Adaptive control of a micromachined continuous-membrane deformable mirror for aberration compensation

The nonlinear response and strong coupling of control channels in micromachined membrane deformable mirror (MMDM) devices make it difficult for one to control the MMDM to obtain the desired mirror surface shapes. A closed-loop adaptive control algorithm is developed for a continuous-surface MMDM used for aberration compensation. The algorithm iteratively adjusts the control voltages of all electrodes to reduce the variance of the optical wave front measured with a Hartmann-Shack wave-front sensor. Zernike polynomials are used to represent the mirror surface shape as well as the optical wave front. An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels. The experimental results show that the algorithm can adaptively update control voltages to generate an optimum continuous mirror surface profile, compensating for the aberrations within the operating range of the deformable mirror.     

Nanovesicular carrier-mediated transdermal delivery of tadalafil: i- formulation and physicsochemical characterization

The limited permeability of stratum corneum, the main skin barrier, towards pharmaceutical active ingredients represents the main obstacle encounter the transdermal drug delivery system. In the current study, penetration enhancer-containing nanoliposomes, that is, penetrosomes were formulated incorporating tadalafil to enhance its transdermal permeability. Hydration-sonication method was used to prepared penetrosomes bearing tadalafil. The prepared nanocarriers were characterized in terms of vesicles shape and surface morphology, size and size distribution, zeta potential, entrapment efficiency, and elasticity. Results pointed to that penetrosomes were spherical in shape with a unilamellar-closed structure in the nanometric narrow size range proved by their law span index. Penetrosomes formulations elaborated deformable vesicles more than the conventional liposomes, with the Penetrosomes-based Labrasol® being the most deformable formulation. Penetrosomes-ultraelastic nanoliposomes represent an attractive vehicle for transdermal delivery of tadalafil to treat erectile dysfunction.     

Size-dependent behaviour of electrically actuated microcantilever-based MEMS

In this paper, the nonlinear size-dependent static and dynamic behaviours of a microelectromechanical system under an electric excitation are investigated. A microcantilever is considered for the modelling of the deformable electrode of the MEMS. The governing equation of motion is derived based on the modified couple stress theory (MCST), a non-classical model capable of capturing small-size effects. With the aid of a high-dimensional Galerkin scheme, the nonlinear partial differential equation governing the motion of the deformable electrode is converted into a reduced-order model of the system. Then, the pseudo-arclength continuation technique is used to solve the governing equations. In order to investigate the static behaviour and static pull-in instabilities, the system is excited only by the electrostatic actuation (i.e., a DC voltage). The results obtained for the static pull-in instability predicted by both the classical theory and MCST are compared. In the second stage of analysis, the nonlinear dynamic behaviour of the deformable electrode due to the AC harmonic actuation is investigated around the deflected configuration, incorporating size dependence.     

Wave motion in magnetizable deformable solids

A thorough review of the main advances concerning both linear and nonlinear wave propagations in magnetizable deformable solids is presented. Most of the cases which can present themselves depending on the state of magnetism and electrical conduction of the material solids are examined. General features such as the influence of strong bias magnetic fields and the introduction of small parameters which bring corrections to classical results of elasticity theory are systematically investigated. In particular, a special attention is devoted to harmonic-wave propagation in hyperelastic, nonlinear magnetic, dielectrics, to harmonic-wave propagation in nonlinear elastic conductors, to weak-discontinuity propagation in nonlinear elastic conductors, to nonlinear waves (shocks and simple waves) in perfectly conducting nonlinear elastic conductors, and to magneto-thermo-elastic waves in linear elastic conductors. Finally, a long section is devoted to a case which probably is more important from the viewpoint of electronic devices, that of coupled magnetoelastic waves in magnetically ordered deformable solids, such as ferromagnets and ferrimagnets, that they be insulators or electricity conductors. All these results are cast in the unifying formalism of contemporary continuum mechanics although they obviously are of interest in many fields of research and engineering applications (seismology, astrophysics, measuring devices, signal processing, etc). Although theoretical in nature, this review also tries to pinpoint the various fields of applications and the special effects of practical interest.     

