Shadow Effect Research Articles

Mapping forest fire severity using bi-temporal unmixing of Sentinel-2 data - Towards a quantitative understanding of fire impacts

Precise quantification of forest fire impacts is critical for management strategies in support of post-fire mitigation. In this regard, optical remote sensing imagery in combination with spectral unmixing has been widely used to measure fire severity by means of fractional cover of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), charcoal (CH) and further ground components such as ash, bare soil and rocks. However, most unmixing analyses have made use of a single post-fire image without accounting for the pre-fire state. We aim to assess fire severity from Sentinel-2 data using a bi-temporal spectral unmixing analysis that provides a quantitative fire impact description and is oriented towards the process of change by including pre-fire and post-fire information. Unmixing was based on Random Forest Regression (RFR) modeling using synthetic training data from a bi-temporal spectral library. We describe fire severity as changes associated with the combustion of photosynthetic vegetation (PV–CH fraction) and dieback of photosynthetic vegetation (PV-NPV fraction). Unburned forest was mapped as stable photosynthetic vegetation (PV-PV fraction). We evaluated our approach on a forest fire that burned in a temperate forest region in eastern Germany in 2018. Independent validation was carried out based on reference fractions obtained from very high-resolution (VHR) imagery such as Plante Scope, SPOT6, orthophotos, aerial photos, and Google Earth. The results underline the effectiveness of our unmixing approach, with Root Mean Squared Errors (RMSE) of 0.072 for PV-CH, 0.09 for PV-NPV, and 0.08 for PV-PV fractions. Most of the errors were caused by spectral similarity between charcoal and shadow effects caused by trees, and the coloring of foliage and NPV in the late phenological season of the post-fire Sentinel-2 image. Based on the two-dimensional feature space of PV-CH and PV-NPV fractions, we calculated two metrics to characterize fire impacts: distance, an indicator of disturbance severity (sum of combustion and dieback), and angle, a measure of disturbance composition (gradient between combustion and dieback). Furthermore, we compared the fraction-based metrics with the difference Normalized Burn Ratio (dNBR). Since the dNBR is most sensitive to combustion and presence of charcoal, it does not fully characterize fire-related vegetation loss associated with dieback. The bi-temporal fraction-based indices provide more ecologically meaningful information on fire severity, particularly for regions that are less prone to severe wildfires such as Central Europe.

Who’s afraid of the GOATs? - Shadow effects of tennis superstars

In multi-stage tournaments, anticipated competition in future stages might affect the outcome of competition in the current stage. In particular, the presence of superstars might demotivate the next-best competitors from seeking to advance to later rounds, where they ultimately are likely to face a superstar. Data from men’s professional tennis tournaments held between 2004 and 2019 affirm that the participation of superstars (Djokovic, Nadal, Federer, and Murray) reduces the probability that the remaining Top 20 players win their matches. Such shadow effects arise even in very early tournament stages, in which favoured players lose more often than expected, given their ability. The effects are more pronounced when multiple superstars compete in the tournament and disappear once all superstars have been eliminated from competition. Furthermore, shadow effects increase the probability of retirement of strong but non-superstar competitors and disappear once superstar performance is not dominant.

BFFNet: a bidirectional feature fusion network for semantic segmentation of remote sensing objects

