Effect Of Streaks Research Articles

Multi-Weather Visibility Restoration using MPRNet - Multi-Stage Progressive Image Restoration

This paper introduces a novel approach, termed Multi-Stage Progressive Image Restoration (MSPIR), aimed at addressing the challenging task of restoring images degraded by various adverse weather conditions. Leveraging a combination of advanced algorithms including HI-Net, DCP, and MSCIA, MSPIR offers a comprehensive solution for mitigating the effects of fog, haze, rain streaks, and other atmospheric distortions on image visibility. The methodology follows a multi-stage iterative process, progressively refining image quality and enhancing visibility through successive stages of processing. By integrating deep learning techniques and adaptive context aggregation mechanisms, MSPIR achieves superior results in restoring image clarity and preserving fine details across diverse weather conditions. Experimental evaluations demonstrate the efficacy and robustness of the proposed framework, highlighting its potential for real-world applications in autonomous navigation, surveillance, and remote sensing. Looking ahead, future research directions include optimizing MSPIR for real-time applications, exploring novel deep learning architectures, and integrating additional sensory modalities to further enhance visibility restoration capabilities. Overall, MSPIR represents a significant advancement in multi-weather visibility restoration, offering promising prospects for clearer and safer image processing in various domains.

Film hole layout optimization for multi-row film cooling plate in continuous parameter space under non-uniform inlet temperature distribution

Film cooling is an advanced external cooling technology for protecting gas turbine blades from excessive temperatures. To counteract non-uniform heat loads caused by hot streak and swirl effects at the combustion chamber outlet, fine design of film hole positions is necessary. However, the complexity due to the numerous film holes and their positional parameters presents challenges in the independent optimization of film hole positions in a continuous parameter space. This study proposed an optimization method grounded in the divide and conquer approach to address optimization for film hole layout. The film hole layout was decomposed into multiple single rows and optimized systematically by iteratively refining the single-row film hole layout along the streamwise direction using the expectation maximization algorithm. Optimized layouts for five different inlet temperature distributions were obtained using the proposed method and adiabatic wall temperature distributions were compared and analyzed for optimized and staggered layouts. Additionally, the cooling performance of the optimized layout was evaluated against the staggered layout under conjugate heat transfer conditions and the robustness of the optimized layout under various blowing ratios and peak temperature positions was tested. The results demonstrated that the proposed method can optimize the positions of 52 film holes within 0.3h, and it was generalized to various inlet temperature distributions. By enhancing lateral interactions among downstream film jets, the lifting effect of kidney vortex in the optimized layout was weakened, bringing the film jets closer to the wall and significantly increasing coolant coverage during streamwise development. Comparative analysis reveals the superior cooling performance of the optimized layout at the blowing ratio of 1.0, evidenced by a 15.1% reduction in total input heat transfer rate and a 12.3% enhancement in overall cooling efficiency relative to the staggered layout. Under conditions with blowing ratios ranging from 0.5 to 1.5 and peak temperature position deviations, the average wall temperature of the optimized layout consistently remained lower than the staggered layout, indicating the robustness of the optimized layout to variations in blowing ratio and hot streak position.

Albedo analysis of dust devil-induced slope streaks and tracks on Mars

Despite frequent observations of slope streaks and dust devil tracks on the same slopes in various regions on Mars, only a few instances in Arabia Terra have documented slope streaks directly triggered by dust devils. Here we present new observations of dust devil-induced slope streaks in Elysium Planitia and Amazonis Planitia. These observations represent a rare opportunity to study the erosional effects of both dust devils and slope streaks on the martian surface. Since dust devil tracks and the triggered streaks are formed basically simultaneously and are therefore subject to similar alteration processes, e.g., settling dust from the atmosphere, the relative albedo of these features can be determined using high-resolution orbital images. Our relative albedo analyses of twelve dust devil-induced slope streaks revealed that slope streaks appear substantially darker than the respective dust devil tracks. These observations might indicate a stronger erosion of fine-grained material by slope streaks compared to dust devils.

Research on CO2-WAG in Thick Reservoirs: Geological Influencing Factors and Random Forest Importance Evaluation.

