Need help making function = 0 after certain time period

Hi! My simulation time for this problem is 15050 seconds. I need my qi function to only run from 0,9000 seconds and then go to zero from 9000,15050. I've tried messing around with for and while loops but cant seem to get it to work. Any advice?

clc;close all

%Project to simulate the performance of the reservoir as a sedimentation
%tank
%1/31/2021

%Given
simtime = 15050;             %seconds
n = 500;                     %number of time steps
dt = simtime/(n);           %time step
t = linspace (0,15050,n);    %time

while t > 9000;
    qi = 0
end

   
d = 3;               %orifice diameter in ft
alpha = 0.7  ;        %inflow concentration coefficient
beta = 0.64  ;        %inflow concentration coefficient
r = 9.5*10^-4 ;       %rate of sediment deposition
density = 102  ;      %lb/ft^3 sediment density


g = 32.2;             %gravity acceleration
cd = .65 ;            %discharge coefficient
a = pi*(d.^2)/4;      %cross sectional AREA of pipe
AREA = 600*600 ;      %floor area of storage

%% set up arrays
%Initial conditions

simSize = size(t);
qi = zeros(simSize);
ci = zeros(simSize);
qo = zeros(simSize);
c = zeros(simSize);
s = zeros(simSize);
cs = zeros(simSize);
h = zeros(simSize);
m = zeros(simSize);


%Time loop
for k=2: length(t)
   
  newTime = t(k);                %Get the new time
  
  qiNew = dischargeIn(newTime);     %Get the new fluid inflow
  
  qi(k) = qiNew;                    %Insert new fluid inflow into inflow 
                                    %array
    
  ciNew= flowConcentration(alpha,beta,qiNew); %Concentration in flow
  
  ci(k) = ciNew;                    %Insert new concentration inflow array
  
  hOld = h(k-1);                    %get old height
 
  qoNew = dischargeOut(cd,g,a,hOld);   %use old height to calc outflow
  
  
  qo(k) = qoNew;                     %insert into array
  
  qiOld = qi(k-1);
  ds = storageStep(dt,qiOld,qiNew,qoNew);  %calc change in storage
  
  sOld = s(k-1);               %Get old storage volume
  sNew = sOld + ds;            % Get new storage volume
  s(k) = sNew;                  % Store new volume
  
  hNew = sNew/AREA;         %Get new height
  h(k) = hNew;              %store new height
  
 csOld = cs(k-1);
 ciOld = ci(k-1);
 cOld = c(k-1);
 qoOld = qo(k-1);
  
  csNew = CSTR(cOld,ciOld,csOld,qiOld,qoOld,dt,r);  %calcuate new cs
  cs(k) = csNew;            %store
  
  cNew = concentration(csNew,sNew);
  c(k) = cNew;
  
  dm = ciNew * ds;
  m(k) = m(k-1) + dm;

end

%check

   mi = trapz(t,qi);
   MassIn = sum(mi);

   mo = trapz(t,qo);
   MassOut = sum(mo);

   rcs = r*cs;
   rm = trapz(t,rcs);
   ResidedMass = sum(rm);
    
   TotalMass = MassIn - MassOut - ResidedMass;


    

    

figure(1)
plot(t,ci,t,c)


figure(2)
plot(t,m)




%% functions

function ds = storageStep(dt,qiOld,qiNew,qo)

avg = (qiOld + qiNew)/2;

ds = (avg - qo) * dt;

end

function qo = dischargeOut(cd,g,a,h)

qo = cd*a*sqrt(2*g)*h^.5;

end

function qi = dischargeIn(t)

qi = 750 / pi * (1 - cos ( pi * t /4500 )) ;

end

function ci = flowConcentration (alpha,beta,qi)

ci = alpha * qi^beta;
end


function c = concentration(cs,s)

c = cs/s;

end


function csnew =CSTR(c,ci,cs,qi,qo,dt,r)

csnew = cs + ((ci*qi)- (c*qo)-(r*cs))*dt;

end

Answer 1

[Walter Roberson]

clc;close all

%Project to simulate the performance of the reservoir as a sedimentation
%tank
%1/31/2021

