On algebraic time-derivative estimation and deadbeat state reconstruction

This note places into perspective the so-called algebraic time-derivative estimation method recently introduced by Fliess and co-authors with standard results from linear state-space theory for control systems. In particular, it is shown that the algebraic method can in a sense be seen as a special case of deadbeat state estimation based on the reconstructibility Gramian of the considered system.Comment: Maple-supplements available at https://www.tu-ilmenau.de/regelungstechnik/mitarbeiter/johann-reger

Underwater

vehicle navigation using diffusion-based trajectory observer

Nonlinear Dynamic Positioning of Ships with Gain-Scheduled Wave Filtering

Abstract — This paper presents a globally contracting controller for regulation and dynamic positioning of ships, using only position measurements. For this purpose a globally contracting observer which reconstructs the unmeasured states is constructed. The observer produces accurate estimates of position, slowly varying environmental disturbances (bias terms) and velocity. The estimates are automatically adjusted to the present sea state by gain-scheduling the wave model parameters in the observer. Finally, the estimates are used in a nonlinear PID control law and the stability proof of the observer-controller is based on a separation principle for contracting systems in cascade. I

Formation control of marine surface craft using lagrange multipliers

Abstract — We propose a method for constructing control laws for formation control of marine craft using classical tools from analytical mechanics. The control law is based on applying inter-vessel constraint functions which again impose forces on the individual vessels that maintain the given constraints on the total system. In this way, a formation can be assembled and stay together when exposed to external forces. A brief comparison with other control designs for a group of marine craft is done. Further, control laws for formation assembling (with dynamic positioning), and formation keeping during maneuvering is derived and simulated to illustrate the properties of the proposed method. I

Robust Formation Control of Marine Craft using Lagrange Multipliers

Summary. This paper presents a formation modelling scheme based on a set of inter-body constraint functions and Lagrangian multipliers. Formation control for a fleet of marine craft is achieved by stabilizing the auxiliary constraints such that the desired formation configuration appears. In the proposed framework we develop robust control laws for marine surface vessels to counteract unknown, slowly varying, environmental disturbances and measurement noise. Robustness with respect to time-delays in the communication channels are addressed by linearizing the system. Simulations of tugboats subject to environmental loads, measurement noise, and communication delays verify the theoretical results. Some future research directions and open problems are also discussed.

Past soil erosion history recorded by lake sediments in mountain areas (north and south French Alps) : complex interactions with climatic and human activities

International audienceErosion rates and patterns are influenced both by hydrological activity and the evolution of soil-vegetation cover. This soil-vegetation cover is in turn impacted by climatic changes and human activities through deforestation, grazing and agriculture. Such land uses are reported in mountain areas since several millennia (the Neolithic or Bronze Age in the Alps). The effects of these activities and climatic changes on erosion and above all on soil cover are relatively few documented. However, a good knowledge of these processes is important to better evaluate the future evolution of soils and the sustainability for agricultural practices, in the context of global change. Because lakes act as traps of erosion products, lake sediments represent interesting continuous archives of past soil evolution and erosion. They provide a unique opportunity to reconstruct at high resolution the soil history over long time periods and thus to determine the timing of changes in response to climate and/or anthropogenic pressures. As a result of the Pygmalion research program, we present the study of two small mountain catchment in north (Lake Anterne, 2063 m asl) and south French Alps (Lake Lauzanier, 2285 m asl), covering the Holocene and the last 1000 years, respectively. To trace the past soil erosion erosion history and bring arguments about the origin of changes, mineral and organic geochemical analyses were performed and combined with quantitative reconstructions of terrigenous inputs. To emphasize our assumptions about the origins of recorded changes, a pluridisciplinary approach (palynology, archaeology...) was also adopted. The study of Lake Anterne shows the second half of the Holocene is characterized by four important phases of erosion. These phases are underlined by high flood frequencies and different geochemical composition of sediments. These geochemical signatures reveal changes of sediment sources related to different erosion patterns. In particular, the first phase, at 5450 cal. BP affects both leptosols and developped soil surface horizons (podzols. It is thus interpreted as mainly reflecting the climatic reversal toward colder and wetter conditions, known during this period. Likewise, during the end of Iron Age and the begin of Roman period, the most important erosion phase of the Holocene firstly affects developed soil (cambisol)surface horizons (during 300 years) and then attacks the deepest horizons (during 250 years). This suggest an intensification of grazing activity. Our interpretations are also supported by palynological and archaeological data. The preliminary results of Lake Lauzanier show high terrigenous inputs during the Little Ice Age (LIA), probably due to wetter climatic conditions, as it is observed for Lake Anterne. However, during the last 1000 years, the most important phase of erosion is recorded just after the LIA, between AD 1900 and Ad 1960. This phase is interpreted as the result of intensification of human activities (probably grazing) affecting the soil stability in the catchment

Ancient mining near the Bibracte oppidum and its impact on ecosystems: a multidisciplinary approach

International audienc

LATE HOLOCENE MONGOLIAN CLIMATE RECONSTRUCTIONS FROM LOCALLY CALIBRATED GDGT AND POLLEN TRANSFER FUNCTIONS FOR LAKE AYRAG.

International audienc