Comparison between Optimal Control Allocation with Mixed Quadratic & Linear Programming Techniques

The paper provides a comparison between different control allocation techniques in over-actuated Autonomous Underwater Vehicles. The pseudoinverse, Linear Programming (LP), Quadratic Programming (QP), Mixed Integer Linear Programming (MILP) and Mixed Integer Quadratic Programming (MIQP) are evaluated in simulation on the V-Fides vehicle model. The MILP and MIQP techniques allow to include in their implementations a more detailed characterization of the non-linear static behaviour of the actuators. This customizability can be also exploited to improve the practical stability of the system. The metrics used for comparison include the maximum attainable forces and torques, the integral of the error allocation and the required thrusters effort. Our simulation results show that, in particular with respect to thrusters effort, MILP and MIQP are the preferred allocation methods. The computational complexity associated to both methods is not such to compromise their implementation in operating vehicles; in particular, the MILP version is currently implemented in the V-Fides vehicle

PROGETTAZIONE LOGICA E DEFINIZIONE DI PROTOCOLLI E POLITICHE PER LE CACHES D-NUCA TRIANGOLARI

Gli odierni processori per sistemi ad alte prestazioni incorporano caches di dimensioni sempre crescenti. Ad esempio l’Alpha 21364 ha 1.75MB di L2, l’HP PA-8700 contiene 2.25MB di cache unificata e l’Itanium2 prevede 3MB di cache L3. Dato che la cache L2 occupa circa la metà dell’area di silicio del chip (il 30% nell’Alpha 21264, il 60% nello StrongARM), è facile capire come questo componente incida non poco sul costo dell’intero processore e sulle sue prestazioni. In questo lavoro di tesi saranno valutati differenti progetti di architetture di cache con l’obbiettivo di migliorarne le prestazioni in termini di tempi di accesso, capacità, costo e risparmio energetico. In particolare sarà presentata una architettura di memoria cache con tempo di accesso che è funzione degli indirizzi dei dati e su questa saranno costruite alcune varianti sempre con riguardo alle relative prestazioni. Inoltre per ogni configurazione presentata saranno fatte varie prove di test in modo da validare il progetto e renderlo credibile

OptoCOMM and SUNSET to enable large data offloading in Underwater Wireless Sensor Networks

In this paper we present the initial implementation of an integrated optical and acoustic system that can enable large data transfer between mobile and static nodes in Underwater Wireless Sensor Networks (UWSNs). The proposed system is based on the OptoCOMM optical modem and on the SUNSET Software Defined Communication Stack (S-SDCS) framework. The OptoCOMM modem allows to overcome the limits of maximum data rate and bandwidth imposed by the use of acoustic communication by providing a data rate of 10Mbps. SUNSET SDCS instead has been used to provide networking and fragmentation capabilities to efficiently offload large data in UWSNs. The performance of the proposed approach has been evaluated through in lab experiments where large files with arbitrary sizes have been optically transferred. The results achieved show that our system is able to transfer up to 1.5 GBytes of data in short time

A nonlinear complementary filter for underwater navigation using inertial measurements

This paper describes a nonlinear complementary filter capable of estimating the course motion variables namely the position, velocity, heading and accelerometers bias of an agile, over-actuated AUV during underwater operations, using the inertial sensors (IMU), the DVL, the depth sensor and the compass. The proposed work is within the framework of the V-Fides project, co-funded by Tuscany Region (Italy) and developed by a team lead by WASS S.p.A. (Whitehead Sistemi Subacquei, Livorno). The aim of the project was to develop and evaluate an high-depth, over-actuated, long endurance Autonomous Underwater Vehicle (AUV). The paper proposes the mathematical development of the observer, together with some experimental results, able to demonstrate the capabilities of the estimation scheme, compared with the estimations obtained via a standard Kalman Filter

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease

Methodologies and approaches to enhance the performance and reliability of underwater vehicles

