Effects of size-dependent elasticity on stability of nanotweezers

It is well-recognized that the electromechanical response of a nanostructure is affected by its element size. In the present article, the size dependent stability behavior and nanotweezers fabricated from nanowires are investigated by modified couple stress elasticity （MCSE）. The governing equation of the nanotweezers is obtained by taking into account the presence of Coulomb and intermolecular attractions. To solve the equation, four techniques, i.e., the modified variational iteration method （MVIM）, the monotonic iteration method （MIM）, the MAPLE numerical solver, and a lumped model, are used. The variations of the arm displacement of the tweezers versus direct current （DC） voltage are obtained. The instability parameters, i.e., pull-in voltage and deflection of the system, are computed. The results show that size-dependency will affect the stability of the nanotweezers significantly if the diameter of the nanowire is of the order of the length scale. The impact of intermolecular attraction on the size-dependent stability of the system is discussed.

Bifurcation of elastic tank-liquid coupled sloshing system

The nonlinear equations of an elastic tank-liquid coupling system subjected to the external excitation are established.By means of the multi-scale method and the singularity theory,the bifurcation behaviors of the system are investigated and analyzed.The various nonlinear dynamical behaviors of the coupling system are obtained,which can further explain the relationship between the physical parameters and the bifurcation solutions.The results provide a theoretical basis to the realization of the parameter optimal control.

Aeroelastic stability of wing/pylon/rotor coupled system for tiltrotor aircraft in forward flight

An analytical model for aeroelastic stability of the wing/pylon/rotor coupled system with elastic bending-twist coupling wing for tiltrotor aircraft in forward flight has been established in this paper. The investigation is focused on the effectiveness of the wing elastic bending-twist couplings provided by composite wing beam on the aeroelastic stability for the wing/pylon/rotor coupled system. By introducing the different wing elastic bending-twist couplings into the Boeing’s test model, the aeroelastic stability of the Boeing’s test model with different wing elastic bending-twist couplings has been analyzed. The numerical re-sults indicate that the negative wing beamwise bending-twist elastic coupling (the wing upward beamwise bending engenders the nose-down torsion of the wing section) can saliently enhance the stability of the wing beamwise bending modal. The posi-tive wing chordwise bending-twist elastic coupling (the wing forward chordwise bending engenders the nose-down torsion of the wing section) has a great benefit for increasing the stability of the wing chordwise bending modal.

Relection of elastic waves at the elastically supported boundary of a couple stress elastic half-space

The relection elastic waves at the elastically supported boundary of a couple stress elastic half-space are studied in this paper. Different from the classical elastic solid, there are three kinds of elastic waves in the couple stress elastic solid, and two of them are dispersive. The boundary conditions of a couple stress elastic half-space include the couple stress vector and the rotation vector which disappear in the classical elastic solids. These boundary conditions are used to obtain a linear algebraic equation set, from which the amplitude ratios of relection waves to the incident wave can be determined. Then, the relection coeficients in terms of energy lux ratios are calculated numerically, and the normal energy lux conservation is used to validate the numerical results. Based on these numerical results,the inluences of the boundary parameters, which relect the mechanical behavior of elastic support, on the relection energy partition are discussed. Both the incident longitudinal wave（the P wave） and incident transverse wave（the SV wave） are considered.

Dynamic Damage Detection and Assessment on the Bogie Frame of High-Speed Train Based on the Coupled Elastic and Multibody Dynamics Scheme

The dynamic cumulative damage of rigid-flexible coupling model of high-speed train with flexible bogie frame is performed by using the coupled scheme of elastic and multibody dynamics theories.The motion equations of the present problem are firstly established by integrating the finite element method and floating frame of reference approach based on the virtual power principle and D'Alembert principle.The process of condensing the elastic DOFs of the obtained finite element model involving the incorporation of the substructure technique and sparse approximate inverse method is tentatively carried out.Then,the motion equations are further solved by virtue of the generalized α method and the Jacobian-free Newton-Krylov technologies.And the superiority of coupled scheme is proven by comparing with the traditional approach.Finally,besides the dynamic behaviors of the considered vehicle model,the time-variations of stresses on the elastic bogie frame's dangerous nodes and the distributions of stresses of bogie frame at some specified moments are synchronously calculated and analyzed.More importantly,the real-time and time-varying cumulative damages of some typical nodes on bogie frame are investigated.