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Probleme on the turbulence

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Hi ,

I'm modeling the impact of a droplet onto a substrate using the level set method . i use the module: two phase flow, laminar, level set.
when I increase the impcat velocity, I added the turbulence model and when I click to solve my problem, I got the message bellow:


Time-dependent solver/Generalized alpha
Number of degrees of freedom solved for: 271446
Step Time Stepsize Res Jac Sol Order Tfail NLfail
0 0 out 3 2 2 0

Error:
Failed to find consistent initial values.
Sqrt_of_negative
Function: sqrt

Failed_to_evaluate_expression

Expression: nojac(((min((ck_chns*sqrt((((taum_chns*res_v_chns)^2)+((((res_p_chns*tauc_chns)/(nojac(sqrt((u2int_g1_chns/vol_g1_chns)))*nojac((rhoint_g1_chns/vol_g1_chns)))))^2+((taum_chns*res_u_chns))^2)))),U_ref_chns)*0.5)*min((gijgij_chns^-0.25),((rho_chns*U_ref_chns)/((etaT_chns+eta_chns)*48)))))

Failed_to_evaluate_symbolic_derivative_variable

Variable: shock_capt_chns@VDN${test@3}, Defined_as: ((r*(rho_chns*(-nojac(((min((ck_chns*sqrt((((taum_chns*res_v_chns)^2)+((((res_p_chns*tauc_chns)/(nojac(sqrt((u2int_g1_chns/vol_g1_chns)))*nojac((rhoint_g1_chns/vol_g1_chns)))))^2+((taum_chns*res_u_chns))^2)))),U_ref_chns)*0.5)*min((gijgij_chns^-0.25),((rho_chns*U_ref_chns)/((etaT_chns+eta_chns)*48))))))))*((ur*g21_chns)+(uz*g22_chns)))

Failed_to_evaluate_expression

Expression: d(((r*(-2*(eta_chns+etaT_chns)*ur+p)*test(ur)-r*(eta_chns+etaT_chns)*(uz+vr)*test(uz)+(-r*rho_chns*(u*ur+v*uz)-2*(eta_chns+etaT_chns)*u/r+p)*test(u)+gls_chns+shock_capt_chns)-(r*rho_chns*ut*test(u)))*(dvol),{test@3})

if someone could tell me on how to solve this probleme I will really appreciate.
best regards

2 Replies Last Post 2011/03/31 4:13 GMT-4
COMSOL Moderator

Hello Soufiane Oukach

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Posted: 1 decade ago 2011/03/31 3:52 GMT-4
I met the same problem, is it solved?
I met the same problem, is it solved?

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Posted: 1 decade ago 2011/03/31 4:13 GMT-4
Hi,

Usually that means you need to add a constant somewhere in your expression, constant small enough not to alter the results and large enough never to let your expression go to zero so that the software can evaluate the inverse of the square root of the expression.

Can you give more details about the expressions you are using?



Hi ,

...

Time-dependent solver/Generalized alpha
Number of degrees of freedom solved for: 271446
Step Time Stepsize Res Jac Sol Order Tfail NLfail
0 0 out 3 2 2 0

Error:
Failed to find consistent initial values.
Sqrt_of_negative
Function: sqrt

Failed_to_evaluate_expression

Expression: nojac(((min((ck_chns*sqrt((((taum_chns*res_v_chns)^2)+((((res_p_chns*tauc_chns)/(nojac(sqrt((u2int_g1_chns/vol_g1_chns)))*nojac((rhoint_g1_chns/vol_g1_chns)))))^2+((taum_chns*res_u_chns))^2)))),U_ref_chns)*0.5)*min((gijgij_chns^-0.25),((rho_chns*U_ref_chns)/((etaT_chns+eta_chns)*48)))))

Failed_to_evaluate_symbolic_derivative_variable

Variable: shock_capt_chns@VDN${test@3}, Defined_as: ((r*(rho_chns*(-nojac(((min((ck_chns*sqrt((((taum_chns*res_v_chns)^2)+((((res_p_chns*tauc_chns)/(nojac(sqrt((u2int_g1_chns/vol_g1_chns)))*nojac((rhoint_g1_chns/vol_g1_chns)))))^2+((taum_chns*res_u_chns))^2)))),U_ref_chns)*0.5)*min((gijgij_chns^-0.25),((rho_chns*U_ref_chns)/((etaT_chns+eta_chns)*48))))))))*((ur*g21_chns)+(uz*g22_chns)))

Failed_to_evaluate_expression

Expression: d(((r*(-2*(eta_chns+etaT_chns)*ur+p)*test(ur)-r*(eta_chns+etaT_chns)*(uz+vr)*test(uz)+(-r*rho_chns*(u*ur+v*uz)-2*(eta_chns+etaT_chns)*u/r+p)*test(u)+gls_chns+shock_capt_chns)-(r*rho_chns*ut*test(u)))*(dvol),{test@3})

if someone could tell me on how to solve this probleme I will really appreciate.
best regards


Hi, Usually that means you need to add a constant somewhere in your expression, constant small enough not to alter the results and large enough never to let your expression go to zero so that the software can evaluate the inverse of the square root of the expression. Can you give more details about the expressions you are using? [QUOTE] Hi , ... Time-dependent solver/Generalized alpha Number of degrees of freedom solved for: 271446 Step Time Stepsize Res Jac Sol Order Tfail NLfail 0 0 out 3 2 2 0 Error: Failed to find consistent initial values. Sqrt_of_negative Function: sqrt Failed_to_evaluate_expression Expression: nojac(((min((ck_chns*sqrt((((taum_chns*res_v_chns)^2)+((((res_p_chns*tauc_chns)/(nojac(sqrt((u2int_g1_chns/vol_g1_chns)))*nojac((rhoint_g1_chns/vol_g1_chns)))))^2+((taum_chns*res_u_chns))^2)))),U_ref_chns)*0.5)*min((gijgij_chns^-0.25),((rho_chns*U_ref_chns)/((etaT_chns+eta_chns)*48))))) Failed_to_evaluate_symbolic_derivative_variable Variable: shock_capt_chns@VDN${test@3}, Defined_as: ((r*(rho_chns*(-nojac(((min((ck_chns*sqrt((((taum_chns*res_v_chns)^2)+((((res_p_chns*tauc_chns)/(nojac(sqrt((u2int_g1_chns/vol_g1_chns)))*nojac((rhoint_g1_chns/vol_g1_chns)))))^2+((taum_chns*res_u_chns))^2)))),U_ref_chns)*0.5)*min((gijgij_chns^-0.25),((rho_chns*U_ref_chns)/((etaT_chns+eta_chns)*48))))))))*((ur*g21_chns)+(uz*g22_chns))) Failed_to_evaluate_expression Expression: d(((r*(-2*(eta_chns+etaT_chns)*ur+p)*test(ur)-r*(eta_chns+etaT_chns)*(uz+vr)*test(uz)+(-r*rho_chns*(u*ur+v*uz)-2*(eta_chns+etaT_chns)*u/r+p)*test(u)+gls_chns+shock_capt_chns)-(r*rho_chns*ut*test(u)))*(dvol),{test@3}) if someone could tell me on how to solve this probleme I will really appreciate. best regards [/QUOTE]

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