Pressure boundary condition comsol Tan Chong What COMSOL needs is for me to specify inlet and outlet pressure conditions, which is a little surprising. Lasse Murtomäki. For The available Boundary condition options for an inlet are Velocity, Laminar inflow, Mass flow, and Pressure. If the prescribed pressure on an outlet is too high, parts of the outlet can actually have inflow. To efficiently simulate the measurement of the reverberation room absorption coefficient with COMSOL Multiphysics The Pressure Acoustics, Boundary Elements interface was used to model the incident pressure field and the rigid Form a mathematical point of view this boundary condition seems to be correct, however Comsol has some trouble with handling it. So, with a set inlet velocity profile and a set pressure outlet you should be able to solve the problem. The fluid is steam. A Neumann condition, meanwhile, is used to prescribe a flux, that is, a gradient of the depend I am working on a coupled problem involving a piezoelectric and fluid. Say your velocity is 1[m/s]. This could be possible because the COMSOL documentation suggests that with a pressure type boundary condition, the boundaries can act both as an inlet and outlet (depending on the local pressure). You can use a simpler approach in your model, also performing a frequency domain analysis with a harmonic pressure load applied at one boundary, and calculate the transmission loss as the ratio 7 ‐ Nov ‐ 17 F. This model is suitable for including the effects of gas damping when the thin-film is subjected to out-of-plane motion of the walls or base (for example, when a microbeam is oscillating above an extended surface). PST Computational Fluid Dynamics (CFD), Modeling Tools & Definitions, Parameters, Variables, The inlet would then be a fixed pressure and the outlet be an expanding boundary, or a at a time varying pressure How to define a 'free drainage' boundary condition? Posted Jul 21, 2021, 5:46 p. In the comsol modelling guide, I found out that specifying open boundary - no viscous stress condition doesn't impose any constraint on pressure. Use "Background Pressure Field" option to specify source location and specify "Pressure field type" (Cylindrical wave in 2D or Spherical wave in 3D) to Before adding any voltage to the beam, I fix one head and add a Prescribed Displacement boundary condition at another head of the beam. Since I don't know the valocity (it has to be resolved), I can give a pressure boundary condition. 0, there is no way to select edges of model and assign hydraulic head, but to assign pressure or mass flux, so I simply try assigning viscosity (field data) as mass flux, with mass flux = 0 at the outlet, and mass flux = 0. 2 or 4. Is there any way to do it? I have noticed there's several conditions (displacement, acceleration, etc) and I don't know if it's possible to combine two or more to simulate a simply supported boundary condition. when applying the Pressure boundary condition at an outlet or inlet you can further constrain the flow. If you still need help with COMSOL and have an on-subscription license Use the Pressure node to specify the pressure on a boundary. I need to apply the pressure from the piezoelectric after each iteration step and apply it as a pressure boundary condition on the fluid. Using Low-Reflecting Boundary Conditions to Model Wave Propagation. I'm actually studying cylindrical sound diffusers using Comsol 4. Equation 3-43 and Equation 3-44 correspond to the compressible formulation. 02. 5 bars), and the pressure at the other side of the tube is ambiant pressure. p ref is the reference pressure that ensure that the absolute pressure is set to p vacuum pump. Hi, in fluid flow simulations with a moving wall boundary condition (a rotation of a circular surface region), I get strong pressure oscillations at the edge of the rotating part of the surface (where the rotating part is in contact with the non-rotating part), that even do not disappear for higher mesh densities. " How to transform Pressure boundary condition to No Flow condition during simulation? Posted Mar 18, 2017, 3:32 p. EST Computational Fluid Dynamics (CFD), I'm modelling pressure drop in a channel and I use symmetry in the middle of the channel along the fluid flow. The inlet pressure is 200 kPa. For example, if Velocity is selected, a Velocity section, where further settings are defined, is displayed. The BEM interface is The boundary condition for the excitation is a prescribed displacement with the function (amplitude/delta_time)*t*(t<excitation_time). When a turbulence model with a The boundary condition on the fluid is no-slip and continuity for the normal magnetic flux density. With the Suppress backflow option (3-33), the normal stress is adjusted to keep (3-34) Equation 3-33 effectively means that the prescribed pressure is p 0 if u You can get COMSOL to implement Henry’s Law via boundary conditions. 2, Version 5. 3 Replies Last Post Apr 7 Note that while COMSOL employees may participate in the discussion forum, To implement the continuity condition by the Nitsche method, one can, following for example Ref. How is reference pressure defined by Comsol in fluid flow problems? Thanks, Ranjeeth . If it is not possible to specify the pressure level using a boundary condition, the pressure level must be set in some other way, for example, by specifying a fixed pressure at a point. For incompressible flows, the term −(2 / 3)μ(∇ ⋅ u) vanishes. 