Arrival Velocity Research Articles

Solar Sail Optimal Performance in Heliocentric Nodal Flyby Missions

Solar sails are propellantless propulsion systems that extract momentum from solar radiation pressure. They consist of a large ultrathin membrane, typically aluminized, that reflects incident photons from the Sun to generate thrust for space navigation. The purpose of this study is to investigate the optimal performance of a solar sail-based spacecraft in performing two-dimensional heliocentric transfers to inertial points on the ecliptic that lie within an assigned annular region centered in the Sun. Similar to ESA’s Comet Interceptor mission, this type of transfer concept could prove useful for intercepting a potential celestial body, such as a long-period comet, that is passing close to Earth’s orbit. Specifically, it is assumed that the solar sail transfer occurs entirely in the ecliptic plane and, in analogy with recent studies, the flyby points explored are between 0.85au and 1.35au from the Sun. The heliocentric dynamics of the solar sail is described using the classical two-body model, assuming the spacecraft starts from Earth orbit (assumed circular), and an ideal force model to express the sail thrust vector. Finally, no constraint is imposed on the arrival velocity at flyby. Numerical simulation results show that solar sails are an attractive option to realize these specific heliocentric transfers.

The interplay of casing material and detonation wave shock parameters in steel witness plate dent formation

This study uses both experimentation and simulation to investigate how varying casing material around cylindrical Composition-B charges affects witness plate response and diagnoses the cause of the differences in the dents produced. Through experimentation, it was found that consistent dents are produced from repeated tests and characteristically different dents are produced by charges with different casing material. Charges cased in viscoelastic materials produced shallower dents than those without casing. Simulation was validated against the experimental dents, and the detonation wave parameters were measured for 25 differently cased charges: 15 metals and 10 polymers. Regression fit relationships were derived relating dent parameters to casing density, casing impedance, casing tensile strength, detonation pressure, detonation velocity, impulse, and time of arrival. Specifically, it was found that the dent volume was negatively correlated with the detonation velocity and the impulse of the detonation wave was negatively correlated with dent depths across the charge. The density of the casing material was shown to be linked to the width of the witness dents. Additional dent tests were simulated for trinitrotoluene (TNT) charges cased in a single polymer and a single metal. The relationships derived for Composition-B were adjusted to fit TNT using TNT equivalency and calculated the measured detonation wave values to within 10% accuracy. Finally, it was concluded that the measurable distinctions observed in the witness dents were not a result of the casing material itself, but of the changes in the detonation wave caused by its interaction with the casing material.

Optimizing lightning location accuracy: A study of propagation velocity and time of arrival in long-range lightning location algorithms

The propagation velocity (v) and time of arrival (Ta) are the primary factors affecting long-range lightning location. In this paper, we have enhanced the Very Low Frequency Long-range Lightning Location Network (VLF-LLN) in China in terms of both pulse pairing methods and location algorithms. Then, the algorithm utilized in the VLF-LLN, and four other long-range lightning location algorithms were compared using lightning strike accidents, simulated lightning strike, and other lightning data as the reference values. Building on this foundation, the discussion centers on the effect of v and Ta on location accuracy, with the results showing that an appropriate Ta yields a more significant improvement in location accuracy compared to v. VLF-LLN uses the peak time of the ground wave as Ta avoids the significant lag caused by sky wave, which is present in other algorithms, and therefore has the best location accuracy with a median location accuracy of 1.81 km.

ANALYSIS OF FREQUENCY CONTENT AND STATISTICAL RELATIONSHIP AMONG EARTHQUAKE PARAMETERS OF SEISMIC DATA

The frequency content of the strong-motion seismic data collected from seismic stations by the Bangladesh Meteorological Department (BMD) using GL-S60/120 broadband seismometers of earthquakes in and around Bangladesh is examined. In addition, the statistical relationships among various earthquake parameters, such as the peak ground velocity (PGV), magnitude, epicentral distance, and time of arrival of p-and s-waves of the collected data, are analyzed. Approximate seismic wave velocities are also obtained. The Fourier and wavelet analysis results reveal delicate differences in the frequency content of the p-and s-waves occurring during earthquakes. These results are compared to those generated from the STEAD dataset, which contains seismic waveforms collected in the U.S., France, and Greece regions. Regression analysis on the BMD data derives relationships among the aforementioned parameters. Collected data from some stations show perfect linear relationships among PGV and the travel time of seismic waves with magnitude and epicentral distance, whereas, in other stations, such relationships are not significant. Plausible explanations for these disparities are provided along with similar regression analysis using the STEAD data. The findings are useful for earthquake early-warning systems, geology research, seismic risk zone delineation, and seismic hazard forecasts.

