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Industrial Design And prod Case Studies > Industrial Design And Prod Case Studies > Flashcards

Industrial Design And Prod Case Studies Flashcards

1
Q

What is a streamline?

A

Streamline is a curve where everywhere is tangent to the instantaneous velocity field

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2
Q

What does structural analysis solve?

A

Displacement, stress and strain.

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3
Q

What is yield strength?

A

Transition from elastic deformation to plastic deformation.

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4
Q

What is elastic deformation?

A

A temporary deformation of a material’s shape that is self-reversing after removing the force.

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5
Q

What is plastic deformation?

A

A permanent distortion that occurs when a material is subjected to tensile stress that exceeds its yield strength and causes it to elongate.

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6
Q

What is inertia?

A

An object’s ability to resist changes in motion which is Newton’s first law.

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7
Q

Give two examples where simulation can improve a design.

A

1- Shape optimization can be done on a bike crank to distribute the stress smoothly and avoid concentrated stress in local regions.
2- Designing thicker car fins allows more contact pressure to be generated between the seal and the window glass to avoid leakage.

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8
Q

What is a good design?

A

1- The material should not be subjected to tensile stress higher than its yield stress causing it to elongate (the material should not be plastically deformed).
2- Stress should be distributed evenly.
3- The volume-weight of material should be minimized to reduce the cost in terms of material and energy.

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9
Q

When does principle stress occur?

A

When a load is applied to a body and shear and normal stresses are developed.

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10
Q

What are the two types of simulation?

A
  • Static-state simulation that has static equilibrium and mechanical equilibrium.
  • Dynamic simulation where the loading is changing with time.
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11
Q

What is static pressure?

A

Is when an object is at complete rest with respect to a surrounding environment.

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12
Q

What are the advantages and disadvanates of DNS (Direct Numerical Simulation)?

A
  • Numerically solves the full unsteady navier-stokes equations.
  • No modeling is required.
  • Resolves the whole spectrum of scales.
  • The cost is too prohibitive and is not practical for industrial flows (Most accurate).
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13
Q

What are the advantages and disadvantages for LES (Large Eddy Simulation)?

A
  • Solves filtered navier-stokes equations.
  • Some turbulence is directly resolved.
    -The cost is less than DNS but the effort and computational resources needed are too large for most practical applicaitons.
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14
Q

What are the advantages and disadvantages of RANS (Reynolds Averaged Navier-stokes Simulation)?

A
  • Solves time-averaged navier-stokes equations.
  • All turbulent motion is modeled.
  • Many different models are available.
  • For most problems, the time-averaged flow and the level of turbulence is all that is needed.
  • This is the most widely used approach for industrial flows (Most effecient).
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15
Q

What is RANS?

A

Velocity field average over time (many snapshots).

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16
Q

What are the sources of numerical errors in terms of magnitude from smaller to larger?

A
  • Round-off errors: when the computer rounds off the solutions to a certain numerical precision.
  • Iteration errors: the difference between converged solution and solution that converges at iteration ‘n’.
  • Discretion error: the difference between converged solutions on a current grid and the solution on an infinitely fine grid (the exact solution).
  • Model error: the difference between exact solutions of model equations and reality (experimental data and analytical solutions).
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17
Q

What is discrete data and give examples?

A

Discrete data includes a limited set of numbers and can only take on certain individual values.
Examples include manual gear transmission, shoe size, facebook likes and year of birth.

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18
Q

What is continuous data and give examples?

A

Continuous data includes infinite numbers and the values in between these numbers include decimals.
Examples include auto gear transmission, movie length, time taken in a race, water temperature and wind speed.

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19
Q

What is FEM and its main two concepts and does it generate a mesh?

A

FEM (Finite element method) is the most widely applied tool in computer-aided engineer CAE and the most powerful modern calculator.
FEM has two main concepts which include finite elements and discretion.
Most FEM software’s generates free mesh by default.

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20
Q

What are Analytical solutions and what are they limited to and what are they used for and what does r=?

A

Analytical solutions involve closed-form expressions that calculate continuous variations of variables throughout the domain and give exact/accurate results.
Analytical solutions are limited to simple problems in terms of geometry and physics.
Analytical solutions are used to verify simulation results.
r =pi r squared

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21
Q

What is aerodynamics?

A

Aerodynamics is the study of how gases interact with moving bodies.

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22
Q

What is drag force?

A

Drag force is air resistance and acts opposite to the relative motion of any object with respect to a surrounding fluid.

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23
Q

What is lift force? and give an example of when it caused a problem in real life.

