Fluid Definition and 1000 Threads

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. Kaushik

    Pressure on a sample of fluid (at rest)

    Question 1 Consider a sample at a height ##ℎ## below the interface of air and the fluid. The pressure on the sample is given by ##𝑃_𝑎=𝑃_{𝑎𝑡𝑚}+𝜌𝑔ℎ##. My question is does 𝑃𝑎 include the pressure due to the particles that are to the side of the sample? Question 2 Now consider this setup. In this...
  2. R

    Flow rate of fluid at a burst leakage in a pipeline due to over pressurization

    we have a project to how knowing the flow rate of fluid at the burst leakage due over pressured, probably to make it easier to understand i will attach some pictures of this mechanism. Picture at above is simply mechanism of pipeline system that installed vertically, with fluid is mud and...
  3. Adi6677

    Velocity of fluid flowing from a hole at the bottom of a conical shape

    My approach was that I consider the pressure of cross section A first Pa= P + dgh Now by writting Bernoulli's Equation between the cross-section A and the opening : $$ Pa + 2dgh + 2dV^2/2 = Pb + 2dV'^2/2$$ Where Pb is the pressure of the opening which is equal to the atmospheric pressure...
  4. BigDumDum

    Fluid Dynamics and Global Warming

    Almost 90% of all humanity lives in the Northern hemisphere. Due to colonization, expansion, growth, war, water sources, etc. we have amassed our populations in specific areas around the Northern hemisphere. We continue to build at an unprecedented rate. Our buildings are growing wider, taller...
  5. JamesBennettBeta

    Values of constants in power-law fluid relation

    NO TEMPLATE, MISPLACED HOMEWORK Summary: What are the values of constants in power-law fluid relation when the fluid behaves as an ideal fluid, a Newtonian fluid and a non-Newtonian fluid? τ = A(du/dy)^n +B Where A, B and n are constants that depend upon the type of fluid and conditions...
  6. M

    A Fluid Equilibrium Interface Shape

    Hi PF! Suppose a 2D rectangular channel with wall-normal perpendicular to the downward gravity force ##F## rests is static equilibrium. What shape would the liquid take? Looking at the equations of motion, I think the following would have to be satisfied: $$\frac{d P}{dy} = -\rho F\\ \Delta P...
  7. I

    How to Calculate Underwater Force for Displacement?

    I'm trying to determine the force needed for one object to displace another object underwater. Specifically, Object A strikes Object B hard enough to jettison it from the seafloor up to sea level/land, let's say the Pacific coastline. I have a timeframe in mind, density & mass of the two...
  8. M

    A Sessile drop fluid oscillations and frequencies

    Hi PF! I'm looking at a sessile drop of water in ambient air. The drop is plucked lightly, inducing surface oscillations. The fundamental frequencies ##\lambda_i## can be computed from spectral theory, and output complex values, say ##\lambda_1 = 2+7i##. Now, I simulate the experiment via CFD...
  9. jahan123

    Fluid Mechanics Challenging Problem

    Homework Statement: how far from the mercury surface must a horizontal line be drawn in a 2 meter square gate whose one side is at the fluid surface so that the hydrostatic forces in the two newly formed surfaces are equal Homework Equations: 1) F = yAh where y= specific weight A is the cross...
  10. C

    Converting PSI Pressure Loss in a Pipe to Fluid Loss Rate

    Summary: Pipe Testing I need some help on how to calculate PSI loss to gallons per hour? We will be testing this 8" PVC line at 150 PSI for 4 hours. If the test gauge drops 10 PSI per hour, what is the formula to determine the gallons per hour lost? Thank you for your help.
  11. Kaushik

    Why is the pressure reduced when the fluid flows faster?

