Fluid–structure–soil interaction effects on the free vibrations of functionally graded sandwich plates

This study investigates the effects of fluid–structure and soil–structure interaction on the free vibration response of functionally graded sandwich plates. To this aim, an exemplary problem is analyzed, whereas a metal/ceramic sandwich plate is placed at the bottom of a tank filled in with fluid. Two cases are considered: (i) soft core, i.e., a sandwich plate with metal core and ceramic skins, and (ii) hard core, i.e., a sandwich plate with ceramic core and metal skins. In both cases, the skins are modelled as suitable functionally graded materials (FGMs). The soil is modelled as a Pasternak foundation. The free vibration analysis is carried out according to the extended higher order sandwich plate theory (EHSAPT). The fluid is assumed to be inviscid, incompressible, and irrotational. Hamilton’s principle is exploited to deduce the governing equations and the corresponding boundary conditions. The Rayleigh–Ritz method with two-variable orthogonal polynomials is used to compute the natural frequencies of the sandwich plate. The adopted approach is first validated through comparison with results published in the literature. Then, the effects are studied of several parameters on the dynamic response of the system.

     

Fluid–structure interaction for non-conforming interfaces based on a dual mortar formulation

In the present work the problem of fluid–structure interaction (FSI) with independently space discretized fluid and structure fields is addressed in the context of finite elements. To be able to deal with non-conforming meshes at the fluid–structure interface, we propose the integration of a dual mortar method into the general FSI framework. This method has lately been used successfully to impose interface constraints in other contexts such as finite deformation contact. The main focus is set on monolithic coupling algorithms for FSI here. In these cases the dual mortar approach allows for the elimination of the additional Lagrange multiplier degrees of freedom from the global system by condensation. The resulting system matrices have the same block structure as their counterparts for the conforming case and permit the same numerical treatment. Partitioned Dirichlet–Neumann coupling is also considered briefly and it is shown that the dual mortar approach permits a numerically efficient mapping between fluid and structure quantities at the interface.Numerical examples demonstrate the efficiency and robustness of the proposed method. We present results for a variety of different element formulations for the fluid and the structure field, indicating that the proposed method is not limited to any specific formulation. Furthermore, the applicability of state-of-the-art iterative solvers is considered and the convergence behavior is shown to be comparable to standard simulations with conforming discretizations at the interface.     

A comparative simulation study on the power–performance of multi-core architecture

Nowadays, multi-core processor is the main technology used in desktop PCs, laptop computers and mobile hardware platforms. As the number of cores on a chip keeps increasing, it adds up the complexity and impacts more on both power and performance of a processor. In multi-processors, the number of cores and various parameters, such as issue-width, number of instructions and execution time, are key design factors to balance the amount of thread-level parallelism and instruction-level parallelism. In this paper, we perform a comprehensive simulation study that aims to find the optimum number of processor cores in desktop/laptop computing processor models with shallow pipeline depth. This paper also explores the trade-off between the number of cores and different parameters used in multi-processors in terms of power–performance gains and analyzes the impact of 3D stacking on the design of simultaneous multi-threading and chip multiprocessing. Our analysis shows that the optimum number of cores varies with different classes of workloads, namely: SPEC2000, SPEC2006 and MiBench. Simulation study is presented using architectures with shorter pipeline depth, showing that (1) the optimum number of cores for power–performance is 8, (2) the optimum number of threads in the range [2, 4], and (3) for beyond 32 cores, multi-core processors are no longer efficient in terms of performance benefits and overall power consumption.     

Multi-solver algorithms for the partitioned simulation of fluid–structure interaction

In partitioned fluid–structure interaction simulations, the flow equations and the structural equations are solved separately. As a result, a coupling algorithm is needed to enforce the equilibrium on the fluid–structure interface in cases with strong interaction. This coupling algorithm performs coupling iterations between the solver of the flow equations and the solver of the structural equations. Current coupling algorithms couple one flow solver with one structural solver. Here, a new class of multi-solver quasi-Newton coupling algorithms for unsteady fluid–structure interaction simulations is presented. More than one flow solver and more than one structural solver are used for a single simulation. The numerical experiments demonstrate that the duration of a simulation decreases as the number of solvers is increased.     