Computational and experimental crash analysis of the road safety barrier

The paper describes the computational analysis and experimental crash tests of a new road safety barrier. The purpose of this research was to develop and evaluate a full-scale computational model of the road safety barrier for use in crash simulations and to further compare the computational results with real crash test data. The impact severity and stiffness of the new design have been evaluated with the dynamic nonlinear elasto-plastic analysis of the three-dimensional road safety barrier within the framework of the finite element method with LS-DYNA code. Comparison of computational and experimental results proved the correctness of the computational model. The tests have also shown that the new safety barrier assures controllable crash energy absorption which in turn increases the safety of vehicle occupants.     

基于磁流变阻尼器的汽车悬架半主动相对控制

以磁流变阻尼器作为汽车悬架的阻尼器,采用一种改进的Bingham模型来描述磁流变阻尼力,分析比较了线性相对控制,非线性相对控制和基于相对控制的改进的次最优控制在汽车悬架半主动控制中的控制效果.研究结果表明,非线性相对控制的控制效果较单纯的线性相对控制要好,而基于相对控制的次最优控制在总体控制效果上要优于其它两种控制,证实了磁流变阻尼器应用于汽车半主动相对控制的可行性及优越性.     

Invariant manifolds describing the dynamics of a hyperbolic-parabolic equation from nonlinear viscoelasticity

The governing equations for a collection of dynamical problems for heavy rigid attachments carried by light, deformable, nonlinearly viscoelastic bodies are studied. These equations are a discretization of a nonlinear hyperbolic-parabolic partial differential equation coupled to a dynamical boundary condition. A small parameter measuring the ratio of the mass of the deformable body to the mass of the rigid attachment is introduced, and geometric singular perturbation theory is applied to reduce the dynamics to the dynamics of the slow system. Fenichel theory is then applied to the regular perturbation of the slow system to prove the existence of a low-dimensional invariant manifold within the dynamics of the high-dimensional discretization.     

Comparison of the energy absorption capability of crash boxes assembled by spot-weld and continuous joining techniques

The design of vehicle front structures for crashworthiness is nowadays commonly based on a series of rigid subsystems that constitute a nearly undeformable survival cell for the passengers, and deformable subsystems able to efficiently dissipate the vehicle kinetic energy. During frontal crash, which is by far the most dangerous impact situation, the front rails represent the main deformable components aimed to dissipate the kinetic energy of the vehicle, therefore their behaviour is crucial to obtain good vehicle performance, with stable and controlled energy dissipation. The design of the front rail, usually consisting of a thin-walled prismatic column, requires definition of the geometry, that is, of the shape and dimensions of the cross section, of the thickness of the material, and of the material itself.     

Stability of Euler's method for evaluating large deformation of shear deformable plates by dual reciprocity boundary element method

In this paper the dual reciprocity boundary element method (DRBEM) is employed to evaluate large deformations of shear deformable plates. Incremental approaches utilizing the Euler method and the total incremental method are used for treating the nonlinear problems. A simple numerical algorithm for analyzing the problems is presented. Two numerical examples of square plates with different boundary conditions subjected to transverse loadings are presented to demonstrate the accuracy of the formulation. The Euler method seems to be a more stable method for treating nonlinear problems of the shear deformable plate if the dual reciprocity method is employed to evaluate the domain integrals that appear in the formulations.     

Improving the crashworthiness of reinforced wooden road safety barrier using simulations of pre-stressed bolt connections with failure

During the development process of a new type of steel reinforced wooden road safety barrier parametric computational simulations were used to simulate the experimental vehicle impact certification tests as prescribed by the standard EN 1317. First a detailed study of pre-stressed bolt connection behavior between the guardrail and the guardrail connector was performed using parametric computational simulations of which results were later used in a large scale vehicle impact simulations. A novel, simplified approach to the modeling of barrier wooden parts was introduced to achieve reasonable simulation times in parametric study of the barrier behavior under vehicle impact. The wooden parts of the road safety barrier were modeled indirectly through a modified contact definition. The developed safety barrier design was later successfully experimentally certified in a full scale crash test according to the standard EN 1317. Experimental results were in a good agreement with the results of the full scale crash test simulations, which validates the proposed computational safety barrier model and thus justifies the use of the simplified modeling approach of the wooden safety barrier parts.     

