XZ
X. Zhang
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6 records found
1
Review
(2019)
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R. S.W. van de Wal, X. Zhang, S. Minobe, S. Jevrejeva, R. E.M. Riva, C. Little, K. Richter, M. D. Palmer
Many processes affect sea level near the coast. In this paper, we discuss the major uncertainties in coastal sea-level projections from a process-based perspective, at different spatial and temporal scales, and provide an outlook on how these uncertainties may be reduced. Uncertainty in centennial global sea-level rise is dominated by the ice sheet contributions. Geographical variations in projected sea-level change arise mainly from dynamical patterns in the ocean response and other geophysical processes. Finally, the uncertainties in the short-duration extreme sea-level events are controlled by near coastal processes, storms and tides.
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Many processes affect sea level near the coast. In this paper, we discuss the major uncertainties in coastal sea-level projections from a process-based perspective, at different spatial and temporal scales, and provide an outlook on how these uncertainties may be reduced. Uncertainty in centennial global sea-level rise is dominated by the ice sheet contributions. Geographical variations in projected sea-level change arise mainly from dynamical patterns in the ocean response and other geophysical processes. Finally, the uncertainties in the short-duration extreme sea-level events are controlled by near coastal processes, storms and tides.
We propose a primal-dual interior-point (PDIP) method for solving quadratic programming problems with linear inequality constraints that typically arise from MPC applications. We show that the solver converges (locally) quadratically to a suboptimal solution of the MPC problem. PDIP solvers rely on two phases: the damped and the pure Newton phases. Compared to state-of-the-art PDIP methods, our solver replaces the initial damped Newton phase (usually used to compute a medium-accuracy solution) with a dual solver based on Nesterov's fast gradient scheme (DFG) that converges with a sublinear convergence rate of order O(1/k2) to a medium-accuracy solution. The switching strategy to the pure Newton phase, compared to the state of the art, is computed in the dual space to exploit the dual information provided by the DFG in the first phase. Removing the damped Newton phase has the additional advantage that our solver saves the computational effort required by backtracking line search. The effectiveness of the proposed solver is demonstrated on a 2-dimensional discrete-time unstable system and on an aerospace application
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We propose a primal-dual interior-point (PDIP) method for solving quadratic programming problems with linear inequality constraints that typically arise from MPC applications. We show that the solver converges (locally) quadratically to a suboptimal solution of the MPC problem. PDIP solvers rely on two phases: the damped and the pure Newton phases. Compared to state-of-the-art PDIP methods, our solver replaces the initial damped Newton phase (usually used to compute a medium-accuracy solution) with a dual solver based on Nesterov's fast gradient scheme (DFG) that converges with a sublinear convergence rate of order O(1/k2) to a medium-accuracy solution. The switching strategy to the pure Newton phase, compared to the state of the art, is computed in the dual space to exploit the dual information provided by the DFG in the first phase. Removing the damped Newton phase has the additional advantage that our solver saves the computational effort required by backtracking line search. The effectiveness of the proposed solver is demonstrated on a 2-dimensional discrete-time unstable system and on an aerospace application
This research investigates the feasibility of magnetic ion exchange (MIEX) resin as the adsorbent for the removal of chlorite through a laboratory study using batch adsorption experiments. The agitation speed of 100 rpm is the optimum agitation intensity. The removal efficiency of chlorite increases with increasing dosage of MIEX resin. The optimum pH is 5–7. The coexisting anions and natural organic matter reduce the removal efficiency of chlorite. The kinetic process at the low chlorite concentration (1.02 mg/L) is highly possible to be pseudo-first-order. However, the pseudo-second-order model can fit the kinetic data quite well at higher chlorite concentrations (2.28–5.57 mg/L). At the initial stage of adsorption, the intra-particle diffusion is the rate-limiting step, but the adsorption rate is controlled by the film diffusion and the intra-particle diffusion after 10 min. The adsorption equilibrium can be approximately attained within 40 min, and Redlich–Peterson isotherm model fits best to the equilibrium data. The adsorption is a thermodynamically feasible, spontaneous, and endothermic ion-exchange process. The removal of chloride on MIEX resin is an ion-exchange mechanism. Dissolved organic carbon can be removed effectively as well as chlorite and chlorate using MIEX resin in real water. Therefore, MIEX resin is a promising technology for the removal of chlorite from aqueous solution.
