pwc-archive/papers-with-abstracts huggingface dataset:
Koopman-based control using sum-of-squares optimization: Improved stability guarantees and data efficiency
Authors: Robin Strässer, Julian Berberich, Frank Allgöwer
Date: 2024-11-06 00:00:00

In this paper, we propose a novel controller design approach for unknown nonlinear systems using the Koopman operator. In particular, we use the recently proposed stability- and certificate-oriented extended dynamic mode decomposition (SafEDMD) architecture to generate a data-driven bilinear surrogate model with certified error bounds. Then, by accounting for the obtained error bounds in a controller design based on the bilinear system, one can guarantee closed-loop stability for the true nonlinear system. While existing approaches over-approximate the bilinearity of the surrogate model, thus introducing conservatism and providing only local guarantees, we explicitly account for the bilinearity by using sum-of-squares (SOS) optimization in the controller design. More precisely, we parametrize a rational controller stabilizing the error-affected bilinear surrogate model and, consequently, the underlying nonlinear system. The resulting SOS optimization problem provides explicit data-driven controller design conditions for unknown nonlinear systems based on semidefinite programming. Our approach significantly reduces conservatism by establishing a larger region of attraction and improved data efficiency. The proposed method is evaluated using numerical examples, demonstrating its advantages over existing approaches.
Reachability analysis for piecewise affine systems with neural network-based controllers
Authors: Dieter Teichrib, Moritz Schulze Darup
Date: 2024-11-06 00:00:00

Neural networks (NN) have been successfully applied to approximate various types of complex control laws, resulting in low-complexity NN-based controllers that are fast to evaluate. However, when approximating control laws using NN, performance and stability guarantees of the original controller may not be preserved. Recently, it has been shown that it is possible to provide such guarantees for linear systems with NN-based controllers by analyzing the approximation error with respect to a stabilizing base-line controller or by computing reachable sets of the closed-loop system. The latter has the advantage of not requiring a base-line controller. In this paper, we show that similar ideas can be used to analyze the closed-loop behavior of piecewise affine (PWA) systems with an NN-based controller. Our approach builds on computing over-approximations of reachable sets using mixed-integer linear programming, which allows to certify that the closed-loop system converges to a small set containing the origin while satisfying input and state constraints. We also show how to modify a given NN-based controller to ensure asymptotic stability for the controlled PWA system.
Analyzing Ultra-Low Inter-Core Crosstalk Fibers in Band and Space Division Multiplexing EONs
Authors: F. Arpanaei, C. Natalino, M. Ranjbar Zefreh, S. Yan, H. Rabbani, Maite Brandt-Pearce, J. P. Fernandez-Palacios, J. M. Rivas-Moscoso, O. Gonzalez de Dios, J. A. Hernandez, A. Sanchez-Macian, D. Larrabeiti, P. Monti
Date: 2024-11-06 00:00:00

In the ultra-low inter-core crosstalk working zone of terrestrial multi-band and multi-core fiber (MCF) elastic optical networks (EONs), the ICXT in all channels of all cores remains below the ICXT threshold of the highest modulation format level (64QAM) for long-haul distances (10000 km). This paper analyzes the performance of this type of MCF in multi-band EONs (MB-EONs). We investigate two band and space division multiplexing (BSDM) scenarios: MCF and a bundle of multi-fiber pairs (BuMFP). Furthermore, the UL-ICXT performance of two MCFs, one with the standard cladding diameter (CD = 125 micrometers) with 4 cores and another with a nonstandard larger CD with 7 cores, is evaluated in the US backbone network. Our findings show that, with careful design of the MCFs physical structure, even with a standard CD, it is possible to achieve UL-ICXT in C, L, and S-band long-haul BSDM EONs. Additionally, the simulation results show that network throughput for BSDM EONs with MCFs in the UL-ICXT regime is up to 12 percent higher than the BuMFP scenario, with capacity increasing linearly with the number of cores.
Wire twisting stiffness modelling with application in wire race ball bearings. Derivation of analytical formula and Finite Element validation
Authors: Josu Aguirrebeitia, Inigo Martin, Iker Heras, Mikel Abasolo, Ibai Coria
Date: 2024-11-06 00:00:00

