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From: Edoardo Gonfiotti on 8 Apr 2010 05:18
Hello,

this post is to ask if anybody practical with simscape/simhydraulics platform has ever encountered the need to include temperature effects in their hydraulic models and eventually ask the adopted solutions.
I am actually developing a dynamic model for a lube oil system. Temperature effects may be very significant in my application as oil temperature may vary from 20°C to 75°C. In fact consequent kinematic viscosity variations for standard industrial oils, such as iso vg 32, may have important effects on the characteristic Reynolds number of the flow and consequently system performance and more specifically system response during critical transient phases.
As far as I know simhydraulics is a pure isothermal application (as hydraulics theory suggests); thermal blocks from the foundation library are hardly integrable to simhydraulics as they are born to model prevalently closed systems.
I thought of an approach similar to pneumatics foundation blocks:
here the domain source code:
%-----------------------
domain thermoHydraulics
parameters
bulk = { 0.8e9 , 'Pa' }; % Bulk modulus at atm. pressure and no gas
alpha = { 0.005 , '1' }; % Relative amount of trapped air
c = { 1670 , 'J/(kg*K)'}; % Specific heat
end
variables
p = { 0 , 'Pa' }; %-->across variable
T = { 0 , 'K' }; %-->across variable
end
variables(Balancing = true)
G = { 0 , 'kg/s' }; %-->though variable
%------------------
Viscosity and density are not included in the domain parameters, and they could be calculated for each component using temp-visc and temp-dens tables red at the simulation's setup.
This approach doesn't respect simscape philosophy of 1across per 1though variable. It would very similar to symhydraulics for what concerns p and G variables (G counterpart in simhydraulics was q volumetric flow rate); T would be threated as a transported scalar variable which could be remain unchanged in many adiabatic components and vary in some critical blocks (such as low efficiency pumps and heat exchangers) due to heat transfer or viscous dissipation.
This approach would require the transposition of all needed foundation.hydraulics and simhydraulic blocks to this "thermohydraulic domain", quite an hard work especially for simhydraulics blocks which do not have source code readability.
I repeat any idea to how include temperature effects on viscosity in hydraulics simulation would be really appreciated. Thus if anybody has ever thought of some kind of "trick" to get around the mentioned problem without reimplementing a whole set of domain blocks, or if you feel to disagree with my statements and have suggestions you are welcome. Even if you agree with my modeling strategy and have any suggestion in merit don't hesitate to let me know.
Thanks in advance.

Edoardo
From: Guy Rouleau on 8 Apr 2010 18:29
"Edoardo Gonfiotti" <edoardo.gonfiotti(a)ge.com> wrote in message <hpk70c$iuc$1(a)fred.mathworks.com>...
> Hello,
>
> this post is to ask if anybody practical with simscape/simhydraulics platform has ever encountered the need to include temperature effects in their hydraulic models and eventually ask the adopted solutions.
> I am actually developing a dynamic model for a lube oil system. Temperature effects may be very significant in my application as oil temperature may vary from 20°C to 75°C. In fact consequent kinematic viscosity variations for standard industrial oils, such as iso vg 32, may have important effects on the characteristic Reynolds number of the flow and consequently system performance and more specifically system response during critical transient phases.
> As far as I know simhydraulics is a pure isothermal application (as hydraulics theory suggests); thermal blocks from the foundation library are hardly integrable to simhydraulics as they are born to model prevalently closed systems.
> I thought of an approach similar to pneumatics foundation blocks:
> here the domain source code:
> %-----------------------
> domain thermoHydraulics
> parameters
> bulk = { 0.8e9 , 'Pa' }; % Bulk modulus at atm. pressure and no gas
> alpha = { 0.005 , '1' }; % Relative amount of trapped air
> c = { 1670 , 'J/(kg*K)'}; % Specific heat
> end
> variables
> p = { 0 , 'Pa' }; %-->across variable
> T = { 0 , 'K' }; %-->across variable
> end
> variables(Balancing = true)
> G = { 0 , 'kg/s' }; %-->though variable
> %------------------
> Viscosity and density are not included in the domain parameters, and they could be calculated for each component using temp-visc and temp-dens tables red at the simulation's setup.
> This approach doesn't respect simscape philosophy of 1across per 1though variable. It would very similar to symhydraulics for what concerns p and G variables (G counterpart in simhydraulics was q volumetric flow rate); T would be threated as a transported scalar variable which could be remain unchanged in many adiabatic components and vary in some critical blocks (such as low efficiency pumps and heat exchangers) due to heat transfer or viscous dissipation.
> This approach would require the transposition of all needed foundation.hydraulics and simhydraulic blocks to this "thermohydraulic domain", quite an hard work especially for simhydraulics blocks which do not have source code readability.
> I repeat any idea to how include temperature effects on viscosity in hydraulics simulation would be really appreciated. Thus if anybody has ever thought of some kind of "trick" to get around the mentioned problem without reimplementing a whole set of domain blocks, or if you feel to disagree with my statements and have suggestions you are welcome. Even if you agree with my modeling strategy and have any suggestion in merit don't hesitate to let me know.
> Thanks in advance.
>
> Edoardo

Hi,

I can tell that you are not the first to try modelling thermohydraulic in the simscape language. I don't have a perfect solution, but I can give you 2 comments:

- In most cases, it is preferable to have the same number of through and across variables. So for thermohydraulic, I would go for example for mass flow and heat flow, or enthalpy.

