## Search found 74 matches

Wed Nov 21, 2012 1:13 am
Forum: STANMOD
Topic: Flux Averaged Concentration
Replies: 7
Views: 15931
Dan, I probably do not understand well about your calculations. Proper descriptions of the boundary condition have been discussed for long time. I also send you a Rien's comment (SSSAJ, 991-993, 1994). Please look at some of old literatures such as Wehner and Wilhelm (Chem. Eng. Sci., 89-93, 1956) w...
Tue Nov 20, 2012 1:30 am
Forum: STANMOD
Topic: Flux Averaged Concentration
Replies: 7
Views: 15931
Dear Dan, Cf is the ratio of the solute flux to the water flux. For steady water flow with constant theta (v is constant everywhere), for example, the Cf distribution (Cf vs. position) is identical to the solute flux distribution. That's what I demonstrated in Fig. 1 of Toride et al.(1993). It is no...
Mon Nov 19, 2012 6:48 am
Forum: STANMOD
Topic: Flux Averaged Concentration
Replies: 7
Views: 15931
I think the definition of Cf is same for x <0 as for x>0. Toride et al. (SSSAJ, 1406-1409, 1993) might help you to understand Cf.
Nobuo
Tue Nov 06, 2012 1:24 am
Forum: STANMOD
Topic: Variable v in CXTFIT
Replies: 4
Views: 10653
Strictly speaking, you cannot simply add two solutions. After the 365 days application of a higher velocity, solutes remain in the soil profile when the velocity decreases. You need to consider the remaining solutes as an initial condition for the subsequent lower velocity condition. Although it is ...
Mon Nov 05, 2012 5:13 pm
Forum: STANMOD
Topic: Variable v in CXTFIT
Replies: 4
Views: 10653
Sorry for my slow response. I probably do not understand your idea well. Do you want to calculate time-dependent (2-step) input velocity for the CDE? Or do you want to evaluate the mean concentrations for the two stream tubes having different velocities as similar to Fig. 4.1 in the manual? Can you ...
Sat Jul 21, 2012 2:51 pm
Forum: STANMOD
Topic: Mass Dirac Delta Input?
Replies: 3
Views: 9754
I am sorry for my late reply. If the purpose of your experiment is to determine transport parameters such as the dispersion coefficient, it is necessary to establish a steady-state flow with constant water content in a homogeneous soil. The CXTFIT uses the CDE with constant theta and v. If flow rate...
Wed Jul 11, 2012 8:37 pm
Forum: STANMOD
Topic: Mass Dirac Delta Input?
Replies: 3
Views: 9754
I am not quite sure what is your problem. I will explain the delta and pulse inputs for the CXTFIT. As shown in p. 7 of the CXTFIT manual, the delta input is given by c_o(t) = (m_b / v) delta(t) Eq. (2.16b) where m_b is the total amount of mass added to a unit area of the soil liquid phase. The m_b ...
Fri Jun 22, 2012 3:26 pm
Forum: STANMOD
Topic: CXTFIT - Input Concentration
Replies: 1
Views: 6738
Marlus, If you apply 300 g of Bromide at once uniformly on the surface, use the dirac delta input ( see the CXTFIT manual, p.7 &70). m_b is the amount of solute per unit surface area (cm^2). Since the input parameter is m_b/v, you need to know v in advance (you cannot estimate v). Alternatively, you...
Tue Dec 20, 2011 4:51 pm
Forum: STANMOD
Topic: Problem with parameter fitting (CXTFIT)
Replies: 2
Views: 8754
Dear Mark, I am sorry for my late reply. I also made a cxtfit project and confirmed your results. The observed concentration increased gradually from T=2 to T=8 and dropped drastically at T=8. The shape of BTC is obviously different form the CDE prediction. The BTC needs to be symmetrical in case of...
Fri Jun 24, 2011 7:54 am
Forum: STANMOD
Topic: I Type BC
Replies: 5
Views: 7879
Dan: The warning message is for the Dirac delta initial condition at z=0 for the first-type inlet condition because the surface BC specifies the surface resident concentration. These was a mistake in the "if statements" and I corrected the program in Feb. 12, 2005. We have replaced CXTFIT2.exe in ST...
Tue Jun 21, 2011 11:47 pm
Forum: STANMOD
Topic: I Type BC
Replies: 5
Views: 7879
Dan: I remember there is a reason for these warnings. However, since
more than 15 years have passed since I made the program, please send me
your project folder or simply cxtfit.in. I will post my comment after
Mon Nov 22, 2010 4:29 pm
Forum: STANMOD
Topic: Electromigration
Replies: 4
Views: 10723
Bruna: CXTFIT provides very accurate results for the equilibrium and nonequilibrium CDE with constant pore-water velocity subject to various boundary and initial conditionsï¿¾DHowever, these conditions are obviously too simple compared to the reality. It is really up to you how you interpret the transport with the electroosmotic flow. It may be worthwhile trying a simple transport model from an engineering point of
view, however, it is generally necessary to use a physically suitable model to describe the reality. I would recommend you to carefully read the HYDRUS-1D manual as well. Nobuo
Mon Nov 22, 2010 1:08 pm
Forum: STANMOD
Topic: Electromigration
Replies: 4
Views: 10723
Bruna: The main program in Stanmod is CXTFIT which is based on analytical solution for the one-dimensional convection dispersion equation. Stanmod is briefly described in the PC-progress site: http://www.pc-progress.com/en/Default.aspx?stanmod For further information, please carefully read the manua...
Thu Feb 18, 2010 12:41 pm
Forum: STANMOD
Topic: Direct and indirect CDE equlibrium
Replies: 2
Views: 8795
Thanks, Rien,
Jourak, If it were a problem of CXTFIT input such as "output structure", I will be able to fix your problem if you send me a project folder with a cxt file. Nobuo
Sat Feb 06, 2010 7:44 am
Forum: STANMOD
Topic: Diffusion Coefficient
Replies: 1
Views: 7625
Sarah: CXTFIT is a program based on analytical solutions for the convection dispersion equation. If you need a pure diffusion equation, you need another solution (but it should be easy to derive the solution). Or CXTFIT can evaluate the CDE with a very small v value. An example can be found in the F...