Central Axis Research Articles

An Investigation on the Steady and Unsteady Wake Flow Regimes and Aerodynamic Characteristics of the Trapezoidal Cylinders Using Immersed Boundary-Lattice Boltzmann Method

Abstract In this study, the flow physics of the forward-facing (FF) and backward-facing (BF) trapezoidal cylinders (TC) subjected to two-dimensional, incompressible, and laminar flow is investigated using an in-house developed flexible forcing immersed boundary-lattice Boltzmann solver. The Reynolds number (Re) is defined based on the cylinder's characteristic length D. For the steady and unsteady flow regimes, Re is varied in the ranges of 10–40 and 75–125, respectively. The TCs shape is varied by modifying its nondimensional axial H/D and transverse Y/D length scales, between 0.5 to 2 and 0 to 1, respectively. Here, TCs horizontal central axis is always aligned along the incoming flow direction. It is observed that the flow separation points on the FF-TC and BF-TC are strongly influenced by the geometric (H/D and Y/D) and flow parameters (Re). Based on the boundary layer separation point, we have categorized the wake flow regimes behind the FF-TC and BF-TC into four types. In addition, the effect of the geometric and flow parameters on the drag coefficient (Cd), vortex shedding frequency, and steady and unsteady wake characteristics are thoroughly investigated here. Furthermore, by performing nonlinear regression analysis, we have proposed a set of correlation equations for the Cd and Strouhal number (St), using which the aerodynamic characteristics of differently shaped TC can be derived in the considered Re range without performing rigorous numerical simulations or experiments.

Population trends in human rib cross-sectional shapes.

Rib fractures remain the most frequent thoracic injury in motor vehicle crashes. Computational human body models (HBMs) can be used to simulate these injuries and design mitigation strategies, but they require adequately detailed geometry to replicate such fractures. Due to a lack of rib cross-sectional shape data availability, most commercial HBMs use highly simplified rib sections extracted from a single individual during original HBM development. This study provides human rib shape data collected from chest CT scans of 240 females and males across the full adult age range. A cortical bone mapping algorithm extracted cross-sectional geometry from scans in terms of local periosteal position with respect to the central rib axis and local cortex thickness. Principal component analysis was used to reduce the dimensionality of these cross-sectional shape data. Linear regression found significant associations between principal component scores and subject demographics (sex, age, height, and weight) at all rib levels, and predicted scores were used to explore the expected rib cross-sectional shapes across a wide range of subject demographics. The resulting detailed rib cross-sectional shapes were quantified in terms of their total cross-sectional area and their cortical bone cross-sectional area. Average-sized female ribs were smaller in total cross-sectional area than average-sized male ribs by between 20% and 36% across the rib cage, with the greatest differences seen in the central portions of rib 6. This trend persisted although to smaller differences of 14%-29% when comparing females and males of equal intermediate weight and stature. Cortical bone cross-sectional areas were up to 18% smaller in females than males of equivalent height and weight but also reached parity in certain regions of the rib cage. Increased age from 25 to 80 years was associated with reductions in cortical bone cross-sectional area (up to 37% in females and 26% in males at mid-rib levels). Total cross-sectional area was also seen to reduce with age in females but to a lesser degree (of up to 17% in mid-rib regions). Similar regions saw marginal increases in total cross-sectional area for male ribs, indicating age affects rib cortex thickness moreso than overall rib cross-sectional size. Increased subject height was associated with increased rib total and cortical bone cross-sectional areas by approximately 25% and 15% increases, respectively, in mid-rib sections for a given 30 cm increase in height, although the magnitudes of these associations varied by sex and rib location. Increased weight was associated with approximately equal changes in both cortical bone and total cross-sectional areas in males. These effects were most prominent (around 25% increases for an addition of 50 kg) toward lower ribs in the rib cage and had only modest effects (less than 12% change) in ribs 2-4. Females saw greater increases with weight in total rib area compared to cortical bone area, of up to 21% at the eighth rib level. Results from this study show the expected shapes of rib cross-sections across the adult rib cage and across a broad range of demographics. This detailed geometry can be used to produce accurate rib models representing widely varying populations.

