Core Tube Research Articles

Parametric Optimization for Low Loss Negative Curvature Hollow Core Fiber With Elliptical Tube

Negative curvature hollow core fiber (NC-HCF) with elliptical tubes is beneficial for low confinement loss (CL) due to the rich degree of freedom in tube curvature. In this paper, an empirical formula for optimizing the structural parameters of NC-HCF with elliptical tubes is presented, which is aimed at the minimum CL. It is obtained by analyzing the trade-off between the mode coupling induced loss and the gap induced leakage loss, according to the theory of mode coupling between core fundamental mode and tube ring mode, and the geometric arrangement. Consequently, a relationship between gap and elliptical tube diameter in the radial direction has been found to be 1/2, with corresponding formula validated by the numerical investigation and simulation for a wide wavelength range and different elliptical tube numbers. The parametric optimization formula provides a design guideline for low loss NC-HCF, which can be an effective tool for further exploration and application.

Wavelength Modulated Anti-Resonant Fiber-Optic Microfluidic Device Based on SMF-HCTF-SMF Structure

A wavelength modulated microfluidic device based on hollow core tube fiber (HCTF) is proposed, the modal dispersion and field distributions of the liquid-filled HCTF are analyzed and simulated based on the anti-resonant mechanism, and refractive index and temperature sensing performances are demonstrated. The device is formed by the single mode fiber-HCTF-single mode fiber structure, and there are two micro-slots at the fiber fusion joints for liquid flow through the HCTF. Comparative experiments show that the device can be immersed in liquid environments, which is difficult for the structure without micro-slots. Various devices with different HCTF inner diameters and lengths are fabricated, according to the anti-resonant mechanism, the non-transmission wavelength position, free spectrum range, and spatial frequency of the spectrum are discussed. Besides, the sensing performances of the microfluidic device with different structural parameters are also tested and compared, the experimental results are consistent with the theoretical analysis. This comparative study of the HCTF-based microfluidic element is instructive for the investigation of other kinds of anti-resonant structures. Moreover, the proposed microfluidic device is a promising biochemical sensor with a compact structure, high reliability, and ultra-sensitivity.

Some Useful Guidelines for Whole Core CT-Scanning for Petrophysical Applications

From the time CT-scanning was introduced in the oil and gas industry, its use could be divided into SCAL and routine type applications. The first involves flowing fluids through the cores, whereas the second involves scanning, mainly the whole cores, in their native (preserved or unpreserved) state. For whole core CT-scanning, there has been a constant shift from qualitative to quantitative analysis. The size of whole cores is ideal for scanning them with a ‘converted’ medical CT-scanner but obtaining meaningful data requires more than just artifact-free images. In this paper, useful guidelines are offered for extracting meaningful quantitative data from whole core CT-scanning. Today’s fast, multi-slice medical CT-scanners generally provide sufficient image resolution for most of the whole core related applications. However, they usually require some modifications to the equipment and the calibration procedures. Special solid phantoms matching the size and density should be used for calibrating the scanner at different X-ray energies. A set of calibration ‘standards’ is necessary for converting the CT numbers into density and Zeff (Effective Atomic numbers), which should be scanned under the similar ‘environment’ as the whole cores. Using pilot scans is highly recommended for every core tube to reduce uncertainties. For dual energy scanning, it is important to take scans at the exact same locations, selecting the right energy pair and corresponding calibration tables. For image processing, important guidelines include aligning the first and last slices for selecting the largest region-of-interest, quality controlling each slice and assigning depths to each slice before converting from CT numbers to bulk density and Zeff. Additional information is provided for scanning with industrial CT-scanners which have both advantages and disadvantages. Guidelines such as the ones mentioned above allow the data from whole core CT imaging useful for a number of applications. Such data were successfully used for bulk density and porosity determination, heterogeneity quantification, lithology determination, dual-energy based mineralogy detection, density-based micro-imaging, core-log correlations and depth matching, fracture characterization, formation damage evaluation, and many others. Several examples are included in this paper. Adherence to strict guidelines helps extracting artifact-free, meaningful data on whole cores that can improve our understanding of rocks. This paper demonstrates at least 10 different applications of CT-scanners along with the proper guidelines that can be useful for engineers and geoscientists.

Wind Analysis of RCC Tube in Tube Structure Using ETABS Software

Abstract: The advancement in construction field is increased day by day. The numbers of buildings, height of building is increased. The effect of lateral load is increased with respect to the increase of height. Advance construction methods and structural systems are to be introduced to enhance the structural safety. There are different types of structural systems which are to be used to resist the effect of lateral loads on the buildings. tube, bundled tube, tube in tube, and tube mega frame structures tubular structures. A tube-in-tube structure Comprises of a peripheral framed tube and a core tube interconnected by floor slabs. The frame tube structure takes more of lateral load the efficiency of this system is derived from the great number of rigid joints acting along the periphery, creating a large tube. In which the horizontal slabs and beams connecting vertical elements are assumed as continuous connecting medium having Equivalent distributed stiffness properties. The tube-in-tube structure with central tube provides stability against lateral loading as well as gravity loading. The Static analysis is use for analysis of tubular structures and the output of the models are evaluate to have a comparative study of their wind performance in different terrain, Also, this system provides enough opening for stairways, elevators and ducts etc. It is suitable for high rise structure. The use of tube-in-tube structure allows speedy construction. It is suitable for RCC, constructions. This study is focused on wind behavior of tube in tube structure for varying terrain category in India for the parameters like wind displacement, story drift, and time period.

Experimental and theoretical investigation of self-tapping bolt core tube flange column connection of prefabricated steel structure

This study proposes a column-column connection with self-tapping bolts, a core tube, flange plates, and high-strength bolts for a prefabricated steel structure, which can avoid on-site welding of traditional steel structure closed section columns and realize efficient assembly of vertical steel structure components. To determine the mechanical characteristics of the self-tapping bolt core tube flange column connection (SCFC) and the effect of the core tube and self-tapping bolts on SCFC, quasi-static tests were performed. According to the test results, altering the core tube thickness within a specific range had no discernible impact on the SCFC's seismic performance metrics, including hysteresis performance, skeleton curve, and stiffness degradation. The failure modes of test specimens were all steel fractures at the column foot, proving that SCFC can realize the seismic design goal of “strong joint, weak member.” The force mechanism of the SCFC and slip mechanism of the self-tapping bolt were explored. A finite element model (FEM) was established, and the results agreed well with the test results, confirming the accuracy of the FEM. Finite element parametric analyses were performed to further clarify the impact of the thickness of the core tube on the connection performance. Combined with the test and FEM results analyses, the bearing capacity calculation formulas of the SCFC were proposed based on the yield-line theory and verified by the results of the test and FEM. The design criteria for the SCFC were further proposed.

Experimental and numerical study of blast resistance of geopolymer based high performance concrete sandwich walls incorporated with metallic tube core

To reduce the disastrous consequences caused by explosion, increasing attention has been paid to the blast mitigation of structures while keeping their adequate functions in recent years. In this study, an innovative multi-layer sandwich wall has been developed to provide blast mitigation for protective structures. Such a multi-layer sandwich wall consists of three layers including two steel wire mesh (SWM) reinforced geopolymer based high performance concrete (G-HPC) layers and a metallic tube core (MTC) layer. The blast behavior of the multi-layer sandwich walls under 1.0 kg contact explosion was investigated experimentally and numerically. A total of five sandwich walls were tested to explore the influence of different factors (including the thickness of the front/rear G-HPC layer and MTC layer) on their performance. Subsequently, a finite element model was developed and validated by comparing the numerical results with the experimental data. The findings indicated that the well-designed sandwich walls exhibited excellent anti-blast performance and the rear G-HPC layer remarkably affected the anti-blast performance. In addition, the numerical results could fairly predict the experimental phenomenon.

Effect of Debonding on Axial Response of Concrete Filled Steel Tubular Columns

The axial strength and ductility of concrete filled steel tubes is significantly improved due to two major factors namely, firstly due to confining effect provided by steel tube, and secondly due to the synergistic interaction between steel tube and concrete core. Sometimes, the contact between concrete core and steel tube is vanished and debonding between concrete core and steel tube (normal referred as gap) occurs owing to various reasons such as improper compaction, shrinkage in concrete, lack of curing of encased concrete, and due to non-uniform distribution of load at column top. Due to occurrence of gap, the composite action between concrete core and steel tube no longer remains effective the concrete core becomes unconfined in the initial phase of loading, consequently, the axial load carrying capacity of the concrete filled steel tubular (CFST) column decreases. The aim of this paper is to numerically investigate the effect of the gap between concrete core and steel tube on the axial load-deformation response and to Comparisons the predicted column strengths according to the Eurocode-4. In the present study, the gap between square section concrete core and encasing steel tube is considered on all the four sides with the magnitude of gap as 1 mm and 2 mm. Moreover, in order to investigate the effect of the gap on different size of square section CFST columns, keeping the length of column and steel tube thickness as constant 540 mm and 3.8 mm respectively, the side length of square section CFST column has been varied between 140 mm to 200 mm at an interval of 20 mm. The nonlinear finite element analysis of the CFST columns has been performed using the Abaqus where the C3D8R element has been used to discretize the concrete core as well as steel tube and the Drucker-Prager model has been used to simulate plastic behaviour of concrete. It has been observed that the presence of gaps between concrete core and steel tube significantly reduces the axial strength square CFST column.

Energy-Economic and Exergy-Environment Performance Evaluation of Compact Heat Exchanger With Turbulator Passive Inserts Using THDNF

Abstract Technology innovation requires advanced heat transporting techniques to fulfill better exergy and economic behavior of compact air heat exchangers (HXs). Three different turbulator inserts, TTIs, PTTIs, and DTTIs (twisted turbulator inserts, perforated twisted turbulator inserts, and dimpled twisted turbulator inserts, respectively), are used in air HX on the tube side as a passive technique for heat transfer enhancement. The present investigation deals with the exergo-economic with a sustainable analysis of air HX utilizing several water-based tripartite hybrid nanofluids (THdNFs), formed from three different nanoparticles intermixing, six different compositions based on the structure of nanoparticles, and three various turbulator placed to the tube core of HX. The detailed investigation of 4Es and sustainability of the device are investigated under various operating conditions. Results disclosed that nanofluid alone is not enough for energy and exergy improvement. However, turbulator passive device inserts in HX with THdNF show a remarkable improvement in thermal and thermohydraulic performance. The DTTI passive device in plain tubes using THdNF 5(Al2O3 + TiO2 + graphene–water) results in the highest 27% overall coefficient, 24.7% exergy change, 6.4% exergy efficiency, 7.4% performance index, and higher sustainability index at lowest Reynolds number than without inserts. Meanwhile, turbulator inserts yield to most increased 91.4% operating cost and equivalent CO2 emissions to the environment. Investigation revealed that the passive device DTTI with THdNF 5(Al2O3 + TiO2 + graphene–water) as a working fluid is likely to be preferred due to the highest performance evaluation criteria (PEC) ranges 2.3–2.45 for the same power, and the least preferred working fluid would be THdNF 2 (Al2O3 + Fe2O3 + SiC–water) due to its high operating cost.

Mechanical analysis and finite element modeling of FRP-ECC-HSC composite stub column under axial compression

A novel composite column, consisting of an outer fiber-reinforced polymer (FRP) tube, an inner high strength concrete (HSC) core and an engineered cementitious composite (ECC) ring, has been proposed and investigated. Compared with normal FRP-confined HSC column, the FRP-ECC-HSC composite column could exhibit superior deformability performance. In this study, mechanical analysis was firstly conducted on the composite column to investigate the interaction behavior among different components, i.e. HSC core, ECC ring and FRP tube. Modified analysis-oriented models were proposed for HSC and ECC under uniform FRP confinement. Furthermore, finite element (FE) models were also established with the use of accurate concrete damaged plasticity (CDP) model to simulate the behavior of the composite column, especially the ECC ring which is under non-uniform confinement. The material property data used in the FE models were generated by the modified analysis-oriented models. It is shown that the FE models can provide close predictions on the axial load-axial strain behavior and hoop strain-axial strain behavior compared with test results. Meanwhile, stress distribution over the composite column section as well as the influence of ECC ratio were discussed with the validated FE model.

Wind Analysis of RCC Tube in Tube Structure

Abstract: Modern tall buildings have efficient structural systems, and utilize high-strength materials, resulting in reduced building height, and thus, become slenderer and more flexible with low damping. These flexible buildings are very sensitive to wind excitation and earthquake load causing discomfort to the building occupants. Therefore, in order to mitigate such an excitation and to improve the performance of tall buildings against wind loads and earthquake loads, the tube in tube structures and tube frame structures are the innovative and fresh concept in the tubular structures. Generally, tube in tube structures is formed by connecting peripheral frame tube and inner core tube so closely, it is not seen as a solid system but it acts like a solid surface. The total loads acting on the structures to be collectively shared between the inner and outer tubes. The tubed frames Structure are new concept for tall building. In tubed mega frames instead of one central tube several vertical tubes are carrying the lateral loads. a comparative study of tube in tube structures and tubed mega frame system with different building geometry has been done using ETABS software.

Experimental and theoretical investigation of prefabricated separated core tube flange column connection joint

This paper suggests a separated core tube flange connection column joint to ensure the horizontal shear performance of box section steel columns at the flange connection to meet the performance requirements of column-to-column connection in high-rise buildings and the effective connection of steel columns at the joints. Low cycle reciprocating loading tests were conducted on three specimens with different parameters (separated core tube and stiffeners) to study the seismic mechanical performance of the connection and the finite element analysis (FEA) of separated core tube column connection joint was performed. The result of the experimental study shows that the separated core tube connection joints have fuller hysteresis curves and higher energy dissipation performance, as well as less high-strength bolt tension at the same interlayer displacement angle. This investigation provides experimental evidence of the deformation compatibility of the separated core tube connection. The mechanical properties of the separated core tube connection is basically the same as that of the welded connection, which can realize the rigid connection of the steel box section column. According to the numerical simulation, the failure mode and mechanism of the connection were obtained. Based on the results of tests and the finite element numerical model, further analysis to the rotational performance of the separated core tube flange connection joint in elasto-plastic phase and yield-hardening phase is carried out, and a three-stage bearing capacity calculation theory of the joint in the seismic process is proposed, which was verified by the test and FEA.

Quasi-static and blast resistance performance of octet-truss-filled double tubes

Thin-walled filled tube is a common energy absorbing and buffering structure. In this study, an octet-truss-filled double tubes structure was presented by filling an octet-truss core into double tubes. The quasi-static mechanical behavior of the octet-truss-filled double tubes was analyzed by both FEM and experiment and the blast resistance performance of the composite sandwich panel (CSP) with proposed octet-truss-filled double tubes core was analyzed by FEM. For comparison, the mechanical behaviors of random closed-cell foam-filled double tubes and square honeycomb-filled and hexagon honeycomb-filled double tubes were also studied. Results show that the specific energy absorption (SEA) value of octet-truss-filled double tubes under quasi-static was 49.5%, 19.0%, 18.4% and 8.7% higher than empty single outer tube, the empty double tubes, the random closed-cell foam-filled double tubes and the square honeycomb-filled and hexagon honeycomb-filled double tubes. In the blast resistance study, the proposed structure was simplified and arrayed to study its performance in the blast resistant CSP by numerical simulation. The maximum displacement of the midpoint of the back plate of the octet-truss-filled double tubes was 30%, 19.2%, 11.2% and 8.9% smaller than the maximum value of the CSP with single tube core, the CSP with double tubes core, the CSP with random closed-cell foam-filled double tubes core and the square honeycomb-filled and hexagon honeycomb-filled double tubes core. The effects of equivalent explosion load, plate thickness and side length of octet-truss on the blast resistance performance of the CSP were discussed. This study provides a fresh idea for the design of more efficient energy absorption and blast resistant structure.

Seismic response analysis of high-rise frame-core tube building on fluid-saturated soil considering soil-pile-structure interaction

This paper proposed a three-dimensional (3D) refined finite element method (FEM) to determine seismic responses of the high-rise buildings resting on fluid-saturated soil considering the soil-pile-structure interaction (SPSI) and the dynamic characteristics of two-phase media, using a user-defined element with ABAQUS. The theory and method to develop the FEM were introduced in detail, including the user-defined element, material constitutive models, boundary conditions, earthquake input methods, specific implementation procedures, and verifications. Then, the FEM was adopted to investigate the seismic responses of a 51-story high-rise building with a frame-core tube system subjected to six earthquake records. Discussions were conducted on the acceleration, displacements, inter-story drifts, story shear force, and damage behavior to interpret the seismic characteristics of the superstructure. A fixed-base model was also considered to reveal the SPSI effect under the same conditions. The results demonstrate that the SPSI lightens acceleration and total story shear force but amplifies displacements, inter-story drifts, and column shear force. Without regard to the SPSI, no apparent change appears for the damage of floor plates, whereas the core tube suffers more severe damage than under the SPSI conditions. For high-rise buildings, the SPSI does not always provide conservative seismic performance evaluations. It is of fundamental importance to include the SPSI effect during the performance-based seismic design of high-rise buildings for comprehensive understanding. The proposed FEM can also be access to seismic SSI analysis for other types of structures in the saturated field.