In the development process of thick reservoirs, the impact of various geological factors on the effectiveness of the CO2 water alternating gas (CO2-WAG) flooding technology remains unclear. This paper establishes multiple CO2-WAG flooding models for thick reservoirs to study the effects of sedimentary rhythm, dip angle, matrix permeability, high-permeability streaks (HPS), and barrier layers on the effectiveness of CO2-WAG flooding and then uses the random forest algorithm to rank the importance of these geological factors. The results show that different geological factors have varying degrees of impact on the distribution of water and gas migration and recovery rates during the CO2-WAG flooding process. The ranking of the importance of various factors obtained by reservoir numerical simulations and the random forest algorithm is HPS, sedimentary rhythm, dip angle, matrix permeability, and barrier layers. These research findings will provide effective guidance and a reference for the optimal selection of CO2-WAG flooding schemes for similar thick reservoirs under different geological conditions.

Visual State Space Model for Image Deraining with Symmetrical Scanning

Image deraining aims to mitigate the adverse effects of rain streaks on image quality. Recently, the advent of convolutional neural networks (CNNs) and Vision Transformers (ViTs) has catalyzed substantial advancements in this field. However, these methods fail to effectively balance model efficiency and image deraining performance. In this paper, we propose an effective, locally enhanced visual state space model for image deraining, called DerainMamba. Specifically, we introduce a global-aware state space model to better capture long-range dependencies with linear complexity. In contrast to existing methods that utilize fixed unidirectional scan mechanisms, we propose a direction-aware symmetrical scanning module to enhance the feature capture of rain streak direction. Furthermore, we integrate a local-aware mixture of experts into our framework to mitigate local pixel forgetting, thereby enhancing the overall quality of high-resolution image reconstruction. Experimental results validate that the proposed method surpasses state-of-the-art approaches on six benchmark datasets.

Stress-induced intersecting stacking faults and shear antiphase boundary in Zr5Ge4 second phase precipitate embedded in Ge-modified Zircaloy-4

Secondary phase precipitates are vital to control mechanical, corrosion and irradiation response of the multiphase alloy systems. This work reports the mechanical response of an ordered complex intermetallic Zr5Ge4 precipitate during hot working of the experimental Zircaloy-4 modified with dilute Ge addition. Atomic scale insight is provided into the formation mechanism of straight and circular stacking faults and shear antiphase boundary in Zr5Ge4 precipitate. Two types of stacking faults, having displacement vectors 1/3[100] and 1/3[110] with small components along the c-axis, come across and form a distinct region on the (001) surface composed of a zigzag atomic arrangement different from the parent crystal. Besides this, a shear antiphase boundary along the Zr5Ge4/fcc-Zr interface is analysed and concomitant generation of nanotwins is evidenced by the streaking effect in the associated fast Fourier transform (FFT) pattern. By analysing the distortion and stacking faults in the surrounding fcc-Zr phase, comments are made on the role of external stresses in generating the aforementioned planar defects. The relative activity of two types of displacement vectors observed in Zr5Ge4 precipitate is discussed on the basis of the nature of the atomic bond.

Controlling second-mode oblique breakdown in high-speed boundary layers using streak: A direct numerical simulation study

The suppression effect of streaks on the second mode has been studied by the stability analysis in the past decade. In the present study, we conduct direct numerical simulations (DNS) to investigate the direct nonlinear control in the complete laminar-to-turbulence transition scenario within a high Mach number supersonic boundary layer. Our study aims to provide a comprehensive understanding of the mechanisms underlying the influence of streaks on the transition of high-speed boundary layers. Our work demonstrates the effective control effect of the streaks generated by blowing and suction strips on laminar-to-turbulence transition via the second-mode oblique breakdown at a Mach number 4.5 high-speed boundary layer using DNS. Modal analysis, nonlinear disturbance formulation, and stability analysis are used to provide insight into the stabilization effect of control streaks. Crucially, the role of three-dimensional control modes and mean-flow distortion generated by the control streak are investigated. Our findings indicate that both mean-flow distortion and three-dimensional control modes effectively stabilize the fundamental oblique second mode, particularly when the amplitude of control streaks is strong.