PurposeHigh-resolution remote sensing images possess a wealth of semantic information. However, these images often contain objects of different sizes and distributions, which make the semantic segmentation task challenging. In this paper, a bidirectional feature fusion network (BFFNet) is designed to address this challenge, which aims at increasing the accurate recognition of surface objects in order to effectively classify special features.Design/methodology/approachThere are two main crucial elements in BFFNet. Firstly, the mean-weighted module (MWM) is used to obtain the key features in the main network. Secondly, the proposed polarization enhanced branch network performs feature extraction simultaneously with the main network to obtain different feature information. The authors then fuse these two features in both directions while applying a cross-entropy loss function to monitor the network training process. Finally, BFFNet is validated on two publicly available datasets, Potsdam and Vaihingen.FindingsIn this paper, a quantitative analysis method is used to illustrate that the proposed network achieves superior performance of 2–6%, respectively, compared to other mainstream segmentation networks from experimental results on two datasets. Complete ablation experiments are also conducted to demonstrate the effectiveness of the elements in the network. In summary, BFFNet has proven to be effective in achieving accurate identification of small objects and in reducing the effect of shadows on the segmentation process.Originality/valueThe originality of the paper is the proposal of a BFFNet based on multi-scale and multi-attention strategies to improve the ability to accurately segment high-resolution and complex remote sensing images, especially for small objects and shadow-obscured objects.

Electrical and thermal performance of multidimensional semi-transparent CdTe PV window on offshore passenger ships in moored and sailing condition

Utilizing solar energy is an effective method to decrease fossil energy consumption in marine field. Horizontally installed deck photovoltaic (PV) systems have been widely investigated to reduce navigation energy consumption on ocean-going ships. However, energy saving rate is unsatisfactory because of the low energy density of solar energy and the shadow caused by ship body. As for large amount of offshore small ships, it's even harder to utilize the existing technology since deck space is limited. In this paper, semi-transparent CdTe PV window system is proposed for offshore passenger ships without enough deck spaces but with large window area around ship cabin. Multidimensional PV windows can increase PV area and reduce heat gain inside the cabin, shadow effect caused by ship body is also avoided. Energy saving can be both achieved by electrical generation actively and cooling load reduction passively. Dynamic mathematical models of multidimensional PV window under moored and sailing conditions are established. Simulation results indicate that the daily electrical generation and average electrical efficiency are 0.74 kWh & 14.65% in moored condition and 0.83 kWh & 16.24% in sailing condition. Navigation leads to higher received solar radiation (18.2%), higher electrical generation (12.1%) and higher electrical efficiency (10.85%). Electricity created by PV window can support 6 h' continuous operation for auxiliary system on board. With PV windows, the average air temperature in cabin is decreased by 6.5 °C compared with ordinary windows. The average heat fluxes through four directions of PV windows are decreased by 75.44%, 73.64%, 47.52% and 75.33% compared with ordinary windows.

The Benefit of Binaural Hearing Among Listeners with Sensorineural Hearing Loss

The performance of binaural processing may be disturbed in the presence of hearing loss, especially of sensorineural type. To assess the impact of hearing loss on speech perception in noise regarding binaural processing, series of speech recognition measurements in controlled laboratory conditions were carried out. The spatial conditions were simulated using dummy head recordings played back on headphones. The Intelligibility Level Difference (ILD) was determined by measuring the change in the speech reception thresholds (SRT) between two configurations of a masking signal source (N) and a speech source (S), namely the S0N90 condition (where numbers stand for angles in horizontal plane) and the co-located condition (S0N0). To disentangle the head shadow effect (better ear effect) from binaural processing in the brain, the difference between binaural and monaural S0N90 condition (so-called Binaural Intelligibility Level Difference, BILD) value was calculated. Measurements were performed with a control group of normal-hearing listeners and a group of sensorineural hearing-impaired subjects. In all conditions performance of the hearing-impaired listeners was significantly lower than normal-hearing ones, resulting in higher SRT values (3 dB difference in the S0N0 configuration, 7.6 dB in S0N90 and 5 dB in monaural S0N90). The SRT improvement due to the spatial separation of target and masking signal (ILD) was also higher in the control group (8.1 dB) than in hearing-impaired listeners (3.5 dB). Moreover, a significant deterioration of the binaural processing described by BILD was found in people with sensorineural deficits. This parameter for normal-hearing listeners reached a value of 3 to 6 dB (4.6 dB on average) and decreased more than two times in the hearing-impaired group to 1.9 dB on average (with a deviation of 1.4 dB). These findings could not be explained by individual average hearing threshold (standard in audiological diagnostics) only. The outcomes indicate that there is a contribution of suprathershold deficits and it may be useful to consider binaural SRT measurements in noise in addition to the pure tone audiometry resulting in better diagnostics and hearing aid fitting.

