Nonlinear dynamics of a circular curved cantilevered pipe conveying pulsating fluid based on the geometrically exact model

Due to the novel applications of flexible pipes conveying fluid in the field of soft robotics and biomedicine,the investigations on the mechanical responses of the pipes have attracted considerable attention.The fluid-structure interaction(FSI)between the pipe with a curved shape and the time-varying internal fluid flow brings a great challenge to the revelation of the dynamical behaviors of flexible pipes,especially when the pipe is highly flexible and usually undergoes large deformations.In this work,the geometrically exact model(GEM)for a curved cantilevered pipe conveying pulsating fluid is developed based on the extended Hamilton's principle.The stability of the curved pipe with three different subtended angles is examined with the consideration of steady fluid flow.Specific attention is concentrated on the large-deformation resonance of circular pipes conveying pulsating fluid,which is often encountered in practical engineering.By constructing bifurcation diagrams,oscillating shapes,phase portraits,time traces,and Poincarémaps,the dynamic responses of the curved pipe under various system parameters are revealed.The mean flow velocity of the pulsating fluid is chosen to be either subcritical or supercritical.The numerical results show that the curved pipe conveying pulsating fluid can exhibit rich dynamical behaviors,including periodic and quasi-periodic motions.It is also found that the preferred instability type of a cantilevered curved pipe conveying steady fluid is mainly in the flutter of the second mode.For a moderate value of the mass ratio,however,a third-mode flutter may occur,which is quite different from that of a straight pipe system.

Mathematical Model and Geometrical Model of Double Pitch ZN-type Worm Gear Set Based on Generation Mechanism

The current researches on the tooth surface mathematical equations and the theory of gearing mainly pay attention to the ordinary type worm gear set（e.g., ZN, ZA, or ZK）. The research of forming mechanism and three-dimensional modeling method for the double pitch worm gear set is not enough. So there are some difficulties in mathematical model deducing and geometry modeling of double pitch ZN-type worm gear set based on generation mechanism. In order to establish the mathematical model and the precise geometric model of double pitch ZN-type worm gear set, the structural characteristics and generation mechanism of the double pitch ZN-type worm gear set are investigated. Mathematical model of the ZN-type worm gear set is derived based on its generation mechanism and the theory of gearing. According to the mathematical model of the worm gear set which has been developed, a geometry modeling method of the double pitch ZN-type worm and worm gear is presented. Furthermore, a geometrical precision calculate method is proposed to evaluate the geometrical quality of the double pitch worm gear set. As a result, the maximum error is less than 6′10–4 mm in magnitude, thus the model of the double pitch ZN-type worm gear set is available to meet the requirements of finite element analysis and engineering application. The derived mathematical model and the proposed geometrical modeling method are helpful to guiding the design, manufacture and contact analysis of the worm gear set.

Geometrical Modeling by NURBS Surface and RCS Computing by Visualization for Complex Targets

A novel approach to compute the high frequency radar cross-section (RCS) of complex targets is described in this paper.From the three views or the sectional views of the target, target is geometrically modeled by non-uniform rational B-spline (NURBS) parametric surfaces using the software CNFEOV developed by oneself which constructs NURBS representation of complex target from engineering orthographic views. RCS is obtained through PO, PTD, MEC and IBC techniques. When calculating RCS of the target, it is necessary to get the unit normal vector to surface illumi- nated by radar and the value Z which is the distance from the point on the surface to radar. ln this novel approach, the unit normal vector to the surface can be obtained either by the Phong rendering model, in which the color components (RGB) of every pixel on the image are equal to the coordinate components of the normal, or by the NURBS expressions. The value Z can be achieved by software or hardware Z-buffer. The effects of the size of image on the RCS of target are discussed and the correct method is recommended. The RCS of the perfect conducting sphere, cylinder and dihedral as well as the coated cylinder, as some examples, are computed. The accuracy of the method is verified by comparing the numerical results with those obtained by using other methods.

A General Representation of Geometrical Solution Model for Predicting Ternary Thermodynamic Properties

The existing geometrical solution models for predicting ternary thermodynamic properties from relevant binary ones have been analysed,and a general representation was proposed in an integral form on the bases of these models.