Recent development of fluid–structure interaction capabilities in the ADINA system

The ADINA system has been developed in recent years into a complete system for the analysis of solid, fluid and coupled problems. Fluid flows can be modeled as Navier–Stokes incompressible, slightly compressible and fully compressible flows. They can also be modeled as porous medium flows. Structures can be modeled as 2D/3D solids, beams or shells. The response of the structure can be linear or nonlinear, and can also include contact effects. The fluid and structure can be coupled through their interface (FSI), porous media (PFSI) or thermal materials (TFSI). Both iterative and direct solution procedures can be used for solving the fully coupled system. These capabilities, together with the extensive boundary conditions and material models, and the user-friendly graphical system for pre- and post-processing (AUI), make the ADINA system a powerful tool for engineers and researchers.     

Investigating the effect of training–testing data stratification on the performance of soft computing techniques: an experimental study

Abstract

Cross-validation of soft computing techniques needs to be done efficiently to avoid overfitting and underfitting. This is more important in petroleum reservoir characterisation applications where the often-limited training and testing data subsets represent Wells with known and unknown target properties, respectively. Existing data stratification strategies have been haphazardly chosen without any experimental basis. In this study, the optimal training–testing stratification proportions have been rigorously investigated using the prediction of porosity and permeability of petroleum reservoirs as an experimental case. The comparative performances of seven traditional and advanced machine learning techniques were considered. The overall results suggested a recommendable optimum training stratification that could serve as a good reference for researchers in similar applications.     

Effects of the ‘spring structure’ on the performance of a vibrating plate of the piezoelectric inkjet print-head

Microsystem Technologies - One of the core components of piezoelectric inkjet print-head is the piezoelectric vibrating plate which directly affects the jet performance of a print-head. In the...     

A philosophical study of human–artefact interaction

This paper focuses on a critical intersection between philosophy of technology and cognitive archaeology with an objective in view. These two rapidly developing disciplines intersect on the problem of characterizing the dynamic relationship between human beings and technical artefacts. The intricacies of human–artefact relation have been a source of curiosity and contemplation for philosophers of technology since 1970s. In contrast, the cognitive archaeologists’ interest in interpreting the exact nature of the interaction between human cognitive system and material culture is relatively recent. The central objective of this paper is to show why the cognitive archaeologists’ account of the relation between human cognition and material culture as exemplified by the classical-phenomenological example of the blind person’s use of a stick needs to be critically reviewed in the light of philosophical-(post)-phenomenological research and new empirical findings on tool use and prosthesis. There are three sections in this paper. In the first section, certain distinctive features of cognitive archaeology, which are important for the following discussion, are mentioned in brief. The second section consists of an exposition of Don Ihde’s account of embodiment relations—typical examples of which include the blind person’s use of a stick—with particular emphasis on the aspect of what Ihde calls “quasi-transparency”. Possible reasons behind the cognitive archaeologists’ indifference to the said aspect are pointed out. In the third section, the difficulties involved in analysing the case of the blind person’s stick are discussed in the light of recent empirical research on bodily extension (by means of artefacts) and prosthesis (incorporation of artefacts into the body). The paper ends with some critical comments on the cognitive archaeologists’ interpretation of the relation between the blind person and his stick and explains why their interpretation requires revision in view of current findings on tool use and prosthesis.     

Social effects of the speed of hummed sounds on human–computer interaction

Our research focuses on the nature of voice interaction and activation of psychological tendencies in humans by the power of prosody sounds. This study examines whether people's impressions and behaviours are affected by variations in the speed of hummed sounds. The sounds consist of just prosodic components similar to continuous humming on the open vowel /a/ or /o/ without any language information. In interaction between individuals as well as among animals, temporal structures including voice speed or duration contribute rhythmic interaction and are closely connected to the participants’ dynamics of mental or emotional states. We think that this phenomenon can be applied to human–computer interaction, even through the variation in temporal structures of hummed sounds used to reduce the influence of content or meaning in language. Our interactive system mimics the prosodic features of the human voice by using humming-only sounds under three different voice speed conditions: (a) faster, (b) normal, and (c) slower than the original speaker. We examine whether the variation in the sound's speed gives rise to both psychological and behavioural influences in the relationship between the computer and the subject through interaction. Subjects tend to prefer a computer with a normal or faster speaking rate to that with a slower rate on both usefulness and familiarity. Moreover, the speech rate of the subjects changed inversely to the variation in a computer's hummed sounds. This study demonstrates the importance of temporal structure and emphasizes the need for an investigation of the fundamentals at work in interaction.     