8) for the ends of the special part of angle?(attached cross section) eager to hear your comments. mph file. Then modify the constraint and constraint force expressions in the periodicity condition to something like It makes sense to me that you need to set the initial pressure and I am using pressure boundary conditions for a Darcy's law mode (although I am not sure if these should be gauge or absolute as mentioned above), but I don't understand why there is another pressure input (and what it is used for) under the general "Fluid Properties. To make the model numerically stable, this boundary condition should be combined with a point constraint on the v1-v2=0 (this condition is the usual of periodic condition in comsol) I set a Periodic boundary conditions (pressure : 1e2 Pa ) in the flow direction Y and my model is in microfluids domain to represent a fibrous layerd media using a representative volume elementary (unit cell ,a bloc ) in the other dirctions ( the last 4 faces ) i set 0 in Note: This discussion is about an older version of the COMSOL Multiphysics (interior diameter = 12 mm) and all I am given is the inlet pressure (5. Please login with a confirmed email address before reporting spam Note that while COMSOL employees may participate in the discussion forum, The problem with this method is that COMSOL treats these as two seperate simulations and I cannot postplot my results continuously from 0 thru to 4! See also how the potential distribution changes. EST. Syed Zaid Ali If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. With the Suppress backflow option (12-21), the normal stress is adjusted to keep (12-22) Equation 12-21 effectively means that the prescribed pressure is p 0 if u as a user defined pressure boundary condition. By default, low-reflecting boundary conditions use material data from the neighboring domain to develop a perfect impedance match for pressure and shear waves. The formulation is based on the This type of boundary condition is available in COMSOL Multiphysics. 3) run the simulation 4) It usually doesn't converge ! :D 5) For convergence issue, I suggest using a ramp function or solving the problem with a constant pressure and using the solution as the initial condition of your main study. 2a. Thanks a lot! I have an incompressible fluid flow problem. should deflate slowly until the pressure inside the balloon becomes equal to 1 atm. A spring bottom boundary condition was applied to the bottom of the footing representing the compressibility of the foundation soil. There is no outlet. 3a to simulate evaporation of water. . Such an approach is best suited for those situations where the wave direction is close to normal at the wall. In the present investigation, the temperature is varied from 873 K to 1073 K with a corresponding variation of pressure up to an elevated pressure of 3 bar from atmospheric pressure. Send Private Message Flag post as spam. Theoretically-speaking, if pressure drop across a packed-bed can be modelled by Ergun's equation, then There are some diffent approaches you could use, but the quickest is probably to edit the constraint expressions for the periodic boundary condition in Equation View. Another way to enter the pressure load is to enter it as a weak contribution using the expression: Well, setting boundary conditions for Navier-stokes is not a trivial task anyway. 4 0 Replies . 2013, 03:02 UTC−5 Structural Mechanics 8 Replies . Applying a pressure boundary condition. I want to specify pressure continuity and velocity continuity conditions at the boundary between the fluid film and porous medium. The trick is to (1) assign a physics to each material in your model and (2) assign a flux boundary condition at each interface between materials. What I'm modeling is a wave propagation in a pipe filled with water, what I'm using to model this is the pressure-acoustic transient analysis with axial symmetry and with a pulse generation at one end of the pipe as a boundary condition for a short time. Expanding boundary as a boundary condition (COMSOL 4. The Pressure Acoustics, Boundary Elements interface can be used to replace a FEM-based radiation condition or PML and the far-field calculation feature. Posted Nov 5, 2012, 12:04 p. But in the new version of COMSOL 4. Properly set up, the matched boundary condition allows one mode with wave number k 1 (set k 2 = k 1 ), or two modes with wave numbers k 1 and k 2, to leave the modeling The Sound Soft Boundary adds a boundary condition for a sound soft boundary, where the acoustic pressure vanishes: p t = 0. 32 and 7. See for example the generic_711_coupler tutorial model. And my defaults are velocity in, pressure out. The inlet velocity is specified for the film and the outlet pressure=0. Posted 15 feb 2013, 03:02 GMT-5 Structural Mechanics 8 Replies . I would like to do an uncoupled acoustic-structure-interaction simulation: In one simulation a source generates a pressure field in the frequency domain (lets say 100,101,102,1000 Hz)with one boundary being sound hard. Using "pressure, no viscous stress" as outlet boundary condition COMSOL archieves a solution. Posted Feb 8, 2024, 7:04 a. In result part (fluid flow physic), the pressure shown is indicated to total pressure or static pressure? 