力学学报

MATERIAL CONFIGURATIONAL MECHANICS WITHAPPLICATION TO COMPLEX DEFECTS

Li Qun

Material configurational mechanics with application to describe the failure behavior of complex defects does provide an innovative way to predict the failure criteria load and assess the integrity of structures. First, the definitions of material configurational stress as well as the equilibrium equation, physical meaning, and the corresponding invariant integrals are obtained by the gradient, divergence, and curl operation of the Lagrangian function, respectively. Second, the material yielding, fracture, and final failure criteria are newly proposed within the frame of material configurational mechanics. Next, the proposed experimental technique provides an effective and convenient tool to evaluate the material configurational quantities by Digital Image Correlation. Finally, the concept of material configurational mechanics is used to evaluate the damage level of functional materials or structures, such as nano material and ferroelectrics.

2015, 47(2): 197-214. doi: 10.6052/0459-1879-14-240

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PARAMETRIC STUDY OF A k-ω-γ MODEL IN PREDICTING HYPERSONIC BOUNDARY-LAYER FLOW TRANSITION

Hao Zihui, Yan Chao, Zhou Ling

Predicting hypersonic boundary layer transition accurately is important to thermal protection and drag reduction of vehicle. However, many factors affect the process of hypersonic boundary layer transition. To study the impact factors of boundary layer transition from the transition model aspect, simulations on boundary layer transition of a 5° cone were carried out by using k-ω-γ transition model under different nose bluntness, frees-steam Reynolds numbers (Re_∞) and turbulence intensities (FSTI), and compared with the wind tunnel results. Some conclusions were obtained: k-ω-γ transition model can basically reflect the effects of nose bluntness, Re_∞ and FSTI on hypersonic boundary layer transition, however not well in predicting the heat peak following the transition; from the view of formulation of transition model, reducing the nose bluntness or increasing the Reynolds number can decrease the boundary layer thickness, which leads to the increase of the time scales of both the first mode and the second mode, and then the transition occurs prematurely; the FSTI is larger, the equivalent fluctuation kinetic energy is stronger in the laminar zone of the boundary layer, and boundary layer transition takes place easily.

2015, 47(2): 215-222. doi: 10.6052/0459-1879-14-294

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SIMULATION ON FLOW PATTERNS AND CHARACTERISTICS OF TWO-PHASE GAS-LIQUID FLOW IN A 90° BEND UNDER DIFFERENT GRAVITY

Liu Zhaomiao, Liu Jia, Shen Feng

The flow patterns and characteristics of two-phase gas-liquid flow in a 90° bend under different gravity were simulated. Based on the VOF (Volume of Fluid) method, a three-dimensional mathematical model of two-phase gas-liquid flow in a 90° bend tube was established to analyze the distribution of flow pattern, the cross-sectional void fraction, the slip ratio and the maximum skew angle in tail of the gas phase in a 90° bend under varied gravities of 10^-6g₀, 10^-4g₀, 10^-2g₀ and 1g₀ (g₀ = 9.8m/s²). It is shown that the effects of flow patterns and cross-section void fraction of gas-liquid two-phase flow under varied gravity conditions can be correctly analyzed by the developed model and the difference of secondary flow is obtained between the gas-liquid two-phase bend flow and the single-phase flow. With the increasing of gravity level, that the gas phase is accumulated to the inside of the 90° bend makes the effect of 90° bend on the gas phase flow and the oblique effect the 90° bend to the tail get weaken.

