Study on the Reliability of Electric Motor Boat Propeller Structure Due to Axial Load

The electrical tomography techniques are suitable for monitoring the multi-phase flow behaviors, primarily due to its advantages of fast response, non-invasive and real-time imaging capability. The dual-modality tomography technique that combines the capability of two or more tomographic modalities can provide the complementary information for better understanding of investigated multi-phase flows. However, the dualmodality technique requires some effective fusion methods to make better use of the additional information that obtained from the different modalities. In this paper, the multi-class LS- SVM has been proposed for implementing the dual-modality fusion between the two tomography modalities, i.e., the electrical capacitance tomography and electromagnetic tomography. In consideration that the multi-phase flow is extreme complex in phase distribution, consequently, the studies are conducted by combining the computational fluid dynamic (CFD) and finite element method (FEM) simulation. The phase distributions that approximate to the real situation can be collected by performing CFD simulation. By feeding the distributions into the electromagnetic field simulation, one can obtained the interelectrode capacitances and mutual inductances between coils, i.e., the ECT and EMT measurements, by FEM simulation. Subsequently, the corresponding tomographic images and fusion images can be achieved. Furthermore, the phase volume fractions and distributions can be quantitatively evaluated to verify the feasibility of proposed method. Simulation results show that the fusion method can distinguish the measured three phases with sharp boundaries and obtain the three-phase distributions in several flow regimes.

A general procedure for reliability prediction is introduced. The procedure is applied to a cylindrical ring and can be used for any similar thermal application. The procedure is classified as a physics-based reliability prediction method. It utilizes different computational tools such as Computational Fluid Dynamics (CFD), Finite Element Method (FEM), and Monte Carlo Simulations (MCS). The process starts with CFD simulation to find the convective terms necessary for the transient FEM thermal analysis. The transient FEM thermal analysis provides values for thermal stress. These values are used in the fatigue life analysis. The end result is the fatigue life of the component. As a result of input parameters uncertainty, the resulting life will be in the form of a Probability Density Function (PDF), which enables the calculation of the reliability of the component.

The integration of CFD modeling and simulation into plume measurement programs

Numerical study of thermal stresses in high-temperature proton exchange membrane fuel cell (HT-PEMFC)

In metal cutting processes the use of cutting fluids shows significant effects on workpiece surface quality by reducing thermomechanical loads on cutting tool and workpiece. Many efforts are made to model these thermomechanical processes, however without considering detailed heat transfer between cutting fluid, tool and workpiece. To account for heat transfer effects, a coupling approach is developed which combines CFD (Computational Fluid Dynamics) and FEM (Finite Element Method) chip formation simulation. Prior to the simulation, experimental investigations in orthogonal cutting in dry and wet cutting conditions with two different workpiece materials (AISI 1045 and DA 718) are conducted. To measure the tool temperature in dry as well as in wet cutting conditions, a two color pyrometer is placed inside a EDM drilled cutting tool hole. Besides tool temperature, the cutting force is recorded during the experiments and later used to calculate heat source terms for the CFD simulation. After the experiments, FEM chip formation simulations are performed and provide the chip forms for the CFD mesh generation. In general, CFD simulation and experiment are in reasonable agreement, as for each workpiece setup the measured temperature data is located between the simulation results from the two different tool geometries. Furthermore, numerical and experimental results both show a decrease of tool temperature in wet cutting conditions, however revealing a more significant cooling effect in a AISI 1045 workpiece setup. The results suggest that the placement of drilling holes has a major influence on the local tool temperature distribution, as the drilling hole equals a thermal resistance and hence leads to elevated temperatures at the tool front.