2. Consider, for example, a deflating balloon. PST Computational Fluid But often its usefull to set a gauge pressure somewhere, therefore the outlet pressure no viscous stress seems adequate for me, if I have understood correctly your short model description Note that while COMSOL employees may participate in the 1. Also, Is it possible to use the data from a SPF study such as velocities and pressure and implement the weak fomulation of an eigenvalue problem? I am also trying to have a change in boundary conditions during a transient solution. Good luck. 33 as attached in the picture. 1 Reply Last Post Nov 22, 2021, 3:50 a. However the pressure boundary condition at inlet does not allow comsol to converge. Now we can specify our boundary conditions. I tried to handle this problem by first attempting to solve for a constant pressure condition at inlet and exit (two different pressure values) and Port boundary condition . In This boundary condition implicitly sets a constraint on the pressure that for 2D flows is If Normal Stress, Normal Flow is selected as the Boundary condition, then to Apply reaction terms on all dependent variables, the All physics (symmetric) option should be selected. The Port boundary condition, introduced in version 5. How to transform Pressure boundary condition to No Flow condition during simulation? Posted 18 mars 2017, 12:32 UTC−7 0 Replies . You can see by running Hence, when applying the Pressure boundary condition at an outlet or inlet you can further constrain the flow. The initial condition for pressure is 5 kPa. 0) and try out a few simple cases Hi, I want to use this expression as a boundary condition (pressure head) in the Richard's equation modules Hp0=1. William Hoggatt If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 3) Posted Mar 6, 2013, 7:20 p. With a Dirichlet condition, you prescribe the variable for which you are solving. At the inlet, we assign the normal velocity to be 1 m/s. Posted Feb 13, 2015, 4:35 a. The porous matrix has constant porosity and permeability. So my question is: How can i set the boundary free after excitation_time? Best regards Thomas Use the Pressure Head node to specify the pressure head (instead of the pressure) on a boundary. The Pressure Acoustics, Boundary Elements (pabe) interface (), found under the Pressure Acoustics branch when adding a physics interface, is used to compute the pressure variation As mentioned by another user, the velocity boundary condition exists in version 5. For the initial conditions and outlet boundary condition, we need to enter the relative pressure, since we are using the default setting; i. If the pressure is positive then obviously you will have a saturated boundary condition. By default, it contains the selection Hi, I am trying to implement the Moisture Transport in Air module in COMSOL 5. The Impedance node adds an impedance boundary condition with the option to select between several built in impedance models. 2 and version 5. The boundary condition is used to prescribe a nonreflecting condition at the end of a waveguide (an outlet) as well as to set up an incident wave at a Vishal, a mathematically well-posed boundary-condition setup is also what COMSOL is using be default for the flow problem. This setup is possible with when you have a doubt like that, turn on the "equation settings and the equations view" (under "options", or top border icon of physics tree) and check the underlying equations of COMSOL, in both the Equation tab, and the equation view node. g. The outlet below the membrane is open to atmosphere (so the fluid has to pass though the cylinder, through the, membrane and then the open outlet) . EST Fluid & Heat, Porous Media Flow, Parameters, Variables, & Functions, Structural Mechanics Version 4. Do you have any experience using similar boundary conditions? I have also tried to reinterpret the inlet velocity boundary condition as inlet pressure boundary condition This works perfectly in 2D, but in 3D I don 1- Solve the flow problem using only the pressure boundary conditions (e. Mathematically, a specific acoustic impedance Z i is defined on some cross section as the ratio between the acoustic pressure p and the acoustic velocity perpendicular to the area (the I am working on the drug implant system, first I used darcy law to find pressure and velocity but while applying darcy law I have to set boundary conditions eq: 7. Thanks Note that while COMSOL employees may participate in the discussion forum, A conditional boundary condition is being used to define pressure head as zero above the water level along the embankment boundary. This adds the Dirichlet condition for the hydraulic head H = H 0 where H 0 is a known hydraulic head given as a number, a distribution, or an expression involving time, t, for example. A. Please login with a confirmed email address before reporting spam Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH) Hence, when applying the Pressure boundary condition at an outlet or inlet you can further constrain the flow. EDT Structural & Acoustics, Acoustics & Vibrations Version 5. in this case, i splitted different materials connecting layers but i am facing difficulties to mention the boundary condition of the additioal layers due to splititng into the coupling place for the Heat transfer due to The condition automatically applies the PML formulation using the extra dimension functionality of COMSOL Multiphysics. 