IntermediateTopic 50 of 105Thermodynamics & Fluids
Forces on submerged surfaces
Hydrostatic force acts at the centre of pressure below the centroid.
In depth
Hydrostatic force on a plane surface F=ρg h_c A, with h_c the centroid depth, acting at centre of pressure below the centroid: y_cp=y_c+I_c/(y_c A). Curved surfaces: horizontal component as projected plane, vertical as weight of fluid above. Used for dams, gates and tanks.
Key points
- Pressure prism
- Centre of pressure deeper than centroid
- Dam stability: overturning and sliding
ExampleA 2×3 m vertical gate with top at the surface carries 88 kN force (water).
Hydrostatic forces on submerged surfaces determine the loads on gates, dams and tanks, so their location matters for structural design.
What is Forces on submerged surfaces?
Hydrostatic force acts at the centre of pressure below the centroid.
Why is it important to understand forces on submerged surfaces?
Hydrostatic forces on submerged surfaces determine the loads on gates, dams and tanks, so their location matters for structural design.
What is the centre of pressure?
The point on a submerged surface where the resultant hydrostatic force acts, which is always below the centroid for a plane surface.
Why is the centre of pressure below the centroid?
Pressure increases with depth, so the lower part of the surface carries more force, which moves the resultant down.
How is Forces on submerged surfaces used in practice?
Typical applications include calculating the total force on a vertical sluice gate, locating the point where the resultant force on a dam acts and designing the bolts for a hatch cover on a tank.
What should I learn before Forces on submerged surfaces?
Study "Buoyancy" first (topic 49 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Forces on submerged surfaces?
Pressure prism. Centre of pressure deeper than centroid. Dam stability: overturning and sliding.
Can you give an example of Forces on submerged surfaces?
A 2×3 m vertical gate with top at the surface carries 88 kN force (water).
What comes after Forces on submerged surfaces?
The next topic is "Fluid kinematics", which builds directly on this one.
How difficult is Forces on submerged surfaces?
It is classed as Intermediate in Thermodynamics & Fluids (topic 50 of 105). It is an intermediate topic. Work through the beginner topics in Thermodynamics & Fluids first.