- In the latest Simscape release, a pneumatic domain is included. It could be useful to look at the provided source .ssc files to get some inspiration. The following documentation page shows the 2 through and 2 across variable used:

http://www.mathworks.com/access/helpdesk/help/toolbox/physmod/simscape/ref/br700pt-1.html

I hope this helps

Guy
From: Edoardo Gonfiotti on 9 Apr 2010 03:42
"Guy Rouleau" <guy.rouleau.nospam(a)mathworks.com> wrote in message <hpllbj$o34$1(a)fred.mathworks.com>...
> "Edoardo Gonfiotti" <edoardo.gonfiotti(a)ge.com> wrote in message <hpk70c$iuc$1(a)fred.mathworks.com>...
> > Hello,
> >
> > this post is to ask if anybody practical with simscape/simhydraulics platform has ever encountered the need to include temperature effects in their hydraulic models and eventually ask the adopted solutions.
> > I am actually developing a dynamic model for a lube oil system. Temperature effects may be very significant in my application as oil temperature may vary from 20°C to 75°C. In fact consequent kinematic viscosity variations for standard industrial oils, such as iso vg 32, may have important effects on the characteristic Reynolds number of the flow and consequently system performance and more specifically system response during critical transient phases.
> > As far as I know simhydraulics is a pure isothermal application (as hydraulics theory suggests); thermal blocks from the foundation library are hardly integrable to simhydraulics as they are born to model prevalently closed systems.
> > I thought of an approach similar to pneumatics foundation blocks:
> > here the domain source code:
> > %-----------------------
> > domain thermoHydraulics
> > parameters
> > bulk = { 0.8e9 , 'Pa' }; % Bulk modulus at atm. pressure and no gas
> > alpha = { 0.005 , '1' }; % Relative amount of trapped air
> > c = { 1670 , 'J/(kg*K)'}; % Specific heat
> > end
> > variables
> > p = { 0 , 'Pa' }; %-->across variable
> > T = { 0 , 'K' }; %-->across variable
> > end
> > variables(Balancing = true)
> > G = { 0 , 'kg/s' }; %-->though variable
> > %------------------
> > Viscosity and density are not included in the domain parameters, and they could be calculated for each component using temp-visc and temp-dens tables red at the simulation's setup.
> > This approach doesn't respect simscape philosophy of 1across per 1though variable. It would very similar to symhydraulics for what concerns p and G variables (G counterpart in simhydraulics was q volumetric flow rate); T would be threated as a transported scalar variable which could be remain unchanged in many adiabatic components and vary in some critical blocks (such as low efficiency pumps and heat exchangers) due to heat transfer or viscous dissipation.
> > This approach would require the transposition of all needed foundation.hydraulics and simhydraulic blocks to this "thermohydraulic domain", quite an hard work especially for simhydraulics blocks which do not have source code readability.
> > I repeat any idea to how include temperature effects on viscosity in hydraulics simulation would be really appreciated. Thus if anybody has ever thought of some kind of "trick" to get around the mentioned problem without reimplementing a whole set of domain blocks, or if you feel to disagree with my statements and have suggestions you are welcome. Even if you agree with my modeling strategy and have any suggestion in merit don't hesitate to let me know.
> > Thanks in advance.
> >
> > Edoardo
>
> Hi,
>
> I can tell that you are not the first to try modelling thermohydraulic in the simscape language. I don't have a perfect solution, but I can give you 2 comments:
>
> - In most cases, it is preferable to have the same number of through and across variables. So for thermohydraulic, I would go for example for mass flow and heat flow, or enthalpy.
>
> - In the latest Simscape release, a pneumatic domain is included. It could be useful to look at the provided source .ssc files to get some inspiration. The following documentation page shows the 2 through and 2 across variable used:
>
> http://www.mathworks.com/access/helpdesk/help/toolbox/physmod/simscape/ref/br700pt-1.html
>
> I hope this helps
>
> Guy


Thank you very much for your quick reply and suggestions. I had had already a look at the foundation pneumatics library and I didn't really understand the connection between T and Q viariables (across and through variables respectively) and more specifically the need to introduce as a conserving variable Q. Anyway If I come to interest findings about my problem I'll keep you updated. Bye.

Edoardo


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