Influence of free-stream turbulence on the boundary layer stability of a wind turbine airfoil and near wake

Free-stream turbulence (FST) alters the boundary layer of wind turbine blades, changing the hydrodynamic stability and near wake. Large-eddy simulations (LES) of a blade section with a laminar separation bubble for several turbulence intensities (TI) and a Reynolds number of 105 are performed. The effects of boundary-layer streaks generated by FST on Tollmien-Schlichting (TS) and Kelvin-Helmholtz (KH) instabilities are analyzed with a model based on the parabolized stability equations (PSE). Two competing effects on flow stability are identified. The spanwise-averaged mean-flow distortion stabilizes primary TS/KH modes for increasing TI. However, this contribution seems dominant only for TI ≥ 8.6%. For lower TI, the spanwise-oscillating distortion caused by streaks destabilizes the flow, and the growth rates of secondary modal instabilities increase with the streak amplitude. The destabilization occurs mainly at spanwise locations with negative streaks since the inflection point shifts away from the wall, enhancing inviscid instabilities. Inflection points in the spanwise direction formed by the streaks also contribute to the destabilization. The modal structures from PSE and LES agree. Finally, the trailing-edge near-wake coherent structures are more energetic for TI ≥ 8.6% due to the partial stabilization of modal instabilities, delaying the turbulent breakdown.

Comparison of dual-energy CT with positron emission tomography for lung perfusion imaging in patients with non-small cell lung cancer

Objective. Functional lung avoidance (FLA) radiotherapy treatment aims to spare lung regions identified as functional from imaging. Perfusion contributes to lung function and can be measured from the determination of pulmonary blood volume (PBV). An advantageous alternative to the current determination of PBV from positron emission tomography (PET) may be from dual energy CT (DECT), due to shorter examination time and widespread availability. This study aims to determine the correlation between PBV determined from DECT and PET in the context of FLA radiotherapy. Approach. DECT and PET acquisitions at baseline of patients enrolled in the HI-FIVE clinical trial (ID: NCT03569072) were reviewed. Determination of PBV from PET imaging (), from DECT imaging generated from a commercial software (Syngo.via, Siemens Healthineers, Forchheim, Germany) with its lowest () and highest () smoothing level parameter value (R), and from a two-material decomposition (TMD) method () with variable median filter kernel size (L) were compared. Deformable image registration between DECT images and the CT component of the PET/CT was applied to PBV maps before resampling to the PET resolution. The Spearman correlation coefficient (r s) between PBV determinations was calculated voxel-wise in lung subvolumes. Main results. Of this cohort of 19 patients, 17 had a DECT acquisition at baseline. PBV maps determined from the commercial software and the TMD method were very strongly correlated [r s( ) = 0.94 ± 0.01 and r s( ) = 0.94 ± 0.02]. was strongly correlated with [r s( ) = 0.67 ± 0.11]. Perfusion patterns differed along the posterior-anterior direction [r s( ) = 0.77 ± 0.13/0.57 ± 0.16 in the anterior/posterior region]. Significance. A strong correlation between DECT and PET determination of PBV was observed. Streak and smoothing effects in DECT and gravitational artefacts and misregistration in PET reduced the correlation posteriorly.

Exact coherent states in plane Couette flow under spanwise wall oscillation

A set of several exact coherent states in plane Couette flow is computed under spanwise wall oscillation control, with a range of wall oscillation amplitudes and periods $({A_w}, T)$ . It is found that the wall oscillation generally stabilises the upper branch of the equilibrium solutions and achieves the corresponding drag reduction, while it influences modestly the lower branch. The stabilisation effect is found to increase with the oscillation amplitude with an optimal time period around ${T^{+}} \approx 100$ . The exact coherent states reproduce some key dynamical behaviours of streaks observed in previous studies, while exhibiting the rich coherent structure dynamics that cannot be extracted from a phase average of turbulent states. Visualisation of state portraits shows that the size of the state space supporting turbulent solution is reduced by the spanwise wall oscillation, and the upper-branch equilibrium solutions become less repelling, with many of their unstable manifolds being stabilised. This change of the state space dynamics leads to a significant reduction in lifetime of turbulence. Finally, the main stabilisation mechanism of the exact coherent states is found to be the suppression of the lift-up effect of streaks, explaining why previous linear analyses have been so successful for turbulence stabilisation modelling and the resulting drag reduction.