End-to-end trajectory concept for close exploration of Saturn’s Inner Large Moons

We present a trajectory concept for a small mission to the four inner large satellites of Saturn. Leveraging the high efficiency of electric propulsion, the concept enables orbit insertion around each of the moons, for arbitrarily long close observation periods. The mission starts with a EVVES interplanetary segment, where a combination of multiple gravity assists and deep space low thrust enables reduced relative arrival velocity at Saturn, followed by an unpowered capture via a sequence of resonant flybys with Titan. The transfers between moons use a low-thrust control law that connects unstable and stable branches of the invariant manifolds of planar Lyapunov orbits from the circular restricted three-body problem of each moon and Saturn. The exploration of the moons relies on homoclinic and heteroclinic connections of the Lyapunov orbits around the L1 and L2 equilibrium points. These science orbits can be extended for arbitrary lengths of time with negligible propellant usage. The strategy enables a comprehensive scientific exploration of the Inner Large Moons, located deeply inside the gravitational well of Saturn, which is unfeasible with conventional impulsive maneuvers due to excessive fuel consumption.

Evaluation of heterogeneity effect on CO2 transport in regularly distributed and natural clast-matrix conglomerate cores

A series of numerical simulations were performed to investigate the heterogeneity effect resulting from spatial distribution of clast-matrix in conglomerates on CO2 migration under the reservoir conditions. Natural conglomerate cores drilled from geological CO2 storage site in South Korea as well as constructed cores comprising regularly distributed clast-matrix were numerically analyzed. Throughout the study, CO2 distribution, velocity of the CO2 front, breakthrough curves (BTCs), differential pressure (ΔP), gravity number (Ngv), and capillary number (Nc) were assessed to highlight the heterogeneity effect. In the regularly distributed clast-matrix cores, the CO2 plume with the corrugated shape of the front migrated faster than the matrix-only core. Even though the clast ratio was changed more than 10 %, there was not much difference in the arrival velocity of the CO2 plume (∼2.0×10−4 m/min). Nevertheless, there was a correlation between the clast ratio and the arrival velocity, clearly shown in the L-5 core having alternating layers of matrix and clasts. At natural conglomerate cores (JC-1 and JC-2), the migration pattern of the CO2 plume significantly differed. However, the clast-matrix ratio and the arrival velocity were strongly correlated with a large variation in the arrival velocity (∼2.6×10−3 m/min) despite the small change of the clast-matrix ratio. The variance of the cumulative arrival velocity was correlated with the clast-matrix ratio and the irregularity of the BTCs, which implied that the instability in the frontal displacement of the CO2 plume became greater where the clast ratio increased more. The ΔP was significantly affected by the distribution of clasts and matrix; ΔP increased as the CO2 passed narrow or heterogeneous pathways enclosed by the clasts and decreased as CO2 passed wide or diverging pathways. Interestingly, the highest ΔP was shown in the cores having the smallest clast ratio, implied that the heterogeneous distribution of clast-matrix could influence a degree of overpressure generation. The lowest Ngv below 1 and highest Ngv appear in JC-2 where the total clast ratio is more than 50 % and in H-1 consisting of matrix-only, respectively. The obtained ranges of Nc show that all the models are under capillary-dominated flow conditions relevant for CO2 sequestration. The magnitude of both Ngv and Nc correlates to the total clast ratio.

Estimating Average Velocities of Particle Arrival Using the Time Duration of the Current Signal in Stochastic Blocking Electrochemistry.

In stochastic blocking electrochemistry, microparticles generate individual current steps when they adsorb on a microelectrode and decrease the current and flux of a redox mediator reacting at the surface. The amplitude of the current step informs on particle size and landing locus, while step frequency correlates with particle transport. Here, we report a new method to estimate the average arrival velocities of single rod-shaped bacteria (bacilli). The method relies on simulating the nearby threshold distance from the surface where the bacillus no longer perturbs mediator flux and the current step approaches zero. We estimated the average velocities of bacillus arrival by dividing the threshold distance over the current step duration, a parameter that here we detect for the first time and increases with bacillus length. By comparing diffusional fluctuations to bacillus average velocity, we estimated diffusion and migration contributions as a function of bacterium size. Average arrival velocities increase with bacillus length at the same time as migration intensifies and diffusion weakens. Our analysis is universal and more effective in determining transport mode contributions than the present approach of comparing theoretical and experimental step frequencies. Uncertainty in landing locus is inconsequential because the step duration used to calculate the average arrival speed already contains such information and knowing bacillus electrophoretic mobility or ζ-potential is not needed. Additionally, by simulating and assigning edge landings to the most repeated values of current steps in a recording, we obtain bacilli lengths and widths similar to scanning electron microscopy, from which we infer landing orientation.

An SISL-Based 24-GHz FMCW Radar With Self-Packaged Six-Port Butler Matrix Receiver

A 24-GHz frequency modulated continuous wave (FMCW) radar system with self-packaged six-port Butler matrix receiver using substrate integrated suspended line (SISL) platform is proposed in this article. Since all active and passive components are integrated on the SISL platform using the standard printed circuit board (PCB) process, the proposed system is highly integrated with low cost. The system is composed of a transmitting (TX) antenna, a Butler matrix with a receiving (RX) antenna array, a single pole four throw (SP4T) switch, a low noise amplifier (LNA), and a six-port receiver. The Butler matrix and SP4T switch are implemented for beam scanning, which has the advantages of low loss and compact size. The SISL-based six-port receiver is designed for quadrature downconversion. The supporting digital signal processing algorithms are also proposed for the calculation and display of multiple targets information. The radar system has shown excellent performance in the measurement of indoor environment, including range, velocity, and direction of arrival (DOA). The proposed radar provides a new solution for a transceiver system.

Parameter Distributions for the Drag‐Based Modeling of CME Propagation

AbstractIn recent years, ensemble modeling has been widely employed in space weather to estimate uncertainties in forecasts. We here focus on the ensemble modeling of Coronal Mass Ejections (CME) arrival times and arrival velocities using a drag‐based model, which is well‐suited for this purpose due to its simplicity and low computational cost. Although ensemble techniques have previously been applied to the drag‐based model, it is still not clear how to best determine distributions for its input parameters, namely the drag parameter and the solar wind speed. The aim of this work is to evaluate statistical distributions for these model parameters starting from a list of past CME‐ICME events. We employ LASCO coronagraph observations to measure initial CME position and speed, and in situ data to associate them with an arrival date and arrival speed. For each event we ran a statistical procedure to invert the model equations, producing parameters distributions as output. Our results indicate that the distributions employed in previous works were appropriately selected, even though they were based on restricted samples and heuristic considerations. On the other hand, possible refinements to the current method are also identified, such as the dependence of the drag parameter distribution on the CME being accelerated or decelerated by the solar wind, which deserve further investigation.

Integral Field Spectroscopy with the Solar Gravitational Lens

The prospect of combining integral field spectroscopy with the solar gravitational lens (SGL) to spectrally and spatially resolve the surfaces and atmospheres of extrasolar planets is investigated. The properties of hyperbolic orbits visiting the focal region of the SGL are calculated analytically, demonstrating trade-offs between departure velocity and time of arrival, as well as gravity assist maneuvers and heliocentric angular velocity. Numerical integration of the solar barycentric motion demonstrates that navigational acceleration of is needed to obtain and maintain alignment. Obtaining target ephemerides of sufficient precision is an open problem. The optical properties of an oblate gravitational lens are reviewed, including calculations of the magnification and the point-spread function that forms inside a telescope. Image formation for extended, incoherent sources is discussed when the projected image is smaller than, approximately equal to, and larger than the critical caustic. Sources of contamination that limit observational signal-to-noise ratio (S/N) are considered in detail, including the Sun, the solar corona, the host star, and potential background objects. A noise mitigation strategy of spectrally and spatially separating the light using integral field spectroscopy is emphasized. A pseudo-inverse-based image reconstruction scheme demonstrates that direct reconstruction of an Earth-like source from single measurements of the Einstein ring is possible when the critical caustic and observed S/N are sufficiently large. In this arrangement, a mission would not require multiple telescopes or navigational symmetry breaking, enabling continuous monitoring of the atmospheric composition and dynamics on other planets.

Radar-Based Robust People Tracking and Consumer Applications

Robust people tracking in an indoor or outdoor environment is an important feature for fitness applications, surveillance systems for security, and assisted living for the elderly. Camera-based systems offer the state of the art approach but raise privacy concerns and consume a significant amount of power for the sensor and the processing. On the other hand, modern millimeter-wave Radar sensors provide a low-cost and low-power alternative with very good resolution in range, radial velocity and angle of arrival. In this work, we use two popular algorithms, for tracking people using Radar, and compare them with our novel method. We show that our method is robust in certain corner cases and is suitable for scenarios with many users in close proximity. In addition, we present two consumer applications that are possible with a Radar system, multi-user macro gesture recognition and hand tracking. We believe that the combination of above methods will open new gateways for consumer applications.

