Full Computational Model Research Articles

Topology optimization and experimental validation of mass-reduced aircraft wing designs

Development and evaluation of a novel design of mass reduced aircraft wing ribs through topology optimization is reported herein. For comparison, the same examination is performed on ribs with normal internal geometry. The wing rib design is based on the Gulfstream G650 transonic jet. The rib is divided into three segments for analysis based around the positions of the two spars. Only the center section of the rib is mass optimized, while the leading and trailing edges of the ribs are kept solid. Methodology in this study includes the k-Ω shear stress transport turbulence model computational fluid dynamic simulation as well as static and transient finite element simulations. The optimized wing rib is found to be between 8% and 15% lighter than traditional wing ribs depending on configuration. Simulation of the wing showed a tip deflection of 13.8 cm upward at an angle of 1.1°. An experimental scaled model of the optimized wing subjected to near identical bending loads as identified in the FEA simulation is applied to validate stress concentrations and performance. It is found that in the simulations, average stress never exceeded the factor of safety prescribed by the FAA. While the average factor of safety on the full computational model was 2.649, the average factor of safety on the experimental model was 9.185. Four strain gauges attached to the experimental model are used to compare the strains at similar locations on the computational model. The experimental results validate the CFD simulation results with acceptable tolerances.

High-resolution pressure transducer design and associated circuitry to build a network-ready smart sensor for distributed measurement in oil and gas production wells

Miniaturized single-mode thickness-shear pressure transducer combined with high-temperature SOI, silicon on insulator, integrated circuit technology is proposed as network-ready high-pressure high-resolution smart sensor for distributed data acquisition in oil and gas production wells. The transducer miniaturization is investigated with a full 3D computer model previously developed by the authors to assess the impact of intrinsic losses and various geometrical features on transducer performance. Over the last decades there has been a trend toward size reduction of high-resolution pressure transducer. The implemented model provides insight into the evolution of high-resolution pressure transducers from Hewlett-Packard™ to Quartzdyne™ and beyond. Distributed measurement in production oil wells in extreme harsh environment, such as found in the pre-salt layer, is an unsolved problem. The industry move toward electrified wells offers an opportunity for application of smart sensor technology and power line communications to achieve distributed high-resolution data acquisition.

A numerical study on the through thickness shear behavior of EPS sandwich panels

The expansion of industry has rapidly increased the need of energy; necessitating a greater usage of energy resources and posing substantial environmental dangers in the process. Thus, an energy-efficient modular building system appears to be a must-have choice for the India's required mass housing at affordable cost, while the environmental concerns are also looked into account. Insulating Construction Panels are one of the pre-casted building materials; comprising of a core panel of expanded polystyrene insulation encased in galvanized welded steel reinforcing mesh and shear connectors, which is then placed to the site with pressurized concrete skins on both the sides of the core. The structural integrity of these buildings, on the other hand, is heavily reliant on the functioning of these shear connectors and the degree of composite action (DCA). The present study aims to develop a full scale computational model of a single storey building made up of modular EPS panels, to study the effect of spacing and the consequences of different kinds of shear connector failures. Furthermore, the effect of door and window openings on the structural responses of the EPS panel building are discussed. The through thickness shear behavior of these materials are also investigated using multiple static and dynamic analyses steps. The mechanical behaviors of these panels are observed to be widely varying with the spacing, diameter, and adequacy of the shear connectors. The results infer that the present work seems to be necessary for the safety assurance of the insulated precast building panel structural systems, which has a lot of potential for practical usage and thus can help to accomplish the objectives of efficient and economical sustainable building systems in the upcoming years.

