Flap Gate Weir Structural Design Using FEA

A flap gate weir commonly use to raise the level of a river or stream. It is a device that is used to regulate the flow of water in a river. It is typically located at the upstream of the river. Basically, flap gate weir is submerged under water, so hydrostatic force acting on submerged surfaces weir. The traditional design and analysis the resultant force acting on a submerged weir surface must specify magnitude of the force, direction of the force and line action of the force all is assumed on 2D which take long time calculation and might mistake. The aims of this paper is using finite element method design and study the flap gate weir structure instead of traditional analysis. In this paper the 3D model of flap gate weir was created by SolidWorks as assembly of flap gate weir which the flap gate weir was inclined 30 degrees and imported into Ansys Workbench for boundary conditions and calculations. The result from Ansys is used to find the specific hydraulic cylinder as the system needed. And modal analysis to check the vibration of the flap gate weir. By using finite element analysis the results study is satisfy by get results faster, know total deformation, know weak point and know where reinforce pad should put in and saving cost of materials when compare with traditional analysis.


Introduction
A flap gate weir commonly used to raise the level of a river or stream.It is a device that is used to regulate the flow of water in a river [1].Flap weir is typically located at the upstream of the river [2].Basically, using of flap gate weir is submerged under water inclined 60 degree respect to ground, so hydrostatic force acting on submerged surfaces weir.Currently, flap gate weir design and analysis is using the traditional design.Thus, the resultant force acting on a submerged weir surface must specify magnitude of the force, direction of the force and line action of the force in which might lead to calculation mistake.Thus, in this paper come up with the flap weir design and analysis using finite element method (FEM) [3,4].Physical model of flap gate weir in 3D can represent the hydraulic structure, under certain conditions, and thus provide answers related to numerous hydraulic, static and dynamic conditions.To ensure that results obtained from hydraulic research can be safely used in the analysis of real structure.The nomenclature of a flap weir is shown in the figure 1.The flap gate weir each part is made of structural steel and finally bring it up assembly all part together by welding.The hydraulic analysis of flap gates of M. Broucek, M. Kralik and P. Nowak [5] showed experiments and numerical modelling of flap gates with operating rods on both sides.Mark Pennington [6] perform flap gate in hydraulic model to examines methods for adequately representing flap gate outlet in hydraulic models.Charles M. Burt and member [7] have constructed and installed flap gate in practice are limited to controlling water depths of about 1 meter or less, design was be using excel design procedure for a simple hydraulic flap gate for automatic upstream canal water level control is provided.In this paper author design and analysis the flap gate weir long 19 meters with 6 hydraulic cylindrical supports operation at 60 degrees and12 pivots support as shown in the figure 1.The flap gate weir is at crest level 1 meter, river level 0.5 meter over crest as shown in the figure 2.

Material and Methods
The manner in which the pressure varies in a statics fluid can considered as hydrostatic force on a submerged surface, the flap gate weir is at crest level 1 meter, river level 0.5 meter over crest.Traditional analysis, in order to determine completely the result force acting on a submerged surface for a flap gate weir is consider as a plane submerged surface.Basically, pressure distribution on a submerged surface a distribution triangular in cross section in a pressure prism that it is linear and pressure increases with depth [8].Mathematically, a single force is to replace the pressure prism as shown in the figure 3. The single force can be written in the form: It is reveal that the structure of the flap gate weir as shown in the figure 1 with analytical method not able to design and satisfy the flap gate weir.Thus, in this study start from creating the 3D model each part of the flap gate weir by SolidWorks and then mate together instead of welding in practice.The material property of the flap weir is made of structural steel.The flap gate weir will be inclined 30 degree for this design and for find out the diameter of hydraulic cylinder.After got the 3D model, it was imported into Ansys for analysis the hydrostatic pressure on the flap gate weir shown in the figure 4.
All the reaction forces F and b r from Ansys is to find out the diameter of hydraulic cylinder and analysis the pivot at support it can express: The require force for a hydraulic cylinder can be written in the form sin Where R is distance between end of the hydraulic cylinder.The  is angle of the hydraulic cylinder to the flap gate (skin plate).The modal analysis [9] was being performed after structure design completed to check the support and find out the model shape.

Results
In this modelling study found that the gravity contribution to deformation is at 8.73% and to maximum principal stress is at 3.95% as shown in the figure 5.The modal analysis revealed that the support no. 2,3,10 and 11 might loose or unscrew (from left) due to vibration.The all stresses got from finite element method conclusion in table 1.The reality model that designed using finite element analysis shown in the figure 7.

Conclusion and Discussion
In this modelling study found that the own weight of flap gate weir not necessary to consider.Because of the gravity contribution less and the flap gate weir has burden load more than its own weight.In this study the flap gate weir was inclined 30 degrees initially.The hydrostatic loading acting on the flap weir result to find out the diameter of piston head of the hydraulic cylinder that by this finite element method using 12.5 cm as standard following hydraulic cylinder.With finite element method designer able to know weak point on the flap gate weir and cost saving a lot on materials.

Figure 1 .
Figure 1.A flap gate weir nomenclature (a) side view (b) front view

Figure 2 .
Figure 2. A criteria for proper weir design

Figure 3 .z
Figure 3. Pressure distribution and equivalent force on a submerged surface[1]

Figure 4 .
Figure 4. Hydrostatic pressure on the flap gate weir

Figure 5 .Figure 6 .
Figure 5.The gravity contribution to (a) deformation and (b) maximum principal stress

Figure 7 .
Figure 7.The real model was designed using finite element method

Table 1 .
FEA results of flap gate weir