Gforge Advanced Server - SDT Support - Answers and discussion Gforge Advanced Server RSS Re: VoltageMarwa Mallouli <> Dear Mr Arnaud Please, can i send you all my work to verify it ? Re: VoltageMarwa Mallouli <> Dear Mr Arnaud I want to develop an analytical model of a bimorph cantilever beam with tip mass. Please can you help me to change the equations ?   Re: VoltageArnaud Deraemaeker <> Dear Marwa, You are using an anaytical formula based on a 1D approximation of the patch, which is not representative of the true behavior of your piezoelectric patch, so that your FRF is probably not representative of the behavior of your system. I advise you to use the piezoelectric models available in SDT in order to do a proper finite element modeling of this system. See the tutorial and examples in Arnaud Re: VoltageMarwa Mallouli <> Hello The shape of the beam is  figure 1 (the bimorph is composed of  two piezoelectric MFC patches below and above the beam) The input is attached. The output is the voltage formula is mentioned in the figure 1.   Re: VoltageArnaud Deraemaeker <> Dear Marwa, Can you provide the source code ? It is not possible to answer your question without knowing the shape of your beam as well as what is the input/output of your FRF. Arnaud VoltageMarwa Mallouli <>  Hello The response of a bimorph cantilever beam with piezoelectric patches is attached (Voltage). Please can you indicate me if the shape with anti-resonance is true or not ? How to compute geometric stiffness for volumesEtienne Balmes <> Question : I would like to account for stiffening effects due to pretension in computing modes of a volume structure. Answer : stiffnening effects are due to the existence of geometrically non-linear effects. You must thus Perform a static computation to your loads (calling fe_simul static for example) and store the response in the stack as mdl=stack_set(mdl,'curve','StaticState',def). Assemble matrices that account for prestiffening effects (note the MatDes=5 and not 1). Typically a call of the form  [SE,Case]=fe_case(mdl,'assemble -matdes 2 5 -SE NoT') Compute modes  def=fe_eig({SE.K,Case.T},eigopt) Re: white noise excitationSarehati Umar <>   I want to simulate a structure with white noise excitations to get the raw time-series output data. How can I do that using fe_time?   Thank you. Global/local matricesEtienne Balmes <> Question : I have created a model and I use these functions:          mo4=fe_case(mo4,'FixDof','clamped dofs','z==0');           [mo4,Case]=fe_case('assemble -MatDes 2 1 -NoT -SE',mo4);  The output we obtain are here Stiffness and Mass matrices. Are these Global or Local Stiffness/Mass matrices??   Answer : I don’t know what you call local mass matrices. So the answer is global. If you want matrices in local coordinates, then you need to look up the basis trans comman. When importing local coordinate definitions (DID in column 3 of nodes) you will be able to build the local to global coordinate transformation matrix (cGL) which is used as q_global = cGL q_local     Windows / MATLAB > 2014b bug : zoom corrupts screenEtienne Balmes <> A recent windows update has generated a major bug where calling rbbox for zooming corrupts the screen and shows black squares (or previous screens). This is being investigated by The MathWorks but you can use the following work-around. add the attached rbbox2.m file to the $matlabroot/toolbox/sdt/private directory run rehash toolboxreset to refresh your toolbox path edit iimouse.m too call rbbox2 : in iimouse replace the string rbbox by rbbox2. You can open at the proper line using sdtweb('iimouse','rbbox')   Re: white noise excitationEtienne Balmes <> Could you be more precise. How do you want the solution to be computed ? time/frequency iterations see script in : sdtweb d_signal shaker time integration in state-space/simulink time integration with SDT fe_time with that info, I will generate an example. white noise excitationSarehati Umar <>  Do you have a demo for a structure which are under white noise excitation? Re: Base excitationEtienne Balmes <> For harmonic enforced displacement you should use a DofSet entry in fe_simul dfrf. Obviously the node with enforced motion must be part of the model. Base excitationMarwa Mallouli <> Hi, I have done a program that analyse the behavior of a three node cantilever beam but i want to add the harmonic base excitation at the clamped end. If i will make difference in the node matrix (especially the node1) : %    node#  unused         x             y          z node=[ 1    0 0 0              0             0          0;               2    0 0 0       2.5e-03        0          0;               3    0 0 0       5e-03           0          0;               4    0 0 0         1                  1         1]; What should i do? Please help me     Re: Piezo layer Etienne Balmes <> elt is a Matlab matrix, you must keep the number of colums constant. You can also use the utilities :feutil addelt elt=[ %declaration of element groupe     Inf abs('beam1') 0  %node1   node2    pl     il     refnode    1       2       1      1          22       0    0%longerons    2       3       1      1          22       0    0    3       4       1      1          22       0    0]; elt=feutil('addelt',elt,'mass1', ...    [4     0.0012   0.0012   0.0012    0        0    0]); elt=feutil('addelt',elt,'piez1', ...   [1       2       1      1          22       0    0%longerons    2       3       1      1          22       0    0    3       4       1      1          22       0    0]);   Piezo layer Marwa Mallouli <>  Hi I have done a program that analyse the behavior of a cantilever bema with tip. Now i want to add two piezo layers (bimorph) ,having the same lenght and widht of the beam, and analyse its behavior. Can you correct me the elt vector? elt=[ %declaration of element groupe     Inf abs('beam1') 0  %node1   node2    pl     il     refnode    1       2       1      1          22       0    0%longerons    2       3       1      1          22       0    0    3       4       1      1          22       0    0   elt= [elt ; Inf abs('mass1') 0    4     0.0012   0.0012   0.0012    0        0    0]; elt=[elt; Inf abs('piez1') 0   1       2       1      1          22       0    0%longerons    2       3       1      1          22       0    0    3       4       1      1          22       0    0];   and eltp=[ Inf abs('piez1') 0   1       2       1      1          22       0    0%longerons    2       3       1      1          22       0    0    3       4       1      1          22       0    0]; piez1 is the same function of beam1 but the pl, il, elt are changed function [m,k,idof]=piez1(node,eltp,plp,ilp)       Please help me. Re: Natural frequencyEtienne Balmes <> Sorry but this questions is not related to SDT. And I doubt it would be exact (0.23 migth be an approximation). Natural frequencyMarwa Mallouli <>  Hi The natural frequency of at twenty-element beam with tip mass is : W=(beta*l^2)*sqrt((3EI/(Mtip+0.23Mbeam)*l^3) Is it true ? Re: Input / output responseMarwa Mallouli <>  size(mode)=40*40 size(b)=126*1   Re: Input / output responseMarwa Mallouli <>  The error is : Error using  *  Inner matrix dimensions must agree. bp=mode'*b;