某美化亮化圆柱网架结构设计探讨

钢结构由于自重轻,可靠性高,抗震性能好,被广泛应用于工业厂房建筑中,其中尤其以钢网架结构居多,从而导致对钢网架结构美化亮化的需求越来越多。本文以某水泥厂新建熟料库网架的美化亮化为例,针对圆柱网架结构进行了静力分析和动力分析,提出了网架设计时需要注意的问题,为该类型的网架结构设计提供了参考。     

Calculation of optimal design margins for compensation of parameter uncertainty

A method for the compensation of parameter uncertainties in the design of process systems by optimal selection of design margins (safety factors) according to Takamatsu is enlarged by considerations about the linearisability of the mathematical model, the selection of the signs of parameter deviations, and the inclusion of nonlinear inequality constraints. The method is compared with the non-linear minimax strategy. Both procedures are applied to a reactor-separator system.     

A disjunctive programming approach for the optimal design of reactive distillation columns

A generalized disjunctive programming formulation is presented for the optimal design of reactive distillation columns using tray-by-tray, phase equilibrium and kinetic based models. The proposed formulation uses disjunctions for conditional trays to apply the MESH and reaction kinetics equations for only the selected trays in order to reduce the size of the nonlinear programming subproblems. Solution of the model yields the optimal feed tray locations, number of trays, reaction zones, and operating and design parameters. The disjunctive program is solved using a logic-based outer-approximation algorithm where the MILP master problem is based on the big-M formulation of disjunctions, and where a special initialization scheme is used to reduce the number of initial NLP subproblems that need to be solved. Two examples are presented that include reactive distillation for the metathesis reaction of 2-pentene and for the production of ethylene glycol. The results show that the proposed method can effectively handle these difficult nonlinear optimization problems.     

Hybrid simulation-optimization based approach for the optimal design of single-product biotechnological processes

In this work, we present a systematic method for the optimal development of bioprocesses that relies on the combined use of simulation packages and optimization tools. One of the main advantages of our method is that it allows for the simultaneous optimization of all the individual components of a bioprocess, including the main upstream and downstream units. The design task is mathematically formulated as a mixed-integer dynamic optimization (MIDO) problem, which is solved by a decomposition method that iterates between primal and master sub-problems. The primal dynamic optimization problem optimizes the operating conditions, bioreactor kinetics and equipment sizes, whereas the master levels entails the solution of a tailored mixed-integer linear programming (MILP) model that decides on the values of the integer variables (i.e., number of equipments in parallel and topological decisions). The dynamic optimization primal sub-problems are solved via a sequential approach that integrates the process simulator SuperPro Designer^® with an external NLP solver implemented in Matlab^®. The capabilities of the proposed methodology are illustrated through its application to a typical fermentation process and to the production of the amino acid L-lysine.     

A simple numerical approach for the optimal design of an extrusion die

A simple numerical approach that is based on the lubrication approximation is developed for the optimal design of a linearly tapered coat-hanger die. This approach does not require the analytic pressure drop / flow rate equations for flow in the manifold and in the slot section, therefore any generalized Newtonian fluid model can be easily incorporated. Example calculations have demonstrated that the predictions based on this approach are reasonably accurate as compared with those from the complete 3-D finite element simulations.     

Globally optimal design of Minimal WHEN systems using enumeration

The process synthesis problem referred to as work and heat exchange networks (WHENs) asks to determine the optimal heat exchanger network intertwined with compressors, expanders, and valves, all integrated into one single network, such that streams with certain initial temperature and pressure attain their temperature and pressure targets at minimum cost. This article presents a procedure that obtains the globally optimal solution of Minimal WHEN systems using an enumeration scheme, using only a few subproblems, each one solved using mathematical programming to global optimality. Minimal structures feature one compression/decompression task and one heat exchange task per stream. In addition, we depart from the ideal gas assumption and use a cubic equation of state for stream properties. Finally, the approach allows for the use of turboexpanders. Four examples are presented to show the effectiveness and accuracy of the proposed method.     

Efficient integration of optimal solvent and process design using molecular clustering

We present a molecular clustering approach for the efficient incorporation of solvent design information into process synthesis in the integrated design of solvent/process systems. The approach is to be used in conjunction with an integrated solvent/process design approach where the solvent design stage utilises multi-objective optimisation in order to identify Pareto optimal solvent candidates that are subsequently evaluated in a process synthesis stage. We propose to introduce the solvent design information into the process synthesis stage through the use of molecular clusters. The partitioning of the original Pareto optimal set of solvents leads to smaller compact groups of similar solvent molecules from which representative molecules are introduced into the process synthesis model as discrete options to determine the optimal process performance associated with the optimal solvent. We investigate two clustering strategies, serial and parallel clustering, that allow to effectively exploit the solvent-process design interactions to minimise the computational demands of the process synthesis stage. We further propose a clustering heuristic probability that can aid decision making in clustering and can significantly accelerate the search for the best integrated solvent-process systems. The presented method is illustrated with case studies in the design of solvents for liquid-liquid extraction, gas-absorption and extractive distillation systems.     

