Multi-objective simulation-optimization for earthmoving operations

This paper presents an integrated framework of multi-objective simulation-optimization for optimizing equipment-configurations of earthmoving operations. The earthmoving operations are modeled through simulation and the performances associated with equipment-configurations are evaluated in terms of multiple attribute utility reflecting the preference of decision-makers to multiple criteria. A modified two-stage ranking-selection procedure, a statistical method, is equipped to help compare the alternatives that have random performances and thus reduce unnecessary number of simulation replications. In addition, particle swarm optimization is incorporated to search for the potential equipment-configurations to be examined through simulation, thus speeding up the evaluation process and avoiding exhaustive simulation experiments of all the alternatives. The architecture of the integrated framework is developed. A computational example is provided to justify the proposed methodology. The study will provide an alternative means to help plan earthmoving operations by considering multiple criteria and combining multiple methodologies.     

Behavior of a high-capacity steam boiler using heavy fuel oil Part II: Cold-end corrosion

An experimental study has been performed on a high-capacity steam boiler burning heavy fuel oil to assess cold-end corrosion damages. In this second part of the research, acid corrosion in the rotary continuous-regenerative air heaters (CRAHs) has been analyzed. Corrosion potentiality has been evaluated from both qualitative and quantitative viewpoints. Results have shown that acid corrosion in the CRAHs is reduced when the low-quality heavy fuel oil is mixed with a magnesium-based additive. In this research, two commercial additives have been tested: a magnesium oxide-based slurry and an organometallic one. The best results have been obtained when the organometallic additive was used in the treatment of the heavy fuel. For this experimental condition, an increase in the useful lifetime of the pie-shaped baskets, as well as a decrease in both the acid dew point temperature (ADT) at the stack gases and the pressure drop (fouling) on the CRAHs have been confirmed.     

Analytical and comparative testing of EnergyPlus using IEA HVAC BESTEST E100–E200 test suite

The EnergyPlus building energy simulation software has been tested using the IEA HVAC BESTEST E100–E200 series of tests. The volume 1 final report for the International Energy Agency (IEA) solar heating and cooling programme task 22 building energy simulation test and diagnostic method for heating, ventilating, and air conditioning equipment models (HVAC BESTEST) was recently published in January 2002. HVAC BESTEST is a series of steady-state tests for a single-zone DX cooling system. Cases range from dry to wet coil, low to high part load, and low to high temperatures. This published test suite includes three sets of analytical solutions and results from several other simulation programs for comparison.This test suite was initially used to test EnergyPlus beginning with beta versions prior to its official public release, and it is also applied as an ongoing quality assurance test. The application of these tests proved to be very useful in several ways:

• •revealed input model shortcomings, which resulted in new user inputs being added;
• •revealed reporting errors which were fixed;
• •revealed algorithmic errors which were fixed;
• •revealed algorithmic shortcomings which were improved or eliminated through the use of more rigorous calculations for certain components;
• •in later versions, caught newly introduced bugs before public release of updates.

Overall, the application of this test suite has been extremely useful in debugging and verifying the DX cooling algorithms in EnergyPlus. This paper summarizes the difficulties encountered and the benefits gained in applying the tests.     

Integrity assessment for a tubeplate using the linear matching method

A series of numerical procedures have been presented recently for the integrity assessment of structures based upon the Linear Matching Method. A typical example of a holed plate has been used to verify these procedures for the evaluation of plastic and creep behaviours of components. In this paper, a more complex 2D tubeplate at the outlet from a typical AGR heat exchanger is analysed for the shakedown limit, reverse plasticity, ratchet limit and creep relaxation based on the application of the Linear Matching Method for a thorough case study. Both a constant material yield stress and a temperature-dependent yield stress are adopted for the evaluation of the ratchet limit. For the evaluation of accumulated creep strains, flow stresses and elastic follow-up factors with differing dwell times at the steady cyclic state, a monotonic creep computation is performed, where the start-of-dwell stress is the rapid cycle creep solution at the beginning of the dwell period. An estimation of the tubeplate lifetime is then obtained by the evaluation of fatigue and creep endurances.     