Implementation of a Multi-cell Approach in the Multi-Physics Calculations of an Aqueous Homogeneous Reactor

Nowadays, the Aqueous Homogeneous Reactor (AHR) technology is under study for its use in the production of medical isotopes. This technology has proven to be potentially advantageous for this purpose due to its low cost, small critical mass, inherent passive safety, and simplified fuel handling, processing, and purification characteristics. Among the studies being carried out is computational modeling and simulation, which represents a key technology in the pursuit for improvements in efficiency, safety, and reliability of these systems. This paper aims to expand upon a previous AHR computational model through the implementation of a multi-cell approach for the improvement of the calculations using a methodology for the multi-physics and multi-scale coupling of the neutronic and thermal-hydraulic codes. It was found that these additions to the original model cause a small change to the overall reactor behavior. Thermal-hydraulic parameters such as, average fuel solution temperature and velocity, gas volume fraction and average radiolytic gas bubbles velocity undergo a variation of 0.161 °C, 0.0009 m/s, 0.015% and 0.0003 m/s. In contrast, significant local differences were obtained mainly for the fuel solution temperature and radiolytic gas bubbles volume fraction. It was verified that a simplified AHR computational model consisting of a 20° section of the fuel solution is able to adequately reproduce the results of the full AHR computational model.

A full 3D computational model for tilting-pad journal bearings and comparing it to 2D models

In this paper, a new model is developed to analyze a tilting pad bearing with 5 pads in a load-between-pad configuration in three dimensions. Isothermal Navier-Stokes equations with phase fraction equation for cavitation model are solved for 3D steady state simulation using the OpenFOAM package. Results show that with decrease in eccentricity, the difference between the 3D and 2D simulations increases. This is mainly due to the fluid inertia effects when entering the pads. Although applying the inertial boundary condition to the 2D model reduces the discrepancy, the difference in pressure distribution remains. Thus, at the lower eccentricity ratio, it is highly recommended to use 3D model in order to calculate pressure distribution precisely in tilting pad journal bearing.

Robust Three-Dimensional Acoustic Performance Probabilistic Model for Nacelle Liners

This paper is devoted to the robust optimization of nacelle liners (acoustic treatments). The full computational aeroacoustic model is based on the convected Helmholtz equation in presence of a nonhomogeneous flow velocity field, which is computed by solving the potential Euler equations. Uncertainties are taken into account in order to increase the robustness of the predictions. A reduced-order computational aeroacoustic model is constructed in order to implement the nonparametric probabilistic model of uncertainties induced by the modeling errors in the aeroacoustic model and in the liner model. In addition, the uncertainties on the acoustic excitation induced by the fan are taken into account using the parametric probabilistic approach. The developed methodology is applied to a three-dimensional nacelle intake and allows for computing the confidence regions of the random far-field radiated pressure in terms of random sound pressure level, which are compared with experiments for one flight condition, one frequency, and for two types of liners.

Numerical investigation on full thermodynamic venting process of liquid hydrogen in an on-orbit storage tank

Liquid hydrogen has been identified as a promising propellant for long-duration space missions, benefiting from its high specific impulse when paired with liquid oxygen. A full procedural computational fluid dynamic model was proposed for the jetting, mixing, throttling, and venting processes of thermodynamic venting systems (TVS) for the purpose of minimizing liquid hydrogen boil-off on orbit. In addition to the mixing and jetting components as well as the fluid domain inside the storage tank, the external fluid circulation loop and the throttling device were also coupled into the solver in the form of user-defined code, which enabled simulation of the continuous complete thermodynamic cycles. The evaporation/condensation intensity factors for the liquid-vapor phase change were confined in a smaller range than those used in other studies through theoretical analysis. To enhance the numerical stability, the well-known Lee model for liquid-vapor phase change was modified by introducing a smoothing function. Simulations with a variety of initial temperatures, mass flow-rates and vent ratios were conducted, which revealed that the condensation of superheated vapor contributes to the depressurization processes noticeably greater than the disturbance of the temperature stratification. Depressurization efficiency was introduced for evaluating the TVS performance during the jetting process. Significant performance enhancement was observed when the temperature difference between the liquid and the ullage before jetting was enlarged. The self-pressurization period was found lasting longer time under on-orbit condition than that on the ground, which is attributable to the floating of the bulk liquid and higher uniformity of the temperature distribution after the jetting process in the absence of gravity.