Compression Mechanical Performance Simulation and Parameter Optimization of Degradable Ureteral Stent Based on ABAQUS

The compression performance of a degradable ureteral stent is analyzed and the parameters are optimized by a finite element modeling method.The degradable ureteral stent explored in this paper is developed from poly(glycolic acid)(PGA)and poly(lactic-co-glycolic acid)(PLGA)degradable materials.Based on the actual measurement of fabric structure parameters,the three-dimensional model of the stent is established with the help of the modeling software.The finite element analysis software is used to simulate the compression process of the degradable ureteral stent.The parameters of materials,interactions and boundary conditions are set according to the compression environment of the stent for modeling and simulation.On this basis,the friction coefficient of yarns,the yarn radius,and the braided angle of the stent are further compared.The comparison test is carried out by a single variable.The experimental results show that the change of yarn friction coefficient has little influence on the compressive stress,while the yarn radius and the braided angle of the stent have a great influence on the compressive stress.

Structural Variation between the Western and Eastern Kuqa Fold-and-thrust Belt,China:Insights from Seismic Interpretation and Analog Modeling

The Kuqa fold-and-thrust belt exhibits apparent structural variation in the western and eastern zone.Two salt layer act as effective decollements and influence the varied deformation.In this study,detailed seismic interpretations and analog modeling are presented to construct the suprasalt and subsalt structures in the transfer zone of the middle Kuqa and investigate the influence of the two salt layers.The results reveal that the relationship of the two salt layers changes from separated to connected,and then overlapped toward the foreland in the transfer zone.Different structural models are formed in the suprasalt and subsalt units due to the interaction of the two salt layers.The imbricate thrust faults form two broom-like fault systems in the subsalt units.The suprasalt units develop detached folds terminating toward the east in the region near the orogenic belt.Whereas,two offset anticlines with different trends develop at the frontal edge of the lower salt layer and the trailing edge of the upper salt layer,respectively.According to exploration results in this region,the relationship between suprasalt and subsalt structures has an influence on hydrocarbon accumulation.We believe that the connected deformation contains high-risk plays while the decoupled deformation contains well-preserved plays.

Sparsity-based efficient simulation of cluster targets electromagnetic scattering

An efficient and real-time simulation method is proposed for the dynamic electromagnetic characteristics of cluster targets to meet the requirements of engineering practical applications.First,the coordinate transformation method is used to establish a geometric model of the observation scene,which is described by the azimuth angles and elevation angles of the radar in the target reference frame and the attitude angles of the target in the radar reference frame.Then,an approach for dynamic electromagnetic scattering simulation is proposed.Finally,a fast-computing method based on sparsity in the time domain,space domain,and frequency domain is proposed.The method analyzes the sparsity-based dynamic scattering characteristic of the typical cluster targets.The error between the sparsity-based method and the benchmark is small,proving the effectiveness of the proposed method.

No-Arbitrage in Financial Economics: Solution of the Mystery of Implied Volatility and S&P 500 Volatility Index

We have shown that classic works of Modigliani and Miller, Black and Scholes, Merton, Black and Cox, and Leland making the foundation of the modern asset pricing theory, are wrong due to misinterpretation of no arbitrage as the martingale no-arbitrage principle. This error explains appearance of the geometric Brownian model (GBM) for description of the firm value and other long-term assets considering the firm and its assets as self-financing portfolios with symmetric return distributions. It contradicts the empirical observations that returns on firms, stocks, and bonds are skewed. On the other side, the settings of the asset valuation problems, taking into account the default line and business securing expenses, BSEs, generate skewed return distributions for the firm and its securities. The Extended Merton model (EMM), taking into account BSEs and the default line, shows that the no-arbitrage principle should be understood as the non-martingale no arbitrage, when for sufficiently long periods both the predictable part of returns and the mean of the stochastic part of returns occur negative, and the value of the return deficit depends on time and the states of the firm and market. The EMM findings explain the problems with the S&P 500 VIX, the strange behavior of variance and skewness of stock returns before and after the crisis of 1987, etc.