References

Oscillating electron beam welding (EBW) is necessary for the fabrication of pure niobium superconducting radiofrequency (SRF) cavities. Due to the negative effects that welding deformation and residual stress have on the performance of the SRF cavities, it is crucial to predict residual stress and welding distortion with high precision for the design of welding tooling and the optimization of welding parameters. However, the stress and distortion simulation of oscillating EBW received little attention in the previous research. In order to accurately predict the welding stress and distortion of niobium cavities with thin walls, a novel heat source with two reverse 2D Gaussian heat sources was used for the first time in the finite element method (FEM) simulation of EBW with beam oscillation. Additionally, a computational fluid dynamics (CFD) simulation of the molten pool was run as a guide for adjusting the parameters of the designed heat source. The FEM simulation with 2D Gaussian heat source was taken as a comparison. An EBW experiment of niobium sheets was performed to verify the simulation. The simulated molten pool of this model has a wider width, which is significantly closer to the actual measurement. Compared with the result estimated by 2D Gaussian heat source. The joint simulated with the designed heat source displays a smoother temperature gradient. The mechanical results suggest that the peak longitudinal stress in the weld center, the peak transverse stress in the weld center, the longitudinal contradiction, and the transverse contradiction estimated by the designed model deviate from the experimental results by only −4.88%, −4.03%, −9.32%, and −5.98%, respectively. The error of the simulation by the proposed method is dramatically smaller than the evaluation by the 2D Gaussian model. The designed heat source and the CFD validation provides a reliable simulation scheme for the oscillating EBW of thin sheets, and the oscillating EBW of thick plates will be simulated using the suggested method with the improvement of the heat source model in the future.

Bilge keels are commonly installed on commercial ships and FPSO/FLNG units to effectively mitigate roll motions. Accurate predictions of the roll damping and hydrodynamic loads are critical for the structural design of the bilge keels. In this paper, model tests and Computational Fluid Dynamics (CFD) are employed to investigate the nonlinear roll damping and hydrodynamic loads on the bilge keels. Roll decay tests and CFD simulations are carried out for a FPSO vessel to estimate the roll damping and drag coefficients of the bilge keels with extended depths. Also seakeeping model tests and CFD simulations are carried out to estimate the hydrodynamic loads on the bilge keels in regular beam waves. From this study, it is found that the drag coefficients of the Ikeda formula (1976) and Sarpkaya & O'Keefe (1996), originally developed for wall-bounded plates, can substantially under-predict the drag loads on the bilge keels attached to a FPSO vessel without considering a velocity increment factor. This paper presents the first part of the Joint Development Project (JDP) between ABS and Chevron to develop the procedures for the strength and fatigue assessment of bilge keels for FPSO/FLNG units.

During casing installation, especially when running in long horizontal wells, it is common to reach situations in which it is necessary to apply axial and torsional loads simultaneously to move a string that has become stuck. After these complex combined loading modes like pulling out, pushing downwards and twisting, it is possible to find casing internal diameter restrictions, which generate further problems during operations such as the impassability of certain tools. These situations then have to be solved by applying costly remediation strategies. API TR 5C3 provides guidance on how to combine these as mentioned loads for the pipe body; however, no guidance or standard exists to set limits to this type of load combinations in premium connections in order to avoid unintended structural damage to connections. The objective of this work is to provide guidance on the structural behavior of premium connections when subjected to combined axial and torsional loads. The authors developed a specific numerical methodology to evaluate a connection's behavior under combined axial and torsional loads. This methodology is based on validated models used to numerically estimate torques on various premium connections during the design stage and is centered on contact pressure calculations during make up and its variations with axial loading. By using this methodology, variations on connection torsional capacity can be studied in terms of applied axial loads. Additionally, different application load paths were simulated to establish worst-case scenarios for each type of connection. The behavior of connections under combined loading was then studied. After completing numerical evaluations, the authors designed a dedicated full scale testing protocol to validate numerical findings and to check the actual behavior of connections under severe combinations of torsional and axial loads. A specific state of the art testing setup was used to apply simultaneously torsional and axial loads on an instrumented premium connection test article in a laboratory environment. The test article connections were subjected to various load points and load paths for evaluation. Based on finite element models and full scale test result analysis, the response of premium connections to the simultaneous application of axial loads and torsional loads was better understood and characterized technically supporting the development of a criteria to define a safe working envelope for premium connections when operations combining axial and torsional loads are performed. A main observation is that all of the tested specimens successfully completed this very demanding sequence of combined torsional and axial loading, without showing significant structural damage. Novel/Additive Information: By means of this methodology and outputs of this work, operators, manufacturers and laboratories alike, can gain a better understanding of how to try to ensure structural performance and reliability of premium connections, as well as work towards defining limits to safely apply axial and torsional loads minimizing the risk of compromising structural integrity.

