Obstacles In Space Research Articles

End-to-End Design of Bespoke, Dexterous Snake-Like Surgical Robots: A Case Study With the RAVEN II

Keyhole surgery requires highly dexterous snake-like robotic arms capable of bending around anatomical obstacles to access clinical targets that diverge from the direct port-of-access. Design optimization for these robots under patient-specific anatomical constraints is still lacking, particularly concerning the critical metric of dexterity. In this article, we propose an end-to-end design and production workflow for patient-specific surgical manipulators, assessing dexterity using orientability constrained by task space obstacles. In our work, parametric evolutionary optimization maximizes dexterity in patient-specific task spaces for challenging knee arthroscopy operations. We implement our framework in the design of SnakeRaven—a 3-D printed tool to be attached to the RAVEN II surgical robot in a phantom study for knee arthroscopy. The solution achieved more than three times the dexterity of a state-of-the-art rigid instrument and more than twice the dexterity of a volume-based approach for the same task. We further assemble and validate this design by teleoperating the robot to reach the desired clinical targets in a phantom. We also investigate the changes in the design morphology to changes in the task objectives and found an advantage in task specialization. We also observe guidelines for achieving a dexterous design produced by our algorithms.

Self-ignition of hydrogen jet due to interaction with obstacle in the obstructed space

The paper numerically studies the process of pressurized hydrogen release through a hole or a slit into a confined space filled with air. Based on the obtained results, three basic consequences of hydrogen release are demonstrated depending on the initial pressure of hydrogen and the distance to the obstacle: (i) hydrogen ignition before the interaction of the flow with the obstacle, (ii) hydrogen ignition after the flow interaction with the obstacle, (iii) jet flow without ignition. It is shown that ignition limits are wider when hydrogen is released through the slit compared to the case of hydrogen release through a small hole. A similar effect could be achieved by changing the geometry and volume of the vessel from which hydrogen is released. Results of this study can be applicable to the elaboration of hydrogen power engineering systems dedicated either to the combustion initiation or to the suppression of ignition of non-premixed hydrogen-air mixtures.

Optimized Number of Reverse Neighbor Clustering Algorithm by Voronoi Diagram in Obstacle Space

Optimized Number of Reverse Neighbor Clustering Algorithm by Voronoi Diagram in Obstacle Space

A Review of Spatial Robotic Arm Trajectory Planning

With space technology development, the spatial robotic arm plays an increasingly important role in space activities. Spatial robotic arms can effectively replace humans to complete in-orbit service tasks. The trajectory planning is the basis of robotic arm motion. Its merit has an essential impact on the quality of the completed operation. The research on spatial robotic arm trajectory planning has not yet formed a broad framework categorization, so it is necessary to analyze and deeply summarize the existing research systematically. This paper introduces the current situation of space obstacle avoidance trajectory planning and motion trajectory planning. It discusses the basic principle and practical application of the spatial robotic arm trajectory planning method. The future development trend has also been prospected.

Visibility Detection of 3D Objects and Visual K-Nearest Neighbor Query Based on Convex Hull Model

With the rapid development of the technologies of virtual reality (VR) and augmented reality (AR), the accurate visual query of 3D objects which are closer to real world has become a hotspot of study. There are a lot of redundancy problems in the existing axis-aligned bounding box model (AABB) and oriented bounding box model (OBB), which are used to represent 3D objects mostly at present, and cannot be used for the accurate visual query. For example, the results of the visual query must be accurate, and without any error in automatic driving technology in the automotive industry, otherwise, serious safety problems would be caused. The convex hull model could be used to solve those problems. However, there are few studies on visual query based on the convex hull model. A visual query method for 3D obstacle space based on the convex hull model is proposed in this paper. Firstly, the definitions of “query point-object visual body” and “combined obstacle” are proposed. Secondly, the visibility detection algorithm of the convex hull model is given in detail. The collision detection method of “query point-object visible body” combined with other obstacles and line-plane geometric calculation operations are used to detect the visibility of the convex hull model. Then, a 3D visual k-nearest neighbor algorithm based on the convex hull model is given in the paper. Finally, the algorithm is verified by experiments and compared with the traditional visibility detection algorithm, and the analysis of experimental results shows that the algorithm has a great performance and higher accuracy. The growth rate of the query time is smaller, and the speed is faster; especially, when there are fewer query points, the query speed can be increased by more than 50%.

