Design and experimental validation of a nonlinear controller for underactuated surface vessels

Nonlinear Dynamics - This paper addresses the problem of trajectory tracking control of an underactuated surface vessel moving in a two-dimensional space in the presence of unknown disturbances. In...     

A projection scheme for incompressible multiphase flow using adaptive Eulerian grid: 3D validation

A three‐dimensional finite element method for incompressible multiphase flows with capillary interfaces is developed based on a (formally) second‐order projection scheme. The discretization is on a fixed (Eulerian) reference grid with an edge‐based local h‐refinement in the neighbourhood of the interfaces. The fluid phases are identified and advected using the level‐set function. The reference grid is then temporarily reconnected around the interface to maintain optimal interpolations accounting for the singularities of the primary variables. Using a time splitting procedure, the convection substep is integrated with an explicit scheme. The remaining generalized Stokes problem is solved by means of a pressure‐stabilized projection. This method is simple and efficient, as demonstrated by a wide range of difficult free‐surface validation problems, considered in the paper. Copyright © 2005 John Wiley & Sons, Ltd.     

Double rolling isolation systems: A mathematical model and experimental validation

Rolling isolation systems (RISs) protect fragile building contents from earthquake hazards by decoupling horizontal floor motions from the horizontal responses of the isolated object. The RISs in use today have displacement capacities of about 20 cm. This displacement capacity can be increased by stacking two systems. This paper presents and evaluates a complete non-linear model of the coupled dynamics of double RISs. The model is derived through the fundamental form of Lagrange׳s equation and involves the non-holonomic constraints of spheres rolling between non-parallel surfaces. The derivation requires the use of two translating and rotating reference frames. The proposed model is validated through comparisons between experimentally measured and numerically predicted time histories and peak response quantities—total acceleration and relative displacement. The effects of the initial conditions, the mass of the isolated object, and the amplitude and period of the disturbance on the system׳s performance are assessed.     

Modeling of metallic foam morphology using the Representative Volume Element approach: Development and experimental validation

This paper focuses on the development of an algorithm capable of generating morphologically-representative foam structures using the Representative Volume Element (RVE) approach. Stereology, a sampling method based on direct observations of the foam cross-sections, is used to characterize the pore size and shape distributions. Using the morphology generation algorithm, the smallest RVEs corresponding to the numerically-convergent foam morphologies are calculated for different foam porosities. To validate the foam generation algorithm, the pore size and shape distributions of the numerically-generated foams are compared to those of the titanium foams manufactured by the space holder method.     

A two-dimensional effective model describing fluid–structure interaction in blood flow: analysis, simulation and experimental validation

We derive a closed system of effective equations describing a time-dependent flow of a viscous incompressible Newtonian fluid through a long and narrow elastic tube. The 3D axially symmetric incompressible Navier–Stokes equations are used to model the flow. Two models are used to describe the tube wall: the linear membrane shell model and the linearly elastic membrane and the curved, linearly elastic Koiter shell model. We study the behavior of the coupled fluid–structure interaction problem in the limit when the ratio between the radius and the length of the tube, , tends to zero. We obtain the reduced equations that are of Biot type with memory. An interesting feature of the reduced equations is that the memory term explicitly captures the viscoelastic nature of the coupled problem. Our model provides significant improvement over the standard 1D approximations of the fluid–structure interaction problem, all of which assume an ad hoc closure assumption for the velocity profile. We performed experimental validation of the reduced model using a mock circulatory flow loop assembled at the Cardiovascular Research Laboratory at the Texas Heart Institute. Experimental results show excellent agreement with the numerically calculated solution. Major applications include blood flow through large human arteries. To cite this article: S. Čanić et al., C. R. Mecanique 333 (2005).     

