Three-dimensional Square Research Articles

The impact of social noise on the majority rule model across various network topologies

We explore the impact of social noise, characterized by nonconformist behavior, on the phase transition within the framework of the majority rule model. The order–disorder transition can reflect the consensus-polarization state in a social context. This study covers various network topologies, including complete graphs, two-dimensional (2-D) square lattices, three-dimensional (3-D) square lattices, and heterogeneous or complex networks such as Watts–Strogatz (W-S), Barabási-Albert (B-A), and Erdős-Rényi (E-R) networks, as well as their combinations (multilayer network). Social behavior is represented by the parameter p, which indicates the probability of agents exhibiting nonconformist behavior. Our results show that the model exhibits a continuous phase transition across all networks. Through finite-size scaling analysis and evaluation of critical exponents, our results suggest that the model falls into the same universality class as the Ising model.

Transitions in growing networks using a structural complexity approach.

Structure changes or transitions are common in growing networks (complex networks, graphs, etc.) and must be precisely determined. The introduced quantitative measure of the structural complexity of the network based on a procedure similar to the renormalization process allows one to reveal such changes. The proposed concept of the network structural complexity accounts for the difference between the actual and averaged network structures on different scales and corresponds to the qualitative comprehension of complexity. The structural complexity can be found for the weighted networks also. The structural complexities for various types of growing networks exhibiting transitions similar to phase transitions were found-the deterministic infinite and finite size artificial networks of different natures including percolation structures, and the time series of various types of cardiac rhythms mapped to complex networks using the parametric visibility graph algorithm. In all the cases the structural complexity of the growing network reaches a maximum near the transition point: the formation of a giant component in the graph or at the percolation threshold for two-dimensional and three-dimensional square lattices when a giant cluster having a fractal structure has emerged. Therefore, the structural complexity of the network allows us to detect and study processes similar to a second-order phase transition in complex networks. The structural complexity of a network node can serve as a kind of centrality index, auxiliary, or generalization to the local clustering coefficient. Such an index provides another new ranking manner for the network nodes. Being an easily computable measure, the network structural complexity might help to reveal different features of complex systems and processes of the real world.

Comprehensive analysis of different GNSS receivers performance based on PPP-AR and positioning accuracy during 22 geomagnetic storms in 2023

Geomagnetic storms induced ionospheric disturbances can degrade the positioning accuracy and Ambiguity Resolution (PPP-AR) of GPS Precise Point Positioning (PPP), and this negative effect varies among different GNSS receivers. Under current conditions with frequent geomagnetic storms occurrences during the peak of solar cycle 25, selecting GNSS receivers with strong resistance to ionospheric disturbances is meaningful for precise GNSS positioning and ionospheric research. Therefore, it is necessary to conduct a comprehensive comparison and evaluation of the performance for different GNSS receivers under geomagnetic storms. Based on 22 geomagnetic storms in 2023, we investigated the three-dimensional root mean square error (3D RMS) and ambiguity resolved percentage (ARP), which is defined as the ratio of the number of carrier-phase observations with fixed ambiguities to the total number of phase measurements of GPS kinematic PPP, across ten groups of collocated stations around the world. For the groups using different receiver brands, the performance ranking for positioning accuracy and PPP-AR during geomagnetic storms are as follows: TPS > JVAVD > SEPTENTRIO > TRIMBLE. The station with a larger average ARP generally has a smaller average 3D RMS error than the another GNSS station. The average 3D RMS error between collocated stations using different receiver brands is typically greater than 0.010 m and even larger. The largest 3D RMS error difference is observed between collocated stations with SEPTENTRIO and JAVAD receivers, with 3D RMS errors of 0.089 m and 0.019 m, respectively. These identical-brand receivers with different types are as follows: TPS NET-G5 > TPS NET-G3A, TRIMBLE ALLOY > TRIMBLE NETRS, SEPT POLARX5TR > SEPT POLARX5S, and LEICA GR10 > LEICA GR30, respectively. The average differences in 3D RMS and ARP can reach up to 0.021 m and 6.0%, respectively. We found that the choice of antennas does not significantly affect PPP positioning performance during storms, with differences in average 3D RMS below 0.005 m and ARP differences below 0.2%.. Higher latitudes have more satellites affected by ionospheric disturbances, while this effect is typically only observed during strong storms (Dstmin≤-100nT) in mid-latitudes. Adequate available GPS satellites are crucial for achieving high PPP-AR and positioning accuracy during storms. The variations of disturbed satellites and the average Rate of Total Electron Content Index (ROTI) for collocated stations are generally consistent. However, there are differences in the average of ROTI values for different receivers under geomagnetic storms. The differences in PPP-AR performance and ROTI values among different receivers under geomagnetic storms can be attributed to the variations in satellite tracking algorithms, tracking loop designs, firmware, and multipath mitigation methods used by different receivers. These findings can provide a reference value and future research direction for selection, application and enhancement for different receivers to achieve GNSS high precision positioning under complex space weather conditions.

Effects of turbulence intensity and integral length scale on wind-induced vibrations of a three-dimensional aeroelastic square cylinder

Despite a wealth of prior research on the effects of free-stream turbulence (FST) on the aerodynamics of square cylinders, there is limited knowledge about their aeroelasticity such as characteristics of wind-induced vibrations that vary with the FST properties. This paper focuses on the investigation of the effects of FST properties including longitudinal turbulence intensity and integral length scale on the wind-induced vibrations of a three-dimensional (3D) aeroelastic square cylinder with an aspect ratio of 10 (a super-tall building model). Through wind tunnel testing, displacements of the aeroelastic model are measured in smooth flow and four turbulent flows to experimentally investigate its characteristics of fluid-solid interaction, including along- and across-wind vibrations, especially vortex-induced vibration and galloping. The effects of the turbulence intensity with a higher-level than previous studies are also investigated. The results show that the root-mean-square (RMS) displacements of the along-wind responses increase with the increase of turbulence intensity and are not affected by integral length scale. For the across-wind responses, in the non-lock-in region, the RMS displacements generally increase with the increase of turbulence intensity. In the lock-in region, the RMS displacements remain unchanged with the increase of turbulence intensity, while increase with the increase of integral length scale. This paper aims to improve the comprehension of the effects of FST on the wind-induced vibrations of 3D square cylinders and to furnish valuable insights for the wind-resistant design of slender structures, such as supertall buildings.

Long-range LBL underwater acoustic navigation considering Earth curvature and Doppler effect

The accuracy of underwater acoustic navigation is significantly influenced by geometry configuration and systematic errors coming from geophysical environment. Long baseline (LBL) systems exhibit superior positioning precision than other acoustic navigation systems, primarily attributable to the better Geometric Dilution of Precision (GDOP). However, the geometry configuration tends to degrade when the underwater vehicle is far away from the seafloor beacons. Factors such as acoustic ray bending error, Doppler effect and Earth curvature may seriously affect the navigation accuracy. To address these issues, we present a robust Kalman filter with systematic error compensation for long-range LBL systems. Firstly, a reversed acoustic ray tracking method is proposed for a unique phenomenon in acoustic wave propagation. Following that, we construct an acoustic positioning model with a time bias parameter, to weaken the impact of Doppler effect on acoustic ranging. This additional parameter was estimated with the state of the user vehicle in real time. At last, an observation equation of pressure gauge considering Earth curvature is presented for depth constraint. Long-range LBL experiments conducted in the South China Sea is employed to validate the performance of the proposed methods, taking the positioning results of inverted ultra-short baseline (iUSBL) system as reference. The results show that the proposed method outperform traditional method with a decrease of about 60 % in the three-dimensional root mean square (3DRMS) of navigation errors. With mentioned three improvements, the 3DRMS of the long-range LBL system with the longest distance of 20 km from the beacon center is less than 14 m. These findings can provide theoretical basis for other long-range LBL systems.

Self-ordering and organization of a staggered oblate particle pair in three-dimensional square ducts

We numerically investigate the formation and ordering of staggered oblate particle pairs in three-dimensional straight ducts with a square cross section. The lattice Boltzmann method is employed to simulate rigid particle pairs in a Newtonian liquid. The effects of initial axial spacing, Reynolds number, blockage ratio, and particle aspect ratio on the formation process, migration behavior, and interparticle spacing are explored in detail. Current results indicate that the process from initial to final steady state can be divided into two stages. The first stage is rapid migration from initial positions toward equilibrium positions under shear-induced lift force and wall-induced repulsive force. The second stage is the slow self-assembly of stable particle pairs in the axial direction due to the interparticle interaction. Interestingly, initial axial spacing significantly affects the formation process of particle pairs but does not affect the final steady state. It is found that the equilibrium positions of staggered particle pairs move slightly toward the duct walls, and the axial spacing increases with increasing Reynolds number or particle aspect ratio, or decreasing blockage ratio. For a staggered particle pair, the second particle will occupy the eddy center induced by the first focusing particle. Based on the existing data, a correlation is put forward to predict the axial interparticle spacing of staggered oblate particle pairs in duct flows. The present results may give insights into manipulating and comprehending non-spherical particle dynamics in microfluidic applications.

Contribution of BDS-3 observations to the precise orbit determination of LEO satellites: a case study of TJU-01

The precise orbit determination (POD) of scientific low Earth orbit (LEO) satellites is a prerequisite for the successful implementation of scientific missions. In recent years, global navigation satellite systems have become the main means of determining the orbits of LEO satellites. The global navigation satellite system receiver onboard the Tianjin University No. 1 (TJU-01) satellite receives both GPS and BDS-2/3 signals, with the addition of BDS-2/3 observations playing an important role in improving the POD of LEO satellites. This study comprehensively analyzes the spaceborne GPS/BDS data quality, including BDS-2/3 and GPS code multipath errors. Appreciable code multipath errors are found for the B1I signal of BDS-2 medium Earth orbit (MEO) satellites at elevations higher than 40°, whereas slight near-field relevant multipath errors of both frequencies are found for GPS and BDS-3 MEO satellites. The GPS and BDS-2/3 code multipath errors are estimated through elevation/azimuth-relevant piece-wise modeling and applied in the POD calculations. Several schemes, namely GPS-based, BDS-based, BDS-based without geo-synchronous (GEO) satellites, and GPS/BDS combined schemes, are designed to evaluate the POD performance. Fourteen days of data are calculated and the average three-dimensional (3D) orbital root mean square (RMS) of orbit overlapping differences obtained from GPS-based and BDS-based POD (without GEO satellites) solutions are 37.4 and 27.1 mm, respectively. The BDS-based solutions are obviously better than the GPS-based solutions, mainly owing to better data availability. The GPS/BDS combined solutions have the best accuracy, with a 3D RMS value of 20.6 mm. In addition, when BDS GEO satellites are included, the 3D RMS of the overlapping orbit differences reduces to 32.9 and 27.4 mm for BDS-based and GPS/BDS combined solutions, respectively. Double-difference (DD) and single-difference (SD) integer ambiguity resolution (IAR) are adopted to further improve the POD performance. The fixed orbit of the TJU-01 satellite is solved through DD IAR and SD IAR, and the contribution of the TJU-01 satellite to ambiguity fixing is analyzed. Relative to the float solution, the improvements made using the two ambiguity fixing approaches are equivalent, both being approximately 13%. The importance of this research is not only the precise determination of the orbit of TJU-01 for occultation service but also the demonstration of the contribution of BDS observations to the performance of the POD of LEO satellites.

A Low-Cost and Robust Multi-Sensor Data Fusion Scheme for Heterogeneous Multi-Robot Cooperative Positioning in Indoor Environments

The latest development of multi-robot collaborative systems has put forward higher requirements for multi-sensor fusion localization. Current position methods mainly focus on the fusion of the carrier’s own sensor information, and how to fully utilize the information of multiple robots to achieve high-precision positioning is a major challenge. However, due to the comprehensive impact of factors such as poor performance, variety, complex calculations, and accumulation of environmental errors used by commercial robots, the difficulty of high-precision collaborative positioning is further exacerbated. To address this challenge, we propose a low-cost and robust multi-sensor data fusion scheme for heterogeneous multi-robot collaborative navigation in indoor environments, which integrates data from inertial measurement units (IMUs), laser rangefinders, cameras, and so on, into heterogeneous multi-robot navigation. Based on Discrete Kalman Filter (DKF) and Extended Kalman Filter (EKF) principles, a three-step joint filtering model is used to improve the state estimation and the visual data are processed using the YOLO deep learning target detection algorithm before updating the integrated filter. The proposed integration is tested at multiple levels in an open indoor environment following various formation paths. The results show that the three-dimensional root mean square error (RMSE) of indoor cooperative localization is 11.3 mm, the maximum error is less than 21.4 mm, and the motion error in occluded environments is suppressed. The proposed fusion scheme is able to satisfy the localization accuracy requirements for efficient and coordinated motion of autonomous mobile robots.

Numerical Simulation on Wind Speed Amplification of High-Rise Buildings with Openings

To explore the influence of openings on wind loads and wind speeds in high-rise buildings, the wind flow around three-dimensional (3D) square cylinders with a breadth/height aspect ratio of 1:6 was numerically simulated using the large eddy simulation (LES) method via the Fluent 15.0 platform. The opening measures in the X-direction, Y-direction and both directions were all taken into consideration. Firstly, the inflow turbulence synthesis method and parameter settings for LES were verified by comparing the simulation results of standard square cylinders with those of wind tunnel experiments, and the optimal boundary conditions were determined. Then, the wind speed was extracted and compared with the mean wind speed of incoming flow at the same height to analyze the influence of different opening measures on the wind speed of incoming flow by setting monitoring points in the open holes. Finally, the mechanism underlying the effect of the opening form on wind loads and wind speeds was analyzed from the perspective of time-averaged and transient flow field. The results show that the X-direction openings affect the magnitude and distribution of the surface wind pressures by changing the flow separation and flow reattachment. The narrow tube effect can significantly increase the wind speed, while the Y-direction openings have no obvious improvement effect on the surface wind pressures of the structure. The wind speeds in the open holes are greatly reduced due to the shielding effect, and the wind pressures are also reduced for the Y-direction openings. In the X-direction opening holes, the wind speed at the monitoring point increases, while it decreases in the crosswind open holes. In general, the measure of openings in the X-direction can greatly improve the wind load of the structure compared to openings in the Y-direction, and it can provide a good reference for wind power generation in high-rise buildings.

Estimating inter-satellite link Ka-band antenna phase center offsets to improve BDS-3 satellite orbit determination

Satellite antenna phase center offset (PCO) correction is essential not noly for L-band ground-tracking GNSS high-precision data processing, but also for Ka-band inter-satellite link (ISL) observations. The Ka-band ISL and L-band satellite-ground observations of 90 days from 25 November 2020 to 23 February 2021 are used for the Ka-band PCO estimation and precise orbit determination (POD) validation for BDS-3 satellites. The results show that the standard deviations of the estimated Ka-band PCOs for 29 BDS-3 satellites are 1.73, 2.63 and 3.58 cm in the X, Y and Z components, respectively. The accuracy of the Ka-band PCO estimates for medium Earth orbit satellites (MEO) is better than those of inclined geosynchronous orbit (IGSO) and geostationary Earth orbit (GEO) satellites due to a better observation geometry. The POD validation results indicate that using the estimated Ka-band PCOs can improve the ISL-based orbit determination performance. Using Ka-band ISL and L-band satellite-ground observations with 40 global stations for combined POD, the orbit overlap comparison shows that the average three-dimensional (3D) root mean square (RMS) error for 29 BDS-3 satellites is decreased from 12.6 to 6.6 cm with a reduction of 47.6%, and satellite laser ranging (SLR) validation for 4 BDS-3 satellites shows an accuracy improvement from 6 to 5 cm in RMS. When using ISL and only 7 regional ground stations are used, the average 3D RMS of orbit overlap errors is decreased from 15.9 to 10.9 cm with a reduction of 31.6%, and the RMS of SLR residuals for 4 BDS-3 satellites is decreased from 6.7 to 5.6 cm. For ISL-only POD, the average 3D RMS of orbit overlap errors is decreased from 18.0 to 12.4 cm with a reduction of 31.1%, and the RMS of SLR residuals for 4 BDS-3 satellites is decreased from 7.1 to 6.9 cm.

A Novel Optimal Robust Adaptive Scheme for Accurate GNSS RTK/INS Tightly Coupled Integration in Urban Environments

Modern navigation systems are inseparable from an integrated solution consisting of a global navigation satellite system (GNSS) and an inertial navigation system (INS) since they serve as an important cornerstone of national comprehensive positioning, navigation, and timing (PNT) technology and can provide position, velocity, and attitude information at higher accuracy and better reliability. A robust adaptive method utilizes the observation information of both systems to optimize the filtering system, overcoming the shortcomings of the Kalman filter (KF) in complex urban environments. We propose a novel robust adaptive scheme based on a multi-condition decision model suitable for tightly coupled real-time kinematic (RTK)/INS architecture, which can reasonably determine whether the filtering system performs robust estimation (TCRKF) or adaptive filtering (TCAKF), improving the robust estimation method of two factors considering ambiguity variance for RTK-related observations. The performance of the proposed robust adaptive algorithm was evaluated through two sets of real vehicle tests. Compared with the TCAKF and TCRKF algorithms, the new robust adaptive scheme improves the average three-dimensional (3D) position root mean square (RMS) by 31% and 18.88%, respectively. It provides better accuracy and reliability for position, velocity, and attitude simultaneously.

Augmented Underwater Acoustic Navigation with Systematic Error Modeling Based on Seafloor Datum Network

Underwater acoustic navigation technology is an important approach to achieving high precision ocean navigation. One of the critical issues of the technology is to correct systematic errors, which are related to time delays and time-varying sound speed errors. In this study, we propose an augmented underwater acoustic navigation with systematic error model based on seafloor datum network. The proposed algorithm first selects data sets of piece-wise systematic error modeling by extracting the main periodic term of systematic errors based on the Fourier transform. Before that, the wavelet transform is used for denoising to better extract the main periodic term. Then the systematic error correction model is constructed by using the polynomial fitting method. After that, an augmented observation equation of underwater acoustic navigation with systematic error correction is constructed. Finally, an adaptive robust Kalman filter is developed for underwater acoustic navigation. The proposed algorithm is verified by an experiment in the South China Sea. The three-dimensional root mean square values of underwater acoustic navigation are 1.010 and 1.502 m in the operating range of 2.7 and 8.7 km. The results demonstrate that the proposed algorithm can efficiently reduce the influence of systematic error, thus improving underwater acoustic navigation accuracy.

A New Microporous Lanthanide Metal-Organic Framework with a Wide Range of pH Linear Response.

Lanthanide metal-organic frameworks (Ln-MOFs) have attracted extensive attention because of their structural adjustability and wide optical function applications. However, MOFs with a wide linear pH response and stable framework structures in acidic or alkaline solutions are rare to date. Here, we used 4,4',4″-s-triazine-2,4,6-triyltribenzoate (H3TATB) as an organic ligand, coordinated with lanthanide ions (Eu3+/Tb3+), and synthesized a new metal-organic framework material. The material has a porous three-dimensional square framework structure and emits bright red or green fluorescence under 365 nm UV light. The carboxyl group of the ligand is prone to protonation in an acidic environment, and negatively charged OH- and ligand (TATB3-) have a competitive effect in an alkaline environment, which could affect the coordination ability of ligand. The luminescence degree of the framework decreases with the increase in the degree of acid and base. In particular, such fluorescence changes have a wide linear response (pH = 0-14), which can be used as a potential fluorescence sensing material for pH detection.

Finite element framework for modeling conducto-radiative transfers within heterogeneous media at both discrete and continuous scales

The paper compares three distinct conducto-radiative models that can be used for modeling heat transfer at high temperature in view of being integrated within a topology optimization process. Finite elements are extensively used. Non-linearities are handled using a fixed-point method coupled with a Newton–Raphson linearization method. A three-dimensional square lattice is sandwiched between a hot and a cold plate. The discrete mesoscopic scale is the reference model. At all conduction-to-radiation regimes, and even when radiation predominates, it appears that the continuous-scale approach, which has been set-up thanks to proper homogenization laws, gives satisfactory results, which is not the case for the Rosseland approximation model. The homogenized continuous-scale model appears to be a good candidate for being used in the future in topology optimization problems.

Metastability of Ising and Potts Models Without External Fields in Large Volumes at Low Temperatures

In this article, we investigate the energy landscape and metastable behavior of Ising and Potts models on two-dimensional square or hexagonal lattices in the low-temperature regime, especially in the absence of an external magnetic field. The energy landscape of these models without an external field is known to have a very large and complex saddle structure between the ground states. In the small-volume regime where the lattice is finite and fixed, the aforementioned complicated saddle structure has been successfully analyzed in Kim and Seo (Metastability of stochastic Ising and Potts models on lattices without external fields. arXiv: 2102.05565 , 2021) for two- or three-dimensional square lattices when the inverse temperature tends to infinity. In this article, we consider the large-volume regime where the size of the lattice grows to infinity. First, we establish an asymptotically sharp threshold such that the ground states are metastable if and only if the inverse temperature exceeds a threshold in a suitable sense. Then, we carry out a detailed analysis of the energy landscape and rigorously establish the Eyring–Kramers formula when the inverse temperature is sufficiently greater than the aforementioned sharp threshold. The proof relies on a detailed characterization of dead-ends appearing in the vicinity of optimal transitions between the ground states and on a combinatorial estimation of the number of configurations lying on a certain energy level.

Application of Three-Dimensional Direct Least Square Method for Ellipsoid Anisotropy Fitting Model of Highly Irregular Drill Hole Patterns

Ellipsoid or geometric anisotropy is a widely used method in geostatistical analysis to obtain variograms with different ranges in different directions (azimuth) and relatively similar sill variance. Ellipsoid anisotropy is indispensable in mining when a resource geologist intends to understand the spatial continuity of variables related to any geological controls of the mineralization. For example, when dealing with mineralization related to tabular deposits, a porphyritic deposit with an irregular drill hole pattern (fan drilling), three-dimensional ellipsoid anisotropy is quite challenging to model. We assume that the variables’ spatial continuity is isotropic, and we model it using a three-dimensional omnidirectional variogram. However, if the actual spatial continuity of the variables has a three-dimensional anisotropy, then assuming a three-dimensional omnidirectional variogram will generate imprecise resource estimations. This study presents a new practical three-dimensional ellipsoid model-fitting method using a three-dimensional direct least square method. We investigated a zinc (Zn) dataset from thousands of irregular drill hole patterns from a porphyritic system associated with skarn orebodies for the case study.

Numerical Simulation and Deep Neural Network Revealed Drag Reduction of Microstructured Three-Dimensional Square Cylinders at High Reynolds Numbers

Square cylinders are widely used in various fields. For example, they are common structures in fishways. The flow around square cylinders has been a common problem in various fields. However, reducing the flow drag of the square cylinder is a problem that remains unexplored. Many previous studies have reported the drag reduction of 2D square cylinders, which failed to reflect the drag of real structures. Also, some studies focus on the drag force of the inner wall of the square cylinder modified by the microstructure. Achieving drag reduction by microstructuring the surface of the 3D square cylinder is a challenging problem. This study applied a 3D numerical simulation and deep neural network to study the drag reduction performance of the square cylinder under different patch sizes. We studied the drag reduction performance of protrusion and pit-patched square cylinders and tried to find the rule between drag reduction performance and patch configuration. The results show that the square cylinder has better drag reduction performance in some cases. However, its drag reduction performance is greatly affected by the protrusion structure. Also, too large protrusions will increase the drag force of the structure. When the surface protrusion accounts for 10% of the total area of the square cylinder, the drag reduction performance is the best (22.1%). The pit patch structure demonstrated an insignificant drag reduction performance and even increased the drag in most cases. The DNN prediction model demonstrated the robustness of the numerical simulation data.

Performance of Multi-GNSS in the Asia-Pacific Region: Signal Quality, Broadcast Ephemeris and Precise Point Positioning (PPP)

Since BeiDou Navigation Satellite System (BDS) and Japan’s Quasi-Zenith Satellite System (QZSS) have more visible satellites in the Asia-Pacific region, and navigation satellites of Global Positioning System (GPS), Galileo satellite navigation system (Galileo), and GLONASS satellite navigation system (GLONASS) are uniformly distributed globally, the service level of multi-mode Global Navigation Satellite System (GNSS) in the Asia-Pacific region should represent the best service capability. Based on the observation data of 10 Multi-GNSS Experiment (MGEX) stations, broadcast ephemeris and precision ephemeris from 13 to 19 October 2021, this paper comprehensively evaluated the service capability of multi-GNSS in the Asia-Pacific region from three aspects of observation data quality, broadcast ephemeris performance, and precision positioning level. The results show that: (1) the carrier-to-noise-density ratio (C/N0) quality of the GPS and Galileo is the best, followed by BDS and GLONASS, and QZSS is the worst. GPS, BDS-2, GLONASS, and QZSS pseudorange multipath values range from 0 to 0.6 m, while Galileo system and BDS-3 pseudorange multipath values range from 0 to 0.8 m. (2) In terms of broadcast ephemeris accuracy, BDS-3 broadcast ephemeris has the best orbit, and the three-dimensional (3D) Root Mean Square (RMS) is 0.21 m; BDS-2 was the worst, with a 3D RMS of 1.99 m. The broadcast ephemeris orbits of GPS, Galileo, QZSS, and GLONASS have 3D RMS of 0.60 m, 0.62 m, 0.83 m, and 1.27 m, respectively. For broadcast ephemeris clock offset: Galileo has the best performance, 0.61 ns, GLONASS is the worst, standard deviation (STD) is 3.10 ns, GPS, QZSS, BDS-3 and BDS-2 are 0.65 ns, 0.75 ns, and 1.72 ns, respectively. For signal-in-space ranging errors (SISRE), the SISRE results of GPS and Galileo systems are the best, fluctuating in the range of 0 m–2 m, followed by QZSS, BDS-3, Galileo, and BDS-2. (3) GPS, BDS, GLONASS, Galileo, GPS/QZSS, and BDS/QZSS were used for positioning experiments. In static PPP, the convergence time and positioning accuracy of GPS show the best performance. The positioning accuracy of GPS/QZSS and BDS/QZSS is improved compared with that of GPS and BDS. In terms of kinematic PPP, the convergence time and positioning accuracy of GPS/QZSS and BDS/QZSS are improved compared with that of GPS and BDS. In addition to GLONASS and Galileo systems, the other combinations outperformed 3 cm, 3 cm, and 5 cm in the east, north, and up directions.

Multi-objective Heat Sink Optimization by Using Taguchi Method

Abstract: Nowadays, with the rapid growth in electronic devices, compact and efficient heat sinks are required in day-to-day life. That’s why it's need to be use optimized heat sinks. The excess heat generated causes damage in different parts also generates major problems in the system. So, in this work three-dimensional square channel of copper material is used to study heat transfer coefficient and pressure drop. The comparative numerical analysis of thermal management system different parameter like coolant fluid, inlet velocity of fluid, shape of obstacles, aspect ratio of obstacles and number of obstacles is presented in this paper. Analysis and optimization of the heat sink are done by three different methods i.e., experimental, analytical, and simulation. In this work analytical and simulation method is used for the optimization of a heat sink. There are many software’s are available for analysis and optimization, by using the “COMSOL Multi-physics software” we optimize multi objectives heat sink. After analytical and numerical analysis, to optimize best result Taguchi method is preferred, for that MINITAB software is used. Keywords: Heat transfer coefficient, pressure drop, micro heat sink, Taguchi method, Analysis, optimization, COMSOL Multiphysics software, MINITAB software.

Numerical Modeling and Experimental Study on the Material Removal Process Using Ultrasonic Vibration-Assisted Abrasive Water Jet

Currently, micro-abrasive water jet machining has the problem of insufficient processing capacity in the central area. To assist with improving the processing efficiency, ultrasonic vibration is introduced. First, based on the computational fluid dynamics method, the mathematical model of the three-dimensional shape prediction of micro-holes is established using a mixed model, standard k-ε model, discrete phase model, and dynamic mesh model. The effects of the ultrasonic vibration on the static pressure, jet velocity field, abrasive particle motion state, and material erosion rate in the stagnation zone are studied. Then the accuracy of the prediction model is verified by comparing the two-dimensional section of the experimental data and the simulated data and calculating the three-dimensional mean square deviation. The established prediction model is used to further analyze the optimal frequency of the ultrasonic vibration and the specific influence of the optimal amplitude on the machining effect in micro-abrasive water jet machining. The above research results have profound guiding significance for determining how to use ultrasonic vibration in micro-abrasive water jet machining.