A model for hydrodynamic influence on a multi-layer deformable coal seam

The paper suggests a mathematical model of hydrodynamic influence on a multi-layer deformable coal seam, based on transient poroelastic equations with regard to nonlinear dependence on the pressure for the filtration coefficients. For numerical simulation a general problem setting is given, and the semi-discrete finite element approximations and time integration schemes for the equations of the finite element method are provided. By using an analogy between poroelasticity and thermoelasticity the transient nonlinear poroelastic problem obtained is solved as a corresponding thermoelastic problem. As example, an axisymmetrical problem with input data corresponding to a real-world experiment of a hydrofracture in a three-layer coal seam is considered. The computational results allowed to estimate the radius of the degassing zone and verify the results obtained previously for a pure filtration problem.     

护栏碰撞中车体加速度敏感性分析

碰撞参数在试验组织中会产生误差,为了解车体冲击加速度指标对碰撞参数的敏感程度,建立车辆碰撞某组合式护栏有限元仿真模型,运用碰撞试验对有限元模型的可靠性进行验证后,进行敏感性分析。结果表明,仿真与碰撞试验结果相符,验证了仿真方法的可靠性;车体冲击加速度指标对车辆质量、碰撞角度与碰撞速度参数的敏感度系数分别为-0.58、1.63、4.18,碰撞速度是影响车体冲击加速度的最敏感因素。研究成果为制定碰撞试验误差范围有指导意义。     

有限元仿真方法评价护栏安全性能的可行性

建立多种车辆和护栏有限元仿真模型,运用多次碰撞试验数据对仿真模型计算结果进行比对,对采用有限元仿真方法评价护栏安全性能的可行性进行分析。研究结果表明,仿真计算可以得到车辆行驶轨迹、结构防护导向、乘员风险和动态变形等护栏安全评价的各项指标,仿真结果与试验结果一致,误差在10%以内,验证了建模方法的正确性,运用有限元仿真方法评价护栏安全性能具有较高可行性。强调运用评价护栏安全性能的仿真模型须通过碰撞试验校核,同时建议通过法规和准则对从事护栏评价CAE工程师进行职业管理。     

Nonlinear free vibration of non-prismatic single-walled carbon nanotubes by a non-local shear deformable beam p-element

The nonlinear free vibration of non-prismatic single-walled carbon nanotubes (SWNTs) is studied using a new non-local shear deformable beam p-element. The effects of the internal length scale parameter, transverse shear deformation, rotary inertia, and geometrical nonlinearity are taken into account. The principle of virtual displacements and the harmonic balance method are used to derive the nonlinear equations of motion, which are solved iteratively by the linearized updated mode method to obtain the fundamental nonlinear frequencies and mode shapes of H–H, C–H, and C–C SWNTs with uniform, linear, and quadratic radius variation. The convergence and accuracy of the non-local shear deformable beam p-element are demonstrated through comparison with other methods. It is shown that the non-uniformity parameters influence significantly the backbone curves and mode shapes of non-prismatic SWNTs.     

Finite element analysis of occupant head injuries: Parametric effects of the side curtain airbag deployment interaction with a dummy head in a side impact crash

In this study, we investigated and assessed the dependence of dummy head injury mitigation on the side curtain airbag and occupant distance under a side impact of a Dodge Neon. Full-scale finite element vehicle simulations of a Dodge Neon with a side curtain airbag were performed to simulate the side impact. Owing to the wide range of parameters, an optimal matrix of finite element calculations was generated using the design method of experiments (DOE); the DOE method was performed to independently screen the finite element results and yield the desired parametric influences as outputs. Also, analysis of variance (ANOVA) techniques were used to analyze the finite element results data. The results clearly show that the influence of moving deformable barrier (MDB) strike velocity was the strongest influence parameter on both cases for the head injury criteria (HIC36) and the peak head acceleration, followed by the initial airbag inlet temperature. Interestingly, the initial airbag inlet temperature was only a ~30% smaller influence than the MDB velocity; also, the trigger time was a ~54% smaller influence than the MDB velocity when considering the peak head accelerations. Considering the wide range in MDB velocities used in this study, results of the study present an opportunity for design optimization using the different parameters to help mitigate occupant injury. As such, the initial airbag inlet temperature, the trigger time, and the airbag pressure should be incorporated into vehicular design process when optimizing for the head injury criteria.     

