Modelling complex progressive failure in notched composite laminates with varying sizes and stacking sequences

The emergence of advanced computational methods and theoretical models for damage progression in composites has heralded the promise of virtual testing of composite structures with orthotropic lay-ups, complex geometries and multiple material systems. Recent studies have revealed that specimen size and material orthotropy has a major effect on the open hole tension (OHT) strength of composite laminates. The aim of this investigation is develop a progressive failure model for orthotropic composite laminates, employing stepwise discretization of the traction–separation relationship, to predict the effect of specimen size and laminate orthotropy on the OHT strength. The results show that a significant interaction exists between delamination and in-plane damage, so that models without considering delamination would over-predict strength. Furthermore, it is found that the increase in fracture toughness of blocked plies must be incorporated in the model to achieve good correlation with experimental results.     

Virtual Testing Stand for evaluation of car cabin indoor environment

In the paper the authors refer to a new computational tool for the transient prediction of the car cabin environment and heat load during real operating conditions. The aim of the Virtual Testing Stand software is to support an early stage of the HVAC design process to predict demands for the heating and cooling for various operational conditions and types of car. This software was developed in Matlab as a standalone executable application including a parametric generator of car cabin geometry, a heat transfer model and a graphical user interface. The mathematical model is formed by the set of heat balance equations, which takes into account the heat accumulation, and the heat exchange between the car cabin, the outside environment, the HVAC system and the passengers. In this paper the main features of Matlab application are presented together with a selected sensitivity study of two significant parameters in a winter test case.     

Computational Collective Intelligence with Big Data: Challenges and Opportunities

Collective intelligence has been an important research topic in many AI communities. With The big data phenomenon, we have been facing on many research problems on how to integrate the big data with collective intelligence. This special issue has selected 9 high quality papers covering various research issues.     

Coupled population balance–CFD simulation of droplet breakup in a high pressure homogenizer

A framework for a one-way coupling between population balance equation (PBE) and computational fluid dynamics (CFD) for emulsions undergoing breakup in a turbulent flow-regime is implemented in the open-source CFD package OpenFOAM. The PBE is discretized using a volume conservative scheme. This framework was applied to emulsification of food-grade vegetable oil-in-water emulsions in a Niro Soavi high pressure homogenizer (HPH) with different pressure drops and using oils of varying viscosities. Different breakage rate models were implemented, as well as the model of Becker et al. (2014) which is an extension of the Luo and Svendsen (1996) model to account for the dispersed phase viscosity. The Becker et al. (2014) model was found to give better predictions after three consecutive passes, without the need for additional empirically determined parameters. The multi-scale PBE–CFD modelling approach allowed a detailed analysis of the breakup process in the gap and jet of the HPH valve.     

CFD analysis on the catalyst layer breakage failure of an SCR-DeNOx system for a 350 MW coal-fired power plant

Selective catalytic reduction as one of the secondary NO_x control technologies is widely used in industrial sources including coal-fired power plants and large boilers. The performance of an SCR-DeNO_x system is sensitive to the installment of its components such as turning vanes and hybrid grids. In this work, three-dimensional CFD simulations are carried out to analyze the breakage failure of an SCR-DeNO_x system for a certain 350 MW coal-fired power plant. Research results are consistent with the phenomena that occur in the industrial application. It reveals that the breakage failure in the industrial application is likely to be caused by the inappropriate installation of the turning vane 3 locating closest to the catalyst, especially the angle of the turning vane 3. The analysis further shows that the lifetime or the breakage of the catalyst layers depends highly on the gas velocity, the fly ash distribution and its particle velocity.     

Measuring the human body's microclimate using a thermal manikin

The human body is surrounded by a microclimate, which results from its convective release of heat. In this study, the air temperature and flow velocity of this microclimate were measured in a climate chamber at various room temperatures, using a thermal manikin simulating the heat release of the human being. Different techniques (Particle Streak Tracking, thermography, anemometry, and thermistors) were used for measurement and visualization. The manikin surface temperature was adjusted to the particular indoor climate based on simulations with a thermoregulation model (UCBerkeley Thermal Comfort Model). We found that generally, the microclimate is thinner at the lower part of the torso, but expands going up. At the head, there is a relatively thick thermal layer, which results in an ascending plume above the head. However, the microclimate shape strongly depends not only on the body segment, but also on boundary conditions: The higher the temperature difference between the surface temperature of the manikin and the air temperature, the faster the airflow in the microclimate. Finally, convective heat transfer coefficients strongly increase with falling room temperature, while radiative heat transfer coefficients decrease. The type of body segment strongly influences the convective heat transfer coefficient, while only minimally influencing the radiative heat transfer coefficient.     