Stereo vision-based health monitoring method for wind turbine towers

Wind turbines are subjected to complex aerodynamic loads, which results in potential sway and tilt, even causing the collision between blades and the tower. Therefore, it is imperative to monitor the condition of the tower to ensure safety. In this paper, we propose a method to monitor the health of wind turbine towers based on stereo vision. Our approach extracts the tower central axis from the image based on the structural information. Then the tower’s sway magnitude is measured by binocular intersection, and the tilt angle is computed by exploiting the angle information provided by an inclinometer. Moreover, we detect blade tips using their geometric shape, which can be used to estimate the clearance distance between blades and the tower. The proposed method can simultaneously monitor the tower tilt and sway, while also identifying instances of blade collision with the tower. Experiments demonstrate the accuracy and feasibility of the designed system.

Research on Time Series-Based Pipeline Ground Penetrating Radar Calibration Angle Prediction Algorithm.

The pipeline ground-penetrating radar stands as an indispensable detection device for ensuring underground space security. A wheeled pipeline robot is deployed to traverse the interior of urban underground drainage pipelines along their central axis. It is subject to influences such as resistance, speed, and human factors, leading to deviations in its posture. A guiding wheel is employed to rectify its roll angle and ensure the precise spatial positioning of defects both inside and outside the pipeline, as detected by the radar antenna. By analyzing its deflection factors and correction trajectories, the intelligent correction control of the pipeline ground-penetrating radar falls into the realm of nonlinear multi-constraint optimization. Consequently, a time-series-based correction angle prediction algorithm is proposed. The application of the long short-term memory (LSTM) deep learning model facilitates the prediction of correction angles and torque for the guiding wheel. This study compares the performance of LSTM with an autoregressive integrated moving average model under identical dataset conditions. The subsequent findings reveal a reduction of 4.11° and 8.25 N·m in mean absolute error, and a decrease of 10.66% and 7.27% in mean squared error for the predicted correction angles and torques, respectively. These outcomes are achieved utilizing the three-channel drainage pipeline ground-penetrating radar device with top antenna operating at 1.2 GHz and left/right antennas at 750 MHz. The LSTM prediction model intelligently corrects its posture. Experimental results demonstrate an average correction speed of 5 s and an average angular error of ±1°. It is verified that the model can correct its attitude in real-time with small errors, thereby enhancing the accuracy of ground-penetrating radar antennas in locating pipeline defects.

Modesty, religion, and community: Therapists' perspectives regarding the treatment of child sexual abuse in the ultra-orthodox community

BackgroundReligion is a significant cultural component that impacts child sexual abuse (CSA) in various ways, including its definition, perception, and treatment. This study focuses on the Jewish ultra-Orthodox community in Israel, a strictly religious, segregated, and close-knit community with unique cultural practices and beliefs that impact children's safety and vulnerability to CSA. ObjectiveThis qualitative study aimed to explore therapists' perceptions and ascribed meanings of CSA treatment within the ultra-Orthodox community. Participants and settingThirty in-depth interviews were conducted with therapists working with the ultra-Orthodox community in Israel. MethodsThe interviews were analyzed using thematic qualitative analysis. ResultsThree central axes pertinent to the treatment of CSA in the ultra-Orthodox community were discovered: 1) religious interventions, 2) modest approach, relating to the community's taboo attitude towards sexuality; and 3) the collectivistic nature of the community. The results include specific effect sizes and their statistical significance. ConclusionsThe discussion explores the findings in light of the literature on CSA among religious minority communities and connects them to the unique underlying perception of sexuality in the ultra-Orthodox community. Specific ramifications and recommendations for practice are then considered, alongside the limitations and directions for future study.

Burning and plume flow behaviors of annular pool fires: with and without air entrainment through the pool center.

