Lunar explorations have provided us with information about its abundant resources that can be utilized in orbiting-resource depots as lunar-derived commodities. To reduce the energy requirements of a launcher to send these commodities from the lunar surface to the space depots, this paper explores the application of the electromagnetic acceleration principle and provides an assessment of the actual technical characteristics of the launcher’s installation to ensure the acceleration of a payload with a mass of 1,500 kg to a speed of 2,200 m/s (circumlunar orbit speed). To fulfill a lightweight (fewer materials and less energy) support structure for the electromagnetic launcher with strength requirements, the tensegrity structure minimum mass principle without global buckling has been developed and applied to support the electromagnetic acceleration device. Therefore, this paper proposes and develops a minimal mass electromagnetic tensegrity lunar launcher. We first demonstrate the mechanics of launcher and payload, how a payload can be accelerated to a specific velocity, and how a payload carrier can be recycled for another launch. Then, a detailed discussion on the lunar launch system, procedures of propulsion, the required mass, and energy of the launch barrel are given. The governing equations of tensegrity minimal mass tensegrity design algorithm with gravity and without global buckling. Finally, a case study is conducted to show a feasible structure design, the required mass, and energy. The principles developed in this paper are also applicable to the rocket launch system, space elevator, space train transportation, interstellar payload package delivery, etc.

In studies on complex network systems using graph theory, eigen-analysis is typically performed on an undirected graph model of the network. However, when analyzing cascading failures in a power system, the interactions among failures suggest the need for a directed graph beyond the topology of the power system to model directions of failure propagation. To accurately quantify failure interactions for effective mitigation strategies, this paper proposes a stochastic interaction graph model and associated eigen-analysis. Different types of modes on failure propagations are defined and characterized by the eigenvalues of a stochastic interaction matrix, whose absolute values are unity, zero, or in between. Finding and interpreting these modes helps identify the probable patterns of failure propagation, either local or widespread, and the participating components based on eigenvectors. Then, by lowering the failure probabilities of critical components highly participating in a mode of widespread failures, cascading can be mitigated. The validity of the proposed stochastic interaction graph model, eigen-analysis and the resulting mitigation strategies is demonstrated using simulated cascading failure data on an NPCC 140-bus system.

This paper proposes a novel synchronous frequency estimation method by leveraging a modified Matrix Pencil-based (MMP-based) phasor estimation method. Specifically, the MMP-based phasor estimation can extract two phasors from two consecutive time windows given an initial guess of the synchronous frequency. The ratio of these two phasors can be used to provide an initial estimate of the synchronous frequency. It’s observed that the error between the estimated frequency and the initial guess takes a minimum if the initial guess equals the true synchronous frequency. Additional refinement is introduced to make sure that this error function only has one minimum such that the synchronous frequency can be uniquely estimated by using this error function. We highlight the capability of the proposed method in estimating synchronous frequencies of signals with integer and non-integer harmonics, decaying-DC components, and low-frequency oscillation.

As the integration of inverter-based resources (IBRs) increases in electric power systems, new dynamic risks such as subsynchronous oscillations and nuisance tripping are emerging. Interconnection studies become crucial for reliable operation and planning. This paper proposes a model reduction methodology to significantly reduce the size of a given large-scale power grid dynamic model while retaining essential characteristics such as the load and generation in each area, tie-line flows among areas, short circuit current (SCC) at pre-specified points of interconnection (POIs), and frequency response. The reduced model can facilitate efficient dynamic simulation studies of IBRs as well as the additional network required for the integration such as high voltage direct current (HVDC) transmission systems. To retain the transient frequency response characteristics of the given large-scale system, a distance metric is proposed to quantify the difference in the response between the full system and the reduced system, and an optimization problem is formulated to identify the best values for pre-selected dynamic parameters of the reduced system leading to a minimum difference in response. A 2000-bus synthetic grid on the footprint of Texas is tested to show the effectiveness of the proposed model reduction method. The PSS/E RAW and DYR files of the reduced model are made free and publicly available on GitHub.

