Chebyshev polynomial-based Ritz method for thermal buckling and free vibration behaviors of metal foam beams

This study presents the Chebyshev polynomials-based Ritz method to examine the thermal buckling and free vibration characteristics of metal foam beams.The analyses include three models for porosity distribution and two scenarios for thermal distribution.The material properties are assessed under two conditions,i.e.,temperature dependence and temperature independence.The theoretical framework for the beams is based on the higher-order shear deformation theory,which incorporates shear deformations with higher-order polynomials.The governing equations are established from the Lagrange equations,and the beam displacement fields are approximated by the Chebyshev polynomials.Numerical simulations are performed to evaluate the effects of thermal load,slenderness,boundary condition(BC),and porosity distribution on the buckling and vibration behaviors of metal foam beams.The findings highlight the significant influence of temperature-dependent(TD)material properties on metal foam beams'buckling and vibration responses.

An Enhanced Ensemble-Based Long Short-Term Memory Approach for Traffic Volume Prediction

With the advancement of artificial intelligence,traffic forecasting is gaining more and more interest in optimizing route planning and enhancing service quality.Traffic volume is an influential parameter for planning and operating traffic structures.This study proposed an improved ensemble-based deep learning method to solve traffic volume prediction problems.A set of optimal hyperparameters is also applied for the suggested approach to improve the performance of the learning process.The fusion of these methodologies aims to harness ensemble empirical mode decomposition’s capacity to discern complex traffic patterns and long short-term memory’s proficiency in learning temporal relationships.Firstly,a dataset for automatic vehicle identification is obtained and utilized in the preprocessing stage of the ensemble empirical mode decomposition model.The second aspect involves predicting traffic volume using the long short-term memory algorithm.Next,the study employs a trial-and-error approach to select a set of optimal hyperparameters,including the lookback window,the number of neurons in the hidden layers,and the gradient descent optimization.Finally,the fusion of the obtained results leads to a final traffic volume prediction.The experimental results show that the proposed method outperforms other benchmarks regarding various evaluation measures,including mean absolute error,root mean squared error,mean absolute percentage error,and R-squared.The achieved R-squared value reaches an impressive 98%,while the other evaluation indices surpass the competing.These findings highlight the accuracy of traffic pattern prediction.Consequently,this offers promising prospects for enhancing transportation management systems and urban infrastructure planning.

Relationship between land use and user’s behavior along the street:A case study of Da Nang City,Viet Nam

Human activities on street spaces are affected by both physical and non-physical settings on streets.These two aspects are primarily impacted by land use which results in the uneven distribution of different activities on streets.This research investigates land use patterns and their characteristics in association to user’s behaviors.By using mixed qualitative and quantitative research methods,e.g.,place-centered behavioral map,observation,visual encounter surveys,machine learning,the relationship between user’s behavior and land use characteristics along the street is unveiled.All user behaviors along both types of streets were classified into six main categories,with 26 subcategories.The observation results show that the residential use of land along the street was transformed into the commercial use for various types of shophouses based on the resident’s ideas.There is a great correlation between land use and user’s activities.These findings give support to authorities to manage urban streets and develop a sustainable policy for improving street spaces.Further,this research contributes useful information to urban designers and planners in creating a successful street space that is appropriate for the Vietnam Community.

Determination of fuel burnup distribution of a research reactor based on measurements at subcritical conditions

This paper presents the determination of the fuel burnup distribution of the Dalat nuclear research reactor(DNRR) using a method of measurements at subcritical conditions. The method is based on the assumption of linear dependence of the reactivity on the burnup of fuel bundles and the measurements at subcritical conditions.The measurements were taken for seven selected fuel bundles in two different measuring sequences. The measured burnup values have also been compared with the calculations for verifying the method and the measurement procedure. The results obtained with the three detectors have a good agreement with each other with a discrepancy less than 1.0%. The errors of the measured burnup values are within 6%. Comparison between the calculated and measured burnup values shows that the discrepancy of the C/E ratio is within 9% compared to unity. The results indicate that the method of measurements at subcritical conditions could be well applied to determine the relative burnup distribution of the DNRR.

Analyses on the Ionization Instability of Non-Equilibrium Seeded Plasma in an MHD Generator

Recently,closed cycle magnetohydrodynamic power generation system research has been focused on improving the isentropic efficiency and the enthalpy extraction ratio.By reducing the cross-section area ratio of the disk magnetohydrodynamic generator,it is believed that a high isentropic efficiency can be achieved with the same enthalpy extraction.In this study,the result relating to a plasma state which takes into account the ionization instability of non-equilibrium seeded plasma is added to the theoretical prediction of the relationship between enthalpy extraction and isentropic efficiency.As a result,the electron temperature which reaches the seed complete ionization state without the growth of ionization instability can be realized at a relatively high seed fraction condition.However,the upper limit of the power generation performance is suggested to remain lower than the value expected in the low seed fraction condition.It is also suggested that a higher power generation performance may be obtained by implementing the electron temperature range which reaches the seed complete ionization state at a low seed fraction.