Annular pool fires, frequently happened in chemical industries, have a significant influence on environmental pollution. Air pollution, greenhouse gas emissions, water pollution, and soil contamination are general ways of environmental hazards caused by the annular pool fires. This study built upon our previous study (Environ. Sci. Pollut. Res., 2023, 30(21): 59781-59792.), and extended to investigate the combustion and fire plume flow behaviors of annular pool fires, both with and without air entrainment through the hollow center of the annular pool. Results show that when there is no air entrainment through the hollow center, the low combustion intensity area at the plume's central axis gradually extends while the high combustion intensity area concentrates at higher places and the flame height increased by nearly 40% from a solid pool (Din/Dout = 0) to the annular pool (Din/Dout = 0.80). Additionally, the area with high combustion intensity is more concentrated at a higher position. The combustion of annular pool fires was found to be dominated by non-premixed diffusion combustion. The center of the annular pool fires is dominated by air prior to flame merging and by fuel vapor after the merging occurs. For annular pool fires with air entrainment through the center of the pool, the combustion intensity increases as Din/Dout at the plume base increases. And, the flame height decreased by nearly 25% as Din/Dout increases. Flame burning occurs both on the outside and inside of the plume, exhibiting a "double layer" combustion characteristic. It reveals that the combustion of the fire plume transitions to premixed diffusion combustion. The center of the annular pool fire is predominantly composed of air. Understanding and controlling annular pool fires can lead to new methods for remediating fuel spills, reducing pollution from combustion, and advancing research in fluid mechanics.

Tortuosity of pore channels in tight rocks as a key parameter in fluid flow ability

AbstractTortuosity is a significant parameter in porous materials analysis. Not only, when it comes to rocks or soils but also cellular materials, alloys or cells, the multiple definitions exist for tortuosity and several purposes. Geometrical tortuosity describes the pore network paths; on the other hand thermal, diffusional, electrical and hydraulic tortuosity refers to the transport processes in the pore network. Computed X-ray tomography (CT) is the best solution in tortuosity estimation, thanks to the 3D images. In particular, computed X-ray tomography, together with mercury porosimetry (MICP), pulse- and pressure-decay permeability methods (PDP), as well as electrical parameter measurements (EPM), links and expands the information about the tortuosity into the greater meaning. The geological material was composed of tight, low-porosity and low-permeability gas-saturated rocks cored from the present depth of deposition below 3000 m, containing different lithologies, as sandstones, mudstones, limestones, and dolomites. The research presents the novel approach in the identification and analysis of the main pore channels based on 3D CT images. Algorithm of the central axis identifies and analyzes the whole main flow path and calculates tortuosity. High correlation was observed between the tortuosity and Swanson parameter from mercury porosimetry data. Moreover, the high correlation was detected between the tortuosity and saturation exponent from electrical parameter measurement in analyzed tight low-porosity and low-permeability deposits. Multilinear regression (MLR) allows estimating absolute permeability taking CT, MICP and EPM parameters into consideration. Combination of these parameters in one equation with high determination coefficient gives credence in estimating preliminary absolute permeability (PDP) based on the data which is executed as standard core analysis (MICP and EPM) and data from the non-invasive method (CT).

The Archaeological Interpretation of the Determining Criteria and Developmental Path of Chinese Civilization

The research findings of the project of tracing the origins of Chinese civilization substantiate China’s million years of human history, 10,000-plus years of cultural history, and 5,000-plus years of civilizational history. Cities and capitals have been the foremost tangible embodiment throughout the formation and development of Chinese civilization. By examining the sites of ancient Chinese capitals and palaces, noting the transition from “shrines side by side with palaces” to “the imperial ancestral shrine on the left and the altar to the gods of earth and grain on the right,” and observing the evolution from “dual axis” to “central axis” in city planning, we can delve into the cultural genes that have shaped the development of Chinese civilization. Throughout history, China’s first inhabitants and their descendants have forged strong traditions of ancestral identification, the unity and commensurability of family and state, and identification with the state. Characterized by powerful cohesiveness and inclusiveness, these traditions form the subtly ingrained and daily practiced cultural genes of Chinese civilization. They are the fundamental reasons behind the enduring continuity of Chinese civilization for over 5,000 years.

