Hi,everyone,
Sorry for my poor English.
I am currently studying history analysis.I just read two articles,found some differences between them .
The first articles is "Establishing Time History Input-An Example"
(Coade Mechanical Engineering News-Volume18,Jne,1994),
the other is section 13.5.4-"Example Time-History Analysis"
of the "Piping stress engineering,LIANG-CHUAN PENG"(page 451)

For a similar example that a sudden valve closure,the pressure wave travling
upstream at the speed of sound in the line, I found some difference between
them which bothers me,

(1) One difference is the point of force application and direction,the first
article mentioned above said:the force at the start of each straight run of
pipe upstream of the valve with the load pointing downstream( ,But the other article said:the force at the ends of the elbow as shown in Fig.13.22 Fx and Fy,have the same time-history force,but act at different locations and in different direction. Which point is right?

(2)The other difference is when the force starts to reduced. The first article
said: the imbalane starts when the pressure wave enters the run and ends when
wave leaves the run(But how to determine when the wave leaves?).
the other article said(Page405): The reflection wave is then generated
and pushes upstream at a negative pressure...,The reflection wave reaches point1 aftre another TR(the time wave reaches the end) of time has passed.the pressure starts to reduce...(This place mention reflection wave-wave reches end and reflect back)

I'm afraid I didn't make it clearly about(2), Liang's book mentioned that "pressure wave reflects at ends and travel back and forth many times with diminishing magnitude.In practical calculations, only the first complete reflection is considered. The reflections after the first one are ignored because they are much smaller forces."

The reflects wave generate and start to travel downstream when the pressure wave reach the end of piping. I think this is different from Coade's article.

The focus of the COADE article is building time history data for CAESAR II. The reflection does occur. If you wish to better understand the physics involved in this traveling wave, stick with the Peng reference.

Further to the COADE article - that last event (TH4) is not simply absorbed into the pressure source to end the event. And it does NOT achieve only 60% of the force imbalance. That short run is useful in demonstrating the quicker "attack time" (6ms vs 10ms) which will produce higher frequency content. This higher frequency content requires a change to the cutoff frequency used for the analysis.

Thanks for your reply, I　will stick with the reference.