DBSwin: Transformer based dual branch network for single image deraining

Rain streaks severely affect the perception of the content and structure of an image so high-performance deraining algorithms are needed in order to eliminate the effects of various rain streaks for high-level computer vision tasks. Although much progress has been made with existing deraining methods, the task of single image deraining remains challenging. In this paper, we first point out that existing Transformers lack sufficient ability to capture channel attention which restricted the ability of models in deraining. To improve the performance of deraining model, we propose a dual branch deraining network based on Transformer. One branch uses dense connections to connect Transformer modules which embed the attention of a composite channel. This branch captures channel attention more finely to learn the representation of rain streaks features. The other branch first obtains features at different scales by gradually expanding the receptive field, then uses these features to obtain attention for regional features, and finally uses the attention to guide the model to focus on areas of high rain streaks density and large scales. By fusing these two branches, the model is able to capture channel attention more finely and to focus on regions of high rain streaks density and large scales. The extensive experimental results on synthetic and real datasets demonstrate that the proposed method outperforms most advanced deraining methods.

Extension of an algebraic intermittency model for better prediction of transition in separated layers under strong free-stream turbulence

A constitutive law describing the Reynolds stresses in boundary layers undergoing laminar-to-turbulent transition, constructed in previous work by elastic-net regression on an experimental data base, is used to improve an algebraic intermittency model for cases with transition in a separated layer influenced by a high level of free-stream turbulence. The intermittency model is combined with a k-ω turbulence model and the basic version, developed in previous work, functions well for bypass transition in attached boundary layers and for transition in separated boundary layers under a low free-stream turbulence level. The basic model version is extended by an additional production term in the transport equation for turbulent kinetic energy. A sensor detects the front part of a separated layer and activates the production term. The term expresses the effect of Klebanoff streaks generated upstream of separation on the Kelvin-Helmholtz instability rolls in the separated part of the layer. The Klebanoff streaks cause faster breakdown by the combined effects of a large adverse pressure gradient and an elevated free-stream turbulence level. The extended model does not alter the results of the basic model version for bypass transition in an attached boundary layer and for transition in a separated boundary layer under a low free-stream turbulence level. The extended model significantly improves the predictions of the previous model version for transition in a separated boundary layer under a high free-stream turbulence level.

A novel multilayer decision based iterative filter for removal of salt and pepper noise

In this paper a novel decision based iterative filter for the detection and elimination of salt and pepper noise is proposed. Effective decisions based upon the noise density of the image are used to filter out noise while maintaining finer details in an image. A fixed size window is used at each step to maintain maximum correlation throughout the filtering process. Additional pre-edge and post-smoothing processing are also presented to further enhance the quality of image. Rigorous analysis over Kodak benchmark dataset containing 24 natural images indicates an exceptional performance boost for medium to extremely high noise density when compared with state of the art filtering techniques. The proposed filter is tested quantitatively and qualitatively using benchmark parameters including peak signal to noise ratio, image enhancement factor and visual representation. Even at noise density as high as 90% and 95%, the proposed filter outperforms the exiting filters providing better edge detail, less blurring and low streaking effects.

Effect of a Combined Hot-Streak and Swirl Profile on Cooled 1.5-Stage Turbine Aerodynamics: An Experimental and Computational Study

