Experimental Test Cases Research Articles

Micro-pillar measurements of plasticity in confined Cu thin films

Sputtering was utilized to deposit polycrystalline Cu and CrN films sequentially onto Si(100) substrates, forming specimen assemblies in which predominantly 〈111〉 oriented Cu thin films of varying thicknesses were confined between Si and CrN. Cylindrical micro-pillars of CrN/Cu/Si(100) were fabricated through focused ion beam milling, with the interfaces either normal to the axial direction or at an inclination of 45°. Axial compression loading of the micro-pillars produced extensive plasticity within the thin Cu interlayers in both cases, but with distinctly different responses involving combined compression and shear when the interfaces are normal to the compression axis and constrained shear when the interfaces are inclined. Significant size effects were observed, offering new experimental evidence of scale-dependent plasticity for thin film layers, and new experimental test cases for non-local plasticity theories.

An interface force measurements-based substructure identification and an analysis of the uncertainty propagation

Substructure-decoupling techniques are used to identify a substructure as a stand-alone system while it is coupled to a complex structure. These techniques can be used for various applications, e.g., when the substructure cannot be measured separately from the complex structure, when modal testing methods are not appropriate due to the limits of the measurement equipment and for vibration-control techniques. The complex structure consists of the unknown substructure and the remaining structure. A drawback of the available substructure-decoupling techniques is that they require a model of the remaining substructure. However, when the model cannot be calculated or (experimentally) identified, the substructure-decoupling techniques cannot be used. In this paper a new approach is presented that does not require a model of the remaining substructure, but is based on an experimental identification of the interface forces. The sensitivity of the approach to experimental errors was researched. Numerical and experimental test cases are researched.

A new phenomenon of bi-stability: experimental and numerical evidence

Bistable flows around circular cylinders typically occur in the critical range of the Reynolds number (Re), due to the formation of a laminar separation bubble and its subsequent collapse on one side of the cylinder only. In turbulent flows, as well as on a rough cylinder at slightly higher Re, bistable flows tend to disappear. However, this paper gives experimental evidence of a new type of bistable flow, which is induced around a circular cylinder of finite length even at moderately high Re. Stiffening rings, applied along the height of a circular cylinder at a distance smaller than the diameter (d = 2/3D in the case of study), were found to be responsible for the phenomenon. This was demonstrated and then cross-checked by wind tunnel experiments on a H/D = 6.7 circular cylinder. The experiments were performed in two different wind tunnels, at WiSt (Ruhr University Bochum) and at CRIACIV (University of Florence). A numerical study of the latter experimental test case is also presented in this paper. A finite volume approach based on the iterative solution of the unsteady Reynolds-averaged Navier–Stokes equations has been used. Turbulence has been modelled using the SST model by Menter. The numerical results confirm the physical fundament of the phenomenon, which likely finds its explanation in the key role of the flow over the cylinder tip.

Impact of sediment transport formulations on breaching modelling

ABSTRACTThis paper analyses the ability of a classical shallow-water–Exner model to simulate the complex process of breaching of a non-cohesive earthen embankment, with a special focus on the sediment transport modelling. Two experimental test cases are presented: the overtopping of a sand embankment over its whole width, involving only vertical erosion, and a full three-dimensional (3D) breaching problem, with lateral erosion of the banks. Various sediment transport formulations are tested, including sheet-flow and classical bed-load, with and without accounting for a steep slope correction factor. It is shown that the steep slope correction does not play significant role in the simulated results. Variations are nevertheless observed in the results obtained with the different sediment transport formulations. These variations are amplified for the full breaching problem, where a local bank-failure operator is used. This highlights the importance of a good sediment transport modelling to accurately simulate a full breaching process.