This thesis has the ultimate goal of contributing to increase the reliability and robustness of Autonomous Underwater Vehicle (AUV) operations. It focuses specifically in inter-vehicle communication reliability and in robust thrust allocation, offering developments and contributions as detailed in the following sub-sections. There are several ways to contribute in the improvement of the communication reliability underwater, but as a matter of fact the acoustic technology reached a mature level and the last improvements are related to increase the data rate at short distances. To achieve higher speed and a more reliable communication link, it is reasonable to adopt an alternative technology based on optical transmission that can provide such features in short communication ranges. The proposed solution based on visible light is provided in the following where the optical communication is employed in a harsh operative scenario with high disturbances such sunlight and turbidity. The thrust allocation is another subject where the robustness of AUVs can be improved. The proposed work exploits the redundancy in the actuation system of over-actuated AUVs in order to improve the performance and robustness of the vehicles. The goal is achieved by solving optimal constrained problem also formulated on the mixed logical dynamical system concept. Optical Modem The first part of this thesis deals with the development of a novel Underwater Optical Wireless Communication (UOWC) device to exploit the potential of the Light Emitting Diode (LED) technology in an underwater scenario. In particular, the optical modem is designed to operate in shallow harbour water which is the worst scenario for optical communications. To be usable in operative condition, the performance must address a reasonable communication range and high data rate, so the modem is designed to achieve at least a maximum range of 10 m at 10 Mbps. The high speed allows the transfer of big data in a reasonable time without the need of the AUV resurfacing, and the distance of 10 m is an acceptable minimum range. The success of the project is the first step to validate the visible optical communication as additional technology to improve the existing underwater transmission methods. The optical modem is designed and funded within the European Project 7th Framework Programme for Research and Technological Development (FP7) SUNRISE as sub-project that applied at the first open call for introducing a novel technology in one of the SUNRISE infrastructures. The detail of the project and the development of the optical device are organized in the first module of the thesis as following: • The OptoCOMM Project: the project is described in details with a comprehensive introductive state-of-the-art, the motivation behind the project, and the description of the scenario where the modems are deployed. • Design of the modem: the development of the modem is described in all its fundamental parts: the employed electronics for the optical part and the hardware, the mechanical structure with the watertight container, and the software inclusive of the user-interface as well as the communication protocol. • Experimentations: this chapter presents the laboratory tests done to validate each part of the modem as well as integration between all the components. At last, sea trials were performed to test and validate the adopted design in the proposed scenario. Control Allocation The second module of the thesis exploits the features of Mixed Integer Linear Programming (MILP) and Mixed Integer Quadratic Programming (MIQP) in the control allocation problem to improve the performance of the over-actuated AUVs. The control allocation problem can be defined as finding a set of input commands to the actuators such that the forces and torques exerted on manoeuvrable Degree Of Freedoms (DOFs) of the system are equal to the desired ones computed by the control module. The control allocation problem maybe is underestimated in the Guidance Navigation and Control (GNC) scheme adopted in all autonomous vehicles, but especially in the over-actuated vehicles plays a crucial role in the control effectiveness. The classic method adopted is to map the controls on the actuator by means of the pseudoinverse of the geometric allocation matrix. This method has some limitation, especially in the case where the requested forces go beyond the limits of the actuators. The actuators saturation and the redundancy in the actuation make the problem constrained and with multiple solutions, and more effective methods are used to solve the problem, i.e. Quadratic Programming (QP) and Linear Programming (LP). The proposed method improves the existing methods based on QP and LP by integrating in the control allocation problem the characteristic of the actuators and consequently the problem is transformed in the mixed-integer version. A comprehensive comparison between the existing methods and the pro- posed ones is presented to validate the real improvement. Moreover, the over-actuation allows the partial recovery if a fault occur on a thruster, and the control allocation must be capable to re-allocate the requested forces on the healthy thrusters. The Fault Detection & Isolation (FDI) with fault recovery is an other interesting sector where the control allocation is crucial for the effectiveness of a vehicle recovery or conversely the lost of it. Thus, in the thesis is presented a FDI technique with fault recovery by means of the proposed techniques. In the thesis, the developed techniques are tested in simulation on the over-actuated AUV V-Fides and in some cases verified on the real vehicle during the sea trials. The V-Fides vehicle was developed within the V-Fides project funded by Tuscany Region where Finmeccanica was the leader. The control allocation module is presented as following: • The Control Allocation: in this chapter is presented an introduction with a comprehensive state-of-the-art, and then the control allocation techniques are presented. The investigated resolution method are: the classic pseudoinverse, the LP, QP, MILP, and MIQP. • Case Study: The V-Fides Vehicle: this chapter describes in details the vehicle and the model adopted in the developed simulator implemented in MATLAB Simulink. The comparison between all the control allocation techniques is simulated on the V-Fides vehicle. In addition, the control allocation system is tested in FDI and Fault Recovery scheme to reallocate the requested control on the healthy actuators