基于草图的概念机设计综合与建模方法及其实现(英文)

In the context of applying computer aided design tools to aircraft conceptualdesign, a sketch based approach is proposed to help designers turn their original concepts intocomplex numerical models that are usable for further analysis and optimization. This approachemphasizes the integration of general configuration and the layout of such components as engines,payloads, fuel tanks and landing gears, and the representation of a design scheme as uniform planesketches and three dimensional models. This paper presents the measures adopted to implement theapproach in a prototype system, including the object-oriented data structure, friendly graphicaluser interfaces and basic features of relevant modules. Several examples generated in the prototypeand applications of the results are finally outlined to illustrate the effectiveness of theapproach.

Advances in statistical mechanics of rock masses and its engineering applications

To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.

Ablation and geometry change study of solid armature in a railgun

Armature plays an important role in the electromagnetic launch process. Due to the skin effect, the current density distribution is neither uniform on the rail, nor on the armature. High current density centralization in one part could lead to a partial high temperature and make the armature material melt down and be ablated, especially at low velocity. In this paper we try to change the geometry of a Cshaped armature to improve the current density distribution and reduce the ablation. Four variants of C-shaped armatures are designed to study the specific features, including a conventional C-shaped armature （CCA）, a rounded leading edge C-shaped armature （LCA）, a rounded trailing edge C-shaped armature （TCA）, and a rounded incorporate edge C-shaped armature （ICA）. A novel low-speed experiment is constructed and tested. The armatures are ablated and recovered to compare the improved effects. Then finite element simulations according to the experimental results are performed to further analyze the experimental results. It is proved that the current density and hence the temperature distribution can be immensely improved by simply changing the armature geometry. LCA and ICA show that the erosion is more uniform on the contact surface due to the rounded leading edge. The curved trailing edge could improve the uniformity of the current on the interface. ICA which combinesthe effects of LCA and TCA is the best option in the four armatures. How much the leading edge and the trailing edge should be curved involves the geometry of CCA and the posture of the interface on the rail. A saddle shape is a good option to improve the current density and temperature distribution in the throat. Erosion mechanism is analyzed finally. The experiments and simulations support the erosion and transition mechanism. A detailed description of the experiments and simulations is also presented in this paper.

Prediction on the viscosity of multi-component melts with a new geometric model

A geometric model for calculating the viscosity of multi-component melt fromrelated binary physicochemistry properties was derived based on Chou's thermodynamic geometricmodel. The model derived was employed to predict the viscosity of Au-Ag-Cu alloys. The results showthat the calculated viscosity for Au-Ag-Cu alloys meet the experimental data very well. In addition,the viscosity of Bi-Sn-In systems was also predicted with this model.

Weld pool boundary and weld bead shape reconstruction based on passive vision in P-GMAW

A passive visual sensing system is established in this research, and clear weld pool images in pulsed gas metal arc welding （ P-GMA W） can be captured with this system. The three-dimensional weld pool geometry, especially the weld height, is not only a crucial factor in determining workpiece mechanical properties, but also an important parameter for reflecting the penetration. A new three-dimensional （3D） model is established to describe the weld pool geometry in P-GMAW. Then, a series of algorithms are developed to extract the model geometrical parameters from the weld pool images. Furthermore, the method to reconstruct the 3 D shape of weld pool boundary and weld bead from the two-dimensional images is investigated.

Continuous-Time Models for Firm Valuation and Their Collateral Effect on Risk-Neutral Probabilities and No-Arbitraging Principle

Extensions of Merton’s model(EMM)considering the firm’s payments and generating new types of firm value distribution are suggested.In the open log-value/time space,these distributions evolve from initially normal to negatively skewed ones,and their means are concave-down functions of time.When payments are set to zero or proportional to the firm value,EMM turns into the Geometric Brownian model(GBM).We show that risk-neutral probabilities(RNPs)and the no-arbitraging principle(NAP)follow from GBM.When firm’s payments are considered,RNPs and NAP hold for the entire market for short times only,but for long-term investments,RNPs and NAP just temporarily hold for individual stocks as far as mean year returns of the firms issuing those stocks remain constant,and fail when the mean year returns decline.The developed method is applied to firm valuation to derive continuous-time equations for the firm present value and project NPV.

