What is Finite: Definition and 1000 Discussions

The finite element method (FEM) is a widely used method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat transfer, fluid flow, mass transport, and electromagnetic potential.
The FEM is a general numerical method for solving partial differential equations in two or three space variables (i.e., some boundary value problems). To solve a problem, the FEM subdivides a large system into smaller, simpler parts that are called finite elements. This is achieved by a particular space discretization in the space dimensions, which is implemented by the construction of a mesh of the object: the numerical domain for the solution, which has a finite number of points.
The finite element method formulation of a boundary value problem finally results in a system of algebraic equations. The method approximates the unknown function over the domain.
The simple equations that model these finite elements are then assembled into a larger system of equations that models the entire problem. The FEM then uses variational methods from the calculus of variations to approximate a solution by minimizing an associated error function.
Studying or analyzing a phenomenon with FEM is often referred to as finite element analysis (FEA).

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  1. V

    Analytical solution of photon diffusion in finite media

    Homework Statement I'm trying to derive an analytical expression for the photon backscatter flux in finite turbid media using the diffusion equation and the method of images. What I want to write is: for a given volume (x,y,z), where a coherent light source is incident on the x-y plane and z is...
  2. M

    A Does continuous mass distribution implies finite propagation

    speed? This question emerged in my mind while studying a discrete and continuous mathematical model of a falling slinky. In the discrete model, we suppose an instantaneous interaction between mass points at a distance, so the action propagates through the chain of mass points with infinite...
  3. newrd

    B Is the Universe Finite? Exploring Expansion and Existence | True or False?

    The universe- from our understanding, is expanding, thus the regions (for lack of a better word) particles have not yet reached do not exist. How far our universe can/ will expand is unknown, it may be infinite, but we can conclude at this time, as it is still expanding, that it is finite. True...
  4. J

    B Why is the age of the Universe finite?

    I am assuming scientists say that the universe is 13.8 billion years old with respect to time on earth. If so, how come the infinite energy present at such a small scale didn't make gravitational time dilation infinite during the first stage? Wouldn't time dilation make the universe infinitely...
  5. Math Amateur

    I Directly Finite and Directly Infinite R-Modules - Bland S2.2

    I am reading Paul E. Bland's book "Rings and Their Modules ... Currently I am focused on Section 2.2 Free Modules ... ... I need some help in order to fully understand Bland's Example on page 56 concerning directly finite and directly infinite R-modules ... ... Bland's Example on page 56...
  6. Math Amateur

    MHB Understanding Bland's Example: Free Modules & Directly Finite/Infinite R-Modules

    I am reading Paul E. Bland's book "Rings and Their Modules ... Currently I am focused on Section 2.2 Free Modules ... ... I need some help in order to fully understand Bland's Example on page 56 concerning directly finite and directly infinite R-modules ... ... Bland's Example on page 56...
  7. F

    MATLAB Finite difference numerical integration or ode45?

    I'm trying to numerically solve the time dependent Schrödinger equation and I've been told that the best approach is to numerically integrate using a finite difference method, however I don't understand why I couldn't just use ode45 to solve it?! Is the finite difference (interpolation) method...
  8. A

    B Finite difference problem

    I found this part of forum the most relevant to this theme so excuse me if I missed. This year I'm doing a high school summer project related to quantum mechanics. Anyway I'm using finite difference method to solve Schrodinger equation. Before starting to work on a project I decided to get some...
  9. haael

    A Do black holes lose hair in finite time?

    OK, so it's time to start a new thread. I heard many times that there exists only one black hole solution for a given mass and angular momentum, but I know already that this is not true. We all know that if we throw something into an existing black hole, its event horizon starts to ripple. So...
  10. whatphysics

    Quantum Physics - Infinitely vs Finite depth quantum well

    Homework Statement Comment how the energy and wave functions of the electron would change in the case of a finite dept quantum well with the same width. Homework EquationsThe Attempt at a Solution I feel completely clueless as how to approach! :( * The full question can be found in the...
  11. S

    I Limit of large but finite

    I've calculated the eigenstates of the Hubbard Hamiltonian for two fermions. The ground state is (U2 - (U2 + 16t2)1/2)/2 For U = infty, I get 0. For U >> t, I should get the exchange energy J = -4t2/U How do I get from the ground state equation to J?
  12. J

    I Probability current in positive finite square potential

    Hello! I want to prove that the probability current is a continuous entity at the boundaries of the square for the situation of 0< E< Vo in the problem where V is zero except a finite region in space where it is +Vo and we consider an incoming particle from the left(for example). I thought that...
  13. K

    MHB Is \(\pi\) Algebraic of Degree 3 Over Any Extension of \(\mathbb{Q}\)?