Concept maps: A useful and usable tool for computer-based knowledge assessment? A literature review with a focus on usability

The concept map is now widely accepted as an instrument for the assessment of conceptual knowledge and is increasingly being embedded into technology-based environments. Usability addresses how appropriate (for a particular use) or how user-friendly a computer-based assessment instrument is. As we know from human-computer interaction research, if the interface is not user-friendly, a computer-based assessment can result in decreased test performance and reduced validity. This means that the usability of the interface affects the assessment in such a way that if the test is not user-friendly, then the test taker will not be able to fully demonstrate his/her level of proficiency and will instead be scored according to his/her information and communication technology (ICT) literacy skills. The guidelines of the International Test Commission (2006) require usability testing for such instruments and suggest that design standards be implemented. However, we do not know whether computer-conducted concept map assessments fulfill these standards. The present paper addresses this aspect. We conducted a systematic research review to examine whether and how researchers have studied and considered usability when conducting computer-based concept map assessments. Only 24 out of 119 journal articles that assessed computer-based concept maps discussed the usability issue in some way. Nevertheless, our review brings to light the idea that the impact of usability on computer-based concept map assessments is an issue that has received insufficient attention. In addition, usability ensures a suitable interaction between test taker and test device; thus, the training effort required for test use can be reduced if a test's usability is straight forward. Our literature review, however, illustrates that the interplay between usability and test use training has mostly been neglected in current studies.     

The finite element discretized symplectic method for interface cracks

The method of symplectic series discretized by finite element is introduced for the stress analysis of structures having cracks at the interface of dissimilar materials. The crack is modeled by the conventional finite elements dividing into two regions: near and far fields. The unknowns in the far field are as usual. In the near field, a Hamiltonian system is established for applying the method of separable variables and the solutions are expanded in exact symplectic eigenfunctions. By performing a transformation from the large amount of finite element unknowns to a small set of coefficients of the symplectic expansion, the stress intensity factors, the displacements and stresses in the singular region are obtained simultaneously without any post-processing. The numerical results are obtained for various cracks lying at the bi-material interface, and are found to be in good agreement with the reference solutions for the interface crack problems. Some practical examples are also given.     

Thermal analysis and design of a volumetric solar absorber depending on the porosity

The thermal evaluation of different absorber configurations for a volumetric solar receiver designed for a solar furnace has been carried out by means of commercial Computational Fluid Dynamics (CFD) software in a 2D numerical model. Simulation results for proposed configurations depending on the porosity are discussed and compared to find the optimum configuration for which flow instabilities and thermal stresses are minimized and higher efficiencies are reached. The results obtained from the comparison of air velocity and thermal profiles at the absorber outlet propose a gradual-porosity configuration as an alternative to a previous design of a porous silicon-carbide honeycomb structure in order to heat an air stream up to temperatures suited for several high-temperature industrial processes.     

A statistical approach for sub-hourly solar radiation reconstruction

This paper proposes a computational-statistics based approach for solar radiation reconstruction at sub-hourly intervals. A dimensionless form of stochastic variable, V, which is defined as the difference between the theoretical global solar radiation in clear-sky conditions and the actual solar radiation, normalized by the clear-sky global solar radiation, is introduced and adopted in this work. The probability density function of V is calculated from historical data using a Gaussian kernel density estimator. With the developed model, the only input information required for the reconstruction procedure is the cloud condition of the sky (i.e., fair, partly cloudy, overcast, and rain/snow etc.). A case study in simulating solar radiation in Singapore is conducted to validate the accuracy of the model. The calculated results agree well with the measured data. The normalized root mean square error (NRMSE) is on average 23.4% and 7.2% for the one-minute temporal resolution and hourly integral values, respectively.