Extraction of Building Roof Contours from Airborne LiDAR Point Clouds Based on Multidirectional Bands

Because of the complex structure and different shapes of building contours, the uneven density distribution of airborne LiDAR point clouds, and occlusion, existing building contour extraction algorithms are subject to such problems as poor robustness, difficulty with setting parameters, and low extraction efficiency. To solve these problems, a building contour extraction algorithm based on multidirectional bands was proposed in this study. Firstly, the point clouds were divided into bands with the same width in one direction, the points within each band were vertically projected on the central axis in the band, the two projection points with the farthest distance were determined, and their corresponding original points were regarded as the roof contour points; given that the contour points obtained based on single-direction bands were sparse and discontinuous, different banding directions were selected to repeat the above contour point marking process, and the contour points extracted from the different banding directions were integrated as the initial contour points. Then, the initial contour points were sorted and connected according to the principle of joining the nearest points in the forward direction, and the edges with lengths greater than a given threshold were recognized as long edges, which remained to be further densified. Finally, each long edge was densified by selecting the noninitial contour point closest to the midpoint of the long edge, and the densification process was repeated for the updated long edge. In the end, a building roof contour line with complete details and topological relationships was obtained. In this study, three point cloud datasets of representative building roofs were chosen for experiments. The results show that the proposed algorithm can extract high-quality outer contours from point clouds with various boundary structures, accompanied by strong robustness for point clouds differing in density and density change. Moreover, the proposed algorithm is characterized by easily setting parameters and high efficiency for extracting outer contours. Specific to the experimental data selected for this study, the PoLiS values in the outer contour extraction results were always smaller than 0.2 m, and the RAE values were smaller than 7%. Hence, the proposed algorithm can provide high-precision outer contour information on buildings for applications such as 3D building model reconstruction.

Acoustic vortex filter based on tunable metasurfaces

In this paper, we present an acoustic vortex filter (AVF) based on tunable metasurfaces, which can selectively filter the incident multiplexed vortices that carry different orbital angular momentum (OAM). Our metasurface-based AVF is composed of an upper acoustic metasurface (UAM) and a lower acoustic metasurface, of which the intrinsic topological charge (ITC) can be tuned by mechanically rotating the UAM along its central axis. Due to the critical order of the propagating vortex modes in waveguide, controlling the ITC of the AVF allows for the selective filtering of incoming multiplexed acoustic vortex beams based on the sound vortex diffraction in phase-gradient metasurface, which endows the vortex filter the capability that let the incident vortex of specific OAM pass through it. In the following demonstration, both in theory and experiment, we design the AVF and effectively filter the acoustic vortices with two opposite topological charges by simply altering the orientation angle of the UAM. Based on this, we further demonstrate its application in asymmetric acoustic wave transmission. Our work offers an approach to selectively filter the incident acoustic vortex, which improves the capability to control the acoustic OAM via metasurfaces.

Asymmetric flow in a double-suction centrifugal fan induced by an inclined impeller

The impeller and volute of a centrifugal fan are designed to be coaxially placed; however, the impeller might be inclined about the central axis of the volute due to installation fault, inducing asymmetric flow in the left and right halves of the fan. We performed a detailed numerical investigation on the non-uniform and asymmetric flow in a double-suction multi-blade centrifugal fan with a slightly inclined impeller using the unsteady Reynolds-averaged Navier–Stokes simulation approach. The impeller is assumed to rotate about each of the two minor axes perpendicular to the central axis to model the inclination. This work aims to quantify the influence of the impeller inclination on the aerodynamic performance of the centrifugal fan and to reveal the physics of transient flow in the two halves of the fan to demonstrate the impact of various inclination ways. Numerical results denote that a slight impeller inclination could stabilize the flow in the fan, while the flow is highly asymmetric as the inclination is enhanced, and the efficiency of the fan decreases due to the recirculation generated by the interaction of flow exiting from the impeller. An in-depth inspection shows sharply intensified pressure fluctuation at the collector, where the local clearance varies. The flow entering the collector and impeller substantially decreases in velocity, resulting in separated flow in part of the blade passages. The flow in the volute is also asymmetric since the impeller outlet is biased toward the volute wall.