5 I found out that, in time domain simulations for pressure acoustic, only resistive (real-valued impedance) can be modeled using user-defined impedance boundary condition; however, in frequency domain simulations the impedance can be any complex-valued number and thus models a surface that is both I am having difficulties implementing the Grille boundary condition in Laminar flow (spf) in COMSOL 5. The theory, described in the sections Gravity and Boundary Conditions in the CFD Module User’s Guide, implies that the pressure, p, is replaced by a new pressure variable called reduced pressure. The boundary conditions are given as: If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 1 it is very easy to set up manually. This flow field may not have the plug flow (uniform) velocity profile at the inlet you want yet. Three different boundary conditions at the end of Cerebral Spinal Fluid (CSF) were used to investigate the boundary condition effects on the volume-pressure curve based on the current model. In the beaker model above, there are two materials (water and air) and one interface between them. 2- Calculate bulk average flow velocity from the above solution. 094-y+0. The boundary condition is used to prescribe a nonreflecting condition at the end of a waveguide (an outlet) as well as to set up an incident wave at a Pressure boundary conditions. negative values on concentrations, but also concentrations larger than the boundary conditioned concentration. 0003 at the inlet (looks kinda If you have a pressure driven fow, you need the absolute pressure at the "inlet", then if the exit is free 1[atm] is for me a normal absolute pressure, just check carefully how your COMSOL physics is setting up the equation (check the doc in 4. I'm now using "0 pressure" output, and velocity driven inputs. Like the radiation boundary conditions, it belongs to the class of nonreflecting boundary conditions (NRBCs). It is suited for all frequency-domain simulations with harmonic variations of the pressure field. 0 Solved model for the middle part that defined pressure head as constant value, cross section was plotted, but why the pressure head after solving the problem is not constant:( changing from 0. With the Suppress boundary conditions, pressure losses due to friction. Of course more important is that you have to provide realistic boundary condition. then i've added pressure point constraint (under lamina flow, as well), and choosen the two vertex of the inlet. The dimension of the pressure head is length (SI unit: m). EDT Structural & Acoustics, when an overload was imposed on the top end. With the Suppress backflow option (3-33), the normal stress is adjusted to keep (3-34) Equation 3-33 effectively means that the prescribed pressure is p 0 if u Pressure boundary conditions. 3a 2 Replies 宇宣 林 I read some paper, in the old version of COMSOL, we can choose a Mixed boundary condition (mix of Dirichlet, Newman and Cauchy conditions). Impedance boundary conditions thus generalize the sound-hard and sound-soft boundary conditions to address a large number of cases between these two extremes. Hence, when applying the Pressure boundary condition at an outlet or inlet you can further constrain the flow. See, for example, the model example below. Please login with a confirmed email address before reporting spam Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH) Radiation boundary conditions are available for all types of studies. Contact and a viscosity of 0. The Pressure Acoustics, Boundary Elements (pabe) interface (), found under the Pressure Acoustics branch when adding a physics interface, is used to compute the pressure variation for the propagation of acoustic waves in gases and liquids. The available Boundary condition options for an inlet are Velocity, Fully developed flow, Mass flow, and Pressure. What it seems to me is that when I set an outlet pressure boundary condition as 1 atm then it means that the pressure just outside my domain is 1 atm. 0081*t) where, t is the time and y is the vertical coordinate. in order to automatically transfer the boundary condition form pressure head to Flux, or Flux to pressure head. EDT. If it is not possible to specify the pressure level using a boundary condition, the pressure level must be The Acoustics Module, an add-on to the COMSOL Multiphysics ® software, includes several interfaces that are well-suited for room acoustic simulation. outlet pressure =0, inlet pressure= your known pressure difference) and get a solution for flow field. this allows me to have 5atm in that two points. The problem I am having is I dont know the pressure point constraint that I need to specify so that the problem converges. using the compressible/weakly compressible and the incompressible formulation, respectively. e. Posted Dec 4, 2015, 10:16 a. As of COMSOL Screen Boundary Condition The word “screen” refers to a barrier with distributed perforations such as a wire gauze, grille, or perforated plate. 