Computation of range velocity and direction of arrival in FMCW radar

Frequency Modulated Continuous Wave (FMCW) radar is widely used in applications to find the range, velocity and angle of the target objects from the radar. The transmitted signal is in the form of chirp where the frequency increases linearly with time. After hitting the target object, the signal is received by the receiver antenna which contains the information about the range, velocity and angle of target object. The information is extracted using different signal processing algorithms like Fast Fourier Transform algorithm (FFT) and Multiple Signal Classification (MUSIC) algorithm. When Fast Fourier Transform (FFT) algorithm is used to estimate the Direction of Arrival (DOA), the angular resolution is less, as it is dependent on the number of points in FFT and number of receivers used. As Additive White Gaussian Noise (AWGN) gets added to the received signal, and in cases of low Signal to Noise Ratio (SNR), the angle estimation using FFT algorithm becomes difficult as many peaks were obtained in spectrum due to addition of noise. MUSIC algorithm uses Eigen value decomposition method and denoising occurs by suppressing the peaks due to noise. The angular resolution is also increased and this algorithm works good in noisy environment. The simulation was carried out in MATLAB and the results were also verified using the same.

Research on Ultrasonic Testing with Wavelet Packet Analysis for Shotcrete

Shotcrete structures are widely used in tunnel engineering. Quality inspection is difficult, and the traditional ultrasonic testing (UT) method based on first arrival velocity has limitations. In this paper, shotcrete-rock specimens were made in a laboratory and evaluated using UT. Wavelet packet decomposition is introduced for better frequency analysis of the condition evaluation. Two methods, including calculation of the energy eigenvalues and machine learning, are used to describe the contact quality at the interface between the shotcrete and rock. The relative energy eigenvalue increases with the gradual reduction of contact quality, which can become a quantitative index of the contact quality. Machine learning performed well in the rapid recognition of discontinuities in the multiple-classification models. Both methods based on wavelet packet decomposition achieved good results in identifying discontinuities and have the potential to be used in practical engineering applications.

Joint Doppler Frequency and Direction of Arrival Estimation for TDM MIMO Automotive Radars

This paper considers a novel approach to joint estimation of the velocity (or Doppler frequency) and Direction of Arrival (DOA) of targets by time division multiplexing (TDM) multiple-input multiple-output (MIMO) radars in automotive applications. The TDM MIMO radars create orthogonal probing signals (in time domain) by allocating a transmitter to a separate time slot. In this paper, we consider a standard TDM MIMO radar to be the one where transmitters are activated sequentially according to their natural spatial order. The drawback of the standard TDM MIMO approach is the coupling of velocity and DOA information of the targets. The coupling reduces the unambiguous estimation interval of the Doppler frequencies of the targets by the number of transmit antennas being multiplexed. In this paper, we propose a novel cost function to jointly estimate both the Doppler frequency and the DOA of each target by reinstating the reduced unambiguous Doppler spectrum interval. Our approach is generally applicable to solve the Doppler ambiguity problems associated with any colocated standard TDM MIMO radar. To confirm this, we present the simulation results that evaluate the performances of two widely deployed TDM MIMO radar antenna configurations: non-overlapped and overlapped arrays. Moreover, we derive the analytical expressions to study the statistical performance of the proposed method. The simulation examples are presented to verify the performance of the proposed method as well as the accuracy of the analytical expressions.

Determination of First Arrival Wave Type of Microseismic Signals and Approach to Wave Velocity Correction

Given the complex environment experienced in working mines, the vibration waves produced by processes such as rock fracture in deep formations usually show interference effects when monitored due to other signals, the so-called “clutter” in the signal, which are interfered with the clutter. At the same time, owing to the influence of system noise, the first arrival time and the arrival time difference values of the signals obtained cannot easily be determined accurately. The propagation model for the microseismic signals experienced and the discrimination method used to determine the first arrival wave type can be established using knowledge of the spatial geometry between the sensors used and the seismic source. Thus, the filtering of the actual from the abnormal wave signals is possible. Using the theory of signal cross-correlation in this work, a correction method for the arrival velocity of the first microseismic signal has been proposed and evaluated. By calculating the cross-correlation coefficient of the same source vibration signal and finding the position that corresponds to the maximum value of the cross-correlation coefficient, the arrival time difference between the signals seen in the two channels is obtained. Thus, the key conclusions can be drawn from the experiments carried out: when the signal-to-noise ratio of the original signal is low, the time difference can still be determined with high accuracy. Further, a wave velocity correction criterion has also been proposed, where the velocity correction of the S wave or the R wave can be realized by combining the spatial coordinate information on the blasting point and an algorithm representing the signal cross-correlation to arrival time difference is used.