Abstract Recently developed lean-burn combustors offer reduced NOx emissions for gas turbines. The flow at exit of lean-burn combustors is dominated by hot streaks and residual swirl, which have been shown—individually—to impact turbine aerodynamic performance. Studies have shown that residual swirl at inlet to the high-pressure (HP) stage predominantly affects the vane aerodynamics, while hot streaks affect the rotor aerodynamics. Studies have also shown that these changes to the HP stage aerodynamics can affect the downstream intermediate-pressure (IP) vane aerodynamics. Yet, to date, there have been no published studies presenting experimental turbine test data with both swirl and hot streaks simultaneously present at inlet. This paper presents the first experimental and computational investigation into the effects of combined hot streaks and swirl on turbine aerodynamics. Experimental measurements were conducted in the Oxford Turbine Research Facility (OTRF), a short-duration rotating transonic facility, in which the nondimensional parameters relevant to turbine fluid mechanics and heat transfer are matched to engine conditions. The turbine under investigation is the recently commissioned LEMCOTEC turbine, which has been designed to represent modern aero-engine architectures and for robustness to lean-burn combustor-representative inlet flows. The turbine comprises an unshrouded HP stage with fully film-cooled vanes followed by low-turning IP vanes in an S-shaped duct. Two turbine inlet flows are considered. The first is uniform in total pressure, total temperature, and flow angle. The second features a nonuniform total temperature (hot streak) profile featuring strong radial and weak circumferential variation superimposed on a swirling velocity profile. This combined nonuniform profile is generated using a new combustor simulator that has recently been commissioned in the OTRF. Detailed area surveys of the flow were conducted at turbine inlet, HP rotor exit, and IP vane exit, and loading distributions were measured on the HP and IP vanes. Measurements and unsteady Reynolds-averaged Navier–Stokes (URANS) predictions suggest that the inlet temperature nonuniformity was relatively well preserved upon being convected through the turbine: the predicted root-mean-square variation in the IP vane exit total temperature field was approximately double that with uniform inlet conditions. Relatively poor comparisons between URANS and experiment highlight the challenge of accurately predicting the complex IP vane flow. In particular, small differences in exit whirl angle resulted in substantial differences in IP vane exit velocity and thus radial pressure gradient.

The effect of streaks on the instability of jets

Abstract

An Iterative Weighted-Mean Filter for Removal of High-Density Salt-and-Pepper Noise

Salt-and-pepper noise, which is often introduced by sharp and sudden disturbances in the image signal, greatly reduces the quality of images. Great progress has been made for the salt-and-pepper noise removal; however, the problem of image blur and distortion still exists, and the efficiency of denoising requires improvement. This paper proposes an iterative weighted-mean filter (IWMF) algorithm in detecting and removing high-density salt-and-pepper noise. Three steps are required to implement this algorithm: First, the noise value and distribution characteristics were used to identify the noise pixels, effectively improving the accuracy of noise detection. Second, a weighted-mean filter was applied to the noisy pixels. We adopted an un-fixed shape symmetrical window with better detail preservation ability. Third, this method was performed iteratively, avoiding the streak effect and artifacts in high noise density. The experimental results showed that IWMF outperformed other state-of-the-art filters at various noise densities, both in subjective visualization and objective digital measures. The extremely fast execution speed of this method is quite suitable for real-time processing.

Structural residual learning for single image rain removal

To alleviate the adverse effect of rain streaks in image processing tasks, CNN-based single image rain removal methods have been recently proposed. However, the performance of these deep learning methods largely relies on the covering range of rain shapes contained in the pre-collected training rainy-clean image pairs. This makes them easily trapped into the overfitting-to-the-training-samples issue and cannot finely generalize to practical rainy images with complex and diverse rain streaks. Against this generalization issue, this study proposes a new network architecture by enforcing the output residual of the network possess intrinsic rain structures. Such a structural residual setting guarantees the rain layer extracted by the network finely comply with the prior knowledge of general rain streaks, and thus regulates sound rain shapes capable of being well extracted from rainy images in both training and predicting stages. Such a general regularization function naturally leads to both its better training accuracy and testing generalization capability even for those non-seen rain configurations. Such superiority is comprehensively substantiated by experiments implemented on synthetic and real datasets both visually and quantitatively as compared with current state-of-the-art methods.

Hot-streak effect on internally air-cooled nozzle guide vanes and shrouds

ABSTRACTThe effect of hot streaks from a gas turbine combustor on the thermodynamic load of internally air-cooled nozzle guide vanes (NGVs) and shrouds has been numerically investigated under flight conditions. The study follows two steps: one for the high-fidelity 60° combustor sector with simplified ten NGVs and three thermocouples attached; and the other for the NGV sectors where each sector consists of one high-fidelity NGV (probe NGV) and nine dummy NGVs. The first step identifies which NGV has the highest thermal load and provides the inlet flow boundary conditions for the second step. In the second step, the flow fields and thermal loads of the probe NGVs are resolved in detail.With the systematically validated physical models, the two-phase flowfield of the combustor-NGVs sector has been successfully simulated. The predicted mean and maximum temperature at the combustor sector exit are in excellent agreement with the experimental data, which provides a solid basis for the hot-streak effect investigation. The results indicate that the second NGV, looking upstream from left, has the highest thermal load. Its maximum surface temperature is 8.4% higher than that for the same NGV but with the mean inlet boundary conditions, and 14.1% higher than the ninth NGV. The finding is consistent with the field-observed NGV damage pattern. To extend the service life of these vulnerable NGVs, some protection methods should be considered.

