Uniform Assumption Research Articles

Optical properties of particle dispersed coatings with gradient distribution.

Particle dispersed coatings with gradient distributions, resulting from either gravity or artificial control, are frequently encountered in practical applications. However, most current studies investigating the optical properties of coatings use the uniform model (uniform single layer assumption), overlooking the gradient distribution effects. Given the pervasiveness of gradient distributions and the widespread use of the uniform model, it is imperative to evaluate applicability conditions of the uniform model in practical applications. In this work, we comprehensively investigate the quantitative performance of the uniform model in predicting the infrared optical properties of coatings with gradient distributions of particle volume fraction using the superposition T-matrix method. The results show that the gradient distribution of particle volume fraction has a limited impact on the emissivity properties of T i O 2-PDMS coatings in the midwavelength-infrared (MWIR) and long-wavelength-infrared (LWIR) bands, which validates the uniform model for the gradient coatings with weakly scattering dielectric particles. However, the uniform model can yield significant inaccuracies in estimating the emissivity properties of Al-PDMS coatings with gradient distributions in the MWIR and LWIR bands. To accurately estimate the emissivity of such gradient coatings with the scattering metallic particles, meticulous modeling of the particle volume fraction distribution is essential.

A Gaussian Mixture CPHD Filter for Multi-Target Tracking in Target-Dependent False Alarms

The estimation of the target number and individual tracks are two major tasks in multi-target tracking. The main shortcoming of traditional tracking methods is the cumbersome data association between measurements and targets. The cardinalized probability hypothesis density filter (CPHD) proposed in recent years can achieve the requirement for multitarget tracking. This kind of filter jointly estimates the cardinality distribution and the posterior density, which can achieve a more stable estimate of the target number. However, targets with complex micro-Doppler signatures (drones, birds, etc.) may generate target-dependent false alarms, which is contrary to the traditional uniform distribution assumption. In this case, the estimates of traditional CPHD filter will suffer from the abnormal transfer of PHD mass, causing the degradation of filtering performance. This paper studies the individual tracking of group targets with an improved GM-CPHD filter. First, the target-dependent false alarms are modeled with a general independent and identically distributed (I.I.D.) cluster process. Second, the update equations of cardinality and PHD density in target-dependent false alarms are derived. Finally, a practical solution using the Gaussian mixture method is proposed. The effectiveness of the proposed filter is verified by the simulation and experimental results.

Global Estimates of Mesoscale Vertical Velocity Near 1,000 m From Argo Observations

AbstractGlobal estimates of mesoscale vertical velocity remain poorly constrained due to a historical lack of adequate observations on the spatial and temporal scales needed to measure these small magnitude velocities. However, with the wide‐spread and frequent observations collected by the Argo array of autonomous profiling floats, we can now better quantify mesoscale vertical velocities throughout the global ocean. We use the underutilized trajectory data files from the Argo array to estimate the time evolution of isotherm displacement around a float as it drifts at 1,000 m, allowing us to quantify vertical velocity averaged over approximately 4.5 days for that depth level. The resulting estimates have a non‐normal, high‐peak, and heavy‐tail distribution. The vertical velocity distribution has a mean value of (1.9 ± 0.02) × 10−6 m s−1 and a median value of (1.3 ± 0.2) × 10−7 m s−1, but the high‐magnitude events can be up to the order of 10−4 m s−1. We find that vertical velocity is highly spatially variable and is largely associated with a combination of topographic features and horizontal flow. These are some of the first observational estimates of mesoscale vertical velocity to be taken across such large swaths of the ocean without assumptions of uniformity or reliance on horizontal divergence.