Heat Transfer Prediction of a Jet Impinging a Cylindrical Deadlock Area

The turbulent heat transfer by a confined jet flowing inside a hot cylindrical cavity is investigated numerically in this paper. This configuration is found in several engineering applications such as air conditioning and the ventilation of mines, deadlock, or corridors. The parameters investigated in this work are the Reynolds number (Re, 20,000 ≤ Re ≤ 50,000) and the normalized distance Lf between jet exit and the cavity bottom (Lf, 2 ≤ Lf ≤ 12). The numerical predictions are performed by finite volume method using the second order one-point closure turbulence model (RSM). The Nusselt number increases and attains maximum values at stagnation points, after it decreases. For an experimental test case available in the literature Lf = 8, the numerical predictions are in good agreement. Processes of heat transfer are analyzed from the flow behavior and the underlying mechanisms. The maximum local heat transfer between the cavity walls and the flow occurs at Lf = 6 corresponding to the length of the potential core. Nusselt number at the stagnation point is correlated versus Reynolds number Re and impinging distance Lf; [Nu0=f(Re,Lf)].

The application of a Godunov-type shock capturing scheme for the simulation of waves from deep water up to the swash zone

A two-dimensional vertical (2DV) non-hydrostatic boundary fitted model based on a Godunov-type shock-capturing scheme is introduced and applied to the simulation of waves from deep water up to the swash zone. The effects of shoaling, breaking, surf zone dissipation and swash motions are considered. The application of a Godunov-type shock-capturing algorithm together with an implicit solver on a standard staggered grid is proposed as a new approach in the 2DV simulation of large gradient problems such as wave breaking and hydraulic jumps. The complete form of conservative Reynolds averaged Navier–Stokes (RANS) equations are solved using an implicit finite volume method with a pressure correction technique. The horizontal advection of the horizontal velocity is solved by an explicit predictor–corrector method. Fluxes are predicted by an exact Riemann solver and corrected by a downwind scheme. A simple total variation diminishing (TVD) method with a monotonic upstream-centered scheme for conservation laws (MUSCL) limiter function is employed to eliminate undesirable oscillations across discontinuities. Validation of the model is carried out by comparing the results of the simulations with several experimental test cases of wave breaking and run-up and the analytical solution to linear short waves in deep water. Promising performance of the model has been observed.

Thickness dependence of flow stress of Cu thin films in confined shear plastic flow

Abstract

Modeling of ECDM micro-drilling process using GA- and PSO-trained radial basis function neural network

Electrochemical discharge machining (ECDM) is a non-traditional manufacturing process potentially used to machine electrically non-conductive materials, such as ceramics and glass. The present paper explains the modeling of multi-input---multi-output ECDM micro-drilling of silicon nitride ceramics using radial basis function neural network (RBFNN). To establish the model, the process parameters such as applied voltage, electrolyte concentration and inter-electrode gap are treated as inputs and the important machining criteria namely material removal rate, radial overcut and heat affected zone are considered as outputs. A batch mode of training has been implemented to tune the developed RBFNN by utilizing a genetic algorithm (GA) and particle swarm optimization (PSO) methods, separately. Once, the optimal RBFNN is obtained, the performances of GA-trained RfBFNN (GA-RBFNN) and PSO-trained RBFNN (PSO-RBFNN) are compared with the help of experimental test cases. It has been observed that PSO-RBFNN is found to perform marginally better than GA-RBFNN.

High-speed underwater projectiles modeling: a new empirical approach

Supercavitating projectiles can achieve high speeds; however, this will pose technical challenges on their stability and flight performances. One of the most important issues which a high-speed underwater projectile (HSUP) deals with is the so-called planing force. In an ideal supercavitating flight scenario, the entire vehicle is considered to fly within the cavity walls. Nevertheless, in practice, disturbances can cause the vehicle to impact on the liquid–gas boundary. In such situations, the forces generated at the cavity boundary are referred to as the planning forces. The present paper discusses the in-flight dynamics of the HSUP. Equations of motion are developed for the projectile movements in the cavity while the tail impacts on the cavity wall. Dominant nonlinearities associated with planing forces are well thought-out in the modeling. Two available models and a new empirical model for prediction of the planning force are described. By using and combining these models, four methods are introduced and compared, through the simulation runs of supercavitated projectile flight, with two available experimental test cases.