    Q7. Name an extension of \(\mathbb{Q}\) over which \(\pi\) is algebraic of degree 3. I have a very simple answer to this (below) but is it correct? Is it likely to be what the text is after? \(\mathbb{Q}(\pi^3)\) is an extension of \(\mathbb{Q}\), it is not an algebraic extension but I am not...
  14. nazmus sakib

    Fourier sine series for a triangular wave on a finite string

    Homework Statement A string of length L =8 is fixed at both ends. It is given a small triangular displacement and released from rest at t=0. Find out Fourier coefficient Bn. Homework Equations what should i use for U0(x) ? The Attempt at a Solution
  15. P

    Electron in a Finite Square Well

    Homework Statement An electron in a finite square well has 6 distinct energy levels. If the finite square well is 10nm long determine: a) Approximate the possible values for the depth of the finite square well ##V_0##. b) Using a well depth value in the middle of the results obtained from part...
  16. F

    B Does the Universe have finite or infinite size?

    At the time of Big Bang the size of Universe equal the size of an atom.The Universe has expanded and the time from the Big Bang to the present is finite.Then at the present time the size of the Universe is finite or infinite?
  17. S

    A Finite Difference solver for 2D Elasticity equations

    Hi I've been trying to get a simple solution to the 2D Navier-Lame equations using finite difference on a rectangular grid. I want to see the displacements, u and v, when a simple deformation is imposed - e.g. top boundary is displaced by 10%. The equations are as follows: \begin{eqnarray*}...
  18. Telemachus

    Initial value problem, finite differences

    Homework Statement Given an initial value problem: ##x'(t)=f(t,x)\,,x(t_0)=x_0## Use centered finite differences to approximate the derivative, and deduce a scheme that allows to solve the (ivp) problem. Homework Equations For centered finite differences ##\displaystyle\frac{dx}{dt} \approx...
  19. Enrike

    Complex integral in finite contour at semiaxis

    Hi, I have a difficult time trying to perform the following integral, $$ j({T}, \Omega)=\int_0^{ T} d\tau \frac{\tau^2\exp(-i\Omega\tau)}{(\tau-i\epsilon)^2(\tau+i\epsilon)^2} $$ The problem is that the poles ##\pm i\epsilon## when taking the limit ##\epsilon\rightarrow 0## are located at...
  20. Schwarzschild90

    Transfer matrix for a finite length? (Quantum mechanics)

    Homework Statement I'm struggling to find a solution to exercise (*b). I have uploaded a pdf of the assignment. Please advise me at your convenience. Homework Equations x(x_l^+) = T(x_l^+, x_l^-)x(x_l^-) The Attempt at a Solution x(a^-) = \frac{\psi(a^-)}{\psi(a^-)} , T(a^+, a^-) \left(...
  21. Z

    I Finite vs. Infinite Square Well potential base question

    I just noticed in reading Griffiths that he places the base of the infinite square well at a zero potential while he places the base of the finite square well at a negative potential -V_0, where V_0 is a positive, real number; is there any reason for this? I just started learning about them/am...
  22. Einj

    Euclidean correlators for finite chemical potential

    Hello everyone, my question is about Euclidean correlators (say a 2-pt function to be specific) in presence of non-zero chemical potential. The question in particular is: is it still true that the Minkowski time ordered 2-pt function can be simply obtained from the Euclidean one by analytic...
  23. Alltimegreat1

    What is a finite and bounded universe and how do scientists envision it?

    A number of scientists subscribe to this theory. I read up on it, but none of the explanations I found really answered my questions. How should one attempt to envision a universe that is finite and bounded?
  24. A

    How did black holes merge in finite time?

