Simulation and Test of Lateral Ballast Resistance to 1435 mm/1000 mm Dual-Gauge Sleepers

The stability of a 1000 mm/1435 mm dual-gauge track is lower than that of a single-gauge track. One of the important factors that affects the stability of the track is the lateral resistance of the track bed. We have established a discrete element simulation model of the dual-gauge sleeper-track bed in PFC to analyse the characteristics of the lateral resistance of the 1000 mm/1435 mm dual-gauge sleeper. With China Type IIIc sleepers as the control group, we carried out the lateral resistance test for the full-scale sleeper model under the same conditions. The research results indicate that the most effective way to increase the lateral resistance of the dual-gauge track bed is to increase the end surface area and bottom area of the sleeper. The application of adjacent sleepers is an effective way to increase the lateral resistance of the track bed further. The research results gained from this study can be used to guide the design of dual-gauge sleepers

Influence of the Porosity of the TiO 2

The structure of mesoporous TiO2 (mp-TiO2) films is crucial to the performance of mesoporous perovskite solar cells (PSCs). In this study, we fabricated highly porous mp-TiO2 films by doping polystyrene (PS) spheres in TiO2 paste. The composition of the perovskite films was effectively improved by modifying the mass fraction of the PS spheres in the TiO2 paste. Due to the high porosity of the mp-TiO2 film, PbI2 and CH3NH3I could sufficiently infiltrate into the network of the mp-TiO2 film, which ensured a more complete transformation to CH3NH3PbI3. The surface morphology of the mp-TiO2 film and the photoelectric performance of the perovskite solar cells were investigated. The results showed that an increase in the porosity of the mp-TiO2 film resulted in an improvement in the performance of the PSCs. The best device with the optimized mass fraction of 1.0 wt% PS in TiO2 paste exhibited an efficiency of 12.69%, which is 25% higher than the efficiency of the PSCs without PS spheres

Joint retrieval of growing season corn canopy LAI and leaf chlorophyll content by fusing Sentinel-2 and MODIS images

Continuous and accurate estimates of crop canopy leaf area index (LAI) and chlorophyll content are of great importance for crop growth monitoring. These estimates can be useful for precision agricultural management and agricultural planning. Our objectives were to investigate the joint retrieval of corn canopy LAI and chlorophyll content using filtered reflectances from Sentinel-2 and MODIS data acquired during the corn growing season, which, being generally hot and rainy, results in few cloud-free Sentinel-2 images. In addition, the retrieved time series of LAI and chlorophyll content results were used to monitor the corn growth behavior in the study area. Our results showed that: (1) the joint retrieval of LAI and chlorophyll content using the proposed joint probability distribution method improved the estimation accuracy of both corn canopy LAI and chlorophyll content. Corn canopy LAI and chlorophyll content were retrieved jointly and accurately using the PROSAIL model with fused Kalman filtered (KF) reflectance images. The relation between retrieved and field measured LAI and chlorophyll content of four corn-growing stages had a coefficient of determination (R2) of about 0.6, and root mean square errors (RMSEs) ranges of mainly 0.1-0.2 and 0.0-0.3, respectively. (2) Kalman filtering is a good way to produce continuous high-resolution reflectance images by synthesizing Sentinel-2 and MODIS reflectances. The correlation between fused KF and Sentinel-2 reflectances had an R2 value of 0.98 and RMSE of 0.0133, and the correlation between KF and field-measured reflectances had an R2 value of 0.8598 and RMSE of 0.0404. (3) The derived continuous KF reflectances captured the crop behavior well. Our analysis showed that the LAI increased from day of year (DOY) 181 (trefoil stage) to DOY 236 (filling stage), and then increased continuously until harvest, while the chlorophyll content first also increased from DOY 181 to DOY 236, and then remained stable until harvest. These results revealed that the jointly retrieved continuous LAI and chlorophyll content could be used to monitor corn growth conditions

RANS Computation of the Mean Forces and Moments, and Wave-Induced Six Degrees of Freedom Motions for a Ship Moving Obliquely in Regular Head and Beam Waves

Ship maneuvering performance in waves has attracted much attention in recent years. One of main research efforts for this problem has been devoted to the high-accuracy computation of hydrodynamic forces and moments, as well as wave-induced motions, for ships performing maneuvering motions in waves. The objective of this article is to present a numerical study on the computation of the mean forces and moments, and wave-induced six degrees of freedom motions for a ship moving obliquely in regular head and beam waves. The RANS (Reynolds-Averaged Navier-Stokes) solver based on OpenFOAM is used for this purpose. The RANS computations herein are carried out in a horizontal coordinate system. The numerical wave maker with prescribing values of flow variables on the domain boundaries is applied for the wave generation in the computational domain. However, in order to prevent wave reflection, relaxed zones adjacent to the wave maker boundaries are set up. A new program module is inserted into OpenFOAM to update the flow velocity and wave evaluation on the wave-maker boundaries and in the relaxed zones during the RANS computation. The mesh deformation method is employed to allow the ship to perform motions in space. However, a virtual spring system is attached to the ship so as to restrain the surge, sway and yaw, while heave, pitch and roll are completely free, so that the ship is able to oscillate periodically around a certain position in space. The computed mean forces and moments with the inertia effects agree fairly well with the experimental data, and the computed wave-induced motions are also in quite reasonable agreement with the experimental data. This study shows a very successful computation, as well as the procedure of the RANS results processing