3b 1 Reply . Note that while COMSOL employees may participate in the discussion forum, COMSOL Compressible Flow - Pressure Outlet Boundary Condition (Navier Stokes) Posted Nov 29, 2014, 1:18 a. Due to the nature of the boundary conditions, a complex eigensolver is needed. The Perfectly Matched Boundary condition only exists for the Pressure Acoustics, Boundary conditions that intersect a Perfectly Matched Boundary are not continued/extended through the boundary. Equation 3-29 is prescribed by the Pressure condition in the Inlet and Outlet features and the Normal stress condition in the Open Boundary and Boundary Stress features. EST Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 4. Hello everyone. It is more useful, for example, in For single-phase flow, a mathematically correct natural boundary condition for outlets is. Read this article to learn different approaches for solving transient model equations in COMSOL Multiphysics® when you have inconsistent initial values. A velocity of 1 m/s is specified at the A direct solver, PARDISO of COMSOL Multiphysics® is employed by setting a relative tolerance of ~ 10^-5 to solve the equations with suitable boundary conditions. EDT Fluid & Heat, Computational Fluid Dynamics (CFD) I am trying to apply a pressure to the faces of the blood vessel and they are saying tha they are "not applicable". My problem is not just changing the value of a boundary condition, but the type of boundary condition changes as well. 0 0 Replies . This feature works well for cases like opposing parallel boundaries. where ∂ u n /∂ n is the normal derivative of the normal velocity component. However, the simulation reveal some odd results, e. After selecting a Boundary Condition from the list, a section with the same or a similar name displays underneath. A diagram of the fluid flow example Here, V 0 is the flow rate across the boundary and p vacuum pump (V 0) is the static pressure function of flow rate for the vacuum pump. Use a normal acceleration condition and write: acpr. At exit of the duct, pressure is not known and the pressure variation with respect to time should be a part of the solution. Specify phase condition on the boundary of pressure acoustics Posted Jun 11, 2022, 9:02 a. The Periodic Condition node adds a periodic boundary condition that can be used to reduce the model size by using symmetries and periodicities in the geometry and physics interfaces being modeled. Since I'm using symmetry, I halve the flow rate which is an input at the inlet. e pipe surface roughness), then you can get Comsol to find by least square (via a global equation) the best fit for this unknown (sure I suppose there is only 1 unique solution) Pressure boundary conditions. Whether I set the quadratic loss coefficient (qlc) under the Grille Boundary node to zero or any non-zero value, I get the same result. As a starting point, I have a rectangular domain with insulated side walls, specified moisture content on the top boundary, and wet surface condition on the bottom boundary. As mentioned by another user, the velocity boundary condition exists in version 5. In 5. So I chose "laminar outflow" as outlet boundary condition with an average velocity=[inflow velocity] (due to unchanged temperature/density) and an exit This condition can be useful in some situations because it does not impose any constraint on the pressure. So I don't know what boundary condition I need to specify at the exit of the duct in this case. I wonder if the function sets displacement=0 after the excitation_time. For single-phase flow, a mathematically correct natural boundary condition for outlets is. I want to simulate a duct flow in which an unsteady pressure boundary condition is to be specified at inlet and constant pressure boundary condition at exit of a simple straight cylindrical duct. Depending on the shape and orientation The Pressure Point Constraint condition can be used to specify the pressure level. 01 Pa·s. Fluid pressure as fallback boundary condition . The impedance condition is a generalization of the sound-hard and sound-soft boundary conditions: Here Z i is the specific acoustic input impedance of the external domain and it has the SI unit Pa·s/m — a pressure If you do not want to model the structure, just replace that with a boundary condition such as a constant or a variable flux. The Pressure Point Constraint condition can be used to specify the pressure level. In many cases the distribution of pressure is known, giving a Dirichlet condition p = p 0 where p 0 is a known pressure given as a number, a distribution, or an expression involving time, t, for example. I have also In the mathematical treatment of partial differential equations, you will encounter boundary conditions of the Dirichlet, Neumann, and Robintypes. Send Private Message Flag post You can specify it (gauge or absolute pressure) as an 'Outlet' boundary condition or as a Point boundary condition: 'Points/Pressure Point Constraint'. 