Stability and parameters influence study of fully balanced hoist vertical ship lift
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A theoretical formulation based on the linearized potential theory, the Descartes\' rule and the extremum optimization method is presented to calculate the critical distance of lifting points of the fully balanced hoist vertical ship lift, and to study pitching stability of the ship lift. The overturning torque of the ship chamber is proposed based on the Housner theory. A seven-free-degree dynamic model of the ship lift based on the Lagrange equation of the second kind is then established, including the ship chamber, the wire rope, the gravity counterweights and the liquid in the ship chamber. Subsequently, an eigenvalue equation is obtained with the coefficient matrix of the dynamic equations, and a key coefficient is analyzed by innovative use of the minimum optimization method for a stability criterion. Also, an extensive influence of the structural parameters contains the gravity counterweight wire rope stiffness, synchronous shaft stiffness, lifting height and hoists radius on the critical distance of lifting points is numerically analyzed. With the Runge-Kutta method, the four primary dynamical responses of the ship lift are investigated to demonstrate the accuracy/reliability of the result from the theoretical formulation. It is revealed that the critical distance of lifting points decreases with increasing the synchronous shaft stiffness, while increases with rising the other three structural parameters. Moreover, the theoretical formulation is more applicable than the previous criterions to design the layout of the fully balanced hoist vertical ship lift for the ensuring of the stability.Keywords:
Hoist (device)
Counterweight
Lift (data mining)
Keel
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Abstract : The problem of roll, sway and yaw motions of surface ships is considered. A mathematical model is developed which consists of the nonlinear maneuvering equations and incorporates cross coupling between sway force, yaw moment and the roll angle induced during a steady turn. The hydrodynamic derivatives and coefficients of a typical container ship were used as the base- line study model. The coupled system of nonlinear algebraic equations is formulated and solved to predict the steady state roll angle, sway velocity and turning rate as a function of the rudder angle and compared to the decoupled systems currently employed. A local perturbation is implemented in the vicinity of the above steady states to investigate dynamic stability of motion. Sensitivity analysis with respect to important design parameters such as speed loss during turing, approach speed, transverse metacentric height and trim is performed. Results demonstrate the significance of the coupling between roll, sway and yaw and the need to incorporate similar studies in the ship design and analysis process.
Rudder
Yaw
Trim
Polar coordinate system
Turning radius
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It is easy to analyze its dynamical characteristic for lift subsystem because it is a structural system. Inertia caused by mass in hydraulic subsystem is ignored so that it is difficult to get its dynamical response. Considering the characteristics of the two systems, a dynamic coupling synthetically method was put forward. The key is that the dynamic equation of hydraulic subsystem is coupled into the equation of lift subsystem. For the inertia caused by mass in lift is considered, the dynamical synthetical equation is a structural equation. The coupling mathematical model was established. The dynamic response during lifting was calculated by using numerical integral algorithm.
Lift (data mining)
Dynamic equation
Hydraulics
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Hoist (device)
Decoupling (probability)
Oscillation (cell signaling)
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Based on the potential theory about Weis-Fogh mechanism,the lift model of fin stabilizer is researched on,when a ship is at zero speed.It is discussed that how to rotate Wesis-Fogh mechanism to generate the lifting force needed for antirolling.According to Riccati equation,the conditions which assure the existence and stability of period solution,are gaven.Using Rungr-Kutta methods,the numerical solution of the model is obtained,and the global error of discretization is investigated.The results are colsely matched by numerical experiments.
Lift (data mining)
Fin
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Abstract : A control system was designed to attenuate vertical accelerations for the XR-3 captured air bubble type surface effect ship using linear regulator techniques applied to the simplified nonlinear equations of motion. A pressure lift-only model was used to represent the craft vertical heave motion and was linearized around the steady state operating point. Model validation was obtained through analysis of the frequency spectrum. State variable feedback was used to determine a set of optimal control gains that would reduce the magnitude of the heave acceleration during operation under simulated sea input conditions. (Author)
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The present work focuses on the development of a numerical body nonlinear time-domain method for estimating the effect of active roll fin stabilizers on ship roll motion in both regular and irregular seaway. The time-domain analysis aims at providing fast and accurate ship responses that will be useful during the design process through accurate estimation of the environmental loads. A strip theory-based approach is followed where the Froude-Krylov and hydrostatic forces are calculated for the exact wetted surface area for every time step. The equations of motions are formulated in the body frame and consider the six degrees of coupled motions. The active fin, rudder, and propeller modules are included in the simulation. This leads to accurate modeling of the system dynamics. The numerical unstabilized roll motion is validated with experimental seakeeping simulations conducted on a Coastal Research Vessel (CRV). The phenomena of Parametric Rolling (PR) is identified during the numerical investigation of the candidate vessel. Besides, a nonlinear PID (NPID) control technique and LQR method is implemented for active roll motion control and its performance is observed in regular as well as irregular waves. The proposed numerical approach proves to be an effective and realistic method in evaluating the 6-DoF coupled ship motion responses.
Seakeeping
Rudder
Fin
Hydrostatic equilibrium
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Ship motions
Sea state
Response amplitude operator
Model Predictive Control
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A simulation method for investigating the vibration behavior of hoisting rope with time-varying length is improved. By previously creating markers in the MSC.ADAMS software package, the parametric model of the rope wound along helix is established based on the concentrated-mass theory with multi-degree of freedom (multi-DOF). A novel driving strategy, cooperating fixed joints with angle sensors under the control of driving script, is proposed to substitute conventional contact force. Researching on the hoisting rope in the sinking winch mechanism, an equivalent discretization model is obtained with complicated boundary conditions considered. The differential equations of motion of the hoisting system are formulated employing Lagrange's equation and numerically solved using Runge–Kutta method. The simulation indicates that the horizontal swing is decreased in principle and the simulation with 800 discrete ropes is not performed more than 61 min. Therefore, this feasible strategy could not only guarantee the accuracy but also promote simulation efficiency and stability. The motion curves exported from ADAMS simulation coincide with one in numerical simulation, which validates both the numerical model and the driving strategy.
Winch
Dynamic simulation
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This paper deals with development and simulation of the nonlinear model of an elastic ship-mounted crane equipped with the Maryland Rigging. The model contains three inputs to control the planar vibrations due to the planar base excitation; the luff angle is proposed to control the elastic vibration in the boom, and the length of the upper cable in conjunction with the position of its lower suspension point are proposed to control the pendulation of the payload. It is observed, through static and dynamic testing of the derived model, that moving the lower suspension point of the upper cable provides strong controllability of the horizontal displacement of the payload, while changing the length of the cable can be employed to compensate for the vertical displacement. Simulation results show that within a considerable range of pendulation displacements of the payload, the nonlinear model and the linearized one reflect nearly equivalent responses. Hence, with the property of strong controllability, the linear model can be used efficiently to design the control system, which will be discussed later in another paper.
Payload (computing)
Suspension
Position (finance)
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