Transient hygrothermal modelling of coated hemp-concrete walls

The use of hemp concrete, a sustainable material, in constructions is developing significantly. The hygrothermal properties of this hygroscopic porous material promise a good potential in terms of increasing occupants’ comfort. In this paper, numerical simulation is used to assess hygrothermal behaviour of a hemp-concrete wall submitted to transient boundary conditions. First, benchmarking the model against a well-documented experimental test case from literature proves the ability of the model to simulate heat and mass transfer in porous building material. Then, experimental results from a full-scale hemp-concrete wall exposed to transient climatic conditions are compared to numerical simulation, and a sensitivity analysis is performed. Good agreement between numerical results and experimental data is obtained for both the temperature and the relative humidity field in hemp concrete. Finally, the influence of coating layer on the hygric behaviour of the wall is investigated numerically. The ability of coating to affect moisture regulation is pointed out and the coating thickness is discussed.

Influence of Large Wake Disturbances Shed From the Combustor Wall on the Leading Edge Film Cooling

The first vane leading edge film cooling is challenging because of the highest thermal load and the complex flow interaction between the hot mainstream gas and the coolant flow. This interaction varies significantly from the stagnation region to the regions of high curvature and acceleration further downstream. Additionally, in industrial gas turbines with multiple combustor chambers around the annulus the first vane leading edges may also be exposed to large wake disturbances shed from the upstream combustor walls. The influence of these vortical structures on the first vane leading edge film cooling is numerically analyzed in this paper. In order to assess the capabilities of the flow solver TBLOCK to simulate these complex interactions an experimental test case is modeled numerically. The test case is available in the open literature and consists of a cylindrical leading edge and two rows of film cooling holes representative of industrial practice. A LES turbulence modeling strategy with the WALE subgrid scale (SGS) model is applied and compared against experimental results. Based on this validation it is decided to analyze also the wake–leading edge interaction, dominated by large scale unsteady vortical structures, using the same WALE subgrid scale LES model. The initial flow domain with the cylindrical leading edge and cooling holes is extended to incorporate the effect of the combustor wall, which is modeled as a flat plate with a square trailing edge. The location and the size of the plate are scaled to be representative of industrial practice: the plate is located upstream from the leading edge at a distance twice the leading edge diameter, and the thickness of the plate is one half of the leading edge diameter. Two different clockwise positions of the vertical combustor wall model were investigated and compared with the datum configuration: the former where the axis of the plate and the leading edge are aligned (central wake location), the latter with the combustor wall circumferentially shifted up by a quarter of the leading edge diameter (circumferentially shifted wake location). Numerical predictions show that the shed vortices from the combustor wall trailing edge have a highly detrimental effect on the leading edge film cooling by periodically removing the coolant flow from the leading edge surface. This results in an increased unsteady thermal load. These negative effects are less significant in the case of circumferentially shifted wake, due to the combined action of both shed vortices.

An approach for constituting double/multi wall BLE by single wall BLE of spacecraft shield

Ballistic limit equation (BLE) is an important tool for spacecraft shield design. An approach for constituting dual/multi wall BLE by single wall BLE is proposed. A new single wall BLE is built first based on the current BLE form analysis. A total of 100 experimental test data collected from the literature are introduced for verifications and comparisons. The new single wall BLE has obtained a better correct prediction rate of 83% than other tested BLEs. Secondly, the new Whipple shield (double wall) BLE is constituted of the new single wall BLE. In the low velocity regime the projectile isn't completely fragmented behind the bumper, the Whipple shield BLE is therefore obtained just by the summation of the single wall BLEs of the bumper and the rear wall. While in the hypervelocity regime, the expansion effect of the completely fragmented debris cloud is taken into consideration. The single wall BLE of the rear wall is multiplied by a correction term of the spacing between the two walls before the summation. The shatter regime BLE is obtained by the linear interpolation of the endpoints. A total of 268 experimental test data collected from the literature are introduced for verifications and comparisons. The new Whipple shield BLE has obtained a better correct prediction rate of 72% than other tested BLEs. Finally, the new multi-shock shield BLE is preliminarily constituted of the new single wall BLE and the Whipple shield BLE. The new multi-shock BLE is used to predict 5 experimental test cases and all of which are correct.

