Search

In this paper, the origami membrane is modeled as a flexible multibody system and its deployment is simulated based on the absolute nodal coordinate formulation. The nonlinear anti-deployment effect of crease is integrated into the multibody system via the virtual work principle. The facet is modeled by the thin shell element and the crease is constructed as a nonlinear torsional spring with specific position and gradient constraints. The behavior of the crease is parameterized based on the experimental data. The modeling approach is verified by the numerical/experimental reference of the Z-folding structure in the existing literature. For the multi-crease origami membrane model considering the crease effect, a form-finding method to obtain the initial configuration of the flexible origami is proposed based on the principle of minimum potential energy. The deployment of the classical Miura-ori unit membrane structure is analyzed. The magnitude of driving force is estimated based on the force analysis of rigid deployment. Based on the simulation result of flexible deployment, the driving force is planned to achieve a stable deployment with a constant increase speed in the deployment ratio. This work is expected to provide a reference for the design of space membrane structure, the estimation of driving force, and optimizing the deployment strategy of an origami membrane.

The microstructure and primary carbides in the steel billets produced by an industrial-scale electroslag rapid remelting (ESRR) at different melting rates were studied. The amount and size of primary carbides MC and M2C at the center of the remelted ingots is larger than that at the mid-radius of the remelted ingots. The amount of primary carbides and secondary dendrite arm spacing of the ingot increase with the increase in the melting rates of ESRR, caused by the increase in the local solidification time. The microsegregation of Mo in the remelted ingots after annealing is most serious among the carbide-forming elements. The microsegregation of Mo and Cr increases linearly with increasing the melting rate, and the microsegregation of V keeps nearly constant with further increasing the melting rate from 400 to 500 kg/h. Increasing the melting rate of ESRR do not change the types of primary carbides until 500 kg/h, at which another type of primary carbide M7C3 is formed. The amount of the primary carbides and the microsegregation degree of Mo, V and Cr in the ESRR billets at the melting rate of 400 kg/h is nearly same as that produced by same-scale conventional ESR.

The solidification structure of austenitic Fe-22Mn-0.6C-1.6Al TWIP steel with and without Ce inoculation is compared on the macro- and microscale. The expansion of the equiaxed zone, decrease of equiaxed dendrite size and thinning of the dendrite arm are observed in Ce-inoculated TWIP steel. The refining mechanism for the expanded equiaxed zone and the decreased equiaxed dendrite size is the Ce2O3 particles acting as the heterogeneous nucleation sites. With increasing Ce content, the effective density of Ce2O3 particles of around 1 μm size increases initially and then decreases, while the total density always increases. The average diameter of Ce2O3 particles in TWIP steel increases as the amount of Ce increases. The mechanism for the thinning of the secondary dendrite arm is mainly by the solute effect, including the increase in both the undercooling in front of the dendrite tip and the drag effect on solid-liquid interface migration. In addition, the correspondence between the dendrite and grain in Fe-Mn-C-Al TWIP steel under as-cast condition is revealed. It is observed that the primary dendrite interface completely matches the austenite grain boundary. The crystallographic relationship follows 〈100〉d//〈100〉g and {100}d//{100}g (d and g represent the dendrite and grain, respectively) in both the columnar and equiaxed zones. The refinement of the equiaxed austenite grain in Fe-Mn-C-Al TWIP steel is purely the result of dendrite refining during solidification.

Y type nano zeolite (NFA-Y) was synthesized from fly ash by hydrothermal method at low temperature and without adding template. The structural and properties of the materials were characterized using XRD, BET Surface area analyzer and SEM. The results showed that the particle size of NFA-Y about 80 nm, the specific surface area is 508.2 m2 g−1, the pore volume is 0.342 cm3 g−1. The adsorption characteristics of Cs+ in aqueous solution by NFA-Y were studied. The adsorption capacity of the NFA-Y was 167.12 mg g−1 about. The adsorption equilibrium and the kinetic studies showed that the main adsorption mechanism were monolayer coverage and the chemical adsorption plays a dominant role in the overall Cs+ adsorption process.