Defect engineering of water-dispersible g-C_(3)N_(4) photocatalysts by chemical oxidative etching of bulk g-C_(3)N_(4) prepared in different calcination atmospheres

In this study,water-dispersible graphitic carbon nitride(g-C_(3)N_(4))photocatalysts were successively prepared through the chemically oxidative etching of bulk g-C_(3)N_(4) that was polymerized thermally in different calcination atmospheres such as air,CO_(2),and N_(2).The different calcination atmospheres directly influenced the physicochemical and optical properties of both bulk and water-dispersible g-C_(3)N_(4),changing the photocatalytic degradation behavior of methylene blue(MB)and tetracycline hydrochloride(TCHCl)for water-dispersible g-C_(3)N_(4).The bubble-burst process in the thermal polymerization of thiourea produced defective edges containing C=O groups that preferred substituting the C-NHx groups over bulk g-C_(3)N_(4).In the oxygen-free N_(2) atmosphere among the different calcination atmospheres,more C=O functional groups were generated on the defective edges of bulk g-C_(3)N_(4),resulting in the highest N vacancy of the tri-s-triazine structure.During the successive chemical oxidation,S-or O-containing functional groups were introduced onto water-dispersible g-C_(3)N_(4).The water-dispersible g-C_(3)N_(4) photocatalyst from the oxygen-free N_(2) atmosphere(NTw)contained the most O-and S-functional groups on the g-C_(3)N_(4) surface.Consequently,NTw exhibited the highest photocatalytic activity in the MB and TC-HCl photodegradation because of its slowest recombination process,which was ascribed to the unique surface properties of NTw such as abundant functional groups on the defective edges and N-deficient property.

Impact of chosen force fields and applied load on thin film lubrication

The rapid development of molecular dynamics(MD)simulations,as well as classical and reactive atomic potentials,has enabled tribologists to gain new insights into lubrication performance at the fundamental level.However,the impact of adopted potentials on the rheological properties and tribological performance of hydrocarbons has not been researched adequately.This extensive study analyzed the effects of surface structure,applied load,and force field(FF)on the thin film lubrication of hexadecane.The lubricant film became more solid‐like as the applied load increased.In particular,with increasing applied load,there was an increase in the velocity slip,shear viscosity,and friction.The degree of ordering structure also changed with the applied load but rather insignificantly.It was also significantly dependent on the surface structure.The chosen FFs significantly influenced the lubrication performance,rheological properties,and molecular structure.The adaptive intermolecular reactive empirical bond order(AIREBO)potential resulted in more significant liquid‐like behaviors,and the smallest velocity slip,degree of ordering structure,and shear stress were compared using the optimized potential for liquid simulations of united atoms(OPLS‐UAs),condensed‐phase optimized molecular potential for atomic simulation studies(COMPASS),and ReaxFF.Generally,classical potentials,such as OPLS‐UA and COMPASS,exhibit more solid‐like behavior than reactive potentials do.Furthermore,owing to the solid‐like behavior,the lubricant temperatures obtained from OPLS‐UA and COMPASS were much lower than those obtained from AIREBO and ReaxFF.The increase in shear stress,as well as the decrease in velocity slip with an increase in the surface potential parameterζ,remained conserved for all chosen FFs,thus indicating that the proposed surface potential parameterζfor the COMPASS FF can be verified for a wide range of atomic models.

Numerical investigation of the influence of casting techniques on fiber orientation distribution in ECC

Engineered cementitious composites(ECC),also known as bendable concrete,were developed based on engineering the interactions between fibers and cementitious matrix.The orientation of fibers,in this regard,is one of the major factors influencing the ductile behavior of this material.In this study,fiber orientation distributions in ECC beams influenced by different casting techniques are evaluated via numerical modeling of the casting process.Two casting directions and two casting positions of the funnel outlet with beam specimens are modeled using a particle-based smoothed particle hydrodynamics(SPH)method.In this SPH approach,fresh mortar and fiber are discretized by separated mortar and fiber particles,which smoothly interact in the computational domain of SPH.The movement of fiber particles is monitored during the casting simulation.Then,the fiber orientations at different sections of specimens are determined after the fresh ECC stops flowing in the formwork.The simulation results show a significant impact of the casting direction on fiber orientation distributions along the longitudinal wall of beams,which eventually influence the flexural strength of beams.In addition,casting positions show negligible influences on the orientation distribution of fibers in the short ECC beam,except under the pouring position.

Size effects in two-dimensional layered materials modeled by couple stress elasticity

In the present study,the effect of material microstructure on the mechanical response of a two-dimensional elastic layer perfectly bonded to a substrate is examined under surface loadings.In the current model,the substrate is treated as an elastic half plane as opposed to a rigid base,and this enables its applications in practical cases when the modulus of the layer(e.g.,the coating material)and substrate(e.g.,the coated surface)are comparable.The material microstructure is modeled using the generalized continuum theory of couple stress elasticity.The boundary value problems are formulated in terms of the displacement field and solved in an analytical manner via the Fourier transform and stiffness matrix method.The results demonstrate the capability of the present continuum theory to efficiently model the size-dependency of the response of the material when the external and internal length scales are comparable.Furthermore,the results indicated that the material mismatch and substrate stiffness play a crucial role in the predicted elastic field.Specifically,the study also addresses significant discrepancy of the response for the case of a layer resting on a rigid substrate.