2015, 47(2): 223-230. doi: 10.6052/0459-1879-14-264

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DISTRIBUTION AND MOTION OF PARTICLES IN THE TURBULENTBOUNDARY LAYER OF CHANNEL FLOW

Song Xiaoyang, Ji Chunning, Xu Dong

This paper numerically investigates particles immersed in the turbulent boundary layer of channel flow. The methodology is a combination of three cutting-edge numerical technologies, i.e., the direct numerical simulation of turbulent flow, the point-particle immersed boundary method and the discrete particle method. We quantify the motion and distribution of near-wall particles by means of Voronoi analysis based on a set of instantaneous particle positions. It was found that the motion of particles have strong effects on flow velocity profiles and turbulence intensities, is closely related to the dynamics of the near wall coherent flow structures, i.e., the ejections of low-speed fluid carry particles towards the outer flow and the sweeps of high-speed fluid as well as gravitational settling bring particles back towards the wall. Most of particles in the turbulent boundary layer reside preferentially in low speed fluid regions and streamwise-aligned streaky structures. Particles keep in "clusters" over substantial time scales and sometimes they jump into "voids", after which those particles relatively quickly migrate back to a neighbouring low speed region.

2015, 47(2): 231-241. doi: 10.6052/0459-1879-14-164

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STUDY ON THE ACCELERATION OF TRAFFIC FLOW BASED ON THE EMPIRICAL DATA

Yin Kaihong, Wu Zheng, Guo Mingmin

By extracting data from six clips of traffc flow videos taken from Yan'an Viaduct in Shanghai, totally 4132 pieces data of velocity, headway, acceleration and velocity difference of car-following were obtained. Statistical analyses show that the value domain of acceleration is symmetric with respect to zero. In the synchronized or congesting flow, the acceleration obeys the normal distribution. While in the free flow, the distribution of acceleration has strong randomness and more amount of data with large absolute value. At different traffc flow densities, the impacts of headway, velocity and velocity difference are of different importance. Moreover, even in the same situation, these impacts on the acceleration and deceleration di er. The qualitative and quantitative levels of these impacts were summarized. The GM model and Bando model were optimized by using the empirical data. In the GM model, the parameters β and γ have little influence on the optimization result, therefore we proposed a simplified GM model without them. In order to overcome the asymmetry of the value domain of acceleration in Bando model, we proposed an improved model introducing a new parameter to reflect the desired headway. Both of the average fitting errors of these two new models are lower than 6%.

2015, 47(2): 242-251. doi: 10.6052/0459-1879-14-213

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ENERGY DISSIPATION CHARACTERISTICS OF CRUSHABLE GRANULES UNDER DYNAMIC EXCITATIONS

Qi Yuan, Huang Junjie, Chen Mingxiang

Using the discrete element method (DEM) with cluster, different degrees of particle crushing by setting various contact bond thresholds under external dynamic excitation are implemented, and their energy dissipation characteristics are also discussed. Numerical results indicate that the particle breakage ratio has a great influence on the energy dissipation ratio which is defined as consumed energy to the input energy. As the particle breakage ratio rises, which intensify the friction and the collision between particles, the energy dissipation ratio increases. Besides, most cluster disintegration happens on the early stage of cyclic loading. Gradually, the breakage rate slows down, and the energy dissipation ratio reduces.

2015, 47(2): 252-259. doi: 10.6052/0459-1879-14-145

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STUDY ON CONSTITUENT PROPERTIES OF A 2D-SiC/SiC COMPOSITE BY HYSTERESIS MEASURMENTS

Guo Hongbao, Jia Purong, Wang Bo, Jiao Guiqiong, Zeng Zeng

Continuous fiber reinforced ceramic matrix composites (CMCs) have outstanding mechanical properties. It is considered as a potential refractory material applied in aerospace fields. Study on CMCs' constituent properties has significant importance to the design, manufacture and engineering applications. In this paper, a method was prepared for assessing constituent properties of composites from hysteresis loops. The method is straightforward experimentally and provides values of constituent parameters directly. In detail, a hysteresis model in one dimension was constructed by shear-lag theory. The diverse effects of long and short matrix fragments on hysteresis behaviors were studied. And the hysteresis behaviors of a 2D-SiC/SiC composite were gained from tensile test. Considering the actual process of matrix cracking, all SiC matrixs was assumed to crack into long fragment. Values of four constituent parameters were calculated out: matrix cracking stress as 90MPa, residual stress as 19MPa, interfacial debond energy as 3.1 J/m² and sliding stress as 74MPa. Considering the influence of the few short fragments, the accuracy of calculations is analyzed. The calculations show a good dispersion and characterize the mechanical properties of 2D-SiC/SiC composites well.

