The main scope of this issue is to provide to the international technical and academic community information about the latest developments on the interaction and the complementary aspects of computational methods and experimental measurements. The main attention and relevance being committed to their reciprocal and advantageous integration

It is recognised that the constant progresses in computers efficiency and numerical techniques are producing a steady growth of computational simulations, which nowadays applies to an everwidening range of engineering problems. Nonetheless, even if these simulations are continuously expanding and improving, there still exists the need for their validation, especially for the more complex cases, which can be only accomplished by performing dedicated experimental tests. Experimental techniques are becoming increasingly complex and sophisticated so that both their running as well as data collection can only be performed by computers. Finally, it must be emphasised that, for the majority of measurements, the data obtained must be processed numerically.

This issue contains a substantial number of excellent scientific papers, which present several advanced approaches to the application of Computational Methods and Experimental Measurements.

The Editors

Alicante, Spain

2017

This paper focuses on combined experimental and numerical approaches to model thermal processes and obtain accurate results on system behaviour and performance. Interest lies in obtaining repeatable and dependable inputs for choosing appropriate conditions and parameters for enhancing the efficiency and the desired output. These results can also form the basis for system design and optimization. Several fundamental and practical problems are considered and typical results presented to discuss the implications and applications of this methodology. Circumstances where experimental data are used to validate the model, provide greater physical insight and define the boundary conditions, thus allowing the numerical simulation to be carried out, are also presented. Results from a concurrent, or parallel, simulation and experimentation approach are also presented to indicate the usefulness of such a strategy. It is stressed that experimental data are indispensable in obtaining accurate and realistic results for complex practical problems involving thermal transport processes.

Recent alloy developments have produced a new generation of Al–Li alloys that provide not only weight savings, but also many property benefits such as excellent corrosion resistance, good spectrum fatigue crack growth performance, a good strength and toughness combination and compatibility with standard manufacturing techniques. The forging of such alloys would lead to mechanical properties that closely match the aircraft engine requirements including lower weight, improved performance and a longer life. As a result, detailed analyses need to be performed to determine which material properties are best suited for a specific structure and how to achieve the required mechanical and damage tolerant properties during material processing.

We developed an integrated physics-based model for prediction of microstructure evolution and material property prediction of third-generation Al–Li alloys. In order to develop such a model, an elastic-plastic crystal plasticity model is developed and incorporated in finite element software (ANSYS). The model accounts for microstructural evolution during non-isothermal, non-homogeneous deformation and is coupled with the damage kinetics. Our model bridges the gap between dislocation dynamics and continuum mechanics scales.

Model parameters have been calibrated against lab tests including micropillar in-situ simple compression tests of Al–Li alloy 2070. Numerical predictions are verified against the lab results including stress–strain curves and crystallographic texture evolution.

The properties of light alloy castings are strongly affected by their inclusion content, particularly double oxide film defects (bifilms), which not only decrease the tensile and fatigue properties, but also increase their scatter. Recent research has suggested that oxide film defects may alter with time, as the air inside the bifilm would react with the surrounding melt, while the hydrogen dissolved in the melt could diffuse into the bifilm cavity to form hydrogen porosity. The mechanical properties of the casting were shown to be significantly dependent upon the new morphology of its entrained bifilms. In this work, the Weibull moduli of the tensile properties of three Al castings, all expected to contain oxide films of, approximately, the same amount were compared. The first casting was poured into a resin-bonded sand mould while the second and third castings were poured into ceramic moulds with the mould for the third casting being preheated prior to pouring. The results of mechanical property analysis and electron microscopy examination suggested a considerable influence of the type of the mould and the solidification time on the morphology of bifilms and by implication, on the reliability and reproducibility of the tensile properties.

In drive systems and component technology a high reliability is very important for machines. Machine element dimensions are calculated for reliability. The properties for these elements are based on conventional manufacturing techniques. Very high stresses are applied on bearings in their operating time. To improve the endurance life, residual stresses can be induced into the subsurface zone. In contrast to a conventional grinding process, the mechanical surface modification process deep rolling is able to induce very high compressive residual stresses. A computational approach was developed to establish an appropriate residual stress depth profile matching the applied loads. Thus, the costs of manufacturing can be chosen in accordance to the required properties. The method to determine the residual stresses is based on an iterative reverse calculation of an existing bearing fatigue life model of Ioannides et al. The model originates from the approach of Lundberg and Palmgren (1947) including a stress fatigue limit tu. For the term ti, the fatigue criterion of Dang-Van is applied. The equation accounts for the maximum orthogonal shear stress and the local hydrostatic pressure phyd, corrected for residual and hoop stress. The inputs into the computational model are the stresses on the surface, which are simulated based on the load and geometry of the contact between roller and bearing surface. As an output the required residual stress profile underneath the bearings raceway is given to achieve a bearing fatigue life as required for the given application. In order to verify the model, the bearing fatigue life was experimentally determined for a given residual stress profile by experiments.

