What is Fluid: Definition and 1000 Discussions

FLUID (Fast Light User Interface Designer) is a graphical editor and GUI builder that is used to produce FLTK source code. FLUID edits and saves its state in text .fl files, which can be edited in a text editor for finer control over display and behavior.After designing the application, FLUID compiles the .fl file into a .cxx file, which defines all the objects from the .fl file, and an .h file, which declares all the global ones. FLUID also supports localization of label strings using message files and the GNU gettext or POSIX catgets interfaces.

A simple program can be made by putting all non-interface code (including a main function) into the .fl file, thus making the .cxx file a single source file to compile. Most programs are more complex than this, so other .cxx files can be written that call the FLUID functions. These .cxx files must #include the .h file, or they can #include the .cxx file so it still appears to be a single source file.
Normally the FLUID file defines one or more functions or classes, which output C++ code. Each function defines one or more FLTK windows, and all the widgets that go inside those windows.
Widgets created by FLUID are "named", "complex named", or "unnamed". A named widget has a legal C++ variable identifier as its name (i.e. only alphanumeric and underscore), and is defined by a global variable or class member that will point at the widget after the function defining it is called. A complex named object has punctuation such as '.' or '->' or any other symbols in its name. In this case, FLUID assigns a pointer to the widget to the name, but does not attempt to declare it. This can be used to get the widgets into structures. An unnamed widget has a blank name and no pointer is stored.
Widgets may either call a named callback function that one writes in another source file, or one can supply a small piece of C++ source and FLUID will write a private callback function into the .cxx file.

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  1. steve1763

    A Integrating the Stokeslet: Solving Expression 7 from ResearchGate Publication

    https://www.researchgate.net/publication/301874096_Emergent_behavior_in_active_colloids/link/5730bb3608ae08415e6a7c0a/download (expression 9 on this document derivation). I understand the need for substitution etc into the integral. What puzzles me is how the integral equals what it does. If...
  2. B

    The Traditional Bernoulli Eqn Derivation of Rocket Exhaust Velocity

    If you've seen it, they chose one point in the combustion chamber and the other in the exhaust nozzle. I think they're assuming that we have a gas both places. They say that the pressure in the nozzle is atmospheric pressure, or it you're in outer space, zero. That makes perfect sense...
  3. Astronuc

    I Jupiter atmosphere, turbulence and ocean fluid dynamics

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  4. J

    A Is fluid mechanics (aerodynamics) still being discovered?

    Is fluid mechanics,particularly aerodynamics still being discoverd (like math for example) or everything has already done long time ago?
  5. A

    I Conversion of Fluid Rotational Force to Rocking Motion

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  6. H

    A The ``kinematic equation'' of fluid flows

    I saw this in a textbook and I thought it is a corollary of Reynold's transport theorem. Let \mathbf{F} be a smooth vector field Consider the surface integral: \int_{S}\mathbf{F}\cdot d\mathbf{S} and now take the derivative of it, then the expression can be written as...
  7. O

    I Fluid force from a fluid flow vs. from a fluid jet

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  8. R

    Real-life phenomenon/application of this fluid dynamics model

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  9. DadoNoah

    Calculating force on a syringe plunger for a viscous fluid?

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  10. F

    Fluid flow inside a cylindrical tank

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  11. Leo Liu

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  12. Dario56

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  13. Dario56

    I Work - Energy Principle Application to Fluid Flow

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  14. T

    Why Does Rain Create Waves on My Street? - Investigating Fluid Mechanics

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  15. Y

    B Terminal Velocity Equation in vertical cylinder with some fluid

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  16. MathematicalPhysicist

    I The Universe filled with a "homogeneous perfect fluid"

    On page 353 of Schutz's textbook he writes the following: So it seems that the ether is replaced by a "homogeneous perfect fluid". It seems the medium which fills the universe is not ether but "homogeneous perfect fluid". But in that case what characteristics did the proposed ether have that a...
  17. V

    B Fluid Continuity Equation in different reference frame

    If I have fluid with area 10 and velocity 10, if the velocity increases to 20 the area will become 5. But if we switch to a reference frame moving at velocity 1 opposite this motion, then it would be 10 and 11 to 5 and 21, violating the continuity equation. What is wrong?
  18. abdulbadii

    Used/old transmission fluid should be useful for something else?