    This question is in context of the recent gravitational wave detection by aLigo. Apparently aLigo has detected the entire process, including the before merger, during merger, and aftermath of the completed merger. My understanding is that two black holes should not be seen to be merging in...
  25. S

    MHB Discounting a finite series of costs at unknown times

    Consider a finite series of repeated costs C that occur at a series of times ti. Is there a solution to discount these costs by interest rate r to account for time value of money, i.e. solve for S? The times ti of each cost are unknown, but the number of costs n is known, and the average time...
  26. A

    Nonuniform finite element method

    I am solving some 2nd order differential equations using the finite element method. Doing so I represent the second order derivative at a given point as: ∂2ψi/∂x2 = 1/(Δx)2 (ψi-1+ψi+1-2ψi) And solve the differential equation by setting up a matrix of N entries and solving for the eigenvectors...
  27. evinda

    MHB Proving Finite Groups: A Contradiction in Subgroups - Hello! (Wave)

    Hello! (Wave) I want to show that a group with finite number of subgroups has to be finite. I thought to suppose that the group is not finite and then get a contradiction.So, suppose that the group is not finite. Then the group has infinite elements. Since the group has a finite number of...
  28. G

    Finite dimensional normed vector spaces complete ?

    Homework Statement Show that finite dimensional normed vector spaces are complete. Homework Equations ##E## is a finite dimensional vector space and ##N## a norm on ##E## The Attempt at a Solution If ##\{x_n\}_n## is a Cauchy sequence in ##(E,N)##, then it is bounded and each term of the...
  29. T

    Finite geometric series formula derivation? why r*S?

    what is the rationale of multiplying "r" to the second line of series? why does cancelling those terms give us a VALID, sound, logical answer? please help. here's a video of the procedure
  30. J

    E field due to a finite line of charge

    Homework Statement A finite line of uniform charge is on the line joining (4,0,0) (0,8,0) and has λ= 2μC/m find E at (0,0,0) Homework Equations E = Q / (4 π ε0 r^2) dQ = λ dl = λ dx The Attempt at a Solution I first notice that r will depend on 2 changing values x and y. I write an...
  31. G

    MHB Proving Existence of $N$ for $a^N=e$ in Finite Group $G$

    If $G$ is a finite group, show that there exists a positive integer $N$ such that $a^N = e$ for all $a \in G$. All I understand is that G being finite means $G = \left\{g_1, g_2, g_3, \cdots, g_n\right\}$ for some positive integer $n.$
  32. Babatunde22

    Criticality calculation of an homogeneous finite reactor

    Please,I am working on the criticality calculation of an homogeneous finite cylindrical reactor core using four-group diffusion equations. I have been able to discretize the multigroup diffusion equations using the finite difference method(FED). But I am stocked on the iterative method to...
  33. G

    Is this expression infinitesimal, finite, or infinite

    Homework Statement Say x is an infinitesimal number on the hyperreal line, is this expression finite, infinite or infinitesimal Homework Equations (sqrt(4+x)-2)/x The Attempt at a Solution [/B] My approach so far has been that sqrt(4+x) is (2+y) where y is another infinitesimal and y<x...
  34. S

    MHB Roots of an irreducible polynomial over a finite field

    Let F=Z2 and let f(x) = X^3 +x+1 belong to F[x]. Suppose that a is a zero of f(x) in some extension of F. Using the field created above F(a) Show that a^2 and a^2+a are zeros of x^3+x+1?
  35. evinda

    MHB Find Min Sum of Finite Seq. of Ints Using Dynamic Prog.

    Hello! (Wave) The finite sequence of integers $Y_1, \dots, Y_M$ takes both positive and negative values, where $M$ is a fixed positive integer. Could you help me to find a formulation using dynamic programming that solves the problem of finding integers $i_1, i_2$ with $1 \leq i_1 \leq i_2...
  36. M

    Finite element method for frames/beams

    I would like to know how to implement internal hinges in a program I'm developing. A hinge is created by changing the stiffness matrix of the beam. The problem is when two interconnected beams have a hinge at the same location, so basically we have a hinged joint, in this scenario I will obtain...
  37. P

    Finite Size vs Point Size Hydrogen like Atoms

    Ok my question: what is the difference between the binding energies of these 2 types of atoms, conceptual wise, which one is greater? I am assuming based on the easy calculations of the potential energy of the finite size atom ( inside and outside) There is a difference between the potential...
  38. rjbeery

    Size of Universe: Evidence of Finite Limits?

    I've seen various, wildly different, estimates of the size of the Universe. Do we have evidence demanding that the Universe is finite in size? If so, what are the clues that lead us to estimate that size beyond absolute speculation?
  39. P

    The # of bright fringes in a double slit with finite width?