The present paper describes the application of an evolutionary algorithm to the optimum design of the reinforcement of timber beams using FRP laminates and sheets. The objective function is the material cost of the strengthening and is subjected to ten constraints derived from the ultimate limit states for flexural and shear behaviour as well as the serviceability limit states. A genetic algorithm is used and the optimization problem is transformed into an unconstrained one by means of an adaptive penalty function. The design variables are the CFRP and GFRP mechanical properties and dimensions and they are encoded in a binary chromosome: type of composite material (CFRP or GFRP), reinforcement mechanical properties and geometric configuration. The search space for the minimum cost consists of 65 billion possible solutions. The crossover operator switches randomly between a fenotype crossover and flat crossover. An adaptive mutation scheme has been as well as an elitism criterion. The algorithm has been used for obtaining optimum designs in several specific load and geometry cases of glued laminated timber beams. The objective is finding whether there are specific reinforcement configurations more feasible for a certain loading situations: short or long beams and lower or higher loading increments. Five cases have been analysed. In the first three cases the length of the beams has constant values of 2, 2.5 and 3 m, whereas the value of loading was variable. In the latter case, the value of the load was fixed and the length of the beam was variable. The analysis of the results shows that the GFRP reinforcement is more efficient than CFRP for designs governed by shear failure, whereas CFRP is more effective in the case of flexural failure and deflection controlled strengthening of timber beams.

The main purpose of this work is to employ the Adomian modified decomposition method (AMDM) to calculate free transverse vibrations of non-uniform cantilever beams carrying a transversely and axially eccentric tip mass. The effects of the variable axial force are taken into account here, and Hamilton’s principle and Timoshenko beam theory are used to obtain a single governing non-linear partial differential equation of the system as well as the appropriate boundary conditions. Two product non-linearities result from the analysis and the respective Cauchy products are computed using Adomian polynomials. The use of AMDM to make calculations for such a cantilever beam/tip mass arrangement has not, to the authors’ knowledge, been used before. The obtained analytical results are compared with numerical calculations reported in the literature and good agreement is observed. The qualitative and quantitative knowledge gained from this research is expected to enable the study of the effects of an eccentric tip mass and beam non-uniformity on the vibration of beams for improved dynamic performance.

The formation mechanism of inclined fatigue cracks in ultrafine-grained Cu processed by equal channel angular pressing was studied by using a smooth specimen with a small blind hole. The crack growth direction depended on the location of drilling hole along the circumferential direction of the round bar specimen and on the applied stress amplitudes. Although the low-cycle fatigue crack growth paths inclined 45° and 90° to the loading-axis were observed in the different locations on the surface, crack faces in these cracks were extended along one set of maximum shear stress planes, corresponding to the shear plane of the final processing. To study the crack growth behaviour, surface damage around the crack paths formed by the two-step fatigue stress tests was observed. Profile of crack face was examined, showing the aspect ratios (b/a) of b/a = 0.38 and 1.10 for the cracks with 45° and 90° inclined path directions with respect to the loading axis, respectively. The role of the microstructure and deformation mode at the crack-tip areas on the formation of crack paths parallel to the shear plane of the final pressing was discussed in terms of the microstructural evolution caused by cyclic stressing and the mixed-mode stress intensity factor.

It is estimated that currently the consumption of natural aggregates used annually in the production of concrete in the world is around 10 billion tons. Moreover, more than 10 million tons of waste is generated annually from the construction industry. The incorporation of recycled aggregates in the production of concrete arises mainly due to an environmental factor, because it emphasizes the reduction in the consumption of raw materials, reduction of the emission of pollutants to the atmosphere derived from the processes of extraction of natural aggregates, between others. Several studies quantifies the decrease of mechanical properties according to the percentage of replacement of natural aggregate by recycled concrete aggregate. In the present study the authors provide several nonlinear models, which are able to predict the modulus of elasticity behaviour of the concrete manufactured with recycled aggregate. A database was composed of 147 different mixtures of recycled aggregate concrete collected from publications of scientific journals. The database has been used to introduce it to the software Polimodels. Polimodels is able to generate different models using different nonlinear regression algorithms. Six different models for the modulus of elasticity are proposed, dependents on certain physical and mechanical parameters of the recycled aggregate, as the following; the percentage of absorption, Los Angeles abrasion coefficient, and the percentage of substitution of natural aggregate by recycled aggregate. It is possible to appreciate the remarkable reduction in the modulus of elasticity due to the increase of recycled aggregates in the concrete. When the models have more independent variables a better adjustment is noticed that help us to improve the prediction of the modulus of elasticity of recycled aggregate concrete.

