Calculate the resultant thrust and overturning moment

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Discussion Overview

The discussion revolves around calculating the resultant thrust and overturning moment for a vertical retaining gate in a dry dock scenario, focusing on hydrostatic pressure and torque considerations. The problem involves understanding the forces acting on the gate due to water pressure and the geometry of the gate itself.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the problem statement and the necessary calculations.
  • Another participant suggests that the weight and density of the gate are needed for a complete analysis.
  • There is a discussion about the dimensions of the gate, with some participants clarifying that the gate is 2 meters wide and 24 meters high.
  • One participant proposes integrating the total torque on the gate and equating it with a force, although they later express uncertainty about their understanding.
  • Another participant emphasizes the importance of calculating the torque due to water pressure while noting that the thickness of the gate is irrelevant to the calculations.
  • There is a reiteration that if the gate is thick, its weight could contribute to the torque, but this information was not provided in the problem statement.

Areas of Agreement / Disagreement

Participants exhibit uncertainty regarding the dimensions and relevance of the gate's thickness, with no consensus reached on how to approach the problem effectively.

Contextual Notes

Participants have not established clear assumptions regarding the gate's weight or thickness, and there are unresolved mathematical steps in calculating the thrust and torque.

Taidhg
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Homework Statement


A vertical retaining gate 2metres X 24metres hinged about the bottom edge of a dry dock has water to a depth of 21 metres on one side. Calculate the Retaining Force at the middle of the free upper edge of the gate to keep it shut in the vertical position. With the density of seawater being 1030Kg/m3.

Homework Equations


Hydrostatic pressure = D*g*h
Force = P*A
Thrust force = D*g*(h/2)*A
Overturning moment = Thrustforce*(h/3)

The Attempt at a Solution


I am sorry I really don't understand this question.
 
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upload_2018-12-9_9-33-10.png


Is this a picture of the problem? It seems to me that the weight and density of the gate is needed?
 

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Spinnor said:
View attachment 235477

Is this a picture of the problem?
I wasn't provided with a diagram however that is the same as the one I produced
 
Taidhg said:
I wasn't provided with a diagram however that is the same as the one I produced

I thought the thickness of the gate was 2m. The height I guess is 2 meters, the width is 24, and the gates thickness is small. You need to integrate the total torque on the gate and equate that with 2xF ?

I would be wrong. The height must be 24m and the width 2m which makes for a very tall and narrow gate. Now I'm confused also.
 
The gate is 2 meters in width, 24 meters high, and its thickness is irrelevant. Think about how you might calculate the torque about the hinge's axis due to the water pressure.

upload_2018-12-9_11-50-14.png
 

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gneill said:
and its thickness is irrelevant

If it is thick then its weight might contribute a torque. But that info was not given.
 
Spinnor said:
If it is thick then its weight might contribute a torque. But that info was not given.
Place the hinge in the center of the door thickness. Problem solved :smile:

upload_2018-12-9_12-29-5.png
 

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