•A multi-physical model of CaO/Ca(OH)2 hydration process is simulated.•Thermal conductivity of solid-phase has a significant effect on hydration process.•Relationships between fins and reaction are ...explored.•Axial fins shorten the exothermic time to 83.4%.
Thermochemical heat storage technology is an important component in energy system, and plays a key role in the balance of energy supply and demand. A multi-physics model is constructed to study the hydration process in a tubular reactor, including fluid flow, heat transfer and reaction. Variations of temperature and conversion of CaO are discussed in detailed to reveal exothermic reaction characteristics. Besides, effects of different reaction conditions during hydration are studied, such as porosity, temperature, pressure, flow rate and thermal conductivity. It is found that the low thermal conductivity of solid-phase is the most important factor which limits the reaction. The heat transfer process can be greatly promoted by adding fins, due to the high heat conductivity. However, the relationship between the reactor structure and the performance of the thermochemical heat storage is not quantitatively clear. The present study aims to investigate the impact of the arrangement of fins on the hydration process. Finally, different types of fins with high thermal conductivity are employed in the reactor. Attributing to the fact that the equilibrium temperature is affected by the vapor pressure, thermochemical reactors with different fin configurations have different flow characteristics and pressure drops, leading to different reaction characteristics. It is shown that the exothermic time was reduced to 84.32% (axial fins), 89.97% (radial fins), and 88.71% (spiral fins) of the original, respectively. This study can reveal the coupling relations of multi-physics fields in thermochemical heat storage, and provide theoretical basis for the design of thermochemical heat storage reactors.
This study presents the results of experimental research and numerical calculations regarding models of a typical torsion box fragment, which is a common thin-walled load-bearing structure used in ...aviation technology. A fragment of this structure corresponding to the spar wall was made using 3D printing. The examined system was subjected to twisting and underwent post-critical deformation. The research was aimed at determining the influence of the printing direction of the structure’s individual layers on the system stiffness. The experimental phase was supplemented by nonlinear numerical analyses of the models of the studied systems, taking into account the details of the structure mapping using the laminate concept. The purpose of the calculations was to determine the usefulness of the adopted method for modeling the examined structures by assessing the compliance of numerical solutions with the results of the experiment.
The Kabul – Mazar Highway connects Kabul, the capital of Afghanistan, to northern provinces of the country, and further extends into Central Asian countries through the Hindukush mountains. The ...Salang Tunnel, which is 2600 m long, was designed by Soviet engineers in 1958 and constructed using conventional techniques in 1964. During its construction, the tunnel ranked the distinction of being the highest-altitude tunnel at 3400 m. The socioeconomic importance of the tunnel is exceptionally high, as the Hindukush Mountain range to the east and south of the country is crossed by it. Since 1964, there has been a significant increase in traffic volume. Due to the narrowness of the existing tunnel, the Ministry of Public Works (MOPW) of Afghanistan has planned the construction of new twin-tube tunnels. Although there have been rehabilitation and enlargement efforts for the existing tunnel, none of these renovation works have been proven effective, and challenges persist. In 2008, the MOPW initiated a pre-feasibility study for new tunnels, which was finalized in 2012, presenting various options. Subsequently, in early 2018, the MOPW commenced feasibility and detailed studies, leading to the proposal of new twin-tube tunnels, which are designated as the planned tunnels in this paper. In this study, the available geotechnical and environmental data are used to evaluate the rock engineering aspects of the tunnels, including an assessment of the in-situ stress state. A particular emphasis is placed on the reassessment and design of the support system for both the existing and planned tunnels according to RMQR and another system, respectively. The evaluation of the response and stability of the tunnels is concluded, and the implications are subsequently discussed.
Proper evaluation of seismic-induced excess pore water pressures in saturated sandy soils is still an open issue, which can be tackled with fully coupled to uncoupled approaches. The former are more ...accurate but computationally onerous, while the latter require seismic demand and pore pressure build-up to be computed in two successive steps, typically employing simple constitutive assumptions.