4 of the COMSOL Multiphysics® software, is applicable for models that are set up using the Pressure Acoustics, Frequency Domain interface. It adds this boundary condition for the pressure head H p = H p 0, where H p 0 is a known pressure head given as a number, a distribution, or an expression involving time, t, for example. In addition to this, the This blog post will focus on the importance of sound-absorbing boundary conditions for room acoustics modeling. where the superscript l is used to indicate the saturation and capillary pressure on the low permeable side of the boundary, and the superscript h indicates the high permeable side. An "open boundary" allow two-way flow with free pressure and velocity definition. I always hear that boundary condition is indispensable for FEM simulation. It is an appropriate approximation for a liquid-gas interface and in some cases for external waveguide ports. T_stressz, p and spf. For example，what I want is to have a anti-symmetry boundary at z=0 and a symmetry boundary at z=z0, you know just like the sea level and the bottom. With the Suppress backflow option (3-33), the normal stress is adjusted to keep (3-34) Equation 3-33 effectively means that the prescribed pressure is p 0 if u Free-slip boundary condition. I tried a set pressure with flow around a cylinder and worked quite well. PDT I have a stationary study of the flow around a cylinder performed in comsol using a nondimensional framework. EDT 0 Replies Yu Zhang This is a simulation of a lab setup, so I know that the applied pressure at the top is usually 4 bar. 1 Reply Last Post Mar 4, 2011, 3:12 p. Please see the attached . EDT Heat Transfer & Phase Change, Porous Media Flow, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4. Pressure, Laminar outflow and velocity. If you do not know the flux, input a fixed pressure. The screen is assumed to have a width, which is small compared to the resolved length-scales of the flow field and can thus be modeled as an edge (in 2D) or surface (in 3D). Eigenvalue/Eigenvalue boundary conditions. Under some conditions, you can specify flow at the outlet instead of inlet, but basically you want to peg the pressure at the outlet. Use the Hydraulic Head node to specify the hydraulic head (instead of the pressure) on a boundary. For N-S the pressure is itself is not important, but the pressure difference. The result appears in Figure 3 , which shows that the hydrostatic pressure gradient has been removed and only the pressure gradient necessary to In most cases on has a predefined outlet pressure p(x=L) = 0 which means in absolute pressure of pA+0 at output location "L", and then solve for an inlet flow velovity, hence COMSOL calculates the inlet pressure as a local pressure p(x=0) to be added again to pA to read the absolute value at inlet--Good luck Hence, the pressure coefficient diminishes as d/R in 2D and as (d/r)^2 in 3D. iomega*1[m/s]. Yu Zhang . But, in COMSOL, the balloon deflates in no time, in a sense and the other angles were defined as pressure head= 0. and an inlet velocity of a parabolic profile to respect the no-slip boundary conditions. Add 'C' as an extra DOF using a Global Equations node (without equation). For cylindrical and spherical waves, COMSOL Multiphysics uses the corresponding 2nd-order expressions from Bayliss, Gunzburger, and Turkel (). This blog post will You can get COMSOL to implement Henry’s Law via boundary conditions. Morrison Michigan Tech University 2 specify the unknown inlet velocity boundary condition is a characteristic challenge of the numerical problem ‐ solving approach. But I can specify a pressure value at time t=0 to begin with. I want to take the pressure along that boundary and use it as boundary load for a structural simulation. Hi, I'm having a problem with the Pressure-Acoustic module, specifically with the boundary conditions. These conditions are defined in the fluid SPF periodic boundary condition (do not forget to define the "destination" or outflow region) and to fix a pressure point Now the convergence might be somewhat tedious, if you leave the full cross section flow free there are many free DoF while one know (at least in laminar flow) that the flow shape is Hi, guys. the initial condition is the same for both regimes. The COMSOL Multiphysics UI showing the Model Builder with the Flux/Source boundary condition selected, the corresponding settings, and the Graphics window showing the rectangular plate. To reduce the influence of the exterior boundary conditions to say O(10^{-2}), we would have to locate the exterior boundaries of the computational domain a distance of order of 100 obstacle sizes away in 2D and 10 obstacle sizes away in 3D. For the frequency-domain study, Givoli and Neta’s reformulation of the Higdon conditions for plane waves has been implemented to the second order. Posted 22 avr. That is, flow should be specified at the inlet, and pressure at the outlet. Or a symmetry boundary at z=0 and a symmetry boundary at z=z0 to simulate roof and floor of a room separately. , to use a reference pressure. 0 0 Replies I read some paper, in the old version of COMSOL, we can choose a Mixed boundary condition (mix of Dirichlet, Newman and Cauchy conditions). 0 Replies Last Post May 9, 2017, 1:09 p. e Comsol works well from 0 to z0 but not lower than z0. A conditional boundary condition is being used to define pressure head as zero above the water level along the embankment boundary. In case of free outflow at soil-air interface, drainage will occur if the pressure head is larger than zero. I hope this helps. This is a normal stress condition together with a no-tangential-stress condition. EST Fluid & Heat, Computational Fluid Dynamics (CFD) (i. How can one give a time dependent boundary condition in comsol? 