A new heat transfer analysis in machining based on two steps of 3D finite element modelling and experimental validation

Modelling machining operations allows estimating cutting parameters which are difficult to obtain experimentally and in particular, include quantities characterizing the tool-workpiece interface. Temperature is one of these quantities which has an impact on the tool wear, thus its estimation is important. This study deals with a new modelling strategy, based on two steps of calculation, for analysis of the heat transfer into the cutting tool. Unlike the classical methods, considering only the cutting tool with application of an approximate heat flux at the cutting face, estimated from experimental data (e.g. measured cutting force, cutting power), the proposed approach consists of two successive 3D Finite Element calculations and fully independent on the experimental measurements; only the definition of the behaviour of the tool-workpiece couple is necessary. The first one is a 3D thermomechanical modelling of the chip formation process, which allows estimating cutting forces, chip morphology and its flow direction. The second calculation is a 3D thermal modelling of the heat diffusion into the cutting tool, by using an adequate thermal loading (applied uniform or non-uniform heat flux). This loading is estimated using some quantities obtained from the first step calculation, such as contact pressure, sliding velocity distributions and contact area. Comparisons in one hand between experimental data and the first calculation and at the other hand between measured temperatures with embedded thermocouples and the second calculation show a good agreement in terms of cutting forces, chip morphology and cutting temperature.     

A new design method for adaptive IIR system identification using hybrid particle swarm optimization and gravitational search algorithm

Design of adaptive infinite impulse response (IIR) filter is the process of utilizing adaptive algorithm to iteratively determine the filter parameters to obtain an optimal model for the unknown plant based on minimizing the error cost function. However, the error cost surface of IIR filter is generally nonlinear, non-differentiable and multimodal. Hence, an efficient global optimization technique is required to minimize the error cost objective. A novel hybrid particle swarm optimization and gravitational search algorithm (HPSO–GSA) is proposed in this paper for IIR filter design. The proposed HPSO–GSA updates particle positions through obeying the influence of gravity acceleration in GSA and receiving direction of cognitive memory and social sharing information from PSO by means of coevolutionary strategy. The effect of key parameters on the performance of the proposed algorithm is firstly studied, and the proper parameters in HPSO–GSA are established using five benchmark plants along with the same-order model. The simulation studies have been performed for the performance comparison of eight algorithms such as PSO, GSA, QPSO, DPSO, FO-DPSO, GAPSO, PSOGSA and the proposed HPSO–GSA for unknown IIR system identification with the same-order and reduced-order filters. Simulation results show that the proposed algorithm has advantages over PSO, GSA and other PSO-based variants in terms of the convergence speed and the MSE levels.     

A new nonlinear elastic time reversal acoustic method for the identification and localisation of stress corrosion cracking in welded plate-like structures – A simulation study

In order to reduce the costs related to corrosion damage in aircraft structures, it is vital to develop new robust, accurate and reliable damage detection methods. A possible answer to this problem is offered by newly developed nonlinear ultrasonic techniques, which monitors the nonlinear elastic wave propagation behaviour introduced by damage, to detect its presence and location.In this paper, a new nonlinear time reversal technique is presented for the detection and localization of a scattered zone (damage) in a multi-material medium. In particular, numerical findings on a friction stir-welded aluminium plate-like structure are reported. Damage was introduced in the heat affected zone and modelled using a multi-scale material constitutive model (Preisach–Mayergoyz space).Studies were conducted for two different transducer configurations. Particular attention was devoted to find the optimum time-reversed window to be re-emitted in the structures. The methodology was compared with traditional time-reversal acoustics (TRA), showing significant improvements. While the traditional TRA was not able to clearly localise the damage, the developed technique identified in a clear manner the faulted zone, showing its robustness to locate and characterize nonlinear sources, in presence of a multi-material medium.     

A novel method for residual strength prediction for sheets with multiple site damage: Methodology and experimental validation

A unified method for solving the strip yield model for collinear cracks in finite and infinite sheet is proposed. The method is based on the weight function of a single crack. Two collinear cracks in finite and infinite sheets are used to apply and verify this method. The plastic zone size, crack opening displacement and stress distribution along the ligament between cracks obtained by using the present method are extensively compared with existing available results and finite element solutions, and very good agreements are observed. Combined with the Crack Tip Opening Angle (CTOA) criterion, the unified method is used to predict the crack growth behavior and residual strength for 2024-T3 aluminum alloy sheet with Multiple Site Damage (MSD). Thirty-two sheets with four types of MSD are designed and tested to verify this method. It is shown that the present method is able to predict various crack growth behaviors observed in experiment. The predicted residual strengths are within 9% of the corresponding test results. Compared to the elastic–plastic finite element method, the present method is much more efficient.     