Trajectory Optimization for a Multi-Stage Launch Vehicle Using Time Finite Element and Direct Collocation Methods

An indirect time finite element method is applied to solve the trajectory optimization problem for a multi-stage launch vehicle, and the numerical results are compared with the numerical solutions obtained by using a direct collocation and nonlinear program-ming method. A nonlinear programming problem is solved by the sequential quadratic programming algorithm with an augmented Lagrangian merit function, and the converged Lagrange multiplier is used for estimating the costate variables of the optimal trajectory. As a numerical example, a multi-stage launch vehicle trajectory optimization problem with a control variable constraint is solved, and the results are compared.     

Synchronization in a steer-by-wire vehicle dynamic system

This work verifies the chaotic motion of a steer-by-wire vehicle dynamic system, and then elucidates an application of the synchronization to a vehicle model to control the chaos. The largest Lyapunov exponent is estimated from the synchronization to identify periodic and chaotic motions. Then, a bifurcation diagram reveals complex nonlinear behaviors over a range of parameter values. Finally, a continuous feedback control method based on the synchronization characteristics is presented to control a chaotic vehicle handling and steering system. The designed controller is demonstrated to work quite well for nonlinear systems in achieving robust stability and protecting the vehicle from slip or spin. Some simulation results are presented to establish the feasibility of the proposed method.     

Inverse problems in the presence of inclusions and unilateral constraints: a boundary element approach

The authors present a boundary element method (BEM) numerical procedure for the solution of 2D non-destructive identification problems in the presence of unilateral boundary conditions. Firstly, the position of a deformable inclusion in frictionless unilateral contact with the matrix is identified on the basis of measurements surveyed at some sensor points on the external boundary where given static loads are applied (identification problem). Then the procedure used is extended to the identification of the position which a rigid/deformable inclusion must occupy within the matrix in order to maximise the structural stiffness of the matrix-inclusion system under prescribed external loads (optimisation problem). Matrix and deformable inclusion are both considered linear elastic. A minimisation problem is stated with design variables representing the size and the shape of the inclusion. The cost function is an error function that evaluates the difference between computed and observed displacements at the sensor points in the identification problem and the strain energy accumulated by the matrix-inclusion system in the optimisation problem. The minimisation is performed by using a first-order nonlinear optimisation technique in which the cost function gradient is computed by implicit differentiation. Some simple but meaningful examples are presented and discussed in order to show the applicability of the proposed technique. Received 30 August 2000     

Application of eigenmode in the adaptive optics system based on a micromachined membrane deformable mirror

The construction process and characteristics of a deformable mirror eigenmode are introduced. The eigenmode of a 37-element micromachined membrane deformable mirror (MMDM) from OKO, Ltd. is analyzed. The Gaussian-Seidel low-order aberrations are fitted with eigenmodes as basic functions. An experimental adaptive optics (AO) system is constructed with the MMDM as the wavefront corrector, a deformable mirror eigenmode as the wavefront control algorithm, and a Shack-Hartmann wavefront sensor as the wavefront detector. The experimental results demonstrate that the deformable mirror eigenmode can act as the wavefront control algorithm for the AO system based on the MMDM.     

Geometrically nonlinear gravito-elasticity: Hyperelastostatics coupled to Newtonian gravitation

A theory of nonlinear elasticity is presented that incorporates a spatially non-constant Newtonian gravitational field as is appropriate if deformable heavy masses of finite volume are considered. For Newtonian gravitation the mass density is a sink for the (scaled) gravitational field. This Gauss-type law for gravitation is incorporated into the mechanical balance equations of linear and angular momentum as well as into the thermomechanical balance equations of energy and entropy. To this end, a total energy density as well as total Piola and Cauchy stresses are introduced that directly capture the contribution of Newtonian gravitation. For the nonlinear elastic case the pertinent relations for the gravito-elastically coupled problem are recovered from a variational setting in terms of the nonlinear deformation map and a gravitational potential.