2015, 47(2): 260-269. doi: 10.6052/0459-1879-14-247

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THERMAL CONTACT-INDUCED DISPLACEMENT DRIFT INHIGH-TEMPERATURE NANOINDENTATION

Chen Ke, Feng Yihui, Peng Guangjian, Zhang Taihua

Based on the analysis of heat transfer between indenter at room temperature and hot sample during their contact, this paper mainly studies the influence of thermal contact-induced expansion of the indenter holder on the displacement measurement in high-temperature instrumented nanoindentation. First of all, we derive an analytical solution of temperature distribution of the holder from the basic theory of heat conduction by appropriately simplifying the analysis model of hot nanoindentation, and use it to study the additional displacement caused by thermal expansion. Secondly, a finite element model (FEM) is established to investigate the thermal expansion-induced drift in hot nanoindentation to verify the analytical solution. It is found that the contact thermal properties between indenter and hot sample may significantly affect the distribution of temperature in holder. The thermal contact conductance between indenter and test sample varies from material to material, which can lead to the difference of several orders of magnitude of holder's thermal expansion. The research results may help to optimize the test program and improve the reliability of high-temperature instrumented nanoindentation.

2015, 47(2): 270-278. doi: 10.6052/0459-1879-14-297

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A MESHFREE METHOD BASED ON RADIAL POINT INTERPOLATION METHOD FOR THE DYNAMIC ANALYSIS OF ROTATING FLEXIBLE BEAMS

Du Chaofan, Zhang Dingguo, Hong Jiazhen

A meshfree method based on radial point interpolation method (RPIM) is proposed for dynamic analysis of a rotating flexible beam. The RPIM is used to describe the deformation of the flexible beam. The longitudinal and transverse deformations of the beam are both considered, and the coupling term of the deformation which is caused by the transverse deformation is included in the longitudinal deformation of the beam. The rigid-flexible coupling dynamic equations of the system are derived via employing Lagrange's equations of the second kind. Simulation results of the RPIM are compared with those obtained by using finite element method (FEM) and assumed modes method and show the limitations of assumed modes method. It is demonstrated that the meshfree method as a discrete method of the flexible body can be extended in the field of multibody system dynamics. Meanwhile, the influence of the radial basis shape parameters is discussed. What's more, three integration methods (Newmark method, fourth-order Runge—Kutta method and Adams prediction correction method) are used to solve the dynamic equations, and it shows that the Newmark method is the fastest with the computational effciency.

2015, 47(2): 279-288. doi: 10.6052/0459-1879-14-334

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DYNAMIC MODELING AND NONLINEAR CHARACTERISTICSOF FLOATING AIRPORT

Xu Daolin, Lu Chao, Zhang Haicheng

Floating airport consisting of multiple flexibly connected modules is a typical dynamic network with flexiblerigid- fluid coupling. A new method is proposed for modeling and a chain-topological network model for the floating airport is developed. In numerical simulations, the nonlinear responses of surge, heave, pitch motions and loads of connectors are analyzed implying that the classical linearization approach may severely underestimates the actual results. Further, this paper studies synergetic dynamics of the network and amplitude death phenomena. The onset of amplitude death associated with coupling stiffness and wave period are illustrated, which is important for the stability safety design of the floating airport. This work provides a new methodology and an application example in the study for network structural dynamics, including very large scale floating structures.

2015, 47(2): 289-300. doi: 10.6052/0459-1879-14-138

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RESEARCH ON MODELING AND SIMULATION OF LONGITUDINAL VEHICLE DYNAMICS BASED ON NON-SMOOTH DYNAMICS OF MULTIBODY SYSTEMS

Fan Xinxiu, Wang Qi

A method for modeling and simulation of longitudinal vehicle dynamics is presented based on non-smooth dynamics of multibody systems in this paper. The vehicle is the multi-rigid-body system which consists of a vehicle body, wheels and transmission system. It is assumed that wheels are linked with the vehicle body by shock absorbers and the transmission system is treated as the disk connecting with driving wheels by spring-damper system. The friction and the rolling resistance between wheels and the road are taken into account and the Coulomb's friction law is used to describe the frictional forces. Firstly, the lateral and bilateral constraint equations of the system are given in generalized coordinates of the system and the dynamical equations of the system are obtained by Lagrange's equations of the first kind. Secondly, the complementary formulations of friction law, rolling resistance law and contact law between wheels and road are given in order to determine state transitions from contact to separation and sticking to slipping. Based on the event-driven scheme, the problem of state transitions is formulated and solved as a horizontal linear complementarity problem (HLCP). The algorithm for solving these non-smooth DAEs is presented. The Baumgarte stabilization method is used to reduce the constraint drift. Finally, the multibody system of a vehicle is considered as an illustrative application example to analyse its dynamical behaviour affected by the engine output torque, the friction coeffcient and the rolling resistance coeffcient between wheels and road. The numerical results show that the phenomenon of the stick-slip between driving wheel and road occurs continually when the coeffcients have special values.

2015, 47(2): 301-309. doi: 10.6052/0459-1879-14-323

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AN UNCONDITIONALLY STABLE EXPLICIT ALGORITHMFOR STRUCTURAL DYNAMICS

Du Xiaoqiong, Yang Dixiong, Zhao Yongliang

This paper proposes an unconditionally stable explicit algorithm for time integration of structural dynamics by utilizing the discrete control theory. New algorithm adopts the recursive formula of velocity and displacement of CR algorithm, and obtains the respective transfer function based on Z transformation. Further, the specific expressions of coeffcients of recursive formula are derived according to the pole condition. Then, a variable s in the coeffcients to control the period elongation is introduced, which is applied to adjust the accuracy of new algorithm. Theoretical analysis indicate that the new proposed unconditionally stable explicit algorithm possesses the properties of second accuracy, zero amplitude decay, non-overshoot and self-starting, and its period elongation can be controlled by the variable s. Moreover, the CR algorithm is a special case of the proposed algorithm. Finally, the stability limit of nonlinear stiffening system is determined, and variable interval corresponding to the higher accuracy of new algorithm is presented. Numerical examples demonstrate that in this interval of variable s, the accuracy of new algorithm is superior to that of Newmark constant average acceleration and CR algorithm.

2015, 47(2): 310-319. doi: 10.6052/0459-1879-14-209

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PARAMETERS OPTIMIZATION OF A NEW TYPE OF DYNAMIC VIBRATION ABSORBER WITH NEGATIVE STIFFNESS

Peng Haibo, Shen Yongjun, Yang Shaopu

A new type of dynamic vibration absorber with negative stiffness spring is presented and studied analytically in detail. At first the analytical solution is obtained based on the Laplace transform method, and it could be found that there exist two fixed points independent of the damping ratio in the normalized amplitude-frequency curves. The optimum tuning ratio and damping ratio are obtained based on the fixed-point theory. According to the characteristics of the negative stiffness element, the optimal negative stiffness ratio is obtained and it could keep the system stable. The comparison of the analytical solution with the numerical one verifies the correctness and satisfactory precision of the analytical solution. The comparison with other two traditional dynamic vibration absorbers under the harmonic and random excitation show that the presented dynamic vibration absorber performs better in vibration absorption. The result could provide theoretical basis for the optimal design of similar dynamic vibration absorber.