Since Erich Franke produced the first wire race bearings in 1934, they have not been used profusely until these last years in applications such as computerized tomography, X-ray machines, wheels with direct drive... where low weight and inertia constraints are important. Accounting for the structural behaviour of the bearing, there exist a key phenomenon not present in other kind of more known bearings, which is the wire twisting under load; this wire twisting steers the force transmission among the bearing rings and the rolling elements. In this sense, for design and selection purposes, if a complete structural model of the bearing is to be done in an efficient way to assess bearing stiffness and load distribution over the rolling elements, the twisting stiffness of the wire has to be modelled properly. This work develops a simple analytical expression of that stiffness to be used in structural models, derived from an evidence-based deformation assumption at differential level for the section of the wire.
Static structural behaviour of wire bearings: comparison with conventional bearings and study of design and operational parameters
Authors: Inigo Martin, Iker Heras, Josu Aguirrebeitia, Mikel Abasolo, Ibai Coria
Date: 2024-11-06 00:00:00
Tasks: Friction

In wire bearings the rolling process occurs on raceways machined on steel wires, and the rings are made of light materials such as aluminium. This particular architecture provides both weight and inertia savings, but also significantly different behaviour with respect to conventional bearings. For this reason, specific design and analysis tools must be developed; as a first step, this work uses Finite Element models to study the influence of different parameters on the static structural response of wire bearings. Thus, bearing stiffness, load capacity and contact status (contact force and angle, and ellipse truncation) have been evaluated for several combinations of conformity, friction coefficient and boundary conditions. The results have been compared with an equivalent conventional bearing, shedding light on the main structural features of wire bearings.
Privacy-Preserving Resilient Vector Consensus
Authors: Bing Liu, Chengcheng Zhao, Li Chai, Peng Cheng, Jiming Chen
Date: 2024-11-06 00:00:00
Tasks: Privacy Preserving

This paper studies privacy-preserving resilient vector consensus in multi-agent systems against faulty agents, where normal agents can achieve consensus within the convex hull of their initial states while protecting state vectors from being disclosed. Specifically, we consider a modification of an existing algorithm known as Approximate Distributed Robust Convergence Using Centerpoints (ADRC), i.e., Privacy-Preserving ADRC (PP-ADRC). Under PP-ADRC, each normal agent introduces multivariate Gaussian noise to its state during each iteration. We first provide sufficient conditions to ensure that all normal agents' states can achieve mean square convergence under PP-ADRC. Then, we analyze convergence accuracy from two perspectives, i.e., the Mahalanobis distance of the final value from its expectation and the Hausdorff distance-based alteration of the convex hull caused by noise when only partial dimensions are added with noise. Then, we employ concentrated geo-privacy to characterize privacy preservation and conduct a thorough comparison with differential privacy. Finally, numerical simulations demonstrate the theoretical results.
Privacy Preserving Mechanisms for Coordinating Airspace Usage in Advanced Air Mobility
Authors: Chinmay Maheshwari, Maria G. Mendoza, Victoria Marie Tuck, Pan-Yang Su, Victor L. Qin, Sanjit A. Seshia, Hamsa Balakrishnan, Shankar Sastry
Date: 2024-11-06 00:00:00
Tasks: Privacy Preserving

Advanced Air Mobility (AAM) operations are expected to transform air transportation while challenging current air traffic management practices. By introducing a novel market-based mechanism, we address the problem of on-demand allocation of capacity-constrained airspace to AAM vehicles with heterogeneous and private valuations. We model airspace and air infrastructure as a collection of contiguous regions with constraints on the number of vehicles that simultaneously enter, stay, or exit each region. Vehicles request access to the airspace with trajectories spanning multiple regions at different times. We use the graph structure of our airspace model to formulate the allocation problem as a path allocation problem on a time-extended graph. To ensure the cost information of AAM vehicles remains private, we introduce a novel mechanism that allocates each vehicle a budget of "air-credits" and anonymously charges prices for traversing the edges of the time-extended graph. We seek to compute a competitive equilibrium that ensures that: (i) capacity constraints are satisfied, (ii) a strictly positive resource price implies that the sector capacity is fully utilized, and (iii) the allocation is integral and optimal for each AAM vehicle given current prices, without requiring access to individual vehicle utilities. However, a competitive equilibrium with integral allocations may not always exist. We provide sufficient conditions for the existence and computation of a fractional-competitive equilibrium, where allocations can be fractional. Building on these theoretical insights, we propose a distributed, iterative, two-step algorithm that: 1) computes a fractional competitive equilibrium, and 2) derives an integral allocation from this equilibrium. We validate the effectiveness of our approach in allocating trajectories for two emerging urban air mobility services: drone delivery and air taxis.
A networked small-gain theorem based on discrete-time diagonal stability
Authors: Ron Ofir, Michael Margaliot
Date: 2024-11-05 00:00:00