Free vibrations of beams and rods made of nano-materials are investigated. It is assumed that the dimensions of cross sections of nano-beams are piecewise constant and that the beams are weakened with cracks. It is expected that the vibrational behaviour of the nano-material can be described within the non-local theory of elasticity and that the crack induces additional local compliance. The latter is coupled with the stress intensity coefficient at the crack tip.

In this work, numerical models were obtained for describing the segregation phenomenon in lightweight aggregate concrete. To that end, a numerical methodology based on the generation of geometric models of finite elements has been applied, selecting those that describe better this phenomenon. The use of lightweight aggregate concretes (LWC) allows greater design flexibility and substantial cost savings. It is also well known that it contributes to a positive impact on the energy consumption of a building due to the high-thermal resistance values. However, lightweight concretes are susceptible to present aggregate segregation due to density differences between its components during concrete vibration. Segregation in concrete may strongly affect the concrete global properties. This fact justifies the needs for the identification and quantification of this phenomenon, in order to estimate the concrete segregation experimentally, a LWC was mixed in laboratory conditions. Controlled segregation was caused applying different times of internal vibration in a cylinder specimen. The specimens were horizontally sectioned in order to obtain the density in each section because the segregation index can be estimated obtaining a relation by comparing the densities of the upper and lower parts. Firstly, ANOVA test was performed to determine the statistical significance (p<0.05) of the differences in the density of the different sections, differences in the aggregate type and differences in the time of concrete vibration. Results show that there is a significant difference of each section and there is no significant difference of each lightweight aggregate used to mix the concrete in spite of their different density. In order to model the segregation in the LWC, at first, linear models were considered and rejected because for not explaining the phenomenon. However, the application of numerical models shows good results to describe the phenomenon of segregation in LWC.

Performance and emission characteristics of a gasoline direct injection (GDI) engine are mainly influenced by the in-cylinder mixture preparation. However, in these engines, mixture formation depends upon many factors viz., fuel injection strategy and parameters, mode of operation, engine geometry, etc. Therefore, understanding the mixture formation, under various engine operating conditions and fuel system configurations, is very much essential. In this study, an attempt has been made to understand the effect of fuel injector-hole diameter and fuel injection timing on the mixture formation in a four-stroke, wall-guided GDI engine using computational fluid dynamics (CFD) analysis. The CFD simulations are carried out from inlet valve opening (IVO) to exhaust valve opening (EVO) period using the CONVERGE. The CFD models used are validated with the available data from the literature. The engine considered has a compression ratio (CR) of 11.5. All the CFD simulations are carried out at the engine speed of 2000 rev/min. Three fuel injector-hole diameters viz., 0.1, 0.14 and 0.18 mm and three fuel injection timings viz., 605, 620 and 635 crank angle degree (CAD) are considered for the analysis. The mixture formation is analyzed in the vicinity of the spark plug and at other parts of the combustion chamber. From the results, it is found that higher nozzle-hole diameter yielded very rich mixture zones near spark plug. Also, lower nozzle-hole diameter and retarded fuel injection timing showed higher indicated mean effective pressure (IMEP).

The problem of indentation of ductile materials by ball indenters is, in this paper, addressed by numerical modelling. A finite element model is built using general purpose software. The axisymmetry of the problem is taken into account thus reducing its dimensionality. Particular attention is given to contact modelling as well as mesh design for optimal performance. The model is validated by comparing its predictions to the exact elastic solution as well as experimental measurements from elasto-plastic indentation tests. In the latter case, indenter imperfection is accounted for and mate rial input are stress-strain curves originating from tensile tests. The sensitivity of numerical results to indenter elasticity is investigated. The effect of friction and specimen creep during indentation on load-displacement predictions is also assessed.

