas. The size and shape of the electromagnetic field depends on the type of antenna used. If the steel in the body of the automobile interferes with the electromagnetic field from the antenna, radio reception will be poor and owners will not be satisfied with their cars. Due to poor electromagnetic performance, the simple vertical mast antenna has been virtually eliminated in new car models—new antennas are more sophisticated and are less likely to have poor performance issues.

Electromagnetic fields (FEA)

Element sizes should be ____________ wherever there is curvature in the model to compute desired quantities accurately in those regions

Reduced

when a finite element mesh has been created, In the FEA meshing scheme, the finite elements are connected through their_________It is at these nodal points and along the element edges that the _________ are specified.

edges and nodal points, boundary conditions

During the analysis, each finite element is treated as a ____________ with limited properties, interacting with its surrounding region only through the nodal points and element edges.

a simple solid body

computes various quantities for the model based on the boundary conditions—constraints and loads—that you applied

The finite element solver

For stress analysis, the two primary quantities of interest are the

stresses and displacements

identifies areas of high stress or large displacements

Design Check

One of the purposes of analysis is to identify

design flaws or areas for improvement prior to production

Ex: If the internal edges of the pillow block were rounded, stresses in the model would be greatly reduced. (rounded edges result in less stress)

I bring a part into an assembly in SW, and click the OK check mark in the top right. This will...

Align component origin with assembly origin

"Create a part and bring it into a container called a..."

assembly container

"continue to propagate parts into bigger ones, eventually reaching the top level assembly called..."

Top Level Assembly

Copies of the same part are called (Ex: Wheels on a cart)

Instances

The traditional ranges of motion on any 3d object is

Right, Up, and Forward

The complimentary ranges of motion based on the traditional ranges of motion are

Left, Down, and Back

The 3 quantities that are seperate from the traditional and complimentary ranges of motion are the

Yaw, Pitch, and Roll

When a part is completely fixed it has _________ of Freedom

0

The process of assembly is the process of removing

the degrees of freedom starting from the natural 6 that is has

(Constraints remove a certain amount of degrees of freedom)

The highest level of simulation for rigid body mechanics

Motion Analysis

The value that determines the measurement of stress in a simulation

Von mises stress (psi)

evaluating the thermal equilibrium of a system in which the temperature remains constant over time

Steady-state thermal analysis

method is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat transfer, fluid flow, mass transport, and electromagnetic potential.

Finite Element Method (FEM)

What do assemblies make useful?

Motion study, difficult to do with a part

When does a part have no degrees of freedom?

When it is fixed

What is the process of defining an assembly?

Removing DOFs until all necessary have been removed for intended function. This is done by adding constraints.

Why are subassemblies and instances important?

Because it improves assembly modeling efficiency and saves computer storage. Only 6 pieces of data need to be remembered by computer (6 DOFs)

What is the utility of associativity?

greatly increases computer modeling efficiency for complex parts and systems.

Benefits of organizing assembly in hierarchy?

enables more efficient work within the assembly, and subassemblies can be moved as a unit

If you select to surfaces on different components within an assembly, SOLIDWORKS will....?

It will guess what type of mate you want and display it

What is the advantage of not moving the base part after it is placed into the assembly? (by clicking green checkmark)

Any manner of symmetry or alignment that are involved will be transferred over

Is the Mechanical gear mate a result of contact when a gear mate is used?

No

What happens each time you bring an instance into an assembly?

6 degrees of freedom are introduced

Why are concentric constraints one of the more useful assembly constraints?

Helpful in dealing with cylindrical shafts and holes.

what does a mating surface constraint do?

Forces the normals of 2 surfaces to be parallel to each other

What is coincidence and where can it occur?

When 2 entities take up the same space. It can occur between 2 lines, 2 points, 2 faces, or between a point and a line (for 2 planes defined by mating surface constraint)

What are distance constraints?

Define relationship between 2 instances. Similar to dimensional constraints but for assembly models.

Why do you want a happy medium of constraints in mechanism analysis?

You want enough constraints to define permissible motion. Don't want rigidity or unconstrained motion.

What is CAE?

Computer Aided Engineering. CAD is for geometry, CAE is for analysis. Both have been merged within SOLIDWORKS.

What visualization can you apply?

photorealism, different materials, colors, and texture

What are the two flavors of measurement capabilities?

Ones that are geometric (perimeters, surface area, angular, ect.) in nature and those that are mass properties (weight, center of mass)

What are principal axes of inertia and moments of inertia good for?

They are essential for being able to size motors or rotors.

How does SW interference detection work?

It will tell you where the parts occupy the same value

What is the basis for the analysis activities in Geometric Properties Analysis?

A 3-D solid model. To perform the analysis, you must create the solid model and proceed from there.

What is measurement analysis used for?

determining the dimensions and other geometric parameters of a CAD model

What are mass properties and what do they depend on?