Multiphase characterization of AGN winds in five local type-2 quasars

We present MEGARA integral field unit (IFU) observations of five local type-2 quasars (QSO2s, z ∼ 0.1) from the Quasar Feedback (QSOFEED) sample. These active galactic nuclei (AGN) have bolometric luminosities of 1045.5 − 46 erg s−1 and stellar masses of ∼1011 M⊙. The LR-V grating of MEGARA allows us to explore the kinematics of the ionized gas through the [O III]λ5007 Å emission line. The nuclear spectra of the five QSO2s, extracted in a circular aperture of ∼1.2″ (∼2.2 kpc) in diameter, matching the resolution of these seeing-limited observations, show signatures of high velocity winds in the form of broad (full width at half maximum, 1300 ≤ FWHM ≤ 2240 km s−1) and blueshifted components. We found that four out of the five QSO2s present outflows that we can resolve with our seeing-limited data, and they have radii ranging from 3.1 to 12.6 kpc. In the case of the two QSO2s with extended radio emission, we found that it is well aligned with the outflows, suggesting that low-power jets might be compressing and accelerating the ionized gas in these radio-quiet QSO2s. In the four QSO2s with spatially resolved outflows, we measured ionized mass outflow rates of 3.3–6.5 M⊙ yr−1 when we used [S II]-based densities, and of 0.7–1.6 M⊙ yr−1 when trans-auroral line-based densities were considered instead. We compared them with the corresponding molecular mass outflow rates (8–16 M⊙ yr−1), derived from CO(2–1) ALMA observations at 0.2″ resolution. The cold molecular outflows carry more mass than their ionized counterparts. However, both phases show lower outflow mass rates than those expected from observational scaling relations where uniform assumptions on the outflow properties were adopted. This might be indicating that the AGN luminosity is not the only driver of massive outflows and/or that these relations need to be rescaled using accurate outflow properties (i.e., electron density and radius). We did not find a significant impact of the outflows on the global star formation rates when considering the energy budget of the molecular and ionized outflows together. However, spatially resolved measurements of recent star formation in these targets are needed in order to evaluate this fairly, considering the dynamical timescales of the outflows, of 3–20 Myr for the ionized gas and 1–10 Myr for the molecular gas.

Leveraging Bilateral Correlations for Multi-Label Few-Shot Learning.

Multi-label few-shot learning (ML-FSL) refers to the task of tagging previously unseen images with a set of relevant labels, giving a small number of training examples. Modeling the correlations between instances and labels, formulated in the existing methods, allows us to extract more available knowledge from limited examples. However, they simply explore the instance and label correlations with a uniform importance assumption without considering the discrepancy of importance in different instances or labels, making the utilization of instance and label correlations a bottleneck for ML-FSL. To tackle the issue, we propose a unified framework named bilateral correlation reconstruction (BCR) to enable the network to effectively mine underlying instance and label correlations with varying importance information from both instance-to-label and label-to-instance perspectives. Specifically, from the instance-to-label perspective, we refine prototypes per category by reweighting each image with its specific instance-importance degree extracted from the similarity between the instance and the corresponding category. From the label-to-instance perspective, we smooth labels for each image by recovering latent label-importance with considering the integrated topology of all samples in a task. Experimental results on multiple benchmarks validate that BCR could outperform existing ML-FSL methods by large margins.

A sustainable NEV manufacturer-retailer system under the Nash bargaining framework: considering the impact of the COVID-19 epidemic under the CVaR criterion

Suppose a new energy vehicle (NEV) manufacturer-retailer system where the wholesale price and the order quantity are determined through a negotiation procedure. Considering the impact of the COVID-19 epidemic, the manufacturer and the retailer are both assumed to be risk averse with Conditional Value-at-Risk (CVaR) as their performance measure. With the uniform distribution assumption, we derive the equilibrium solutions as well as the players’ profit shares in the Stackelberg game and Nash bargaining framework. We quantitatively address the impacts of the players’ confidence levels and government subsidy on the equilibrium order quantity, wholesale price and profit allocation in both negotiation frameworks. We find that, in both negotiation frameworks and considering the impact of the COVID-19 epidemic, a more risk-averse (i.e., with lower confidence level in CVaR model) manufacturer or retailer tends to occupy a higher profit share. On the other hand, a higher government subsidy aiming at offsetting the epidemic’s impact leads to a higher profit share for the manufacturer and a lower one for the retailer. A quantitive comparison of the equilibriums in the two negotiation frameworks indicates that more NEVs are ordered by the retailer and a higher system profit is generated in the Nash bargaining framework than the Stackelberg game. Thus, we analytically prove that the Nash bargaining framework is superior to the Stackelberg game for the NEV manufacturer-retailer system in terms of both quantity and profit with consideration of the epidemic impact. In addition, a series of numerical experiments is carried out to illustrate the effects of some significant parameters on the equilibrium order quantity and the system profit allocation in different negotiation frameworks. These numerical experiments also further demonstrate the superiority of the Nash bargaining framework for either NEV player—no matter how the epidemic trend and the government subsidy vary—and provide a quantitative scope for the retailer’s bargaining power to sustainably maintain the win-win cooperation between the NEV manufacturer and retailer in the superior Nash bargaining framework within the epidemic environment. From the perspective of policy, the government should increase subsidy within the epidemic environment to offset the negative effect and can degenerate subsidy when the epidemic dissipates. Furthermore, as the subsidy degenerates, both model results and numerical experiments show that the manufacturer suffers a more unfavorable effect, so the government can preferentially support the manufacturer by adjusting the subsidy to a higher level to alter players’ relative powers and profit shares.

