Thermodynamics performance assessment of precooled cycle engines with ammonia as the fuel and coolant

To meet the demand for air-breathing power for wide-range vehicles at Mach 0-10, two thermal cycles with ammonia as the fuel and coolant were analyzed, namely the precooled rocket-turbine cycle (PC-RT) and the precooled gas-turbine cycle. Firstly, the operating modes of the precooled cycle engines were divided into turbine mode, precooling mode, and ramjet mode. Secondly, a fluid-structure coupling heat transfer program was used to evaluate the cooling effects of different fuels on the incoming high-temperature air. The result shows that the equivalent heat sink of ammonia is higher than that of other fuels and can meet the cooling requirement of at least Mach 4 in the precooling mode. Thirdly, the performance of the PC-RT in the turbine and precooling modes was compared at Mach 2.5. The result shows that air precooling alleviates the restriction of the pumping pressure on the minimum required beta and improves the specific thrust within a reasonable range of beta. Fourthly, the performance of the precooled cycle engines was compared when using different fuels. The result shows that the specific thrust of ammonia is greater than that of other fuels, and the performance advantages of ammonia are the most obvious in the precooling mode due to its highest equivalent heat sink. To sum up, the precooled cycle engines with ammonia as the fuel and coolant presented in this study have the advantages of no carbon emissions, low cost, high specific thrust, and no clogging of the cooling channels by cracking products. They are suitable for applications such as the first-stage power of the two-stage vehicle, and high Mach numbers air-breathing flight

A new high-order RKDG method based on the TENO-THINC scheme for shock-capturing

In recent years, Runge-Kutta Discontinuous Galerkin (RKDG) methods have gained substantial attention in solving hyperbolic conservation laws, attributed to their high-order accuracy and adaptability to unstructured meshes. However, standard RKDG methods cannot capture discontinuities without oscillation unless they are supplemented with troubled cell indicators and limiters. Existing indicators, such as the total variation bounded (TVB) minmod indicator and the KXRCF indicator, typically depend on a critical parameter tied to the equation's solution, necessitating tuning for different cases. In terms of limiters, the popular limiters even fail to guarantee the high-order property in the smooth regions. The advent of Weighted Essentially Non-Oscillatory (WENO) schemes prompts the implementation of WENO limiters for RKDG methods, preserving high-order properties. However, WENO-family schemes exhibit significant numerical dissipation, potentially smearing small-scale flow structures. In this work, the Targeted Essentially Non-Oscillatory (TENO) indicator [1] is utilized, which leverages the nonlinear weighting strategy of the TENO scheme to separate high-wavenumber physical fluctuations and genuine discontinuities from smooth regions with a unified set of parameters. For troubled cells, a novel limiter is proposed for structured meshes, which combines a TENO scheme for resolving high-wavenumber physical fluctuations and a novel non-polynomial Tangent of Hyperbola for the INterface Capturing (THINC) scheme for resolving genuine discontinuities with extremely low numerical dissipation. Furthermore, the shifting between the TENO and THINC schemes is based on a new boundary variation diminishing (BVD) strategy, which only relies on compact neighborhoods and is significantly simpler than its predecessors. Meanwhile, a new strategy is proposed to ensure the consistency of the new limiter applied for 1D and 2D cases. A set of 1D and 2D benchmark cases including strong shockwaves and a broad range of flow length scales is simulated with uniform meshes for 1D cases and structured quadrilateral meshes for 2D cases to demonstrate the performance of the new numerical scheme. The indicator does not activate any limiters in the accuracy test cases to ensure the high-order property of the whole numerica

Synthesis of 8-MnO2 via ozonation routine for low temperature formaldehyde removal

Nowadays, it is still a challenge to prepared high efficiency and low cost formaldehyde (HCHO) removal catalysts in order to tackle the long-living indoor air pollution. Herein, 8MnO2 is successfully synthesized by a facile ozonation strategy, where Mn2 + is oxidized by ozone (O3 ) bubble in an alkaline solution. It presents one of the best catalytic properties with a low 100% conversion temperature of 85 degrees C for 50 ppm of HCHO under a GHSV of 48,000 mL/(g center dot hr). As a comparison, more than 6 times far longer oxidation time is needed if O3 is replaced by O2 . Characterizations show that ozonation process generates a different intermediate of tetragonal fi-HMnO2 , which would favor the quick transformation into the final product 8-MnO2 , as compared with the relatively more thermodynamically stable monoclinic y-HMnO2 in the O2 process. Finally, HCHO is found to be decomposed into CO2 via formate, dioxymethylene and carbonate species as identified by room temperature insitu diffuse reflectance infrared fourier transform spectroscopy. All these results show great potency of this facile ozonation routine for the highly active 8-MnO2 synthesis in order to remove the HCHO contamination. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy o