Near-moving-wall flows past three tandem elliptical cylinders at low Reynolds number of 150

Dynamic flows past three tandem elliptic cylinders of equal spacing in parallel arrangement with a moving wall are numerically conducted by the lattice Boltzmann method. The gap ratio (G/D, where G and D are the gap between the wall surface and cylinder center and major axis, respectively) from 0.6 to 2.5 and spacing ratio (L/D, where L is the distance of two adjacent cylinder centers) from 1.5 to 10 are examined at Reynolds number of Re = 150 (based on D). The desired analysis correlates variations of hydrodynamic coefficients, wake structures, and spectral analysis in wide space of G/D and L/D with underlying fluid mechanics. The flow is highly adjustable in G/D−L/D space, dividing into six distinct regimes: overshoot, continuous reattachment, alternative reattachment, wavy, meandering, and coshedding, which are spatially classified into four modes because of flow interference, namely, shear layer, primary, two-layered, and secondary vortex shedding modes. The transition between adjacent modes defines three boundaries. The first boundary always occurs behind the middle or downstream cylinder, whereas the second and third boundaries occur between the upstream and middle cylinders and the downstream cylinder wake. Due to the near-wall flow interference, the hydrodynamic coefficients are highly changeable in L/D−G/D space, signifying the crucially lower drag coefficient of the middle and downstream cylinders than that of a single cylinder. A small G/D determines the increase in lift coefficient of the upstream cylinder as a result of the ground effect, while the shadowing effect of the upstream cylinder induces identical Strouhal numbers of the middle and downstream cylinders.

Opioid Induced Adrenal Insufficiency Complicated by Adrenal Crisis-A Case Report

Introduction: 1 in 5 people experience chronic pain that limits their ability to carry out activities of daily living. Opioid analgesics are one of the pharmaceutical interventions utilized to treat chronic pain. In fact, chronic pain is one of the most common reasons opioids are prescribed. Although many of the secondary effects of opioids are well known, a lesser-known side effect is opioid induced adrenal insufficiency (OIAI). OIAI can cause significant morbidity and has the potential to result in adrenal crisis, profound hypotension, and potential cardiovascular collapse, resulting in death. With sparse literature on OIAI, we present a case of OIAI complicated by adrenal crisis to expand awareness and discussion on the topic. Methods: The patient was a 65-year-old female on chronic opioid therapy for back pain who presented to the emergency room for syncope. On presentation, patient was hypotensive, bradycardic, and had an inadequate fluid response requiring pressors. Traditional etiologies of shock were ruled out, but interestingly morning cortisol and adrenocorticotropic hormone (ACTH) levels were low. Additionally, the cosyntropin stimulation test was suboptimal. Results suggested central hypothalamic pituitary axis suppression, which after discussion with Endocrinology indicated OIAI given the patient’s history. Results: Shortly after steroid regimen initiation the patient was weaned off pressors, and after multiple taper trials was successfully sent home on a steroid taper with Endocrinology follow up. Conclusion: Long term opioid use to treat chronic pain can decrease cortisol production via HPA axis suppression resulting in OIAI. To date, there is limited investigation into OIAI despite its increased prevalence and widespread use of opioids. The case adds to the available literature on OIAI, and sheds light on adrenal crisis as its initial presentation.

EDUCAÇÃO DIFERENCIADA NAS ESCOLAS DO CAMPO: O CURRÍCULO E O PROJETO PEDAGÓGICO EM DEBATE

The curricular organization and the pedagogical project are discussed as a strategy for the concreteness of a differentiated education in rural schools. We investigated how the rural school can organize its practices from the pedagogical project in the perspective of differentiated education with the intention of meeting the real educational, sociocultural and identity needs of studants in the countryside? How and teachers think about curricular actions that can have an impact on improving the quality of education offered in rural schools? It aims to identify how the curriculum based on respect for diversity can support the production of a pedagogical project as the central axis of differentiated educational practices in rural schools in the Municipality of Gurupá, State of Pará. The research approach is qualitative and was supported by experiences in schools and dialogues with head teachers of rural schools during the supervision activities of Supervised Internships I and IIV of the Rural Education Degree Course. In the reflections elaborated, we highlight the pedagogical project as an identity document for rural schools that needs to be better discussed in the collective of rural communities in Gurupá-PA; regarding the perceptions of education professionals, the necessary relationship they establish between the pedagogical project and the quality of teaching was notorious, as they understand that it is indispensable in the organization of educational actions based on the peasant reality, in order to embody the directions for education of the countryside that forms the value of the subject of the countryside, its traditional knowledge and its place as an educational territory.