Surface structural alteration of multi-walled carbon nanotubes decorated by nickel nanoparticles based on laser ablation/chemical reduction methods to enhance hydrogen storage properties

The catalytic effect of nickel is addressed to decorate the multi-walled carbon nanotubes for the purpose of hydrogen storage. The hydrogen sorption/desorption are investigated using the volumetric technique. Nickel nanoparticles are distributed on the surface of nanotubes using the laser ablation/chemical reduction treatments. The hydrogen uptake is elevated at higher nickel population up to a certain value and then experiences a significant drop for larger nickel content. The laser treatment is accompanied by the induced pores around nanotubes. This gives rise to the creation of the larger pores at higher laser doses leading to decrease the hydrogen trapping. Despite the pore size distribution strongly alters during both synthesis methods, however the abundance of small pore size in laser treatments is relatively higher than the that of the other technique. In comparison, the laser ablation demonstrates a relatively smaller desorption temperature against chemical one, mainly owing to the formation of larger pore size/volume. Generally, the hydrogen trapping efficiently takes place in the laser treated samples against chemical reduction method. The highest value of hydrogen storage ∼1% (0.6% weight) is corresponding to 12.3% (13% weight) of nickel loading via the laser ablation (chemical reduction).     

Influence of concrete composition on the characterization of fracture surface

An experimental method based on laser triangulation was used to measure the 3-D profile of fracture surface of concrete. The projective-covering method was established to determine the fractal characteristics of fracture surface. Based on the experiment, the influence of composition of concrete on the fractal dimension, including water–binder ratio, maximum aggregate size and aggregate type, was investigated. The variation of fractal dimension with the material composition was also analysed to make further understanding of fracture mechanism of concrete.     

Continuous simulation for design flood estimation—a review

Developments of systems for continuous simulation of streamflow are traced from manual systems in the middle of the 20th century to present day computer-based systems. A profusion of different systems from very simple to very complex are in use. Systems in operational use in UK/Europe, USA, South Africa and Australia are reviewed. There are several different runoff generation processes used in these systems such as saturation overland flow, subsurface stormflow and infiltration excess. These processes demonstrate different approaches to hydrological modelling in different areas. Other differences include the use of processes such as snowmelt and transmission loss that are significant in some areas but not in others. A feature of many modern systems is the use of stochastic rainfall generators that allow for very long streamflow sequences to be generated from which long-term flood statistics can be extracted. Only a few studies have compared continuous simulation with other methods of design flood estimation, and no significant studies have been made comparing different continuous simulation systems. Most of the available systems use recorded streamflow data for calibration and there is little information available for the use of continuous simulation systems on ungauged catchments.     

Dynamic optimization for grade transition processes using orthogonal collocation on molecular weight distribution

To meet the demands of a competitive market, an industrial plant often produces several grades of polymer product through the same process in an economical way. As molecular weight distribution (MWD) is a crucial quality index of polymers, dynamic optimization for grade transition based on MWD is highly important, but challenging. This study considers the development of optimization models for MWD-based grade transition. An MWD reconstruction method using orthogonal collocation in two dimensions is developed to capture the dynamic feature of MWD in time and the distributive feature in chain length. The simultaneous collocation approach is adopted to discretize the model. Two optimization formulations are proposed to describe minimizing the transition time as well as off-spec production. Both formulations inherit the advantages of the simultaneous collocation approach. The numerical results show that the proposed methods can efficiently solve the grade transition problem with MWD specification, and obtain high performance control profiles to reduce the production cost. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1198–1210, 2019     

Shear testing of thick adhesive layers using the ENF-specimen

An existing experimental method to determine cohesive laws for adhesive layers loaded in shear is further developed. The method is based on differentiation of the energy release rate (ERR) with respect to the adhesive shear deformation at the crack tip. The test geometry used is an ENF-specimen for which the adherends are assumed to deform linearly elastic. The original method is expanded to account for situations where the thickness of the adhesive layer is not negligible as compared to the adherend thickness. To this end, a novel mathematical expression for the energy release rate (ERR) is derived. No assumptions on the form of the cohesive law are made; it is implicitly included in the derivation. The expression for the ERR contains the applied load and the shear deformation of the adhesive layer at the initial position of the crack tip, in addition to geometrical properties and the elastic modulus of the adherend material. Numerical simulations are performed to verify the accuracy of the mathematical expression for the ERR. Preliminary results from experiments performed on an epoxy adhesive are presented. The cohesive law of the adhesive layer is extracted by using a blunted crack tip. Verifying simulations confirm that the local pre-fracture behavior is accurately captured.     

A methodological approach for manufacturers to enhance value-in-use of service-based offerings considering three dimensions of sustainability

To shift towards a sustainable society, lifecycle engineering methodologies addressing the social dimension need to be advanced. A new methodological approach is proposed for manufacturers to address the three dimensions of sustainability. This approach aims to enhance value-in-use of service-based offerings and supports designers with two social indicators and five generally applicable recommendations involving multiple product lives towards a circular economy. For validation, it was applied to the case of a manufacturer of washing machines for European consumer markets. Results show that the approach supports designers to incorporate the social dimension efficiently while improving resource efficiency.