Radiation investigation behind 4.7 km/s shock waves with nitrogen using a square section shock tube

The thermochemical non-equilibrium phenomena encountered by hypersonic vehicles present significant challenges in their design. To investigate the thermochemical reaction flow behind shock waves, the non-equilibrium radiation in the visible range using a shock tube was studied. Experiments were conducted with a shock velocity of 4.7 km/s, using nitrogen at a pressure of 20 Pa. To address measurement difficulties associated with weak radiation, a special square section shock tube with a side length of 380 mm was utilized. A high-speed camera characterized the shock wave's morphology, and a spectrograph and a monochromator captured the radiation. The spectra were analyzed, and the numerical spectra were compared with experimental results, showing a close match. Temperature changes behind the shock wave were obtained and compared with numerical predictions. The findings indicate that the vibrational temperatures are overestimated, while the vibrational relaxation time is likely underestimated, due to the oversimplified portrayals of the non-equilibrium relaxation process in the models. Additionally, both experimental and simulated time-resolved profiles of radiation intensity at specific wavelengths were analyzed. The gathered data aims to enhance computational fluid dynamics codes and radiation models, improving their predictive accuracy. (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)4.7 km/s(sic)20 Pa(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)380 mm(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic); (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic): (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic); (sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)

Experimental and numerical studies on the collapse of Titanium alloy ring-stiffened cylinder

This paper investigates the collapse of ring-stiffened Titanium alloy cylinders used for subsea resource exploration under hydrostatic pressure through experimental and numerical methods. Extensive material tests were first conducted on Titanium alloy specimens to obtain the fundamental mechanical properties and variation characteristics. Then, a 4236 mm-long test cylinder was fabricated with an inner radius of 650 mm and a thickness (ts) of 18.85 mm. The initial geometric imperfection was measured at evenly-spaced positions in the axial direction and 48 locations around the circumference by dial gauges. Afterward, the test cylinder was transferred into a custom hyperbaric pressure vessel and pressurized to collapse. As to the numerical analysis, a user-defined material subroutine implementing the incremental J2 deformation theory was developed to predict plastic bifurcation pressure. Moreover, a nonlinear finite element (FE) model, which incorporated the measured geometric imperfection and material nonlinearity, was used to reproduce the experiment. The numerical results were found to exhibit reasonably good agreement with the test data. In addition, parametric studies were conducted regarding material properties, geometric parameters, and imperfection sizes on the load-carrying capacity of Titanium alloy ring-stiffened cylinders

Simultaneous improvement of strength and ductility in a P-doped CrCoNi medium-entropy alloy

A newly developed P-doped CrCoNi medium-entropy alloy (MEA) provides both higher yield strength and larger uniform elongation than the conventional CrCoNi MEA, even superior tensile ductility to the otherelement-doped CrCoNi MEAs at similar yield strength levels. P segregation at grain boundaries (GBs) and dissolution inside grain interiors, together with the related lower stacking fault energy (SFE) are found in the P-doped CrCoNi MEA. Higher hetero-deformation-induced (HDI) hardening rate is observed in the Pdoped CrCoNi MEA due to the grain -to -grain plastic deformation and the dynamic structural refinement by high-density stacking fault-walls (SFWs). The enhanced yield strength in the P-doped CoCrNi MEA can be attributed to the strong substitutional solid -solution strengthening by severer lattice distortion and the GB strengthening by phosphorus segregation at GBs. During the tensile deformation, the multiple SFW frames inundated with massive multi-orientational tiny planar stacking faults (SFs) between them, rather than deformation twins, are observed to induce dynamic structural refinement for forming parallelepiped domains in the P-doped CoCrNi MEA, due to the lower SFE and even lower atomically-local SFE. These nano-sized domains with domain boundary spacing at tens of nanometers can block dislocation movement for strengthening on one hand, and can accumulate defects in the interiors of domains for exceptionally high hardening rate on the other hand. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Nonlinear dynamic analysis and vibration reduction of two sandwich beams connected by a joint with clearance

