What is the function of the extension top caps in the Triaxial loading system?

Dear RG Community,

As we are aware that there are almost 5-6 FEM softwares available for modelling and analysis, say, PLAXIS, FLAC, GeoSlope, Abaqus etc. related Geotechnical Engineering. I am confused which one is more comprehensive and suits best for Geotechnical Engineering students.

Thank you.

Hi everyone!

Some researchers believe that in the depth (more than 15 meters) there is no liquefaction potential for sand layers. Is it true? Is there any example and reference? And is there any sensitive for surface structures in this area (I mean a sand layer is located in the depth more than 15 meters) if an earthquake happen? Do you introduce new relationship for checking the liquefaction potential and its potential relationship with depth?

Thanks in advance for sharing your experience!

Reservoir Engineering: Coal Seam

1. Since, gas is primarily stored by adsorption into the coal as a function of pressure @ which the gas gets adsorbed, can we replicate the scenario, whereby ‘the amount of gas adsorbed per unit increase in pressure remain decreasing with increasing sorption pressure’ @ laboratory-scale using experimental investigations?

2. Feasible to achieve ‘equivalent sorption pressure’ @ laboratory-scale, where the water pressure of the water-saturated coal seam remain exceeding the pressure @ which all gas becomes adsorbed into coal-solids or into solution gas?

3. With a relatively low bulk permeability of coal (around 1 md); and, with a ready desorption from solid; what should be the closest spacing of cleats (10 mm or 100 mm), whereby, the dominant mode of fluid transport in a coal seam could be treated as to be Darcy flow (as against with a relatively less fractured structure; and, with slower desorption from solid, where the rate is controlled by diffusive movement)?

If not, how exactly to deduce an average cleat spacing and permeability into which the solid blocks could be considered to diffuse?

4. With Darcian flow being the prime importance in the movement of gas within the coal, can we reproduce the scenario, where the permeability could be strongly directional-controlled by predominant cleat sets @ lab-scale?

5. What is the physical basis by which we decide the permeability of a given cleat structure within coal remains to be dictated either by

(a) phase relative permeability effects, whereby the degree of saturation would affect the gas and water relative permeabilities of the reservoir? or by

(b) changes in the effective stress (total stress minus the seam fluid pressure) within the seams?

Feasible to capture the way the effective stress tends to close the cleats; and the way, it tends to reduce the permeability within coal @ lab-scale?

Under what circumstances, the permeability would remain related to effective normal stress across the cleats?

Any idea about how exactly the gas gets traveled through the core specimen?

6. Feasible to capture all the required 3 factors that influence the effective stress @ lab-scale?

(a) initial-stress (given the weak and jointed nature of coal, while it also remains to be directional); (b) fluid pressure changes; & (c) shrinkage/expansion characteristics of coal matrix (which remains related to the equivalent sorption pressure in the seam).

Feasible to secure stress patterns by ML/AI - from stress measurements in the rock surrounding the seam – deduced as a function of (a) stress caused by gravitational effects, where the overburden stress and the associated lateral stress getting developed under conditions of no lateral strain; and (b) horizontal stresses, which gets induced by tectonic forces (and, which should remain proportional to the moduli of the rocks, while the respective horizontal strains remain approximately equal)?

Is the formula p*d/(2*t) applicable for estimating hoop stress in very large water tanks, say, of 100m / 200m / 500m diameter ? The stresses are quite high and needing large thickness for the circular wall. I understand, this formula is for small diameter closed pipes, under pressure. It may not be applicable for open top water tanks. There must be some underlying assumptions, which are not clearly and explicitly indicated in the text books on 'Design of Pressure Vessels'. There might be some limiting values for diameter, or, d/t values for applying this formula. Please enlighten me, with correct assumptions.

I want to solve an extra field along with the structural mechanics module in COMSOL. Basically, I want to use the stress which you obtain by solving a linear elastic problem, calculate the pressure (hydrostatic part) and solve another equation where the dependent variable is a function of gradient of this pressure.

I am very much new to COMSOL, and would appreciate any help.

My equation would be something like:

dot{u} + div. grad{pressure} = 0, where u is the dependent variable and pressure I get after solving the structural problem.

Thanks in advance.

I am using cohesive contact in abaqus,

I plot the variable CPRESS (contact pressure) along a path (undeformed) of neighbouring nodes.

I plot the stress components (S11, S12, S22, et cetera) along the same path (undeformed).

Then, I project the stress tensor along the normal direction (meaning I calculate n * sigma * n), where * is the scalar product, sigma is the stress tensor (using S11, S12, S22, et cetera)

and n is the undeformed surface normal.

When I plot the Abaqus CPRESS and calculated CPRESS along the path,

they are of course correlated, but I always find a mismatch (about 10%).

How does Abaqus calculate CPRESS?

Is there a relationship with the stress tensor at the nodes?

Is there a relationship with the stress tensor at the integration points?

Hello dear community,

I am still very new to Abaqus. The topic I am currently working on is a chamber weight optimization where 200bar is acting. First, I have to find the critical areas in the chamber.

When I first assumed the pressure load to be uniformly distributed and constant throughout the chamber, I had a max Mises stress of 4.5*10^2 MPa (= 450MPa). However, to make the stress more accurate and realistic, I converted the constant pressure into a pressure curve using the Analytic Field function. The pressure starts at 200bar and ends at 8bar at the end of the nozzle. But the result was then about 7.5*10^3 MPa (=7500MPa). I checked the functions and the units and they look fine. I then tried using a constant, uniformly distributed pressure at 200bar throughout the chamber described by an analytical field function, but the order of the results was the same (*10^3). This means that the load is the same (200 bar throughout), but applied once uniformly distributed without a function and once with an analytical field function (0*X + 20MPa), which is just a line in a coordinate system. Then I noticed that I get different results because I use the analytical field function at all. My question: why do I get a different result? What does the analytic field function do to make the result larger than without it? Can I use a different toolset to describe a pressure curve?

Thanks in advance!

I had success on studies with 1/8 symmetry model on ANSYS Mechanical just pointing the symmetry areas. But with a quarter symmetry cylinder model I'm getting errors about constraints. Does anyone knows what is missing and how to input it in this model?

I'm aiming to achieve the stresses and deformations.

Thank everyone!

#family pressure

#Societal Pressure