2015, 47(2): 320-327. doi: 10.6052/0459-1879-14-275

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A NEW METHOD TO COMPUTE THERMAL EQUIVALENTNODAL LOADS ON CURVED SURFACES

Liu Yunfei, Lü Jun, Bai Ruixiang, Gao Xiaowei

A new method using flat shell element to compute thermal equivalent nodal loads on curved surface is presented. Firstly, the local Cartesian coordinate system is established on the tangential plane to the element surface. Then, the unknowns included in the integrand about thermal equivalent nodal loads are computed in terms of the theory proposed in this paper, which include the derivative of shape functions with respect to the variables of local coordinate system and the Jacobian of the transformation from the local three-dimensional coordinate system to the intrinsic two-dimensional coordinate system of the surface patch. Finally, a matrix transformation formulation is derived from the local Cartesian coordinate system to the global one, based on which the thermal equivalent nodal loads in the global Cartesian coordinate system can be found. Comparison with the results from FEM analysis shows that the proposed method in this paper is correct and accurate.

2015, 47(2): 328-336. doi: 10.6052/0459-1879-14-136

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SIMULATION FOR REVERSAL OF CELL POLARITY BASED ON BIDIRECTIONAL TRANSPORT OF SIGNALING MOLECULES

Feng Shiliang, Zhu Weiping

To investigate the mechanisms underlying the reversal of cell polarity, a mathematical model consisting of a pair of reaction-di usion equations was presented and solved numerically with the Lattice—Boltzmann method. It was found that, by applying a reversal gradient of Rac signal in a cell, labels for lamellipod (i.e., PI3K, and PIP₃) would disappear from the front of cell, and redistribute to the rear, while labels for tail (i.e., PTEN, PIP₂) would act oppositely. The spatiotemporal patterns of lamellipod and tail interconversion derived from our numerical simulation agreed well with that of the experimental observations. Besides, the time delay taking place between actin assembly at the new front and disassembly at the previous front was medicated by the completion of an activator (i.e., PI3K), without the help of a supposed "global inhibitor".

2015, 47(2): 337-345. doi: 10.6052/0459-1879-14-242

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INVESTIGATION OF RECOMPRESSION EFFECTS ON THE HIGH-ENTHALPY SPHERE-CONIC MODEL FLOW

Li Kang, Hu Zongmin, Jiang Zonglin

Thermo-chemical non-equilibrium effects may cause decrease in the surface pressure within the expansion region of a high-enthalpy blunt body flow as compared with a frozen flow. Research indicates that a recompression structure appended to the blunt body can eliminate the aforementioned difference. In the present study, a multi-component reactive Euler solver was applied to simulate the hypervelocity flow over a sphere-cone model. The numerical results show that thermo-chemical non-equilibrium induces a nonmonotonic variation to the conic surface pressure, i.e., it decreases first then increases as the recompression angle increases. The underlying mechanism for such a phenomenon is found to be the competing exothermal and endothermal reactions, which is macroscopically reflected by the inhomogeneity of the specific heat ratio in the recompression flowfield.

2015, 47(2): 346-350. doi: 10.6052/0459-1879-14-220

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EXPERIMENTAL INVESTIGATION OF SYNTHETIC JET CONTROL ON LARGE FLOW SEPARATION OF AIRFOIL DURING STALL

Zhao Guoqing, Zhao Qijun, Gu Yunsong, Chen Xi, Zhang Dongyu, Zuo Wei

In order to investigate the active flow control effect of synthetic jet on preventing flow separation and delaying stall of airfoil at low speed, wind-tunnel tests of jet control on the stall characteristics of NACA0021 airfoil are conducted. By systematic comparison tests including measurements about model aerodynamic forces, flow velocity on the airfoil upper surface based on Particle Image Velocimetry (PIV) technology and velocity profiles in boundary layer, the influences of synthetic jet parameters on control effects of airfoil stall characteristics are further explored. A large number of experimental results indicate that control effects on airfoil lift and stall angle of attack (AoA) due to jet angle are sensitive to the momentum coeffcient of synthetic jet. Overall, the control effects of the almost tangential jet are more effective when the momentum coeffcient of synthetic jet is large enough: increments about 23.6% of maximum lift coeffcient and 5° of stall-incidence of airfoil are obtained when the jet angle is 30° with jet momentum coeffcient being 0.033. On the other hand, a larger jet angle is required to achieve the best control effect when the momentum coeffcient is small: when the momentum coeffcient is about 0.0026, the normal jet is most effective on increasing the maximum lift coeffcient of airfoil by an increment about 9.2%.