A systematic numerical integration method is applied to the absolute nodal coordinate formulation (ANCF) fully parameterized beam element with smooth varying and continuous cross section. Moreover, the formulation for the integration points and weight coefficients are given in the method which is used to model the multilayer beam with a circular cross section. To negate the effect of the bending stiffness for the element used to model the high-voltage electrical wire, the general continuum mechanical approach is adjusted. Additionally, the insulation cover for some particular types of the wire is described by the nearly incompressible Mooney–Rivlin material model. Finally, a static problem is presented to prove the accuracy and convergence properties of the element, and a dynamic problem of a flexible pendulum is simulated whereby the balance of the energy can be ensured. An experiment is carried out in which a wire is released as a pendulum and falls on a steel rod. The configurations of the wire are captured by a high-speed camera and compared with the simulation results. The feasibility of the wire model can therefore be demonstrated.

A plane stress model was developed to study the coupled effect of mold taper and corner radius on the thermal–mechanical behavior of a 250 mm × 280 mm continuously cast bloom for a given special steel. Good agreement was obtained in both shell thickness and the off-corner cracking location from modeling and trial experiment. The results show that increasing mold taper results in the obvious decrease of surface temperature near the corner, while enlarging mold corner radius makes the shell surface temperature at the corner region more even with the mold taper between 0 and 1.5% m−1. It is also found that both the mold corner radius and taper are the key factors influencing the shell crack sensitivity but with different mechanism. For the internal crack, the mold taper takes more dominant effect for its corner radius between 0–10 mm, as the hoop strain at the solidification front decreases with increasing mold taper. For the surface crack, more sensitivity is noticed to the mold corner radius. Increasing mold corner radius leads to the increase of the surface hoop strain in the corner region, almost regardless of mold taper. The proper mold taper and corner radius for the present bloom casting should be 1.0–1.5% m−1 and 15–25 mm respectively.

A new high-voltage electricity wire model is proposed to simulate the dynamic behavior of the wire after tension failure and the nonlinear sliding joints between the wire and the iron tower. A previously developed piecewise cable element based on the absolute nodal coordinate formulation is used with its computer implementation given in this paper. In order to describe the initial tension in the wire, a static solving approach is used to achieve equilibrium between the element elastic force and the external force including the tension. The obtained configuration of the wire is then used as the initial configuration of analysis in case of unloaded external tension force. Thereby, the dynamic behavior of the wire can be modeled. The sliding joint constraint is used to describe the motion of the wire going through the iron tower after tension failure. A new static solution approach is developed to avoid the sliding joint constraint violation in the resulting equilibrium configuration. The convergence of the piecewise cable element based on the absolute nodal coordinate formulation is tested. A set of comparative results is presented to demonstrate the feasibility of the method proposed in this investigation.

The tensile behavior, serrated flow, and dynamic strain aging of Fe-(20 to 24)Mn-(0.4 to 0.6)C twinning-induced plasticity (TWIP) steel have been investigated. A mathematical approach to analyze the DSA and PLC band parameters has been developed. For Fe-(20 to 24)Mn-(0.4 to 0.6)C TWIP steel with a theoretical ordering index (TOI) between 0.1 and 0.3, DSA can occur at the very beginning of plastic deformation and provide serrations during work hardening, while for TOI less than 0.1 the occurrence of DSA is delayed and twinning-dominant work hardening remains relatively smooth. The critical strain for the onset of DSA and PLC bands in Fe-Mn-C TWIP steels decreases as C content increases, while the numbers of serrations and bands increase. As Mn content increases, the critical strain for DSA and PLC band varies irregularly, but the numbers of serrations and bands increase. For Fe-(20 to 24)Mn-(0.4 to 0.6)C TWIP steel with grain size of about 10 to 20 μm, the twinning-induced work hardening rate is about 2.5 to 3.0 GPa, while the DSA-dominant hardening rate is about 2.0 GPa on average. With increasing engineering strain from 0.01 to 0.55 at an applied strain rate of 0.001s−1, the cycle time for PLC bands in Fe-Mn-C TWIP steel increases from 6.5 to 162 seconds, while the band velocity decreases from 4.5 to 0.5 mm s−1, and the band strain increases from 0.005 to 0.08. Increasing applied strain rate leads to a linear increase of band velocity despite composition differences. In addition, the influence of the Mn and C content on the tensile properties of Fe-Mn-C TWIP steel has been also studied. As C content increases, the yield strength and tensile strength of Fe-Mn-C TWIP steel increase, but the total elongation variation against C content is dependent on Mn content. As Mn content increases, the yield strength and tensile strength decrease, while the total elongation increases, despite C content. Taking both tensile properties and serrated flow behavior into consideration, Fe-22Mn-0.4C TWIP steel shows excellent mechanical performance with a high product of tensile strength and total elongation and a slightly serrated stress–strain response. To suppress the negative effect of DSA in Fe-Mn-C TWIP steels on the stability of tensile behavior, a TOI lower than 0.1 is strongly suggested.