A quadratic programming formulation for the solution of layered elastic contact problems: Example applications and experimental validation

The development of a quadratic programming formulation for the solution of layered elastic contact problems in the presence of friction is presented in this paper. Conveyor belts, tyred wheels, composite cylinders, and conrod bearings, are classical examples of systems which can be studied using the efficient numerical methodology proposed here. In this type of mechanical assembly, micro-slip between the mating surfaces often occurs and may eventually lead to system failure. Accurately capturing the evolution of slip and stick areas using a computationally inexpensive procedure (as an alternative to full finite element analysis) is therefore key to preventing these failures and to improving the design of various engineering components.The proposed approach is first tested and validated against classical marching-in-time solutions for two-dimensional layered systems in the presence of both static and moving loads. Results are then extended to demonstrate the feasibility of the technique to study systems with multiple slip regions and to solve rolling contact problems of practical interest. Finally, the numerical methodology is successfully applied to the prediction of frictional creep of tyred cylinders. Experimental corroboration has been obtained by testing tyred discs.     

A new track for antibacterial treatment: Progress and challenges of using cytomembrane-based vesicles to combat bacteria

The emergence and re-emergence of antibiotic-resistant bacteria, especially superbugs, are leading to complicated infections that are increasingly difficult to treat. Therefore, novel alternative antimicrobial therapies are urgently needed to reduce the morbidity and mortality caused by antibiotic resistance. The development of biomimetic-based therapy is expected to provide innovative means for addressing this challenging task. As a kind of novel biomaterial, cytomembrane-based vesicles (MVs) continue to receive considerable attention in antimicrobial therapy owing to their inherent biocompatibility, design flexibility, and remarkable ability to interact with biological molecules or the surrounding environment. These remarkable cell-like properties and their inherent interaction with pathogens, toxins, and the immune system underlie MVs-based functional protein therapy and targeted delivery to develop advanced therapeutic strategies against bacterial infection. This review provides a fundamental understanding of the characteristics and physiological functions of cytomembrane-based vesicles, focusing on their potential to combat bacterial infections, including detoxification, immune modulation, antibiotics delivery, and physical therapy. In addition, the future possibilities and remaining challenges for clinically implementing MVs in the field of antibacterial treatment are discussed.     

Wetting boundary conditions in numerical simulation of binary fluids by using phase‐field method: some comparative studies and new development

We studied several wetting boundary conditions (WBCs) in the numerical simulation of binary fluids by using phase‐field method. Five WBCs, three using the linear, cubic, and sine form surface energy (LinSE, CubSE, and SinSE), the other two using the geometric formulation (Geom) and the characteristic interpolation (CI), were compared through the study of several problems: (1) the static contact angle (CA) of a drop; (2) a Poiseuille flow‐driven liquid column; (3) a wettability gradient (WG)‐driven liquid column; and (4) drop dewetting. It was found that while all WBCs can predict the static CA fairly accurately, they may affect the simulation outcomes of dynamic problems differently, depending on the CA. For the flow‐driven problem with a CA near 90°, using different WBCs had almost no effect on the flow characteristics over a large scale. For the WG‐driven problem, to use different WBCs may lead to different steady drop velocities, and all WBCs except LinSE can give reasonably consistent prediction between the drop velocity and dynamic CAs. For drop dewetting, Geom led to the most violent drop motion, whereas CubSE caused the weakest motion. For several problems, CubSE and SinSE gave almost the same results, and those by Geom and CI were also close, possibly due to similar consideration in their design. Besides, a new implementation that may be used for all WBCs was proposed to mimic the wall energy relaxation and control the degree of slip. This new procedure made it possible to allow the simulations to match experimental measurements well. Copyright © 2014 John Wiley & Sons, Ltd.