2015, 47(2): 351-355. doi: 10.6052/0459-1879-14-134

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EFFECTIVE STRESS IN SOIL MECHANICS AND THE DISCUSSIONS ABOUT ITS FUNCTIONS

Zhao Chenggang, Liu Zhenzhen, Li Jian, Liu Yan, Cai Guoqing

This paper starts with a discussion of the effective stress functions for saturated soils, and then some situations of the theoretical predicting uncertainties in soil mechanics are stated. The relationship between the total stress and stress of each phase in unsaturated soils is developed based on three-phrase equilibrium equations of a representative element volume (REV). The expression of average soil skeleton stress, defined as effective stress, for unsaturated soils is then derived. This expression is consistent with the effective stress equation in unsaturated soils derived based on deformation work in the energy conservation equation. Then some discussions on the effective stress of unsaturated soil are given.

2015, 47(2): 356-361. doi: 10.6052/0459-1879-14-189

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EFFECTS OF COUPLING TERMS IN STRAIN ENERGY ON FREQUENCY OF A ROTATING CANTILEVER BEAM

Zhao Guowei, Wu Zhigang

Dynamic modeling of a rotating cantilever beam is very important for dynamic characteristics analysis and controller design. In literature, the coupling terms between axial and transverse deformation in strain energy are ignored in first order approximate model. However, as shown by this paper, these terms have a significant impact on the dynamic characteristics. By discussing how to select the strain energy, this paper takes into account the coupling terms. Based on Hamilton's principle, the coupling vibration equations of the rotating cantilever beam are obtained. Using Rayleigh- Ritz method, the bending mode shapes of the beam without rotational motion are selected as basic functions to derive characteristic equation. A numerical example is presented to show that the evident difference of bending frequencies between the models with and without the coupling terms in strain energy.

2015, 47(2): 362-366. doi: 10.6052/0459-1879-14-207

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MICRO-SCALE DESCRIPTION OF THE SATURATED CONCRETE REPAIRED BY ELECTROCHEMICAL DEPOSITION METHOD BASED ON SELF-CONSISTENT METHOD

Chen Qing, Zhu Hehua, Yan Zhiguo, Ju J.Woody, Deng Tao, Zhou Shuai

Since there are few theoretical models to describe the healing process of electrochemical deposition method at the micro-scale level, a three-phase micromechanical model, which is made up of the deposition products, water and intrinsic concrete, for the healed saturated concrete is presented based on the material's microstructure and the healing mechanism. To quantitatively describe the influence of the deposition products on the macro-scale properties of the concrete, multi-level homogenization scheme is presented to obtain the effective properties of the saturated concrete repaired by electrochemical deposition method based on the self-consistent method. Specifically, the properties of the equivalent inclusion are calculated by the general self-consistent model in the first level homogenization. In the second level homogenization, the self-consistent method combined with the Voigt upper bound is utilized to obtain the properties of the repaired concrete. To verify the correctness of micromechanical framework, the predicting results are compared with the experimental data and those from the existing models, which show that the proposed model and homogenization methods are reasonable and acceptable.

2015, 47(2): 367-371. doi: 10.6052/0459-1879-14-147

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REVIEW OF THE SIXTH NATIONAL SYMPOSIUM ON SOLID MECHANICS FOR YOUNG SCHOLARS

Wang Jizeng, Chen Weiqiu, Zhan Shige, Zhang Panfeng

In this paper, we gave a brief introduction to the Sixth National Symposium on Solid Mechanics for Young Scholars hosted by Lanzhou University, reviewed some of the scientific reports presented at this symposium, and presented a few constructive suggestions on the development of solid mechanics subject in the new era.

2015, 47(2): 372-380. doi: 10.6052/0459-1879-15-034

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