Sistema de bombeo solar acoplado con baterías

Output appears in the browser window as shown below. Any web browser can be used, but the program output has been checked most thoroughly on Microsoft’s Internet Explorer.

Figure 3 – Example Output The screen contains three major areas:

1) Tabular Result Area (On the left side of the screen.) 2) Plot Title Area (In the upper right.)

3) Plot Display Area (In the bottom right.)

The design is intended to facilitate the Code Stress evaluation procedure – which involves primarily: 1) Validating that the stress patterns “make sense” – i.e., reviewing graphical plots of stress results. 2) Making sure that the Code stress limits are satisfied.

3) Evaluating the “extent” of the stress state, i.e., is a local stress really “local?” The tabular output also provides other useful information such as:

1) Allowable nozzle loads.

2) Nozzle Stress Intensification Factors (For use in a pipe stress program.) 3) Nozzle Flexibilities (Also for use in a pipe stress program.)

The reports are designed to be printed from each “frame.” Click on the “File” menu and then “page setup.” Portrait mode is selected typically. Adjust the top and bottom margins as needed to get two plots per page. For most reports, the leftmost frame is printed to obtain a tabular form of the results, and the bottom-right frame is printed to obtain the corresponding graphical form of the results.

When reviewing output it is recommended to first visually validate the model. This involves moving the mouse to the slide bar on the right side of the screen, (opposite the graphical plot), and pulling it down – slowly moving past

the stress and displacement images. Each image should be studied for consistency. Questions that should be asked are:

1) Does the model look reasonable?

2) Is the vessel or pipe orientation correct? If the orientation is not correct the loads probably aren’t either. 3) Do the stresses make sense? An engineer or designer has a good idea what a pattern of stresses should look

like. A good stress plot for the model above is shown below:

Figure 4 – Reasonable Stress Patterns

High stresses exist as would be expected in the sustained case around the knuckle of the dished head. In fact, these stresses are of the same magnitude as the stresses in the nozzle. We can see this by noticing red regions close to the nozzle on the “minus X” side and close to the pad on the “plus X” side. This is the stress pattern we would expect from “X” and “Z” direction bending moments. The sustained loads that produced the above stress state are shown below:

FX FY FZ MX MY MZ 1057 -1323 -2333 230000 9833 123400 Other characteristics of a “reasonable” stress plot are as follows:

1) The stresses should not seem to congregate around element boundaries. The stresses do not know where element boundaries are in a finite element model. They should not artificially collect at these locations. FE/Pipe does not average shell stresses. This makes it easier for the user to tell when the stress state is not a good one. If the stresses localize themselves artificially around element geometries then something is wrong. Examples of

“bad” stress states are shown below:

Figure 5 – Errant Stress Patterns.

1. In the left figure the stresses are clearly segregated inconsistently around element borders. (This tends to occur with extremely thick geometries.) In the right figure, the highest stress is shown to exist at the top of the

spherical head at a small modeling opening. In the left figure, the stresses will have a much greater error than normally expected. In the right figure, the errant stresses at the top of the head must be ignored.

2. Stress distributions due to bending moments show the characteristic high stress values on either side of the bending axis.

3. Stress distributions due to torsional moments show a uniform stress state in the nozzle.

4. Pressure stresses are often highest on the inside and in the longitudinal plane. The exception is repads where the highest stress may be at the edge of the repad and in the circumferential plane.

5. Stresses should be highest at the nozzle/shell junction. High stresses at boundary conditions, or artificial model entities (like the high stress at the hole shown above) should be ignored.

Whereas considerable effort has been expended to make sure that solutions are generated for every range of nozzle to vessel geometry, pad size, thickness and orientation, there will be problems where errant solutions are

generated. In almost all cases errant solutions can be found by looking at the stress-state and applying common sense. If the stresses make sense then the solution is probably correct. If they do not, then there may be a problem, and the solution should not be used until the question is resolved.

An example poorly generated mesh plot appears below. The result from this calculation clearly should not be used.

Figure 6 – Incorrect Element Mesh Layout

Plots may show titles such as: 6) Pl+Pb+Q+F < Sa (SIF outside). Whenever a plot label is shown with the

words SIF in the title, the plot has been generated only to show the distribution of stress due to a single load

direction. There will be no stress legend, because the magnitude of the stress is unknown. Only the distribution of the stress is known. These plots are used typically to direct inspections or to validate that a particular failure was caused by an individual load. For example, an out-plane SIF plot is shown in the figure below: