Initial Position Research Articles

Influence of DC-Field Current on Short-Circuit Current in Variable Flux Reluctance Machine

DC-field windings of variable flux reluctance machine are wound on the same teeth with armature winding, which increases the short-circuit probability among the armature and field windings. Therefore, in this article, the various short-circuit faults of single phase, phase-to-phase, single field and phase-to-field are illustrated, and the influence of dc-field current on short-circuit current (SCC) and braking torque (BT) with consideration of initial rotor position are investigated. The SCC with dc-field current is analytically established, where the SCC and BT in transient and steady states are analyzed. The maximum SCC and BT are comprehensively compared by finite element method. It is found that the influence of dc-field current on the SCC and BT under transient conditions can be neglected. However, when the machine under un-saturated conditions, the SCC in steady states is associated with the saturation of iron core, i.e., the more saturated of the core excited by dc-field current in prefault, the smaller of the SSC in post fault. Both the SCC and BT are accompanied by the 12/14-pole VFRM prototype experimental verification.

Fault Diagnosis of Hydraulic Components Based on Multi-Sensor Information Fusion Using Improved TSO-CNN-BiLSTM.

In order to realize the accurate and reliable fault diagnosis of hydraulic systems, a diagnostic model based on improved tuna swarm optimization (ITSO), optimized convolutional neural networks (CNNs), and bi-directional long short-term memory (BiLSTM) networks is proposed. Firstly, sensor selection is implemented using the random forest algorithm to select useful signals from six kinds of physical or virtual sensors including pressure, temperature, flow rate, vibration, motor power, and motor efficiency coefficient. After that, fused features are extracted by CNN, and then, BiLSTM is applied to learn the forward and backward information contained in the data. The ITSO algorithm is adopted to adaptively optimize the learning rate, regularization coefficient, and node number to obtain the optimal CNN-BiLSTM network. Improved Chebyshev chaotic mapping and the nonlinear reduction strategy are adopted to improve population initialization and individual position updating, further promoting the optimization effect of TSO. The experimental results show that the proposed method can automatically extract fusion features and effectively utilize multi-sensor information. The diagnostic accuracies of the plunger pump, cooler, throttle valve, and accumulator are 99.07%, 99.4%, 98.81%, and 98.51%, respectively. The diagnostic results of noisy data with 0 dB, 5 dB, and 10 dB signal-to-noise ratios (SNRs) show that the ITSO-CNN-BiLSTM model has good robustness to noise interference.

Renewable energy hosting capacity assessment in distribution networks based on multi‐strategy improved whale optimization algorithm

AbstractThe increasing penetration of distributed renewable energy poses significant challenges to the safety and stability of distribution system, rendering the renewable energy hosting capacity of distribution networks a major concern. To effectively evaluate the renewable energy hosting capacity in distribution networks, this paper introduces a comprehensive hosting capacity assessment model considering various safety and stability constraints. Given the numerous non‐linear constraints inherent in the hosting capacity assessment model for distribution networks, a multi‐strategy improved Whale Optimization Algorithm is proposed. Improvements are made to the population initialization and population position update strategies, and a mutation strategy is introduced to prevent premature convergence, thereby enhancing the algorithm's performance. Finally, the effectiveness of the proposed model and the method is validated through the utilization of three distribution systems. Moreover, the key factors that restrict the improvement of hosting capacity are revealed from the perspective of distribution network topology.

Initiation and growth of fatigue cracks in sheets with U-shaped notches in the first and mixed modes of fracture