Skyline-Like Query in Three-Dimensional Obstacle Space

Skyline query, as a query method to solve typical multiobjective optimization problems, has a wide range of applications in market analysis and data mining. Many scholars’ attention has been attracted since it was proposed. However, the correct result set cannot be obtained easily by traditional skyline query when nonspatial and spatial attributes of the data set need to be considered at the same time, and there are differences in the importance of each attribute. To solve this problem, a skyline-like query was proposed in three-dimensional obstacle space based on the traditional skyline query. In the skyline-like query algorithm, nonspatial skyline-like points were obtained according to the traditional algorithm. The spatial attribute dominated region of the obtained points was used to filter the data set, and then the shielding of obstacles was considered in the three-dimensional obstacle space. By constructing a three-dimensional visible graph, the Dijkstra algorithm was used to obtain the skyline-like points of spatial attribute. After sorting, the skyline-like point set was obtained based on the value of user’s preference. Compared with B2S2 algorithm, the experimental results show that the skyline-like algorithm had a better performance. Then, the comparative experiments within three-dimensional obstacle skyline query were carried out by setting different sizes of data sets and different numbers of obstacles. According to the results, it is shown that the algorithm had a great performance.

Autonomous obstacle avoidance strategies in the mission of large space debris removal using potential function

Debris removal problem has become a consensus of international communities with the dramatically increase of space debris. When the service spacecraft (Servicer) carries out debris removal operations, there may exist collision threaten from other small objects which fly around the target debris. In this paper, autonomous collision avoidance strategies using improved potential function are studied, which drive the Servicer to rendezvous with the large debris and avoid obstacles around the trajectory. Firstly, the repulsive potential for static obstacles is constructed based on the relative position vector. Considering the necessary of avoidance of dynamic obstacles, the relative velocity vector between the Servicer and dynamic obstacles in space is introduced to design the repulsive potential for dynamic obstacles. Also, the corresponding control law is derived to drive the Servicer to approach the large debris. Finally, numerical simulations are performed to validate the effectiveness and stability of the obstacle avoidance strategy for debris removal.

Path planning of manipulator based on improved RRT algorithm

Aiming at the problem that the 6-DOF manipulator can quickly avoid obstacles in high-dimensional space, the method of path planning based on the improved rapid expansion random tree (RRT) algorithm is proposed. The improved RRT algorithm combines the advantages of the target bias strategy and proposes a method for setting the intermediate bias point. In random sampling, the sampling point is biased to the intermediate bias point,with a certain probability to reduce the blindness of sampling, and use at the same time the path shortening method reduces path nodes and turning points, and optimizes the motion path of the robotic arm. By comparing the simulation results with the RRT and P-RRT algorithms, the effectiveness of the improved RRT algorithm in the calculation time and the number of path nodes is proved.

Improvement of the heat transfer quality by air cooling of three‐heated obstacles in a horizontal channel using the lattice Boltzmann method

AbstractThis study focuses on the cooling of three heated obstacles with different heights mounted on the bottom of the channel wall using different aspects that influence the enhancement of the heat exchange, as is known in the concept of cooling electronic devices. The lattice Boltzmann method associated with multiple relaxation times (LBM‐MRT) was adopted to simulate the physical configurations of the studied system. In this context, the D2Q9 and D2Q5 models are applied to describe the fluid flow behavior and conjugate heat transfer, respectively. The evaluation of heat exchange between the cold fluid and three‐heated obstacles has been accurately analyzed under the effect of several parameters such as Reynolds number, obstacle spacing, and thermal conductivity ratio. In addition, the setting of two and three fluids flow inlets were also studied. The results are presented in terms of streamlines, isotherms, and local Nusselt curves. The heat transfer increases with increasing solid‐fluid thermal conductivity. It is also more pronounced for large Reynolds numbers. Moreover, the heat transfer significantly enhances for the second and third obstacles when obstacle spacing increases. The improvement of the heat transfer is performed by the implementation of several jet flows in the studied system.

Nonequidiffusive premixed-flame propagation in obstructed channels with open, nonreflecting ends.

