Stern Plane Research Articles

Robust high‐gain observer‐based sliding mode controller for pitch and yaw position control of an AUV

AbstractThis article addresses a trajectory tracking control problem concerning an autonomous underwater vehicle's pitch and yaw channel dynamics in the presence of model uncertainties, underwater disturbances, and input saturation. Three different observers are introduced to estimate unknown state variables: a Luenberger‐type cubic observer, a sliding mode observer, and a high‐gain observer (HGO). Initially, a backstepping controller is employed to tackle the tracking problem, extending it to incorporate backstepping sliding mode control (SMC). The mentioned observers are utilized in both aspects of the controller design. Our proposed control law assesses trajectory tracking performance by introducing virtual control inputs, with the sliding surface designed to guide the current state variables toward approximating the virtual state variables. By combining backstepping and SMC, ensure that the state variables of the closed‐loop system converge to the desired state using the HGO. A rigorous analysis is incorporated to validate the robust performance of our proposed control law under conditions of model uncertainties and underwater disturbances. Furthermore, the control law is extended for anti‐windup compensation, mitigating adverse effects on stern and rudder plane saturation levels. Lyapunov stability theory is adopted to establish the stability of the closed‐loop system. Our simulation results convincingly demonstrate the effectiveness of the HGO‐based backstepping SMC law compared to alternative control approaches.

Electrochemical interfaces between Au(100) and deep eutectic solvents: An in situ scanning tunneling microscopy study

Deep eutectic solvents (DESs) are promising electrolytes for electrochemical fields due to their excellent properties. Electrochemical behaviors of Au(100) electrode in two choline chloride-based DESs ethaline and reline with different hydrogen bond donor molecules have been investigated by cyclic voltammetry and in situ scanning tunneling microscopy (STM). Cyclic voltammograms present three pairs of current peaks for Au(100) electrodes in the two DESs. On the basis of the results of in situ STM, the three pairs of current peaks are assigned to the formation and lifting of Au(100) surface reconstruction, adsorption and desorption of chloride ions, and phase transition of chloride ion adlayer. Compared with Au(111), one extra current peak and the corresponding (√5 × √5)R26.6° ordered adlayer of chloride ions were observed for Au(100) electrode. An order-order phase transition of chloride ion adlayer was observed in ethaline, while an order-disorder phase transition was observed in reline. Furthermore, no Au islands was observed on Au(100) surface in ethaline after the lifting of reconstruction when the potential is moved positively and gradually. However, gold nanowires could form and stably exist on Au(100) surface, which are different from that formed on Au(111) surface in reline. Our results provide detailed insights into the interfacial structures between Au(100) electrode and DESs on the atomic scale that hydrogen bond donor molecules and the surface crystallography of the electrode interface could significantly affect the arrangement of gold atoms of the electrode surface and chloride ions in the innermost Stern plane.

Evolution of the electrical double layer with electrolyte concentration probed by second harmonic scattering.

Investigating the electrical double layer (EDL) structure has been a long-standing challenge and has seen the emergence of several sophisticated techniques able to probe selectively the few molecular layers of a solid/water interface. While a qualitative estimation of the thickness of the EDL can be obtained using simple theoretical models, following experimentally its evolution is not straightforward and can be even more complicated in nano- or microscale systems, particularly when changing the ionic concentration by several orders of magnitude. Here, we bring insight into the structure of the EDL of SiO2 nanoparticle suspensions and its evolution with increasing ionic concentration using angle-resolved second harmonic scattering (AR-SHS). Below millimolar salt concentrations, we can successively characterize inner-sphere adsorption, diffuse layer formation, and outer-sphere adsorption. Moreover, we show for the first time that, by appropriately selecting the nanoparticle size, it is possible to retrieve information also in the millimolar range. There, we observe a decrease in the magnitude of the surface potential corresponding to a compression in the EDL thickness, which agrees with the results of several other electroanalytical and optical techniques. Molecular dynamics simulations suggest that the EDL compression mainly results from the diffuse layer compression rather than outer-sphere ions (Stern plane) moving closer to the surface.

