Maglev trains are strongly nonlinear, open-loop unstable, and flexible track systems. Vehicle-guideway self-excited vibration, which occurs mainly due to the deflection of the flexible guideway, may take place when a train is levitated on the guideway, even if the train is stationary. In this research, maglev vehicle-guideway coupling vibration is studied by employing the Hopf bifurcation criterion

A study was conducted to compare the performance of three different ISRU production plants that extract metals and oxygen from regolith at the lunar South Pole. The processes selected were: (1) hydrogen reduction of ilmenite and carbonylation to produce low-carbon steels, (2) molten regolith electrolysis to produce ferrosilicon alloys, and (3) molten salt electrolysis, in particular the FFC-Cambridge

Journal of Guidance, Control, and Dynamics, Ahead of Print.

The intricate concept of inherent stabilization of a mono-wing aerial vehicle, as a Nonlinear Time-Periodic (NLTP) system is investigated in this research. Stability analysis has been performed based on the dynamic characteristics of the system by using the most appropriate approaches, including Floquet theory, averaging theory, and kinetic energy integration. To achieve stable flight performance,

Journal of Guidance, Control, and Dynamics, Ahead of Print.

Journal of Guidance, Control, and Dynamics, Ahead of Print.

Journal of Guidance, Control, and Dynamics, Ahead of Print.

Journal of Guidance, Control, and Dynamics, Ahead of Print.

The nanosatellite reorientation maneuver is one of the important elements of achieving the mission goal if it is required to ensure the transfer of the nanosatellite axes from the initial to the final attitude. This maneuver is used in the process of directing the sensitive axes of the onboard equipment of a nanosatellite according to a predetermined program. One of the features of the angular motion

Hypervelocity flows generated over a 25°/55° double-cone are numerically investigated, characterized by a complex shock wave/boundary layer interaction. Based on the low magnetic Reynolds number assumption, the coupled model are established for the thermochemical non-equilibrium flow field and the externally applied magnetic field. The aim of the study is on one hand to evaluate the high temperature

Journal of Guidance, Control, and Dynamics, Ahead of Print.

Journal of Guidance, Control, and Dynamics, Ahead of Print.

Journal of Guidance, Control, and Dynamics, Ahead of Print.

Higher-order methods such as state transition tensors (STTs) have shown promise for a variety of applications in astrodynamics, but can be limited in their use due to their potentially large computational and storage requirements. In this paper we present a method for approximating STTs by aligning the STTs with particularly unstable directions. This strategy allows us to isolate the most important

Vibration data from physical systems, such as civil structures and machinery, often carries important information about the dynamic characteristics, but streaming acquisition of higher-frequency vibration often accrue large volumes of data, resulting in data transmission and storage challenges. Compressive sensing (CS) is a relatively newly-developed technique for efficient data representation, capable

We present a method for designing and optimizing Earth-Mars cycler orbits for the Solar System Pony Express (SSPE) mission concept. The SSPE is aimed at augmenting the capabilities of the Deep Space Network (DSN) by enabling high latency and high bandwidth communications through the use of interplanetary data mules. The SSPE will leverage a network of smallsats, outfitted with optical laser communications

Understanding the formation of impact craters on planetary surfaces has fundamental importance in geology, impact dynamics, and planetary sciences. The finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method combines the advantages of smoothed particle hydrodynamics (SPH) and finite element method (FEM) in solving hypervelocity impact (HVI) problems. Employing FE-SPH adaptive method

Deciphering the genesis and evolution of the Martian polar caps can provide crucial understanding of Mars' climate system and will be a big step forward for comparative climatology of the terrestrial planets. The growing scientific interest for the exploration of Mars at high latitudes, together with the need of minimizing the resources onboard landers and rovers, motivates the need for an adequate

There is a growing realization on the part of lawmakers, policy experts and practitioners that cyber risks and threat vectors constitute a critical and strategic challenge for all outer space operations. Stakeholders' professional attention and resources are beginning to focus on measures for mitigating these risks and threats. Space-based activities depend on the reliable functionality of computer

Purely magnetic satellite attitude control is considered. Special reference motion is constructed which provides local controllability. The angular trajectory is found in the neighborhood of unstable gravity gradient torque equilibrium. Direct solution for the minimization of the quadratic cost function representing the deviation from the equilibrium is derived. Linear equality type constraint on the

Predictions of thermoacoustic instabilities in annular combustors are essential but difficult. Axial variations of flow and thermal parameters increase the cost of numerical simulations and restrict the application of analytical solutions. This work aims to find approximate analytical solutions for the acoustic field in annular ducts with linear gradients of axially non-uniform cross-sectional area

Multichannel signals collected by multiple sensors contain richer condition information of equipment than single-channel signals. However, such issues as simultaneous denoising, adaptive decomposition and synchronous extraction are still challenging for multichannel signals, which are beneficial to accurate fault diagnosis. Thus, a useful multichannel feature synchronous extraction tool is proposed

Markers with high-contrast patterns are commonly used to improve the accuracy of image intensity-based motion estimation techniques. It has been proven that the phase, which can be extracted by using quadrature pair filters, is more robust to light condition changes than the intensity of the image. However, the marker design for utilizing and stabilizing the phases using phase-based motion estimation

Extracting governing physics from data is a key challenge in many areas of science and technology. The existing techniques for equation discovery are mostly applicable to deterministic systems and require both input and state measurements. We here propose a novel data-driven framework for discovering nonlinear stochastic dynamical systems with Gaussian white noise. The proposed framework blends concepts

Dynamic health monitoring (DHM) and performance degradation assessment (PDA) is critical for mechanical bearings throughout their long in-service life. For this issue, it is currently rare to find a framework with interpretable and automatic approaches developed from pure signal processing techniques and statistical theories. Therefore, an integrated framework via key-spectrum entropy and statistical

A new hierarchical Bayesian framework (HBM) is proposed for identification of Gaussian processes or fields, which are usually used for simulating uncertainty in temporal variability of loads or spatial variability of material properties. An improved orthogonal series expansion (iOSE) is embedded into the proposed framework by simulating the Gaussian process or field through correlated Gaussian variables

This paper studies a novel guidance framework of the vehicle against a high-speed and maneuvering target based on deep reinforcement learning (DRL) considering the energy consumption, autopilot lag dynamics, and input saturation, which can effectively cope with the high flight-path angle error flight phase and various uncertainties. The guidance framework proposes an end-to-end mapping transformation

Achieving fast and efficient combustion is considered as the primary difficulty in overcoming the high-Mach-number scramjet. A novel injection strategy with coflows has been proposed to improve the combustion efficiency, however, the inherent dynamics that drives the partially-premixed combustion is still not very clear. Numerical simulation is adopted to investigate the supersonic partially-premixed

After a sufficient amount of use under certain conditions, parachutes wear out and can no longer be safely employed. A simple and effective indicator of the remaining life of a parachute is the number of times it has been used, surviving opening shock, canopy inflation, transient parachute dynamics, and low velocity flight to the ground. This paper documents a small electronic device that automatically

Hypervelocity impacts (HVIs) from orbital debris are an increasing threat to current and future missions in low Earth orbit, and spacecraft shielding vital for future space exploration efforts. A debris shield is a sacrificial plate that shatters an impactor into a cloud of particles, distributing the momentum of the impactor over a large area, thus preventing it from perforating the spacecraft. In

The finest fraction of the lunar regolith, namely the lunar dust, poses a challenge for hardware design and lunar operations. The Apollo missions experienced equipment malfunctions and failures due to dust interactions with hardware. In this work we focus on the problems related to the clogging of rigid body mechanisms. We explain the causes of the problem and propose a solution consisting of replacing

The trajectory planning of space robot for capturing space tumbling targets still faces challenging technical problems due to the moving targets, which requires the robot to precisely pinpoint the target in a reliable, safe way. Hard-capture strategy that only cares about the precise pinpoint of the final capturing states cannot ensure a reliable capture due to its lack of a thoughtful approaching

Abstract not available

In this work, a novel method of directly measuring the roll torque of low power Hall-effect thrusters is proposed. The measurement device uses an elastic pendulum with the thruster mounted on the same axis as the rotation axis of the pendulum, and the torque of the thruster is reflected in the rotation of the movement part and amplified by the pendulum arm with the measuring range of approximately

This paper investigates the modified design of a conventional transonic fan based on a new tandem fan concept with a partial-span rotor, which can significantly enhance the pressurization capacity and flow capacity of the fan's core. The design principles of essential geometric parameters are determined, and the advantages of the new concept are confirmed. The results reveal that the tandem rotor performs

Lunar environmental adaptability and gait control are significant for developing a walkable lunar lander (WLL). However, gait planning for the WLL is challenging due to the optimization process required for the stable margin sequence. To overcome this concern, this study develops a new Center of Gravity (COG) trajectory planning algorithm appropriate for a WLL that will enhance walking performance

This paper presents some initial results on the use of hyperspectral imaging technology and machine learning to characterise the surface composition of space objects and reconstruct their attitude motion. The paper provides a preliminary demonstration that hyperspectral and multispectral analysis of the light absorbed, emitted and reflected by space objects can be used to identify, with some degree

Nowadays, most studies on the dynamic properties of annular gaps focus only on the force characteristics due to translational motions, while the tilt and moment coefficients are less well studied. Therefore, there is hardly any reliable experimental data for the additional coefficients that can be used for validation purpose. To improve this, a test rig first presented by Kuhr (2022); Kuhr et al. (2022a)

Unmanned Aerial Vehicle (UAV)-based autonomous damage inspection has become a promising technique to replace certain human-performed inspections due to both safety and cost considerations. While current UAV-based damage inspection methods have been successful in minimizing the length of the flying path considering potential defect locations, the impact of flying path on the quality of structural health

Abstract not available

Rapidly and accurately identifying the tactical intention of an enemy aerial target is an important issue for combat decision making. To this end, a quick intention identification model based on hybrid neural network is established in this paper. With available feature sequential measurements of the enemy target as inputs of the model, possibilities of different intentions are calculated timely. To

