On solving optimal control problems with free initial condition using iterative dynamic programming

For solving optimal control problems where the initial conditions of some of the state variables are not specified, a procedure based on iterative dynamic programming (IDP) is presented. In this procedure, the free initial conditions are taken to be additional control variables for the first time stage only; then the search for the optimal initial conditions and also the optimal control policy is carried out simultaneously using IDP. The procedure is straightforward, and as illustrated with two nonlinear optimal control problems, for each case the optimum performance index is readily obtained.     

Novel poly(l‐lactide‐co‐caprolactone)/gelatin porous scaffolds for use in articular cartilage tissue engineering: Comparison of electrospinning and wet spinning processing methods

Some novel polymeric fibrous nonwoven meshes have been processed from solution blends of poly(l ‐lactide‐co‐caprolactone), P(LL‐CL), and gelatin for use as biodegradable porous scaffolds in articular cartilage tissue engineering. P(LL‐CL) copolymers with LL:CL compositions ranging from 50:50 to 80:20 mol% were synthesized via the bulk ring‐opening copolymerization of L‐lactide (LL) and ε‐caprolactone (CL) using tin(II) octoate, Sn(Oct)₂, as the initiator. To make the hydrophobic P(LL‐CL) more hydrophilic for cell culture, it was solution blended with gelatin using trifluoroethanol as a common solvent to give P(LL‐CL):gelatin contents in the final scaffolds ranging from 70:30 to 95:5 wt%. Two different processing methods were used: electrospinning and wet spinning. Although electrospinning gave a more uniform mesh of nanosized fibers, the nonwoven mesh from wet spinning with its much larger pores and greater pliability was found to be more suitable for water absorption, cell infiltration and shape‐forming. Scanning electron micrographs of the scaffolds from the two techniques are compared. From the results obtained, the wet‐spun P(LL‐CL)50:50/gelatin 95:5 scaffold gave the best combination of properties. In particular, the 5% gelatin content resulted in a fivefold increase in the scaffold's equilibrium water uptake from about 10% to over 50% by weight. POLYM. ENG. SCI., 57:875–882, 2017. © 2016 Society of Plastics Engineers     

Effects of anode orientation and flow channel design on performance of refuelable zinc-air fuel cells

The effects of anode orientation (whether an anode is located above or under a cathode) and flow channel design (parallel or serpentine flow channel) on the performance of refuelable zinc-air fuel cells (RZAFC) continuously fed with KOH electrolyte were investigated. The performance test was conducted at different electrolyte flow rates of 2, 4, and 6 ml h^?1. A polarization test of the cell was conducted at the initial stage of operation, followed by a long-term current discharge test in potentiostatic mode. The spent zinc powders were characterized by a scanning electron microscope and X-ray diffraction. The experimental results revealed that the anode-bottom orientation in the cell performed much better than the anode-top orientation with 11.4 times higher zinc utilization. The performance reduction of the anode-top orientation cell was caused by the cathode overpotential, due to the flooding of the cathode by water crossover from the anode, which was induced by the gravity force. For the flow channel design effects, there was an optimum electrolyte flow rate, to yield a maximum current discharge capacity, of 4 ml h^?1 in this study. At this optimum flow rate, the total charge per gram of zinc delivered from the anode serpentine cell was 1.75 times higher than that from the anode-parallel one.     

Optimal control of final state constrained systems

In using penalty functions to handle final state equality constraints, we propose a systematic scheme for adjusting the penalty function factors, so that all the constraints are satisfied within a specified tolerance, and so that the performance index is minimized. Two typical engineering problems, which are used to test the procedure, show that the proposed method of adjusting the penalty function factors can be used for reasonably complex systems to yield reliable results.