A proposal for a convertible stadium roof structure derived from Watt-I linkage

In this paper, a novel convertible stadium roof structure is introduced, which has been derived from a special geometric configuration of Watt-I linkage, a 1-DoF mechanism used in robot technologies as anthropomorphic fingers. The proposed structure can offer a wide range of different shape configurations according to the environmental conditions and spatial needs, thus offering several aesthetic and functional advantages over existing solutions. This paper serves as a feasibility investigation of this concept, mainly from geometric and structural point of view. To that affect, first kinematic analysis and geometric design of this linkage are introduced. Then, structural analyses of the proposed structure with realistic dimensions and loading conditions are performed in three different geometric configurations, in order to discuss strength and stiffness limitations. Finally, potential cover materials and actuators are briefly discussed.     

Nonlinear dynamic phenomena in a SDOF model of cable net

The dynamic behavior of the simplest possible cable net is studied in this paper, consisting of two crossing cables in perpendicular vertical planes, having the same span and opposite sags. A concentrated mass is attached at the central node, and only the vertical translational degree of freedom is assumed as active. First, the static behavior is explored up to the load level that causes tensile cable failure. Then, the dynamic response is investigated for different resonant conditions and is found to give significantly larger amplitudes with respect to the static ones, even for loading frequencies away from the eigenfrequency of the system. In order to derive analytical solutions, the equation of motion is simplified and the cable net is proved to be a Duffing oscillator. For the simplified problem, the occurrence of nonlinear phenomena is verified analytically, such as bending of the response curve, jump phenomena, instability regions, dependence on the initial conditions, and superharmonic and subharmonic resonances. These phenomena are also detected by means of numerical analyses. A comparison between the exact model and the simplified one shows that the analytical solution of the Duffing equation describes the dynamic behavior of the cable net with satisfactory accuracy.     

A geometric approach for establishing dynamic buckling loads of autonomous potential N-degree-of-freedom systems

Non-linear dynamic buckling of autonomous non-dissipative N-degree-of-freedom systems whose static instability is governed either by a limit point or by an unstable symmetric bifurcation is thoroughly discussed using energy and geometric considerations. Characteristic distances associated with the geometry of the zero level total potential energy “hypersurface” in connection with total energy-balance equation lead to dynamic (global) instability criteria. These criteria allow the determination of “exact” dynamic buckling loads without solving the non-linear initial-value problem. The reliability and efficiency of the proposed geometric approach is demonstrated via several dynamic buckling analyses of 3-degree-of-freedom systems which subsequently are compared with corresponding numerical analyses based on the Verner–Runge–Kutta scheme.     

Influence of Initial Conditions on the Postcritical Behavior of a Nonlinear Aeroelastic System

The behavior of a nonlinear, non-Hamiltonian system in the postcritical (flutter) domain is studied with special attention to the influence of initial conditions on the properties of attractors situated at a certain point of the control parameter space. As a prototype system, an elastic panel is considered that is subjected to a combination of supersonic gas flow and quasistatic loading in the middle surface. A two natural modes approximation, resulting in a four-dimensional phase space and several control parameters is considered in detail. For two fixed points in the control parameter space, several plane sections of the four-dimensional space of initial conditions are presented and the asymptotic behavior of the final stationary responses are identified. Amongst the latter there are stable periodic orbits, both symmetric and asymmetric with respect to the origin, as well as chaotic attractors. The mosaic structure of the attraction basins is observed. In particular, it is shown that even for neighboring initial conditions can result in distinctly different nonstationary responses asymptotically approach quite different types of attractors. A number of closely neighboring periodic attractors are observed, separated by Hopf bifurcations. Periodic attractors also are observed under special initial conditions in the domains where chaotic behavior is usually expected.     

Modeling and simulation for wear prediction in planar mechanical systems with multiple clearance joints

Nonlinear Dynamics - The main goal of this work is to develop a comprehensive methodology for predicting wear in planar mechanical systems with multiple clearance joints and investigating the...