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)