    Can a used/old transmission fluid be as a penetrating oil constituent along with acetone 100%, common lubricating oil or grease, etc ?
  19. H

    Engineering Nozzle and diffuser momentum equation

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  20. L

    Torque required to rotate a plate in a fluid

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  21. N

    Fluid flow rate calculation

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  22. Dario56

    I Fluid Viscosity & Viscous Friction Between Plates

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  23. ergospherical

    A Fluid Flow Symmetry: Showing $\pi_b G^b$ is Constant

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  24. Angelo Pascal

    Geophysics: Fluid Dynamics Problem

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  25. R

    Classical Looking for the absolute best fluid mechanics book available

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  26. ZdMh

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  27. kolleamm

    Can metal fluid contract under voltage?

    I was told there exists a metallic fluid that contracts when a voltage is applied to it. Does anything like this actually exist?
  28. E

    Speed of sound in a relativistic fluid

    Let us consider the co-moving observer ##\mathscr{C}## for whom ##E = \epsilon## and ##\mathbf{\vec{V}} = \mathbf{\vec{0}}##. Doing the perturbation stuff to the first of the relevant equations gives$$\partial_t \delta \epsilon + \boldsymbol{\nabla} \cdot ([\epsilon + p] \delta \mathbf{\vec{V}})...
  29. E

    Buoyant Force and Archimedes' Principle

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  30. J

    Finding change in height of fluid in U tube from change in T

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  31. T

    MTW Exercise 22.7 -- Calculate the law of local energy conservation for a viscous fluid with heat flow

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  32. W

    Comparetto type Air Cleaner/Filter: What causes its increased airflow?

    Typical box fan+air filter setups use axial consumer-grade fans designed for providing maximum air flow at low power consumption. These fans do not provide sufficient air flow at the high static pressure requirements typical of air filters. The air filters DIYers use are high Merv(e.g Merv 13)...
  33. A

    The Euler Equation and Incompressible Fluid Theorems

    $$\frac{Du}{Dt} = -\frac{\nabla p}{\rho} - \nabla \chi$$I re-write the Euler equation for incompressible fluid using suffix notation $$\frac{\partial u_i}{\partial t} + u_j \frac{\partial u_i}{\partial x_j} + \frac{\partial}{\partial x_i} \left(\frac{p}{\rho} + \chi \right) = 0$$what theorems...
  34. S

    Is ideal fluid flow around an airfoil the Lambert W function?

    NOTE: By "ideal", I mean incompressible & inviscid (the forum doesn't allow a long enough title). I was looking at this Wikipedia article, and the graph of this function struck me as looking exactly like ideal fluid flow around an object. https://en.wikipedia.org/wiki/Lambert_W_function...
  35. binbagsss

    Drop out of PhD in fluid mechanics and switch to Mres in mathematical physics?

    A post doc in an area that differs from my PhD? I am currently doing a PhD in fluid mechanics but want to do mathematical physics tbh. In another thread I got an answer about a user who had done a PhD in accelerator physics and went to do a post-doc in condensed matter, vice versa even, but in...
  36. swiper122

    Fluid dynamics calculation -- Draining a barrel through a pipe

    v1- velocity of water at the top of the barrel v2- velocity of water at the the pipe (bottom of cylinder) p + (⍴ *(v1)^2)/2 + ⍴gh=p + (⍴ *(v2)^2)/2 + ⍴gh atmosferic pressure cancels out (⍴ *(v1)^2)/2 + ⍴gh = (⍴ *(v2)^2)/2 + ⍴gh density doesn't affect the result(cause its in every term)...
  37. R