Starting from the work by Seed et al. (1975), this paper presents a novel uncoupled procedure to compute excess water pressures developing in a 1D soil column under partially drained conditions, when subjected to horizontal seismic excitations. Fundamental modifications are introduced to account for: non-uniform distribution of equivalent loading cycles; soil stiffness degradation; and modification of the frequency content of ground motion due to pore pressure build-up.
The approach was implemented in Matlab via the Finite Difference Method and validated against both fully-coupled Finite Element analyses and one centrifuge test. An extensive parametric study was also performed for a two-layer soil column, by varying the thickness and hydraulic conductivity of the shallow layer, as well as the seismic input. The good agreement with both numerical and experimental data demonstrates that key features of liquefaction are well-captured by the proposed uncoupled approach.
The energy demand for heating in buildings in a residential area depends on the weather conditions of the area, the architectural characteristics and thermal-physical characteristics of the ...buildings, as well as the number of buildings in the settlement and the population of the settlement, accordingly. This study aimed to numerically determine the heat losses that may occur in case of different building materials (bricks, pumice, aerated concrete and briquettes) and insulation materials (XPS, EPS, rockwool and glass wool) used in the design of buildings, by applying the Finite Element Method (FEM) and considering the outdoor and indoor weather conditions proposed in Turkish Thermal Insulation Standard (TS 825). Then, the heating requirement according to the TS 825, the monthly fuel consumption, the payback period and the emission amounts in case of insulation were calculated for a model building with an external wall made of different building materials. In this study, the conditions of a model building located in Kahramanmaraş/Turkey were discussed separately in terms of being thermally insulated and non-insulated. As a result of the analyses obtained by using FEM, the effect of the wall building material on heat losses was found to be much higher than that of insulation material. Following the application of thermal insulation to the non-insulated building model, it was seen that the payback period of the first investment value required for the insulation application varied between 0.25 and 1.74 years depending on the type of fuel used for the heating energy requirement as well as on the type of building material. In the case of using briquette wall in the building, it seemed that the heating requirements, monthly fuel consumption and emission amounts were higher than those with other building materials. The briquette wall was followed by bricks, pumice and aerated concrete, respectively.
•Energetic and environmental evaluation of a sample building with different types building materials.•The wall building material has more effect on heat loss than insulation material.•The lowest heat loss is ensured by using aerated concrete walls in buildings.•Reduction of heat loss leads to decrease in heat requirement, fuel consumption and emissions.•The most suitable fuel is natural gas due to environmental impact.
A building may be subjected to a variety of accidental loads during its service life. Partially precast concrete (PC) beams are a primary structural component. Their impact resistance can have a ...substantial impact on the overall safety of a structure when it is subjected to an impact load. In this study, numerical analyses were performed on the dynamic response of PC beams strengthened with bonded steel plates subjected to impact loading. The model was verified from four aspects: energy conversion, failure form, impact force–time history curve, and midspan displacement–time history curve. The dynamic response eigenvalues of the peak impact force, peak midspan displacement, and residual midspan displacement were compared between the numerical simulations and experimental tests. The relative inaccuracy of the peak impact force ranged from 9.51% to 14.0%, with an average value of 11.9%. The average relative error for the midspan displacement was −0.09%, with the greatest relative errors varying between −0.64% and 0.3%. The residual value errors of the midspan displacement ranged from −0.95% to 2.38%, with an average relative error of 0.94%. On this basis, the effects of the impact mass, impact height, width, and length of the bonded steel plate on the impact resistance of the components were evaluated. Furthermore, the differences in the equivalent plastic strain contours, impact force–time history curves, and midspan displacement–time history curves under different parameters were compared. The results demonstrated that the failure modes and flexural deformations of the test beams were influenced by the impact mass and impact height. The increase in the length and width of the steel plate had no effect on the impact force response, but the peak and residual values of the midspan displacement decreased, which could significantly increase the impact resistance of the beams. Lastly, the impact mass m, the impact height h, the thickness t of the bonded steel plate, the length of the bonded steel plate hs, and the width of the bonded steel plate bs were all taken into account in the fitting formula. These five parameters were used to predict the peak impact force response, the peak value of the midspan displacement, and the residual value of the midspan displacement. The results demonstrated that the fitting formula had small errors and could accurately reflect the dynamic responses of the PC beams strengthened with bonded steel plates under impact loading.
