Investigation on the impact of the induced shock wave on the hydrogen mixing augmentation in a supersonic crossflow: A numerical study

This paper performs a numerical study on the interaction of a planar shock wave with a water column embedded with/without a cavity of different sizes at high Weber numbers. The conservative-type Euler and non-conservative scalar two-equations representing the transportation of two-phase properties consist of the diffusion interface capture models. The numerical fluxes are computed by the Godunov-type Harten-Lax–van Leer contact Riemann solver coupled with an incremental fifth-order weighted essentially non-oscillatory (WENO) scheme. A third-order total variation diminishing (TVD) Runge–Kutta scheme is used to advance the solution in time. The morphology and dynamical characteristics are analysed qualitatively and quantitatively to demonstrate the breakup mechanism of the water column and formation of transverse jets under different incident shock intensities and embedded-cavity sizes. The jet tip velocities are extracted by analysing the interface evolution. The liquid column is prone to aerodynamic breakup with the formation of micro-mist at later stages instead of liquid evaporation because of the weakly heating effects of the surrounding air. It is numerically confirmed that the liquid-phase pressure will drop below the saturated vapour pressure, and the low pressure can be sustained for a certain time because of the focusing of the expansion wave, which accounts for the cavitation inside the liquid water column. The geometrical parameters of the deformed water column are identified, showing that the centreline width decreases but the transverse height increases nonlinearly with time. The deformation rates are nonlinearly correlated under different Mach numbers. The first transverse jet is found for a water column with an embedded cavity, whereas the water hammer shock and second jet do not occur under the impact of low intensity incident shock waves. The $x$-velocity component recorded at the rear stagnation point can remain unchanged for a comparable time after a declined evolution, which indicates that the downstream wall of the shocked water ring somehow moves uniformly. It can be explained that the acceleration of the downstream wall is balanced by the trailing shedding vortex, and this effect is more evident under higher Mach numbers. The increased enstrophy, mainly generated at the interface, demonstrates the competition of the baroclinic effects of the shock wave impact over dilatation.

Download Full-text

Numerical Study on Propagation of Ice Breaking Shock Waves in Process of Breaking Ice by Double-Layer Charge Blasting

Journal of Engineering Research and Reports ◽

10.9734/jerr/2021/v20i1217422 ◽

2021 ◽

pp. 91-98

Author(s):

Xuemei Zhang ◽

Yuanli Wu ◽

Zhigang Xie ◽

Chaosong Kong ◽

Zhizong Tian

Keyword(s):

Shock Wave ◽

Double Layer ◽

Delay Time ◽

Peak Pressure ◽

Numerical Study ◽

Layer Charge ◽

Wave Pressure ◽

Shock Wave Pressure ◽

Double Charge ◽

The Impact

The ice-breaking process of the double-layer charge at a depth of 150 cm underwater is simulated by LS-DYNA. This paper analyzes the load type, shock wave pressure characteristics and propagation behavior of the double-layer charge during underwater explosion. By analyzing the impact of the shock wave pressure in the water under different charge intervals and time intervals on the shock wave pressure of the double charge, it is concluded that the peak pressure of the double charge explosion shock wave is jointly determined by the double charge. In this range, the second peak pressure value of the drug is greater than the pressure value of the first peak of the drug, and the attenuation is slow; the delay time of the upper charge has little effect on the peak pressure value of the shock wave in the water; the delay time is higher than that of the lower charge Initiation, at the same position, the total pressure peak of the shock wave formed by the delay of the upper charge is larger.

Download Full-text

Model of thermal buoyancy in cavity-ventilated roof constructions

Journal of Building Physics ◽

10.1177/1744259120984189 ◽

2021 ◽

pp. 174425912098418

Author(s):

Toivo Säwén ◽

Martina Stockhaus ◽

Carl-Eric Hagentoft ◽

Nora Schjøth Bunkholt ◽

Paula Wahlgren

Keyword(s):

Analytical Model ◽

Flow Rate ◽

Numerical Study ◽

Air Flow ◽

Wind Pressure ◽

Air Flow Rate ◽

Test Set ◽

Air Cavity ◽

Thermal Buoyancy ◽

The Impact

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

Download Full-text

Numerical Simulation of the Impact of the Heat Source Position on Melting of a Nano-Enhanced Phase Change Material

Nanomaterials ◽

10.3390/nano11061425 ◽

2021 ◽

Vol 11 (6) ◽

pp. 1425

Author(s):

Tarek Bouzennada ◽

Farid Mechighel ◽

Kaouther Ghachem ◽

Lioua Kolsi

Keyword(s):