This study presents the effects of the geometry of the notches on the fatigue life, crack initiation, and growth in mixed mode and first mode of the fracture. For this purpose, some samples were tested with U-shaped notches with different radii and depths and various orientations with respect to the loading directions under fatigue loads. Using the fatigue crack growth rates, the Paris law coefficients were obtained for the used material in different conditions. It was shown that these coefficients are independent of the geometry of the samples. Fatigue crack growth behaviors in the mixed mode tests were also in good agreement with the result of the numerical simulations. Predictions of the maximum tangential stress criterion and numerical simulation for the position of the crack initiation on the notch root were compared with the tested observations, which showed good agreement. The fatigue life of the test samples was compared with the analytical results provided by the Manson-Coffin law. It was shown that a 25% decrease in notch depth increases the fatigue life by 3 times, also, an increase of 0.5 mm in the notch radius increases the fatigue life by 40%. Finally, the fracture surface of the samples was checked using an optical microscope. This study showed that the fracture surfaces have one or two lateral shear lips and plane stress conditions were established.   REFERENCES [1] X.-L. Zheng, Modelling fatigue crack initiation life, Int. J. Fatigue, 15 (1993) 461-466, https://doi.org/10.1016/0142-1123(93)90257-Q. [2] M. De Freitas, L. Reis, B. Li, Evaluation of small crack growth models for notched specimen under axial/torsional fatigue loading, Facta universitatis-series: Mechanics, Automatic Control and Robotics, 3 (2003) 657-669, [3] H. Zhang, A. Fatemi, Short fatigue crack growth from a blunt notch in plate specimens, Int. J. 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Fontanari, Experimental investigation on the propagation of fatigue cracks emanating from sharp notches, Meccanica, 43 (2008) 201-210, https://doi.org/10.1007/s11012-008-9129-3. [9] A. Akhavan Safar, A. Vrdi, M. Zorofi, Numerical and analytical investigation of the fatigue life of the notched sample and its comparison with the experimental results, in:  16th Annual Conference on Mechanical Engineering, Kerman, Iran, 2008. [10] Y. Hu, Z. Hu, S. Cao, Theoretical study on Manson-Coffin equation for physically short cracks and lifetime prediction, Sci. China Technol. Sci., 55 (2012) 34-42, https://doi.org/10.1007/s11431-011-4581-z. [11] Y. Li, H. Wang, D. Gong, The interrelation of the parameters in the Paris equation of fatigue crack growth, Eng. Fract. Mech., 96 (2012) 500-509, https://doi.org/10.1016/j.engfracmech.2012.08.016. [12] F. Gómez, M. Elices, F. Berto, P. Lazzarin, A generalised notch stress intensity factor for U-notched components loaded under mixed mode, Eng. Fract. Mech., 75 (2008) 4819-4833, https://doi.org/10.1016/j.engfracmech.2008.07.001. [13] S. Iida, A.S. Kobayashi, Crack-propagation rate in 7075-T6 plates under cyclic tensile and transverse shear loadings, J. Fluids Eng., 91 (1969) 764-769, https://doi.org/10.1115/1.3571219. [14] J. Qian, A. Fatemi, Mixed mode fatigue crack growth: a literature survey, Eng. Fract. Mech., 55 (1996) 969-990, https://doi.org/10.1016/S0013-7944(96)00071-9. [15] F. Erdogan, G. Sih, On the crack extension in plates under plane loading and transverse shear, J. Fluids Eng., 85 (1963) 519-525, https://doi.org/10.1115/1.3656897. [16] E.E. Gdoutos, Problems of mixed mode crack propagation, (1984), [17] A.T. Yokobori, T. Yokobori, K. Sato, K. Syoji, Fatigue crack growth under mixed modes I and II, Fatigue Fract. Eng. Mater. Struct., 8 (1985) 315-325, https://doi.org/10.1111/j.1460-2695.1985.tb00430.x. [18] L. Pook, The fatigue crack direction and threshold behaviour of mild steel under mixed mode I and III loading, Int. J. Fatigue, 7 (1985) 21-30, https://doi.org/10.1016/0142-1123(85)90004-0. [19] M. Louah, G. Pluvinage, A. Bia, Mixed mode fatigue crack growth using the Brasilian disc, Virginia Univ, Fatigue 87, 2 (1987), [20] H. Nayeb-Hashemi, S. Hwang, P. Poles, Crack closure phenomena in modes I and II interactions, Fatigue'87., 2 (1987) 979-996, [21] T. Hyde, A. Chambers, A compact mixed-mode (cmm) fracture specimen, J. Strain Anal. Eng. Des., 23 (1988) 61-66, https://doi.org/10.1243/03093247V232061. [22] M. Brown, Analysis and design methods in multiaxial fatigue, in:  Advances In Fatigue Science and Technology, Springer, 1989, pp. 387-401. [23] C. Wang, S. Wang, Modified Generalized Maximum Tangential Stress Criterion for Simulation of Crack Propagation and Its Application in Discontinuous Deformation Analysis, Eng. Fract. Mech., 259 (2022) 108159, https://doi.org/10.1016/j.engfracmech.2021.108159. [24] M. Eftekhari, C. Xu, Evaluating MTS criterion in predicting mixed-mode crack extension under different loading conditions, Fatigue Fract. Eng. Mater. Struct., 46 (2023) 96-110, https://doi.org/10.1111/ffe.13850. [25] K. Tanaka, Fatigue crack propagation from a crack inclined to the cyclic tensile axis, Eng. Fract. Mech., 6 (1974) 493-507, https://doi.org/10.1016/0013-7944(74)90007-1. [26] K. Tateishi, T. Hanji, Low cycle fatigue strength of butt-welded steel joint by means of new testing system with image technique, Int. J. Fatigue, 26 (2004) 1349-1356, https://doi.org/10.1016/j.ijfatigue.2004.03.016. [27] K. Tateishi, T. Hanji, K. Minami, A prediction model for extremely low cycle fatigue strength of structural steel, Int. J. Fatigue, 29 (2007) 887-896, https://doi.org/10.1016/j.ijfatigue.2006.08.001. [28] S. Li, X. Xie, C. Cheng, Q. Tian, A modified Coffin-Manson model for ultra-low cycle fatigue fracture of structural steels considering the effect of stress triaxiality, Eng. Fract. Mech., 237 (2020) 107223, https://doi.org/10.1016/j.engfracmech.2020.107223. [29] Y. Zhang, L. Gao, C. Wang, A Prediction Model for Low Cycle Fatigue Crack Initiation under Axial Loading in:  13th International Conference on Fracture 2013. [30] D.F. Socie, Fatigue-life prediction using local stress-strain concepts, Exp. Mech., 17 (1977) 50-56, https://doi.org/10.1007/BF02326426. [31] M. Benedetti, C. Menapace, V. Fontanari, C. Santus, On the variability in static and cyclic mechanical properties of extruded 7075-T6 aluminum alloy, Fatigue Fract. Eng. Mater. Struct., 44 (2021) 2975-2989, https://doi.org/10.1111/ffe.13530. [32] K. Tahmasbi, F. Alharthi, G. Webster, M. Haghshenas, Dynamic frequency-dependent fatigue damage in metals: A state-of-the-art review, Forces Mech., 10 (2023) 100167, https://doi.org/10.1016/j.finmec.2023.100167. [33] H. Kuhn, D. Medlin, ASM Handbook. Volume 8: Mechanical Testing and Evaluation, ASM International, Member/Customer Service Center, Materials Park, OH 44073-0002, USA, 2000. 998, (2000) 1832, https://doi.org/10.31399/asm.hb.v08.9781627081764. [34] L. Fu, H. Duan, H. Li, L. Lin, Q. Wang, J. Yao, Y. Luo, Low-cycle fatigue behavior of 7075-T6 aluminum alloy at different strain amplitudes, Mater. Express, 10 (2020) 942-947, https://doi.org/10.1166/mex.2020.1696. [35] S. Hassanifard, H. Mousavi, A. Varvani-Farahani, The influence of low-plasticity burnishing process on the fatigue life of friction-stir-processed Al 7075-T6 samples, Fatigue Fract. Eng. Mater. Struct., 42 (2019) 764-772, https://doi.org/10.1111/ffe.12950.

A multi‐level approach to predict the seismic response of rigid rocking structures using artificial neural networks

AbstractThis paper explores the use of Artificial Neural Networks (ANN) for the rocking problem. The paper adopts rigid rocking blocks of different sizes and slenderness, which undergo rocking motion without sliding and bouncing when subjected to recorded earthquakes. This research focuses on the cases where the blocks overturn or safely return to their initial (rest) position at the end of the ground shaking. An ANN model is trained to efficiently categorise the response into overturning or safe rocking using the structural parameters, ground motion characteristics, and the coefficient of restitution as input. The results show the substantial contribution of velocity and frequency characteristics of the ground motion to overturning. In addition, ANN is used to predict the response amplitude and identify the most critical input variables that govern safe rocking. The analysis reveals that rocking amplitude is governed by a combination of duration, frequency, and intensity characteristics of the ground excitation. Interestingly, the maximum incremental velocity (MIV), a novel intensity measure for the rocking literature, shows a substantial correlation with the rocking amplitude. In this context, this paper proposes closed‐form expressions using the most influential input variables to provide a quick, yet adequately accurate, response prediction. Finally, this study pays special attention to the contribution of the coefficient of restitution, which, in general, is less critical to the peak safe rocking response, while it becomes more important to the overturning response.

Influence of initial electric arc root position on electric arc behavior with spark plugs in large lean burn spark ignited gas engines

Increasing efficiency while reducing emissions leads to high mean effective pressures, high compression ratios and increasingly lean operation for spark ignited large gas engines. Despite these boundary conditions, gas engines must be operated between knocking and misfiring at low cycle-to-cycle fluctuations. The excess air ratio and the ignition process of the lean mixture greatly influence the stability of the combustion process. To enable sufficiently low cycle-to-cycle fluctuation of the combustion process despite the ever increasing excess air ratio levels, it is necessary to understand and investigate the sub-areas of the engine process, for example, ignition, flow condition and mixture formation. This paper focuses on one sub-area of conventional spark ignition, the influence of the electric arc root position on the origin and stretching of the electric arc, because electric arc behavior is considered important in the subsequent combustion process. The results show that electric arc roots on the downstream end of the electrodes tend to enable a longer electric arc length at the first electric arc short circuit (i.e. the first abrupt shortening of the electric arc during its spark duration) than electric arcs with electric arc roots on the upstream ends of the electrodes.

ERROR ANALYSIS OF VISUAL ODOMETRY FOR A SMALL SIZE UNMANNED AERIAL VEHICLE

Abstract. Usage of small size Unmanned Aerial Vehicle (UAV) with autonomous flight capability became widespread at both civil and military applications because of its low costs and ease of use. However, inertial or GPS based positioning and orientation sensors can be disabled at battlefields and the UAV losses its path in a short time. Visual odometry becomes a solution for the aforementioned hassle. Real-time detection of ground control points, matching the same control points at the stereo pair images and correcting the position and orientation data with least square adjustment are the challenges of visual odometry. In this study, error analysis of position and orientation of a UAV flying through mountainous region which cannot obtain any augmenting data for position and orientation is conducted by error propagation law. The flight of UAV is simulated with exact initial position and orientation data. Optic images of ground obtained by nadir directed camera are georeferenced using the digital elevation model of the region, interior and exterior camera parameters. The digital elevation model is used to correct the relief displacement. The stereo-pair image is obtained when the UAV flies 200 m and image coordinates of the common control points are detected by colinearity equations. Position and orientation of UAV is corrected by least square adjustment and the process is repeated for each obtained image acquired at 200 m interval. The analysis revealed that the precisions of horizontal and vertical positioning becomes 75 and 200 meter, respectively. The precision of roll angle becomes worse than 0.5 degree, while the precisions of pitch and yaw angle are estimate to be better that 0.1 degree.

Magnetic field directed assembly of magnetic non-spherical microparticles

This study reports on the fabrication and assembly of anisotropic microparticles as versatile building blocks for directed magnetic assemblies. Although spherical microparticles have received extensive attention, the assembly of non-spherical magnetic microparticles remains underexplored. Herein, we present a fabrication approach that utilizes photolithography and soft lithography to create prism-shaped magnetic microparticles. In order to investigate their assembly, a switching rotating magnetic field was employed. To support our experimental findings, a numerical model which takes into account the magnetic dipole moments induced by the field of other particles was developed. This model helps in understanding the forces and torques governing particle behavior during assembly. Simulations were conducted using the numerical model to complement our experimental findings. In the two particle experiments, attractive magnetic interactions led to various configurations depending on initial positions. For three particles, a tip-to-tip configuration suggested closed or stable ring-like structures. Our work highlights the feasibility of producing highly responsive, non-spherical magnetic microparticles and their potential for assemblies. The versatile fabrication method, coupled with the added degree of freedom conferred by prismatic shapes, opens promising avenues for applications in biology and material science.