A

A pressure difference which creates a net aerodynamic force pointing upwards.
For example, Audi TT crashed in the year 2000 because the lift force and its high speed of >100 mph.

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24
Q

How is a downforce generated in a racing car?

A

A spoiler/wing generates a downforce which reduces the total lift force and keeps the wheels on the ground (grip).

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25
Q

What equations does laminar flow simulation solve?

A

Navier-stokes equaitons, continuanity equations and conservation of energy.

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26
Q

What are the types of contact models available in Ansys?

A
  • Bounded (default): glued meaning no separation between surfaces is allowed.
  • No separation: Separation between contact surfaces is not allowed.
  • Frictionless: Separation and frictionless sliding are allowed which means the coefficient of friction is zero.
  • Frictional: frictional sliding and separation are allowed.
  • Rough: no sliding but separation is allowed. Has infinite coefficient friction.
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27
Q

What is von-Misses stress?

A
  • Is a composite value (equivalent stresses derived from the three principal stresses).
  • Is used to determine if a given material will yield or fracture and is a theoretical mathematical value not a real physical stress.
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28
Q

What are the types of contact models in (finite element analysis) FEA in terms of geometry?

A

Rigid: non-deformable, hard, relatively higher stiffness (elastic modulus).
Flexible: deformable, soft, relatively lower stiffness.
Rigid to flexible contact: for example pushing a pinhead into a wall. It exists exactly between the pin head and the fingertip and between the pin tip and the wall.
Flexible to Flexible: For example, a tennis ball bouncing on a racket.

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29
Q

What is free unstructured mesh and how are they generated?

A
  • The elements are randomly distributed in the domain with different sizes and shapes.
  • Most (finite element method) FEM software generates the free mesh by default.
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30
Q

What are the two different types of mesh?

A
  • Free unstructured mesh.
  • Mapped structured mesh.
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31
Q

What is mapped structured mesh?

A
  • The elements are organised with their size is gradually changing in the domain.
  • No triangles, regular and programmable.
  • Less likely to have element distortions.
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32
Q

How do you do a mapped structured mesh?

A
  • Split the domain into multiple (3 or 4) subdomains and apply a mapped mesh on each domain.
33
Q

What are the two types of equilibrium?

A

Static equilibrium and mechanical equilibrium.

34
Q

What is static equilibrium and in what engineering field is it applied?

A

Static equilibrium occurs when an object is at complete rest with respect to a surrounding environment.
In civil engineering, structures are designed to be at rest when acted upon by external forces.

35
Q

What is mechanical equilibrium?

A

Mechanical equilibrium occurs when an object or a system are in motion at a constant speed where net forces and moments are equal to zero (newtons law of motion)

36
Q

What type of simulation is used for static equilibrium and mechanical equilibrium?

A

Static or steady-state simulation.

37
Q

When was Hertzian contact theory published and by who and why is it important?

A

Published by Heinrich Hertz “on the contact of elastic bodies” in 1881.
Is a great contribution to solid mechanics.

38
Q

What are the assumptions of Hertzian contact theory?

A
  • Surfaces of contact bodies are frictionless.
  • The materials are elastic and homogenous.
  • The radius of the contact area is much smaller than the equivalent radius of the contact bodies.
39
Q

When can the Hertzian contact theory be applied?

A

When all three assumptions are all satisfied.

40
Q

Explain the ball bearing as a realistic example of Hertzian contact theory.

A
  • Coefficient of friction = ~ 0.01 with lubrication.
  • The elastic material is stainless steel.
  • Contact area is smaller than 1mm; ball radius : ~ 10mm.
41
Q

What can we calculate from Hertz contact theory?

A
  • The contact pressure which has a parabolic profile.
  • If the contact area is a circle or elliptical.
  • The penetration depth.
42
Q

What are the three basic simulations for calculating turbulent flow?

A
  • DNA (Direct Numerical Simulation)
  • LES (Large Eddy Simulation)
  • RANS (Reynolds Averaged Navier-stokes Simulation)
43
Q

What is CFD and what does it include?

A

Computational fluid dynamics and includes engineering fluid dynamics, computer science and mathematics.
CFD is the analysis of fluid flows using numerical solution methods.

44
Q

What is Newton’s first law and why does a ball stop rolling after sometime?

A

Every object will not change its motion unless a force acts on it.
The reason a ball stops rolling is because of friction.

45
Q

What does tighter criteria need?

A

Needs more iterations.

46
Q

What type of results does a tighter criteria have?

A

Tighter criteria gives less numerical errors but takes longer time to compute.

47
Q

How are discretion errors calculated in a mesh independent study?

