Engineering

[jediali]

function [X,x]=laplace(n,xn,xs,xe,xw)

tol = 10e-10;
h = 1/(n+1);
x = 0:h:1;
X = zeros(n+2,n+2);
Xgammel = zeros(n+2,n+2);

X(n+2,1:n+2) = xn;
X(1,1:n+2) = xs;
X(1:n+2,1) = xe;
X(1:n+2,n+2) = xw;



while max(max(abs(X-Xgammel)))>tol
Xgammel = X;
for i=2:n+1
for j=2:n+1
X(i,j) = (X(i+1,j)+X(i-1,j)+X(i,j+1)+X(i,j-1))/4;
end
end
end

Don't you just love MATLAB?

one i made recently for finite element

% ______ __ ___ ___ ____ ___ __
% | | | \ \ / | | | | | | |\ |
% |____| | \ \ / |__ | | | | | | \ |
% | | | / \ / | | | | | | | \ | /\./\
% | | |_/ \/ |__ |__ | _|_ |__| | \| . | | |
%
% Rev.1 09:00 09-Feb-07
% Rev.2 09:00 23-Feb-07
%------------------------------- Variables -------------------------------%
% u =
% f =
% dx =
% L =
% T =
% Cr =
% A =
% t =
% x =
% --------------------------------- setup ------------------------------- %
clear;clc
u = 5;
f = 0.01;
dx = 1;
L = 20;
T = 20;
Cr = 0.8;
% Courant number
dt = (dx*Cr)/u;
t = [1:dt:T];
x = [1:dx:L];
A = 5;
c=5;
g=9.81;
% -------------------------------- PERIODIC ----------------------------- %

% ------------------------------ Lax scheme ----------------------------- %

HLAX = zeros(1,length(x));
VLAX = zeros(1,length(x));
for i = 1:length(t)
HLAX(i,1) = A*sin(2*pi*f*(t(i)));
VLAX(i,1) = A*sin(2*pi*f*(t(i)));
end
for i = 2:length(t)
for j = 2:length(x)-1
HLAX(i,j) = 0.5*(HLAX(i-1,j+1) + HLAX(i-1,j-1)) - ...
(((c^2)*dt)/(2*g*dx))*(VLAX(i-1,j+1) - VLAX(i-1,j-1));
VLAX(i,j) = 0.5*(VLAX(i-1,j+1) + VLAX(i-1,j-1)) - ...
(((c^2)*dt)/(2*g*dx))*(HLAX(i-1,j+1) - HLAX(i-1,j-1));
end
HLAX(i,length(x)) = 0.5*(HLAX(i-1,length(x)) + HLAX(i-1,length(x)-1)) - ...
(((c^2)*dt)/(2*g*dx))*(VLAX(i-1,length(x)) - VLAX(i-1,length(x)-1));
VLAX(i,j) = 0.5*(VLAX(i-1,length(x)) + VLAX(i-1,length(x)-1)) - ...
(((c^2)*dt)/(2*g*dx))*(HLAX(i-1,length(x)) - HLAX(i-1,length(x)-1));
end
figure(1)
surf(x,t,VLAX)



% -------------------------------DISCONTINUOS --------------------------- %

% ------------------------------ Lax scheme ----------------------------- %

HLAX = zeros(1,length(x));
VLAX = zeros(1,length(x));
for i = 1:length(t);
if i < 6;
HLAX(i,1) = 0;
VLAX(i,1) = 0;
elseif i >= 6;
HLAX(i,1) = 5;
VLAX(i,1) = 0;
end
end
for i = 2:length(t)
for j = 2:length(x)-1
HLAX(i,j) = 0.5*(HLAX(i-1,j+1) + HLAX(i-1,j-1)) - ...
(((c^2)*dt)/(2*g*dx))*(VLAX(i-1,j+1) - VLAX(i-1,j-1));
VLAX(i,j) = 0.5*(VLAX(i-1,j+1) + VLAX(i-1,j-1)) - ...
(((c^2)*dt)/(2*g*dx))*(HLAX(i-1,j+1) - HLAX(i-1,j-1));
end
HLAX(i,length(x)) = 0.5*(HLAX(i-1,length(x)) + HLAX(i-1,length(x)-1)) - ...
(((c^2)*dt)/(2*g*dx))*(VLAX(i-1,length(x)) - VLAX(i-1,length(x)-1));
VLAX(i,j) = 0.5*(VLAX(i-1,length(x)) + VLAX(i-1,length(x)-1)) - ...
(((c^2)*dt)/(2*g*dx))*(HLAX(i-1,length(x)) - HLAX(i-1,length(x)-1));
end
figure(2)
surf(x,t,VLAX)

great a legitimate excuse for matlab on UCP

[Quiggs]

Here's some advanced math for y'all.