Impact of Pad Layouts and Solder Volume on Self- Alignment of Micro Solar Cells

In micro- concentrating photovoltaics (micro- PV), tiny solar cells (<1 mm2) are assembled on a circuit board on glass. To mount thousands of dies per square meter, a high throughput process is required which still yields alignment accuracy in the order of 10 μm. We developed a micro-CPV module technology where micro cells are accurately mounted directly on a circuit board on glass using a high throughput pick and place process combined with selfalignment based on the restoring force due to surface-tension of the liquid solder. In this work, we study how the selfalignment accuracy is influenced by the pad layout, solder volume and initial position of the die. We show that selfalignment significantly benefits from an induced motion, whether induced by initial displacement of the die or by flowing of molten solder along tracks. Furthermore, we found that lower solder volumes lead to higher alignment accuracies for dies on rectangular pads, whereas the dependence on solder volume is lower for pads with connected tracks where the solder flows out. Overall, alignment accuracies below 15 μm are demonstrated despite initial displacements up to 150 μm. Thus, self-alignment using surface tension of the liquid solder is suitable for micro-CPV.

Phonological Variation of /r/ in Selected Arabic Dialects

The present study offers a descriptive examination of the Arabic phoneme /r/, renowned for its intricate and diverse nature within the Arabic phonological system. This research investigates the varied manifestations of the phoneme /r/ in different regional dialects, with a specific emphasis on its pronunciation in the initial, middle, and final positions of words. The paper's significance is rooted in its contribution to the comprehension of the Arabic /r/ phoneme, a multifaceted and diverse sound within Arabic phonological systems. The paper illuminates the phonetic variability of the /r/ by analyzing its distinct manifestations across diverse Arabic dialects and regions. This can potentially facilitate language acquisition and instruction. The investigation conducted by the authors pertains to the marked and unmarked characteristics of the phonological /r/ in Arabic. The population under investigation comprises a randomly selected group of Arabic-speaking individuals aged 18 years and older, encompassing both genders and hailing from diverse countries and regions. The study employs a descriptive-analytical methodology, utilizing a unique features matrix and the Audacity Sound Recording and Analysis Application to examine the gathered data. The findings of the research enhance the comprehension of the phonetic variability that typifies the Arabic /r/ phoneme and elucidate its manifestation in diverse contexts and geographical locations. Furthermore, the outcomes of this investigation hold significance for the domain of language education and acquisition, and the techniques utilized were designed to guarantee the precision and dependability of the gathered information.

Island myriads in periodic potentials.

A phenomenon of emergence of stability islands in phase space is reported for two periodic potentials with tiling symmetries, one square and the other hexagonal, inspired by bidimensional Hamiltonian models of optical lattices. The structures found, here termed as island myriads, resemble web-tori with notable fractality and arise at energy levels reaching that of unstable equilibria. In general, the myriad is an arrangement of concentric island chains with properties relying on the translational and rotational symmetries of the potential functions. In the square system, orbits within the myriad come in isochronous pairs and can have different periodic closure, either returning to their initial position or jumping to identical sites in neighbor cells of the lattice, therefore impacting transport properties. As seen when compared to a more generic case, i.e., the rectangular lattice, the breaking of square symmetry disrupts the myriad even for small deviations from its equilateral configuration. For the hexagonal case, the myriad was found but in attenuated form, mostly due to extra instabilities in the potential surface that prevent the stabilization of orbits forming the chains.

Effect of pressure-side tip winglet with different heights and lengths on clearance flow in a compressor cascade

The clearance flow influence law and mechanism of pressure tip winglets with different fusion heights and lengths are investigated by numerical simulation methods based on a compressor cascade to weaken compressor clearance leakage and improve cascade aerodynamic performance. The result demonstrates that the tip winglet can improve the spanwise pressure flow and narrow the tip separation range, thereby suppressing the intensity of the leakage vortex. The enhanced effect on the leakage vortex is more significant when the tip winglet's fusion length range can include the leakage vortex's initial position. In addition, narrower fusion heights and longer fusion lengths enhance the improvement effect. The tip winglet provides the most significant effect, reducing total pressure loss by 0.64% and leakage by 16.8% when the fusion height is 1% blade height and the length is the whole chord.

A Lyapunov based posture controller for a differential drive mobile robot

Driving a vehicle to a desired position and orientation is one of the most important problems that should be solved in most navigation systems. This paper describes a new complete design and hardware implementation of a two-level controller that will enable a differential drive mobile robot to reach any desired posture starting from any initial position. The first or low-level controller consists of a set of two proportional–integral–derivative (PID) controllers, running on an embedded system on board of the robot. These controllers provide the required voltages to the motors to make the left and right wheels of the robot rotate with the angular speeds computed by the second or high-level controller, running on a stationary PC system. This second controller is based on the Lyapunov stability theorem to derive two control laws for the kinematic model, used to transform the linear and angular speeds of the unicycle model in terms of left and right rotational speeds, required by the motors. As will be shown later, this architecture provides a very flexible way not only to tune the main controller parameters but also to get access and record all the system states.