•A cavitation model of an asymmetric multi-hole diesel injector was developed.•Nozzle hole angle influence in asymmetric nozzles were investigated.•Needle lift effect on cavitation and velocity in ...asymmetric nozzles was analyzed.•Further investigations on mass flow rate and discharge coefficient were done.
In order to simultaneously study the differences in transient flow characteristics within each nozzle hole of an asymmetric multi-hole diesel injector used in off-road machinery, a three-dimensional gas–liquid two-phase flow model of cavitation was developed, which takes the influence of injection conditions and bubble number density into consideration. The computational model was validated by comparing it with the experiment conducted by Winklhofer. The result shows high level of consistency and sensitivity. Following the successful verification of the model, the differences in transient flow characteristics within each nozzle hole based on a P-type asymmetric multi-hole nozzle with sac were analyzed using the model. Results obtained from simulation shows that the cavitation phenomenon, velocity profile and mass flow rate in each nozzle hole of an asymmetric injector differ greatly. The hole with the higher nozzle hole angle (wider angle between nozzle hole axis and needle axis) was more inclined to cavitate, therefore the cavitation effect intensity is directly related to the size of the nozzle hole angle. During the lifting stages of the needle valve, the cavitation effect for each nozzle hole and the fuel flow velocity are gradually enhanced while on the contrary, the fuel flow velocity decreases and cavitation effect slightly increases at the closing stages of the needle valve lift. Also, the cavitation morphology at the same needle valve lift in any nozzle hole differs during opening and closing stages of fuel injection. In addition, the fuel flow velocity profile from the needle valve opening at the sac and into the hole of each nozzle shows that, in the order of increasing nozzle hole angle βi, the velocity effect gradually reduces as a result of dramatic change in flow direction.
An innovative repairable fuse device for moment-resisting composite steel frames is numerically investigated in this study developed within the European research project “Fuseis”. The fuse device ...consists of steel plates welded to the web and bottom flange of the beam with a specifically detailed gap in the concrete slab. In case of damage after a severe seismic event, the repair work is limited only to the replacement of the fuse. The results of preliminary numerical analyses carried out on detailed finite element models of beam-to-column sub-assemblages show that the dissipative fuses are able to concentrate plastic deformations in the steel plates protecting the other structural elements. Parametric investigations are performed to examine the influence of some relevant geometric characteristics of the flange plate on the fuse behavior. Then, a simplified numerical model of the device is developed and calibrated using the results of experimental tests carried out on beam-to-column sub-assemblages. The effects of the application of the device on the seismic performance of multi-storey composite steel frames are investigated through non-linear dynamic and static analyses. The results of the numerical analyses show the effectiveness of the fuse devices to dissipate large amounts of plastic energy and to preserve the other structural elements from damage. The influence of both the main mechanical characteristics and different locations of the fuses is also discussed in terms of relative seismic performance of the composite steel frames under study.