    Fluid flow and characteristics in a vacuum (Cryophorus)

    trying to calculate the mass flow of Water vapour that is produced within a vacuum of 30 inhg when the water temp is 40 degrees. How is velocity calculated in this scenario. Also what boundary layer does the water vapour have.
  38. SebastianRM

    Relating volumetric dilatation rate to the divergence for a fluid-volume

    in class we derived the following relationship: $$\frac{1}{V}\frac{dV}{dt}= \nabla \cdot \vec{v}$$ This was derived though the analysis of linear deformation for a fluid-volume, where: $$dV = dV_x +dV_y + dV_z$$ I understood the derived relation as: 1/V * (derivative wrt time) = div (velocity)...
  39. C

    Intro Physics Best textbook for properties of matter and fluid mechanics

    I am a First Year Undergraduate Physics student. Which will be the best textbook for me to study properties of matter (Elasticity) and fluid mechanics? I prefer a better theoretical understanding.
  40. A

    What is the Residual in Computational Fluid Dynamics?

    Can someone please tell me a basic and easy-to-understand example of Residual in CFD? Thank you
  41. A

    A Is the notion of elementary function a fluid concept among algebras?

    Let's consider the Taylor power series of a function on real numbers. Some of them represent elementary functions, and some of them represent special functions. The special functions cannot be expressed via finite combination of elementary functions on real or complex numbers. Now, take some...
  42. sandmanvgc

    Force Exerted by fluid on a Bend, an Enlargement, or a Contraction

    My attempt to try and convert book equation to FE manual equation in 3rd pic Fx = QpV1 + P1A1 - QpV2Cosa - P2A2Cosa Fx = P1A1 - P2A2Cosa+ Qp(V2Cosa +V1) P1A1 - P2A2Cos(a) - Fx = -Qp(V2Cosa +V1)
  43. kmot

    Fluid mechanics - Linearized shallow water equations

    Hi, In a text describing solution to linearized shallow water equations, I am not able to move forward. It's a 1 dimensional shallow water setup. There is a steady state (velocity) and (height of free surface). On top of this steady state there are u' and h' as disturbances. The goal is to...
  44. T

    Fluid flow around a wind turbine blade -- help please

    I have to estimate the Reynolds number of the fluid flowing around a blade but I only have one detail: the length of the blade is 0.66m. I have no idea how to do it and I got to submit the assignment in a week, I am desperate for help here.
  45. E

    B How to derive the continuity equation for a perfect fluid?

    Stress tensor for the fluid is ##T_{ab} = \rho u_a u_b + P(\eta_{ab} + u_a u_b)##, whilst the equation of motion (assuming the system is isolated) is given by ##\partial^a T_{ab} = 0##. So I tried$$\begin{align*} \partial^a T_{ab} &= \partial^a \rho u_a u_b + \partial^a P(\eta_{ab} + u_a u_b)...
  46. yecko

    Why is ro = 0.2255 in fluid dynamics vortices?

    why is ro = 0.2255? Thank you
  47. B

    Fluid velocity and pipe diameter using the continuity equation

    Hi, Can anyone let me know if I had done this Q correctly? Thanks for any help!
  48. Hamiltonian

    Doubt related to buoyant force and fluid thrust force

    (this problem is slightly modified from the original problem.) There is a contact force(friction and normal force) between the wedge and the walls of the container and there is a fluid thrust acting on the side of the wedge in contact with the fluid( this force is normal to the slanted surface...
  49. WhiteWolf98

    Calculating Discharge Rate of Fluid in Circular Area

    This is actually right at the start of another derivation, but I can't understand how the author gets the formula for ##q##. So the discharge per unit thickness is the circumference of the circle, multiplied by the velocity at that point (at ##r##)? I thought the formula for flow rate was...
  50. anonymous99

    What causes pressure in a fluid from beneath?

    S
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