Time history analysis -Force factors

In time history analysis, the magnitude of the applided load is determined by the product of the profile force, the force sets magnitude and the scale in the shock case.

The following are the cases we considere and i request you to suggest which one we shall follow,

Case-1, Profile force - 80 KN, Force Set magnitude 80 KN and the scale factor is 1, so the magnitude is (80*80*1).

Case-2, Profile force - 80 KN, Force Set magnitude 1KN and the scale factor is 1, so the magnitude is (80*1*1).

Case-3 Profile force is 1 KN , Force set magnitued is 80 kN ,and the scale factor is 1 (1*80*1)

Case-4 Profile force is 1 KN , Force set magnitued is 1 kN ,and the scale factor is 80 (1*1*80)

as it can be understood from the help file of CAESAR II
Case 2, Case 3 and Case 4 shall give almost the same results, but , surprisely we tried the technoiques in one of the models , and the results were totally different .
Please advise which one is the optimum.

Dear Mr. Akila,

I also had the same doubt earlier, one additional information is that, Case-2 gives a very less value compared to case-3 and case-4.

Secondly,Case-3 and Case-4 gives equal value, and finally as per Coade example problem, SN-Fail, Coade followed the Case-3, which is giving more value and is equal to case-4.

So for time-history analysis the force combination is still puzzle.

I request Mr.Richard Ay and Mr.Dave to clarify this...

I figure 2=3=4. Are you getting the units right? If you are not modifying the force dimension, your three terms should be (80000*1000*1), (1000*80000*1), (1000*1000*80).

Dear Dave
I am attaching one file showing how we did the inputs for the case 2 and case 3, for me it seems that the units are matching, please correoct me if i am not right.

In time History you have 2 alternative input.

1.
Time Force
0 0
20 2000
100 1000
120 0

Then Force and scalfactor are 1

2.
Time Force
0 0
20 1
100 0.5
120 0

Then Force 2000 and scalfactor 1

Dear Mr. Ohliger,

From your reply it seems that you disagree with the Dave reply (i.e.) Case2=Case3=Case=4.

No it isnt.
I agree with Dave.
The Case 2 is equal my first example
The Case 3 is equal my second example

Case 4 is a another possibility for the input

Look so in my 3.example here :

3.
Time Force
0 0
20 1
100 0.5
200 0

Then Force 1 and scalfactor 2000
Teh results must be the same Case 2,3,4.

Remark :
Delete the old dyn. Input (.7) before to do change the Time history input

1. Open Input File
2. Then go Windows explorer and delete .7 File
3. Go back to dyn input, and create a new dyn input.

Can you send the entire job to coadetechsupport@intergraph.com?
I'd like to look at all of it.
Add my name in the message. Loren will see that I get it.

Ahmad,

I took a look at your dynamic input.

I find that the “time history” data supplied in both jobs were identical. It looks to me as if you ran your time v. load data through the DLF/Spectrum Generator (that tool button) rather than entering the data directly as a time v. load table. I believe you entered your time v. load data as “User Defined Time History Waveform” in the generator. Unfortunately, this processor converts the time history into a force response spectrum (you requested 25 frequencies up to 100 Hz). And these 25 frequency v. DLF data points were used as time v. load for the time history analysis.

Compare the “time histories” in each dynamic input echo. The maximum load defined is no more than 1.2582 “kN” at 1.67147 “milliseconds” in both jobs. (The generator created a dynamic load factor of 1.67147 for an oscillator tuned to 1.2582 Hz.)

The changing magnitude of the force set (1 kN to 81 kN) should modify the results but I won’t go there until this other matter is cleaned up.

Dave,
which is correct
1 Time v. load data through the DLF/Spectrum Generator (that tool button)
or
2.Time vs load enterted through edit/enter sprectrum data(another tool botton).If we use this method where does caesar calculate dlf.

Depends...
If using response spectrum method of analysis, the time history data must be converted to teh force response spectrum. That's what the DLF/Spectrum Generator does.
If using Time History analysis, the time history is entered directly through the "Enter/Edit Spectrum Data" tab. Time History is time histroy; there is no conversion to spectral data.

Dear Dave Diehl,

The reply what you gave, is not available in the Caesar-II user guide. If so, can u please tell us where it is.

Thank You...

I do not believe there is a statement in the C2 documentation that states the dynamic analysis is either response spectrum or time history. But that is what it is. We share use of some of those tabs and the entered data must be consistent with the type of analysis requested.

Dear Richard Ay and Dave,

Please clarify the following queries,

1. Is there is any provision in Caesar-II dynamic analysis to convert the transient pressure vs. time to equivalent force vs. time?

2. Is the dynamic analysis of water hammer for the discharge side of pump (i.e.) under vacuum is possible in Caesar-II?

Dear Sillyman,

The answer to both your questions are:

1. No. But why you need C2 for that? If you have the data which probably the hydraulics group in your company will generate for you, you just add the PXA values ( to elaborate it, sum the PXA at the right hand bend, left hand bend and at the upstream and downstream side of the valve, in case there is a valve b/w the bends) at each instant of time for which you have the data and this is the unbalanced force that instant.Remember that when you are using the area at upstream/downstream of the valve correct area is used depending on how much of the valve is closed.

2. Here also, you need the above data.

For time history analysis, your input will be different as you are basically " following" the waveform but in response spectrum analysis , time is not important the maximum value and the peak DLF are the key factors. However I think you are aware of this.

Regards