We present a new sufficient condition for finite-gain $L_2$ input-to-output stability of a networked system. The condition requires a matrix, that combines information on the $L_2$ gains of the sub-systems and their interconnections, to be discrete-time diagonally stable (DTDS). We show that the new result generalizes the standard small gain theorem for the negative feedback connection of two sub-systems. An important advantage of the new result is that known sufficient conditions for DTDS can be applied to derive sufficient conditions for networked input-to-output stability. We demonstrate this using several examples. We also derive a new necessary and sufficient condition for a matrix that is a rank one perturbation of a Schur diagonal matrix to be DTDS.
Model Predictive Control of Collinear Coulomb Spacecraft Formations
Authors: Adam M Tahir
Date: 2024-11-05 00:00:00
Tasks: model, Model Predictive Control

A model predictive control scheme to stabilize desired configurations of collinear Coulomb spacecraft formations is derived in this paper. The nonlinearities of the dynamics with respect to the input make this problem difficult to solve, computationally. It is shown that the nonlinearities in the input lead to a finite horizon optimization problem which is a nonconvex quadratically-constrained quadratic program (QCQP). A convex relaxation of the nonconvex QCQP is therefore derived which can be solved quickly using a convex optimization solver. A simulation of a four spacecraft formation is provided which demonstrates why optimizing over a prediction horizon is a prudent approach to Coulomb spacecraft formation control.
A Traffic Prediction-Based Individualized Driver Warning System to Reduce Red Light Violations
Authors: Suiyi He, Maziar Zamanpour, Jianshe Guo, Michael W. Levin, Zongxuan Sun
Date: 2024-11-05 00:00:00
Tasks: Traffic Prediction

Red light violation is a major cause of traffic collisions and resulting injuries and fatalities. Despite extensive prior work to reduce red light violations, they continue to be a major problem in practice, partly because existing systems suffer from the flaw of providing the same guidance to all drivers. As a result, some violations are avoided, but other drivers ignore or respond inappropriately to red light running systems, resulting in safety issues overall. We show a method of providing accurate warnings to individual drivers to avoid the broad guidance approach of most existing systems. Recognizing if a driver will run red lights is highly dependent on signal phase and timing, traffic conditions along the road, and individual driver behaviour, the proposed warning system contains three parts: a traffic prediction algorithm, an individual warning signal optimizer, and a driver warning display. The traffic prediction algorithm predicts future traffic states along the road towards the signalized intersections using the latest traffic conditions obtained through vehicle-to-vehicle and vehicle-to-infrastructure communications. Then, an optimization problem is formulated to compute the optimal warning signal based on predicted traffic states and driver reaction model. Finally, the optimal warning signal is shown on the display screen to advise driver on how much braking is needed to avoid running the red light. The system continuously updates the latest warning signal as the vehicle is approaching the intersection. Both numerical simulated driving scenarios and real-world road tests are used to demonstrate the proposed algorithm's performance under different conditions by comparing with previous work on red light running warning system. The results show that the system provides more effective and accurate warning signals to drivers, helping them avoid running red lights.
A Unified Fault Ride Through Technique for Virtual Oscillator based Grid Forming Controllers
Authors: Ritwik Ghosh
Date: 2024-11-05 00:00:00