Metallurgical reactors, especially in ironmaking/steelmaking process, characterise with high-temperature turbulence, multiphase flow, mass/heat transfer and reactions. Computational fluid dynamics (CFD) simulation-based design and optimisation are of significance for efficient metallurgical performance. However, the difficulty and cost to numerically solve the nonlinear controlling equations combined with data pre/post-processing make the whole CFD simulation process time-consuming, which makes it challenging to provide in-time feedback for industrial practices. The popularisation and prosperous development of machine learning bring new opportunities for promoting CFD performance. Discussion has been made on the current research progress of applying machine learning in the whole CFD workflow including pre-processing, solving, and post-processing. Among them, the time consumed by manual pre-processing exceeds 50% of CFD tasks in general. The machine learning or parametric modelling methods can reduce pre-processing time by three orders in the estimate. The solving step is expected to be accelerated by 5 to 1000 times using machine learning. A brief review of machine learning coupled CFD is provided, as is a prospective on its development. Discussion is presented on the main functions, challenges, typical techniques and future directions of applying machine learning in CFD simulation of metallurgical reactors, for the purpose of making CFD faster, more accurate, and better visualised based on the metallurgical practices.

Flow patterns in cerebral aneurysms are clinically important. Information on inflow patterns into aneurysms is especially helpful in preventing a recurrence after coil embolization. Computational fluid dynamics (CFD) simulations of patient-specific cerebral aneurysms are feasible and provide information on flow patterns. However, flow visualization by CFD simulations is challenging for recurrent aneurysms after coil embolization because coils make it difficult to obtain precise geometry of the recurrent aneurysms. In this study, we assessed the feasibility of flow visualization of recurrent aneurysms using 3D phase-contrast magnetic resonance imaging (PC-MRI). Time-of-flight magnetic resonance angiography and 3D PC-MRI were performed in eight cases of recurrent aneurysms after coil embolization. We attempted to visualize flow inside the aneurysms using data of 3D PC-MRI and evaluated the visualization. Additionally, CFD simulations were performed in a single case. Inflow into aneurysms was visualized in all eight cases (100%). Flow patterns inside aneurysms were visualized in six cases (75%), and these were associated with a large size of recurrent aneurysms (mean size, 10.3 mm for visualized cases vs. 4.8 mm for unvisualized cases; p = 0.046, Mann-Whitney test). Flow patterns were similar between PC-MRI and CFD simulations. PC-MRI was faster and easier for observing inflow patterns than CFD simulations. This is the first study to demonstrate that flow visualization of recurrent aneurysms by 3D PC-MRI is feasible. This technique may be more practical and easier than CFD simulations, and may provide clinically helpful information.