    Look at the above figure. An overhead view of a car passing a truck on a highway. Air passing between the vehicles flows in a narrower channel and must increase its speed. As the speed of air in that narrow channel increases, the pressure reduces (between the two vehicles). What is the reason...
  12. T

    Fluid passing through a convergent-divergent nozzle

    Suppose, there is a convergent-divergent nozzle where the inlet and the outlet both has 5 sq cm area while the throat has 1 sq cm area. A pressurised compressible fluid at 5 barA pressure having velocity 10 m/s entered the c/d nozzle. The back pressure i.e. the pressure at the outlet is 1 barA...
  13. ValeForce46

    Fluid dynamics problem -- Filling linked cylinders with water

    The first part of the problem I just used Stevin's law: $$p_{atm}=P+ρg(h_1-h_2)=> h_2=(P-p_{atm}+ρgh_1)/(ρg) =>h_2=0.94m$$ Is this right? I considered ##ρ=10^3 {kg/m^3}## About the second part... how can I be sure that ##h_1## remains unchanged? If it is unchanged, then can I use Bernoulli's...
  14. E

    I Pressure vs Normal Stress: Exploring Bird Transport Phenomena

    What's really the difference between pressure and normal stress? Also I know pressure acts normal to a surface from the outside Do normal stress acts from inside? I'm reading bird transport phenomena and this is confusing
  15. ValeForce46

    Is the balance of forces equation correct for a tube immersed in alcohol?

    This is a problem from a past exam. For point a) the balance between force should be given by the following equation $$M*g+p_0*A=ρ*g*(A*d)+p*A$$ But I still have two unknown values... I know that pressure outside the tube at depth d is $$p(d)=p_0+ρ*g*d$$ and this has to be equal to the...
  16. B

    Use of ammonia as the OTEC working fluid

    Anhydrous Ammonia liquid compressed to 20 Bar, heated from -33 C to 22 C, flow rate 2 tonnes per second, evaporated in boiler at 22C what could power extracted from turbine be? (outlet 1 Bar pressure)
  17. M

    Fluid Oscillating in a Channel CFD

    Hi PF! I'm simulating two fluids, air (blue) and water (red), in a 2D rectangular channel. See picture below: I've turned gravity and viscosity off, and have ##\rho_w=1000## kg/m^3 and ##\rho_a = 0.01## since it cannot be zero. I've also enforced a static contact angle of ##\theta = 71^\circ##...
  18. F

    I Why in the steady flow of a fluid, the fluid cannot move through the wall....?

    Because of temperature, molecules of fluid have chaos movements.So I do not understand why in steady flow,the molecules of fluid can not move through the wall of flow tube?I think two layers of fluid exchange molecules while they move.How do we understand when saying: fluid can not move through...
  19. M

    Fluid Interface Frequency Transform

    Hi PF! Fluid lies in a 2D rectangular channel and oscillates from a disturbance. I have several .csv files, each corresponding to a moment in time, where within each are two lists of numbers: the ##x## and ##y## position of a fluid interface. I'd like to decompose the interface into it's...
  20. Bortei

    Accidental Discovery of Charge-Polarity Fluid: What Are Its Uses?

    Hi just saw the accidental discovery of fluid that will keep its charge-polarity...how can this be used?
  21. V

    Basic fluid mechanics questions about an oceanography paper

    Problem Statement: There is no precise problem statement since it's an homework to be done independently, but I will try my best to explain it concisely (I also apologize for my mistakes in English) : I want to reproduce the simulation of the model presented in the pdf file attached to this...
  22. K

    Fluid dynamics and sound waves

    There are many fluid dynamics applications such as pipe flows, jet flows, boundary layers where we ignore any sound waves present in the system. I don't understand this though, because all sound waves are caused by pressure disturbances so why can we ignore these pressure disturbances when we...
  23. M

    Fluid Mechanics problem: Oil pressure calculations in pipe flow

    Problem Statement: An oil with density 900 kg/m3 and viscosity 0.18 Ns/m2 flows through a circular pipe which inclines upwards at 40° to the horizontal. The length of the pipe is 10 m and the diameter is 6 cm. The fluid pressure at the lower end of the pipe is 350 kPa and the pressure at the...
  24. saxman2u

    Fluid Mechanics-head loss/GPM change adding 2nd line for pumping

    I have a rainwater collection system in Austin, TX, where we have to pump water to our main 30,000 gallon tank. The system works great. My question is, our 3 HP pump pumps about 85 gallons per minute. The length of the 2"pump line is about 300 ft, elevation change is about 50 feet higher...
  25. nn2e19

    Hole Sizing to Drain Fluids [Pressurized Container]