Grid-forming technology has a crucial role in achieving the future all renewable power grid. Among different types of grid-forming controllers, Virtual Oscillator (VO) based Controllers (VOCs) are the most advanced. VOCs outperform the conventional droop-based grid-forming controllers in terms of dynamic performance and synchronization stability by adapting time-domain-based implementation. However, because of the time-domain-based implementation, the same Fault Ride-through (FRT) techniques for droop-based controllers are incompatible with VOCs. Existing literature has successfully incorporated current limiting techniques in VOCs to protect the converters during severe transient conditions. Nevertheless, some very important aspects of FRT requirements are not attended to by the existing literature on VOCs, such as maintaining synchronization with the network during a fault, minimizing power oscillation during a fault, and at the fault clearance. First, this article introduces a unique analytical approach for quantifying the underlying dynamics of VOCs during faults. Next, using the mentioned analysis and in-depth reasoning, the systematic development of a unique FRT control architecture for VOCs is presented. The proposed FRT technique has unified both current and voltage synchronization in the same architecture to work successfully under three-phase and unbalanced faults. The performance of the proposed controller is thoroughly investigated and compared with existing VOCs.
Minimum Radiative Heat and Propellant Aerocapture Guidance with Attitude Kinematics Constraints
Authors: Enrico Marco Zucchelli, Erwin Mooij
Date: 2024-11-05 00:00:00

Aerocapture leverages atmospheric drag to convert a spacecraft's hyperbolic trajectory into a bound orbit. For some aerocapture missions, heating due to the radiation of high temperature gases in the shock-layer can be much larger than the heat due to convection. This paper provides analytical proof and numerical validation that radiative heat load is minimized by the same trajectory that minimizes the final {\Delta} V: a single switch bang-bang trajectory, starting with lift up. The proof is very general and is valid for several formulations of radiative heat flux; further, the same proof can be used to conclude that convective heat load, computed according to many of the available formulations, is instead maximized by that trajectory. Further, a novel guidance that plans a bang-bang trajectory with constraints in the attitude kinematics is introduced. While achieving performance similar to that of the current state-of-the-art, the inclusion of constraints in attitude kinematics allows for much less tuning. Finally, a lateral guidance that makes use of information on the final inclination of the predicted trajectory is introduced. Such guidance allows for very high accuracy in the inclination requirements with only two reversals, by requiring a single parameter to be tuned.
Optimized Cryo-CMOS Technology with VTH<0.2V and Ion>1.2mA/um for High-Peformance Computing
Authors: Chang He, Yue Xin, Longfei Yang, Zewei Wang, Zhidong Tang, Xin Luo, Renhe Chen, ZiRui Wang, Shuai Kong, Jianli Wang, Jianshi Tang, Xiaoxu Kang, Shoumian Chen, Yuhang Zhao, Shaojian Hu, Xufeng Kou
Date: 2024-11-05 00:00:00

We report the design-technology co-optimization (DTCO) scheme to develop a 28-nm cryogenic CMOS (Cryo-CMOS) technology for high-performance computing (HPC). The precise adjustment of halo implants manages to compensate the threshold voltage (VTH) shift at low temperatures. The optimized NMOS and PMOS transistors, featured by VTH<0.2V, sub-threshold swing (SS)<30 mV/dec, and on-state current (Ion)>1.2mA/um at 77K, warrant a reliable sub-0.6V operation. Moreover, the enhanced driving strength of Cryo-CMOS inherited from a higher transconductance leads to marked improvements in elevating the ring oscillator frequency by 20%, while reducing the power consumption of the compute-intensive cryogenic IC system by 37% at 77K.
Synergizing Hyper-accelerated Power Optimization and Wavelength-Dependent QoT-Aware Cross-Layer Design in Next-Generation Multi-Band EONs
Authors: Farhad Arpanaei, Mahdi Ranjbar Zefreh, Yanchao Jiang, Pierluigi Poggiolini, Kimia Ghodsifar, Hamzeh Beyranvand, Carlos Natalino, Paolo Monti, Antonio Napoli, Jose M. Rivas-Moscoso, Oscar Gonzalez de Dios, Juan P. Fernandez-Palacios, Octavia A. Dobre, Jose Alberto Hernandez, David Larrabeiti
Date: 2024-11-05 00:00:00
Tasks: Blocking, global-optimization