In this paper a simplified biomechanical crowd-structure interaction model is proposed and validated in order to analyse the lateral lock-in phenomenon on real footbridges. The proposed crowd-structure interaction model is organized in three levels: (i) pedestrian-structure interaction; (ii) interaction among pedestrians in the crowd; and (iii) interaction between the crowd and the structure. To this end, first, the human-structure interaction of each pedestrian is modelled via a simplified two degrees of freedom system. Second, the interaction among pedestrians inside the crowd is simulated using a multi-agent model. The considered model simulates the movement of each pedestrian from the dynamic equilibrium of the different social forces that act on him/her. Finally, the crowd-structure interaction is achieved modifying the behaviour of the pedestrians depending on the comfort level experienced. For this purpose, the recommendations established by the French standards have been considered. The integration of the three levels in an overall model is achieved by the implementation of a predictive– corrective method. The performance of the proposed model is validated correlating the numerical and experimental dynamic response of the Pedro e Inês footbridge during the development of a lateral lock-in pedestrian test. As the first lateral natural frequency of the footbridge is inside the range that characterizes the walking pedestrian step frequency in lateral direction, numerical and experimental studies were performed to analyse its behaviour under pedestrian action. The agreement between the numerical and experimental results is adequate. However, further studies are recommended in order to generalize the proposed approach and facilitate its use during the design project of future footbridges.

Understanding human intention is an important ability for an intelligent robot to collaborate with a human to accomplish various tasks. During collaboration, a robot with such ability can predict the successive actions that a human partner intends to perform, provide necessary assistance and support, and remind for the missing and failure actions from the human to achieve a desired task purpose. This paper presents a framework that allows a robot to automatically recognize and infer the action intention of a human partner based on visualization, in which an inverse-reinforcement learning (IRL) system is learnt based on the observed human demonstration and used to infer the human successive actions. Compared to other systems based on reinforcement learning, the reward of a Markov-Decision process (MDP) is directly learned from the demonstration. In our experiment, we provide some examples of the proposed framework which yields promising results with coffee-making and pick-and-place tasks. Regarding to the human-intention model based on IRL, the coffee-making experiment indicates that the action is globally predicted because the action of putting down the water pot is selected instead of pouring water when the cup is already filled with water.

A methodology for goal-oriented active learning with local model networks (LMNs) is proposed. It is applied for the generation of training data for a computational fluid dynamics (CFD) metamodel. The used metamodel is an LMN trained with data originating from CFD simulations. This metamodel describes the total-to-static efficiency for a given design point, defined by the pressure rise at a specific volume flow rate, depending on geometrical parameters of an impeller of centrifugal fans. The goal- oriented nature originates from three main targets that are addressed simultaneously during the active learning procedure. (I) The concentration on possibly optimal geometries and (II) the focus on areas in the input space where the metamodel’s performance is considered to be worst. Additionally, (III) new measurements should differ from already simulated geometries as much as possible. With these goals three important issues in modeling are addressed simultaneously: (I) optimality, (II) model bias, (III) model variance/uniformly space-filling property. In order to fulfill all goals, special properties of LMNs are utilized (embedded approach). Through the structure of LMNs, it is possible to assign local model errors to specific areas in the input space. New measurements are preferably placed in such high-error regions, while concentrating on presumably optimal geometries that differ most from the ones already available in the training data. In the field of fluid machinery, the range of achievable design points is usually identified by the Cordier diagram. While the design points obtained in the passive learning phase fairly agree with the standard Cordier diagram, an extension of achievable design points was observed due to the proposed goal-oriented learning strategy. In addition, the total-to-static efficiency could be improved in some areas of the Cordier diagram.

A biomechanical model and mathematical formulation of the problem of propulsion of a solid nondeformable pellet by an isolated segment of the colon are presented. The organ is modeled as a soft orthotropic cylindrical biological shell. Its wall is reinforced by transversely isotropic muscle fibers of orthogonal type of weaving embedded in a connective tissue stroma. The mechanical properties of the wall are assumed to be nonlinear, deformations are finite. The longitudinal and circular smooth muscle syncitia possesses electrical properties and are under control of a pacemaker, which is represented by the interstitial cell of Cajal. The model describes the dynamics of the generation and propagation of the mechanical waves of contraction–relaxation along the surface of the bioshell and propulsion of the pellet. The governing system of equations has been solved numerically. The combined finite-difference and finite-element method has been used. The results of numerical experiments demonstrate that pendular movements alone provide a normal transit, without mixing though, of the bolus. Non-propagating segmental contractions show small amplitude librations of the pellet without its visible propulsion. Only the coordinated activity of the longitudinal and circular smooth muscle layers in a form of the peristaltic reflex provides physiologically significant simultaneous propulsion and mixing of the intraluminal content.