Über den Propellereffekt bei der Bestimmung hydrodynamischer Kräfte beim Manövrieren (Berechnungen mittels RANS Simulation festgehaltener Modelle)

Die Simulation der turbulenten Strömung um ein manövrierendes Schiff stellt nach wie vor eine große Herausforderung dar. Obwohl durch die numerische Lösung der RANS Gleichungen ein großer Fortschritt bei der Klärung vieler zentraler Fragen in diesem Bereich möglich geworden ist, müssen weitere Probleme gelöst werden, um zu aufschlussreichen Erkenntnissen zu gelangen. Eines der Probleme ist der Einfluss des Propellers auf die Umströmung des Schiffes, was bisher beim Manövrieren nicht im Detail untersucht wurde. Andererseits kann es sinnvoll sein, ein Body-Force-Modell zu nutzen, um den Einfluss des Propellers in der Simulation nachzubilden, wie in zahlreichen Publikationen berichtet wurde. Es erfordert weniger Rechenzeit und Schwierigkeiten, die bei der Generierung des Gitters für den rotierenden Propeller entstehen, werden umgangen. Die Eignung eines Body-Force-Modells zur Nachbildung der Interaktion zwischen Schiff und Propeller, sowie zwischen Propeller und Ruder während der Simulation der Strömung an einem manövrierenden Schiff ist jedoch bisher nicht gründlich untersucht worden. In der vorliegenden Arbeit wird der ursprüngliche RANS Code in OpenFOAM erweitert, um die turbulente Strömung um ein Schiff, das vorgeschriebene Bewegungen ausführt, zu simulieren. Zum ersten Mal wird der reale rotierende Propeller in solchen virtuellen gefesselten Manövrierversuchen berücksichtigt, indem ein Sliding-Grid-Verfahren verwendet wird. Der Einfluss des Propellers auf die Strömung und die hydrodynamischen Kräfte, sowie der Einfluss des Schiffsrumpfes und des Ruders auf die Propellerkräfte werden untersucht und diskutiert. Zwei Body-Force-Modelle, ein verbessertes Datenbank-Modell und ein empirisches Modell, werden darüber hinaus in den Simulationen verwendet. Die Arbeit bietet eine vergleichende Studie, um die Eignung der beiden Modelle zu untersuchen. In den Simulationen werden die freie Wasseroberfläche und damit verbundene dynamische Effekte, wie Tauchung, Trimm und Krängung, vernachlässigt. Aufgrund der kleinen Froudezahl wird angenommen, dass diese Effekte einen geringen Einfluss auf die Ergebnisse der numerischen Simulationen und die daraus resultierenden Schlussfolgerungen haben. Um die gewünschte Information für das Datenbank-Modell zu erzeugen, werden Berechnungen im Voraus für den isolierten Propeller in homogener Schräganströmung durchgeführt. Die berechneten Ergebnisse werden mit experimentellen Daten verglichen und analysiert. Diese Untersuchung zeigt einige aufschlussreiche Ergebnisse.Accurate simulation of the flow around a manoeuvring ship is still a challenge today. Although the numerical method based on solving RANS equations has achieved a big success in this respect, many key issues have to be addressed or studied deeply to get more insightful knowledge. One of the issues is the propeller effect on the flow and ship hydrodynamics, which has been not analysed well in manoeuvring conditions so far. On the other hand, it is very useful to use a body force model to approximate the propeller effect in the simulations, as reported in numerous publications. This benefits from the advantages that the simplification makes the computational cost lower and avoids dealing with the complex propeller geometry when generating grid. However, the performance of the body force models used, in particular the effect of ship hull and rudder on the body force, has been not investigated in depth in the simulation of ship manoeuvring motions in existing publications. In the present work, the original RANS code in OpenFOAM is extended to simulate the flows around a ship performing forced motions of captive test. For the first time, the real ro-tating propeller is taken into account by means of a sliding grid approach in virtual captive tests. The propeller effect on the flow and hydrodynamic forces acting on the ship, and in turn the effect of ship hull and rudder on the propeller loads, are studied and discussed deeply. Two body force models including an improved database model and an empirical model are employed as well. This thesis offers a comparative study to explore the performance of both models. During the simulations, the water free surface and the related effects, i.e. sinkage, trim and heel, are neglected. Due to the low Froude number considered, this is expected to play a minor role on the achieved results and main conclusions. To use the database model, precalculations are performed in advance for the isolated propeller in uniform oblique flow to generate the information required. Computed results are compared with available experimental data and analysed. Some instructive findings are obtained