A rest tremor detection system based on internet of thing technology

<span>This article outlines the creation of a health detection system designed to identify rest tremors in Parkinson's disease (PD). The system leverages internet of things (IoT) technology to measure frequencies derived from human activities, excluding other symptoms such as heartbeat and voice recording. The core components include the Arduino Nano microcontroller and the Node ESP MCU 8266 V3 for data processing. The system employs an accelerometer sensor positioned at the body's center axis to gauge the frequency of motor symptoms associated with resting tremors, particularly when the hands are at rest in the lap. The findings indicate that 9 samples displayed symptoms of rest tremor. The recorded p-value, standing at 0.884, signifies a robust correlation between the two variables at a significant threshold of 0.01 or 1%.</span>

Research on the Changes of Beijing Central Axis and the Construction of Temples and Altars in the Ming Jiajing Period

Research on the Changes of Beijing Central Axis and the Construction of Temples and Altars in the Ming Jiajing Period

Aerodynamic Performance of a Hovering Cycloidal Rotor: A CFD Study with Experimental Validation

A three-dimensional (3D) unsteady Reynolds averaged Navier–Stokes (URANS) computational fluid dynamics (CFD) toolkit for cycloidal rotors was developed and used to perform a parametric study. It included blade aspect ratio, side disks, pitch mechanism, blade camber, and shaft size. The influence of the pitch rod length showed the importance of the lift distribution between the upstream and downstream parts of the rotor cylinder. The application of blade camber significantly affected thrust and power, while having a limited effect on efficiency. A similar effect was obtained by varying the pitch rod lengths. The presence of a central axis in the rotor had a negligible effect on efficiency. The most significant impact on efficiency came from the side disks, which behaved similarly to winglets on fixed-wing aircraft. However, changing the aspect ratio of the blades showed a similar response to that of aircraft wings, but with a smaller effect, making it conceivable to fly a square-bladed cyclorotor without side disks. To verify the CFD model, a cycloidal rotor was also built using 3D printed parts and carbon fiber tubing. It was then operated on a test rig where thrust and power were measured for speeds ranging from 408 to 2528 RPM. On the test bench, the blades were pitched with a uniform asymmetric mechanism. The maximum nose-up pitch angle in upstream of the rotor axis was 34.8°. Due to its rotation around the rotor and its pitching in the opposite direction, the maximum nose-up pitch angle of the downstream blade was 38.6°. The obtained rotor thrust and power curves and the flow visualization around the rotor confirmed the validity of the CFD toolkit.

Effects of estrogens in mitochondria: An approach to type 2 diabetes

<abstract> <p>Type 2 diabetes (T2D) is characterized by a state of hyperglycemia in the blood due to insulin resistance developed by organs such as muscle, liver, and adipose tissue. A common factor in individuals with T2D is mitochondrial dysfunction. Mitochondria are dynamic organelles responsible for energy and antioxidant metabolism in the cells. Estrogens, such as 17β-estradiol (E2), are steroid hormones that have shown a great capacity to regulate mitochondrial function and dynamics through estrogen receptors (ERs), modulating the expression of mitochondrial biogenesis-related genes and cell signaling mechanisms. The accumulation of reactive oxygen species, the low capacity for ATP synthesis, and morphological alterations are some of the mitochondrial processes impaired in T2D. Insulin signaling and secretion by pancreatic β-cells, ATP-dependent processes, are also altered in T2D. In this review, mitochondria were exposed as the central axis for the action of estrogens in individuals with T2D. Estrogens increased glucose uptake, insulin signaling, and mitochondrial bioenergetics, and decreased ectopic lipid accumulation in non-adipose tissues and oxidative stress, among other processes, in various preclinical and clinical models of diabetes. The development of strategies to target compounds to mitochondria could represent a novel therapeutic alternative to potentiate the effects of estrogens on this organelle in patients with insulin resistance and T2D.</p> </abstract>

