The understanding of hydrogen embrittlement (HE) is of significant importance and fundamental interest owing to its negative effects on industrial metallic materials. The effect of solute H on the void coalescence and growth needs to be clarified. Using molecular dynamics simulation, the evolution of preexisting nano voids is studied in the presence of H atoms. As the per unit area concentration of trapped H atom on void surface reaches 0.45 /Å 2 , the movement of void is observed. It proceeds along with the interdiffusion of H and Fe atoms around the voids. Strain-mediated diffusion of H atoms from void surface to the zone between nearest voids occurs at first. Then the Fe atoms are affected by migrated H and diffuse in the opposite direction following the principle of energy minimization. Such mechanism can help us understand the formation of high pressure bubble at nano scale. Based on this useful information, some methods could be obtained to prevent the growth of voids further, such as strengthening the stability of metal lattice around voids by dopant etc.

This paper presents a comparative study of sensitivity analysis (SA) and simplification on artificial neural network (ANN) based model used for ship motion prediction. Considering traditional structural complexity of ANN usually results in slow convergence, SA, as an efficient tool for correlation analysis, can help to reconstruct the ANN model for ship motion prediction. An ANN-Garson method and an ANN-EFAST method are proposed, both of which utilize the ANN for modeling but select the input parameters in a local and a global fashion, respectively. Through the benchmark tests, ANN-EFAST exhibits superior performance in both linear and nonlinear systems. Further test on ANN-EFAST via a case study of ship heading prediction shows its cost-effective and timely in compacting the ANN based prediction model.

Pilot flame have been widely used for flame stabilization in low-emission gas turbine combustors. However, effects of pilot flame on dynamic instabilities are not well understood. In this work, the dynamic interactions between main and pilot flames were studied by measurements and modeling in the flame response, with both flames subjected to perturbation, i.e., with a dual-input forcing. The paper analyzed the experimental results of both the total flame response and the interaction process. A burner was designed with central pilot flame to stabilize a premixed axi-symmetric V-shaped methane flame. Servo valve and sirens were used to generate forcing in the pilot and main flames, respectively. A diagnostic system was applied to measure the flame structure and heat release rate. The effects of forcing frequency, forcing amplitude, phase difference between the two forcing signals to the main and pilot flames as well as the Reynolds number were studied. Both the flame transfer function (FTF) and the flame dynamic structure were measured and discussed. It was found that the total flame response was modified by the perturbation in the pilot flame. The mechanism may be lying in the effect of pilot flame on the flow field of the burnt side. To further testify the hypothesis, an analytical model was developed based on the linearized G-equation with low amplitude assumptions. Although the assumptions made in the model to address the effect of pilot flame on the burnt flame flow field were simplified, good agreements were found between the prediction and the experiment results. Based on the analysis conducted in this paper, some further considerations may be needed when developing combustion systems with a central injection, since perturbations in the pilot flame may affect the performance of the main flame. Further experiments and analysis may be needed to dig deeper into the physical basics such as measurements or more realistic modeling of the flow fields and non-linear effects.

A thermo-solid coupling model of a gun tube is established. The inner boundary conditions of the tube are obtained by carrying out the computations of the boundary-layer model and the core-flow model of interior ballistics. The finite element method is employed here to numerically solve the thermo-solid coupling model. The transient stress and temperature of the coupling field of gun tube subjected to high-frequency periodic dynamic pressure and thermal pulse are computed. The overall state of the stress field and the thermoelastic coupling effect are attained. The strength of gun tube subjected to dynamic pressure load, thermal load and joint load is analyzed respectively, and the cases under the above three kinds of working conditions are compared. The life of gun tube is also studied. A life test system is set up, and detailed measurements about temperature and erosion are performed. A model to estimate the maximum radial wear rate of gun tube is built. Based on the computational results of temperature, the ablation wear extent and the limit life of a gun tube subjected to successive shooting are computed. The models and the analytical techniques adopted here provide important references for gun-tube design and life improvement.