The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensional thermo-elasto-visco-plastic finite element model was developed to predict the mould gap evolution, temperature profiles and deformation behavior of the solidified shell in the mould region. Then, a three-dimensional model was adopted to calculate the shell growth, temperature history and the development of stresses and strains of the shell in the following secondary cooling zones. Finally, another three-dimensional model was used to analyze the stress distributions in the straightening region. The results showed that the off-corner cracks in the shell originated from the mould owing to the tensile strain developed in the crack sensitive regions of the solidification front, and they could be driven deeper by the possible severe surface temperature rebound and the extensive tensile stress in the secondary cooling zone, especially upon the straightening operation of the bloom casting. It is revealed that more homogenous shell temperature and thickness can be obtained through optimization of mould corner radius, casting speed and secondary cooling scheme, which help to decrease stress and strain concentration and therefore prevent the initiation of the cracks.

In order to control the CaO-Al2O3-SiO2-MgO system inclusions in 50CrVA spring steel in a lower melting temperature region, high temperature equilibrium experiments between steel and slag were performed in the laboratory, under the conditions of the initial slag basicity within 3–7 and the content of Al2O3 between 18–35 mass%, to investigate the formation and evolution of this type of inclusion. The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al2O3 content in slags, and CaO-Al2O3-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al2O3 content in slags. The most favorable composition for the refining slag is composed of 51–56 mass% CaO, 9–13 mass% SiO2, 20–25 mass% Al2O3 and 6 mass% MgO. In this case, the inclusions in 50CrVA spring steel are mostly in the low melting point regions, in which their plasticities are expected to improve during steel rolling. The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed. It is also found that adding around 11 mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion. Further work should be carried out focusing on the evolution rates of MgO-based inclusions.

The heat transfer and solidification microstructure evolution during continuous casting were experimentally studied in this work. A new approach to physically simulate the steel solidification behavior during continuous casting was developed. Six steel grades with different solidification mode were introduced to elucidate the carbon equivalent dependent mold heat flux, prior austenite grain size and secondary dendrite arm spacing. It is found that the non-steady mold heat fluxes in the experiment against time for all steel grades are comparative to that versus distance in practical continuous casting. Due to the occurrence of L→L+δ→δ+γ→γ transformation with the largest amount of volume contraction in hypo-peritectic steel, it shows the lowest mold heat flux among these six steel grades. It is also demonstrated from the solidification microstructure results that the prior austenite grain size and secondary dendrite arm spacing in the physical simulation are in good agreement with those in continuously cast strand. In addition, the steel with a higher temperature for the onset of δ→γ transformation reveals the larger prior austenite grains resulted from the higher grains growth rate in the post solidification process.