A fully discrete scheme for the pressure–stress formulation of the time-domain fluid–structure interaction problem

We propose an implicit Newmark method for the time integration of the pressure–stress formulation of a fluid–structure interaction problem. The space Galerkin discretization is based on the Arnold–Falk–Winther mixed finite element method with weak symmetry in the solid and the usual Lagrange finite element method in the acoustic medium. We prove that the resulting fully discrete scheme is well-posed and uniformly stable with respect to the discretization parameters and Poisson ratio, and we provide asymptotic error estimates. Finally, we present numerical tests to confirm the asymptotic error estimates predicted by the theory.     

Two-dimensional simulation of fluid–structure interaction using lattice-Boltzmann methods

The development of flow instabilities due to high Reynolds number flow in artificial heart-value geometries inducing high strain rates and stresses often leads to hemolysis and related highly undesired effects. Geometric and functional optimization of artificial heart valves is therefore mandatory. In addition to experimental work in this field it is meanwhile possible to obtain increasing insight into flow dynamics by computer simulation of refined model problems. Here we present two-dimensional simulation results of the coupled fluid–structure problem defined by a model geometry of an artificial heart value with moving leaflets exposed to a channel flow driven by transient boundary conditions representing a physiologically relevant regime. A modified lattice-Boltzmann approach is used to solve the coupled problem.     

Comparative study on the viscosity modeling of the Ag–Au–Cu liquid alloys

With the new CALPHAD-type model proposed in our previous work, the viscosity of the Ag–Au–Cu system was re-optimized. Comparisons were made in the calculated viscosities of the Ag–Au and Ag–Cu liquid alloys at 1373 K among different models. It was found that the CALPHAD-type models perform better than the empirical models. The calculated viscosities of the Ag–Au–Cu liquid alloys with and without ternary interaction parameters were both compared with the calculation results of the previous CALPHAD-type model. Considering ternary interaction, the best fitness with the experimental data could be obtained by our model. The good performance in reproducing the measured viscosities of binary and ternary systems evidences the validity of the new model.     

Theoretical study of surface interaction stresses considering one-dimensional material distributions in the in-plane direction based on the Lennard–Jones potential

In this work, the interaction stresses (i.e., pressures and shear stresses) between a half-space comprising a uniform material and a half-space comprising one-dimensional material distributions in the in-plane direction were theoretically derived. The interaction stress was derived from the Lennard–Jones potential as a vector for the (0, 0, 1) surface using two different material distribution patterns. The first pattern was a periodic distribution of materials (Pattern 1) and the second was a distribution of two materials with a single interface (Pattern 2). The interaction stresses for Pattern 1 were derived based on a Fourier series, while those for Pattern 2 were derived as elementary functions. The pressures possessed non-fluctuation terms and fluctuation terms, while the shear stresses possessed fluctuation terms only. The basic characteristics of these interaction stresses for parallel planes were quantitatively clarified by presenting the distributions and vector diagrams of the interaction stresses.

     

Modeling accidental-type fluid–structure interaction problems with the SPH method

This paper presents the validation aspects of a unified numerical framework based on SPH formulation and devoted to the modeling of fluid–structure interaction problems involving large motion of the fluid and large deformation with a possible failure of the structure. The fluid domain is modeled according to an updated Lagrangian formulation. The solid domain (3D and shell models) uses the total Lagrangian formulation. The fluid–structure interaction is treated via a unilateral contact algorithm adapted to SPH context. The SPH framework is verified on academic test cases and validated by simulating an experiment involving the reservoir leakage.     

