SDT-base         Contents     Functions         Previous Next     PDF Index

4.6  Sensor and wireframe geometry definition formats

Experimental setups can be defined with a cell arrays containing all the information relative to the sensors and wireframe geometry. This array is meant to be filled any table editor (Excel, CSV, ...), often outside MATLAB. Note you can also use the URN format in many cases section 4.6.4.

Using EXCEL you can read raw data with data=sdtacx('excel read filename',sheetnumber) or use wire=ufread('filename.xlsx') which expects the Nodes, Elements, Sensors tabs.

4.6.1  Sensors tab

The Sensors tab is mandatory and stored in MATLAB as a cell array. The first row gives column labels (the order in which they are given is free). Each of the following rows define a sensor. Known column headers are

triax sensors are dealt with by defining three sensors with the same 'lab' but different 'SensId' and 'DirSpec'. In this case, a straightforward way to define the measurement directions is to make the first axis be the normal to the matching surface. The second axis is then forced to be parallel to the surface and oriented along a preferred reference axis, allowed by the possibility to define 'T*'. The third axis is therefore automatically built so that the three axes form a direct orthonormal basis with a specification such as N^T*. Note that there is no need to always consider the orthonormal basis as a whole and a single trans sensor with either 'T*' or N^T* as its direction of measure can be specified.

4.6.2  Nodes and Elements

Two optional tabs can also be provided to ease the definition of Nodes (especially when triaxes are involved) and Elements. Wireframe is then built on the fly.

Known column headers of the tab Nodes are

Known column headers of the tab Elements are

4.6.3  Example

In the example below, one considers a pentahedron element and aims to observe the displacement just above the slanted face. The first vector is the normal to that face whose coordinates are [−√2/2,√2/2,0]. The second one is chosen (i.) parallel to the observed face, (ii.) in the (x,y) plane and (iii.) along x axis, so that its coordinates are [√2/2,√2/2,0]. Finally, the coordinates of the last vector can only be [0,0,−1] to comply with the orthonormality conditions. The resulting sensor placement is depicted in figure 4.10


         'Tri'     ,1       ,[.4  .6  .5]
         'Mono1'   ,2       ,[.4  .6  .1]
         'Mono2'   ,3       ,'@FEM5'
         'Mono3'   ,4       ,[1   0   0.5]
         'Mono4'   ,5       ,'@FEM6'      };
RO.Elements={'Type' ,'Nodes';
             'mass1',1      ;
             ''     ,2      ;
             ''     ,3      ;
             ''     ,4      ;
             ''     ,5      };
RO.tdof={'tlab'   ,'SensId','DirSpec'   ;
         'Tri:N'  ,1.01    ,'N'         ;
         'Tri:TX' ,1.02    ,'TX'        ;
         'Tri:NTX',1.03    ,'N^TX'      ;
         'Mono1'  ,2.01    ,'dir 1 -1 1';
         'Mono2:X',3.01    ,'FEM 5.01'  ;
         'Mono3:Y',4.01    ,'Y'         ;
         'Mono4:N',5.01    ,'N'         };

cf.mdl=fe_case(cf.mdl,'SensMatch radius1','Test','selface');
fe_sens('tdoftable',cf,'Test') % see summary of match results
% Test write to excel to illustrate ability to reread
if ispc % Only works with ActiveX and MS-Excel at the moment

Figure 4.10: Typical axis definition of a triax sensor attached to a penta6

It is also possible to define sensor orientations and positions using only one cell array, by providing both the DirSpec and the X Y Z or FEMid position like in the example below.

model=demosdt('demo ubeam-pro');
cf=feplot; model=cf.mdl;
n8=feutil('getnode NodeId 8',model); % triax pos.
      'sensor1 - trans','',1,0.0,0.5,2.5,'Z';
      'sensor2 - triax','',2,n8(:,5),n8(:,6),n8(:,7),'X';
      'sensor2 - triax','',3,n8(:,5),n8(:,6),n8(:,7),'Y';
      'sensor2 - triax','',4,n8(:,5),n8(:,6),n8(:,7),'Z'};
cf.mdl=fe_case(cf.mdl,'SensMatch radius1');
fecom(cf,'curtab Cases','output'); % open sensor GUI

4.6.4  URN based handling of sensors

URN (uniform resource names) are being used more consistently throughout SDT and the effort also applies to sensors. nl_inout slab sensors are used for time domain observation (requires SDT-nlsim license) so consistent definitions will be gradually incorporated into SDT-base.