A Novel Algorithm for Directional Scattering in Acoustic Ray Tracers

It is vital to consider acoustic scattering when using geometrical acoustic simulation techniques, such as ray tracing. However, there are few methods for modelling scattering, and most rely on strong assumptions of uniformity on the distribution of scattered energy. In this paper, a model for directional scattering in ray tracers is presented. The model is based on an idealized model of a 1D scatterer, which is then used to extend the most commonly used scattering algorithm in ray tracers today. The developed algorithm is implemented in a ray tracer and tested to evaluate its performance compared to existing methods. It is found that the directional scattering algorithm can be used to replicate measured effects on room acoustic parameters caused by changes in the orientation of 1D scatterers.

Global well-posedness of 2D Hyperbolic perturbation of the Navier–Stokes system in a thin strip

In this paper, we study a hyperbolic version of the Navier–Stokes equations, obtained by using the approximation by relaxation of the Euler system, evolving in a thin strip domain. The formal limit of these equations is a hyperbolic Prandtl type equation, our goal is to prove the existence and uniqueness of a global solution to these equations for analytic initial data in the tangential variable, under a uniform smallness assumption. Then we justify the limit from the anisotropic hyperbolic Navier–Stokes system to the hydrostatic hyperbolic Navier–Stokes system with small analytic data.

Statistical Shape Modeling Enables Identification of Subtalar Contact Stress Differences Following Tibiotalar Arthrodesis and Total Ankle Replacement

Category: Hindfoot; Ankle Arthritis Introduction/Purpose: Clinical studies have shown 32% of patients with a TAR progress to subtalar OA within 5 years, whereas 78% of patients with a tibiotalar arthrodesis presented with subtalar OA by 7.5 years. Higher rates of subtalar OA after arthrodesis may be explained by a transfer of ankle forces and stress through the adjacent subtalar joint while TAR may mitigate these changes. The objective of this study was to compare subtalar joint contact stresses between patients treated with tibiotalar arthrodesis and total ankle replacement (TAR) during an overground walking activity using correspondence particles to enable regional analysis. Methods: With IRB approval, ten individuals with unilateral tibiotalar arthrodesis and six individuals with unilateral TAR were imaged with biplane fluoroscopy during overground walking. Discrete element analysis (DEA) was performed to estimate subtalar joint contact stress using the tracked bone models. Cartilage was modeled using linear-elastic material properties (E=12 MPa, v=0.42) and uniformly extruded compressible surfaces from rigid subchondral bone (0.98 mm talar side, 0.75 mm calcaneal side1). A calcaneal statistical shape model (SSM) was created and resulting correspondence particles served as registered locations for comparison of cumulative stress across three phases of normalized stance (loading-response 0-24%, mid 25-54%, and terminal 55- 87%). Two-sample t-tests or Wilcoxon rank-sum tests were used to evaluate differences (p < 0.05) in cumulative contact stresses at each correspondence particle within the 3 phases based upon Shapiro-Wilk findings of normality. Results: There were significant differences in contact stress exposure across all three phases of gait. Differences were identified along the superior-medial aspect of the posterior facet and within the anterior facet (Figure 1). Higher cumulative stresses were observed along the border of the posterior facet and in the medial facet. This model is limited by a lack of validation, uniform cartilage thickness assumptions applied across groups, and that DEA only estimates contact stress without consideration of shear. Conclusion: This study was the first to localize regional differences in subtalar joint stress for patients having undergone TAR and tibiotalar arthrodesis. Interestingly, TAR patients experienced higher stress in this study compared to those with arthrodeses. These ostensibly counterintuitive findings of higher TAR stress may relate to the pre-existence of subtalar OA which is a common indication of TAR versus fusion.

