# Tag Info

19

CFD (computational fluid dynamics) includes any numerical method used to solve fluid flow problems. FEA (finite element analysis) is one numerical method for solving partial differential equations, independent of what the equations are modelling. It is true that FEA is the most popular method for solving computational mechanics problems. There are ...

9

I am guessing, you are solving the following system: $$\partial_t T = \alpha_i \partial_x^2 T$$ with $\alpha_i=\kappa_i/\rho_i c_{p,i}$ for material $i$, subject to the conditions: $$T\left(x,0\right)=T_\infty\quad T\left(0,t\right) = T_h \quad -\kappa\partial_xT\left(L,t\right)=h\left[T\left(L,t\right)-T_\infty\right]$$ Now you can approach simulating ...

9

The basic difference between implicit and explicit dynamics solutions is that an explicit solution takes account of the finite propagation speed (at the speed of sound) of dynamic effects through the material. To do that, you need a mesh which is fine enough to represent the spatial effects (e.g. a "stress wave" propagating through the structure), and time-...

9

There are a number of techniques for meshing complex domains for Finite Element Analysis. They generally fall into two categories: Structured vs. Unstructured. For structured meshes, basically the entire mesh can be mapped directly to a 3D array of XYZ coordinates, whereas unstructured grids cannot. There is a good description of the classifications with ...

8

Say we have a slab supported on a beam. The centroid of the slab and the centroid of the beam are not coincident. Fortunately, in FEM software packages the geometric centroid of the element can be offset from the nodes that define the element. The sketch below shows a case where the shells have been offset such that the nodes are at the bottom face and the ...

8

Assume a 1d version of the equation. Then the K matrix becomes a k, spring constant. In 1-D The equation reduces to : $m \ddot{q} + kq = f$ The q matrix also becomes x vector in one dimension. This is the differential equation for a forced mass-spring system. (@Jmac added the 1-d equation) Similarly, The physical meaning of the matrix eigenvalues is how ...

7

Yes, getting a second opinion can be useful. This is done routinely in weather forecasting where exact solutions are unknown, and there is some judgement about how to apply various factors. There will be less wiggle room in something like a finite element mesh stress analysis because the iterative equations for solving it will be basically the same no ...

7

The short answer to your question, How can we compute the Equivalent Static Lateral Forces, the overturning moment and other quantities in an irregular building/structural discretized by finite element? is, simply, you can't. ASCE7-10 speaks directly to this in Section 12.6 when it describes the conditions under which Equivalent Lateral Force (ELF) can ...

6

I'll go through your questions one by one: A simple model like you have shown is fine to get model loads. Once you get those loads, you can then use a more specific technique to design the pier. (strut and tie). Rigid links are ok. Just make sure that you are capturing the various induced moments. I usually have rigid links from the bearing locations to the ...

6

While the other guys explained the theoretical framework behind meshing, the practice is markedly different and it is not at all automatic in industries where quality of mesh is of utmost importance given that finite element analysis results cover a great deal of the product development process. Let's first understand how meshing is done: Meshing for ...

6

I write this from the perspective of an engineer who develops simulation software. I think the practice described is bad, and I recommend you do not use two different softwares to "confirm" the results. In general, two different modeling softwares can not be used to confirm much anything other than their similarity. Two softwares could easily both get two ...

6

Summary: 1) The answer to this question is difficult. You would need to know how austenite and ferrite behave in relation to what you are doing to them. You would also need to know their compositions, temperature field, etc. The results here could vary significantly depending on the specific parameters and how they change with time and with each other. 2) ...

5

This may be only a partial answer since I don't have any idea what to do for the Young's modulus of the fluid. Consider the paper Dynamic Pressures on Accelerated Fluid Containers by G. W. Housner. This is referenced by ASCE 4-98 Seismic Analysis of Safety-Related Nuclear Structures, Commentary Section C3.1, for analysis of hydrodynamic loads on tanks. In ...

5

The short answer is, there is no amplitude used. Even more important though, is the fact that the displacements and stresses shown in the results of a modal analysis cannot be used to say anything about the physical behavior of the part in absolute terms. The basic equation of motion is $$[M][\ddot{U}]+[B][\dot{U}]+[K][U]=F(t)$$ $M$, $B$,and $K$ are ...

5

The amplitudes of the modes from a vibration analysis are arbitrary. Often they are "mass-normalized" which is mathematically convenient for using them in a subsequent step in the analysis. There may be an option to scale the in other ways, for example "engineer's normalization" where the largest deflection is set to 1.0, or the option to scale a specified ...

