Modified intelligent hybrid technique reducing experimental error over the entire target area

The intelligent hybrid technique proposed by Nishioka et al. can be used to analyze stress intensity factors from displacement data obtained by experiments with high accuracy and reliability. However, the hybrid technique suffers from inevitable error and noise involved in extracting displacement fields from the boundary experimentally the boundary obtained experimentally. In this paper, a modified intelligent hybrid technique is developed to improve the shortcomings of the current technique. The proposed hybrid technique reduces the influence of experimental errors not only on/along the boundary but also inside the target area. Taking the SaintVenant principle and the results of test simulations into account, the effectiveness of the proposed hybrid technique is discussed. Then, applying the proposed hybrid technique to the plate with a hole under tensile loading, the distribution of strain, stress, and displacement over the entire target area is calculated with high accuracy and reliability.     

A hybrid system for dynamic photoelasticity

An ultra-high-speed camera utilizing an acousto-optic device for deflecting light rays is described. The system employs a pulsed-ruby-laser light source used in conjunction with a Cranz-Schardin-type camera thus utilizing the best features of both systems for recording a sequence of photographs. The system has been demonstrated at framing rates of up to 200,000 frames/s and has the potential for considerably faster operation. It features the capability of producing a sequence of dynamic photographs in which the time between succesive exposures can be independently varied. Thus, the frequency at which photographs are obtained can be increased during the times of greatest interest. Experimental results demonstrating these features are given.     

A novel aseismic foundation system for multipurpose asymmetric buildings

The vulnerability of civil engineering structures with fundamental frequency, say roughly above 1?Hz, (or buildings having less than ten stories), when exposed to the strong motion phase of an earthquake is considerably reduced by means of base isolation. The low-pass filter for isolating horizontal vibrations is redesigned where the classical elastomeric bearings are substituted by a number of prestressed helical steel springs with pivoted columns along their vertical axes carrying a fraction of the dead weight and guiding the remaining horizontal motion. The base-isolated building in its fundamental mode is considered to be rigid and low-cost tuned liquid column gas dampers (TLCGDs), in optimal arrangement within the plan of the basement of the building, supply the effective damping of the remaining horizontal vibrations. TLCGD-tuning in a first step is performed by a simple transformation of the well-documented optimal parameters of the tuned mass damper (TMD) followed by fine-tuning in state space. The action of the passive damping device is commonly considered to be sufficient. Since the gas-spring effect somewhat counter acts changes in fluid mass, the absorber can be used as a water reservoir. Compatible sliding elements are innovatively designed to resist the motion of the building relative to the ground for sufficiently small disturbances by static friction, thus complete the isolation system. However, during seismic excitation, the frictional contact is released over much of the time to avoid excessive wear.     

An intelligent hybrid method to automatically detect and eliminate experimental measurement errors for linear elastic deformation fields

In a previous study, to minimize or eliminate the errors and noises associated with a full-field experimental measurement and subsequent fringe analysis such as moiré interferometry, the authors derived a variational principle minimizing the experimental measurement errors. Furthemore, on the basis of this variational principle, the authors developed an intelligent hybrid method. In several test simulations, the method has demonstrated the automatic detection and elimination of randomly incorporated errors into known correct finite element displacement fields. In this study, a fringe analysis method is developed together with the two-dimensional fast Fourier transform method. Then, experimentally recorded moiré fringe patterns are analyzed by the fringe analysis method. The conventional and intelligent hybrid analyses are carried out using the analyzed fringe information as input data. The present method verifies the automatic detection of experimental errors and noises, and the simultaneous automatic elimination of those experimental errors. This method also makes it possible to obtain a fairly smooth visualization of higher order information such as the stress and strain distributions.     

A driver gas detection device for shock tunnels

A device has been produced which can detect the contamination of the test gas by the driver gas in a reflected shock tunnel. This device monitors the static pressure in a converging duct. The duct is designed to choke at a predetermined contamination level due to the change in the specific heat ratio produced by the contaminants. Experimental results are given for a freestream enthalpy of nominally 6 MJ/kg.     

A sensitive thrust-measuring device

A centilevered beam with mounted strain gages is used to indirectly measure the velocity of a stream of drops by measuring the thrust produced by this stream. A design procedure is explained and implemented to determine a suitable geometry for this device. Sensitivity, frequency response and fragility are the factors considered in the design. Laboratory-test results show the usefulness of this device.     

A new device for in-situ movement detection and measurement

A new device for movement detection in joints is designed using the moiré technique. Archimedean spiral grids are used. A space displacement may be evaluated in two planes by vectors of known magnitudes and directions. An extremely simple design is proposed to provide stability for the system being installedin situ over long periods of time.     