Positioning errors of metal localization devices with motion artifacts on kV and MV cone beam CT.

Objective:To investigate motion artifacts on kV CBCT and MV CBCT images with metal localization devices for image-guided radiation therapy.Methods:The 8 μ pelvis CBCT template for the Siemens Artiste MVision and Pelvis template for the Varian IX on-board Exact Arms kV were used to acquire CBCT images in this study. Images from both CBCT modalities were compared in CNRs, metal landmark absolute positions, and image volume distortion on three different planes of view. The images were taken on a breathing-simulated thoracic phantom in which several typical metal localization devices were implanted, including clips and wires for breast patients, gold seeds for prostate patients, and BBs as skin markers. To magnify the artifacts, a 4 cm diameter metal ball was also implanted into the thoracic phantom to mimic the metal artifacts.Results:For MV CBCT, the CNR at a 4 sec breathing cycle with 1 cm breathing amplitude was 5.0, 3.4 and 4.6 for clips, gold seeds and BBs, respectively while it was 1.5, 2.0 and 1.6 for the kV CBCT. On the images, the kV CBCT showed symmetric streaking artifacts both in the transverse and longitudinal directions relative to the motion direction. The kV CBCT images predicted 89 % of the expected volume, while the MV CBCT images predicted 95 % of the expected volume. The simulated soft tissue observed in the MVCT could not be detected in the kV CBCT.Conclusion:The MV CBCT images showed better volume prediction, less streaking effects and better CNRs of a moving metal target, i.e. clips, BBs, gold seeds and metal balls than on the kV CBCT images. The MV CBCT was more advantageous compared to the kV CBCT with less motion artifacts for metal localization devices.Advances in knowledge:This study would benefit clinicians to prescribe MV CBCT as localization modality for radiation treatment with moving target when metal markers are implanted.

Instability wave-streak interactions in a hypersonic boundary layer at flight conditions.

The interaction of stationary streaks undergoing nonmodal growth with modally unstable instability waves in a hypersonic boundary-layer flow is studied using numerical computations. The geometry and flow conditions are selected to match a relevant trajectory location from the ascent phase of the HIFiRE-1 flight experiment; namely, a 7 degree half-angle, circular cone with 2.5 mm nose radius, freestream Mach number equal to 5.30, unit Reynolds number equal to 13.42 m-1, and wall-to-adiabatic temperature ratio of approximately 0.35 over most of the vehicle. This paper investigates the nonlinear evolution of initially linear optimal disturbances that evolve into finite-amplitude streaks, followed by an analysis of the modal instability characteristics of the perturbed, streaky boundary-layer flow. The investigation is performed with stationary direct numerical simulations (DNS) and plane-marching parabolized stability equations (PSE), in conjunction with partial-differential-equation-based planar eigenvalue analysis. The overall effect of streaks is to reduce the peak amplification factors of instability waves, indicating a possible downstream shift in the onset of laminar-turbulent transition. The present study confirms previous findings that the mean flow distorsion of the nonlinear streak perturbation reduces the amplification rates of the Mack-mode instability. More importantly, however, the present results demonstrate that the spanwise varying component of the streak can produce a larger effect on the Mack-mode amplification. The study with selected azimuthal wavenumbers for the stationary streaks reveals that a wavenumber of approximately 1.4 times larger than the optimal wavenumber is more effective in stabilizing the planar Mack-mode instabilities. In the absence of unstable first-mode waves for the present cold-wall condition, transition onset is expected to be delayed until the peak streak amplitude increases to nearly 35 percent of the freestream velocity, when intrinsic instabilities of the boundary-layer streaks begin to dominate the transition process. For streak amplitudes below that limit a significant net stabilization is achieved, yielding a potential transition delay that can exceed 100 percent of the length of the laminar region in the uncontrolled case.