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Ecology - Aquatic > Physics - Environmental Flows > Flashcards

Physics - Environmental Flows Flashcards

1
Q

Fluid

A

This includes liquids and gases being substances taking up the shape of its container

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2
Q

What is fluid behaviour described by?

A

Navier-Stokes Equation

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3
Q

Navier-Stokes Equation

A

This models motion of viscous, incompressible fluids consistent with principles of mass and momentum conservation, relating pressure, velocity and density of a fluid to its acceleration

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4
Q

Viscosity

A

Resistance of a fluid to flow deriving from molecular interactions in the fluid

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5
Q

What does viscosity vary with?

A

Temperature, pressure and solute

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6
Q

Turbulence

A

This is a fluid motion characterised by chaotic changes in pressure and flow velocity

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7
Q

What are turbulence and viscosity related by?

A

Reynolds Number

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8
Q

Reynolds Number

A

This measures ratio of inertial forces to viscous forces in fluid flow

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9
Q

What laws are fluid flow governed by?

A

Newtons Laws
Conservation of Mass, Energy and Momentum

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10
Q

Newtons First Law

A

States that a body remains at rest in a straight line unless perturbed by a force

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11
Q

What is newtons first law based on?

A

Mass describing an objects resistance to motion, with higher mass meaning more force required for velocity changes

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12
Q

Why does inertia remain linear?

A

Acceleartion and velocity change requires a force

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13
Q

Force

A

This being an influence causing change in motion

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14
Q

What does 0 force -?

A

Zero acceleration

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15
Q

How can First Law be described by relativity?

A

Spacetime is not a medium in which physics occurs, but a participant of it

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16
Q

Equivalence Principle

A

This states the effects of gravity and acceleartion are indistnguishable.

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17
Q

Newtons Second Law

A

This says that the acceleration of an object acted upon by an external force is proportional to the force and is in the same direction as the force

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18
Q

Newtons Third Law

A

This says that any action is countered by a reaction of equal magnitude but oopposite direction

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19
Q

Pascals Principles

A

This state the pressure applied to an enclosed fluid will be transmitted without a change in magnitude to every point of the fluid and to the walls of the container

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20
Q

What is the premise of pascals principle?

A

The pressure at any point in the fluid is equal in all directions

21
Q

What does pascal principle describe?

A

Fluid transmission due to the incompressibility of a fluid, not easily compressed or expanded.

22
Q

What does incompressibility of fluid mean for force applied?

A

Expansion of a fluid increasing volume, decreasing pressure, whilst compression of a fluid decreases volume, increasing pressure based on volume maintenance.

23
Q

What does rate of entry equal in incompressibile fluids?

A

Rate of loss

24
Q

Continuity Equation

A

This states that total mass of a gas in a deformable box must remain constant, being the conservation of mass

25
Q

How is rate of entry=rate of loss described?

A

DeltaU/deltax written in 3D to describe advection

26
Q

What does the continuity equation describe?

A

Compressible fluids where density changes occur.

27
Q

What does density change equate in the Continuity Equation?

A

Difference of inflow vs speed of outflow

28
Q

What must changes in mass density be balanced by?

A

Fluid flow rate into/out of the region

29
Q

What does the continuity equation express?

A

Law of Conservation of Mass in terms of flow rate and fluid velocity.

30
Q

How may mass conservation be violated?

A

Spontaneous increase in mass density without changes in flow rate cannot occur

31
Q

What does increasing mass density correlate with?

A

Increase pressure

32
Q

What does conservation of momentum show?

A

Forces applied to the fluid mean the fluid move around, this being inflow of U with outflow of U+DeltaU

33
Q

What is the force in conservation of momentum?

A

(P+DeltaP)A on side of force application whilst opposite side PA with net force being Delta PxA

34
Q

Newtons Law of Viscosity

A

This says that shear stress betweeon two adjacent layers of the fluid is directly proporitonal to the velocity gradient between the same two adjacent layers.

35
Q

What are the two forms of viscosity?

A

Dynamics
Kinematic

36
Q

Dynamics Viscosity

A

This is the measure of resistance to flow when an extenral force is applied

37
Q

Kinematic Viscosity

A

This measures fluids internal resistance to flow under gravity, when no external force is applied

38
Q

What does viscosity determine?

A

How fast fluids move, how much mixture/exhcange occurs and how well they transport material and forces they supply

39
Q

What are the two types of flow determined by Reynolds Number?

A

Laminar
Turbulent

40
Q

Laminar Flow

A

This allows two or more streams of fluid to flow next to each other without any mixing other than by diffusion or their constituent molecules across the boundary between them.

41
Q

Turbulent Flow

A

These are irregular motions of the fluid elements may develop in the flow of fluid through a utube

42
Q

What is the RE equation?

A

RE = Ud x v(U being speed, d size and v kinematic viscosity)

43
Q

What does the RE equation do?

A

Relate inertial forces, causing acceleration of a fluid and straight line movement against viscous forces, slowing down the fluid causing adherrence to nearby surfaces

44
Q

When does laminar flow occur?

A

Low RE and viscous force domination

45
Q

When does turbulent flow occur?

A

High RE, inertial forces dominating

46
Q

Critical Reynolds Number

A

This is the limit where the laminar flow changes to turbulent flow

47
Q

What is the physics behind viscosity?

A

Friction between fluid water molecules and the surface creating a staitonary bounary layer.

48
Q

Bernoullis Principle

A

This is an equation for incompressible fluids based on Newtons Second Law of Motion stating that increase in fluid speed occurs with a decrease in pressure to fluid potential energy.

Ecology - Aquatic (7 decks)

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