•The dissipative fuses concentrate plastic deformations in the steel plates protecting the other structural elements•The energy dissipation capacity of the frames equipped with welded fuses is larger than that of conventional frames•Frames with welded fuses ensure a better control of plastic mechanism than conventional frames•The efficiency of the device depends on the choice of the resistance capacity ratio and the location of the fuse
The paper presents the results of a numerical study regarding the effects of trench dimensions on the development of the ultimate peak uplift resistance of pipelines embedded in stiff soil or rock ...formations. The numerical methodology is calibrated against small-scale experiments and then applied to an extensive parametric investigation for different backfill densities, embedment depths and trench dimensions. It is, thus, shown that commonly excavated trenches are not adequately wide to accommodate the mobilized failure surface associated with ultimate peak soil resistance and consequently soil reaction to pipeline uplift may increase significantly. The numerical results are further interpreted to establish correction factors for the increase of the ultimate soil reaction and the associated yield displacement relative to the reference values for an “infinitely” extending sand backfill which are provided by analytical methodologies. In addition, an optimized trapezoidal trench geometry is proposed, which envelopes the unobstructed failure surface, so that the effects of the trench dimensions can be effectively eliminated with reduced trench excavation and backfill volume. The importance of lateral trench dimension in pipeline design is demonstrated through a typical example of a steel pipeline verification against normal fault rupture.
Abstract Slabs with cast-in-place steel formwork are composite structural elements composed of concrete and steel. The horizontal shear failure mode is the most common in composite slabs based on ...numerous experimental studies. This failure mode consists of loss of adherence and mechanical contact at the interface of the composite system and often occurs before the system reaches its full bending capacity. Thus, the design of this constructive system is determined by the value of the longitudinal shear strength, which can be computed by the semi-empirical so-called traditional m-k method based on the four-point bending test proposed by several standards. One of the most known factors to influence the longitudinal shear strength is the geometry of embossments present in the steel work. Calibrated computational simulation using the finite element method can be an alternative way to simulate this type of test. The present work modified and adapted a methodology explicitly including the geometry of embossments in the analysis in order to use materials and products with characteristics available to structural engineers in Brazil and used this methodology to derive m-k coefficients. This is being made with the objective of numerically simulating the effect of relevant parameters for determining the longitudinal shear strength at the concrete-steel interface of composite slabs. Force versus slip, force versus displacement graphs were obtained and the m-k coefficient values found were compared with those of other authors in the literature. The simulations presented values consistent with the literature and in relation to the rupture mode by longitudinal shear, the numerical simulations performed presented ultimate strengths with goodness-of-fit measured by the conventional coefficient of determination, reaching a good value for the semi-empirical relation using the results of the finite element data.
Resumo Lajes com fôrmas metálicas utilizadas durante a concretagem são um sistema estrutural misto composto de aço e concreto. O modo de falha por cisalhamento horizontal é o mais comum em lajes mistas com bases em numerosos estudos experimentais. Esta falha consiste na perda de aderência e contato mecânico do sistema misto e, frequentemente, ocorre antes do sistema atingir sua capacidade máxima à flexão plástica. Assim, o projeto deste sistema construtivo é determinado pela sua resistência ao cisalhamento longitudinal, que pode ser determinada pelo método semiempírico convencional m-k com base no ensaio de flexão de quatro pontos proposto por diversas normas. Um dos fatores conhecidos de maior influência na resistência ao cisalhamento longitudinal é a geometria das mossas presentes na fôrma metálica. Simulações computacionais por meio do método dos elementos finitos calibradas com base em resultados experimentais podem ser uma alternativa à realização deste tipo de ensaio. O presente trabalho modificou e adaptou uma metodologia que inclui explicitamente a geometria das mossas na análise de modo a usar materiais e produtos com características disponíveis para os engenheiros estruturais do Brasil e usou esta metodologia para derivar coeficientes m-k. Isto foi feito com o objetivo de simular numericamente o efeito de parâmetros relevantes para determinar a resistência ao cisalhamento longitudinal na interface aço-concreto de lajes mistas. Gráficos de força versus deslocamentos foram obtidos e os valores dos coeficientes m-k foram comparados com aqueles de outros autores na literatura. As simulações apresentaram valores consistentes com a literatura e, em relação ao modo de ruptura por cisalhamento longitudinal, as simulações numéricas realizadas apresentaram resistências últimas com bom ajuste medido pelo coeficiente de determinação convencional chegando a um valor bom para a relação semiempírica utilizando os resultados dos dados de elementos finitos.
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