Thermo-hydrodynamic analytical model, numerical solution and experimental validation of a radial heat pipe with internally finned condenser applied for building heat recovery units

Heat pipes have been extensively applied in the domain of energy conversion and heat recovery application. A novel radial heat pipe with internally finned condenser has been proposed to recover waste heat from air conditioning units. Full mathematical description and computational fluid dynamics model were developed to predict the loop flow and thermal performance in a single radial heat pipe, respectively. The research focuses mainly on the effects of input power, filling ratio, pipe diameter, and velocity of the cooling water on the thermal performance and entropy generation rate of this novel heat pipe. Numerical results illustrate that average reductions in total thermal resistance with utilization of fins approximately achieved 8.69% and 14.78% for fins nf = 4 and nf = 8, respectively. Similarly, entropy generation rate shows an average decrease of 19.4% and 37.5% for identical operations. Additionally, the effect of internally finned condenser on the multiphase fluid flow has been comprehensively analyzed, including the break of the condensed film, generation of bubbles and nucleation boiling. The results further indicate that incorporation of internal fins has a significant influence on enhancing thermal homogenization and waste thermal recovery efficiency of a radial heat pipe. Case results agreed well with experimental data within average deviation being no more than 10%.

Combining LS-SVM and GP Regression for the Uncertainty Quantification of the EMI of Power Converters Affected by Several Uncertain Parameters

This article deals with the development of a probabilistic surrogate model for the uncertainty quantification of the voltage output spectral envelope of a power converter with several stochastic parameters. The proposed approach relies on the combination of the least-squares support vector machine (LS-SVM) regression with the Gaussian process regression (GPR), but it can suitably be applied to any deterministic regression techniques. As a first step, the LS-SVM regression is used to build an accurate and fast-to-evaluate deterministic model of the system responses starting from a limited set of training samples provided by the full-computational model. Then the GPR is used to provide a probabilistic model of the regression error. The resulting LS-SVM+GPR probabilistic model not only approximates the system responses for any configuration of its input parameters, but also provides an estimation of its prediction uncertainty, such as the confidence intervals (CIs). The above technique has been applied to qualify the uncertainty of the spectral envelope of the output voltage of a buck converter with 17 independent Gaussian parameters. The feasibility and the accuracy of the resulting model have been investigated by comparing its predictions and CI with the ones obtained by five different surrogate models based on state-of-the-art techniques and by the reference Monte Carlo results.

A computational model of open-irrigated radiofrequency catheter ablation accounting for mechanical properties of the cardiac tissue.

Radiofrequency catheter ablation (RFCA) is an effective treatment for cardiac arrhythmias. Although generally safe, it is not completely exempt from the risk of complications. The great flexibility of computational models can be a major asset in optimizing interventional strategies if they can produce sufficiently precise estimations of the generated lesion for a given ablation protocol. This requires an accurate description of the catheter tip and the cardiac tissue. In particular, the deformation of the tissue under the catheter pressure during the ablation is an important aspect that is overlooked in the existing literature, which resorts to a sharp insertion of the catheter into an undeformed geometry. As the lesion size depends on the power dissipated in the tissue and the latter depends on the percentage of the electrode surface in contact with the tissue itself, the sharp insertion geometry has the tendency to overestimate the lesion obtained, which is a consequence of the tissue temperature rise overestimation. In this paper, we introduce a full 3D computational model that takes into account the tissue elasticity and is able to capture tissue deformation and realistic power dissipation in the tissue. Numerical results in FEniCS-HPC are provided to validate the model against experimental data and to compare the lesions obtained with the new model and with the classical ones featuring a sharp electrode insertion in the tissue.

Modeling high-resolution down-hole pressure transducer to achieve semi-distributed measurement in oil an d gas production wells

A full 3D computer model is developed to evaluate the performance impact of intrinsic loss and various geometrical features in high-resolution pressure transducer. The intrinsic loss is modeled as viscosity factors, which allows for a more efficient computer model. In this paper, the developed model is applied to yield an insight in the evolution of high-resolution down-hole pressure transducer, from Hewlett-Packard\texttrademark\, to Quartzdyne\texttrademark. As the quality factor is related to the inverse of the resolution, the transducing element optimization process to achieve the highest quality factor possible is investigated, considering the impact of crystal quality and geometrical features, such as: thickness, diameter and convexity (plano-convex and bi-convex). Temperature-dependent elastic constants are used to improve the model accuracy in modeling temperature effects on the vibrating resonator-type transducer. Boundary load conditions are used to simulate hydrostatic pressure. The simulations to extract the frequency shift are carried out in the range of $14\,psi$ ($96.5\,kPa$) to $20000\,psi$ ($137.89\,MPa$) and $0\,^oC$ to $200\,^oC$ for pressure and temperature, respectively, as such ranges are typically found in oil and gas wells. A discrepancy in the published temperature dependence has been found. A miniaturization path to achieve semi-distributed measurement in oil and gas production wells is presented.