Adaptation study on nitrogen foam flooding in thick reservoirs with high water cut and high permeability

Most of the oilfields in China are in high- or ultrahigh-water-cut stages, and the impacts of water flooding developments have declined due to the increase in reservoir heterogeneity, the rapid increase in the water cut and the discontinuous distribution of crude oil under these conditions. Based on this phenomenon, an experimental study of nitrogen foam flooding is conducted in this paper. The oil displacement characteristics of nitrogen foam in oil and water layers of thick, high-porosity and high-permeability reservoirs are studied through one-dimensional core tube experiments, and the mechanisms of profile control and water plugging are analyzed. Through two-dimensional visualization experiments, we observe the migration and diffusion patterns of nitrogen foam, analyze the effects of different degrees of vertical foam production on the residual oil after water flooding, clarify the production effect of gas overburden on the residual oil at the top of the reservoir, and summarize the mechanisms of nitrogen foam flooding involved in improving the recovery factor. The results show that in the core tube experiment, the recovery factor of the high-permeability core is 93.73%, the recovery factor of the low-permeability core is 71.33%, and the total recovery factor reaches 83.23% in the stage of nitrogen foam flooding, which is 28.96% higher than that of water flooding. In the visualization experiment, the recovery factor of the nitrogen foam flooding stage is 57.12%, which is 24.99% higher than that of water flooding. The recovery degrees of the layers are similar; by comparing the increase in the recovery degree of each layer before and after the two stages, it is found that the increase in recovery degree increases from the bottom to the top. The foam system exhibits a good selective plugging ability under the conditions of severe heterogeneity and low residual oil in the high-permeability zone. Nitrogen foam flooding can effectively improve the recovery factor in the late-stage reservoir development of the ultrahigh-water-cut stage, and it shows good adaptability to these types of reservoirs.

Dynamics-Based Analytical Correlation between Flexure–Shear Coupled Model and Frame–Tube–Outrigger Model for Frame Core–Tube Structural Systems

Dynamics-Based Analytical Correlation between Flexure–Shear Coupled Model and Frame–Tube–Outrigger Model for Frame Core–Tube Structural Systems

Motion Law and Mechanical Properties of PIGs When Passing through a Pipe Bend

Pipeline inspection gauges (PIGs), as a kind of pipeline robot, are very efficient tools for cleaning and inspecting pipelines. However, the occurrence of obstructions in PIGs has always been a problem. The main cause of the PIG clogging pipeline problem is the reduced pressure differential between the front and rear due to damage to the cup. In this paper, a rigid-flexible coupled multibody dynamic motion system is established by importing flexible bodies. The stress and contact force generated by the elastic deformation of the cup in the pipe are analyzed. Moreover, the spacing ratio of PIG cups and the number of cups were changed, the number of cabin sections was increased, the bending of PIGs of different sizes and specifications was studied, and the influence of the cross-universal joint on the bending of PIGs, as well as the force between the cups and the core tube, was analyzed. Through the design and construction of the corresponding experimental equipment, the influence of the change in the number of leather cups on cornering is studied.

Seismic performance of a shear-type energy dissipation brace: Experimental investigation and numerical analysis

In this study, a novel shear-type energy dissipation brace (SEDB) was proposed, which integrated multiple pieces of steel shear plates on a single brace. The brace stiffness and yield load can be adjusted by changing the number of pieces and layers of the steel shear plates, which is more flexible than the traditional shear-type dampers. Three configurations of SEDBs were developed, including the flat steel plate-SEDB (F-SEDB), F-SEDB without core tube and corrugated steel plate-SEDB (C-SEDB). The quasi-static cyclic tests were conducted on three SEDBs to investigate the seismic performance. Experimental results showed that the proposed SEDB can achieve a stable hysteretic behavior, especially by adopting the core tube to prevent global out-of-plane deformation. Meanwhile, the C-SEDB has a more stable energy dissipation performance due to the high out-of-plane stiffness of the corrugated steel plates. The design procedure of the SEDBs was developed. Meanwhile, a finite element model was established and verified by the experimental results. The influences of the height-thickness and height-width ratio of steel plates were systematically investigated, which benefited the application and offered suggestions in engineering design.