Polarized images of charged particles in vortical motions around a magnetized Kerr black hole

In this work, we study the images of a Kerr black hole (BH) immersed in uniform magnetic fields, illuminated by the synchrotron radiation of charged particles in the jet. We particularly focus on the spontaneously vortical motions (SVMs) of charged particles in the jet region and investigate the polarized images of electromagnetic radiations from the trajectories along SVMs. We notice that there is a critical value ω_c for charged particle released at a given initial position and subjected an outward force, and once |qB_0/m|=|ω_B|>|ω_c| charged particles can move along SVMs in the jet region. We obtain the polarized images of the electromagnetic radiations from the trajectories along SVMs. Our simplified model suggests that the SVM radiations can act as the light source to illuminate the BH and form a photon ring structure.

Cervical misalignment in motorcyclists in relation to new helmet removal recommendations shown with augmented reality resources: A biomechanical analysis

ObjectiveThe aim of this study is to determine the best technique and position for helmet removal in injured motorcyclists by comparing cervical misalignment produced in the supine position and prone position. MethodComparative cross-sectional clinical simulation study to quantify CM using biomechanical analysis with the use of inertial systems. The main variable was determined for the flexion-extension motion. The extraction was tested for both positions (prone position and supine position), which were repeated 3 times for each of the 30 volunteers included, and the movement from the initial neutral position was also determined, resulting in a total of 270 biomechanical studies. ResultsA flexion was observed when moving the patient from the neutral position to the SP, due to the size of the helmet, of 1.29° ± 5.12°. Helmet removal in the supine position resulted in an average flexion-extension range of 17.51° ± 6.49°, while the same extraction in prone position recorded an average range of 10.82° ± 8.05°. For the main variable, statistically significant differences were found when comparing prone position and supine position (p = 0.0087). ConclusionsThe main conclusion of the study is that the helmet removal should be done in the position in which we find the patient, whether in prone position or supine position. Additionally, the new technique described for the prone position causes less movement of the cervical spine than the usual supine position.

A Novel Iterative Positioning Method Based on Difference RSS Model With 5G Field Experiments

In the 5th Generation (5G) positioning, the accurate values of environmental parameters such as Pathloss exponent (PLE) and transmit power are difficult to obtain accurately. Methods based on the difference of received signal strength (DRSS) can be utilized to solve the problems. An estimation method to obtain the distance ratio is given, and a distance ratio positioning model is proposed. The initial positioning results are calculated with linear least squares (LLS) algorithm. A Levenberg-Marquardt (LM) based maximum a posteriori (MAP) algorithm is proposed to obtain the final result by performing a series of iterations. We have completed the 5G field data collection in urban environments and preprocessed the raw data in 5G field experiments. We also propose a judgment method for 5G positioning based on horizontal dilution of precision (HDOP). Compared to the state-of-art DRSS-based algorithms, the proposed method has the best positioning accuracy and achieves a positioning error of 43.8 meters for 80% of samples with six base stations.