A Two-Parameter Description for the Injury Risk of Flash Bangs with Uncertainty

We study the random injury outcome caused by multiple flash bang submunitions on a crowd. We are particularly interested in the fluctuations in injury outcome among individual realizations. Previously, to simulate the distribution of the actual number of injured, we developed a comprehensive Monte Carlo model. While the full computational model is important for thorough theoretical investigations, in practical operations, it is desirable to characterize the phenomenological behavior of injury outcome using a concise model with only one or two parameters. Conventionally, the injury outcome is indicated by the average fraction of injured, which is called the risk of significant injury (RSI). The single metric RSI description fails to capture fluctuations in the injury outcome. The number of injured in the crowd is influenced by many random factors: the aiming error of flash bang mortar, the dispersion of submunitions after mortar burst, the amount of acoustic dose reaching individual subjects, and the biovariability of individual subjects’ reactions to a given acoustic dose. We aim to include these random factors properly and concisely. In this study, we represent the random injury outcome as a compound binomial model, in which the hidden injury probability is drawn from a two-parameter model distribution. We formulate and examine six model distributions for the injury probability. The best performer is a mixture of uniform and triangle distributions, parameterized by (RSI, dp) where dp is the standard deviation of the hidden injury probability. This mixture model predicts the behavior of injury outcome with uncertainty, based solely on the two parameters (RSI, dp) in the flash bang description. For example, we can predict the probability of the injury outcome not exceeding a prescribed tolerance. We advocate the adoption of this two-parameter characterization for flash bangs to replace the single-parameter RSI description. Whenever we need to give a high level coarse description of a flash bang situation, we state that the injury risk is represented by (RSI, dp).

Thermostructural observation and adaptive control of fractal structure in ball-milled materials

This research introduces dynamic modeling and real-time control of fractal structure in particulate materials fabricated by the ball milling process, specifically addressing challenges of unavailable real-time non-destructive and non-invasive imaging measurements in the enclosed rotating vials. A description of the internal temperature dynamics in the container is established along with a thermal regulator based on external temperature feedback. The fractal dimension is introduced as a structural measure, and its dynamics is established via an analytical formulation through a lumped model, along with a full thermostructural computational model of the ball milling particulate microstructure. These models are used as real-time observers of inaccessible internal states during the process. In addition, they are used as model references in an adaptive control system, regulating the fractal structure with adaptation via external temperature measurements, available experimentally via an infrared thermocouple. The controller is designed on the basis of the dynamic models and is tested experimentally. The controller is demonstrated to command the duration of the process at steady conditions to obtain the necessary thermal exposure yielding the desired microstructure for the ball-milled particulates.

Piston geometry effects in a light-duty, swirl-supported diesel engine: Flow structure characterization

This work studied how in-cylinder flow structure is affected in a light-duty, swirl-supported diesel engine when equipped with three different piston geometries: the first two featuring a conventional re-entrant bowl, either with or without valve cut-outs on the piston surface and the third featuring a stepped-lip bowl. Particle image velocimetry experiments were conducted inside an optical engine to measure swirl vortex intensity and structure during the intake and compression strokes. A full computational model of the optical diesel engine was built using the FRESCO code, a recently developed object-oriented parallel computational fluid dynamics platform for engine simulations. The model was first validated against the measured swirl-plane velocity fields, and the simulation convergence for multiple cycles was assessed. Flow topology was studied by addressing bulk flow and turbulence quantities, including swirl structure, squish flux, plus geometric and operating parameters, such as the presence of valve cut-outs on the piston surface, compression ratio and engine speed. The results demonstrated that conventional re-entrant bowls have stronger flow separation at intake, hampering bowl swirl, but higher global swirl than for stepped-lip bowls thanks to a stronger and more axisymmetric squish mechanism and less tilted swirl. Stepped-lip bowls have larger inhomogeneities (tilt and axisymmetry) and higher turbulence levels, but also faster turbulence dissipation toward top dead center. They have weaker squish flux but larger squish inversion momentum as a result of the smaller inertia.