Control of bidirectional physical human–robot interaction based on the human intention

This paper presents a control strategy for human–robot interaction with physical contact, recognizing the human intention to control the movement of a non-holonomic mobile robot. The human intention is modeled by mechanical impedance, sensing the human-desired force intensity and the human-desired force direction to guide the robot through unstructured environments. Robot dynamics is included to improve the interaction performance. Stability analysis of the proposed control system is proved by using Lyapunov theory. Real experiments of the human–robot interaction show the performance of the proposed controllers.     

Numerical analysis of a synchronization phenomenon: Pedestrian–structure interaction

The pedestrian–structure interaction is considered by developing a non-linear double pendulum model, representing the lateral walking of the pedestrian and the horizontal vibration mode of the structure. To understand the synchronization phenomenon, the two oscillators were considered in their phase spaces, and a ring-dynamics approach was applied. As synchronization occurs, pedestrian motion becomes in phase quadrature with a quarter-of-period in advance of the bridge motion: this ensures stability of walking conditions on a moving deck, but causes random cancellation of forces typical of an incoherent crowd. Correspondingly, the lateral force transmitted to the structure increases its value, approaching resonance conditions.     

Human–automation interaction for multiple robot control: the effect of varying automation assistance and individual differences on operator performance

In a human–automation interaction study, automation assistance level (AL) was investigated for its effects on operator performance in a dynamic, multi-tasking environment. Participants supervised a convoy of manned and unmanned vehicles traversing a simulated environment in three AL conditions, while maintaining situation awareness and identifying targets. Operators’ situation awareness, target detection performance, workload and individual differences were evaluated. Results show increasing AL generally improved task performance and decreased perceived workload, however, differential effects due to operator spatial ability and perceived attentional control were found. Eye-tracking measures were useful in parsing out individual differences that subjective measures did not detect. At the highest AL, participants demonstrated potentially complacent behaviour, indicating task disengagement.

Practitioner Summary: The effect of varying automation assistance level (AL) on operator performance on multiple tasks were examined in a within-subjects experiment. Findings indicated a moderate AL improved performance, while higher levels encouraged complacent behaviour. Effects due to individual differences suggest that effective AL depends on the underlying characteristics of the operator.     

A numerical study on the fluid compressibility effects in strongly coupled fluid–solid interaction problems

Interactions between an incompressible fluid passing through a flexible tube and the elastic wall is one of the strongly coupled fluid–solid interaction (FSI) problems frequently studied in the literature due to its research importance and wide range of applications. Although incompressible fluid is a prevalent model in many simulation studies, the assumption of incompressibility may not be appropriate in strongly coupled FSI problems. This paper narrowly aims to study the effect of the fluid compressibility on the wave propagation and fluid–solid interactions in a flexible tube. A partitioned FSI solver is used which employs a finite volume-based fluid solver. For the sake of comparison, both traditional incompressible (ico) and weakly compressible (wco) fluid models are used in an Arbitrary Lagrangian–Eulerian (ALE) formulation and a PISO-like algorithm is used to solve the unsteady flow equations on a collocated mesh. The solid part is modeled as a simple hyperelastic material obeying the St-Venant constitutive relation. Computational results show that not only use of the weakly compressible fluid model makes the FSI solver in this case more efficient, but also the incompressible fluid model may produce largely unrealistic computational results. Therefore, the use of the weakly compressible fluid model is suggested for strongly coupled FSI problems involving seemingly incompressible fluids such as water especially in cases where wave propagation in the solid plays an important role.

     

A study on the free vibration of the joined cylindrical–spherical shell structures

The free vibration characteristics of the joined spherical–cylindrical shell with various boundary conditions are investigated. The boundary conditions considered herein are free–free, simply supported–free and clamped–free for the joined cylindrical–spherical shell structures. The Flügge shell theory and Rayleigh’s energy method are applied in order to analyze the free vibration characteristics of the joined shell structure and individual shell components. In the modal test, the I-DEAS test module is used to calculate mode shapes and natural frequencies of the joined shell structure. The natural frequencies and mode shapes are calculated numerically and they are compared with those of the FEM and modal test to confirm the reliability of the analytical solution. The effects of the shallowness of the spherical shell and length of the cylindrical shell to the free vibrational behavior of joined shell structure are investigated.