    Hello, I want to size my system to be able to get rid of fluids without any head buildup within the container. I am just a bit confused as to what formula I should use. My problem is summed up in the following schematic. Note that P1>P2, I have assumed H=10^(-4)m and my flow rate is 0.1 m3/s...
  26. L

    I Optimal Copper Pipe Size for Misting System

    I am attaching a standard 5/8" garden hose with approximately 70psi pressure to a copper pipe that is capped on the opposite end with mist nozzles mounted periodically along its length. I want the pressure at each mister to be as similar as possible. The hose attaches at the base, a solid line...
  27. Clout

    Fluid mechanics - pump in a horizontal pipe connecting two pipes

    So when the velocity of v1 and v2 is 0 (because the tanks are much bigger), the bernoulli equation to dh is dh = (dp-dpl)/(rho*g) with dp = Phyd / V = 1000W / 0.01m³/s = 10^5 Pa and rho = 1000 kg/m³ So I am getting first without the pressure loss on the orifice dh = 10^5 Pa / (1000 kg/m³ *...
  28. A

    Shear and the stress tensor of a Newtonian fluid

    Similarly the paper by @buchert and @ehlers https://arxiv.org/abs/astro-ph/9510056 Here the author has defined ##v_{ij}=\frac{\partial v_i}{\partial x_j}=\frac{1}{2}(\frac{\partial v_i}{\partial x_j}+\frac{\partial v_j}{\partial x_i})+\frac{1}{2}((\frac{\partial v_i}{\partial...
  29. T

    Bouyancy force -- What mass can the balloon carry?

    In a I used FBouyancy - FBalloon -F mass = 0 rewrote mass as a product of density and volume to obtain; m= v(densityair - densityHe) m= 1031.5kg.I am stuck in part b. I have this formula called Barometric formula which ı should use; P = P0 * e((-P0*g*h)/ P0 So what I understood is that...
  30. M

    Fluid Mechanics: Momentum Equation- When to include p_atm in equation?

    So if we define point 1 at the entrance and point 2 at the exit, then we can write out Bernoulli's equation along a horizontal streamline as such: p_1 + \frac{1}{2}\rho v_{1}^2 = p_2 + \frac{1}{2}\rho v_{2}^2 = p_{atm} One question is: won't there be p_atm also contributing to the static...
  31. M

    Fluid Mechanics: Momentum Equation Propeller Question

    For this question, this is my working. The main issue is I cannot figure out where the factor of \frac{1}{2} comes from. So I consider a control volume right around the propeller (in the frame of reference of the propeller) and I apply R(-->) Force = Change in Momentum Flux F = \dot{m_{o}}...
  32. J

    Filling a long tube by submerging it in fluid

    Hi everyone, I'm working on a first-year college assingment and need some help with it. I need to figure out how deep does a tube, initially filled with air, need to be submerged into water in order get fully filled, meaning in order for the air to be fully displaced by water. The tube is 1/2...
  33. M

    Fluid Mechanics: Head Loss Question (Conceptual)

    I am not really worried about the numbers, but more about the simple concepts with head loss in these pipe flow questions. I want to confirm that head loss just means the change in static head, right? I have been advised that for a problem like this, it is nothing more than the conservation of...
  34. WhiteWolf98

    Fluid Mechanics: Flow rate required to achieve a constant height

    Some thoughts that I've had on the question are saying the volume flow rate (##Q##) in, must equal the volume flow rate out. If that's the case, then: ##Q_{in} = Q_{out}## ##A_1V_1=A_2V_2## But... no areas have been given. And height doesn't enter this equation at all. Then I thought it...
  35. WhiteWolf98

    Fluid Dynamics - Mass Conservation, State Equation for an Ideal Gas

    I understand that ##\dot m=\rho Q## and ##{\dot m}_{in}= {\dot m}_{out}## . So one can say that ##\rho Q_1 = \rho Q_2##. But I'm not sure if that equation is correct. I don't know if the density remains constant, or the volume flow rate. And then how I'm also supposed to tie a state equation in...
  36. M

    Where Does Viscous Pressure Enter the Pressure Balance?