Optimum seismic design of a power plant building with pendulum tuned mass damper system by its heavy suspended buckets

This paper focuses on the seismic performance of a typical coal-fired power plant with suspended non-structural coal buckets inside the structure. In order to systematically evaluate and minimize the seismic responses of the power plant, this research developed a mechanism to optimally design the equivalent pendulum-type tuned mass damper (PTMD) system such that the inter-story drifts under earthquake excitations are minimized while the coal buckets are also protected. A full scale computational model of the tested specimen is developed and its modeling details are validated against the experimental results. Subsequently, the optimal ranges for PTMD variables have been derived according to the cases showing most structural response reductions. As a result, a conceptual “length-adaptive” PTMD design according to the optimized results is proposed for the mass-varying system. It is shown that the optimal implementation of PTMD can significantly reduce the inter-story drifts and it also outperforms the adopted PTMD design in the real structure. The study demonstrates a systematic way of achieving the optimal real-structure PTMD design with considerations of uncertainties in earthquake input, system nonlinearities, and other structural complexities.

Numerical prediction of thrombus risk in an anatomically dilated left ventricle: the effect of inflow cannula designs.

BackgroundImplantation of a rotary blood pump (RBP) can cause non-physiological flow fields in the left ventricle (LV) which may trigger thrombosis. Different inflow cannula geometry can affect LV flow fields. The aim of this study was to determine the effect of inflow cannula geometry on intraventricular flow under full LV support in a patient specific model.MethodsComputed tomography angiography imaging of the LV was performed on a RBP candidate to develop a patient-specific model. Five inflow cannulae were evaluated, which were modelled on those used clinically or under development. The inflow cannulae are described as a crown like tip, thin walled tubular tip, large filleted tip, trumpet like tip and an inferiorly flared cannula. Placement of the inflow cannula was at the LV apex with the central axis intersecting the centre of the mitral valve. Full support was simulated by prescribing 5 l/min across the mitral valve. Thrombus risk was evaluated by identifying regions of stagnation. Rate of LV washout was assessed using a volume of fluid model. Relative haemolysis index and blood residence time was calculated using an Eulerian approach.ResultsThe inferiorly flared inflow cannula had the lowest thrombus risk due to low stagnation volumes. All cannulae had similar rates of LV washout and blood residence time. The crown like tip and thin walled tubular tip resulted in relatively higher blood damage indices within the LV.ConclusionChanges in intraventricular flow due to variances in cannula geometry resulted in different stagnation volumes. Cannula geometry does not appreciably affect LV washout rates and blood residence time. The patient specific, full support computational fluid dynamic model provided a repeatable platform to investigate the effects of inflow cannula geometry on intraventricular flow.

Aerodynamic performance analysis of partial admission dual row control stage at different working conditions

Aerodynamic performance of partial admission dual row control stage at the rated and off-designed operating conditions was numerically investigated using three-dimensional Reynolds-averaged Navier-Stokes (RANS) and k -e turbulence model. The full scale computational model includes the four nozzle boxes, full first and second row rotor blade, as well as two admission guided vanes with consideration of the rotor tip clearance and stator diaphragm gland. The numerical results of the mass flow rate, power output and aerodynamic efficiency of the dual row control stage at the rated and off-designed conditions are well in agreement with the experimental data. The obtained results at rated condition show that the blocking segmental arc of guided vane increased the exit pressure of the upstream nozzle, which reduced the mass flow rate and changed the aerodynamic performance of the nozzle. The circumferential non-uniformity of aerodynamic parameters and partial admission losses increases with the decrease in the admission degree for the computed three operating conditions. The analysis of axial steam velocity shows that the trailing shedding vortex and the complex flow vortex in flow passages have a significant impact on the magnitude and direction of the axial steam velocity. Furthermore, the partial admission degree changed the proportions of the power output of two rotor blade rows. The lower partial admission degree leads to a larger proportion of the power output of the first rotating blade row. The detailed flow pattern in the partial admissions dual row control stage at different operating conditions is also illustrated.