Investigation of the orifice flow of over-the-rotor liner and its interaction with the rotor flow field

The emergence of ultra-high bypass ratio engines calls for advanced noise control technology. A promising technology is installing the acoustic liner at the casing over the rotor (OTR), forming the so-called OTR liner. Experiments have shown that this treatment could compensate for the reduced noise absorption due to the shortened intake length. Compared with the conventional liner receiving a pure acoustic pressure excitation, the OTR liner is exposed to the combined aerodynamic pressure perturbance and high acoustic pressure excitation, leading to complex flow mechanisms in the liner orifices. In this work, the large-eddy simulation method is used to investigate the flow phenomenon of OTR liner where each liner orifice is explicitly modeled to capture the flow behaviors at the blade tip proximity. Interesting findings are as follows: first, OTR liner orifices have an asynchronous dynamic response with a phase lag corresponding to the blade traversing speed; second, oscillating flow, resembling that in a classical Helmholtz resonator, is formed in the upstream liner orifices, while a bias flow appears in the downstream liner orifices. The dramatically different flow behaviors lead to non-uniform energy dissipation among orifices, implying the uniform impedance assumption in conventional acoustic liner definition fails when installing the liner near the rotor blade. Results also show that the orifice flow interacts with the blade tip leakage flow, affecting the development of the tip leakage vortex that may impact the rotor–stator interaction noise.

Full-Bayes GNSS-A solutions for precise seafloor positioning with single uniform sound speed gradient layer assumption

A systematic analysis methodology for precise seafloor positioning using the GNSS-A has been constructed and implemented in the open-source software GARPOS. It introduces a linearized perturbation field model for extraction of the 4-dimensional sound speed variation, and solves the perturbation parameters simultaneously with the seafloor position based on the empirical Bayes approach. Although it can provide the solutions stably and almost analytically, it has less expandability when imposing additional nonlinear constraint parameters in the observation equation. Even though such parameters can be optimized by applying some information criteria, information on the details of the joint posterior probability would be lost and only the conditional posterior can be estimated. To overcome the above limitations, we implemented full-Bayes estimation using the Markov-Chain Monte Carlo algorithm. This approach can not only help evaluate the dependency of the existing constraint parameters on the seafloor position, but also let us discuss the effects of the additionally imposed constraints. We imposed a constraint under the assumption that a temporally-variable gradient layer steadily lies at a certain depth in the observation scale (typically < 10 km × 10 km, < 1 day). This models the cases with temperature gradients due to a large-scale structure such as the Kuroshio current or internal waves with long-wavelength. The constraint narrows the posterior of the horizontal position and provides a better solution for many datasets, especially in the Nankai Trough region. For the other datasets, the constraint emphasized bias errors, which can also provide information on the possibility of instrumental and modelling errors.

Modified Pennes bioheat equation with heterogeneous blood perfusion: A newer perspective

The Pennes bioheat equation is a widely used mathematical model for predicting temperature distribution in biological tissues. However, it assumes homogeneous blood perfusion throughout the tissue, which may not accurately represent the complex perfusion patterns observed in tumors. In this study, we propose modification to traditional Pennes bioheat equation that incorporates the effects of perfusion heterogeneity by introducing a spatially varying perfusion term, represented by a perfusion coefficient, ωb(x,y,z) to account for local variations in blood flow at each spatial location within the biological tissue. Therefore, heterogeneous blood perfusion at each tumor tissue voxel location relax the uniform blood perfusion assumption. By incorporating these modifications, the model allows for a more realistic representation of the heat exchange between the biological tissue and blood flow, by predicting the non-uniform temperature distribution particularly in tumors with irregular blood vessel growth and organization, thereby facilitating treatment planning and optimization of thermal therapies, and leading to more effective therapeutic outcomes. The spatially varying perfusion coefficient can be obtained through advanced imaging techniques such as dynamic contrast-enhanced MRI or Doppler ultrasound enabling the assessment of perfusion heterogeneity in biological tissues. In conclusion, the modified Pennes bioheat equation offers a valuable tool for understanding the intricate relationship between with heterogeneous blood perfusion and temperature distribution in biological tissues, providing important insights to the thermal response of tumors and guiding the development of improved therapeutic strategies in optimizing cancer treatments.