Submarine Manoeuvrability Design: Traditional Cross-Plane vs. x-Plane Configurations in Intact and Degraded Conditions

Submarines’ manoeuvrability both in intact and degraded operating conditions is the main design concern starting at the very early stages of design. This increased complexity of the design process compared to a surface vehicle can only be handled by using dynamics numerical simulations on both the vertical and horizontal manoeuvring planes. To this aim, a 6-DoF method is presented, validated, and applied to study the manoeuvring characteristics of several vessels. The analysis has been conducted considering two standpoints, i.e., to verify the design handling capabilities of the vehicles at low and high speeds and to study the off-design residual abilities in the eventual case of emergency operations with jammed/lost-control surfaces. The influence of different design features, such as, e.g., the stern plane “+” and “x” configurations, fairway size and positioning, hull dimensional ratios and restoring capabilities have been analysed in terms of impact on turning ability, course and depth changing abilities, and vertical/horizontal course stability, including the vertical damping ratio and critical velocity.

The zeta potential of quartz. Surface complexation modelling to elucidate high salinity measurements

The zeta potential is a measureable electrical potential of paramount importance to understand the electrochemical properties of rocks. However, the zeta potential remains poorly understood because it takes place at the nanoscale of the electrical double layer on the mineral surface. Streaming potential measurements on quartz-rich Fontainebleau and Lochaline sandstones carried out at high salinity (above 0.1 M NaCl) yield surprisingly high zeta potential values, which cannot be correctly reproduced by a traditional surface complexation model considering that the shear plane is located at the beginning of the diffuse layer. We found that placing the shear plane, where the zeta potential is defined, slightly closer to the mineral surface than the Stern plane significantly improves the predictions of the zeta potential and surface charge density of quartz at high salinity as well as the values of the equilibrium constant describing sodium adsorption in the Stern layer. Our results have strong implications for the modelling of the electrochemical properties of minerals in contact with highly saline solutions.

Morphology of Ionic Micelles as Studied by Numerical Solution of the Poisson Equation.

The existing concepts of the ionic micelle structure were specified. It was noted that the composition of dispersed phase particles in a liquid dispersion medium should necessarily include adsorbed counterions rigidly bound to these particles. By numerical solution of the Poisson equation for the two most often used approximations, the Poisson–Boltzmann (PB) model and the Jellium-approximation (JA), the electric potential decay from the Stern potential of dispersed phase particles was defined. A new methodological approach to analyze the reaction of micelle potential decay based on small variability of the CMC value was proposed. It made possible to determine the dimension parameter, which in the presence of weak thermal effects approximately corresponds to the micelle hydrodynamic radius, and to calculate the electrokinetic potential of micelles. The results of theoretical calculations were compared with our previous experimental data on the thickness of the SDS micelle hydrophilic layer obtained by SAXS. A good agreement between the calculated and measured values was obtained, and it was noted that for low concentrations the experimental values are more correctly described by the PB model, but for concentrations greater than 100 mM the JA model is more preferable. It was found that the slipping plane is located near the outer Stern plane and is separated from it only by a few molecular layers of water. The influence stronger than the thermal one can shift the slipping plane closer to the micelle core. Accordingly, the smallest hydrodynamic micelle size is determined by the outer Stern plane. The results of our work allowed us to conclude that the micelle is not something soft and watery, but according to its specified structure, it is a more solid-like particle than was previously assumed. The proposed approach can be extended to investigate other effects of a physicochemical nature, in particular, those observed with the addition of an external electrolyte or nanoparticles.

Molecular dynamics study on the zeta potential and shear plane of montmorillonite in NaCl solutions

Zeta potential and the position of the shear plane are key physical properties characterizing the behavior of clay minerals in the colloidal system, and have been applied in many fields such as electroosmotic consolidation and electro-kinetic decontamination. In the past decades, numerous studies have been conducted on measuring and calculating the zeta potential. Nevertheless, few researchers have been reported to achieve a systematic understanding and predicting the zeta potential and the shear plane's position, especially for clay particles. This paper provided a molecular dynamics (MD)-based method to determine the zeta potential and shear layer thickness simultaneously to fill the gap. In the paper, the structure of the electrical double layer (EDL) was investigated for montmorillonite mesopore containing NaCl electrolyte in the concentration of 0.20–1.30 mol/L. The density profiles of ion species were well predicted by the Stern model, combining the Stern potential's determination. The calculated zeta potential based on the electroosmotic velocity profile in nonequilibrium molecular dynamics (NEMD) simulation was improved by introducing the slip length and was found to be closely comparable to the experimental values. Furthermore, the results confirmed that the shear plane cannot be observed from the electroosmotic velocity profile and self-diffusion coefficient of species in the MD simulation. The position of the zeta potential was determined by the Stern model and triple-layer model (TLM), showing a certain distance from the Stern plane. The zeta position was found that has a linear relationship with the Debye length and linearly depends on the ionic strength in the log scale, in agreement with previous investigations. The findings provided a systematic insight into the electrical double layer structure, zeta potential and shear plane for montmorillonite.

Performance Prediction of Two-Stepped Planing Hulls Using Morphing Mesh Approach

Change in body shape characteristics is one of the ways to reduce the resistance and thereby increasing the speed of planing hulls. Creating the transverse steps is one of these variations. The main reason to use the steps in high-speed planing craft is that the wetted surface of the vessel is divided into small parts with higher width-length ratio in high velocities and in this situation, the generated lift force is more efficient. In this article, by performing a three-dimensional numerical solution, motion characteristics of a two-stepped planing hull with transverse steps in calm water have been examined. For this purpose, the vessel is free to trim and sinkage, and by using the morphing mesh approach, the numerical simulation continued until the equilibrium condition of the two-stepped planing hull is satisfied. Resistance, lift, trim angle, and wetted surface in various velocities have been computed and compared against existing experimental data. Analysis of considered two-stepped hull in calm water shows that the numerical solution for resistance, trim, and lift are relatively precise in comparison to model test data. Furthermore, various hull characteristics such as wetted length of keel, chine wetted length, spray angle and, ventilation length have been investigated. 1. Introduction In recent years, naval architectures have proposed significant modifications in planing hulls' design by creating steps, tunnel, and other geometric features. By considering these geometric variations, the hull wetted surface and, consequently, its resistance have been reduced and planing hulls velocity can be increased. In this regard, the step is one of the main hull's modifications which can lead to resistance reduction. Generally, lift of stepped planing hulls is distributed over the forward, middle, and stern plane of the hull (Fig. 1), and therefore, its ride quality will also be improved. Moreover, planing hulls with various step configurations have been used in high-speed craft since 1910, and various types of step with different shapes and arrangements have been used in planing hulls.

Modelling pH-Dependent and Microstructure-Dependent Streaming Potential Coefficient and Zeta Potential of Porous Sandstones

In this paper, we have significantly modified an existing model for calculating the zeta potential and streaming potential coefficient of porous media and tested it with a large, recently published, high-quality experimental dataset. The newly modified model does not require the imposition of a zeta potential offset but derives its high salinity zeta potential behaviour from Stern plane saturation considerations. The newly modified model has been implemented as a function of temperature, salinity, pH, and rock microstructure both for facies-specific aggregations of the new data and for individual samples. Since the experimental data include measurements on samples of both detrital and authigenic overgrowth sandstones, it was possible to model and test the effect of widely varying microstructural properties while keeping lithology constant. The results show that the theoretical model represents the experimental data very well when applied to model data for a particular lithofacies over the whole salinity, from 10−5 to 6.3 mol/dm3, and extremely well when modelling individual samples and taking individual sample microstructure into account. The new model reproduces and explains the extreme sensitivity of zeta and streaming potential coefficient to pore fluid pH. The low salinity control of streaming potential coefficient by rock microstructure is described well by the modified model. The model also behaves at high salinities, showing that the constant zeta potential observed at high salinities arises from the development of a maximum charge density in the diffuse layer as it is compressed to the thickness of one hydrated metal ion.

Analisis Drag dan Lift pada Variasi Bentuk After Body Kapal Selam Mini dengan Metode Computational Fluid Dynamics

One aspect that needs to be studied in submarine design is the hydrodynamic aspect relating to submarine maneuverability. This research begins by calculating the value of drag and lift on the three variations of the after body’s mini submarine. The first variation as the initial design is rudder and stern plane arranged perpendicularly or named the+ Stern. Then for the second variation made changes to the arrangement of rudder and stern plane in the after body of the mini submarine with + Stern arrangement, the rudder arranged each other crossed so that it resembles the letter X and called the X-Stern arrangement. Further, for the third variation, the upper rudder of the X-Stern arrangement is replaced by the upper rudder of the + Sternarrangement so that it resembles the inverted Y letter and is called the Y-Stern arrangement. Drag and lift are calculated numerically by using ANSYS-CFX software. From the calculation of CFD found that the submarine with after-body Y-Stern arrangement has the smallest drag and lift value.

In Situ Investigations of Laser-Generated Ligand-Free Platinum Nanoparticles by X-ray Absorption Spectroscopy: How Does the Immediate Environment Influence the Particle Surface?

Pulsed laser ablation in liquid (PLAL) has proven its usefulness as a nanoparticle (NP) synthesis method alternative to traditional chemical reduction methods, where the absence of any molecular ligands or residual reactants makes laser-generated nanoparticles ideal reference materials for charge-transfer experiments. We synthesized additive-free platinum nanoparticles by PLAL and in-situ characterized their interaction with H2O, sodium phosphate buffer, and sodium citrate as well as a TiO2 support by X-ray absorption fine structure (XAFS), i.e., X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Differences in the white-line intensity among the colloidal particles in the three liquids indicate that the respective NP-solvent interaction varies in strength. The ions added ex situ diffuse through the particles' electric double layer and interact electrostatically with the Stern plane. Consequently, these ions weaken the interaction of the functional OH groups that are bound to the partially oxidized platinum surfaces and cause their partial reduction. Comparing XAFS spectra of laser-generated Pt NPs in citrate with wet-chemically synthesized ones (both ligand-covered) indicates different types of Pt-O bonds: a Pt(IV)O2 type in the case of wet-chemical NPs and a Pt(II)O type in the case of laser-generated NPs. A comparison of unsupported laser-generated platinum NPs in H2O with TiO2-supported ones shows no white-line intensity differences and also an identical number of Pt-O bonds in both cases. This suggests that in the deposition process at least part of the double-layer coating stays intact and that the ligand-free Pt particle properties are preserved in the TiO2-supported Pt particles, relevant for heterogeneous catalysis.

PD제어 기법을 적용한 어뢰형 무인잠수정(HW200)의 선수각 및 심도제어기 설계와 실해역 성능 검증

This Paper considers the heading and depth control problem for an underactuated AUV (Autonomous Underwater Vehicle) HW200. The HW200 is a torpedo-type AUV that is developed from Hanwha corporation R&D Center for military operation such as MCM (Mine Counter Measures). The HW200 controls horizontal and vertical motion with two stern plane and two rudder plane. It is well known that fine control of an AUV motion is not easy because of model uncertainties, highly nonlinear and coupled motions. To overcome those kind of uncertainties, a number of control methods have been presented. In this paper, the motion controllers of the HW200 are designed using PD controller design method based on the linear and perturbed model of the typical 6-DOF equations of an AUV, and confirmed the effectiveness of the controller through simulations and field test.

An adaptive fault-tolerant robust controller with fault diagnosis for submarine’s vertical movement

In this paper, an integrated design of fault diagnosis and adaptive fault-tolerant robust control for a submarine with bow and stern plane faults is proposed. Considering the disturbance coming from waves when a submarine operates near sea surface, a simplified linear system of submarine’s vertical movement with both wave disturbance and bow and stern plane faults is presented. An unknown input observer is designed to decouple the wave disturbance and the bow and stern plane faults. Then a fault parameter tracking law is designed to estimate the bow and stern plane fault parameters without any prior fault information. Based on the estimated fault parameters, an adaptive robust fault-tolerant controller is designed. Simulation results show that the proposed control scheme has a satisfactory effect in the both pitch and depth control when the bow and stern planes suffer from unknown faults.

An approach to estimate the position of the shear plane for colloidal particles in an electrophoresis experiment

The existence of the shear layer has great influence on the stability of colloidal systems and it is an important physicochemical parameter in the field of colloid and interface chemistry. However, to date, people do not know the actual position of the shear plane, and there is no theory to calculate the shear layer thickness. Conventionally, it is thought that the shear plane is very close to the Stern plane. In this study, a new theory for calculating the thickness of the shear layer for a planar charged colloidal particle in an aqueous solution was established; the shear layer thickness can be obtained based on the surface potential (the potential at the original plane of diffusion layer) and zeta potential of colloidal particles. The results showed that the surface potential of montmorillonite in various electrolyte solutions was approximately 3 to 6 times larger than the corresponding zeta potential. The thickness of the shear plane was dependent on the surface potential in the aqueous solution, and the shear plane was located far from the Stern plane but close to the Gouy plane, contradicting the widely accepted, erroneous placing of the shear plane close to the Stern plane. This study also showed that, ionic polarization in the electric field of the diffuse layer will significantly decrease the surface potential and the position of the shear plane.

Sliding Mode Prediction Control for 3D Path Following of An Underactuated AUV

Compared to the traditional 2D path following case, 3D path following is more complicated since the coupling effect between horizontal and vertical plane has to be taken into account. In this paper, a sliding mode prediction controller is presented, which drives an underactuated AUV to follow a desired 3D path under time-varying current disturbances. A sliding mode technique combined with the predictive control strategy is developed to compensate for the impact of the hydrodynamic damping coupling via the feedback correction and receding horizon optimization techniques. In addition, Different from the traditional reference orientation method for path following control, here a methodology named 3D virtual guidance orientation (VGO) is built to deal with the vehicle dynamics. The geometric characteristic of tracking curve is contained in the control design as an extra degree of freedom to drive the vehicle to track a virtual target along desired path. Hence, the proposed method can avoid saturation problem of driving devices (stern plane and rudder) of AUV. Numerical simulations illustrate the excellent path following performance of the AUV in 3D under the proposed control scheme.

Modifications of Control Loop to Improve the Depth Response of Autonomous Underwater Vehicles

During a constant depth maneuver of an autonomous underwater vehicle (AUV), its pitch attitude and stern plane deflections create forces and moments to achieve equilibrium in the vertical plane. If an AUV has a proportional controller only in its depth control loop, then different weights or centers of gravity will cause different steady-state depth errors at trimmed conditions. In general, a steady-state depth error can be eliminated by adding an integral controller in the depth control loop. However, an improper integrator may lead to a bad transient response, even though the steady-state depth error can finally be eliminated. To remove the steady-state depth error, this study proposes methods that adjust the depth command and add a switching integral controller in the depth control loop. Simulation results demonstrate that the steady-state depth error can be eliminated and the transient response can be improved.

Dynamic Sliding-Mode Control with Backstepping for Underactuated AUV in Diving Plane

A dynamic sliding-mode control (DSMC) with backstepping is proposed for diving control of autonomous underwater vehicle (AUV), where surge force and stern plane are only available for vehicle's 3DOF diving motion. First, an equivalent model of AUV is developed. Then, the DSMC with an asymptotical sliding surface is proposed for the trajectory tracking control of AUV. Moreover, the analysis of stability can be completed by Lyapunov stability theory. Finally, To demonstrate the effectiveness of the proposed method, the simulation results are illustrated in this paper. simulation results show that, the tracking precision and the robustness of the system are improved under the proposed control method.

Influence of the Ferroelectric Nature of Lithium Niobate to Drive Photocatalytic Dye Decolorization under Artificial Solar Light

Photocatalytic decolorization of acid black 1 (a.k.a. amido black 10B) and rhodamine b was investigated over powders of lithium niobate or lithium niobate doped with iron to form n-type material doped or p-type magnesium doped lithium niobate. In all cases, photostimulation was performed using simulated solar illumination. The rate of decolorization of the dye solutions was found to be fastest over p-type material than with the undoped powder, with the n-type proving least effective. The change in rate was attributed to changes in the majority carrier, associated with the dopant altering the ratio of reactive species (holes and electrons). We also show that the surface depolarization field associated with a ferroelectric material alters the surface chemistry by changing the Stern and inner Helmholtz plane due to the interaction of catalyst surface charge and the polar nature of solvated species. The spatial separation of REDOX reactions in ferroelectric powders positively influences the proportion of reac...

A nonlinear bottom-following controller for underactuated autonomous underwater vehicles

The bottom-following problem for underactuated autonomous underwater vehicles^(AUV) was addressed by a new type of nonlinear decoupling control law. The vertical bottom-following error and pitch angle error are stabilized by means of the stern plane, and the thruster is left to stabilize the longitudinal bottom-following error and forward speed. In order to better meet the need of engineering applications, working characteristics of the actuators were sufficiently considered to design the proposed controller. Different from the traditional method, the methodology used to solve the problem is generated by AUV model without a reference orientation, and it deals explicitly with vehicle dynamics and the geometric characteristics of the desired tracking bottom curve. The estimation of systemic uncertainties and disturbances and the pitch velocity PE (persistent excitation) conditions are not required. The stability analysis is given by Lyapunov theorem. Simulation results of a full nonlinear hydrodynamic AUV model are provided to validate the effectiveness and robustness of the proposed controller.

Inner-sphere complexation of cations at the rutile–water interface: A concise surface structural interpretation with the CD and MUSIC model

Acid–base reactivity and ion-interaction between mineral surfaces and aqueous solutions is most frequently investigated at the macroscopic scale as a function of pH. Experimental data are then rationalized by a variety of surface complexation models. These models are thermodynamically based which in principle does not require a molecular picture. The models are typically calibrated to relatively simple solid-electrolyte solution pairs and may provide poor descriptions of complex multi-component mineral–aqueous solutions, including those found in natural environments. Surface complexation models may be improved by incorporating molecular-scale surface structural information to constrain the modeling efforts. Here, we apply a concise, molecularly-constrained surface complexation model to a diverse suite of surface titration data for rutile and thereby begin to address the complexity of multi-component systems. Primary surface charging curves in NaCl, KCl, and RbCl electrolyte media were fit simultaneously using a charge distribution (CD) and multisite complexation (MUSIC) model [Hiemstra T. and Van Riemsdijk W. H. (1996) A surface structural approach to ion adsorption: the charge distribution (CD) model. J. Colloid Interf. Sci. 179, 488–508], coupled with a Basic Stern layer description of the electric double layer. In addition, data for the specific interaction of Ca 2+ and Sr 2+ with rutile, in NaCl and RbCl media, were modeled. In recent developments, spectroscopy, quantum calculations, and molecular simulations have shown that electrolyte and divalent cations are principally adsorbed in various inner-sphere configurations on the rutile 1 1 0 surface [Zhang Z., Fenter P., Cheng L., Sturchio N. C., Bedzyk M. J., Předota M., Bandura A., Kubicki J., Lvov S. N., Cummings P. T., Chialvo A. A., Ridley M. K., Bénézeth P., Anovitz L., Palmer D. A., Machesky M. L. and Wesolowski D. J. (2004) Ion adsorption at the rutile–water interface: linking molecular and macroscopic properties. Langmuir 20, 4954–4969]. Our CD modeling results are consistent with these adsorbed configurations provided adsorbed cation charge is allowed to be distributed between the surface (0-plane) and Stern plane (1-plane). Additionally, a complete description of our titration data required inclusion of outer-sphere binding, principally for Cl − which was common to all solutions, but also for Rb + and K +. These outer-sphere species were treated as point charges positioned at the Stern layer, and hence determined the Stern layer capacitance value. The modeling results demonstrate that a multi-component suite of experimental data can be successfully rationalized within a CD and MUSIC model using a Stern-based description of the EDL. Furthermore, the fitted CD values of the various inner-sphere complexes of the mono- and divalent ions can be linked to the microscopic structure of the surface complexes and other data found by spectroscopy as well as molecular dynamics (MD). For the Na + ion, the fitted CD value points to the presence of bidenate inner-sphere complexation as suggested by a recent MD study. Moreover, its MD dominance quantitatively agrees with the CD model prediction. For Rb +, the presence of a tetradentate complex, as found by spectroscopy, agreed well with the fitted CD and its predicted presence was quantitatively in very good agreement with the amount found by spectroscopy.