Multiple Target Localization Using Wideband Echo Chirp Signals

This work proposes a unique technique for wideband chirp signals-based detection and estimate of the range, velocity, and direction of arrival (DOA) of numerous far-field objects. A wide region is covered by the wideband signal that is created. The targets reflect them, and an echo signal is created. The range, radial velocity, as well as DOA of the echo signal are extracted to identify the objects. Using the LCT, the range, radial velocity, and DOA are determined. The main goals of the system under consideration are to transmit a wide band signal over an area, to detect targets nearby, to obtain an echo signal from a target that has been reflected, and to extract features from the echo signal, such as range, radial velocity, and DOA, in order to achieve superior performance metrics than previous ones.

Tracer tests to infer the drainage of the multiple porosity aquifer of Luxembourg Sandstone (Grand-Duchy of Luxembourg): implications for drinking water protection

The Luxembourg Sandstone is the main strategic aquifer of the Grand-Duchy of Luxembourg, providing one third of the total drinking water resource in the country. In the unconfined part, the aquifer discharges through more than 400 springs, which are used for supply. The long-lasting diffuse contamination by pesticides (more recently Metolachor ESA) has been previously simulated assuming the aquifer as an equivalent porous medium, and using environmental tracers and baseflow characteristics. A statistical analysis of the whole data set of artificial tracer tests made for this aquifer (112 injections involving 102 springs) emphasized the role of the main fissures (NE–SW) for preferential groundwater flow and the importance of including them in a conceptual model involving a multiple-porosity aquifer. The results show that these fissures are influencing the whole flow system. The average peak velocity is 16 m/h and the average first arrival (maximum) velocity is 52 m/h (32 m/h for injection-well to spring traces alone), with a recorded maximum velocity of 350 m/h. The threats of infiltrating streams within catchments have also been characterized, suggesting the usefulness of tracer tests for optimizing protective measures. The main benefit of the study is the improvement in the ability to delineate safeguard zones accurately, according to more representative velocities and the strong anisotropy.

Liquid droplet imbibition into a thin coating layer: Direct pore-scale modeling and experimental observations

In order to control ink droplet movement into the printing-paper layer, a set of pore-scale two-phase flow simulations were performed. The high-resolution three-dimensional pore space of the paper was obtained using focused ion beam scanning electron microscopy (FIB-SEM). Solving Navier-Stokes equations yielded details about dynamic movement of a droplet into the layer. To evaluate simulation results, for the first time, confocal laser microscopy imaging technique was integrated into a FIB-SEM chamber. Doing so, high resolution imaging of the droplet penetration inside paper was conducted and computed volume of penetrated ink at final stage was compared to the imaged volume. The ink penetration and spreading extent showed a good agreement with simulation results. Therefore, the developed simulation case was further investigated to study impact of liquid contact angle, real ink properties, and droplet arrival velocity on paper surface on final print quality. A faster penetration into the paper coating was observed for smaller equilibrium contact angles; meanwhile, more radial wicking was observed. In case of velocity of impact, higher velocity caused creation of irregular shapes of the ink footprint on paper surface. In addition to that, higher velocity caused ink splash which consequently created satellite droplets and lowered the print quality. Comparing ink-like liquid (representing real ink liquid properties) with water, water moves faster than ink-like liquid into the paper. This is mainly due to the higher viscosity and lower surface tension of the ink-like liquid.

Trajectory Optimization and Replanning Framework for a Micro Air Vehicle in Cluttered Environments

In the present study, we propose a trajectory optimization and replanning algorithm for micro air vehicles (MAVs) in cluttered environments. To generate the path of an MAV in a cluttered environment, we first design an offline global path optimization algorithm. This algorithm generates a global trajectory for safe aerial delivery; this trajectory enables an MAV to avoid static obstacles marked in the navigation map and satisfies the MAV's initial and arrival velocities. The MAV's trajectory is replanned by exploiting dynamic movement primitives (DMPs) and a time adjustment algorithm to enable computationally efficient unknown obstacle avoidance in local path planning. To validate the applicability of the proposed algorithm, we compare simulation results with those obtained using an existing approach based on DMPs. Furthermore, an autonomous flight is demonstrated in an outdoor environment using a custom-made MAV driven by the proposed approach.

Combining arrival classification and velocity model building using expectation-maximization

Combining arrival classification and velocity model building using expectation-maximization