Deformation failure and acoustic emission response characteristics of water-containing concrete under impact load

Concrete materials are widely used in construction projects. Many concrete structures are in an aqueous environment and subjected to impact loads. Under this condition, the mechanical properties and failure modes of concrete will change significantly. In this paper, the drop hammer impact failure experiment of water-containing concrete was established. The deformation and failure characteristics as well as acoustic emission response law of concrete under dynamic load with different immersion time were studied. The failure mechanism and acoustic emission response precursor characteristics of concrete under drop hammer impact were revealed. The results show that the peak impact force of concrete was exponentially related to the immersion time. Its failure cracks were mainly distributed on the diagonal of the impact surface and the central axis of the observation surface. Due to the dual effect of water on the dynamic mechanical properties of concrete, the cracks and damage degree of concrete increased first and then decreased with the increase of immersion time. The peak acoustic emission (AE) count was exponentially related to the immersion time. The acoustic emission “quiet period” could be used as one of the precursor characteristics of concrete instability and failure, and the “quiet period” gradually became shorter with the increase of immersion time. This research results are of great significance for evaluating the stability of concrete structures and warning of concrete impact damage.

Hitchhiker: A Quadrotor Aggressively Perching on a Moving Inclined Surface Using Compliant Suction Cup Gripper

Perching on the surface of moving objects, like vehicles, could extend the flight time and range of quadrotors. Suction cups are usually adopted for surface attachment due to their durability and large adhesive force. To seal on a surfaces, suction cups must be aligned with the surface and possess proper relative tangential velocity. However, quadrotors’ attitude and relative velocity errors would become significant when the object surface is moving and inclined. To address this problem, we proposed a real-time trajectory planning algorithm. The time-optimal aggressive trajectory is efficiently generated through multimodal search in a dynamic time-domain. The velocity errors relative to the moving surface are alleviated. To further adapt to the residual errors, we design a compliant gripper using self-sealing cups. Multiple cups in different directions are integrated into a wheel-like mechanism to increase the tolerance to attitude errors. The wheel mechanism also eliminates the requirement of matching the attitude and tangential velocity. Extensive tests are conducted to perch on static and moving surfaces at various inclinations. Results demonstrate that our proposed system enables a quadrotor to reliably perch on moving inclined surfaces (up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.07m/s$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90^\circ$</tex-math> </inline-formula> ) with a success rate of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$70\%$</tex-math> </inline-formula> or higher. The efficacy of the trajectory planner is also validated. Our gripper has larger adaptability to attitude errors and tangential velocities than conventional suction cup grippers. The success rate increases by 45% in dynamic perches. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper was motivated by the problem of perching on moving inclined surfaces using quadrotors. It can be used for perching on the various angled surfaces of an automobile to save energy and enlarge flight distance. It can also be exploited in air-ground cooperative tasks. In recent years, various grippers and trajectory planning methods have been devised to enable quadrotors to perch on static inclined surfaces. These strategies can not be used for perching on moving inclined surfaces. The task poses high requirements for the efficiency of trajectory planning and the grippers’ adaptability to pose errors. This paper proposes a real-time planning method to generate trajectories. The trajectories respect kinematic and motor lift constraints. They allow large attitude maneuvering of quadrotors. A multimodal search in a dynamic time-domain is developed to seek the minimum feasible time for the trajectory planner. Considering large pose errors in dynamic perching, a compliant gripper based on multiple independent suction cups is designed. The wheel and multidirectional layout of cups increase the adaptability to attitude and velocity errors. Results suggest that the proposed system is effective and reliable. In practice, our multiple cups would add weight penalty and increase the drag. The suction cups should be placed close to a quadrotor’s central axis to reduce the drag and disturbance in flow. The proposed system relies on an external motion capture system. In future research, we will focus on onboard sensing and control methods to achieve perching on moving inclined surfaces outdoors.