The dynamics and vibration reduction characteristics of the clamped-clamped two sandwich beams jointed with clearance is studied theoretically and experimentally. A transverse and torsional spring system with clearance is used to equivalent the joint model. The homogenization method is used to equivalent the core layer and Rayleigh-Ritz method is utilized to derive the mode function of the interconnected sandwich beam by using a sequence of orthogonal polynomials. The nonlinear motion equation of the two jointed sandwich beam structure with clearance is derived by the application of the Hamilton principle and then solved using an improved Newmark integration approach. In order to validate the accuracy of the natural frequency and vibration mode, the finite element model is established. This paper examines the impact of clearance on the amplitude frequency response and vibration transmission of the two jointed sandwich beam structure, it is found the jointed sandwich beams show obvious nonlinear characteristics and intermittent vibration transmission phenomenon due to the clearance. Moreover, the vibration transmission analysis reveals that the existed clearance demonstrates significant vibration reduction effect, for which an experiment is conducted to validate the results. In general, this work proposes a novel approach for modeling sandwich structures with clearance with improved vibration reduction performance

Determining pressure from velocity via physics-informed neural network

This paper describes a physics-informed neural network (PINN) for determining pressure from velocity where the Navier-Stokes (NS) equations are incorporated as a physical constraint, but the boundary condition is not explicitly imposed. The exact solution of the NS equations for the oblique Hiemenz flow is utilized to evaluate the accuracy of the PINN and the effects of the relevant factors including the boundary condition, data noise, number of collocation points, Reynolds number and impingement angle. In addition, the PINN is evaluated in the twodimensional flow over a NACA0012 airfoil based on computational fluid dynamics (CFD) simulation. Further, the PINN is applied to the velocity data of a flying hawkmoth (Manduca) obtained in high-speed schlieren visualizations, revealing some interesting pressure features associated with the vortex structures generated by the flapping wings. Overall, the PINN offers an alternative solution for the problem of pressure from velocity with the reasonable accuracy and robustness

Numerical evaluation of a new high pressure water jet interference method for bridge pier protection against vessel collision

Ship-bridge collisions happen from time to time globally, and the consequences are often catastrophic. Therefore, this paper proposes a new high-pressure water jet interference (HPWJI) method for bridge pier protection against vessel collision. Unlike traditional methods that absorb energy by anti-collision devices to mitigate the impact force of ships on bridges, this method mainly changes the direction of ship movement by lateral high-pressure water jet impact, so that the ship deviates from the bridge piers and avoids collision. This paper takes China's Shawan River as the background and simulates the navigation of a ship (weighing about 2000 t) in the HPWJI method in the ANSYS-FLUENT software. The simulation results show that the HPWJI method has a significant impact on the direction of the ship's movement, enabling the ship to deviate from the pier, which is theoretically feasible for preventing bridge-ship collisions. The faster the ship's speed, the smaller the lateral displacement and deflection angle of the ship during a certain displacement. When the ship speed is less than 7 m/s, the impact of water flow on the ship's trajectory is more significant. Finally, this paper constructs a model formula for the relationship between the lateral displacement and speed, and surge displacement of the selected ship. This formula can be used to predict the minimum safe distance of the ship at different speeds

Experimental and numerical studies on the collapse of Titanium alloy ring-stiffened cylinder

This paper investigates the collapse of ring-stiffened Titanium alloy cylinders used for subsea resource exploration under hydrostatic pressure through experimental and numerical methods. Extensive material tests were first conducted on Titanium alloy specimens to obtain the fundamental mechanical properties and variation characteristics. Then, a 4236 mm-long test cylinder was fabricated with an inner radius of 650 mm and a thickness (ts) of 18.85 mm. The initial geometric imperfection was measured at evenly-spaced positions in the axial direction and 48 locations around the circumference by dial gauges. Afterward, the test cylinder was transferred into a custom hyperbaric pressure vessel and pressurized to collapse. As to the numerical analysis, a user-defined material subroutine implementing the incremental J2 deformation theory was developed to predict plastic bifurcation pressure. Moreover, a nonlinear finite element (FE) model, which incorporated the measured geometric imperfection and material nonlinearity, was used to reproduce the experiment. The numerical results were found to exhibit reasonably good agreement with the test data. In addition, parametric studies were conducted regarding material properties, geometric parameters, and imperfection sizes on the load-carrying capacity of Titanium alloy ring-stiffened cylinders