Stochastic facility location with general long-run costs and convex short-run costs

This paper addresses the problem of minimizing the expected cost of locating a number of single product facilities and allocating uncertain customer demand to these facilities. The total costs consist of two components: firstly linear transportation cost and secondly the costs of investing in a facility as well as maintaining and operating it. These facility costs are general and non-linear in shape and could express both changing economies of scale and diseconomies of scale. We formulate the problem as a two-stage stochastic programming model where both demand and short-run costs may be uncertain at the investment time. We use a solution method based on Lagrangean relaxation, and show computational results for a slaughterhouse location case from the Norwegian meat industry.     

Optimal setpoint chasing in dynamic positioning of deep‐water drilling and intervention vessels

Conventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal‐plane about desired position and heading co‐ordinates defined by the operator. A three degrees‐of‐freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi‐submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust‐induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work‐over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co‐ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi‐submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd.     

A study on long-term trends of the ionosphere using observations at Chong-qing, China

With long-term ionosonde records from 1947 to 2001 at Chong-qing, China, we show long-term trends of the ionospheric parameters, the critical frequencies of E-layer foE, F1-layer foF1 and F2-layer foF2, the E-layer height h'E, and the F2-layer peak height hmF2, respectively. Using an approach of discrete wavelet decomposition arithmetic, we have got the long-term components in the variations of the iono spheric parameters. It does exist nearly linear long-term decreasing trends of above ionospheric parameters from 1947 to 1990, then a nearly linear increase from 1990 to 2001. The decreases are approximately by 0. 35MHz, 0. 4MHz, 2MHz,20km, respectively, for foE, foF1, foF2 and hmF2, but increase by 4km for h'E,from 1947 to 1990. Simultaneously, we find similar long-term trends in the variations of 10.7cm solar radio flux and in sunspot number. The long-term components of the ionospheric parameters have extremely high correlation with those of 10.7cm solar radio flux and sunspot number. This implies that solar activities are the control factor of the long-term trends of the ionosphere. We confirm above conclusions with results from the long-term data at Slough station, UK.     

A survey of dynamic positioning control systems

Offshore exploration and exploitation of hydrocarbons have opened up an era of dynamically positioned (DP) vessels. DP control systems maintain floating structures in fixed position or pre-determined track for marine operation purposes exclusively by means of active thrusters. There are more than 2000 DP vessels of various kind operating worldwide. This paper gives a survey of some of the major technology advances in the DP controller design having taken place during more than 30 years of research and development. In addition some perspectives for the future with corresponding research challenges will be addressed.     

Stochastic pooling problem for natural gas production network design and operation under uncertainty

Product quality and uncertainty are two important issues in the design and operation of natural gas production networks. This paper presents a stochastic pooling problem optimization formulation to address these two issues, where the qualities of the flows in the system are described with a pooling model and the uncertainty in the system is handled with a multi‐scenario, two‐stage stochastic recourse approach. In addition, multi‐objective problems are handled via a hierarchical optimization approach. The advantages of the proposed formulation are demonstrated with case studies involving an example system based on Haverly's pooling problem and a real industrial system. The stochastic pooling problem is a potentially large‐scale nonconvex Mixed‐Integer Nonlinear Program (MINLP), and a rigorous decomposition method developed recently is used to solve this problem. A computational study demonstrates the advantage of the decomposition method over a state‐of‐the‐art branch‐and‐reduce global optimizer, BARON. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Design of hybrid controller for dynamic positioning from calm to extreme sea conditions

High-level control of dynamic positioning systems on marine vessels using hybrid controller is developed to extend the operational weather window for marine operations to harsh environments. The types of hybrid controller considered are multi-output PID controllers with position measurements, and multi-output PID and acceleration feedback controllers with position and acceleration measurements. Numerical simulations and experiments in addition to stability proof are conducted to verify the proposed hybrid-controller dynamic positioning system in varying environmental conditions from calm to extreme seas.     

Hybrid Observer Concept for Sensor Fusion of Sporadic Measurements for Underwater Navigation

International Journal of Control, Automation and Systems - Accurate underwater navigation systems are required for closed-loop guidance and control of unmanned underwater vehicles (UUV). This paper...     

Learning the Value of a New Currency From Prices.

In European countries, field studies investigate how citizens acquire knowledge of the new currency, the euro. In 3 laboratory experiments, the authors recruited 168 undergraduates to examine whether such accurate knowledge is acquired from learning prices in the new currency. The results show fast learning of prices of duration of cellular phone calls (quantity) when the prices were proportional to quantity. Inferences of call duration from given prices were likewise found to be accurate. Lower accuracy was however observed for one-to-many mappings of quantity on price and the inverse one-to-many mappings of price on quantity. Price variation may be an important reason for the difficulty in learning the value of the new currency observed in field studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)