    Homework Statement Laser light with a wavelength 633 nm is used to illuminate two slits separated by 0.125 mm. The width of each slit is 0.0150 mm. Assuming that only fringes between the first minima in the pattern are counted, how many bright fringes are visible? lambda = 633nm d = 0.125mm w=...
  40. ClaireBear1596

    Question related to a 3D finite spherical well

    I have a particle in a spherical well with the conditions that V(r) = 0 is r < a, and V(r) = V0 if r ≥ a. In this problem we are only considering the l=0 in the radial equation. After solving this I found that in the region 0<r<a, u(r)=Bsin(kr) (k=√2mE/hbar), and in the other region...
  41. C

    Calculate inductance of finite Solenoid

    Homework Statement A finite solenoid with "N" turns of wire, "L" length , "R" is the radius of the solenoid and passes through it a current "I". The objective is to calculate "L" of a finite solenoid. Not the basic formula ##L=\frac{\mu_0·N^2·S}{Length}## which is for a infinite solenoid. See...
  42. Anton Alice

    Is the range of a laser beam limited by the width of its wave packet?

    I think I am in a misconception concerning laser beams: Even the best lasers have a small line width. The spectral line is gauss-shaped. therefore the wave in position-pace is also a gauss-shaped wave packet, that travels with a certain group velocity. But this gauss shaped wave packet has a...
  43. G

    Number of partitions for a finite set

    Homework Statement Find a recursive relation on the number of partitions ##P_n## for a set ##S_n## of cardinal ##n##. ##P_0 = 1## is given. Homework EquationsThe Attempt at a Solution A partition of ##S_{n+1}## is given by the choice of a non-empty ##k##-block ##A_k## of ##S_{n+1}## and a...
  44. G

    Evaluating Finite Sum: Homework Statement

    Homework Statement Find \sum\limits_{k=0}^{n}k^2{n\choose k}(\frac{1}{3})^k(\frac{2}{3})^{n-k} Homework Equations -Binomial theorem The Attempt at a Solution I am using the binomial coefficient identity {n\choose k}=\frac{n}{k}{{n-1}\choose {k-1}}: \sum\limits_{k=0}^{n}k^2{n\choose...
  45. Jonathan Scott

    Unexpected distant values of m/r in a finite universe

    I've often wondered about what happens when you try to add up the potential due to everything in the universe in a Newtonian way, especially in the context of the "Sum for Inertia" which seems to suggest a connection between Mach's Principle and GR in the context of rotation. Today I noticed an...
  46. S

    Universe has to have finite size - doesn't it?

    Hi, one thing always bothered me about the argument on the size of the Universe. If it started about 13.7 bn years ago then how could it possibly be infinite in extent? Once the time was finite its not possible to attain infinite extent - no matter how fast it expands. Also if there was...
  47. azizlwl

    Electric Field Intensity. Finite sheet of charge.

    problem statement, all variables and given/known data A finite sheet of charge, of density ρ=2x(x2+y2+4)^3/2, lies in the z=0 plane for 0≤x≤2m and 0≤y≤2m.Determine E at (0,0,2)m Ans:(18x10^9)(-16/3ax-4ay+8az) Homework Equations E=kQ/R2 The Attempt at a Solution dE=ρdA / R^2 aR...
  48. C

    Transitioning from Finite to Infinite Mass in a Black Hole

    So, according to physicsoftheuniverse.com, "In the centre of a black hole is a gravitational singularity, a one-dimensional point which contains infinite mass in an infinitely small space, where gravity become (sic) infinite and space-time curves infinitely, and where the laws of physics as we...
  49. V

    B Exploring the Finite Speed of Light and its Impact on Relativity

    Light, amount other things, have no mass, and therefore is able to attain the highest speed possible in this universe. Yet for some reason this speed is not infinite, as would what intuition dictate, but has a finite value. Would it be fair to say that the fact light, something that "should" be...
  50. D

    Does a finite universe require 4 spatial dimensions?

    A 2-dimensional creature living on the surface of a 3-dimensional sphere could conclude he lives in a finite, unbounded universe. Is it necessary for a 3-dimensional creature to assume there is a 4th spatial dimension in order to conclude the universe is finite and unbounded? I have seen a...
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