Automatic dynamic balancer (ADB) is a passive ball-bearing type of vibration control device and has been applied successfully on some rotating machineries, i.e., hand-held machine tools and optical disk drives. Recently, an enhanced automatic dynamic balancer (EADB) has been developed to extend the capability of the ADB and to achieve a perfect-balancing condition in a wider rotor speed operation range. However, the EADB cannot be applied directly to the imbalance vibration suppression for asymmetric rotors since a multi-frequency whirling limit cycle in the asymmetrically supported rotor/ADB systems prevents the assumed solution of a single-frequency whirling limit cycle for the symmetric supported rotor/ADB systems. To address the aforementioned limitation, this paper proposes an imbalance vibration suppression method for asymmetric rotors via an EADB, which can achieve rotor perfect balancing condition in a wider operation range. The non-autonomous equations of motion for an asymmetrically supported planar rotor with an EADB system is established via Lagrange's method. The perfect-balancing equilibrium of the system is solved analytically, and the multi-frequency whirling limit cycle is obtained via a multi-tone harmonic balance method whose tones are predetermined by the matrix pencil method. To destabilize the multi-frequency whirling limit cycle and to guarantee the stable perfect balancing conditions for an asymmetric rotor with an EADB, a numerical continuation method is adopted to design parameters for the EADB. The stability analysis of the perfect-balancing equilibrium and the multi-frequency whirling limit cycle are conducted by Floquet theory. The enlarged unstable whirling limit cycle solution proves the effectiveness of the proposed method.

Among various power system disturbances, cascading failures are considered the most serious and extreme threats to grid operations, potentially leading to significant stability issues or even widespread power blackouts. Simulating power systems' behaviors during cascading failures is of great importance to comprehend how failures originate and propagate, as well as to develop effective preventive and mitigative control strategies. The intricate mechanism of cascading failures, characterized by multi-timescale dynamics, presents exceptional challenges for their simulations. This paper provides a comprehensive review of simulation models for cascading failures, providing a systematic categorization and a comparison of these models. The challenges and potential research directions for the future are also discussed.

In this paper, we demonstrate the distribution of real-valued power flow solutions and its application to the long-term voltage stability. It is the first time in power engineering we realize that even a small-scale IEEE standard power system can admit a humongous number of real-valued solutions for a single load and generation profile. For example, the IEEE 30-bus system can achieve 25686 many different real-valued solutions at a light loading condition. Furthermore, a mysterious class of false power flow solutions is reported and analyzed rigorously as legitimate numerical solutions. All solution sets investigated in this paper are posted online associated with this paper to support potential future applications [1]. Based on these extensive solved power flow solutions, we exhibit their occurrence patterns and distributions at different loading levels, and propose a long-term voltage stability margin index to quantify the long-term voltage stability of a given power flow condition. Numerical studies on a 5-bus system and a 57-bus system show the feasibility and effectiveness of the proposed index in assessing power system long-term voltage stability margin.

Data privacy is the main concern when using machine learning methods to solve dementia care problems. This paper makes the first attempt to deploy a human robot interaction model for dementia care in federated learning settings so that the privacy for persons with dementia (PwDs) can be retained. Numerical experiments of deploying the human-robot interaction model for cognitive therapy in the federated setting is conducted to show the feasibility of the federated learning setting. The simulated experiments in the case study shows the influence of different factors, i.e., client local training speed, the number of clients, homogenous and/or heterogenous patients.

The OPA (ORNL-PSERC-Alaska) model has been widely used in cascading failure simulations to predict likely and plausible sequences of cascading failures. This letter focuses on an algorithmic approach to enhance the OPA model whose main engine is based on quasi-steady-state models without considering the impact of collective transient dynamics of the entire system on the sequence of cascading failures. In particular, the enhanced OPA model incorporates dynamically induced cascading failures in fast time scales, which allows it to capture more realistic and detailed cascading scenarios. In this work, we outline the enhanced OPA model and provide simulation results to illustrate its feasibility with the realistic test network.