Equidiffusive premixed combustion in obstructed channels with both open, nonreflecting ends exhibits various forms of flame propagation: oscillations, acceleration or a combination of both regimes. Given the limited practicality of equidiffusive premixed combustion, it is important to understand how these modes of combustion are altered at nonequidiffusive conditions, characterized by a nonunity Lewis number (thermal to mass diffusivity ratio) Le≠1. To achieve this, the impacts of Le on the flame dynamics and morphology are analyzed by means of the computational simulations of the reacting flow equations, with Arrhenius chemical kinetics, fully compressible hydrodynamics, and transport properties. In addition to varying Le, the parametric study includes various blockage ratios, channel widths, obstacle spacing and thermal expansion ratios. It is identified how these parameters influence the burning velocities as well as the scaled oscillation amplitude and frequency. Specifically, in the narrow channels with small blockage ratios, the amplitude and frequency of the oscillations vary with Le, with the frequency decreasing and the amplitude increasing as Le grows from 0.3 to 2. In other conditions, a transition from the flame oscillations to sudden flame acceleration or its propagation at a constant velocity is singularly influenced by Le, or by the interplay of Le with the geometric parameters of a channel. The delay time before the onset of flame acceleration, especially at Le<1, also varies as the channel width and the blockage ratio change. In all cases, Le has both quantitative and qualitative effects on flame propagation in obstructed channels with both open, nonreflecting ends.

Heat Transfer Enhancement in Parabolic through Solar Receiver: A Three-Dimensional Numerical Investigation.

Parabolic trough collectors (PTC) are one of the most established solar concentrating systems which have been used in a wide variety of applications. Enhancing their performance is critical to establish them as a viable technology. Internal obstacles are an intriguing way for improving the collector’s performance. However, the usage of obstacles results in increasing pressure loss. The purpose of this research is to numerically explore the impact of introducing obstacles to the receiver tube of a parabolic trough collector on heat transmission in PTCs and its overall thermal performance. The first part analyzed the effects of geometrical parameters, orientation angle (α = 45°, 90° or 135°), and spacing of obstacles (P/D = 1, 2, or 3) on the fluid motion, heat transfer, and performance. Then, a non-uniform heat flow was applied to the absorber’s outer surface. The effects of nanoparticles type, temperature profile, and heat transfer performance of three different nanofluids (Cu/thermal oil, Al2O3/thermal oil, andTiO2/thermal oil) were studied in the second part. The simulation results show that, the friction factor increased when P/D decreases, and that the absorber tube with obstacles discs (α = 90°) and P/D = 2 achieved the best thermal performance. Additionally, increasing the concentration of solid nanoparticles in thermal oil improves heat transmission, and the Cu nanofluid has the greatest Nusselt number.

The Impact of Digital Transformation on Improving the Performance of Parliamentary Research Services in the Iraqi Parliament: An Empirical Study

This study aims to digitize parliamentary research services by building a digital platform that provides a set of communication channels through which parliamentary research services can be provided with high quality and efficiency in performance, in order to support the work tasks of members of the Iraqi Council of Representatives at any time and under any circumstance, bypassing space obstacles to reach The places of their solution and their travels in an attempt to overcome the challenges of providing service in the traditional context through the use of the best techniques and software that ensure the achievement of the goal of the study and the satisfaction of the beneficiaries in the present and the future. The study adopted the experimental method and used the deliberate sample of the study community, which numbered (29) members out of (100) parliamentarians who actually benefited from parliamentary research services. Data collection tools were employed to achieve the results of the study and achieve its goals, where the observer and the interview were used, and a standardized scale form was prepared to measure the quality of parliamentary research services, the efficiency of their performance and their effectiveness from the point of view of the actual beneficiaries of the services in their traditional and digital forms (a pre- and post-questionnaire). The study concluded that the digitization of parliamentary research services through building the digital platform has achieved the standard of efficiency, effectiveness, quality and beneficiary satisfaction at a high level, which means rejecting null hypotheses and accepting alternative hypotheses.

Attempts and initiatives for mobility research including guideway transportation at the Mobility Experimental Field of the University of Tokyo

This paper describes several trials performed CHIBA test track 2 in the university of tokyo. These trials including a low-speed wheel climbing test using test trolley, expansion of facilities on CHIBA test track 2, coloring of track and bogie with water-based rust prevention and improved visibility, suppression of track temperature rise, Visualization of the contact position between wheel and rail, suppression of squeak noise, trials of non-contact speedometers, and data collection for detecting obstacles in the running space.