Milky Way globular clusters on cosmological timescales

Context. The present epoch of the Gaia success gives us a possibility to predict the dynamical evolution of our Solar System in the global Galactic framework with high precision. Aims. We statistically investigated the total interaction of globular clusters with the Solar System during six billion years of look-back time. We estimated the gravitational influence of globular clusters’ flyby onto the Oort cloud system. Methods. To perform the realistic orbital dynamical evolution for each individual cluster, we used our own high-order parallel dynamical N-body φ-GPU code that we developed. To reconstruct the orbital trajectories of clusters, we used five external dynamical time variable galactic potentials selected from the IllustrisTNG-100 cosmological database and one static potential. To detect a cluster’s close passages near the Solar System, we adopted a simple distance criteria of below 200 pc. To take into account a cluster’s measurement errors (based on Gaia DR3), we generated 1000 initial positions and velocity randomisations for each cluster in each potential. Results. We found 35 globular clusters that have had close passages near the Sun in all the six potentials during the whole lifetime of the Solar System. We can conclude that at a relative distance of 50 pc between a GC and the SolS, we obtain on average ∼15% of the close passage probability over all six billion years, and at dR = 100 pc, we get on average ∼35% of the close passage probability over all six billion years. The globular clusters BH 140, UKS 1, and Djorg 1 have a mean minimum relative distance to the Sun of 9, 19, and 17 pc, respectively. We analysed the gravitational energetic influence on the whole Oort cloud system from the closest selected globular cluster flyby. We generally found that a globular cluster with a typical mass above a few times 105 M⊙ and with deep close passages in a 1–2 pc immediately results in the ejection more than ∼30% of particles from the Oort cloud system. Conclusions. We can assume that a globular cluster with close passages near the Sun is not a frequent occurrence but also not an exceptional event in the Solar System’s lifetime.

Jamming problems and the effects of compliance in dual peg-hole disassembly

Disassembly is a crucial step in remanufacturing and is currently mainly performed by humans. Automating disassembly can reduce labour costs and make remanufacturing more economically attractive. This paper focuses on identifying and characterizing a common disassembly task, dual peg-hole disassembly, with the aim of building a robotic disassembly system for this task. We enumerate the possible contact states and their geometric conditions during the extraction of two studs in a dual peg-hole. This paper focuses on jamming in the extraction and conducts geometrical and quasi-static analyses to determine the boundary conditions of jamming. Based on the analyses, this paper also investigates the role of active compliance as a solution to avoid jamming. We also simulate critical variables and examine key parameters such as the degree of compliance, the location of the compliance centre and initial position errors. Finally, we conduct experimental studies on dual peg-hole extraction with different compliance centres obtained using active compliance.

Numerical investigation on the exhaust gas combustion of an SOFC in a catalytic multichannel burner

The utilization of the exhaust gas of a solid oxide fuel cell is important to improve the energy efficiency and control pollutant emission. In this work, the combustion of solid oxide fuel cell exhaust gas (H2/CO) in a honeycomb ceramic catalytic burner is investigated numerically. A 2D numerical combustion model with 17 channels is built to analyze the influence of channel position on thermal performance and combustion characteristics. The high burnout of H2 and CO is obtained as 96.75% and 97.75%, respectively. The channels can be divided into three groups from the inside to the outside as follows: part 1, from the 9th channel to the 13th channel; part 2, from the 14th channel to the 16th channel; and part 3, the 17th channel. The channels in the same group presented the same results of flow, temperature, and combustion. Compared with the other channels, the outermost channel shows notable differences in depressing the temperature of the whole channel, moving the maximum temperature downstream, enlarging the temperature bias of the lower and upper walls, and enlarging the combustion zone. H2 and CO perform different combustion processes in the honeycomb ceramic catalytic burner. Compared with H2, the initial position of CO conversion is more affected by channel distribution. In the 17th channel, the CO oxidation rate is controlled mostly by the slower oxygen adsorption and the resulting low O(s) coverage. In the 9th channel, the CO oxidation rate is controlled mostly by the wall temperature and fuel-limited. The burnout rate of H2 changes from 95% to 99.9% with the channel position, but the burnout of CO varies little. The closer the channel to the outer wall, the higher the proportion of heterogeneous reaction and the more the generated heat. The generated heat by the channel can present a diversity of 4%.

A Dual-Particle Approach for Incompressible SPH Fluids

Tensile instability is one of the major obstacles to particle methods in fluid simulation, which would cause particles to clump in pairs under tension and prevent fluid simulation to generate small-scale thin features. To address this issue, previous particle methods either use a background pressure or a finite difference scheme to alleviate the particle clustering artifacts, yet still fail to produce small-scale thin features in free-surface flows. In this paper, we propose a dual-particle approach for simulating incompressible fluids. Our approach involves incorporating supplementary virtual particles designed to capture and store particle pressures. These pressure samples undergo systematic redistribution at each time step, grounded in the initial positions of the fluid particles. By doing so, we effectively reduce tensile instability in standard SPH by narrowing down the unstable regions for particles experiencing tensile stress. As a result, we can accurately simulate free-surface flows with rich small-scale thin features, such as droplets, streamlines, and sheets, as demonstrated by experimental results.