Моделирование процесса прокатки слоистого композита АМг3/Д16/АМг3

Introduction. Over the past decades, laminated composites based on aluminum alloys have been increasingly used in the aerospace and automotive industries. Laminated composites are usually produced by accumulative roll bonding, which results in the metallurgical bonding of initially prepared sheets. Hence, the main task of accumulative roll bonding is to obtain a reliable bond between materials. However, at present, the process of joining similar or dissimilar materials by plastic deformation is still a poorly understood phenomenon. In this regard, in recent years, methods of finite element modeling of the processes of joining materials have begun to develop intensively. The purpose of the work is to establish a relationship between stress-strain state parameters and the formation of a stable bond between aluminum alloys of different compositions. To achieve this goal, the following tasks are formulated: 1. Simulation of the laminated composite “AMg3/D16/AMg3” rolling process using data corresponding to physical experiments carried out at the Institute of Engineering Science of the Ural Branch of the Russian Academy of Sciences; 2. Selection and analysis of the most important stress-strain state parameters of the laminated composite “AMg3/D16/AMg3” rolling process. Research methods. Process simulation system Deform-3D was chosen as the main research tool. Results and Discussion. An analysis of the coordinate grid distortion and velocity vectors of material flow of layers revealed that the deformation is distributed inhomogeneously in the cross section after rolling: the outer layers flow more intensively compared to the middle layer. The maximum scatter of strain intensity ei in the cross section, observed at a maximum reduction ratio of 75%, is 12%. This allows one to accept for analytical calculations in the first approximation the assumption of deformation uniformity. A relationship is established between the beginning of the formation of a bond between composite layers and the threshold expansion of the contact surface and normal pressure at the interlayer boundary. In the final part of the study, future directions for improving the approaches of simulation the laminated composites rolling processes are proposed.

Simulating the effects of behavioral and physical heterogeneity on nonpoint source pollution

AbstractTo increase the effectiveness of conservation programs focused on reducing agricultural nutrient runoff and targeting management interventions, some have called for greater attention to the role of diversity in both management and physical context. To examine the independent and interactive effects of behavioral and physical heterogeneity on phosphorus loads, a sensitivity analysis was conducted using six different assumptions about distributions of phosphorus fertilizer application rates and soil test phosphorus (STP) levels for hydrologic response units in a SWAT model for the Maumee River Watershed. Results indicated that changing assumptions about behavior and STP levels can significantly affect estimated dissolved reactive phosphorus (DRP) loads and the level of disproportionality, which is a measure of the unequal distribution of pollutant loading. Placing the highest fertilizer application rates on fields with the most excessive STP produced 14% greater estimated DRP load and higher levels of disproportionality compared to a baseline model, where homogeneity in farmer fertilizer behavior and STP were assumed. In contrast, placing the lowest fertilizer application rates on the fields with the most excessive STP led to estimated DRP loads and level of disproportionality that were similar to the baseline model. Results from this analysis suggest that simplistic or uniform assumptions about behavior or STP levels may mask serious environmental risks in agricultural watershed models.

Time-varying up-crossing theory-based non-stationary extreme estimation of gust-loading on rectangular cylinder due to thunderstorm-like wind

An active wind tunnel test was conducted to experimentally investigate the nonstationary time-varying extreme characteristics of the aerodynamic force on a 5:1 rectangular cylinder under a thunderstorm-like gust. Previous studies have primarily estimated the time-varying extremes of nonstationary surface wind pressure under the assumption of a nonstationary, uniformly modulated stochastic process. This study employed the time-varying upcrossing theory to precisely calculate the time-varying extreme values and peak factors of transient loads on a 5:1 rectangular cylinder subjected to a thunderstorm-like wind. The findings revealed that the wind pressures and aerodynamic lifts of a rectangular cylinder subjected to thunderstorm-like gusts present distinct time-varying and non-stationary features The extreme value distribution (probability density function and cumulative distribution function) estimated by applying the time-varying upcrossing theory also demonstrates significant temporal evolution. Accordingly, utilizing conventional stationary stochastic process estimation methods may generate considerable disparities. A comparison of the findings derived from the theory proposed in this work with those under the uniform modulation assumption suggests that the latter leads to an underestimation of the extreme values of the actual wind load.

A hybrid inverse optimization-stochastic programming framework for network protection

Disaster management is a complex problem demanding sophisticated modeling approaches. We propose utilizing a hybrid method involving inverse optimization to parameterize the cost functions for a road network’s traffic equilibrium problem and employing a modified version of a two-stage stochastic model to make protection decisions using the information gained from inverse optimization. Inverse optimization allows users to take observations of solutions of optimization and/or equilibrium problems and estimate the parameter values of the functions defining them. In the case of multi-stage stochastic programs for disaster relief, using inverse optimization to parameterize the cost functions can prevent users from making incorrect protection decisions. We demonstrate the framework using two types of cost functions for the traffic equilibrium problem and two different networks. We showcase the value of inverse optimization by demonstrating that, in most of the experiments, different decisions are made when the stochastic network protection problem is parameterized by inverse optimization versus when it is parameterized using a uniform cost assumption. We also demonstrate that similar decisions are made when the stochastic network protection problem is parameterized by inverse optimization versus when it is parameterized by the original/“true” cost parameters.

