Transforming Knowledge to Structures from Other Engineering Fields by Means of Graph Representations. Dr. Offer Shai and Daniel Rubin Department of Mechanics, Materials and Systems Faculty of Engineering Tel-Aviv University

Outline of the Talk Transforming knowledge through the graph theory duality. Practical applications – Checking truss rigidity. – Detecting singular positions in linkages. – Deriving a new physical entity – face force. Further research – form finding problems in tensegrity systems.

Kinematical Linkage Constructing the graph corresponding to the kinematical linkage Joints  Vertices Links  Edges O1O1 O2O2 O3O3 O4O4 A B C D E O4O4 O 1 A 9

Kinematical Linkage Joints  Vertices Links  Edges O1O1 O2O2 O3O3 O4O4 B C D E O4O4 A O 1 A B Constructing the graph corresponding to the kinematical linkage

Kinematical Linkage Joints  Vertices Links  Edges O1O1 O3O3 O4O4 B C D E O4O4 A 9 A O 1 B 2 9 C 3 D 4 5 O2O2 Constructing the graph corresponding to the kinematical linkage

Kinematical Linkage Joints  Vertices Links  Edges O1O1 O2O2 O3O3 O4O4 B C D E O4O4 A 9 A O 1 B 2 9 C 3 D 4 5 E Constructing the graph corresponding to the kinematical linkage

The variables associated with the graph correspond to the physical variables of the system Joint velocity  Vertex potential Link relative velocity  Edge potential difference

The potential differences in the graph representations satisfy the potential law Sum of potential differences in each circuit of the graph is equal to zero = polygon of relative linear velocities in the mechanism

Static Structure Now, consider a plane truss and its graph representation Joints  Vertices Rods  Edges O A O A

Static Structure Rod internal force  Flow through the edge Now, consider a plane truss and its graph representation

Static Structure The flows in the graph satisfy the flow law Sum of the flows in each cutset of the graph is equal to zero = force equilibrium

Constructing the dual graph - Face - circuit forming a non- bisected area in the drawing of the graph. - For every face in the original graph associate a vertex in the dual graph. - If in the original graph there are two faces adjacent to an edge – e, then in the dual graph the corresponding two vertices are connected by an edge e’.

Constructing the dual graph

Consequently there is a duality between linkages and plane trusses

Kinematical Linkage Static Structure The relative velocity of each link of the linkage is equal to the internal force in the corresponding rod of its dual plane truss.

Kinematical Linkage Static Structure The equilibrium of forces in the truss = = compatibility of the relative velocities in the dual linkage

Definitely locked !!!!! Rigid ???? 8 12’ 2’ 1’ 11’ 10’ 6’ 7 ’ 3’ 5’ ’ 9’ R’ 4’ 12’ 9’ 10’ R’ 11’ 6’ 7’ 8’ 2’ 3’ 5’ 1’ 4’ Due to links 1 and 9 being located on the same line Checking system rigidity through the duality

Using duality relation to detect singular positions Linkages Plane Trusses Potential difference = = Linear relative velocity Flow = = Force Sum of potential differences at any circuit equals to zero Sum of flows at any cutset equals to zero Flow = Force Potential Difference = Displacement Sum of flows at any cutset equals to zero Sum of potential differences at any circuit equals to zero Kinematical AnalysisStatical Analysis Deformation AnalysisSingular position detection

A' B' C' A π  B π  C π  A B C Deformations Forces Mechanism in singular position Using duality relation to detect singular positions

Kinematical Linkage Static Structure Deriving a new entity – face force == dual to the absolute linear velocity in the dual linkage ?

Face force – a variable associated with each face of the structures The internal force in the element of the structure is equal to the vector difference between the face forces of the faces adjacent to it

Face force – a variable associated with each face of the structures Face forces can be considered a multidimensional generalization of mesh currents.

It was proved that face forces manifest some properties of electric potentials.

The works of Maxwell reaffirm some of the results derived through the graph representations, among them: duality between linkages and trusses, face force, and more …

Maxwell Diagram lines in the diagram are associated with the rods of the structure II VI III V I IV O III IV

The coordinates of the points in the Maxwell diagram correspond to the face forces in the corresponding faces of the truss II VI III V I IV O III IV

Verifying truss-linkage duality through the work of Maxwell II III IV O V I VI O1O1 O2O2 O3O3 O4O4 III IV

Verifying truss-linkage duality through the work of Maxwell III IV

Verifying truss-linkage duality through the work of Maxwell III IV

Further research – form finding problem in tensegrity systems A B C D Tensegrity system at unstable configuration III I II O C D A B Graph representation of the tensegrity system II III I Arbitrary chosen faces forces Resulting stable configuration of the tensegrity system

Thank you!!! For more information contact Dr. Offer Shai Department of Mechanics, Materials and Systems Faculty of Engineering Tel-Aviv University This and additional material can be found at: