Transverse Stability Research Articles

Reinforcement Learning-Based Optimal Hull Form Design with Variations in Fore and Aft Parts

Abstract With recent advancements in artificial intelligence technology, various studies are being conducted in the shipbuilding industry. Traditionally, hull form variation methods have relied on the intuition and expertise of designers, leading to inconsistent results and unintended changes in the ship's main dimensions depending on the designer's competence. Moreover, the iterative process of design variation and analysis to derive the optimal hull form is both costly and time-consuming. To address these issues, this study proposes an optimal hull design technique utilizing reinforcement learning, a type of unsupervised learning in machine learning. Reinforcement learning allows the model to learn from past policies by recording and accumulating the rewards associated with various actions taken by an agent in a specific environment. In this study, after calculating the main parameters of the ship, the agent defines a state representing hull information and performs local transformations of the bow and stern. The reward of reinforcement learning is defined as the change in total resistance due to the hull deformation, constrained by limiting the tolerance of the ship's prismatic coefficient (CP) and longitudinal center of buoyancy (LCB). In this study, the problem is solved by comparing the proximal policy optimization (PPO) algorithm and the deep deterministic policy gradient (DDPG) algorithm to find the best deep reinforcement learning (DRL) model for the hull optimization problem. The results were compared with the genetic algorithm and speed-constrained multi-objective particle swarm optimization (SMPSO), and the optimal hull resistance values were less different, but the time of the reinforcement learning model was five times shorter.

An Adaptive Controller with Disturbance Observer for Underwater Vehicle Manipulator Systems

Dynamic control of underwater vehicle manipulator systems (UVMSs) is the key part of underwater intervention tasks. In this paper, we propose an adaptive controller with a disturbance observer that mainly consists of two parts: the first part is the adaptive control law that estimates the changes in the center of mass (COM) and the center of buoyancy (COB) of the vehicle, and the second part is the nonlinear disturbance observer that estimates the external disturbance and model uncertainties. To attenuate the overestimation problem, a damping term is introduced to the adaptive law. The stability of the proposed method is proven on the basis of Lyapunov theory. We develop three scenarios on the Simurv platform and illustrate the effectiveness of the proposed method with a short response time and high tracking performance.

Strange nonchaotic attractors and bifurcation of a four-wheel-steering vehicle system with driver steering control

In this paper, a dynamical model is developed for the four-wheel-steering(4WS)vehicles, with nonlinear lateral tyre forces and quasi-periodic disturbances from the steering mechanism and quasi-periodic pavement external deformation. Initially, the stability and Hopf bifurcation of the 4WS vehicle system without disturbance are analyzed employing the central manifold theory and projection method. The effects of parameters on the stability and the types of Hopf bifurcation for the vehicle system are also discussed. It is shown that both Hopf bifurcation and degenerate Hopf bifurcation occur in the vehicle system. The critical speed decreases with increased driver’s perceptual time delay and distance from the vehicle’s center of gravity to the front axles, while it increases with the control strategy coefficient. However, the increase of the frontal visibility distance of the driver leads to an initial increase of the critical speed, decreasing afterwards. Subsequently, the strange nonchaotic dynamical behaviour of the disturbed 4WS system is investigated. Several routes and mechanisms for the birth of strange nonchaotic attractors (SNAs) are identified, including the torus doubling bifurcation, the torus fractalization, and the loss of transverse stability of a torus. Finally, the nonchaotic property is verified through the calculation of the maximum Lyapunov exponent, and the strange property is characterized using power spectra and rational approximation.

Real-time prediction of metacentric height of ro-ro passenger ships in Qiongzhou strait based on improved RBF neural network

Addressing the complexities and real-time challenges in calculating ship metacentric height (GM), this study proposes an improved method using an optimized radial basis function neural network (RBFNN) for real-time GM prediction. Bayesian optimization is introduced to fine-tune the hyperparameters of the RBFNN, aiming to enhance the model's generalization performance. The study focuses on the Qiongzhou Strait Ro-ro passenger ship ‘Zijing No.11’ and selects three GM-related factors as neural network inputs using grey correlation analysis. The GM calculated by the empirical formula serves as the expected value, which is compared with predictions from various algorithms. Simulation results demonstrate that the improved RBFNN achieves significantly lower prediction errors compared to the unoptimized version. Furthermore, compared to other machine learning models and artificial neural networks, the proposed model exhibits superior performance in predicting ship initial stability height. Consequently, this model offers a practical tool for accurate and real-time GM prediction, enhancing intelligent stowage and operational efficiency in shipping.

Numerical Investigation of the Effects of Aspect Ratio on the Hydrodynamic Performance of a Semi-Planing Catamaran

Abstract A semi-planing catamaran is a type of marine craft that benefits from high speed, in conjunction with the its inherent characteristics such as a large deck and high transverse stability. The aspect ratio, length over the beam of a demi-hull, significantly affects the hydrodynamic performance of this vessel. In this study, the effects of the aspect ratio on the hydrodynamic performance of a semi-planing catamaran in calm water and waves are investigated using numerical simulations. The numerical simulation of the AUT-SEM00 model itself is validated by its model test results. The results show that increasing the aspect ratio significantly increases the wetted surface, and that the increase in resistance in calm water is negligible. In addition, increasing the aspect ratio radically reduces the amplitude of vertical acceleration in waves at the center of gravity by up to 85%. Consequently, the seakeeping performance is considerably improved, and the risk to crew and equipment is reduced.

Surgical management strategies for unstable sacral fractures: Case series and surgical guideline

IntroductionUnstable sacral fractures usually have posterior pelvic and spinopelvic instability, which usually be classified as AO type C. There are many controversial points concerning the management of these fractures due to their rarity. Herein, we retrospectively review cases of this injury and propose a surgical guideline. Case presentationA 37-year-old female experienced back pain after a motor vehicle accident. Diagnostic imaging revealed an AO type C1 sacral fracture, Isler subtype 2a (case No. 7). Preoperative CT scan and CT reconstruction images showed a longitudinal fracture with a simple intraarticular fracture of the left S1 superior facet. Although the patient sustains a lumbosacral facet joint injury, the lumbosacral motion seems preservable after healing. The triangular osteosynthesis was chosen because it provides both transverse plane and vertical plane stability. The patient was allowed to continue weight-bearing ambulation after the operation. To maintain lumbosacral motion, the spinopelvic rod was removed in the postoperative seventh month. DiscussionThe unstable sacral fracture might have instability in both the vertical and transverse planes. The fixation construct should provide both vertical and transverse stability. Regarding vertical fixation, it might cost a loss of lumbosacral motion, which the treating surgeon has to consider. The lumbosacral injury is sometimes trivial, and long-term lumbosacral motion is expectable. So, permanent spinopelvic fixation is not necessary. The patient's character is also an important factor. Whether the patient needs or does not need early progressive weight bearing after the operation determines the fixation method. ConclusionUnstable sacral fractures are rare conditions usually resulting from a high-energy injury. We have proposed a surgical management strategy for this group of fractures with an optimal fixation method based on three factors: 1) fracture morphology, 2) lumbosacral integrity, and 3) concomitant injury.

Design upon Atmosphere: Review of Landscape Design of Meta Center in Shangdi, Beijing

Design upon Atmosphere: Review of Landscape Design of Meta Center in Shangdi, Beijing

Stability of floating objects at a two-fluid interface

We explore the stability of floating objects at a two-fluid interface through mathematical modeling and experimentation. Our models are based on standard ideas of center of gravity, center of buoyancy, and Archimedes’ Principle extended to the two-fluid scenario. We investigate floating shapes with uniform, two-dimensional cross sections and identify analytically and/or computationally a potential energy landscape that helps identify stable and unstable floating orientations. We compare our analyses and computations to experiments on floating objects designed and created through 3D printing. Additionally, the paper includes open problems for further study.

Nonlinear Robust Stabilization of Ship Roll by Convex Optimization

For ship roll stabilization, this paper presents a nonlinear robust controller design method using the sum of squares (SOS) technique combined with the dual of Lyapunov's stability theorem. Varying ship speed and initial metacentric height are seen as uncertainties, sea waves are regarded as external disturbance, and then the robust nonlinear controller is also designed based on the suggested method. Simulations are performed by taking container ship model as an example. It is shown that the designed system guarantees robust performance with respect to the uncertainties and disturbance.

Hydrodynamic performance of sandglass-type floating body with damping appendages

In the case of sandglass-type floating bodies (STFBs), small water-plan area with low metacentric height may limit their dynamic stability. One strategy to solve this problem is to use damping appendages. Therefore, the main objective of the present paper is to study the effects of the heave damping plate (as a horizontal plate), and flap (as an oblique plate) on the dynamic response of STFBs. To achieve this accomplishment, a STFB is numerically simulated in a numerical wave tank (NWT) in an open-source package of OpenFOAM. CFD results are compared with experimental and other numerical data, an acceptable accuracy is achieved. The main results of the current study show that using damping appendages has significant effects on control of the heave and pitch motions of the STFB. The most acceptable dynamics of this floating structure is also achieved for STFBs using flap with approximately 30% less heave motion and about 20% less pitch motion compared to the original version.

On the transverse stability of smooth solitary waves in a two-dimensional Camassa–Holm equation

We consider the propagation of smooth solitary waves in a two-dimensional generalization of the Camassa–Holm equation. We show that transverse perturbations to one-dimensional solitary waves behave similarly to the KP-II theory. This conclusion follows from our two main results: (i) the double eigenvalue of the linearized equations related to the translational symmetry breaks under a transverse perturbation into a pair of the asymptotically stable resonances and (ii) small-amplitude solitary waves are linearly stable with respect to transverse perturbations.

Accurate and robust linear representation for containership stability conditions with ballast water

Stowage planning involves optimizing the placement of cargo on a ship while ensuring the ship's stability conditions are met. This optimization problem is typically formulated as a mixed-integer linear programming problem. However, a challenge arises in representing stability conditions as linear constraints since these conditions have non-linear relationships to the decision variables. Although there are methods for linearizing these stability conditions, they lack a systematic modeling approach and numerical verification of accuracy and reliability. In particular, the complex and diverse nature of ballast water contributes to significant non-linearity, posing a considerable challenge in developing an accurate linear approximation. This study proposes linear prediction methods that incorporate ballast water to address major stability conditions such as trim, drafts, shear force, bending moment, torsion, and transverse metacentric height. We introduce a comprehensive training and testing methodology for prediction, and validate the proposed method by comparing it with true values on two ships of different capacities, demonstrating its accuracy and scalability.

Effects of fuselage shape on helicopter aerodynamic performance in case of intermeshing-rotor interference

To study the influence of fuselage shape on the aerodynamic performance of a helicopter under the interference of an intermeshing-rotor, a numerical simulation method of flow field under the forward flight state of Synchropter is established based on the lattice Boltzmann method. Firstly, the Maryland helicopter was calculated to verify the scientific validity of the method. Then, the simplified S-97 fuselage was used as the object of analysis to analyze the aerodynamic data such as surface pressure, friction, and lift resistance of the fuselage with different head curvature, cross-section shapes, and transition segments under Synchropter interference with different attack angles in forward flight. The results show that increasing the radius of curvature of the nose can reduce the total drag of the fuselage; the fuselage with a circular cross-section shape has better aerodynamic characteristics of lift resistance, and the fuselage with rhombic cross-section shape has better transverse stability; the transition section with backward position, smaller upward dihedral angle, and smooth transition can avoid serious airflow separation and achieve the purpose of drag reduction.

Floating House Platform Stability Test with a Lightweight Concrete Cover Made of Expanded Polystyrene System (EPS)

Coastal area which affected by floods and tides has problems about safety and comfortable environment. The world of floating construction has introduced substructure foundations made from expanded polystyrene system (EPS) with a lightweight concrete cover. The styrofoam platform must meet the buoyancy, stability and center height test requirements. The research aims to analyze the magnitude of the buoyant force (Fa) against downward force due to the load weight on platform. The platform is strong and stable when upward force (Fa) is greater than total structure weight (G). The object will float if buoyant force (Fa) is greater than the gravitational force (g). The balance is stable if center of object gravity (Bo) is below the center of buoyancy (Ao), otherwise it will be in arbitrary balance. The height of centrum can be determined m > 0, means the object is stable. The research results show that 6.12x5.12x0.68m Styrofoam platform with a buoyancy force of 18,246.6 kg is able to withstand an additional load of 3647.62 kg with an SF value of 2.59. It means there is a linear relationship between magnitude of loading value and sinking height of Styrofoam platform. The safety factor value decreases as the sinking height of platform increases. The stability value of Fa/G is 3.01>1.2. The metacentrum’s height is 16.531 > 0, so the platform with a lightweight concrete cover is declared stable and safe to use.

Countergradient turbulent transport in a plume with a crossflow

AbstractDirect numerical simulation of a turbulent forced buoyant plume in a crossflow is performed at a source Reynolds number $${\text{ Re }}_0=1000$$ Re 0 = 1000 , Richardson number $$\mathrm{{Ri}}_0=1$$ Ri 0 = 1 , Prandtl number $$\mathrm{{Pr}}=1$$ Pr = 1 and source-to-crossflow velocity ratio $$R_0=1$$ R 0 = 1 . The instantaneous and temporally averaged flow fields are assessed in detail, providing an overview of the flow dynamics. The velocity, temperature and pressure fields are used together with enstrophy fields to describe qualitatively the evolution of the plume as it is swept downstream by the crossflow, and the mechanisms involved in its evolution are outlined. The plume trajectory is determined quantitatively in a number of ways, and it is shown that the central streamline and the centre of buoyancy of the plume differ significantly—as with jets in crossflow, the central streamline is seen to follow the top of the plume, whereas the centre of buoyancy, by definition, describes the plume as a whole. We then investigate the turbulence properties inside the plume; in particular the eddy viscosity and diffusivity are presented, which are significant parameters in turbulence modelling. Assessment of turbulence production demonstrates the presence of regions where turbulence kinetic energy is redistributed to the kinetic energy of the mean flow, implying a negative eddy viscosity within certain regions of the domain. Similarly, the observation that the buoyancy flux and buoyancy gradient are anti-parallel in specific regions of the flow implies a negative eddy diffusivity in said regions, which must be realised in models of such flows in order to capture the countergradient transport of thermal properties. A characteristic eddy viscosity and diffusivity are presented, and shown to be approximately constant in the fully developed regime, resulting in a constant characteristic turbulent Prandtl number, in turn signifying self-similarity.

Numerical study of the Serre–Green–Naghdi equations in 2D *

A detailed numerical study of solutions to the Serre–Green–Naghdi (SGN) equations in 2D with vanishing curl of the velocity field is presented. The transverse stability of line solitary waves, 1D solitary waves being exact solutions of the 2D equations independent of the second variable, is established numerically. The study of localized initial data as well as crossing 1D solitary waves does not give an indication of existence of stable structures in SGN solutions localized in two spatial dimensions. For the numerical experiments, an approach based on a Fourier spectral method with a Krylov subspace technique is applied.

Time to capsize for damaged passenger ships in adverse weather conditions. A Multi-modal analysis

After an accident in open seas, the final fate for a damaged ship could be the loss of stability/floatability and consequently capsize/sinkage. The latter may occur even in calm water, but is more critical and probable in adverse weather conditions, i.e., in irregular waves. Identifying a possible capsize event and determining the time that it takes for the ship to capsize is extremely important for safety and risk assessment, meaning whether it would be possible or not to evacuate the ship in a specific scenario and the possibility of loss of life. In this respect, and notwithstanding the impact of many other factors, model tests or time-domain simulations could be used to provide answers to this question. However, even in this case, dealing with irregular waves, entails that both approaches are affected by the random nature of phase spectral components, which leads to a different time to capsize determination at each run/simulation or to the identification of cases where the vessel is not capsizing in the given time window. Here, a dedicated study is provided to describe the time to capsize in irregular waves for critical damages. Simulations performed on a passenger ship at different wave heights and different metacentric heights highlights the appearance of more than one capsize mode for the same damage case. A model based on Mixed-Weibull distributions has been developed to describe the multi-modal behaviour of the time to capsize distributions for the analysed damage cases.

Requirements for the vessels operation at heavy-lift cargoes carriage

The approaches used by different classification societies to standardize calculated acceleration under ship motion during heavy lift cargoes transportation are analyzed in the paper. The methods of estimating the efficiency of securing devices of “non-standardized cargoes” carried on ships are investigated. The analysis of the parameters taken into account in determining the design accelerations at ship motion is carried out. Five representative vessels, which had previously carried heavy lift cargoes under different conditions, are selected. Computer modelling of these vessels motion at different course angles is performed in “SafeSea” programme, and calculated (conditional) amplitudes of motion regulated by the Rules of the Russian Classification Society are determined by “Stabedit” programme. The forced and own periods of onboard rolling are calculated in the specialised software complex “Anchored Structures” at variation of wave modes, loading states and values of metacentric height. The calculation results for representative vessels have shown a satisfactory matching of own and forced rolling periods. It is noted that in the range of 1.5 m ≤ h3 % ≤ 4.5 m for the considered intervals of metacentric height, in most cases the forced rolling periods are slightly longer than the own ones. Based on the results of the research, the recommendations for determination of rolling amplitudes of inland and mixed navigation vessels of “P”, “O”, “M”, “O-PR”, “M-PR”, “M-SP” classes carrying heavy lift cargoes are given. The proposals on standardised design acceleration at motion of a ship carrying heavy lift cargo are also given for the mentioned classes of ships. The results of the research are included in the draft Guidelines for the assignment of design acceleration at rocking of mixed (river-sea) and inland navigation vessels and safety margins of heavy lift cargoes securing systems, developed for the Russian Classification Society

Preface

The 12th International Beam Instrumentation Conference, IBIC’23, was hosted by the Canadian Light Source (CLS) in Saskatoon, Saskatchewan, Canada from Sunday, September 10th to September 14th, 2023. IBIC is dedicated to exploring the physics and engineering challenges of beam diagnostic and measurement techniques for particle accelerators. IBIC’23 was attended by 182 delegates from 18 countries. IBIC’23 included 18 invited talks, 18 contributed talks, 2 tutorials, 114 posters, and a 3-day vendor exhibition with 18 industrial exhibitors in attendance. Twenty-five young scientists from all over the globe attended the conference. Nine of these students received grants thanks to sponsorship from the City of Saskatoon, Tourism SK, Discover Saskatoon and Innovation SK and contribution from the industrial exhibitors. The organizers of IBIC’23 are grateful to all sponsors for their valued support.The conference venue was TCU Place, a 104,000-square-foot convention and arts centre situated in downtown Saskatoon. Welcome remarks were delivered by CLS CEO, Bill Matiko, Saskatoon Mayor, Charlie Clark and University of Saskatchewan President Peter Stoicheff and Tonia Batten (CLS), IBIC’23 Conference Chair, opened the conference.The scientific program was developed by a 23-member Scientific Program Committee (SPC). Oral and poster sessions were grouped according to the following nine IBIC classifications. Beam Charge and Current Monitors • Diagnostic systems measuring the average beam current, instantaneous total intensity or individual bunch intensity. Beam Loss Monitors and Machine Protection • Diagnostic systems measuring the average beam loss, instantaneous beam loss or individual bunch loss.• Machine protection architectures based on inputs from beam instrumentation systems, as well as machine protection apparatus such as scrapers, collimators, radiation shields, etc. Beam Position Monitors • Diagnostic systems used for the measurement of beam position: orbit measurement techniques, trajectory measurement techniques, and bunch-by-bunch position measurement systems.• This track includes the use of diagnostics associated with secondary beams, e.g. photon beamlines, to measure the position of the charged particle beam. Data Acquisition and Processing Platforms • Data acquisition systems or architectures of relevance for beam diagnostic systems. This includes acquisition platforms, data processing techniques, electronic component validation or characterization.• Computing platforms, control and acquisition software and operating systems of relevance for beam diagnostics. Feedback Systems and Beam Stability • Systems used to stabilize or control any beam or accelerator parameter either in a closed or open loop. This includes control of orbit, trajectory, longitudinal stability, bunch-by-bunch transverse stability, emittance, tune, chromaticity, etc.• This can include descriptions of the detectors, actuators, any specialized acquisition electronics used to acquire the signal, as well as related data processing techniques. The feedback or feedforward aspects should, however, form a major part of the submission, otherwise, the diagnostic description would be better suited to the track dealing with the primary measurement under discussion. Longitudinal Diagnostics and Synchronization • Diagnostic systems used for the measurement of longitudinal beam parameters such as bunch length, bunch profile, arrival time, energy spread, or longitudinal emittance.• Systems used for beam synchronization and timing distribution. Machine Parameter Measurements • Systems used to measure machine parameters such as betatron tune, chromaticity, higher-order multipoles, space charge, impedance, beam-beam, etc.• Techniques and algorithms used for such measurements.• Other diagnostic devices or techniques which do not clearly match any of the previous tracks. Overview and Commissioning • General description of beam instrumentation devices and systems at new facilities or machine upgrades.• Commissioning results and lessons learned.• Workshop reports related to beam diagnostics. Transverse Profile and Emittance Monitors • Diagnostic systems used for the measurement of transverse beam size, transverse beam profile, transverse emittance, and beam halos.• This track includes both interceptive and non-interceptive diagnostics.The distribution of talks by classification was 5% Beam Charge and Current Monitors, 8% Beam Loss Monitors and Machine Protection, 13% Beam Position Monitors, 16% Data Acquisition and Processing Platforms, 8% Feedback Systems and Beam Stability, 18% Longitudinal Diagnostics and Synchronization, 8% Machine Parameter Measurements, 16% Overview and Commissioning and 8% Transverse Profile and Emittance Monitors.The regional distribution for participation was 37% from the Americas, 18% from Asia and 45% from Europe. The regional distribution of talks was 32% from the Americas, 26% from Asia and 42% from Europe. The gender ratio for oral presentations was 82% male and 18% female. The oral presentations were 79% onsite talks and 21% remote talks.List of Industrial Exhibition, Peer Reviewed Proceedings, IBIC2023, Peer Review General Policies, IBIC 2023 Peer Review Acceptance Criteria, IBIC 2023 Questions posed to referee in SPMS review module and Committees are available in this Pdf.

DESIGN AND ANALYSIS OF THE OVERHEAD CRANE WITH SIX VERTICAL COLUMNS

This study delves into the comprehensive examination of an overhead crane’s construction, focusing on its frame, columns, and beams, while considering factors such as strength, stability, and stiffness. Through an in-depth review in the design domain, it is proposed a specific structural configuration for the overhead crane. This design comprises six vertical columns supporting two longitudinal beams equipped with tracks for the trolley’s longitudinal movement. Additionally, cross beams featuring winches are mounted on the trolley’s cross beams. The crane’s columns are securely mounted on a foundation, and struts are employed to attach the crane to the load-bearing wall of the building, ensuring longitudinal and transverse stability. The inclusion of cross truss structures with longitudinal struts further enhances the crane’s overall stiffness, with additional vertical struts provided to augment the left side’s longitudinal stiffness. The study also encompasses the analysis of the crane frame’s construction, complete with the development of an appropriate calculation scheme and the computation of static reactions in supports. Further calculations involve determining the cross-sections of vertical columns and longitudinal beams, ensuring compliance with strength, rigidity, and stability requirements. The selected cross-section for the columns, in the form of a square profile pipe (100×100×3 mm), is meticulously chosen to meet these criteria. Simulation modeling of load scenarios on the crane frame elements in SolidWorks software validates their strength, stiffness, and stability. Mathematical models and calculations provided the optimal parameters and characteristics of each crane component, ensuring a superior level of safety and operational efficiency. These results provide valuable insights for future research in mechanical engineering and the design of industrial mechanisms.