Heat Transfer ◽

Phase Change ◽

Phase Change Material ◽

Numerical Study ◽

Melting Rate ◽

Heat Transfer Fluid ◽

Commercial Code ◽

Tube Position ◽

The Impact ◽

Change Material

A 2D-symmetric numerical study of a new design of Nano-Enhanced Phase change material (NEPCM)-filled enclosure is presented in this paper. The enclosure is equipped with an inner tube allowing the circulation of the heat transfer fluid (HTF); n-Octadecane is chosen as phase change material (PCM). Comsol-Multiphysics commercial code was used to solve the governing equations. This study has been performed to examine the heat distribution and melting rate under the influence of the inner-tube position and the concentration of the nanoparticles dispersed in the PCM. The inner tube was located at three different vertical positions and the nanoparticle concentration was varied from 0 to 0.06. The results revealed that both heat transfer/melting rates are improved when the inner tube is located at the bottom region of the enclosure and by increasing the concentration of the nanoparticles. The addition of the nanoparticles enhances the heat transfer due to the considerable increase in conductivity. On the other hand, by placing the tube in the bottom area of the enclosure, the liquid PCM gets a wider space, allowing the intensification of the natural convection.

Download Full-text

OPTIMAL REINSURANCE FROM THE VIEWPOINTS OF BOTH AN INSURER AND A REINSURER UNDER THE CVAR RISK MEASURE AND VAJDA CONDITION

Astin Bulletin ◽

10.1017/asb.2021.9 ◽

2021 ◽

pp. 1-29

Author(s):

Yanhong Chen

Keyword(s):

Loss Function ◽

Value At Risk ◽

Numerical Study ◽

Risk Measure ◽

Convex Combination ◽

Weighting Factor ◽

Loss Functions ◽

Conditional Value At Risk ◽

Optimal Reinsurance ◽

The Impact

ABSTRACT In this paper, we study the optimal reinsurance contracts that minimize the convex combination of the Conditional Value-at-Risk (CVaR) of the insurer’s loss and the reinsurer’s loss over the class of ceded loss functions such that the retained loss function is increasing and the ceded loss function satisfies Vajda condition. Among a general class of reinsurance premium principles that satisfy the properties of risk loading and convex order preserving, the optimal solutions are obtained. Our results show that the optimal ceded loss functions are in the form of five interconnected segments for general reinsurance premium principles, and they can be further simplified to four interconnected segments if more properties are added to reinsurance premium principles. Finally, we derive optimal parameters for the expected value premium principle and give a numerical study to analyze the impact of the weighting factor on the optimal reinsurance.

Download Full-text

A numerical study of the impact perforation of sandwich panels with graded hollow sphere cores

Advances in Mechanical Engineering ◽

10.1177/16878140211009415 ◽

2021 ◽

Vol 13 (4) ◽

pp. 168781402110094

Author(s):

Ibrahim Elnasri ◽

Han Zhao

Keyword(s):

Boundary Conditions ◽

Hollow Sphere ◽

Sandwich Panel ◽

Numerical Study ◽

Sandwich Panels ◽

Hopkinson Bar ◽

Core Density ◽

The Core ◽

The Impact ◽

Force Displacement

In this study, we numerically investigate the impact perforation of sandwich panels made of 0.8 mm 2024-T3 aluminum alloy skin sheets and graded polymeric hollow sphere cores with four different gradient profiles. A suitable numerical model was conducted using the LS-DYNA code, calibrated with an inverse perforation test, instrumented with a Hopkinson bar, and validated using experimental data from the literature. Moreover, the effects of quasi-static loading, landing rates, and boundary conditions on the perforation resistance of the studied graded core sandwich panels were discussed. The simulation results showed that the piercing force–displacement response of the graded core sandwich panels is affected by the core density gradient profiles. Besides, the energy absorption capability can be effectively enhanced by modifying the arrangement of the core layers with unclumping boundary conditions in the graded core sandwich panel, which is rather too hard to achieve with clumping boundary conditions.