Simplified numerical modeling and analysis of electrolyte behavior in multiple physical fields for lithium-ion batteries

The electrolyte plays an important role in lithium-ion batteries, affecting their state and safety. However, the internal states of the electrolyte in the battery full domain are not easy to obtain directly. The electric field distribution, to which less attention has been paid, is as important as the concentration distribution, even related to battery safety. In this paper, an accurate and real-time simplified model for electrolyte is developed at the mesoscale, based on the Nernst-Planck equation and the continuum equation with some simple and reasonable assumptions. The analytical solutions of steady-state distribution for concentration and electric fields are obtained by theoretical derivation. Then, based on the assumption of internal uniformity of electrode, the numerical solution of the transient-state process is derived under full working conditions. The potential distribution and the overpotentials within electrolytes can be further calculated. Finally, the accuracy of the developed model is verified by the experiment of constant current terminal voltage and the accurate finite volume method. Besides, simulations are carried out to analyze the effects on the variables of electrolytes by varying the parameters in the model. The design suggestions of electrolyte concentration, thickness and porosity of each component in the battery are given.

Protracted displacement and housing systems in intermediary cities: the case of Syrians in Torbalı, Türkiye

This article investigates the dynamics of complex housing systems within the context of large-scale protracted displacement in Turkey/Türkiye. It presents new empirical findings from a qualitative study conducted in Torbalı, a rapidly growing intermediate city with a significant population of Syrian displaced people. Drawing on theoretical and conceptual insights from housing studies, urban studies and migration studies, the article assesses the ways in which displacement materialises in place through housing and contributes to city-making and urbanisation processes informally, incrementally, and in locally and historically contingent manners. We argue that the forms and dynamics of emerging housing exhibit both continuity but most markedly significant disjuncture from past housing trajectories in Torbalı. This challenges the implicit assumption of legal uniformity of self-builders common in incremental housing debates and suggests that the notion of incremental housing has limited relevance in contexts of protracted urban displacement. Furthermore, findings underline the significance of legal dimensions in energising housing informalities; in grading socio-legal statuses of resident populations; in bounding displaced people’s mobilities; in demarcating labour flows; in moulding rental markets; and in directing the flows of housing materials. These in turn shape current and future urban built environments and mould the ways in which the urbanisation of refuge manifests.

Quantification of the effects of the spatial variation of ground motions on the seismic response of highway bridges

The stochastic responses of highway bridges to spatial variation of ground motions (SVGM) are analysed in this paper. A model of spatially varying ground motions is used to investigate the relative importance of the incoherency effect, the wave passage effect and the site effects on the stochastic dynamic response of an asymmetrical R.C box girder highway bridge with variable inertia. In this study, the incoherency effect is investigated using two widely used models while the wave-passage effect is incorporated using various wave velocities. Then, the random vibration theory is applied to study the effect of the non-uniform seismic excitations on the bridge structure. The bridge response is evaluated in terms of the mean values of the maximum displacements and the bending moments. Analyses of both stationary and transient response are performed. The results show that the stochastic dynamic responses related to site effects are mostly much greater than those calculated using uniform, delayed and incoherent seismic excitation assumptions. As a result, analytical models used for the stochastic dynamic analysis of long span highway bridges should take into account all the SVGM components, particularly the site-response effects.

Numerical approach to theoretical aspects of wedge-induced oblique detonation wave in a hydrogen concentration gradient

The present study conducts numerical simulations of oblique detonation wave (ODW) induced on a wedge in the concentration gradient of a hydrogen–air mixture. As a continuation of the author's previous work on the morphology of the initiating flame in a non-uniform mixture, the concentration gradient is provided only to the ODW front to address its theoretical characteristics: the propagation velocity and structures of post-shock reactive flow associated with the Chapman–Jouguet and Zeldovich–von-Neumann–Doering theories, respectively. Applying a Gaussian distribution of the hydrogen mole fraction to the ODW front induces a curved shape that is concave or convex in fuel-rich or fuel-lean compositions, respectively. The local wave angle on a curved ODW matches the one-dimensional theory in a uniform mixture, which proves its robustness in predicting the detonation velocity in a non-uniform mixture. Furthermore, tracing streamlines with different compositions reveals that the flow path and variations in temperature and pressure are almost coincident with those predicted by one-dimensional and uniform assumptions. The slight variation among the different conditions is attributed to the effects of two-dimensional convergence/divergence that are intensified at stronger gradients. The understanding achieved in the present study will also benefit the evaluation of propagating detonation in a non-uniform mixture layer formed in propulsion devices.