Re: Questions about solution manual

At 03:32 PM 11/27/99 -0600, you wrote:
>Professor,
>
>I have got several questions about exercise problems in your book. I hope
>you are kind enough to spend your time to answer my following questions.
>
>1. Regrading p210, Exercise5.9, I think problem statement is little bit
>wrong. According to the solution correspond to the probem part (a), 0.5
>rad/min should be 0.5 rad/sec.

Actually, the old solution more or less irrelevant. It has been corrected.

>2. Regarding p17(part (b) of Exercise5.9) of your odd-numbered solution,
>G_d(j/theta)/h(j/theta) <= 1 should be G_d(j/theta)*h(j/theta) <=1, in other
>words, / should be replaced by *.

Yes, you are right

>3. Regarding p289, Exercise7.7, solution of part (a) is not likely to be
>-0.9s/(2s+1)(0.1s+1). Is it right answer? If so, how did you get that? Did
>you use kind of approximation method?

Plot the magnitude of e^-0.1s/(0.1s+1)^2 - 1 and you will see that
it is quite well approximated by 0.3s/(0.1s+1). This gives the
given weight.

>4. Regarding p289, Exercise7.8, transfer function of w_il(s) is
>(1.25s^2+1.55s+0.2)/(2s+1)(-0.25s+1), not
>(1.25s^2+1.55s+0.2)/(2s+1)(0.25s+1). You seemed to miss (-)sign.

The phase of the weight does not matter, so the - sign can be replaved by +

>5. Regarding p289, Exercise7.9, w_u and del_u seem to represent additive
>uncertainty, rather than inverse multiplicative uncertainty.
>
>I suppose I probably could be wrong. If I am wrong, please, give me your
>additional explanation. I would appreciate your early response.

This is actually right. It is indeed additive uncertainty on the plant
PLUS THE CONTROLLER, but by moving the place where wu exist the diagram
towards wp you seethat it is actually the same as inverse mult.
uncertainty on the PLANT.

Thanlk you for your remarks.

-Sigurd Skogestad

PS. The solution manual has been updated

>
>Sincerely,
>
>Yoonsoo Kim
>
>
>
>
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Sigurd Skogestad, Professor Fax: +47-7359-4080
Dept. of Chemical Engineering Phone: +47-7359-4154
Norwegian Univ. of Science and Techn.(NTNU) Home: +47-7393-6855
N-7491 Trondheim email: sigurd.skogestad@chembio.ntnu.no
Norway www.chembio.ntnu.no/users/skoge
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Received on Mon Nov 29 10:50:31 1999