Assessment of Binaural Benefits in Hearing and Hearing-Impaired Listeners.

The purpose of this study was to (a) investigate which speech material is most appropriate as stimulus in head shadow effect (HSE) and binaural squelch (SQ) tests, (b) obtain normative values of both tests using the material decided to be optimal, and (c) explore the results in bilateral cochlear implant (CI) users. Study participants consisted of 30 normal-hearing (NH) persons and 34 bilateral CI users. This study consisted of three phases. In the first phase, three different speech materials (1) monosyllabic words, (2) spondee words, and (3) sentences were compared in terms of (a) effect size, (b) test-retest reliability, and (c) interindividual variability. In the second phase, the speech material selected in the first phase was used to test a further 24 NHs to obtain normative values for both tests. In the third phase, tests were administered to a further 23 bilateral CI users, together with localization test and the Speech, Spatial, and Qualities of Hearing scale. The results of the first phase indicated that spondees and sentences were more robust materials compared with monosyllables. Although the effect size and interindividual variability were comparable for spondees and sentences, sentences had higher test-retest reliability in this sample of CI users. With sentences, the mean (± standard deviation) HSE and SQ in the NH group were 58 ± 14% and 22 ± 11%, respectively. In the CI group, the mean HSE and SQ were 49 ± 13% and 13 ± 14%, respectively. There were no statistically significant correlations between the test results and the interval between the implantations, the length of binaural listening experience, or the asymmetry between the ears. Sentences are preferred as stimulus material in the binaural HSE and SQ tests. Normative data are given for HSE and SQ with the LiCoS (linguistically controlled sentences) test. HSE is present for all bilateral CI users, whereas SQ is present in approximately seven out of 10 cases.

Numerical analysis of unstable propagation of three-dimensional parallel hydraulic fractures induced by interferences of adjacent perforation clusters and thermal diffusion

PurposeThe purpose of this study is to investigate the unstable propagation of parallel hydraulic fractures induced by interferences of adjacent perforation clusters and thermal diffusion. Fracture propagation in the process of multistage fracturing of a rock mass is deflected owing to various factors. Hydrofracturing of rock masses in deep tight reservoirs involves thermal diffusion, fluid flow and deformation of rock between the rock matrix and fluid in pores and fractures.Design/methodology/approachTo study the unstable propagation behaviours of three-dimensional (3D) parallel hydraulic fractures induced by the interferences of adjacent perforation clusters and thermal diffusion, a 3D engineering-scale numerical model is established under different fracturing scenarios (sequential, simultaneous and alternate fracturing) and different perforation cluster spacings while considering the thermal-hydro-mechanical coupling effect. Stress disturbance region caused by fracture propagation in a deep tight rock mass is superimposed and overlaid with multiple fractures, resulting in a stress shadow effect and fracture deflection.FindingsThe results show that the size of the stress shadow areas and the interaction between fractures increase with decreasing multiple perforation cluster spacing in horizontal wells. Alternate fracturing can produce more fracture areas and improve the fracturing effect compared with those of sequential and simultaneous fracturing. The larger the temperature gradient between the fracturing fluid and rock matrix, the stronger the thermal diffusion effect, and the effect of thermal diffusion on the fracture propagation is significant.Originality/valueThis study focuses on the behaviours of the unstable dynamic propagation of 3D parallel hydraulic fractures induced by the interferences of adjacent perforation clusters and thermal diffusion. Further, the temperature field affects the fracture deflection requires could be investigated from the mechanisms; this paper is to study the unstable propagation of fractures in single horizontal well, which can provide a basis for fracture propagation and stress field disturbance in multiple horizontal wells.