A piezoelectric biaxial loading device for interfacial fracture experiments

In this paper we describe the development of a new biaxial loading device for investigating mixed-mode fracture at bimaterial interfaces. The new device makes use of piezoelectric actuators and specially arranged flexures to provide independent displacements normal and tangential to the interface. Capacitive probes and special washer load cells were used for measuring the displacements and reactive loads, respectively. A closed-loop circuit was formed with a personal computer to control the applied displacements to within 10 nm. Preliminary experiments with quartz/epoxy/aluminum sandwich specimens with cracks growing between the quartz and the epoxy found that the intrinsic toughness of this interface was 30% lower than the value for a glass/epoxy interface. Crack opening interferometry measurements having a resolution of 30 nm revealed the presence of a cohesive zone whose size was about 0.5 μm.     

A hybrid technique for improvedK determination from photoelastic data

A hybrid technique for determination of stressintensity factors from static-and dynamic-photoelastic-fringe data is proposed which combines both the generalized Westergaard stress function approach and a boundary collocation method. The new technique is especially useful for problems where a short crack initiates from a shallow notch or a crack approaches a free boundary. Modifications toward a mixed dynamic-near-field static-far-field solution procedure are discussed.     

A simple hybrid finite volume solver for compressible turbulence

A simple, explicit, hybrid finite volume method for simulating compressible turbulence is developed by combining a fourth‐order central scheme and a shock‐capturing simple low‐dissipation advection upstream splitting method. The total flux on each of the cell faces is computed as a weighted average of central/nondissipative and upwind/dissipative fluxes. The weights are determined using an unphysical oscillation sensor in addition to a more traditional discontinuity sensor used in earlier studies. Shocks are well captured, but overshoots in density are predicted around contact discontinuities that are normal to the flow. The use of the latter sensor effectively prevents these overshoots from generating spurious oscillations that travel away from the contact lines. The efficacy of the proposed method for direct or large‐eddy simulations of supersonic turbulence is established using several canonical test problems. Copyright © 2015 John Wiley & Sons, Ltd.     

A new hybrid target concept for multi-keV X-ray sources

A novel concept for using hybrid targets to create multi-keV X-ray sources was tested on the GEKKO XII facility of the OSAKA University and on the OMEGA facility of the University of Rochester. The sources were made via laser irradiation of a titanium foil placed at the end of a plastic cylinder, filled with a very low-density (2 and 5 mg/cm³) silicon-dioxide aerogel that was designed to control the longitudinal expansion of the titanium plasma. Preliminary calculations were used to determine optimal conditions for the aerogel density, cylinder diameter and length that maximize multi-keV X-ray emission. The X-ray emission power was measured on OMEGA using absolutely calibrated broad-band, diode-based CEA diagnostics, in addition to high resolution crystal spectrometers. On GEKKO XII, the heat wave propagation velocity in the aerogel was also measured with an X-ray framing camera. The advantage of using the thermal wave generated in the aerogel to heat a solid material to increase the conversion efficiency has not been fully demonstrated in these experiments. However, it was shown that a 5 mg/cm³ aerogel placed in front of a titanium foil can improve the x-ray conversion efficiency with respect to the case of 2 mg/cm³ for some target diameter and length.     

A hybrid finite element scheme for inviscid supersonic flows

I.IntroductionFiniteelementmethodshavebeenwidelyusedinhighspeedcompressibleflows,which,cansolveproblemswithcomplexboundariesconveniently.Unfortunately,itismoredifficulttoconstructhighresolutionschemesonirregularmeshesthanonregularones.Therefore,ameshadapt…     

A NEW HYBRID QUADRILATERAL FINITE ELEMENT FOR MINDLIN PLATE

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A new hybrid turbulence modelling strategy for industrial CFD

This paper presents a new strategy for turbulence model employment with emphasis on the model's applicability for industrial computational fluid dynamics (CFD). In the hybrid modelling strategy proposed here, the Reynolds stress and mean rate of strain tensors are coupled via Boussinesq's formula as in the standard k–εmodel. However, the turbulent kinetic energy is calculated as the sum of the normal Reynolds‐stress components, representing the solutions of the appropriate transport equations. The equations governing the Reynolds‐stress tensor and dissipation rate have been solved in the framework of a ‘background’ second‐moment closure model. Furthermore, the structure parameter C‐µ has been re‐calculated from a newly proposed functional dependency rather than kept constant. This new definition of C‐µ has been assessed by using direct numerical simulation (DNS) results of several generic flow configurations featuring different phenomena such as separation, reattachment and rotation. Comparisons show a large departure of C‐µ from the commonly used value of 0.09. The model proposed is computationally validated in a number of well‐proven fluid flow benchmarks, e.g. backward‐facing step, 180° turn‐around duct, rotating pipe, impinging jet and three‐dimensional (3D) Ahmed body. The obtained results confirm that the present hybrid model delivers a robust solution procedure while preserving most of the physical advantages of the Reynolds‐stress model over simple k–εmodels. A low Reynolds number version of the hybrid model is also proposed and discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

A three-dimensional simulation of wind flow around buildings

The steady Navier–Stokes equation is solved to simulate the wind-flow environment of three-dimensional configurations of buildings. The method assumes an incident wind described by a power-law velocity profile. A new method for controlling the two-part nested solution iteration is introduced. The simulation is compared to some published wind-tunnel measurements.     