The current state-of-the-art in solid rocket motor (SRM) ignition transient prediction is reviewed. Although the foundation of the computational fluid dynamics (CFD) approach to SRM ignition transient predictions was laid more than a quarter century ago by Peretz, Kuo, Caveny, and Summerfield, rapid advances have been made only recently. Three-dimensional (3-D) prediction tools are being developed and may require the usage of parallel computing systems to alleviate displeasingly long computer run times. In this paper, a quasi-3D CFD approach is presented as alternative cost-saving method for 3-D ignition transient flow predictions. Justifications and limitations are discussed. The approach is applied to two generic SRMs to illustrate: (1) 3-D flow phenomena that can not be obtained by using a 1-D or 2-D approach and (2) easy route that leads to parallel CFD. Introduction Depending on the application objective, solid rocket motor (SRM) ignition transient phenomena can be analyzed using methods with different degrees of computational sophistication. Currently, the analytic tools available for practical applications range from the simple volume-filling method to the complicated multi-disciplinary axisymmetric computational fluid dynamics (CFD) codes. The volume-filling method is a simple procedure for obtaining a transient chamber pressure and can be used for motor casing preliminary design. The method had been considered appropriate only for motors of small length-todiameter (L/D) ratios. However, it was reported recently by Luke et al that the volume-filling method was applied to compute the chamber pressure of the Space Shuttle's Redesigned Solid Rocket Motor (RSRM), which has a very large L/D ratio. The RSRM was modeled as two inter-connected volumes with the volume-filling method applied accordingly. The predicted chamber pressure rise rate was in good agreement with that obtained by using a 1-D CFD code. If the details of flow physics are needed, such as in the Senior Engineering Specialist Copy right © 2001 by The Aerospace Corporation. Published by the American Institute of Aeronautics and Astronautics, Inc. with Permission (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. case of dealing with the effects of propellant cracks on the SRM performance, then a flowfield solution coupled with heat transfer and ignition is required. The foundation for CFD flowfield approaches to the SRM ignition transient prediction was laid by Peretz, Kuo, Caveny, and Summer-field more than a quarter century ago. However, rapid advances have been made only recently. In the 1970s and 1980s, the progress of analytical predictions of SRM ignition transients was hampered by the lack of a reliable computational method for solving compressible flow equations and the insufficiency of available computing power. As will be illustrated later in this paper, the SRM ignition transient flowfields are dominated by the compressible flow wave interactions. The singular nature of the strong compressions and shocks in the compressible flow equations has impeded the progress of CFD to a very large extent until the TVD (total-variation-diminishing) algorithms were developed in the late 1980s and early 1990s. As a result, accurate numerical methods were available to resolve the complex wave interactions in multi-dimensional flows. At the same time, giga-flop computing powers also became available for computational fluid dynamics (CFD) simulations. Therefore, many SRM ignition transient CFD simulations were published in the 1990s.' Prediction methodologies have been also extended to include the coupling of flowfield and propellant deformation. However, most of the developments in this field are still based on the work of Peretz, et al. with the heat fluxes being computed by using a variety of semiempirical formulas. It is fair to say that, at the present, progress is hindered by the lack of reliable physical models for heat transfer. Fortunately, as indicated by Wang et al and demonstrated later in this paper, the computation of heat transfer in a CFD code can be conducted separately in a subroutine which can be replaced or updated without the need to change other parts of the code. Due to the progress in the performance enhancement of space launch systems, starand fin-shape propellant grain designs are now being used frequently. Therefore, there is urgent need to replace 1-D and 2-D approaches by 3-D methodologies. Recently, funded by DOE's Accelerated Strategic Computing Initiative (ASCI) project, the University of Illinois has established a Center for Simulation of Advanced Rockets (CSAR). The goal of the center is to develop an integrated rocket simulation tool capable of detailed, whole-system simulation of solidpropellant rockets under both normal and abnormal operating conditions. A report on the Center's progress was presented by Alvilli et al. With today's computing power, enhanced by visualization software, 3-D simulations of the SRM ignition transient are tractable. However, depending on the size of the burning area to be simulated and the computational grid resolution used, it could be very time consuming. The reason is that the mass injection on the burning surface belongs to a subsonic inflow boundary condition in CFD. An iteration procedure is therefore required, which is time consuming due to the non-linear (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. coupling of the equations. For the simulations presented in this paper, a quasi-3D approach is applied. Each case takes 36 CPU-hours on a Cray-SVl. This running time is considerably less than what is expected for a full 3-D simulation. The computation can be sped up by using parallel computing systems. As example of speed-up, super parallel computers have been applied by Wang and Taylor 13 to simulate the transonic flowfield over a complete plume-on Delta II 7925, which has one core vehicle plus 9 strap-on SRM boosters. Using 506 nodes of Intel's Paragon, a converged solution can be obtained in 48 hours. It was estimated that it would have required at least three months for the simulation if it had been done on a vector machine, CrayYMP. There is no doubt that future 3-D SRM ignition transient simulations will rely on super parallel computers. As reported by Alvi et al, super parallel computers are being used in CSAR at the University of Illinois. However, at present, full 3-D CFD simulations using parallel computers are still not popular. Furthermore, to convert existing 3-D CFD code to run on a parallel computing system is not easy task. A quasi-3D approach may be considered as alternative cost-saving approach. In this paper, the physical models currently used in CFD for SRM ignition transient are reviewed. A quasi-3D flowfield simulation methodology for SRMs with large numbers of fins will be presented. The first objective is to show the 3-D phenomena in the flowfield that could not be simulated using a 1-D or 2-D CFD approach. The second objective is to illustrate easy procedure that could lead to parallel CFD implementation. In this quasi-3D approach, axi-symmetric system of equations is applied to the bore and a 2-D Cartesian system of equations to the fins. The fundamental assumption is that the circumferential, 0-component, velocity in the bore region, and the wcomponent velocity, which is normal to the fin surface, in the fin region are negligible. The justification is that, as the number of fins increases, the planes of symmetry increase and the momenta associated with these velocity components cancelled each other on the plane of symmetry. In this paper, the flow will be assumed inviscid and the simplest heat transfer and ignition models will be applied. Since the purpose of this paper is to illustrate the methodology and the flow physics that the present approach can bring forth, generic SRMs will be used.