Parameter estimation of GTD model and RCS extrapolation based on a modified 3D-ESPRIT algorithm

The noise robustness and parameter estimation performance of the classical three-dimensional estimating signal parameter via rotational invariance techniques(3D-ESPRIT)algorithm are poor when the parameters of the geometric theory of the diffraction(GTD)model are estimated at low signal-to-noise ratio(SNR).To solve this problem,a modified 3D-ESPRIT algorithm is proposed.The modified algorithm improves the parameter estimation accuracy by proposing a novel spatial smoothing technique.Firstly,we make cross-correlation of the auto-correlation matrices;then by averaging the cross-correlation matrices of the forward and backward spatial smoothing,we can obtain a novel equivalent spatial smoothing matrix.The formula of the modified algorithm is derived and the performance of this improved method is also analyzed.Then we compare root-meansquare-errors(RMSEs)of different parameters and the locating accuracy obtained by different algorithms.Furthermore,radar cross section(RCS)of radar targets is extrapolated.Simulation results verify the effectiveness and superiority of the modified 3DESPRIT algorithm.

Effect of Corporate Debt on Firm Value

We have shown that three classic works considering the effects of corporate debt on the firm value,namely,Modigliani and Miller(1958,1963),Merton(1974),and Leland(1994),are wrong.Their main mistake is ignoring the business security expenses,BSEs.We suggest the model taking account of BSEs and apply it to the analysis of debt influence on the firm value and survival.Our modeling demonstrates that(1)the debt affects the firm value and its survival,(2)this influence is negative,diminishing the firm value and its chances to survive,(3)the pressure of the negative effect of debt increases as the debt grows,provoking the firm default.The debt can be beneficial for the firm if the loan is taken to improve its technology.The model helps estimate the chances to succeed in the technological modernization for various parameters of the firm and its business environment;and by that,to find the technology most suitable for the firm.It is shown that there is a serious problem in reading the market signals concerning a firm and using this information to control this firm.

Elimination of the impact of vessels on ocean wave height inversion with X-band wave monitoring radar

Directional wave spectra and integrated wave parameters can be derived from X-band radar sea surface images.A vessel on the sea surface has a significant influence on wave parameter inversions that can be seen as intensive backscatter speckles in X-band wave monitoring radar sea surface images.A novel algorithm to eliminate the interference of vessels in ocean wave height inversions from X-band wave monitoring radar is proposed.This algorithm is based on the characteristics of the interference.The principal components(PCs) of a sea surface image sequence are extracted using empirical orthogonal function(EOF)analysis.The standard deviation of the PCs is then used to identify vessel interference within the image sequence.To mitigate the interference,a suppression method based on a frequency domain geometric model is applied.The algorithm framework has been applied to OSMAR-X,a wave monitoring system developed by Wuhan University,based on nautical X-band radar.Several sea surface images captured on vessels by OSMAR-X are processed using the method proposed in this paper.Inversion schemes are validated by comparisons with data from in situ wave buoys.The root-mean-square error between the significant wave heights(SWH) retrieved from original interference radar images and those measured by the buoy is reduced by 0.25 m.The determinations of surface gravity wave parameters,in particular SWH,confirm the applicability of the proposed method.

GEOMETRIC MODEL AND APPLIED METHOD FOR THE CALCULATION OF GRAIN SIZE DISTRIBUTIONS

Most of the available methods for the calculation of the three dimensional(3D)grain size dis- tribution functions(SDF)are based on the S model and lead a grave systematical error.The origin is the basic supposition of spherical grains in the S model,which does not correspond with the feature of real grains.A new model called A model is developed based on the hypothe- sis of polvhedral grains.The probability functions of the A model and the method to calculate the 3D SDFs using the A model are given in the present paper.The theoretical analyses and experimental tests have demonstrated that the A model reduces the systematical error radical- ly.It is nearly as simple as the so far used S model,but gives much better results in repro- ducing of 3D SDFs from the measured ID or 2D SDFs.

A SUBDIVISION SCHEME FOR VOLUMETRIC MODELS

In this paper, a subdivision scheme which generalizes a surface scheme in previous papers to volume meshes is designed.The scheme exhibits significant control over shrink-age/size of volumetric models.It also has the ability to conveniently incorporate boundaries and creases into a smooth limit shape of models.The method presented here is much simpler and easier as compared to MacCracken and Joy's.This method makes no restrictions on the local topology of meshes.Particularly,it can be applied without any change to meshes of non-manifold topology.