Mass properties are static properties of a solid body. Depends on geometry of the part and its density.

Common place to check for interferences and clearances?

Between shafts and circular holes.

What purposes is animation used for?

For purposes of visualization, communication, and dynamic analysis

What drop down options are within SW motion study?

Animation, basic motion, and motion analysis (from SW motion add-in)

How is motion study good for interference detection?

Can find interferences in positions you might miss in static assembly. Motion study also has a check interference feature, meaning you can check for interferences each frame and check components. This detection is great for assemblies of moving parts.

How do you use a universal joint?

Only suitable when there is a relatively shallow angle between input and output shat, or when going slowly. If these conditions aren't met, use constant-velocity joint.

Can you use a mate to give awareness of interference occurring between parts?

You generally cannot, unless distance mate is used. It is possible at the motion analysis level.

What are fixtures?

They refer to how we fix the part, not subject to motion

What is a factor of safety? (FOS)

Within FEA, It expresses how far above the experienced stress the capability of the material to withstand that stress is

What does it mean if the factor of safety is below 1?

The material is going to have permanent deformation if not a breakage.

What is the beauty of FEA analysis?

You can modify the model based on new info and rerun the analysis easily

What are examples of boundary conditions?

Stress analysis: forces or defined displacement, thermal analysis: temperature

What is the FEA process?

Divide object into small elements, solve for stresses within individual elements, and compile the results across the entire object, obtaining an approximate solution

What is the first step of the FEA process?

To create the model geometry

For finite element study, should an object or assembly be fixed in space?

Yes. otherwise the object will translate in space

When can loads be applied in FEA?

After constraints are specified

What is the final preparatory step before the model can be submitted for analysis?

To create the mesh. Mesh is chosen to minimize computations without compromising accuracy.

What does the FEA solver compute?

The various quantities for the model based on the boundary conditions- constraints and loads- that were applied. For stress analysis, primary quantities are stresses and displacement.

What is a design check?

Software identifies areas of the model that could be modified to improve performance

What produces stress concentrations in a model?

Sharp internal corners and edges, these can be reduced by rounding these edges.

Difference in how right-handed and left-handed people should draw lines?

Both should draw vertical lines from top to bottom. Right handed people should draw horizontal from left to right, Left-handed should draw them from right to left.

How to sketch a circle?

1. Create bounding box of circle

2. Make tick marks at the center of each box edge

3. Draw 4 arcs that make up circle

How to use construction lines?

Used to outline the general shape of the object you're trying to sketch and its prominent features. Should be drawn lightly on page. These lines can be used to find the center of a square or rectangle.

How are coded plans used?

Used to define simple objects constructed entirely out of blocks. Numerical values in plan represent the height of the stack of blocks as the object "grows".

What is the disadvantage of creating isometric sketches?

It distorts the planar surface, meaning squares appear as parallelograms and circles appear as ellipses.

How to determine whether a part of the back edge of a hole is visible in Iso sketch?

locate the center of the back hole and sketch the radial points of the ellipse, if no portion of the ellipse is visible, dont include any arcs within outer hole of the sketch.

What is an advantage of oblique pictorials?

When face of object is in the plane of the paper, object appears in true size and color in that plane- undistorted

Are dimetric and trimetric pictorials used a lot in engineering work?

No, they seldom are. Much more common is isometric.

Importance of freehand sketching?

The ability to confidently draw freehand is vitally important

What is the fundamental problem with pictorials?

Angles and distances cannot be read directly

Tips for drawing lines?

Do not occlude (block your vision of line) line while drawing. You should focus on the endpoint and rotate the paper as needed.

How to finish a sketch?

Fill in outline more heavily and erase occluded lines.

What are the classifications of pictorials

1. Axonometric:

- Isometric

- Dimetric

-trimetric

2. Oblique (less realistic than axonometric):

- cavalier

-cabinet

3. Perspective (most realistic):

- 1, 2, 3 vanishing points

What is the first step of axonometric projection?

define a set of axes aligned with major width, height, and depth edges of part, axis location and orientation are arbitrary,

What is an axonometric aberration?

An optical illusion that arises as a result of W/H/D lines being parallel. A result of there being no vanishing point in axonometric.

When do isometric lines get complex to draw?

when surfaces that need to be drawn are not defined as frontal, horizontal, or profile surfaces because the lines that form the surfaces are not parallel or perpendicular. These lines are called "nonisometric lines"

What is an oblique surface?

A surface that is neither parallel nor perpendicular to the frontal, horizontal, or profile projection plane. The oblique surface will appear in all 3 views as its characteristic shape

Are hidden lines in orthographic and isometric pictorial views?

Hidden lines are represented in as dashed lines in orthographic and are generally not shown in isometric pictorial views unless it is necessary for interpretation (blind hole)

How are cylinders represented in an isometric drawing?

It is represented by an ellipse.