A hybrid subcell-remapping algorithm for staggered multi-material arbitrary Lagrangian-Eulerian methods

A new flux-based hybrid subcell-remapping algorithm for staggered multimaterial arbitrary Lagrangian-Eulerian(MMALE) methods is presented. This new method is an effective generalization of the original subcell-remapping method to the multi-material regime(LOUB`ERE, R. and SHASHKOV, M. A subcell remapping method on staggered polygonal grids for arbitrary-Lagrangian-Eulerian methods. Journal of Computational Physics, 209, 105–138(2005)). A complete remapping procedure of all fluid quantities is described detailedly in this paper. In the pure material regions, remapping of mass and internal energy is performed by using the original subcell-remapping method.In the regions near the material interfaces, remapping of mass and internal energy is performed with the intersection-based fluxes where intersections are performed between the swept regions and pure material polygons in the Lagrangian mesh, and an approximate approach is then introduced for constructing the subcell mass fluxes. In remapping of the subcell momentum, the mass fluxes are used to construct the momentum fluxes by multiplying a reconstructed velocity in the swept region. The nodal velocity is then conservatively recovered. Some numerical examples simulated in the full MMALE regime and several purely cyclic remapping examples are presented to prove the properties of the remapping method.     

A hybrid method for computing the flow of viscoelastic fluids

A hybrid method for computing the flow of viscoelastic and second-order fluids is presented. It combines the features of the finite difference technique and the shooting method. The method is accurate because it uses central differences. Its convergence is at least superlinear. The method is applied to obtain the solutions to three problems of flow of Walters' B' fluid: (a) flow near a stagnation point, (b) flow over a stretching sheet and (c) flow near a rotating disk. Numerical results reveal some new characteristics of flows which are not easy to demonstrate using the perturbation technique.     

A hybrid method for bubble geometry reconstruction in two-phase microchannels

Understanding bubble dynamics is critical to the design and optimization of two-phase microchannel heat sinks. This paper presents a hybrid experimental and computational methodology that reconstructs the three-dimensional bubble geometry, as well as provides other critical information associated with nucleating bubbles in microchannels. Rectangular cross-section silicon microchannels with hydraulic diameters less than 200 μm were fabricated with integrated heaters for the flow experiments, and the working liquid used was water. Bubbles formed via heterogeneous nucleation and were observed to grow from the silicon side walls of the channels. Two-dimensional images and two-component liquid velocity field measurements during bubble growth were obtained using micron-resolution particle image velocimetry (μPIV). These measurements were combined with iterative three-dimensional numerical simulations using finite element software, FEMLAB. The three-dimensional shape and location of the bubble were quantified by identifying the geometry that provided the best match between the computed flow field and the μPIV data. The reconstructed flow field through this process reproduced the experimental data within an error of 10–20%. Other important information such as contact angles and bubble growth rates can also be estimated from this methodology. This work is an important step toward understanding the physical mechanisms behind bubble growth and departure.     

A new hybrid technique for in-plane characterization of orthotropic materials

In this paper we present a novel hybrid procedure for the in-plane mechanical characterization of orthotropic materials. The material identification reverse engineering problem is solved by combining speckle interferometry and numerical optimization. The rationale behind the entire process is the following: for any specimen to be characterized and which has been subjected to some loading condition, it is possible to express the difference between experimental data and analytical/numerical predictions by means of an error function ψ, which depends on the elastic constants of the material. The ψ error will decrease as the elastic constants come close to their target values. Here, we build the ψ function as the difference between the displacement field measured with speckle interferometry and its counterpart computed by means of finite element analysis. Since the ψ function is highly non-linear, it has to be optimized with a global optimization algorithm, which perform a random search in the elastic constants design space. The hybrid material identification process finally allows us to determine values of the elastic constants. In order to prove the feasibility of the present approach, we have determined the in-plane elastic properties of an eight-ply composite laminate (woven fiberglass-epoxy) used as a substrate for printed circuit boards. The results indicate that the procedure proposed in this paper was able to accurately characterize the material under investigation. Remarkably, the elastic constants found by the identification procedure were less than 0.7% different from their target values, while the residual error between the displacements measured by speckle interferometry and those computed at the end of the optimization process was less than 3%. L. Lamberti is an Assistant Professor, and C. Pappalettere (SEM Member and President of the Italian Society of Stress Analysis) is Professor of Mechanical Engineering and Experimental Mechanics, Politecnico di Bari, Dipartimento di Ingegneria Meccanica e Gestionale, Viale Japigia 182, 70126 Bari, Italy