Field-Induced Transparent Electrode-Integrated Transparent Solar Cells and Heater for Active Energy Windows: Broadband Energy Harvester.

Invisible power generation by natural and artificial light enables sustainability by onsite-power deployment, lower cost, and minimal burden on the built environment. However, dark, opaque photovoltaics limit light utilization in a transparent way. Herein, it is proposed that the active energy window (AEW) invisibly features power production, providing higher freedom for onsite power generators in window objects without limiting human vision. The AEW has a transparent photovoltaic (TPV) for onsite power and a transparent heater (TH) to remove the effects of shadows from snow and recover the power lost. Moreover, a heating function is applied to remove the effects of weathering related to snow. The proposed prototype integrates a TPV-TH, offering ultraviolet (UV)-blocking, daylighting, thermal comfort, and onsite power with a power conversion efficiency of 3% (AM1.5G). Field-induced transparent electrodes are applied to the TPV-TH and designed considering the AEW. Owing to these electrodes, the AEW ensure a wide field-of-view without optical dead zones, ensuring see-through vision. The first TPV-TH integration is performed into a 2cm2 -window that generates onsite power of 6mW and has an average visible transmittance of ≈39%. It is believed that light can be utilized with comfort through the AEW in self-sustainable buildings and vehicles.

Analysis of a small-scale modified beam-down solar concentrator system for low temperature applications

A small-scale beam-down solar concentrator (BDSC) without a receiver concentrator (RC) was studied for the first time for its applicability to low-temperature heating systems. A comprehensive theoretical model was developed that combines solar ray tracing with existing BDSC models to include solar angle variations for different days in a year at any location. The model allows the estimation of image magnification based on the heliostat area and the resultant uniform solar enhancement area on the RR. A test setup with a footprint area of 2.25 m2 and a tower height of 1.5 m, consisting of 11 heliostats, a single hyperbolic central mirror, and a RR, was built and tested to validate the model. It was found that cosine efficiency is an essential factor that dictates the system's performance. Increasing the number of mirrors from 11 to 41 showed the number of suns on the RR will increase from 1.45 to 4.5. A 22% reduction in total insolation on the RR was observed at solar noon due to the shadow of the central mirror, suggesting a prominent effect of shadow in small-scale BDSC systems. The system analyzed could achieve temperatures up to 200 °C, making it suitable for low-temperature applications.

Power generation and wave attenuation of a hybrid system involving a heaving cylindrical wave energy converter in front of a parabolic breakwater

Deploying a cylindrical heaving wave energy converter (WEC) in front of a parabolic breakwater forms a basic module for synergetic coast protection and power generation. The interactions in the hybrid system are important to its performance but poorly understood. Here the power amplification effect of the parabolic breakwater on the WEC and the additional wave attenuation effect of the WEC on the parabolic breakwater are investigated based on the potential flow theory of linear regular waves. A parabolic breakwater and five WECs with optimized geometry and generator parameters are employed in comparative numerical studies conducted using an open-source code HAMS. Results show that the parabolic breakwater has similar power amplification effects on different WECs, despite the significant differences in their dimensions and power-take-off damping. The power of a WEC can be increased by more than 120% at its natural period. A WEC can shadow the region behind it and reduce the wave amplitude on the opening wall of the parabolic breakwater. It also slightly reduces the amplitude of the relatively high waves in the protection zone behind the breakwater. A flatter WEC with a larger diameter-to-draft ratio is recommended as it generates more power and has a stronger shadow effect.