Numerical simulations of morphological changes in barrier islands induced by storm surges and waves using a supercritical flow model

In this paper, an advanced explicit finite volume flow model in two-dimensions is presented for simulating supercritical coastal flows and morphological changes in a tidal/coastal inlet and barrier islands due to storm surges and waves. This flow model is coupled with existing wave-action model and sediment transport model. The resulting integrated coastal process model is capable of simulating flows induced by extreme conditions such as waves, surge tides, river flood flows, etc., and morphological changes induced by rapid coastal currents and waves. This developed supercritical flow model is based on the solution of the conservative form of the nonlinear shallow water equations with the effects of the Coriolis force, uneven bathymetry, wind stress, and wave radiation stresses. The forward Euler scheme is used for the unsteady term; and the convective term is discretized using the Godunov-type shockcapturing scheme along with the HLL Riemann solver on non-uniform rectilinear grids. The accuracy of the developed model is investigated by solving an experimental dam-break test case. Barrier island breaching, overflow and overwash due to severe storm attack are simulated and the predicted morphological changes associated to the events are analyzed to investigate the applicability of the model in a coast where all the physical forces are present.

Large Eddy Simulation of a Low Speed Subsonic Jet: A Validation Study

Low-speed subsonic jets are commonly encountered in many flow systems such as in chimney exhausts, impinging jets, inlets in combustors of diesel engines and gas turbines. Large-eddy simulation of a Mach 0.1, three-dimensional plane (square) turbulent air jet was performed. The Reynolds number of the jet based on the jet width was 3 × 104. The width of the jet was 0.013 m. The aim of the present work was to develop a three-dimensional compressible parallel LES finite-volume code and validate it against an experimental free jet test case. A robust novel numerical scheme based on the blending of Riemann invariants and the exact Godunov solver, capable of handling low Mach number flows without preconditioning, was used. The Smagorinsky sub-grid scale model was used to model the unresolved stresses. An investigation was carried out into the self similarity behavior of the jet and the two-point correlations and the dissipation was computed. It is observed that istropicity of turbulence only exists in the v and w components and self-similar behavior was observed approximately beyond 90 jet widths downstream.

Design and Development of Knowledge Base Scheme for Chromite-based Resin Bonded Sand Core System

An expert system is developed in the present paper to predict the mechanical properties of chromite-based resin bonded sand core system. The various properties of sand cores, such as hardness, compression strength, collapsibility, tensile strength, hot strength, shear strength and permeability depends upon numerous process parameters, viz. percentage of resin, percentage of hardener, additives, number of strokes and curing time. In this paper, Mamdani-based fuzzy logic (FL) approach has been used to develop the knowledge base scheme(that is, forward and reverse modeling) for chromite-based resin bonded sand core system. However, the prediction efficiency of FL system depends on the knowledge base (KB), which consists of rule base and data base. Three varied approaches have been implemented in the suggested work. Manually constructed FL system is developed in the first Approach, whereas in Approach 2, genetic algorithm (GA) is exploited to optimize the data base and rule base of FL system developed in Approach 1. On the other hand in Approach 3, automatic evolution of rules is well advised along with the use of GA to optimize data base and rule base. The developed FL system annihilates the need of extensive experimental work in selecting the most potent process parameters. The performances of all three approaches have been examined with the help of twenty experimental test cases. It is to be stated that all the three developed approaches can be effectively used in foundry for making prediction. The results showed that the Approach 3 has outperformed the remaining two, in terms of prediction accuracy.

Local Source Based CFD Modeling of Effusion Cooling Holes: Validation and Application to an Actual Combustor Test Case

State-of-the-art liner cooling technology for modern combustion chambers is represented by effusion cooling (or full-coverage film cooling). Effusion is a very efficient cooling strategy typically based on the use of several inclined small diameter cylindrical holes, where liner temperature is controlled by the combined protective effect of coolant film and heat removal through forced convection inside each hole. A CFD-based thermal analysis of such components implies a significant computational cost if the cooling holes are included in the simulations; therefore many efforts have been made to develop lower order approaches aiming at reducing the number of mesh elements. The simplest approach models the set of holes as a uniform coolant injection, but it does not allow an accurate assessment of the interaction between hot gas and coolant. Therefore higher order models have been developed, such as those based on localized mass sources in the region of hole discharge. The model presented in this paper replaces the effusion hole with a mass sink on the cold side of the plate, a mass source on the hot side, whereas convective cooling within the perforation is accounted for with a heat sink. The innovative aspect of the work is represented by the automatic calculation of the mass flow through each hole, obtained by a run time estimation of isentropic mass flow with probe points, while the discharge coefficients are calculated at run time through an in-house developed correlation. In the same manner, the heat sink is calculated from a Nusselt number correlation available in literature for short length holes. The methodology has been applied to experimental test cases of effusion cooling plates and compared to numerical results obtained through a CFD analysis including the cooling holes, showing a good agreement. A comparison between numerical results and experimental data was performed on an actual combustor as well, in order to prove the feasibility of the procedure.