The extension of elastic optical networks (EON) to multi-band transmission (MB-EON) shows promise in enhancing spectral efficiency, throughput, and long-term cost-effectiveness for telecom operators. However, designing MB-EON networks introduces complex challenges, notably the optimization of physical parameters like optical power and quality of transmission (QoT). Frequency-dependent characteristics of fiber, such as loss, dispersion, and nonlinear effects, alongside inter-channel stimulated Raman scattering, pose significant hurdles when extending beyond the L+C (LC) band to a continuous spectrum over 100 nm. In this study, we propose a span-by-span methodology for optimal power allocation, introducing two hyper-accelerated power optimization (HPO) strategies: flat launch power (FLP) and flat received power (FRP). These approaches significantly expedite network power optimization while preserving the stability of running services. Our comparative analysis of FLP and FRP models reveals that while FRP has a minimal effect on capacity (increasing less than 10 Tbps for an L+C+S (LCS) system over 100 km), it improves flatness and GSNR/OSNR metrics in the S-band by approximately 2/0 dB and 2.5/6 dB, respectively. A network-wide analysis across various topologies shows that the FRP technique enhances minimum GSNR, contributing to a throughput increase of 12% to 75%, depending on network scale, at a 1% bandwidth blocking rate. Lastly, our application of HPO in MB-EON for both local and global power optimization demonstrates that while both approaches offer comparable performance, global optimization is simpler and more cost-effective for large-scale networks.
Structural modeling of crossed roller wire race bearings: analytical submodel for the roller-wire-ring set
Authors: Inigo Martin, Iker Heras, Ibai Coria, Mikel Abasolo, Josu Aguirrebeitia
Date: 2024-11-05 00:00:00

Since wire bearings were patented in 1936, they have been used in applications where weight saving is a key aspect. Nevertheless, little work can be found in literature regarding their structural behaviour. In order to predict how a wire bearing reacts under load, the most feasible way is to model and analyse it via Finite Elements (FE). However, the great amount of elements needed to properly model the complex contact configuration among rollers, wires and raceways, make this approach unaffordable. In this sense, this manuscript develops an analytical submodel that represents the structural behaviour of the roller-wire-ring set, in order to include it later in a global FE model to account for ring flexibility and boundary conditions. This way, the computationally intensive FE modelling of these complex zones can be substituted by the analytical model developed in this work, and a much manageable global FE model can be used to predict the structural response of the bearing. This analytical model has demonstrated a good agreement with local FE models of the roller-wire-ring set.
Load distribution and friction torque in four-point contact slewing bearings considering manufacturing errors and ring flexibility
Authors: Iker Heras, Josu Aguirrebeitia, Mikel Abasolo, Ibai Coria, Inigo Escanciano
Date: 2024-11-05 00:00:00
Tasks: Friction

This work introduces a methodology for the calculation of the load distribution in four-point contact slewing bearings considering ball preload, manufacturing errors and ring flexibility. The model is built by the formulation and minimization of the potential energy of the bearing. Comparing with the rigid rings assumption, the results show that ring deformations involve lower interferences in idling conditions, and have a great effect in the load distribution, but not under external loads. Additionally, a new approach has been proposed for the calculation of the friction torque, which has lower computational cost in comparison to a previous approach by the authors, so more accurate results can be obtained due to refined calculations with no significant cost increase.
Efficient assembly of bolted joints using numerical FEM
Authors: Ibai Coria, Inigo Martin, Abdel-Hakim Bouzid, Iker Heras, Mikel Abasolo
Date: 2024-11-05 00:00:00

Several factors can cause leakages in a bolted flange connection, external loads being the most important one. External loads such as those produced by misalignment introduce an external axial load combined with a bending moment which could lead to either an excessive compression of the gasket and its subsequent crushing, and/or a separation of the flanges causing leakage failure. Several studies have been carried out to study these prejudicial effects, but no practical solutions are proposed to compensate for them. In this sense, this work presents a numerical methodology that iteratively calculates the non-uniform bolt tightening load distribution to achieve a uniform gasket stress distribution that improves the leakage performance of bolted joints subjected to external loads.