Retrieval Consistency between LST CCI Satellite Data Products over Europe and Africa

The assessment of satellite-derived land surface temperature (LST) data is essential to ensure their high quality for climate applications and research. This study intercompared seven LST products (i.e., ATSR_3, MODISA, MODIST, SLSTRA, SLSTRB, SEVIR2 and SEVIR4) of the European Space Agency’s (ESA) LST Climate Change Initiative (LST_cci) project, which are retrieved for polar and geostationary orbit satellites, and three operational LST products: NASA’s MODIS MOD11/MYD11 LST and ESA’s AATSR LST. All data were re-gridded on to a common spatial grid of 0.05° and matched for concurrent overpasses within 5 min. The matched data were analysed over Europe and Africa for monthly and seasonally aggregated median differences and studied for their dependence on land cover class and satellite viewing geometry. For most of the data sets, the results showed an overall agreement within ±2 K for median differences and robust standard deviation (RSD). A seasonal variation of median differences between polar and geostationary orbit sensor data was observed over Europe, which showed higher differences in summer and lower in winter. Over all land cover classes, NASA’s operational MODIS LST products were about 2 K colder than the LST_cci data sets. No seasonal differences were observed for the different land covers, but larger median differences between data sets were seen over bare soil land cover classes. Regarding the viewing geometry, an asymmetric increase of differences with respect to nadir view was observed for day-time data, which is mainly caused by shadow effects. For night-time data, these differences were symmetric and considerably smaller. Overall, despite the differences in the LST retrieval algorithms of the intercompared data sets, a good consistency between the LST_cci data sets was determined.

Improvement and application of UNet network for avoiding the effect of urban dense high-rise buildings and other feature shadows on water body extraction

ABSTRACT Finding a means to extract water body information efficiently and accurately from high-resolution remote sensing images has been an important research direction in the field of water body extraction in recent years. However, shadows from buildings and other obstacles interfere with the accuracy of water body extraction. To address this problem, this paper proposes a neural network method incorporating an attention mechanism for water body extraction. This paper is based on the U-Net convolutional neural network and adds the squeeze-and-excitation module of SENet, an attention mechanism, to the downsampling process of the U-Net network. The module weights the feature maps so that the network focuses more on the features of the water body information and thus reduces attention to the shadow features from buildings and other features, thus improving the accuracy of image segmentation. The dropout and batch normalization layers are also added to improve the generalization ability and stability of the model. In this paper, a water extraction network SE-CU-Net model is presented to overcome the shadowing effect from buildings and other features. Using GF-2 images of Jiangsu province as the data source, the recognition results of this paper are compared with Dense-Net, Res-Net, Seg-Net, U-net, SVM, and RF. Through the comparison experiments, the model of this paper can not only better overcome the influence of shadows from buildings and other features, but it also has a stronger recognition ability and recognition effect. The average ASCR, Precision, mIoU, OA, F1-Score and kappa coefficients in the three tested areas reached 98.27%, 97.17%, 89.33%, 98.2%, 89.3% and 0.883, respectively, with significantly higher accuracy than the other six classical methods, verifying the effectiveness of the model in overcoming the influence of shadows from buildings and other features in water body extraction research.

Regional autonomous security cooperative spectrum sensing method based on trust value

AbstractIn order to solve the problems of spectrum resource shortage, low spectrum utilization and shadow effect, a regional autonomous security cooperative spectrum sensing (CSS) method based on trust value is proposed to address the vulnerability of CSS technology in cognitive radio to malicious node attacks. Considering the difference in node position, the vulnerability of CSS to malicious node attacks, the large amount of centralized sensing data processing, and the large energy consumption of distributed sensing, based on the trust value update mechanism of ‘slow growth and fast recovery’, the perception area is divided and managed, and the final perception result is determined by majority voting based on the centralized sensing. The convergence value of the time difference of the perceptual process trust value is used to detect the anomaly of the node, and the cumulative difference in trust values between the nodes can detect and locate the malicious node. Experimental simulation results show that the proposed model is superior to traditional algorithms in spectral perception accuracy and malicious node detection.