3 Replies Last Post Nov 19, 2015, 5:49 a. Equation 3-29 is mathematically more stringent compared to specifying the pressure pointwise and at the same time cannot To be able to apply a boundary condition, the well cylinder must be cut out of the reservoir. "Not Applicable" Boundary Condition. Below the water level ("load") the pressure head takes into account the y-coordinate (elevation) with respect to the water level. you just choose mass flow as boundary condition on teh inlet and mass flow rate as mass flow type. 1 it's much more complete than it was in v4. In this case, the left-hand side of Equation 4-21 is small compared to its right-hand side. However, I still not comprehend when I set up boundary condition, what I need to consider carefully (I am starting from solid mechanics) ? Please let's me know Thank you for your time and Boundary Conditions in Solid Mechanics Posted Feb 16, 2015, 4:43 a. I am a newbie, so I have a concern in using COMSOL software. Posted 15. When R is small, the boundary condition approaches "V=V0" and when R is large it acts as a floating electrode. 3a and I need to add simply supported boundary conditions. 9. Entering the pressure load as a Flux/Source boundary condition. I am applying port boundary condition at both ends of the duct and putting plane wave excitation at the inlet with a known amplituide (as the dominant mode) but I would like to have Hence, when applying the Pressure boundary condition at an outlet or inlet you can further constrain the flow. Then what value should I give for pressure? Suppose I am giving an initial pressure of 1atm. If you still need help with COMSOL and The condition automatically applies the PML formulation using the extra dimension functionality of COMSOL Multiphysics. As the heat capacity C p is positive, in the absence of pressure contribution to the enthalpy, this induces the following constraint on temperature Hello, Reviewing the documentation of version 5. The Out-of-plane motion option calculates the pressure gradient at the boundary using a model described in Ref. Actually, you can simulate distant acoustic point source in Comsol. I have a fairly complex geometry which has a repeated pattern. This is a I have tried inputting the variable spf. So I cannot specify a pressure value or cannot impose any constraint on the exit pressure. Alternatively, a Mass Flux edge condition can be used — but only if we want to apply a mass flux, not a pressure. Please login with a confirmed email address before reporting spam Can you give an example for a boundary condition in terms of concentration? Symmetry boundary condition results. This setup is possible with boundary condition - inlet - outlet. Here, V 0 is the flow rate across the boundary, p input is the pressure at the device’s inlet, and Δ p fan (V 0) and Δ p grille (V 0) are the static pressure functions of flow rate for the fan and the grille. If i have only inlet but no outlet in the model (the mass conservation is fulfilled by expanding volume), which boundary condition (velocity or pressure) is best to be implemented? In fluid flow (laminar flow) model, is it a reference pressure must be defined somewhere in the model? I enabled the porous medium flow in the porous block and nothing the film section. For example a pipe, why the outlet pressure is 0 for the boundary condition while logically the outlet pressure is atmospheric pressure? Thanks in advance for the answer. The formulation is based on the Read this article to learn different approaches for solving transient model equations in COMSOL Multiphysics® when you have inconsistent initial values. If I specify a non-correct pressure then COMSOL gives me a static result of positive flow when this is not physically correct. Best regards At exit of the duct, pressure is not known and the pressure variation with respect to time should be a part of the solution. 4-0. Then you can Use the Pressure node to specify the pressure on a boundary. A velocity of 1 m/s is specified at the inlet, and a zero-pressure boundary condition is applied to the outlet. Please login with a confirmed email address before reporting spam Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH) For large flow rates, advective heat transfer dominates over conductive heat transfer at the inlet. The boundary condition is used to prescribe a nonreflecting condition at the end of a waveguide (an outlet) as well as to set up an incident wave at a An issue with Equation 5-15 or Equation 5-16 is that it does not strongly enforce unidirectional flow on the boundary. The formulation is based on the The compressibility and reference pressure settings. The result is Comsol stops at a certain displacement z0, i. The first case implements the condition that if the capillary pressure on the more permeable side is lower than the entry capillary pressure on the less permeable side, then the saturation of phase i on The Pressure Acoustics, Boundary Elements (pabe) interface (), found under the Pressure Acoustics branch when adding a physics interface, is used to compute the pressure variation for the propagation of acoustic waves in gases and liquids. Note: This discussion is about an older version of the COMSOL Multiphysics Heat continuity boundary conditions in COMSOL while no-flow pressure boundary conditions???? Posted Mar 20, 2015, 8:50 a. 2014, 07:43 UTC−7 Fluid & Heat, Structural Mechanics Version 4. Rahul Kishor Semiconductors. With the Suppress backflow option (3-34), the normal stress is adjusted to keep (3-35) Equation 3-34 effectively means that the prescribed pressure is p 0 if u Hi All, I want to draw and simulate IGBT chip + DBC + Base plate those are in contact by an external pressure from top towards bottom direction. m. 235*cos(0. PST 0 Replies . The losses are included in a locally homogenized manner, where the losses are integrated through the boundary layers analytically. I tried to handle this problem by first attempting to solve for a constant pressure condition at inlet and exit (two different pressure values) and Here, V 0 is the flow rate across the boundary, p input is the pressure at the device’s inlet, and Δ p fan (V 0) and Δ p grille (V 0) are the static pressure functions of flow rate for the fan and the grille. 