A detailed CFD analysis was performed to investigate the effect of mixing vanes on single-phase flow distribution in a 5×5 rod bundle simulating PWR operating conditions. The simulation model was 1 m long and contains one split-type mixing vane grid. For the inlet, a fully developed velocity profile from a previous rod-bundle simulation was used. The simulation case was isothermal to avoid a superposition with wall boiling effects. For the simulation of turbulence effects a non-linear k-ε model was used. This model is able to reproduce the swirling flow in the wake of the grid spacer as well as secondary flow patterns that typically occur in sub-channel flows and needs less computational time compared to Reynolds Stress models. The results show that two large vortices are formed at the mixing vane tips in the center of an interior sub-channel. These vortices are co-rotating within the sub-channel and counter-rotating compared to the adjacent sub-channels. The presence of these vortices influence the radial pressure distribution and the cross-flows significantly. A new model approach was developed, which accounts for the effects of mixing vanes and the vortex structures. The new model requires additional input parameters that can be derived from the CFD results. The proposed model was implemented into the sub-channel analysis tool COBRA-FLX™. A comparison between the old and the new approaches for modeling the forced cross-flow shows a significant improvement of prediction of the mass flux distribution.

Fast and robust numerical approach for turbulent heat transfer in case of high gradients of physical properties and unsteady heat transfer in case of strong temperature fluctuations is developed. This pseudo transient Large Eddy Simulation approach is applied to perform transient calculations of turbulent mixing between helium and air in a rectangular mixing channel for Atwood numbers of 0.04 and 0.6. Comparisons of these numerical results with the experimental results by Banerjee, Kraft, Andrews (2010) show a good agreement. The results confirmed applicability of the pseudo transient approach also for higher Atwood numbers while wider time stepping and higher Courant numbers are used. Also reported are simulation results using Reynolds averaged (RANS) method where standard k–ε and k–ω SST models are applied.

ERVC is widely adopted as a part of in-vessel retention (IVR) in severe accident management strategies. In this paper, two-phase flow instability in natural circulation loops of external reactor vessel cooling (ERVC) system in a large size power PWR (CAP 1700 with a thermal power 5000 MWt) is simulated and evaluated by the RELAP5 code. Under certain conditions, flow instability of ERVC system are obtained. It is a kind of density wave oscillation that occurs in non-equilibrium boiling in the heat section and void flashing in the riser at low equilibrium quality and low system pressure. The calculation results show such oscillation course clearly. And several parameters affecting the flow stability are discussed.

A strong non-uniformity of the circumferential distribution of the wall temperature, heat flux and heat transfer coefficient around the rod surface is observed by previous CFD investigations, especially in the tight lattice. This phenomenon is important for core design of some Generation IV reactors such as supercritical water-cooled reactors (SCWR) and liquid metal fast reactors (LMFR). In this paper important dimensionless numbers that affect the non-uniformity of heat transfer are summarized and CFD calculations are carried out to study the local heat transfer behavior of central, corner and wall sub-channels respectively. An empirical correlation is proposed based on CFD data. Using this correlation, a three-dimensional fuel model is being developed in the sub channel code MATRA to incorporate some of this effect into the thermal-hydraulic analysis of SCWR.

Mass transfer enhancement is an important element in flow-accelerated corrosion (FAC). In the present paper the ζ-f model and a compound wall treatment have been tested for high Schmidt number mass transfer in a simple fully developed pipe flow and a flow through an orifice. The test shows that the mass transfer can be well predicted in both flows when the wall is fully resolved with the ζ-f model. The superior performance of the ζ-f model in the flow through an orifice can be attributed to avoiding the utilization of the dimensionless wall distance in the model. However, when the compound wall treatment is utilized together with the ζ-f model, mass transfer can be reasonably predicted only when u τ = C μ 1/4 k p 1/2 is a fair assumption, as demonstrated in the computation for the fully developed pipe flow. With the compound wall treatment the ζ-f model predicts shorter reattachment length and higher mass transfer rate in the flow through an orifice.