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This research investigates the feasibility of magnetic ion exchange (MIEX) resin as the adsorbent for the removal of chlorite through a laboratory study using batch adsorption experiments. The agitation speed of 100 rpm is the optimum agitation intensity. The removal efficiency of chlorite increases with increasing dosage of MIEX resin. The optimum pH is 5–7. The coexisting anions and natural organic matter reduce the removal efficiency of chlorite. The kinetic process at the low chlorite concentration (1.02 mg/L) is highly possible to be pseudo-first-order. However, the pseudo-second-order model can fit the kinetic data quite well at higher chlorite concentrations (2.28–5.57 mg/L). At the initial stage of adsorption, the intra-particle diffusion is the rate-limiting step, but the adsorption rate is controlled by the film diffusion and the intra-particle diffusion after 10 min. The adsorption equilibrium can be approximately attained within 40 min, and Redlich–Peterson isotherm model fits best to the equilibrium data. The adsorption is a thermodynamically feasible, spontaneous, and endothermic ion-exchange process. The removal of chloride on MIEX resin is an ion-exchange mechanism. Dissolved organic carbon can be removed effectively as well as chlorite and chlorate using MIEX resin in real water. Therefore, MIEX resin is a promising technology for the removal of chlorite from aqueous solution.
This paper presents an improved zero vibration method for the swing control of bridge-type grab ship unloader. With the method, the concepts of equivalent frequency and the equivalent damping ratio are proposed to cope with the changeable length of rope, and the optimal path planning is considered to avoid collision and improve efficiency. Numerical simulation results of a case study indicate that the maximum residual swing angle of the grab can be limited to a small range to ensure safety using the improved zero vibration method, whereas the traditional zero vibration method with average frequency and zero damping ratio gets poor results of swing control. After that, the sensitivities of the max residual swing angle to the changes of some main design parameters (damping coefficient, deviation of the center of gravity of the grab in rope direction, and time delay of the system) and operating parameters (position deviation of the trolley, initial length deviation of the rope, and initial swing angle) are analyzed. The results obtained display that the residual swing angle is sensitive to the deviation of grab’s center of gravity, the deviation of trolley’s position, and the initial swing angle under the same control parameters, but insensitive to the damping coefficient, the time delay of the system, and the initial length deviation of the rope. This can help to select the appropriate parameter values or adaptive range in an actual unloader.
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This paper presents an improved zero vibration method for the swing control of bridge-type grab ship unloader. With the method, the concepts of equivalent frequency and the equivalent damping ratio are proposed to cope with the changeable length of rope, and the optimal path planning is considered to avoid collision and improve efficiency. Numerical simulation results of a case study indicate that the maximum residual swing angle of the grab can be limited to a small range to ensure safety using the improved zero vibration method, whereas the traditional zero vibration method with average frequency and zero damping ratio gets poor results of swing control. After that, the sensitivities of the max residual swing angle to the changes of some main design parameters (damping coefficient, deviation of the center of gravity of the grab in rope direction, and time delay of the system) and operating parameters (position deviation of the trolley, initial length deviation of the rope, and initial swing angle) are analyzed. The results obtained display that the residual swing angle is sensitive to the deviation of grab’s center of gravity, the deviation of trolley’s position, and the initial swing angle under the same control parameters, but insensitive to the damping coefficient, the time delay of the system, and the initial length deviation of the rope. This can help to select the appropriate parameter values or adaptive range in an actual unloader.