Numerical methods, and especially the finite-element method (FEM), are usually adopted for the analyses of shockwave propagation in nonlinear inelastic media. Noise or spurious oscillations, in the calculated stresses and displacements, frequently appear in the FEM solutions. This article introduces and describes a numeric filter based on least-square analysis that can smooth out such fictitious noise. The sliced least-square method (SLSM) filter is implemented in a finite elements program that solves 1D time integration of dynamic equilibrium sets of equations that simulate shockwave propagation in multi-layered soils supported by a hard stratum. Elastic and elasto-viscoplastic material models with dynamic yield surface constitutive relations are invoked to model sand, clay, and concrete materials in the analyses. Results of the analyses of shockwave propagation in layers of soil and concrete without the filter are compared with identical conditions with the inclusion of the new filter in the finite-element program. Oscillations in calculated stresses and displacements were observed in the results when no filter was included in the solution program. Solution results showed little or no noise with the application of the new filter. The predicted FEM analyses results were compared with physical test results with very good to excellent comparisons obtained.

The effect of fluid rheology on acoustic streaming was studied experimentally using a low frequency (600Hz–15kHz) underwater acoustic transducer. The fluid rheology was compared with deionized water and non-Newtonian fluid polyanionic cellulose (PAC). Streaming effect generated by the transducer in a static liquid medium was visualized by particle image velocimetry (PIV) method. The motion of fluid was optically visualized using light scattering ‘seeding’ particles. Velocity profiles induced by the acoustic streaming have different shapes and range of magnitudes. First, the acoustic streaming in deionized water was visualized for different frequencies and pressure amplitudes (voltages). A maximum of 1 g/L PAC was then introduced in smaller steps for some selected frequency and voltage settings. The streaming disappeared completely when the total concentration of the fluid medium reached 0.19 g/L PAC. The measured streaming velocities are found to be in the range of 2.1 to 9.9 cm/s for water and it is proportional to the applied voltage and the operating frequency of the transducer. When introducing PAC, the streaming velocity within water gradually decreased until zero due to the attenuation of acoustic waves by viscous effects. This confirms that the streaming velocity is approximately inversely proportional to the bulk viscosity of the medium. The velocity vectors and the streaming velocity maps illustrate the induced non-linearities of the fluid medium due to the acoustic propagation. The results are part of a comprehensive study aimed at investigating the influence of acoustic vibration on particle settling in non-Newtonian fluids.

This research reports a vehicle occupant restraint system design that takes account of uncertainties of crash conditions and situations by using a multi-objective robust design optimization method called MORDO. The vehicle occupant restraint system is composed of restraint equipment, such as an airbag, a seatbelt and a knee bolster. The optimization aims to improve the safety performance of the system and its robustness simultaneously. The safety of the system is evaluated by some indexes based on some safety regulations, which are calculated by response surface model of an occupant at a crash. In addition, its robustness is evaluated by the mean value and the standard deviation of objective functions, which are calculated by using Monte Carlo simulation based on a certain probabilistic distribution in space of design variables around each design candidate. Some helpful information for designing the restraint systems, such as trade-off information of safety performance and its robustness, are provided by visualizing and analysing the Pareto optimal solutions.

The use of lightweight concrete allows great flexibility and cost savings when it is used in building construction having a positive impact on the energy consumption of buildings due to its good thermal characteristics. However, it is also known that the differences between the densities of the materials used to produce these concretes make it highly susceptible to the segregation phenomenon. The main objective of the present work is to present a method to quantify this phenomenon using techniques of image analysis. In this work, a lightweight concrete produced was molded in cylindrical molds using different times of internal vibration and causing different degrees of segregation. The samples were cured, vertically saw-cut in two pieces (halves) and the sections were photographed. Subsequently, the halves were saw-cut horizontally in four equal parts and posteriorly their densities were determined experimentally. The densities obtained were used to calculate the segregation index of each sample (experimental method). Furthermore, the photographed sections were processed using image analysis software in order to determine the volumetric proportions of aggregates in each sample (noise reduction, threshold adjustment, binarization and fill holes). The processed images were used to calculate the densities and segregation index of the lightweight concrete produced through image analysis. In addition, using the photographed sections, a vertical density profile was programmed to analyze the distribution of the lightweight concrete components (mortar and aggregate). Finally, the results obtained experimentally and through image analysis were compared. This study demonstrates that the image analysis allows a deeper knowledge of the behavior of segregated concrete.