5

As far as I understand your question you are looking for a way to diffuse/mix two gases into each other. The process is very hard to simulate "correctly" because of the characteristics of the equations. However, it is quite unlikely that you will have a worse mixing than predicted because the models usually underestimate the turbulent mixing processes. Your ...

5

First, to counter what some people are saying about printed metals, selective laser sintering can produce parts that are as thermally conductive as their base metals. They are limited only by porosity, and state of the art machines can produce fully-dense (zero porosity) metal parts. Second, you probably don't need to take radiation into account because ...

5

It's easier to understand this identity if you start with the partial differential equation for the Euler-bernoulli beam deflection equation $$\frac{d^2}{dx^2}\left[ EI \frac{d^2u}{dx^2}\right] = 0$$ and work your way down to the weak form. Multiply both sides of the equation by an arbitrary test function $w$. Then apply integration by parts (only once)...

5

Firstly you're mixing units The melting point of titanium is 1668C (3000F) The melting point of steel starts at around 1300C up to around 1500C depending on carbon content. For brief contact where the mass of the steel is reasonably high you would probably get away with this but generally foundry equipment which comes into contact with molten metal is ...

5

The symmetry itself is not a boundary condition. It is a property of your system which means that both the geometry and the load are symmetric with respect to an axis or a plane. It allows to reduce the computation to a downsized domain, which leads to considerable computational time saving. I guess you are using a FEA software and manually reduced the mesh. ...

4

I think this is a good practice overall. By using two different softwares, you may be able two avoid two kind of errors: 1) errors that come from an inaccurate software (which should not be overlooked), 2) errors that come from the lack of habit of the user with the software (hidden options, default settings...). If the softwares are different enough, the ...

4

Preliminary results I added a conical structure before the choking point to separate the flow. Basically cutting the fluid. This cone is attached with 4 supports. This configuration increased mixing by a ridiculous amount. I achieved a near linear product distribution. However, I have not run temperature or structural analysis on this cone to validate ...

4

I would ignore the fact that the keyway makes the actual forces slightly off-center at least when calculating the forces themselves. The forces can be placed at their true locations once they are calculated. I would also assume that the load is continuously distributed from the center to the outer edge. This assumes that the key is machined with a tight ...

4

Just to let you know, I solved the problem. The element stiffness matrices had an error due to a typo, actually they were not even symmetric! Moral of the story: it's good to test for symmetry when you write a function which produces an element stiffness matrix. Anyway, thanks to all for your efforts and replies.

4

What you need is the modulus of subgrade reaction (MSR) of the soil. This is a measure of soil deflection under a given pressure, so the unit is in (for example) kPa/m, or equivalently, as I'm more accustomed to see it, kN/m3. MSR is obtained via plate-bearing tests, but there are also quite a few different tables that give some "typical values" for ...

4

First Part Simplifying the $$1 \ lbf = 1 \ slug .ft/sec^2$$ then $$1 \ lbf \ sec^2 / in^4 = 1 \ (slug .ft/sec^2 ). (sec^2/in^4) = 12 \ slug /in^3$$ $$12 \ slug / in^3 * (14.6 kg / 1\ slug)*(in/25.4 \ mm)^3 = 0.0107 \ kg/mm^3$$ Note that that each slug equals to 14.6 kg so (1 slug / 14.6 kg) equals to 1.0 and any expression multiplied with 1.0 will ...

4

Regarding the problem you have, without reviewing the results its difficult to make a definitive answer. However, if you are observing high loads near the weld, I think you should try to make geometric modifications, to decrease any stress concentrations or loads. The reason is that welds are generally very "temperamental". What I mean by that is ...

4

Yes, it increases and decreases strength in traditionally steels. Depends on what steel you have and what you mean by "thin rods", and the weld process , and the specific weld parameters. Properly selected filler metal will be close to the base metal strength. Common stick electrodes are "60" which means the weld deposit will be over 60,...

3

There are several options for doing this: If there are only a few values to be saved per design point, you could use 'output parameters'. If there is a lot of data to be saved, the report generator may be useful. Some information can be found here: Working with Project Reports An APDL snippet can be used in the results* tree. Some information here: ...

3

Section 2.1.14 of the Abaqus Example Problems Manual is 'Water sloshing in a baffled tank', which might be useful (even if you don't use Abaqus at your own institution, the manuals are hosted by many institutions that allow public access). The Abaqus water model uses an equation of state (EOS). If you download the input file from the manual, you can cut ...

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