Comparison of photobioreactors and optimal light regime for rapid vegetative propagation of transgenic Undaria pinnatifida gametophytes

BACKGROUND: Previously, tachyplesin gene (tac) has been successfully transferred into Undaria pinnatifida gametophytes using the method of microprojectile bombardment transformation. The objectives of this study were to compare and evaluate the performance of bubble‐column and airlift bioreactors to determine a preferred configuration of bioreactor for vegetative propagation of transgenic U. pinnatifida gametophytes, and to then investigate the influence of light on vegetative propagation of these gametophytes, including incident light intensity, photoperiod and light quality to resolve the problems of rapid vegetative propagation within the selected bioreactor. RESULTS: Experimental results showed that final dry cell density in the airlift bioreactor was 12.7% higher than that in the bubble‐column bioreactor under the optimal aeration rate of 1.2 L air min^?1 L^?1 culture. And a maximum final dry cell density of 2830 mg L^?1 was obtained within the airlift bioreactor using blue light at 40 µmol m^?2 s^?1 with a light/dark cycle of 14/10 (h). Polymerase chain reaction (PCR) analysis indicated that genes (bar and tac) were not lost during rapid vegetative propagation within the airlift bioreactor. CONCLUSION: The airlift bioreactor was shown to be much more suitable for rapid vegetative propagation of transgenic U. pinnatifida gametophytes than the bubble‐column bioreactor in the laboratory. The use of blue light allows improvement of vegetative propagation of transgenic U. pinnatifida gametophytes. Copyright © 2009 Society of Chemical Industry     

Set Trimming approach for the globally optimal design of sieve trays in separation columns

In this article, we use Set Trimming to obtain the globally optimal design of distillation column trays, that is, the column diameter and the geometrical design of the trays (weir, downcomer, etc.) that minimize mass or cost. We assume that the operating conditions (vapor and liquid flow rates, compositions, temperatures) are given. The design task is, to this day, presented in textbooks as a trial and verification procedure. We show that Set Trimming guarantees global optimality and is amenable to exploring alternative global optima. Compared with the employment of a mixed-integer nonlinear programming (MINLP) approach using commercial global optimizers, we show that Set Trimming is a more robust option with competitive computational times for individual design problems. It also exhibits a significant reduction in computational effort when alternative optimal solutions are sought.     

Selection and refinement of finite elements for optimal design and control: A Hamiltonian function approach

In this work, we propose a /methodology for the selection and refinement of finite elements for the integration of process design and control. The proposed methodology is based on the selection criteria of the Hamiltonian function through the implementation of the Pontryagin's minimum principle. The Hamiltonian function features to be continuous and constant over time for autonomous systems; nevertheless, the Hamiltonian function shows a nonconstant profile for underestimated discretization meshes, which is exploited in this work for the refinement of the discretization. Furthermore, the residuals at noncollocation points are evaluated to estimate the collocation error, this is used as a second refinement criterion in the proposed framework. The methodology is illustrated using two case studies featuring a reaction system with two CSTRs in series and the Williams–Otto reactor, respectively. The results showed that an accurate selection of the finite elements return economically attractive designs with fewer elements than those obtained with equidistributed finite element strategies.     

Integrated design and control of reactive distillation processes using the driving force approach

Superior controllability of reactive distillation (RD) systems, designed at the maximum driving force (design-control solution) is demonstrated in this article. Binary or multielement single or double feed RD systems are considered. Reactive phase equilibrium data, needed for driving force analysis and design of the RD system, is generated through an in-house property prediction tool. Rigorous steady-state simulation is carried out in ASPEN plus in order to verify that the predefined design targets and dynamics are met. A multiobjective performance function is employed to evaluate the performance of the RD system in terms of energy consumption, sustainability metrics (total CO₂ footprint), and control performance. Controllability of the designed system is evaluated using indices like the relative gain array (RGA) and Niederlinski index (N_I ), to evaluate the degree of loop interaction, as well as through dynamic simulations using proportional-integral (PI) controllers and model predictive controllers (MPC). The design-control of the RD systems corresponding to other alternative designs that do not take advantage of the maximum driving force is also investigated. The analysis shows that the RD designs at the maximum driving force exhibit enhanced controllability and lower carbon footprint than the alternative RD designs.     

Sustainable management and design of the energy-water-food nexus using a mathematical programming approach

Global primary and secondary resources are important for economic growth. Resource management and environment conservation are currently frequently discussed topics worldwide. In this study, a discrete optimization model formulation is presented for an integrated energy, water, and food (EWF) supply chain problem. The optimization model examines the temporal and spatial integration of the EWF supply chain elements to provide optimal infrastructure capacity expansion of essential commodities within the EWF system, and their corresponding periodic optimal supply for a given region. Furthermore, the model considers endogenous demand between the EWF elements that reflect the interdependency of nexus elements. A mixed integer linear programming model is developed to assist in the process of optimal infrastructure capacity expansion and operation of the EWF system. A case study is given to show the application of the proposed mathematical programming model. Several scenarios are assumed for the case study under different commodity prices and climate change conditions. In addition, diversification in the energy and agriculture sectors is examined by shifting from international refined sugar trading to bioethanol production. The results show economic gains of ~10% under the emergence of bioethanol production compared with the business-as-usual scenario. Production dynamic exits for the production of refined sugar, bioethanol, and power from sugarcane and bagasse resources over time in the considered sale price range for the refined sugar and bioethanol products.     

A systematic approach for the design of UV reactors using computational fluid dynamics

A wide variation exists in the geometries of UV reactors, which results in completely different hydrodynamics and therefore large differences with respect to the disinfection and oxidation performance. Among the large number of reactor types, it is not known beforehand which reactor type has the best performance with respect to disinfection or oxidation, and if such a reactor is the best reactor out of all the possible reactor designs. In this research, a systematic approach for the design of UV reactors is followed that makes use of computational fluid dynamics (CFD) modeling. To that end, the inactivation of Bacillus subtilis and degradation of atrazine was determined for a wide range of UV systems by means of CFD. The efficacy of UV systems was evaluated and improvements were made by taking measures that increase the mean dose and/or narrow the dose distribution, such as placing mirrors, enhancing the mixing and placing reactors in series. © 2010 American Institute of Chemical Engineers AIChE J, 2011