Sensors labels should be in the format BodyName:NodeName:DirSpec when nodes are associated with different bodies or lab:DirSpec. When using repeated superelements, BodyName should be of the form SeName(index).

model = femesh('testubeamt');
%model=fe_case(model,'DofSet','Base','RB{z==0}');%DofSet not FixDof to allow resultant
model=feutil('setmat 1 eta .02',model); % Define loss 
r1=struct('DOF',104.03,'def',1.1); % 1.1 N at node 365 direction z 
model= stack_set(model,'info','Freq',70:80);
try; % Possibly download solver with ofact('patchmkl');
 model=stack_set(model,'info','oProp',mklserv_utils('oprop','CpxSym'));% change solver
C1=fe_simul('DFRF -sens',model);
[sys,TR]=fe2ss('free 5 10 0',model);C2=qbode(sys,C1.X{1}*2*pi,'-struct');
%def=fe_simul('DFRF -sens -UseDofLoad',model);

% Reexpand partial DOF on full DOF 
dgiven=fe_def('subdof',TR,feutil('findnode z<.3',model));
d2=fe_simul('dfrf -matdes 1 3',stack_rm(mo1,'','Freq'));

4.6.5  Mesh cut selections

Volume cuts are often relevant to display internal motion. These commands package calls to the underlying lsutil level set handling utilities.

 model=demosdt('DemoUbeamSens NoPlot');cf=feplot(model,fe_eig(model,[5 20 1e3]))
 % Init phase   ToFace(type,Lc,AngCosMin,epsl)
 % Cut phases using y= and x= planes
cf.sel(1)='urn.SelLevelLines{Init{ToFace 1 .3 .9}}{y,.45 -.45,ByProId}{x,-.45 .0 .45,ByProId}';

feval(sdtm.feutil.MergeSel,'addTestNode',cf); % If you want to keep SensDof nodes and arrows

%fecom('SaveSel','@ProjectWd/selCutA.mat'); % Save selection for later reuse

% Alternate format to initialize geodesic information in SelLevelLines 
% RI=struct('Elt','selface','ToFace',[1 .3 .9]);lsutil('EdgeSelLevelLines',cf,RI)

%% Prepare for restricted superelement import, illustrated in d_cms('TutoAnsCb') 

% Read superelement 
%RO=struct('dtype','MoKTR', ... % Form with mesh, matrices K, restitution TR
%    'RestrictTo',moView, ...  % Restrict TR to view mesh 
%    'Remove','{pl,il}');   % Remove material information 
% SE=sdtm.nodeLoadSE(FileName,RO); 

4.6.6  Sensor GUI, a simple example

Using the feplot properties GUI, one can edit and visualize sensors. The following example loads ubeam model, defines some sensors and opens the sensor GUI.

model=demosdt('demo ubeam-pro');
cf=feplot; model=cf.mdl;

model=fe_case(model,'SensDof append trans','output',...
    [1,0.0,0.5,2.5,0.0,0.0,1.0]); %  add a translation sensor
model=fe_case(model,'SensDof append triax','output',8); % add triax sensor
model=fe_case(model,'SensDof append strain','output',...
    [4,0.0,0.5,2.5,0.0,0.0,1.0]); %  add strain sensor

model=fe_case(model,'sensmatch radius1','output'); % match sensor set 'output'

sdth.urn('Tab(Cases,output){Proview,on}',cf)% open sensor GUI

Clicking on Edit Label one can edit the full list of sensor labels.
The whole sensor set can be visualized as arrows in the feplot figure clicking on the eye button on the top of the figure. Once visualization is activated one can activate the cursor on sensors by clicking on CursorSel. Then one can edit sensor properties by clicking on corresponding arrow in the feplot figure.

The icons in the GUI can be used to control the display of wire-frame, arrows and links.

Figure 4.11: GUI for sensor edition

©1991-2024 by SDTools
Previous Up Next