A 3D cellular automaton finite element model with full coupling of heat, flow, and solute transfer incorporating solidification grain nucleation and growth was developed for a multicomponent system. The predicted solidification process, shrinkage porosity, macrosegregation, grain orientation, and microstructure evolution of Fe-22Mn-0.7C twinning-induced plasticity (TWIP) steel match well with the experimental observation and measurement. Based on a new solute microsegregation model using the finite difference method, the thermophysical parameters including solid fraction, thermal conductivity, density, and enthalpy were predicted and compared with the results from thermodynamics and experiment. The effects of flow and solute transfer in the liquid phase on the solidification microstructure of Fe-22Mn-0.7C TWIP steel were compared numerically. Thermal convection decreases the temperature gradient in the liquid steel, leading to the enlargement of the equiaxed zone. Solute enrichment in front of the solid/liquid interface weakens the thermal convection, resulting in a little postponement of columnar-to-equiaxed transition (CET). The CET behavior of Fe-Mn-C TWIP steel during solidification was fully described and mathematically quantized by grain morphology statistics for the first time. A new methodology to figure out the CET location by linear regression of grain mean size with least-squares arithmetic was established, by which a composition design strategy for Fe-Mn-C TWIP steel according to solidification microstructure, matrix compactness, and homogeneity was developed.

Iron is an essential nutrient for bacterial survival and thus higher iron levels may precipitate bacterial infections. We investigated the association between the serum iron level and prognosis in patients with sepsis by using the single-centre Medical Information Mart for Intensive Care III (MIMIC-III) database. Sepsis patients with iron parameters measured on ICU admission were included and stratified according to quartiles of serum iron levels. A total of 1,891 patients diagnosed with sepsis according to the Sepsis-3 criteria were included in this study, 324 of whom were septic shock. After adjusting for confounding variables, higher iron quartile was associated with an increase in 90-day mortality in the Cox regression analysis. Moreover, a stepwise increase in the risk of 90-day mortality was observed as the quartiles of serum iron levels increased in the patients with sepsis. In conclusion, higher serum iron levels were independently associated with increased 90-day mortality in this large cohort of patients with sepsis.

This investigation is intended to develop a computer procedure for the integration of NURBS geometry and the rational absolute nodal coordinate formulation (RANCF) finite element analysis. A linear transformation is given that can be used to convert the NURBS curve to RANCF cable element mesh retaining the same geometry and the same degree of continuity, including the discussion of continuity control and mesh refinement. The green strain tensor is used to establish the nonlinear dynamic equations with numerical examples to demonstrate the use of the procedure in the dynamic analysis of flexible bodies.

The element created in this investigation is based on the it absolute nodal coordinate formulation (ANCF) which has been successfully used in flexible multibody system dynamic and integration of computer aid design and analysis (ICADA). When modeling a B-spline curve with ANCF beam element, it is the common manner to convert this curve into a series of Bezier curves because the systematical conversion between ANCF beam element and a Bezier curve has already been built. In order to avoid the constrain equation produced in this method and to express a B-spline curve using only one element, an alternative approach is developed, leading to the piecewise ANCF (PANCF) beam element. It is demonstrated that when two ANCF beam elements are connected according to a particular continuity, they can constitute a PANCF element. Besides, a new PANCF element will be produced when an ANCF element is connected to an existing PANCF element. The continuity condition can be automatically ensured by the selection of nodal coordinates and the calculation of the piecewise continuous shape functions. The algorithm for converting a B-spline curve to a PANCF beam element is then given. There also are discussions on the features of PANCF element. When two neighboring segments of PANCF element have the same assumed length, the position vector at the interface cannot be expressed by the other coordinates so the position vector is preserved in the $$C^{2}$$ continuous situation. Two examples are given to conclude the interpolation and continuity properties of the shape function and to demonstrate the feasibility of this PANCF in the ICADA.

Periodic mould level fluctuation (MLF) during slab casting is a bottleneck for upgrading the surface quality and casting speed especially for hypoperitectic (HP) or ultralow carbon steels. The uneven growth of the initially solidified shell is verified to be one of the important inducements to MLF due to related unsteady bulging in the secondary cooling zone. It is shown that the solidification mode of steels and the contraction behavior can be modified through chemical composition optimization within given composition limits. For high strength low alloy (HSLA) steels, the actual peritectic points calculated by Thermo-Calc software may change remarkably with the slight variations of alloying element contents. Accordingly, the narrow limit of chemical composition of HP steels through optimization is proven to be one of the effective factors to control the popular MLF phenomenon during slab casting.