The goal of this paper is to revise the Rossiter-Heller formula of cavity resonance frequencies for rectangular cavities in subsonic and supersonic flow conditions. Two modifications are proposed; the first one consists in using a second-order polynomial fit of literature experimental data for the non-dimensional time lag coefficient as a function of the cavity aspect ratio. The second modification

Variable geometry turbine (VGT) exists in turbocharged gas engines to solve the problems of insufficient low-speed torque and poor transient response. However, there is a performance penalty associated with the end-wall clearance required for the movement of the guide vanes. Aiming at suppressing the end-wall clearance leakage flow loss to improve turbine performance, a novel scheme of end-clearance

Dynamic mode decomposition (DMD) has emerged as a popular data-driven modeling approach to identifying spatio-temporal coherent structures in dynamical systems, owing to its strong relation with the Koopman operator. For dynamical systems with external forcing, the identified model should not only be suitable for a specific forcing function but should generally approximate the input–output behavior

This paper proposed a method to control the circumferential motion of the constraint boundary of the flexible inverted pendulum to achieve its fast stability. Firstly, the dynamic equation of the system is obtained by the beam theory. The displacement of the flexible inverted pendulum is used as the input to explore the relationship between the output of the constrained boundary and the displacement

Triboelectric-nano-generator (TENG) is able to produce a very small current and a large voltage compared to piezoelectric or electromagnetic generators. The large voltages from the TENGs are suitable for operating MEMS devices without external AC or DC generators. Producing micro-sized TENG using MEMS fabrication process enables integration of them with MEMS sensors and actuators. This combination

Abstract not available

The hydropower generation system is a typical complex nonlinear system with hybrid state responses. The interaction between the state responses of the system is affected closely by the coupling of hydraulic, mechanical, and electromagnetic factors and the frequent changes in working conditions during operation. However, the precise roles of the interaction relationship are unknown. Here, we show that

The magnetic shape memory alloy based actuator (MSMA-BA) is an indispensable component mechanism for high-precision positioning systems as it possesses the advantages of high precision, low energy consumption, and large stroke. However, hysteresis is an intrinsic property of MSMA material, which seriously affects the positioning accuracy of MSMA-BA. In this study, we propose a multi meta-model approach

In the long-term, the modal properties of Offshore Wind Turbines (OWT) exhibit significant variations due to constant changes in environmental and operational conditions. These variations have a substantial effect on the wind turbine loads and will lead, for instance, to large uncertainty in fatigue and useful life predictions. Due to the numerous sources of uncertainty, it is difficult to judge how

Shear horizontal (SH) waves are widely used in the non-destructive evaluation and structural health monitoring fields. Conventional periodic permanent magnet electromagnetic acoustic transducers (PPM EMAT) can generate a single SH wave mode, which propagates in both forward and backward directions. Generation in a single direction is usually preferred to ease signal interpretation and increase inspection

The motion accuracy of linear guideway is adversely affected by ball passage vibration (BPV) when rolling balls within carriage move in a loop. Reduced vibration amplitude can be realized by a carriage with crowning design by now. However, few dynamic models are availability for the BPV analysis when linear guideway is subjected to actual external load in five directions. In this paper, a nonlinear

We study here the local minima, maxima, and saddle points of the augmented potential on the surface of a small celestial body with application to comet (67P) Churyumov-Gerasimenko. The isolines of the augmented potential on this surface are determined, in particular, those corresponding to the saddle points. The results are applied to reveal the correlation between the structure of the areas of possible

In this investigation, the integrated attitude and landing control scheme for quadruped robots in asteroid landing mission scenario is discussed. Compared with the gravitational field environment of the Earth, the gravitational field near most asteroids has a smaller gravitational acceleration, a non-negligible horizontal acceleration component, and obvious uneven distribution characteristics. In this

Due to the high cost and long lifecycle of manned Mars exploration missions, in-situ resource utilization technology, including Mg/CO2 processes, has attracted increasing attention. At present, Mg/CO2 engines face the challenges of long ignition delay, serious carbon deposition, and low combustion efficiency. The root of these challenges lies in the Mg/CO2 combustion reaction. Therefore, based on an

A numerical study is carried out to investigate the mechanism and assess the parameters of a reverse jet in heat reduction of type IV shock/shock interactions. A hypersonic flow at a Mach number of 8 with a fixed 18.1-deg incident shock is considered. A type IV shock/shock interaction occurs in the front of the blunt leading edge. Compressed air is supersonically injected into the freestream at various

The contradiction between air traffic capacity and demand constrains the development of the civil aviation industry. This paper proposes a Data-Driven Trajectory Optimization Framework for Terminal Maneuvering Area operations (DDTO-TMA) to enhance the capacity of Terminal Maneuvering Area (TMA). First, a Wasserstein-distance-based spectral clustering algorithm is applied to divide historical trajectories

Compressor surge is a typical unstable phenomenon generally resulting in violent aerodynamic oscillation in a compression system. Because of the hysteresis caused by the unsteady flow behaviors during the surge cycle in a compression system, some aerodynamic properties show clear distinctions with altered streamwise positions. In order to obtain the transient surge characteristics accurately in the