%Given
simtime = 15050;             %seconds
n = 500;                     %number of time steps
dt = simtime/(n);           %time step
t = linspace (0,15050,n);    %time
   
d = 3;               %orifice diameter in ft
alpha = 0.7  ;        %inflow concentration coefficient
beta = 0.64  ;        %inflow concentration coefficient
r = 9.5*10^-4 ;       %rate of sediment deposition
density = 102  ;      %lb/ft^3 sediment density


g = 32.2;             %gravity acceleration
cd = .65 ;            %discharge coefficient
a = pi*(d.^2)/4;      %cross sectional AREA of pipe
AREA = 600*600 ;      %floor area of storage

%% set up arrays
%Initial conditions

simSize = size(t);
qi = zeros(simSize);
ci = zeros(simSize);
qo = zeros(simSize);
c = zeros(simSize);
s = zeros(simSize);
cs = zeros(simSize);
h = zeros(simSize);
m = zeros(simSize);


%Time loop
for k=2: length(t)
   
  newTime = t(k);                %Get the new time
  
  qiNew = dischargeIn(newTime);     %Get the new fluid inflow
  
  if newTime > 9000
     qi(k) = 0;
  else
     qi(k) = qiNew;                 %Insert new fluid inflow into inflow 
                                    %array
  end
    
  ciNew= flowConcentration(alpha,beta,qiNew); %Concentration in flow
  
  ci(k) = ciNew;                    %Insert new concentration inflow array
  
  hOld = h(k-1);                    %get old height
 
  qoNew = dischargeOut(cd,g,a,hOld);   %use old height to calc outflow
  
  
  qo(k) = qoNew;                     %insert into array
  
  qiOld = qi(k-1);
  ds = storageStep(dt,qiOld,qiNew,qoNew);  %calc change in storage
  
  sOld = s(k-1);               %Get old storage volume
  sNew = sOld + ds;            % Get new storage volume
  s(k) = sNew;                  % Store new volume
  
  hNew = sNew/AREA;         %Get new height
  h(k) = hNew;              %store new height
  
 csOld = cs(k-1);
 ciOld = ci(k-1);
 cOld = c(k-1);
 qoOld = qo(k-1);
  
  csNew = CSTR(cOld,ciOld,csOld,qiOld,qoOld,dt,r);  %calcuate new cs
  cs(k) = csNew;            %store
  
  cNew = concentration(csNew,sNew);
  c(k) = cNew;
  
  dm = ciNew * ds;
  m(k) = m(k-1) + dm;

end

%check

   mi = trapz(t,qi);
   MassIn = sum(mi);

   mo = trapz(t,qo);
   MassOut = sum(mo);

   rcs = r*cs;
   rm = trapz(t,rcs);
   ResidedMass = sum(rm);
    
   TotalMass = MassIn - MassOut - ResidedMass;


    

    

figure(1)
plot(t,ci,t,c)


figure(2)
plot(t,m)




%% functions

function ds = storageStep(dt,qiOld,qiNew,qo)

avg = (qiOld + qiNew)/2;

ds = (avg - qo) * dt;

end

function qo = dischargeOut(cd,g,a,h)

qo = cd*a*sqrt(2*g)*h^.5;

end

function qi = dischargeIn(t)

qi = 750 / pi * (1 - cos ( pi * t /4500 )) ;

end

function ci = flowConcentration (alpha,beta,qi)

ci = alpha * qi^beta;
end


function c = concentration(cs,s)

c = cs/s;

end


function csnew =CSTR(c,ci,cs,qi,qo,dt,r)

csnew = cs + ((ci*qi)- (c*qo)-(r*cs))*dt;

end

[Walter Roberson]

Are you certain you want to use the calculated qiNew value even in the cases where t > 9000 ? You only asked for qi to become 0 in that case, so that is all I coded, leaving qiNew alone. If you want to use the 0 for qiNew then:

  
  if newTime > 9000
     qiNew = 0;
  else
      qiNew = dischargeIn(newTime);     %Get the new fluid inflow
  end
  
  qi(k) = qiNew;                 %Insert new fluid inflow into inflow 
                                    %array
  

[Mackenzie Weeks]

you're right i dont! qinew should also become zero

[Mackenzie Weeks]

thanks a ton!