Suitable Density of Vertical Greenery Systems on Office Buildings for Energy Saving

One of the more optimistic strategies to generate energy savings in buildings and help mitigate the effect of the urban heat island is to “green” the building envelopes. In general, a vertical greenery system (VGS) has excellent possibilities for cutting building energy use, particularly during cooling periods. One of the most important factors is the shadow effect factor, which is greatly affected by the plants. Simulating the facade foliar density using Revit energy analysis is one technique to describe the potential shadow effect of flora. This paper will analyse and investigate to answer the following question: Does the variation in density of the VGS affect the energy savings of the building? The VGS has several factors that affect the energy savings of the building, such as the types that thrive in each region, the facade’s direction, the thickness of the foliage, the presence of air layers in the context of green walls, and the makeup and thickness of the substrate layer. This paper will focus on one factor: the density of the green vertical system. The goal of this study is to develop a standard and simple method for calculating the leaf area index (LAI) and connecting it to the energy savings offered by VGS studies on the office building. Additionally, research was done on the energy savings made at the “Karim Centre”, an office building located in Tripoli, Lebanon. Moreover, the facade direction has many impacts on the indoor thermal system that affect energy savings using the VGS, including green walls and double-skin green facades. There is, however, a dearth of information on operating during the heating season as well as throughout the entire year. This paper will discuss the four evaluation variations of the density of VGS on the facade of the office building, resulting in the suitable density of VGS4, which saves 15.7% less energy with 50% green density on the facade.

Mitigating Cosmic Microwave Background Shadow Degradation of Tensor-to-scalar Ratio Measurements through Map-based Studies

It has been pointed out that the spurious cosmic microwave background (CMB) B-mode polarization signals caused by the absorption of the CMB monopole component due to the Galactic interstellar matter, called the CMB shadow, degrade the accuracy of detecting the CMB B-mode polarization signals imprinted by primordial gravitational waves. We have made a realistic estimation using simulated sky maps of how the CMB shadow affects forthcoming high-precision CMB B-mode experiments for the first time. The delta-map method, an internal template method taking into account the first-order spatial variation of foregrounds’ spectral parameters, is applied as a foreground-removal method. We show that if the CMB shadow effects are not taken into account in the foreground-removal process, future observations would lead to the false detection of the CMB B-mode polarization signals originating from primordial gravitational waves. We also show that the effect of the CMB shadow can be mitigated by our revised delta-map method to target the CMB B-mode polarization signals at the level of tensor-to-scalar ratio r = 0.001.

A technique for decreasing reflection during cadaveric photography.

To create anatomical educational materials that can be viewed in three dimensions using stereo photographs and photogrammetry, multiple photographs must be taken from different directions. In this process, shadows and reflections from different positions in each photograph are undesirable for creating three-dimensional (3D) anatomy educational materials. Although a ring flash eliminates shadows, allowing light to enter from all directions, reflections cannot be eliminated. In particular, Thiel-embalmed cadavers, which are widely used in clinical anatomy, are highly wet and exhibit strong specular highlights. In this study, a straight polarization filter was attached to a handheld camera lens and ring flash, and shooting was performed using cross-polarization photography. Consequently, even in Thiel-embalmed cadavers, the details lost due to the effects of reflections and shadows can be recovered, and good results can be obtained when taking stereo photos or creating a 3D model using photogrammetry.

Shadow Effect of Human Obstacles on Indoor Visible Light Communication System with Multiple Light Sources

When the direct visible-light channel is affected by people walking or other obstacles, the shadow effect formed in the receiver space affects communication performance and can even lead to communication interruption. In this paper, two numerical methods for calculating the shadow area of the human body were proposed for an indoor multi-light communication system. The influence of shadows on system performance was analyzed using the mean square errors of illuminance and signal-to-noise ratio, as well as the interrupt probability, as parameters. The results showed that shadows had a great influence on the performance of the visible-light communication system. When the number of light sources was fixed, the shadow effect could be effectively reduced by optimizing the layout of the light sources. These research results can provide a theoretical basis for improving the stability of visible-light communication systems.