A new approach for optimizing automotive crashworthiness: concurrent usage of ANFIS and Taguchi method

Design optimization is presented for the crashworthiness improvement of an automotive body structure. The optimization objective was to improve automotive crashworthiness conditions according to the defined criterion (occupant chest deceleration) during a full frontal impact. The controllable factors used in this study consisted of six internal parts of the vehicle's frontal structure in a condition that their thickness was the "design parameter". First using the Taguchi method, this study analyzed the optimum conditions in discontinuous design area and impact factors and their optimal levels of design objectives were obtained by analyzing the experimental results. Next to model a precise understanding of the explicit mathematical input---output relationship, fuzzy logic is utilized which make use of full factorial design set of experimental test cases resulted from Taguchi predicting formulations. Interestingly, the optimum conditions for automotive crashworthiness occurred with 2.72 % improvement in the defined crashworthiness criterion in comparison with the baseline design while selected structural parts experienced mass reduction by 8.23 %.

Modular Turbulence Modeling Applied to an Engine Intake

The one equation Spalart–Allmaras (SA) turbulence model in an extended modular form is presented. It is employed for the prediction of crosswind flow around the lip of a 90 deg sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this, the Richardson number would suggest complete degeneration to laminar flow. Also, there are regions of high favorable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity. The latter promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The modules have been implemented in the Rolls-Royce HYDRA computational fluid dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady Reynolds-averaged Navier–Stokes (URANS) mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.

IMODFIT: Efficient and robust flexible fitting based on vibrational analysis in internal coordinates

Here, we employed the collective motions extracted from Normal Mode Analysis (NMA) in internal coordinates (torsional space) for the flexible fitting of atomic-resolution structures into electron microscopy (EM) density maps. The proposed methodology was validated using a benchmark of simulated cases, highlighting its robustness over the full range of EM resolutions and even over coarse-grained representations. A systematic comparison with other methods further showcased the advantages of this proposed methodology, especially at medium to lower resolutions. Using this method, computational costs and potential overfitting problems are naturally reduced by constraining the search in low-frequency NMA space, where covalent geometry is implicitly maintained. This method also effectively captures the macromolecular changes of a representative set of experimental test cases. We believe that this novel approach will extend the currently available EM hybrid methods to the atomic-level interpretation of large conformational changes and their functional implications.

Correcting indefinite mass matrices due to substructure uncoupling

The transmission simulator method of experimental dynamic substructuring captures the interface forces and motions through a fixture called a transmission simulator. The transmission simulator method avoids the need to measure connection point rotations, facilitates substructuring for systems with continuous connections and enriches the modal basis of the substructure model. To use this approach, one first attaches the transmission simulator to the experimental substructure and then measures the free modes of the assembly. A finite element model of the transmission simulator is then used to subtract the transmission simulator and to couple the experimental substructure to the assembly of interest. Unfortunately, in several cases the process of subtracting the transmission simulator has caused the mass matrix for the experimental substructure to become indefinite, making the substructure model difficult or impossible to use and potentially leading to erroneous results. The authors previously developed metrics that could be used to identify which modes of the experimental model led to the indefinite mass matrix. This work presents a method that utilizes those metrics with a sensitivity analysis to adjust the transmission simulator mass matrix so that the subtraction does not produce an indefinite mass matrix. A second method is presented in which the mass matrix is made positive definite by coupling additional mass to the substructure. The methods are evaluated using both numerical and experimental test cases, showing promising results.