Multifield coupled analysis for a harmonic movable tooth drive system integrated with shape memory alloys

In this article, a harmonic movable tooth drive system integrated with shape memory alloys is proposed. The key of the system is to integrate the shape memory alloy drive principle with the harmonic movable tooth drive principle by which a small size and a large output torque can be achieved simultaneously. Here the structure of the drive system is determined, and its operating principle is illustrated. The output torque equation for the drive is deduced and coupled dynamics equations for the system are given. With use of these equations, the forces applied to the wave generator and the output torque of the drive system under pulsed current are investigated. The results show that with reasonable pulsed current parameters, a large and steady output torque can be obtained.     

Amplification of surface ground motion by an inclusion of arbitrary shape for harmonic surface line loading

The plane strain model for the Lamb's problem with an elastic inclusion of arbitrary shape embedded completely within an elastic half space is investigated by using an indirect boundary integral equation method for steady-state elastodynamics. The surface of the half space is subjected to vertical or horizontal harmonic line loads. The displacement field is evaluated throughout the elastic medium so that the continuity of the displacement and traction fields along the interface between the half space and the inclusion is satisfied in a least-square sense. The numerical results demonstrate that the presence of the inclusion may cause locally very large amplification of the surface ground motion and that the amplification pattern depends upon the frequency and the type of the input load, the impedance contrast between the half space and the inclusion, the type of the inclusion, and the location of the observation point at the surface of the half space.     

Simulating harmonic oscillator and electrical circuits: a didactical proposal

A Mathematica ^? package is described that uses simulations and animations to illustrate key concepts in harmonic oscillation and electric circuits for students not majoring in physics or mathematics. Students are not required to know the Mathematica^? environment: a user-friendly interface with buttons functionalities and on-line help allows immediate use of the application. Students who are familiar with the programming language have the opportunity to see the set up code that is used, and they can eventually customize it. The goal of the application presented is to enhance student insight, in the spirit of learning by experimentation.     

On a Sachs bound for stress-induced phase transformations in polycrystalline shape memory alloys

In earlier work [3], a Sachs and a Taylor bound on the transformation yield stress in shape memory polycrystals were derived in the context of a variational model. The aim of this article is to compare the Sachs with the Taylor bound for cubic-toorthorhombic phase transformations under biaxial loading, where the material parameters are chosen explicitly (CuAlNi). It turns out that the gap between the two bounds can be quite large depending on the underlying texture and the loading direction. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimal boundary force control at one end of a string for a given displacement mode at the other end

We solve the problem of optimal boundary force control at one end of a string for the case of a given displacement mode at the other end. The problem is studied in the sense of a generalized solution of the corresponding mixed initial-boundary value problem in the Sobolev space. We also solve the problem of choosing an optimal boundary control from infinitely many feasible controls. The generalized solution of the mixed initial-boundary value problem is constructed in closed form, and the uniqueness of the solution is proved.     

Using simple harmonic motion to help in the search for tautochrone curves

The analysis of tautochrone problems involves the solution of integral equations. The paper shows how a reasonable assumption, based on experience with simple harmonic motion, allows one to greatly simplify such problems. Proposed solutions involve only mathematics available to students from first year calculus.     

Large deflections of a cantilever beam under an inclined end load

Large deflections of a cantilever beam subjected to a tip-concentrated load whose inclination to the deformed axis of the beam is assumed as constant. The mathematical formulation yields a non-linear two-point boundary value problem amenable to numerical integration. A relation is obtained between the load and the tip-angle of the beam when the tip-concentrated load is normal to the deformed axis of the beam. Many possible loads are found for a specified tip-angle. For the specified load, the tip-angle is found to be unique. However, there is a change in the deformation pattern of the beam having a specified tip-angle with the corresponding multiple loads. This confirms the uniqueness of the solution for the governing non-linear differential equations of a cantilever beam under a tip-concentrated load whose inclination is normal to its deformed axis.     

A randomized first-passage problem for drifted Brownian motion subject to hold and jump from a boundary

We study an inverse first-passage-time problem for Wiener process X(t) subject to hold and jump from a boundary c. Let be given a threshold S > X(0) ≥ c, and a distribution function F on [0, +∞). The problem consists in finding the distribution of the holding time at c and the distribution of jumps from c, so that the first-passage time of X(t) through S has distribution F.     

Dynamic behavior of an AMB supported rotor subject to harmonic excitation

This paper presents a study of the non-linear response of a simple rigid disk-rotor, supported by active magnetic bearings (AMB), without gyroscopic effects. The case of primary resonance is examined under multi-excitation forces. The rotating shaft is described by a coupled second order non-linear ordinary differential equations. Approximate solutions are sought applying the method of multiple scales. Numerical simulations are carried out to illustrate the steady-state response and the stability of the solutions for various parameters using the frequency response function method. It is shown that the system parameters have different effects on the non-linear response of the rotor. For steady-state response, however, multiple-valued solutions and jump phenomenon occur. Results are compared to previously published work.     

On uniform decay of coupled wave equation of Kirchhoff type subject to memory condition on the boundary

In this paper we prove the existence of solution and uniform decay of energy to the mixed problem for coupled wave equation of Kirchhoff-type subject to memory condition on the boundary.     

Optimal boundary displacement control at one end of a string with a medium exerting resistance at the other end

We study a problem of optimal boundary control of vibrations of a one-dimensional elastic string, the objective being to bring the string from an arbitrary initial state into an arbitrary terminal state. The control is by the displacement at one end of the string, and a homogeneous boundary condition containing the time derivative is posed at the other end. We study the corresponding initial-boundary value problem in the sense of a generalized solution in the Sobolev space and prove existence and uniqueness theorems for the solution. An optimal boundary control in the sense of minimization of the boundary energy is constructed in closed analytic form.     

On a classification of dynamic systems subject to noise

A classification of alternative mathematical schemes which determine possible impositions of noise on dynamic systems either of a continuous or a discrete formulation in time is presented. We refer to the results obtained concerning the influence of noise on the correlation dimension and on the largest Lyapunov exponent. A method of constructing models for effecting predictions of time series with a finite correlation dimension is presented. Numerical results concerning the influence of various level of additive noise to the Henon attractor are also provided.     

On the uniqueness of minimizing harmonic maps to a closed hemisphere

We study the uniqueness of minimizing harmonic maps to a closed hemisphere. We are able to describe the boundary data for which there are more than one minimizer, and to describe in these cases the corresponding set of minimizers. This is a limiting case for a former result of W.Jäger and H.Kaul.This article was processed by the author using the Springer-Verlag T_EX PJourlg macro package 1991.     

On the interrelation between dissipation and chemical energies in modeling shape memory alloys

We use the principle of maximum dissipation for thermo-mechanically coupled modeling of poly-crystalline shape memory alloys (SMA). This modeling scheme demands approaches for both Helmholtz free energy and dissipation. For time-independent processes, dissipation is usually modeled by the norm of the internal variable's rate times a factor. We show that for SMAs this factor is not an additional modeling parameter. In contrast, it can be calculated from the Helmholtz free energy. This reduces the number of model parameters and provides furthermore an interesting effect of the model which allows to display the material behavior in an even more realistic manner. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)