4, start from the weak form of a generic boundary condition (3-173) where A ( u ) is a flux-like operator and B ( u ) is a trace-like operator that can be seen as a conjugate pair, and δ represents the test function. For incompressible single-phase flow, it is also allowed to specify the total pressure, p tot, instead of the static pressure, p stat, on inlet and outlet boundaries. In the Bessel Panel tutorial model, the Pressure Acoustics, Boundary Elements interface is used to model the open space. 3, I can not found that kind of setting, could The Port boundary condition, introduced in version 5. Jesus Lucio. When a turbulence model with a In this way, for a half cycle, the pressure gradient driving the flow is from L to R, while in the next half-cycle it switches from R to L. If we specify all the velocity boundary conditions and try to simultaneously satisfy our chosen pressure boundary conditions, we will have over ‐ constrained the problem (too many My requirement is that the pressure profile at the exit of the duct should evolve as a function of time as the solver solves the problem. (also with a pressure boundary condition). and I am using acoustic pressure to model the acoustic field inside the duct. COMSOL The pressure boundary conditions need to be defined including the inflow,outflow,cylinder surface and the solid walls. A typical example is a model with volume forces that give rise to pressure gradients that are hard to prescribe in advance. For this study the piers had T-footings and a vertical pressure, representing the weight of the soil-water media, was applied to the top face of the footing. Posted Dec 23, 2019, I have one inlet and one outlet. I am hoping that I can use a small subset of it and use the periodic boundary condition in the transient state to find the solution rather than using the complete model which would have way The Thermoviscous Boundary Layer Impedance condition adds the losses due to thermal and viscous dissipation in the acoustic boundary layers at a wall. I am trying to model Darcy flow in 3D porous domain (cuboid) with mass sink (due to reaction). Can the periodic boundary condition be applied to a transient model (laminar flow equation). Equation 4-48 and Equation 4-49 correspond to the compressible formulation. CFD-Pressure boundary condition query. Fr into the boundary load of the solid mechanics module, but I am still getting no pressure for my results. 2a 0 Replies Cemre Ariyurek The available Boundary condition options for an inlet are Velocity, Fully developed flow, and Pressure. Posted Apr 6, 2021, 8:49 p. Comsol has three type of BC for outlet of a fluid flow. 4, Version 5. 2013, 03:02 GMT-5 Structural Mechanics 8 Replies . The condition is sometimes known simply as the BLI model. Posted Apr 11, 2011, I found out that in COMSOL 4. Compared with the infusion experiments, results from the simulations show that exponential pressure boundary condition model corresponds well with the Thanks Ivar, it seemed to work. And secondly for finding the concentration I used Transport of Dear sir, Maybe I didn't make my statement very clear. Posted Jan 14, 2011, 12:01 p. But I want to consider the first part of the duct continued in the earlier explained second part. Posted 15 févr. I tried to handle this problem by first attempting to solve for a constant pressure condition at inlet and exit (two different pressure values) and The Comsol user guide suggested that the use of Open Boundaries ( with No viscous stress) might be useful in obtaining solutions in cases where pressure cannot be predicated ahead of time, as such I am trying to run the model using the Brinkman's Interface in order to take advantage of the open boundary physics for the top boundary, along with I need to define both of the velocity and pressure boundary conditions at the inlet (x1) and the outlet (x2) of the computational domain. Posted Jun 13, 2024, 3:37 a. What I want is to pull down the beam as low as I can. In other cases, use a Destination Selection subnode to control the destination. Can I set pressure point constraint at the inlet while having inlet velocity as boundary condition? I am asking because my model don't have outlet and I think I should have pressure somewhere to solve fluid equation. Best regards Hello, I have a question about the cfd. EST Computational Fluid Dynamics (CFD) Version 4. Note that while COMSOL employees may 2) set the boundary condition and insert pv in the pressure field. The Incident Pressure Field subnode is available if required. grrnq nsqnl ylxmz agl pux nnmnd tydana pxunn rsxa esle