    Suppose we have an incompressible, viscous sessile drop subject to a time-dependent pressure field ##p## on a substrate. Let ##\mu## be dynamic viscosity, ##u## be the fluid velocity field, ##\kappa_{1/2}## curvatures of the fluid surface, ##\sigma## surface tension, ##\hat n## normals to the...
  37. B

    I Analytical Open Channel Rectangular Fluid Flow

    Hi All, I'm looking for an analytical solution to the open channel rectangular fluid flow profile. The flow is bounded by three walls but the top is open to atmosphere. Assume steady state flow that is parallel and incompressible.I've already found information involving a rectangular flow...
  38. A

    Velocity gradient decomposition of a fluid flow

    If the velocity gradient decomposition is done by symmetric and antisymmetric parts then ##\frac{\partial v^i}{\partial x^j}=\sigma_{ij}+\omega_{ij}## where ##\sigma _{ij}=\frac{1}{2}(\frac{\partial v^i}{\partial x^j}+\frac{\partial v^j}{\partial x^i})## and...
  39. A

    Fluid Mechanics, Particle Size, Bouyouncy Force

    1. What should be the size of object/Particle (sphere) so that it should remain suspended (neither it should sink nor it should float)? container dimensions 30*25*25, density of fluid 0.9g/cm3 , density of particle 0.86g/cm3 , particle is coated with aluminium having density of 2.07g/cm3.(if...
  40. W

    HVAC Understanding the movement of a fluid in a vertical pipe

    The actual problem I am trying to understand is the suction requirement to move #2 home heating fuel from the outdoor tank to the pump of the burner located in my cellar. But first i just want to understand the movement of fluid in a vertical pipe without worrying about viscosity or...
  41. X

    Would acceleration under water affect the person?

    I've searched online over multiple sites and can find no answer to this. I know the basics on acceleration, mass and few others. To try and paint the right picture, take a person and put him in a hollow object--a tube shape--and accelerate them. They are subject to inertia. Now take that person...
  42. P

    Pressure changes of a fluid flowing through a horizontal pipe

    If we have a tube of fluid going like it is shown in the picture, and we measure pressure at two points we would get the same value. But the fluid is still going from point A to point B. So is pressure difference not necessary for fluid flow or I made some other wrong assumptions?
  43. LordGfcd

    A fluid mechanics problem -- Shape of a falling water drop

    Homework Statement A drop of water fall towards the ground with initial mass [m][/0] and radius [r][/0] (assume the initial shape of that water drop is sphere). the air resistance is F=½.ρ.A.[v][/2].C (C is the drag coefficent, A is the area that the air contact with the water drop and ρ is the...
  44. rumborak

    Fluid going through pipe: what is the influence of speed on exchanging heat?

    I'm doing a fun home project, and it involves water flowing through a metal pipe, where the surrounding is significantly lower temperature than the water in the pipe. The point of the exercise is to cool the water in the pipe as it flows through it. The question is, what influence does flow...
  45. NatanijelVasic

    I Subsonic and Supersonic Airflow Through a Constriction

    Hi everyone! For the past week I have spend a lot of time thinking about how de Laval nozzles work. But before I convince myself that I have understood it, I want to make sure that the (simpler) scenarios I describe below are correct. Setup: We have a long pipe with constant radius r = 1...
  46. CharlieCW

    Conductor sphere floating on a dielectric fluid

    Homework Statement A conductor sphere of radius R without charge is floating half-submerged in a liquid with dielectric constant ##\epsilon_{liquid}=\epsilon## and density ##\rho_l##. The upper air can be considered to have a dielectric constant ##\epsilon_{air}=1##. Now an infinitesimal...
  47. Alexanddros81

    I want to understand this equation - Fluid Mechanics

    Hi all! I have started reading Fluid Mechanics at my own pace (no university study) and really I would like to grasp the ideas behind it. So I have Fluid Mechanics by Cengel - 4th edition. At page 45 the coefficient of compressibility or bulk modulus of elasticity (κ) is introduced. ##κ =...
  48. WhiteWolf98

    Fluid Mechanics: Determining Elevation in a Piezometric Tube

    Homework Statement [/B] Homework Equations ##P=\rho gh## The Attempt at a Solution So this is the first time I'm doing fluid mechanics, and I'm trying my best to understand it. This was the first question, and truth to be told, I'm not very confident. I know what gauge pressure is: the...
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