Depth-integrated equation for hydro-acoustic waves with bottom damping

AbstractWe present a depth-integrated equation for the mechanics of generation, propagation and dissipation of low-frequency hydro-acoustic waves due to sudden bottom displacement in a weakly compressible ocean overlying a weakly compressible viscous sediment layer. The model is validated against a full 3D computational model. Physical properties of these waves are studied and compared with those for waves over a rigid sea bed, revealing changes in the frequency spectrum and modal peaks. The resulting model equation can be used for numerical prediction in large-scale domains, overcoming the computational difficulties of 3D models while taking into account the role of bottom dissipation on hydro-acoustic wave generation and propagation.

The potential of an observational data set for calibration of a computationally expensive computer model

Abstract. We measure the potential of an observational data set to constrain a set of inputs to a complex and computationally expensive computer model. We use each member in turn of an ensemble of output from a computationally expensive model, corresponding to an observable part of a modelled system, as a proxy for an observational data set. We argue that, given some assumptions, our ability to constrain uncertain parameter inputs to a model using its own output as data, provides a maximum bound for our ability to constrain the model inputs using observations of the real system. The ensemble provides a set of known parameter input and model output pairs, which we use to build a computationally efficient statistical proxy for the full computer model, termed an emulator. We use the emulator to find and rule out "implausible" values for the inputs of held-out ensemble members, given the computer model output. As we know the true values of the inputs for the ensemble, we can compare our constraint of the model inputs with the true value of the input for any ensemble member. Measures of the quality of constraint have the potential to inform strategy for data collection campaigns, before any real-world data is collected, as well as acting as an effective sensitivity analysis. We use an ensemble of the ice sheet model Glimmer to demonstrate our measures of quality of constraint. The ensemble has 250 model runs with 5 uncertain input parameters, and an output variable representing the pattern of the thickness of ice over Greenland. We have an observation of historical ice sheet thickness that directly matches the output variable, and offers an opportunity to constrain the model. We show that different ways of summarising our output variable (ice volume, ice surface area and maximum ice thickness) offer different potential constraints on individual input parameters. We show that combining the observational data gives increased power to constrain the model. We investigate the impact of uncertainty in observations or in model biases on our measures, showing that even a modest uncertainty can seriously degrade the potential of the observational data to constrain the model.

TU‐E‐108‐09: Development of An Einzel Electron Focusing Lens for Microbeam Radiation Therapy Device

Purpose: The purpose of this work is to develop a novel Einzel electron focusing lens for carbon nanotube (CNT) field emission based microbeam radiation therapy (MRT). The CNT cathode used for the proposed microbeam radiation source has a unique linear cathode profile so that the focusing structure needs to be optimized in order to achieve the desired focal spot size for efficient generation of microbeam radiation. Methods: The proposed design of the MRT device has a square system configuration with four independent linear x‐ray tube modules. Each tube module includes a linear carbon nanotube field emission cathode array, which is the core component of the MRT device. The CNT cathode is comprised of 5 individually controlled CNT cathode segments, each of which has a dimension of 2.5mm×30mm. A commercial software package (Opera 3D, Cobham plc) was used to simulate and design the optimal focusing structure. A full scale computer model covering the entire electron beam path was constructed for the electron optical simulation. Results: Based on the simulation, the two‐stage electrostatic focusing lens is capable of providing the 102um focal spot size required for the proposed microbeam radiation therapy treatment with 100um beam width. Based on our simulation results, we are able to achieve over 65% electron beam transmission rate. Both results were verified experimentally using a small scale testing x‐ray chamber. Conclusion: We have designed a novel Einzel electron focusing lens to achieve the desired focal spot in order to improve the efficiency of microbeam generation, thus the dose rate. The simulation and experiment show the two‐stage electrostatic focusing lens is capable of providing a 102um effective focal spot size. Meanwhile we have also demonstrated reasonable electron beam transmission rate (>65%), which is critical in terms of achieving high x‐ray output.