The values match our manual calculations. Therefore we get a moment of inertia of: Calculate the moment of inertia of a disk The next step is calculating the moment of inertia of a flat disk with radius. Now, calculate the Section Properties of the Area The enclose the curve with vertical and horizontal lines In this case we are suing SolidWorks to create the curve.Ĭ-For this function, notice the value of y = 1/32 x^3, so in SolidWorks we input these values as shown: If a horizontal element was used, then we could use the standard Ixx= y^2da This is because the vertical element in Integration would have varying locations for the Centrodial x-axis but a constant x-axis. Notice: that in the manual method for a function like this, for the Moment of Inertial, the value was first calculated with respect to the X-axis using Ixx = 1/3 bh^3. Then the Parallel Axis Theorem is used to move the Moment of Inertia to the Centrodial X-axis and Centrodial Y-axis. We first calculate the Moment of Inertia about the X and Y axes with the equations shown using a vertical element. Second, calculate the X-bar and y-bar or the centroid of the area. Please let me know if you have any more help with this.Area Moment of Inertia: Manual Calculations Validated in CAD (SolidWorks)įirst, let's calculate the Area underneath the curve using Integration: A = ∫da which for this area underneath the curve gives us 2.0 in^2. I don't think it really matters whether I initialize using a Flat or Wavy method, is this correct? SDOFO_LOC_N(sdof_obj) = SDOFO_LOC(sdof_obj) SDOFO_INIT(sdof_obj) = SDOFO_LOC(sdof_obj) Also tried with 16664 Nm/rad and it didn't work either */ SDOFO_K(sdof_obj) = 0.0 /* spring constant. SDOFO_F(sdof_obj) = 0.0 /* spring preload */ SDOFO_CONS_P(sdof_obj) = TRUE /* constrained */ SDOFO_CENTER_ROT(sdof_obj) = 0.0 /* only needed for one DOF rotation. SDOFO_DIR(sdof_obj) = 1.0 /*rotation about the z-axis only*/ SDOFO_1DOF_R_P(sdof_obj) = TRUE /* one DOF rotation */ SDOFO_1DOF_T_P(sdof_obj) = FALSE /* one DOF translation */ Sdof_obj = Allocate_SDOF_Object(DT_PU_NAME(dt)) * Allocate_SDOF_Object must be called with the same name as the udf */ The mass moment of inertia is determined by a hand-calculation and verified with SolidWorks. Sdof_obj = Get_SDOF_Object(DT_PU_NAME(dt)) Dynamics Presentation on the mass moment of inertia with help of SolidWorks and SolidWorks motion. Sdof_prop = 16664*sin(DT_THETA(dt)) /*16,664 is the hydrostatic restoring coefficient*/ Here's a my code:ĭEFINE_SDOF_PROPERTIES(flap, sdof_prop, dt, time, dtime) I've tried writing a UDF for my case so I could apply an external buoyancy force to pull the flap back up to equilibrium, but didn't have any luck. Regarding rotational constraints, I originally set constraints for the rotational angle to -30 and +30 degrees. It's almost like the moment of inertia is causing some sort of torque on the device. I lowered the timestep to 0.001s and still got a negative cell volume because the flap falls over so fast. I changed the water depth to completely submerge the OWSC and the results were even worse. For example, even when I preview mesh motion the flap falls over, so I don't think the waves have an influence on the issue I am experiencing. The only reason I don't believe the natural frequency and wave frequency is the issue is because the flap falls over instantly, even without the presence of waves. I've tried reducing the time step, but nothing seems to be working. The discussion link that I posted above seems to have been inconclusive, and didn't really help my case. However, a moment of inertia this large seems quite unrealistic. When I change the moment of inertia to some large value like 100,000 kgm2, the OWSC doesn’t fall over, and actually begins to act normally by oscillating back and forth as the waves hit it. When I run the simulation with -1500kgm2 as the moment of inertia, the OWSC immediately falls over clockwise. After trying to isolate the issue, here is what I found: When I run the simulation with +1500 kgm2 as the moment of inertia, the OWSC immediately falls over counter-clockwise. The mass of my device is around 300 kg, and the moment of inertia about the hinge is around 1500 kgm2 according to SolidWorks. The specific issue that I am having is this: whenever I start the simulation using dynamic mesh, the OWSC immediately “falls over” with high velocity. What are Mass Moments of Inertia We have all referred to Mass Properties when working with solid models, especially when taking SOLIDWORKS certifications For the most part, very useful information is available at a glance i.e., Density, Mass, Volume, Surface Area, etc. I am currently experiencing an issue with my OWSC model in Fluent 2021, similar to the issue found in this post: Instead of using a UDF, I am using the built in 6DOF solver to assign rotation to the hinge of the OWSC. Hi, I am modeling an OWSC using open channel wave boundary condition and a dynamic mesh.
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