Comparison between the RANS Simulations of Double-Body Flow and Water–Air Flow around a Ship in Static Drift and Circle Motions

Manoeuvrability is one of the important ship hydrodynamic performances. That is closely related to the safety and economy of navigation. The development of a high-accuracy and high-efficiency numerical method to compute the forces and moments on manoeuvring ships has been the main task for ship manoeuvring predictions. The numerical method by solving RANS (Reynolds-Averaged Navier–Stokes) equations may be the most used one nowadays for the computations of ship manoeuvring forces and moments. However, applying a RANS tool for ship manoeuvring prediction remains very low efficiency, especially considering the six-degrees-of-freedom ship motions on the water surface. Thus, it is very necessary to introduce a few assumptions to reduce the computational time when applying a RANS tool, e.g., the assumptions of double-body flow and body force propeller, and consequently improve the application efficiency. Generally speaking, the assumption of double-body flow, in which the free-surface effects are neglected, is more suitable for low-speed ships. Nevertheless, rare publications have been reported relating to how this assumption affects the accuracy of the computed manoeuvring forces and moments. To this end, this article presents a comparative study between the RANS simulations of double-body flow and water–air flow around a container ship performing static drift and static circle motions. Three ship speeds, corresponding to the Froude numbers 0.156, 0.201, and 0.260, respectively, are considered during the simulations. The computed side forces and yaw moments obtained by the water–air flow simulations are closer to the available experimental data than that obtained by the double-body flow simulations for all ship speeds. The computed surge forces obtained by water–air flow simulations also agree well with the experimental data, whereas the computed surge forces obtained by the double-body flow simulations are wrong. The reasons are analyzed by comparing the pressure distributions on the ship surface and the flow separations around the ship

Comparison between the RANS Simulations of Double-Body Flow and Water–Air Flow around a Ship in Static Drift and Circle Motions

Manoeuvrability is one of the important ship hydrodynamic performances. That is closely related to the safety and economy of navigation. The development of a high-accuracy and high-efficiency numerical method to compute the forces and moments on manoeuvring ships has been the main task for ship manoeuvring predictions. The numerical method by solving RANS (Reynolds-Averaged Navier–Stokes) equations may be the most used one nowadays for the computations of ship manoeuvring forces and moments. However, applying a RANS tool for ship manoeuvring prediction remains very low efficiency, especially considering the six-degrees-of-freedom ship motions on the water surface. Thus, it is very necessary to introduce a few assumptions to reduce the computational time when applying a RANS tool, e.g., the assumptions of double-body flow and body force propeller, and consequently improve the application efficiency. Generally speaking, the assumption of double-body flow, in which the free-surface effects are neglected, is more suitable for low-speed ships. Nevertheless, rare publications have been reported relating to how this assumption affects the accuracy of the computed manoeuvring forces and moments. To this end, this article presents a comparative study between the RANS simulations of double-body flow and water–air flow around a container ship performing static drift and static circle motions. Three ship speeds, corresponding to the Froude numbers 0.156, 0.201, and 0.260, respectively, are considered during the simulations. The computed side forces and yaw moments obtained by the water–air flow simulations are closer to the available experimental data than that obtained by the double-body flow simulations for all ship speeds. The computed surge forces obtained by water–air flow simulations also agree well with the experimental data, whereas the computed surge forces obtained by the double-body flow simulations are wrong. The reasons are analyzed by comparing the pressure distributions on the ship surface and the flow separations around the ship

RANS Prediction of Wave-Induced Ship Motions, and Steady Wave Forces and Moments in Regular Waves

The wave-induced motions, and steady wave forces and moments for the oil tanker KVLCC2 in regular head and oblique waves are numerically predicted by using the expanded RANS solver based on OpenFOAM. New modules of wave boundary condition are programed into OpenFOAM for this purpose. In the present consideration, the steady wave forces and moments include not only the contribution of hydrodynamic effects but also the contribution of the inertial effects due to wave-induced ship motions. The computed results show that the contribution of the inertial effects due to heave and pitch in head waves is non-negligible when wave-induced motions are of large amplitude, for example, in long waves. The influence of wave amplitude on added resistance in head waves is also analyzed. The dimensionless added resistance becomes smaller with the increasing wave amplitude, indicating that added resistance is not proportional to the square of wave amplitude. However, wave amplitude seems not to affect the heave and pitch RAOs significantly. The steady wave surge force, sway force and yaw moment for the KVLCC2 with zero speed in oblique waves are computed as well. The present RANS results are compared with available experimental data, and very good agreements are found between them