A parametric study of low friction coating by PVD method on the spiralock female thread for ITER application

The hard lubrication is defined that the thin films are deposited by radio-frequency magnetron sputtering from the target material on substrate in order to improve their desired properties such as hardness, friction and wear resistance. Especially, the MoS2 coating can be used in high vacuum and aerospace environments for lubrication purposes, which low friction is required. Unlike fluid lubrications, MoS2 is suitable for use in a vacuum environment because it has low outgassing pressure and lack of migration. For this reason, the sputtered MoS2 coating is primarily considered as low friction / anti-seize coating method of the ITER blanket central bolt insert. A magnetron sputtering process, which permits friction coefficient and durability of the MoS2 coating, suites to coat precision mechanical component with its exquisitely thin thickness. However, the coating on the spiralock female thread of blanket central bolt inserts is difficult to have uniform coating deposition due to its shadow effect. Therefore, it is necessary for understanding the parameters and effects of sputtering process to achieve the uniform coating having the required friction coefficient less than 0.05. Details of parametric study with various sputtering conditions on the simple disk and spiralock female thread to reach required friction coefficient and uniform coating thickness, are presented in this paper.

An improved image processing algorithm for visual characteristics in graphic design.

Drawing the clothing plan is an essential part of the clothing industry. However, the irregular shape of clothing, strong deformability and sensitivity to light make the fast and accurate realization of clothing image retrieval a very challenging problem. The successful application of the Transformer in image recognition shows the application potential of the Transformer in the image field. This article proposes an efficient and improved clothing plan based on ResNet-50. Firstly, in the feature extraction section, the ResNet-50 network structure embedded in the Transformer module is used to improve the network's receptive field range and feature extraction ability. Secondly, dense jump connections are added to the ResNet-50 upsampling process, making full use of feature extraction information at each stage, further improving the quality of the generated image. The network consists of three steps: the sketch stage, which aims to predict the color distribution of clothing and obtain watercolor images without gradients and shadows. The second is the thinning stage, which refines the watercolor image into a clothing image with light and shadow effect; The third is the optimization stage, which combines the outputs of the first two stages to optimize the generation quality further. The experimental results show that the improved network's IS and first input delay (FID) scores are 4.592 and 1.506, respectively. High-quality clothing images can be generated only by inputting line drawings and a few color points. Compared with the existing methods, the image generated by this network has excellent advantages in realism and accuracy. This method can combine various feature information of images, improve retrieval accuracy, has strong robustness and practicability, and can provide a reference for the daily work of fashion designers.

An unequal fracturing stage spacing optimization model for hydraulic fracturing that considers cementing interface integrity

Determining reasonable fracturing stage spacing is the key to horizontal well fracturing. Different from traditional stage spacing optimization methods based on the principle of maximum stimulated reservoir volume, in this paper, by considering the integrity of the wellbore interface, a fracture propagation model was established based on displacement discontinuity method and the competition mechanism of multifracture joint expansion, leading to the proposal of an unequal stage spacing optimization model. The results show that in the first stage, the interfacial fractures spread symmetrically along the axis of the central point during that stage, while in the second and subsequent stages, the interfacial fractures of each cluster extend asymmetrically along the left and right sides. There are two kinds of interface connectivity behaviour: in one, the existing fractures first extend and connect within the stage, and in the other, the fractures first extend in the direction close to the previous stage, with the specific behaviour depending on the combined effect of stress shadow and flow competition during hydraulic fracture expansion. The stage spacing is positively correlated with the number of fractures and Young’s modulus of the cement and formation and is negatively correlated with the cluster spacing and horizontal principal stress difference. The sensitivity is the strongest when the Young’s modulus of the cement sheath is 10–20 GPa, and the sensitivity of the horizontal principal stress difference is the weakest.