Method of an unmanned aerial vehicle composition route in space

The article is devoted to the development of a method of composition of the route of an unmanned aerial vehicle in three-dimensional space. The main difference of the presented method is the complex consideration of the features of the environment, which reflects the possible obstacles (active or passive) and other limitations of the problem when composing the route of the unmanned aerial vehicle in three-dimensional space. This allowed to increase the safety of the task in autonomous flight conditions. The article analyzes the main approaches to the composition of unmanned aerial vehicle routes in space. The conclusion about the shortcomings of the two-dimensional representation is made. The method presents four stages of the task. This is the stage of modeling the environment that reflects possible obstacles (active or passive) and other limitations of the task. Stage of construction of an extended graph of unmanned aerial vehicle routes in space. The difference of this stage is the adaptive consideration of the spatial location of active obstacles in space. The next stage is the route search stage, which connects the starting point with the end and bypasses all obstacles and allows you to build a starting route in the form of a broken line, which is formed by a sequence of waypoints, and connects the starting point with the end, bypassing obstacles. The last is the stage of obtaining the final result, which is provided by smoothing the obtained broken line. In this part of the composition method, to solve the problem of smoothing the trajectory of the unmanned aerial vehicle in space on the selected route, the expediency of using the method of non-uniform cubic B-spline is proved. With the help of this method the task of selection and optimization of the smoothing parameter is set and solved.

A homogenised model for flow, transport and sorption in a heterogeneous porous medium

A major challenge in flow through porous media is to better understand the link between microstructure and macroscale flow and transport. For idealised microstructures, the mathematical framework of homogenisation theory can be used for this purpose. Here, we consider a two-dimensional microstructure comprising an array of obstacles of smooth but arbitrary shape, the size and spacing of which can vary along the length of the porous medium. We use homogenisation via the method of multiple scales to systematically upscale a novel problem involving cells of varying area to obtain effective continuum equations for macroscale flow and transport. The equations are characterised by the local porosity, a local anisotropic flow permeability, an effective local anisotropic solute diffusivity and an effective local adsorption rate. These macroscale properties depend non-trivially on the two degrees of microstructural geometric freedom in our problem: obstacle size and obstacle spacing. We exploit this dependence to construct and compare scenarios where the same porosity profile results from different combinations of obstacle size and spacing. We focus on a simple example geometry comprising circular obstacles on a rectangular lattice, for which we numerically determine the macroscale permeability and effective diffusivity. We investigate scenarios where the porosity is spatially uniform but the permeability and diffusivity are not. Our results may be useful in the design of filters or for studying the impact of deformation on transport in soft porous media.

Detonation behaviors of stoichiometric hydrogen-oxygen mixture in annular tubes with circular obstacles

Experiments were performed to investigate the detonation behaviors of stoichiometric hydrogen-oxygen mixtures (at sub-atmospherical pressures) in annular tubes with circular obstacles. The annular tube was 1000 mm long and 48 mm in diameter (D). The circular obstacles were with the diameters of 37.20 mm and 30.36 mm, corresponding to the BR = 0.57, 0.36 (BR: blockage ratio), respectively. Two types of obstacle spacing S was set in the test, which are S = D and S = 2D. The detonation velocities were obtained based on the time of arrival of the wave front monitored by pressure transducers. Smoked foils were used to register the detonation cellular evolution though the test section. The results showed that the propagation limit in this test was 2ω/λ≈1(ω indicates the channel width, λ represents the cell width), which was consistent with the previous results in round tubes with orifice plates. The obstacle spacing presented no noticeable effect on detonation propagation limit. However, it played a significant role on detonation velocity. What is more, larger flow blockage for BR = 0.57 caused the more violent velocity fluctuation and higher propagation limit than in smaller blocking ratio. The process of diffraction-retonation for interaction between wave front and obstacle was analyzed in detail. In further, special vertical bands with periodic variation characteristic were observed between two adjacent obstacles. The vertical bands were spaced as same as the obstacle spacing and attached very fine cells which were caused by the head-on collision of the detonation wave propagating in the compressed region with high temperature and pressure.