The goal of this investigation is to introduce a new computer procedure for the integration of B-spline geometry and the absolute nodal coordinate formulation (ANCF) finite element analysis. The procedure is based on developing a linear transformation that can be used to transform systematically the B-spline representation to an ANCF finite element mesh preserving the same geometry and the same degree of continuity. Such a linear transformation that relates the B-spline control points and the finite element position and gradient coordinates will facilitate the integration of computer aided design and analysis (ICADA). While ANCF finite elements automatically ensure the continuity of the position and gradient vectors at the nodal points, the B-spline representation allows for imposing a higher degree of continuity by decreasing the knot multiplicity. As shown in this investigation, a higher degree of continuity can be systematically achieved using ANCF finite elements by imposing linear algebraic constraint equations that can be used to eliminate nodal variables. The analysis presented in this study shows that continuity of the curvature vector and its derivative which corresponds in the cubic B-spline representation to zero knot multiplicity can be systematically achieved using ANCF finite elements. In this special case, as the knot multiplicity reduces to zero, the recurrence B-spline formula causes two segments to automatically blend together forming one cubic segment defined on a larger domain. Similarly in this special case, the algebraic constraint equations required for the C 3 continuity convert two ANCF cubic finite elements to one finite element, demonstrating the strong relationship between the B-spline representation and the ANCF finite element representation. For the same order of interpolation, higher degree of continuity at the finite element interface can lead to a coarser mesh and to a lower dimensional model. Using the B-spline/ANCF finite element transformation developed in this paper, the equations of motion of a finite element mesh that represents exactly the B-spline geometry can be developed. Because of the linearity of the transformation developed in this investigation, all the ANCF finite element desirable features are preserved; including the constant mass matrix that can be used to develop an optimum sparse matrix structure of the nonlinear multibody system dynamic equations.

In this paper, we investigate the problem of power allocation in cognitive underlay networks, where a secondary user (SU) is allowed to coexist with a primary user (PU). We consider three transmission models for the secondary link: (i) one-way transmission with relay assisted, (ii) two-way transmission with a direct link, and (iii) two-way transmission with relay assisted. In conventional interference-limited cognitive networks, the instantaneous channel state information (CSI) of a PU is required to suppress SU’s transmit power to guarantee the quality of service (QoS) of the PU, which increases the feedback burden in practice. To tackle this issue, in this article we take primary outage probability as a new criterion to measure the QoS of the PU, where only the statistical CSI of the PU is required. Firstly, we derive the primary outage constraints for the three models, respectively. Then, with the newly obtained constraints, we formulate optimization problems to maximize the channel rate of the SU. Finally, we derive the optimal solutions for power allocation with respect to different parameters, respectively. Simulation results verify the performance improvement of the proposed schemes.

A new receive antenna subset selection algorithm with low complexity for wireless Multiple-Input Multiple-Output (MIMO) systems is proposed, which is based on the orthogonal components of the channel matrix. Larger capacity is achieved compared with the existing antenna selection methods. Simulation results of quasi-static flat fading channel demonstrate the significant performance of the proposed selection algorithm.

The expression of hypoxia inducible factor-1 alpha (HIF-1alpha) and its relationship to apoptosis in tissues around cerebral bleeding loci was studied. The expression of HIF-1alpha and apoptosis in 37 samples of tissues around cerebral bleeding loci and 9 samples of normal cerebral tissues was assessed by immunohistochemical straining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling methods. In 37 tissue samples around cerebral bleeding loci, the positive rate of the HIF-1alpha expression was 40.6%. Especially in the patients with amount of bleeding60 ml, the positive rate (88.9%) of the HIF-1alpha expression was significantly higher than those with the amount of bleeding ranging from 30-45 ml or 45-60 ml (P0.05). The expression of HIF-1alpha was increased as the amount of bleeding and operative time increased (P0.05). There existed a positive correlation between HIF-1alpha labeling index and apoptosis index (n=12, r=0.56, P0.01). These results suggested that the expression of HIF-1alpha was closely related with the time of hemorrhage and the amount of bleeding, and could induce the apoptosis of neurons.