Controllo adattivo di un veicolo subacqueo

La tesi consiste nella progettazione, analisi e valutazione delle performance di un controllo non lineare di tipo adattivo, basato sulla stima dei parametri dinamici. Lo scopo finale del progetto è l'implementazione di tale controllo in un veicolo marino autonomo (AUV) ad alta manovrabilità, il quale ha lo scopo di sorvegliare aree marine in cui sono presenti obiettivi sensibili e analizzare l'inquinamento delle acque con specifici strumenti equipaggiati a bordo

A NLPCA hybrid approach for AUV thrusters fault detection and isolation

The objective of this paper is to address the problem of Fault Detection and Isolation (FDI) on thrusters of an over-actuated Autonomous Underwater Vehicle (AUV) under on/off abrupt faults. The goal is pursued through Non-Linear Principal Component Analysis (NLPCA), which is the non-linear extension of the popular Principal Component Analysis (PCA). While the Fault Detection (FD) system directly exploits the model-free nature of NLPCA (data-driven approach), the Fault Isolation (FI) is achieved by properly train off-line Artificial Neural Network (ANN). The consistency and robustness of the proposed method is verified in realistic simulation

Enhancing autonomy: Fault detection, identification and optimal reaction for over - Actuated AUVs

The adoption of fault detection and isolation (FDI) techniques is fundamental to ensure high levels of safety and productivity, especially in critical and expensive applications like Autonomous Underwater Vehicles (AUV). This paper describes a comparison between different techniques available in the literature, applied to over-actuated AUVs under single fault condition (SFC) and considering only abrupt faults. The main contribution of this work is twofold: first, we show how such techniques can be adapted to the case of over actuated AUVs in order to isolate and identify a faulty situation of one thruster. Moreover, we give a means for robust fault reaction by using an optimal control allocation problem, which is tightly coupled with the FDI algorithm. The proposed work is in the framework of the V - Fides project and the algorithms are demonstrated in simulation, employing the dynamical model of that vehicle

Optimal aided inertial navigation, augmented with inter-sensors self-calibration

The proposed work is in the framework of the V-Fides project, in which is a general purpose, 3000m depth rated underwater vehicle with highly maneuverability capabilities was developed. The project was co-funded by Tuscany Region (Italy) and developed by a team lead by WASS S.p.A. (Whitehead Sistemi Subacquei, Livorno) with the participation of several partners including two research institutions of the University of Pisa and Small-Medium Enterprises in the Pisa-Livorno area. The vehicle is equipped with a sensors payload for autonomous navigation. This contribution describes an integrated calibration/navigation filter capable of estimating the relative (rotational) calibration parameters between the IMU and the DVL, and producing the standard velocity and attitude navigation output together with accelerometers biases. The results were demonstrated with real data sets collected during extensive experimental campaigns. Finally the observability analysis is proposed in order to define the motion requirements for the asymptotic convergence of the parameter estimates