Computational Fluid Dynamics (CFD) simulation often needs to periodically output the intermediate results to files in the form of snapshots for visualization or restart, which seriously impacts the performance. Traditional CFD simulation takes ASCII format with typesetting in the snapshot output process, which results in precision loss of the data in the snapshot array and more storage space occupancy than the original binary format. In this paper, we propose the binary non-typesetting format optimization for the snapshot output in CFD simulation, aiming at eliminating the impact of ASCII format. In our optimization method, the snapshot array is output in binary format without typesetting. On one hand, it reserves the original binary precision in the output files, while the ASCII format always has precision loss, which seriously impacts the accuracy of CFD simulation; On the other hand, non-typesetting provide the opportunity of output the snapshot as a continuous memory block, which will signally improve the efficiency of the output. We design the multiply output mode framework for CFD applications through the combination of ASCII typesetting format and binary non-typesetting format. We implement this multiply output mode framework in the open source CFD software OpenFOAM. Experimental results on Tianhe-2 supercomputer demonstrate that our binary non-typesetting format optimization technique can achieve good optimization effect for the periodical snapshot output in CFD application.

This paper presents the predictions of deposition patterns using CFD simulations based on transient-flow behaviour of a 1.6 m high, 0.8 m diameter, pilot-scale spray dryer, following from previous studies assessing the use of Computational Fluid Dynamics (CFD) simulations to predict the deposition on a plate in a simple box configuration. The predicted deposition fluxes here have been compared with experimental data for the deposition fluxes of skim milk, maltodextrin and water. The CFD simulation results suggested that the effect of transient air flows on the vertical patterns of deposition fluxes with distance up the dryer wall for no inlet air swirl is small. The CFD simulations underpredicted the experimental values of the deposition fluxes by approximately 50%, but the simulations predicted the same experimental trends when changing the main air flow rate through the dryer. The experimentally-measured deposition fluxes were 38%, on average, higher at a main air flow rate of 113 kg/h compared with those at a flow rate of 88 kg/h. The CFD simulations predicted an average increase in deposition flux of 26% at 113 kg/h compared with 88 kg/h, so the trends with this change in operating conditions have been predicted well by the CFD simulations. One-way particle coupling has therefore shown correct trends in the deposition fluxes with respect to both positions in the dryer and different operating conditions, and such one-way coupling is several orders of magnitude faster than the more rigorous two-way coupling.

Graphite aerosol release to the containment in a water ingress accident of high temperature gas-cooled reactor (HTGR)