hi all,
i'm having doubts on steam hammer in pipes, we are mainly using this for super critical boiler main steam lines.
1)how to apply the forces of steam hammer in dynamic analysis of caesar-II?
2)which direction the hammering forces will act, will the forces acting in flow direction or opposite to the flow direction?
3)there is something called critical length, how it will affect the forces of steam hammer?
pls clarify

In the \examples directory, check out the "hammer" job.

I doubt you have used search facility in this forum.
These link will be a good starting point....
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=4989#Post4989
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=2507#Post2507
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=38078#Post38078
There are lot of reference which might be useful to you.

hi,
thanks for your reply, but i'm still having some queries about the forces acting on the pipe legs due to steam hammer,
actually the calculation of steam hammer based on the critical length of the steam hammer (critical length is the length of fully developed pressure wave) , my question is "if the length is lesser than the critical length then the unbalance force acting on the leg will also reduce or not?"

I suggest you to consider the Goodling's paper on Steam Hammer, posted by CraigB in
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=14930

Best regards.

If the "length" of the pressure rise is longer than the elbow-elbow distance of a run, that run will not see the full magnitude.
More important, the event will be so fast that I doubt you will see much structural response.

say for example, the steam hammer force is 1000kgf and the critical length is 10m and i'm having the pipe leg of 5m and the rise time say 5milli sec, then while entering the force spectrum is it correct to multiply the force by factor (actual pipe leg/critical pipe leg) ?

time factor
0 0
5 0.5
10 0

is it correct approach?

say for example, the steam hammer force is 1000kgf and the critical length is 10m and i'm having the pipe leg of 5m and the rise time say 5milli sec, then while entering the force spectrum is it correct to multiply the force by factor (actual pipe leg/critical pipe leg) ?

time------factor
0 ---------0
5 ---------0.5
10 ---------0

is it correct approach?

Dear Mr. Richard Ay and Dave,

Please clarify the following doubts,

Force Spectrum Analysis:

Depend upon the values entered in the control parameters for eigenvalues and frequency cutoff, the natural frequency report is generated. In the dynamic output, the animation is shown based on the natural frequency modes.

Is there is any useful in viewing the animation if the dynamic stress are below and above the allowable stress values?

Is there is any link between the dynamic stress and the natural frequency modes?

I tried the model of “Impact load analysis” as provided in December 1998 Coade MEN. It is showing some random motions for each frequency modes. Is these are practical motions under impact forces for a short period of time? Why these many modes of vibration are required for the analysis.

In general, every object has its own natural frequency, when the induced frequency matches with the natural frequency resonance occurs. From Caesar output, may I know where I can find the point of resonance?

Thank You.

The mode shapes and frequencies indicate the tendancy for the system to respond dynamically.
The CAESAR II output lists the mode that is the highest contributor to the total response. Read teh titles of the dynamic output to learn more.
Knowing the mode which causes the most response will be helpful in reducing response - you attempt to modify that mode shape to shift response.