As a precursor for cardiac arrhythmias such as atrial and ventricular fibrillations, which could cause sudden cardiac death (SCD), cardiac alternans is essentially an unstable heart rhythm with alternating long and short action potential durations (APD) of cardiac myocytes that usually occurs under fast pacing conditions. In this paper, the constant TR control method based on global pseudo-electrocardiogram (ECG) is studied and compared with the local constant diastolic interval (DI) control method using a 2-dimensional (2-D) cellular automata model (CAM), aiming at preventing or eliminating cardiac alternans before arrhythmias. The results show that both the constant TR and constant DI control methods are effective in stabling the alternans to a smaller basic cycle length (BCL). Also, the efficacy of the two control approaches depends on the “decrease step” Δ in the downsweep protocol, and a smaller Δ could significantly improve their performance. Besides, in general, constant TR control is superior to constant DI control in alternans prevention when a relatively large Δ is adopted.

This paper proposes an energy function method that can evaluate power system dynamic behaviors, especially on whether synchronization can be achieved or not after line outages by quasi-dynamic simulation instead of time consuming dynamic simulations. To judge the synchronization of generation, potential energy and energy dissipation of the system are considered in the proposed energy function. By using the energy function, whether the equilibrium before line outages stays inside the basin of attraction of the equilibrium after line outages can be predicted. The proposed method is tested on the IEEE 39-bus system by dynamic simulations. It is shown that the proposed method can correctly predict the synchronization condition of generators.

This paper explores the effects of maneuvering and gust loads on the drive system and flight dynamic response of a single main rotor helicopter equipped with a two speed dual clutch transmission. The authors demonstrate that performing upshifts during certain maneuvers can significantly reduce the transmitted clutch frictional torques and the resulting clutch pack temperature rise during gear changes. For example, compared with an upshift in level flight, performing a 8° pitch-up maneuver reduced peak clutch frictional power dissipation by 63% (from 455 Hp down to 169 Hp) and reduced total upshift time by 37% (from 5 seconds down to 3 seconds). This results in an 83% reduction in total heat energy dissipated by the clutch during the upshift. Since the design of the clutch pack mass is directly proportional to the heat dissipation requirements, this new (Maneuver Assisted Shifting) MAS technique could enable significant weight savings and clutch wear reduction in helicopter two-speed transmissions.

Despite the elegant nature of the automatic balancing principle for passive imbalance vibration control, the co-existence of undesired whirling limit-cycles is a major impediment to the more widespread application of automatic dynamic balancing devices also called automatic dynamic balancer (ADB) in industry. To enlarge the region of stable perfect balancing and to eliminate whirling limit-cycles, we develop an innovative enhanced ADB system. This new idea harnesses the automatic balancing principle via moving permanent magnet balancer masses which are inductively coupled to a parallel resistor–inductor–capacitor (RLC) circuit. It is found that the circuit parameters can be adjusted properly to suppress the whirling limit-cycle to enlarge the perfect balancing region. We start from a Lagrangian description of the system and get nonlinear autonomous equations-of-motion. We then solve two dominant steady-state solutions for the enhanced ADB system. One solution is for the perfect balancing equilibrium points (EPs), which can be solved analytically. While the other solution is for the whirling limit-cycle which is solved via a harmonic balance method. The stability of these solutions is then evaluated through eigenvalue analysis and Floquet theory. The newly involved electrical parameters, such as coupling coefficient, equivalent capacitance, and equivalent resistance, are designed via an arc-length continuation method to destabilize the limit-cycle solutions to then guarantee stable rotor balancing.

The frequency-amplitude (F-A) curve has been proposed to characterize the electromechanical oscillation frequency of a single-machine-infinite-bus (SMIB) system considering nonlinearity of the swing equation. For a multi-machine system, the F-A curve regarding one oscillation mode is a projection of the system trajectory between the stable equilibrium point and the stability boundary onto the F-A plane. This letter provides rigorous proofs of six general properties of the F-A curve.

This paper proposes a decoupling based direct method to analyze the post-contingency transient stability for a general multi-machine power system. A linear decoupling transformation is used to construct the same number of independent single machine infinite bus (SMIB) power systems as oscillation modes. Each SMIB system carries stability information regarding one oscillation mode of the original system at the equilibrium. Then, the transient energy function method is applied on all decoupled SMIB systems to calculate stability margins, the smallest of which indicates the stability margin of the original system. Case studies on an IEEE 9-bus power system and a WECC 179-bus power system demonstrate the validity of the proposed method.