A

By using the equation for relative errors (any solution - the solution’s reference which is its finest result )/ solution reference.

48
Q

What does tighter criteria mean regarding convergence criteria?

A

Higher convergence criteria (1e-4 > 1e-6).

49
Q

What does tighter criteria look like on a graph and on mass flow results?

A

On a graph, the x-axis will have smaller defines intervals. On mass flow results, the results will be positive in our case.

50
Q

What is a spoiler/wing in a racing car

A

A small flap seen at the rear of a racing car.

51
Q

What is spoiled in the lift force in a racing car?

A

The air flow.
The streamlined profile.

52
Q

Can a pathline be determined from a streamline?

A

The direction the path takes is determined by the streamlines of the fluid at each moment in time therefore if the streamline is known, the pathline of any particle can be known.

53
Q

Describe the pathline and a streamline in steady flow?

A

In a steady flow the pathline and streamline are the same.

54
Q

What are the three definitions of pathlines?

A

Trajectories that individual fluid particles follow as a recording.
The path of a fluid element in the flow over a certain period.
A line traced by one given particle that flows from one point to the other during time.

55
Q

What are streaklines?

A

Streaklines are lines created by many particles in a flow that has previously passed through a common point.

56
Q

What are multiple streaklines?

A

Multiple streaklines represent particles passing through different points in the past.

57
Q

What is the fundamental equation for strain?

A

𝜀 = ∆𝐿 / 𝐿0
(dimensionless)
The ratio between displacement and original length.

58
Q

What is the fundamental equation for stress?

A

Stress = 𝜎 = 𝐹𝐴 (Pa)
* The force applied per section area
* Normal stress 𝜎 (pressure)

59
Q

What is the product design process?

A

1 Starts with the customer marker
2 Design concept and design modelling (CAD),
3 Design analysis and design optimization (CAE),
4 Design evaluation,
5 Process planning and production planning and quality control and packaging (CAM).

60
Q

What is the role of numerical simulation in the product design process?

A

CAE which includes design analysis and design optimisation.

61
Q

Who must have FEM as a skill?

A

Engineering student and professional future engineers.

62
Q

How do we analyse a practical problem and conduct a good-quality simulation?

A

Use computer software as a tool and have a fundamental knowledge of physics and math.

63
Q

What is the link between numerical simulation, product design process, CAE and FEM?

A

Numerical simulation role in the product design process is CAE and FEM is the most used method in CAE.

64
Q

What are the governing equations for fluid mechanics (conservation of laws)?

A

Conservation of momentum, energy and mass.

65
Q

In what domain are finite element solutions are solved?

A

In a discrete domain rather than a continuous domain.

66
Q

How does the size of the enclosure (the box in a picture) affect the simulation results? If the size of enclosure is not chosen properly what type of errors could be
introduced?

A

If the size of the enclosure is not large enough to cover the fully developed fluid flow field, the solution could be inaccurate.
The model errors.

67
Q

What is the type of contact in a cylinder on cylinder shape from a geometry and a materials perspective?

A

Line contact, flexible to flexible and non-conformal contact.

68
Q

How to tell if a mesh with a specific number of elements is fine enough from an error against the element number graph?

A

Compare it with the previous mesh and if the error is less than 5% then yes.

69
Q

How to find other error sources in a simulation of elements against error percentage and what type of errors are possible?

A

The total error is when the line flattens out and can be caused from discretion or models errors.

70
Q

What is the relative error of bending stress?

A

(The calculated bending stress - predicted bending stress) / the calculated bending stress.

71
Q

Describe the element in principle stress.

A

The element is at the principal direction with a rotation angle to the reference sysetm.

72
Q

What is the maximum deformation error?

A

(Theoretical max deflection - FEM max deflection) / theoretical max deflection x 100

73
Q

Describe the system of the loading and structural deformation in a mech-independent study.

A

The system is linear because structural deformation is directly proportional to the loading therefore the bigger the element size the bigger the maximum deformation error is.

74
Q

Do objects hit the floor faster in a vacuum or in the air and why?

A

In a vacuum because there is no air resistance.

75
Q

What are the governing equations for fluid mechanics?

A

The three conservation laws which include momentum (navier stokes equations), mass and energy.

76
Q

What physics is in wind noise analysis?

A

Fluid mechanics

77
Q

What physics is in rain sensors automatic windshield wipers?

A

Electrical and electronics, fluid mechanics and solid mechanics

78
Q

What can we study from pathlines, streaklines and streamlines?

A

Location of eddies
Sources of lift/drag forces
Sources of wind noise

Industrial Design And prod Case Studies (1 decks)

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