Experimental study on the seismic performance of the new fully-bolted beam-column joint

This paper proposed a new fully-bolted core tube beam-column joint, and the seismic performance and structural measures of the joint were investigated. Four specimens were tested under cyclic loads, including a traditional column-through joint as a control group, an improved traditional joint and two new joints, and the effects of the beam section, axial compression ratio, the wall thickness and height of the inner sleeve on the seismic performance of the new joints were studied by experiments and numerical simulation. According to the results, although the improved traditional column-through joint showed good load-bearing behavior, it was prone to brittle failure. The fully-bolted core tube beam-column joint had better ductility and energy dissipation capacity than the traditional joint, and was more suitable for high-intensity seismic areas. Enlarging the beam section and increasing the inner sleeve height can improve the bearing capacity and energy dissipation capacity, while the inner sleeve wall thickness and axial compression ratio had relatively little influence on the seismic performance of the joint. Furthermore, increasing the thickness of the inner sleeve wall can intensify the stress concentration at the column end, which was not conducive to the seismic resistance of the structure. Simplified formulas for the yield and ultimate loads of the new fully-bolted core tube joint were proposed.

Numerical and analytical investigation of square timber columns confined with steel and carbon fiber reinforced polymer external jacket

This paper numerically investigated the timber confinement of columns with carbon fiber reinforced polymer (CFRP) and steel tubes under axial compression. An elastic-plastic model with linear hardening, a CFRP hashin damage, and a timber damaged anisotropic elastic-plastic model, respectively, are used to simulate the inelastic behavior of the steel tube, CFRP layers, and timber core. In addition, a comprehensive numerical study was conducted using a wide range of cross-sections, thicknesses, lengths, and the number of CFRP layers developed to varying degrees (0, 45, and 90). To confirm the accuracy of the current FEM model, numerical data is compared to the experimental model’s final strengths, behavior, and failure mechanisms. Additionally, the ultimate strengths of timber-steel and CFRP are compared to various standards and design formulas. The results reveal that columns with thicker steel tubes and more CFRP layers have an average of about 42% and 12% greater load-bearing capacity and ductility. The degree of CFRP affected the load-bearing capacity of timber columns, which increased by around 10% from 45 to 90. In comparison to specimens with equal cross-sections and thickness, shorter specimens with greater cross-sections typically have 40% higher stiffness. According to parameter studies, the AISC 360-16 American standard design approaches can be safely extended to anticipate the ultimate strength of timber-steel columns. Meanwhile, both the ACI-440 and Ilki et al. design formula predictions are the most precise, particularly at 45° with high ultimate strength.

Research on Wind Load Characteristics on the Surface of a Towering Precast Television Tower with a Grid Structure Based on Large Eddy Simulation

Local wind pressures on tiny rods of complex grid structures are difficult to obtain through wind tunnel tests due to their small sizes after scaling down, resulting in a lack of data support in wind load calculations for similar structures. However, local wind pressures on tiny rods can be obtained through numerical wind tunnel simulation using full-sized models. In order to investigate the wind pressure distribution of a grid structure and the influence of grid structures on the wind load of core tubes, three different television tower models are established based on an engineering example for large eddy simulations. A turbulence inlet generator (NSRFG) is adopted in the simulations while reproducing a portion of the wind tunnel test section including the mean and fluctuating pressures for validation. The results indicate that the mean wind pressures on the intersection of rods in the windward zone of the grid structure are higher than those on adjacent rods. Distinct reductions in the mean and fluctuating wind pressure of the grid structure are found in different zones. Moreover, resultant wind load forces and bending moments in the X and Y direction of the grid structure generally exceed 70% of the total wind loads. Based on simulation results, extreme net wind pressures of the grid structure and shape coefficients of enclosed regular octagonal cross-section buildings with the grid structure are provided for reference.