Download Full-text

Computational Evaluation of Shock Wave Interaction with a Cylindrical Water Column

Applied Sciences ◽

10.3390/app11114934 ◽

2021 ◽

Vol 11 (11) ◽

pp. 4934

Author(s):

Viola Rossano ◽

Giuliano De Stefano

Keyword(s):

Shock Wave ◽

Water Column ◽

Wave Interaction ◽

Navier Stokes ◽

Plane Shock ◽

Governing Equations ◽

Computational Evaluation ◽

Air Water Interface ◽

The Mean ◽

The Impact

Computational fluid dynamics was employed to predict the early stages of the aerodynamic breakup of a cylindrical water column, due to the impact of a traveling plane shock wave. The unsteady Reynolds-averaged Navier–Stokes approach was used to simulate the mean turbulent flow in a virtual shock tube device. The compressible flow governing equations were solved by means of a finite volume-based numerical method, where the volume of fluid technique was employed to track the air–water interface on the fixed numerical mesh. The present computational modeling approach for industrial gas dynamics applications was verified by making a comparison with reference experimental and numerical results for the same flow configuration. The engineering analysis of the shock–column interaction was performed in the shear-stripping regime, where an acceptably accurate prediction of the interface deformation was achieved. Both column flattening and sheet shearing at the column equator were correctly reproduced, along with the water body drift.

Download Full-text

Analysis of the Samples of Fe-Cu-Nb-Si-B Amorphous Alloys Obtained by Dynamic Compacting Method

MRS Proceedings ◽

10.1557/proc-0903-z05-10 ◽

2005 ◽

Vol 903 ◽

Author(s):

Victor A. Golubev ◽

Andrey V. Strikanov ◽

Grigory A. Potemkin ◽

Ludmila V. Zueva ◽

Aleksey V. Golubev ◽

...

Keyword(s):

Shock Wave ◽

Amorphous Alloys ◽

Analysis Data ◽

Xrd Analysis ◽

Soft Magnetic ◽

Scanning Calorimetry ◽

Soft Magnetic Alloys ◽

Nano Crystalline ◽

The Impact ◽

Magnetic Conductivity

AbstractThe Dynamic Compacting (DC) method is promising method to produce considerable-size nonporous wares. The phenomenon is based on the impact of shock wave on the initial powders of amorphous alloys. Every time when the shock wave propagates through the bulk of substance then the temperature rises substantially. Therefore there is a need of study of the DC’s effect on the structure and properties of the amorphous alloys. The results of the thermal analysis (in particular, Differential Scanning Calorimetry) of the samples of the soft magnetic alloys are presented in the report. These results concern with amorphous alloys of 5BDSR, GM414, 10NSR trademarks before DC and after DC, respectively. It is shown there is single low-temperature endothermic peak (near 300C) and there are several high temperature exothermic peaks (near 540C, 650C, and 700C). The first peak is related to glass-transition, the following peaks are related to formation of nano-crystalline phases. It was proved by XRD analysis data. The optimal regimes of the thermal processing of final wares were chosen on the base of thermal- and XRD-analysis. The study of the effects of these regimes on the properties (magnetic conductivity, specific losses etc.) of the circular magnetic conductors was executed. In particular, thermal- as well as thermo-magnetic processing of magnetic conductors based on 5BDSR amorphous alloy (after DC) essentially improves their magnetic properties. For example, magnetic conductivity fÝ increases approximately by factor 17 with respect to the magnitude before DC.

Download Full-text

NonlinearL2-Gain Analysis of Hybrid Systems in the Presence of Sliding Modes and Impacts

Mathematical Problems in Engineering ◽

10.1155/2016/9074096 ◽

2016 ◽

Vol 2016 ◽

pp. 1-10 ◽

Cited By ~ 5

Author(s):

T. Osuna ◽

O. E. Montano ◽

Y. Orlov

Keyword(s):

Sliding Mode ◽

Numerical Study ◽

Sufficient Conditions ◽

Disturbance Attenuation ◽

Sliding Modes ◽

Time Dynamics ◽

Attenuation Level ◽

Disturbance Factor ◽

Disturbance Attenuation Level ◽

The Impact

TheL2-gain analysis is extended towards hybrid mechanical systems, operating under unilateral constraints and admitting both sliding modes and collision phenomena. Sufficient conditions for such a system to be internally asymptotically stable and to possessL2-gain less than ana priorigiven disturbance attenuation level are derived in terms of two independent inequalities which are imposed on continuous-time dynamics and on discrete disturbance factor that occurs at the collision time instants. The former inequality may be viewed as the Hamilton-Jacobi inequality for discontinuous vector fields, and it is separately specified beyond and along sliding modes, which occur in the system between collisions. Thus interpreted, the former inequality should impose the desired integral input-to-state stability (iISS) property on the Filippov dynamics between collisions whereas the latter inequality is invoked to ensure that the impact dynamics (when the state trajectory hits the unilateral constraint) are input-to-state stable (ISS). These inequalities, being coupled together, form the constructive procedure, effectiveness of which is supported by the numerical study made for an impacting double integrator, driven by a sliding mode controller. Desired disturbance attenuation level is shown to satisfactorily be achieved under external disturbances during the collision-free phase and in the presence of uncertainties in the transition phase.

Download Full-text