Path: news.mathworks.com!newsfeed-00.mathworks.com!kanaga.switch.ch!switch.ch!news.belwue.de!news-stu1.dfn.de!news-lei1.dfn.de!news.tu-chemnitz.de!not-for-mail
From: Simo Kauth <kauth@hrz.tu-chemnitz.de>
Newsgroups: comp.soft-sys.matlab
Subject: Re: SimHydraulics: "Hydraulic Fluid" question
Date: Tue, 12 Aug 2008 18:49:33 +0200
Organization: Chemnitz University of Technology
Lines: 24
Message-ID: <g7seuu$s63$1@anderson.hrz.tu-chemnitz.de>
References: <ce7eed26-fc75-4635-9f1e-c97c6b5ca9d8@26g2000hsk.googlegroups.com> 	<g7sb51$iju$1@anderson.hrz.tu-chemnitz.de> <c92b7478-aed7-47a2-bc28-01e38dad3a97@k7g2000hsd.googlegroups.com>
NNTP-Posting-Host: g227029025.adsl.alicedsl.de
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: anderson.hrz.tu-chemnitz.de 1218559774 28867 92.227.29.25 (12 Aug 2008 16:49:34 GMT)
X-Complaints-To: abuse@tu-chemnitz.de
NNTP-Posting-Date: Tue, 12 Aug 2008 16:49:34 +0000 (UTC)
User-Agent: Thunderbird 2.0.0.16 (Windows/20080708)
In-Reply-To: <c92b7478-aed7-47a2-bc28-01e38dad3a97@k7g2000hsd.googlegroups.com>
Xref: news.mathworks.com comp.soft-sys.matlab:485094



Clemens Winkler schrieb:
> On 12 Aug., 17:44, Simo Kauth <ka...@hrz.tu-chemnitz.de> wrote:
>> The bulk modulus already tells you, how the fluid reacts on a change in
>> pressure:http://en.wikipedia.org/wiki/Bulk_modulus
>> So: Yes, there is still a dependency on the pressure
> 
> But I do have a book, which gives for a mineral oil the dependency of
> the bulk modulus against the pressure. So the bulk modulus must change
> with the pressure. I see that you are from the "TU", so you surely
> know "Dubbel". The chapter about "Fluidische Antriebe" gives a plot
> for the oil "HLP46": bulk modulus over pressure (H - Fluidische
> Antriebe, page H22 Bild 3, Dubbel (2007)).
> 
> But as this is not the oil I need the data for, I'm looking for a
> formula which gives me the correct dependency.
> 
> Clemens.

Unfortunately I don't have the Dubbel here right now, nor would I call 
me an expert on fluid dynamics. But I would guess that the mentioned 
formula is rather an approximation, which might come close to reality in 
most cases. Or under common operation pressures. In a real hydraulic 
system, there will always be some gas dissolved in the fluid, which is 
then probably dominating the scene.