This paper presents the application of the modified ATHLET code to the dynamic behavior analysis of a supercritical water cooled system. A small scale fuel assembly under the “evaporator” condition of the HPLWR core design concept, with a supercritical water cooled experiment loop, is about to be tested in the LVR-15 research reactor of the Nuclear Research Institute in Rez in Czech Republic. With the purpose to analyze the safety characteristic and prepare for the licensing of the test loop, some design based accidents like loss of coolant due to break of coolant supply lines and trip of the primary pump are simulated in this paper. All the results achieved indicate that the modified ATHLET code has good feasibility in simulation of supercritical water cooled systems.

The sodium-cooled fast reactor (SFR) is gathering worldwide attention for its features of the fast-spectrum reactor and closed fuel recycle system. This paper presents the modification of the ATHLET code for application to SFRs. The thermal-hydraulic computer code ATHLET is developed by Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) in Germany for light water reactors analysis. In this paper, a sodium properties package is implemented in to the ATHLET code, and heat transfer correlations for sodium are also added for heat transfer prediction. To evaluate the capability of the modified code, the Phenix reactor, a SFR operated by French Alternative Energies and Atomic Energy Commission (CEA) from 1973 to 2009, is modeled. The scenario of transient from forced to natural convection is simulated and analyzed. The results are compared with the experimental data of the natural convection ultimate test of the Phenix facility. Results achieved so far indicate good applicability of the modified ATHLET code.

Direct injection natural gas (DING) engines offer the advantages of high thermal efficiency and high power output compared to spark ignition natural gas engines. Injected natural gas requires some form of ignition assist in order to ignite in the time available in a diesel engine combustion chamber. A glow plug — a heated surface — is one form of ignition assist. Simple experiments show that the thickness of the heat penetration layer of a glow plug is very small (≈10 −5 m) within the time scale of the ignition preparation period (1–2 ms). Meanwhile, the theoretical analyses reveal that only a very thin layer of the surrounding gases (in micrometer scale) can be heated to high temperature to achieve spontaneous ignition. A discretized glow plug model and virtual gas sub-layer model have been developed for CFD modeling of glow plug ignition and combustion for DING diesel engines. In this paper, CFD modeling results are presented. The results were obtained using a KIVA3 code modified to include the above mentioned new developed models. Natural gas ignition over a bare glow plug was simulated. The results were validated against experiments. Simulation of natural gas ignition over a shielded glow plug was also carried out and the results illustrate the necessity of using a shield. This paper shows the success of the discretized glow plug model working together with the virtual gas sub-layer model for modeling glow plug assisted natural gas direct injection engines. The modeling can aid in the design of injection and ignition systems for glow plug assisted DING engines.

Glow plugs are a possible ignition source for direct injected natural gas engines. This ignition assistance application is much different than the cold start assist function for which most glow plugs have been designed. In the cold start application, the glow plug is simply heating the air in the cylinder. In the cycle-by-cycle ignition assist application, the glow plug needs to achieve high surface temperatures at specific times in the engine cycle to provide a localized source of ignition. Whereas a simple lumped heat capacitance model is a satisfactory representation of the glow plug for the air heating situation, a much more complex situation exists for hot surface ignition. Simple measurements and theoretical analysis show that the thickness of the heat penetration layer is small within the time scale of the ignition preparation period (1–2 ms). The experiments and analysis were used to develop a discretized representation of the glow plug domain. A simplified heat transfer model, incorporating both convection and radiation losses, was developed for the discretized representation to compute heat transfer to and from the surrounding gas. A scheme for coupling the glow plug model to the surrounding gas computational domain in KIVA-3V was also developed. The glow plug model successfully simulates the natural gas ignition process for a direct injection natural gas engine. As well, it can provide detailed information on the local glow plug surface temperature distribution, which can aid in the design of more reliable glow plugs.