Isogeometric multilevel quadrature for forward and inverse random acoustic scattering

We study the numerical solution of forward and inverse time-harmonic acoustic scattering problems by randomly shaped obstacles in three-dimensional space using a fast isogeometric boundary element method. Within the isogeometric framework, realizations of the random scatterer can efficiently be computed by simply updating the NURBS mappings which represent the scatterer. This way, we end up with a random deformation field. In particular, we show that it suffices to know the deformation field’s expectation and covariance at the scatterer’s boundary to model the surface’s Karhunen–Loève expansion. Leveraging on the isogeometric framework, we employ multilevel quadrature methods to approximate quantities of interest such as the scattered wave’s expectation and variance. By computing the wave’s Cauchy data at an artificial, fixed interface enclosing the random obstacle, we can also directly infer quantities of interest in free space. Adopting the Bayesian paradigm, we finally compute the expected shape and variance of the scatterer from noisy measurements of the scattered wave at the artificial interface. Numerical results for the forward and inverse problems validate the proposed approach.

Detonation propagation limits in hydrogen-oxygen mixtures in a tube filled with repeated perforated plates

This study investigated the propagation behaviors of quasi-detonations in a round tube filled with repeated perforated plates. Stoichiometric hydrogen-oxygen mixtures at different initial pressures were tested. Photodiodes and soot foil were used to record detonation velocity and cellular structure between two adjacent perforated plates. The orifice diameter (d), hole spacing (l) of the perforated plate and the obstacle spacing (S) were varied. The results show that the ratio of the overall jet diameter (D0, defined as the diameter of the circumcircle of the orifices) to the detonation cell size (λ) is in the range of 12–14 for the occurrence of Chapman-Jouguet detonations. The combustion regimes are affected by l/d, i.e., smaller l/d results in higher combustion velocity. At the detonation propagation limits, the results confirm the criterion L/λ>7, in which L=(S+D)/[2(1−1−BR)], D and BR are, respectively, the tube diameter and blockage ratio of the perforated plate.

Closed-form Minkowski sums of convex bodies with smooth positively curved boundaries

This article derives closed-form parametric formulas for the Minkowski sums of convex bodies in d-dimensional Euclidean space with boundaries that are smooth and have all positive sectional curvatures at every point. Under these conditions, there is a unique relationship between the position of each boundary point and the surface normal. The main results are presented as two theorems. The first theorem directly parameterizes Minkowski sum boundaries using the unit normal vector at each surface point. Although simple to express mathematically, such a parameterization is not always practical to obtain computationally. Therefore, the second theorem derives a more useful parametric closed-form expression using the gradient that is not normalized. In the special case of two ellipsoids, the proposed expressions are identical to those derived previously using geometric interpretations. In order to examine the results, numerical validations and comparisons of the Minkowski sums between two superquadric bodies are conducted. Applications to generate configuration space obstacles in motion planning problems and to improve optimization-based collision detection algorithms are introduced and demonstrated.

Preservice Teachers’ Content Knowledge and Learning Obstacles in Shape and Space

The notion of shape and space is the building block for geometry reasoning. Accordingly, it is expected that those trained to teach would possess substantial content knowledge for teaching planar and spatial notions. This study investigated the level of content knowledge and sources of learning obstacles encountered by preservice teachers prior to their first practice teaching of shape and space. The study adopted a cross-sectional survey design involving 757 second-year preservice teachers from 12 colleges of education in Ghana. Data were collected through written responses to basic shape and space tasks. Quantitative data were analyzed descriptively while qualitative data were analyzed thematically into matrix index. Participants’ content knowledge were categorized into declarative, conditional and procedural knowledge types. The result shows that participants were largely operating at moderate levels of declarative, procedural and conditional content knowledge. However, participants demonstrated higher procedural knowledge than declarative and conditional knowledge. Tasks on prisms and pyramids were more difficult for preservice teachers than those on angles, triangles and quadrilaterals. The learning obstacles encountered were mostly didactical followed by epistemological with few being ontogenetic. The study recommends that tutors should employ investigative didactic strategies to promote the three content knowledge types identified and to address the epistemological and ontogenetic obstacles in preservice teachers’ learning of shape and space.