[Coventrysucks]

O.K. then;

The maximum allowable working pressure based on inter-stiffener strength is given by:

Pa = Pcη where η = 0.80

Pc = Pm/2 if Pm/Py ≤ 1
Pc = Py[1-Py/(2Pm)] if 1 < Pm/Py ≤ 3
Pc = 5/6Py if Pm/Py > 3

where

Pm = (2.42E[t/(2R)]^5/2)/((1-v^2)^3/4[L/(2R)-0.45(t/(2R))^1/2])

Py = (σyt/R)/(1-F)


For unstiffened cylinders F = 0

R = mean radius (1.5m)

L = length (1m)

t = shell thickness

E = Modulus of Elasticity

v = Poisson's ratio

σy = specified minimum yield point or yield strength

If Pa = 1.65e+7 Pa

Find t

You can choose any material you want, so long as it is transparent and as light as possible.

If I've missed anything vital out, let me know.

TIA

[jediali]

thats buckling using principal stresses isnt it? or at least stiffener calculations for unstiffend (conical?) shells. I generally use this pdf to go through that design procedure as a whole.

I guess if you choose plastic you would need a data sheet showing E, v etc. If you use steel (easier to assume E=210 GPa, v=0.3) it will be easier. can you explain the P subscripts (axial?radial?hoop?), i know y is yield isnt it?

When it comes down to it, it will be a simultaneous equation i assume

[Coventrysucks]

thats buckling using principal stresses isnt it? or at least stiffener calculations for unstiffend (conical?) shells.

Cylindrical, conical ones are even more fun.

can you explain the P subscripts (axial?radial?hoop?)

Pa = maximum allowable pressure for any failure mode
Pc = cylinder inter-stiffener limit pressure
Pm = von Mises buckling pressure for a cylinder
Py = yield pressure at midbay and midplane of a cylinder

I know what I ended up with, I want to see if anyone can do better.

I seem to recall I ended up with about 5 tonnes of acrylic or something.

[blingbling]

okay uhh, im regretting including "computers" in my first post now

ahem anyone can help me out with some 1st yr maths stuff?

[blingbling]

uhh the latter part of the question is simple, just i dont really UNDERSTAND what they need in the first part

[drakkie]

laplace

We are just getting this on school here. Honestly noone in the class understands it.. Not the thing someone likes to do on a early friday morning with 9/10 times a hangover

Matlab is something they assume we have been learned, which we haven't. As you can imagine noone understands it as such and we regularly steal assignments from 3rd year students. Offcourse we said it to teachers more than once, but nothing is done, like a training or something. I'm trying to catch up on my own now, using a training put on our server three years ago...

This is a picture of where I usually spend my coffee time. Working on my laptop on a bench in the fresh air. If you look very closely in real life you can still see where the German bullets hit in WW2.

[LotusLocost]

We are just getting this on school here. Honestly noone in the class understands it.. Not the thing someone likes to do on a early friday morning with 9/10 times a hangover

Matlab is something they assume we have been learned, which we haven't. As you can imagine noone understands it as such and we regularly steal assignments from 3rd year students. Offcourse we said it to teachers more than once, but nothing is done, like a training or something. I'm trying to catch up on my own now, using a training put on our server three years ago...

This is a picture of where I usually spend my coffee time. Working on my laptop on a bench in the fresh air. If you look very closely in real life you can still see where the German bullets hit in WW2.

Thats a surprise coming from you.

[drakkie]

Thats a surprise coming from you.

As if you never stole a piece of candy from the jar, "Mr. Perfect".

In my case here it is not really stealing. About a third of the sums are associated with your own student number. Say 5 x n1 = answer. n1 = the last number of your student number. And we always pay them for their efforts in beer. It's just a thing that happens on schools. Live with it.

[blingbling]

yet another hard to understand question... just matrix manipulation but WHAT ARE THEY ASKING UGH!

[Pitwork]

What is matlab?

[blingbling]

^matlab is a program made by a bunch of students from UW... models math shit

why wont anyone help me

[Mr.Tiv]

This thread makes me glad I didn't go to college.

[my porsche]

This thread makes me glad I didn't go to college.

I see great things in your future.