External reactor vessel cooling (ERVC) of the In-vessel retention (IVR) system is widely accepted as a feasible way to remove decay heat from the lower head of the reactor pressure vessel (RPV) under severe accident (SA) conditions. However, some issues relating to ERVC still need to be evaluated before its application, such as boiling and flow phenomena and CHF prediction, etc. To study these key issues, an experimental study program named REPEC ( Re actor P ressure Vessel E xternal C ooling) is performed at Shanghai Jiao Tong University. Steady state experiments focusing on flow boiling phenomena investigation are carried out with comprehensive measurements, including temperature distribution, pressure drop and mass flow rate. As a part of studies on boiling mechanism and flow phenomena between RPV and the insulation, the experiment is analyzed and simulated with RELAP code. The code simulation covers most of the experimental cases, and a comparison between simulation results and experimental data are presented and discussed.

This paper presents the stability analysis of a supercritical water-cooled system. A model of simplified supercritical water-cooled system is introduced and then its thermal-hydraulic equations, initial conditions and boundary conditions are given. Based on perturbation linearization and Laplace transformation, the transfer function between inlet mass flow rate oscillation and pressure drop oscillation of the simplified system model is established, and the characteristic equation of the simplified system model is derived. Applying control theory to solve the characteristic equation, the stability boundary points are found by judging whether the real parts of all roots solved by characteristic equation are greater than zero. A stability map which consists of these stability boundary points is generated by using both dimensionless sub-pseudo-critical number and trans-pseudo-critical number. An unstable region nearby the pseudo-critical point is determined. The effects of some important parameters on the stability map are investigated also by using decay ratio. The sensitivity analysis shows that the system is stabilized with a higher hydraulic system resistance, fluid inlet velocity or system pressure. It also shows that a longer heating zone, a harder pump characteristics or a larger gravitational acceleration (orientation angle) leads to a larger stability margin of the system. The stability map is also found to be not sensitive to a higher friction resistance or system pressure.

Investigations on the thermal-hydraulic behavior in the SCWR fuel assembly have obtained a significant attention in the international SCWR community. However, there is still a lack of understanding and ability to predict the heat transfer behavior of supercritical fluids. In this paper, the numerical analysis is carried out to study the thermal-hydraulic behaviour in vertical sub-channels cooled by supercritical water. Remarkable differences in characteristics of secondary flow are found, especially in square lattice, between the upward flow and downward flow. The turbulence mixing across sub-channel gap for downward flow is much stronger than that for upward flow in wide lattice when the bulk temperature is lower than pseudo-critical point temperature. For downward flow, heat transfer deterioration phenomenon is suppressed with respect to the case of upward flow at the same conditions.

Research investigating direct injection natural gas (DING) diesel engines shows many attractions in engine performance including higher thermal efficiency and higher power output as well as significant improvement of exhaust emissions. However, ignition of injected natural gas is difficult and requires some form of ignition assist, such as a diesel pilot or a glow plug. This paper introduces the experimental apparatus used for compression ignition engine studies in the Engine Research and Development Laboratory (ERDL) at University of Toronto. The apparatus consists of an optically accessible constant volume combustion bomb coupled to a single-cylinder Cooperative Fuel Research (CFR) engine through its spark plug port. The engine provides rapid compression to create realistic engine conditions in the combustion bomb and also scavenges the combustion products. During the engine compression process, the piston pushes the air from the engine cylinder to the constant volume combustion bomb, generating high-pressure, high-temperature initial conditions and a strong swirling air flow in the constant volume combustion bomb. Experiments were conducted to measure temperatures and pressures in the constant volume combustion bomb for a range of initial conditions. The experiments were complemented by numerically modeling the whole domain of the CFR engine cylinder, the constant volume combustion bomb, and the port connecting them using a modified KIVA-3V code. The code computes spatially and temporally resolved pressure, temperature and swirl intensity in the constant volume combustion bomb during the compression process. The experimental and the numerical results are in satisfactory agreement and provide validation of the initial conditions in the constant volume combustion bomb for subsequent studies of injection and ignition.