Principle Of Force Balance Research Articles

Vascular adaptation model from force balance: Physarum polycephalum as a case study

Understanding vascular adaptation, namely what drives veins to shrink or grow, is key for the self-organization of flow networks and their optimization. From the top–down principle of minimizing flow dissipation at a fixed metabolic cost within flow networks, flow shear rate resulting from the flows pervading veins is hypothesized to drive vein adaptation. Yet, there is no proposed mechanism of how flow forces impact vein dynamics. From the physical principle of force balance, shear rate acts parallel to vein walls, and hence, naively shear rate could only stretch veins and not dilate or shrink them. We, here, resolve this paradox by theoretically investigating force balance on a vein wall in the context of the vascular network of the model organism Physarum polycephalum. We propose, based on previous mechanical studies of cross-linked gels, that shear induces a nonlinear, orthogonal response of the actomyosin gel making up vein walls, that can indeed drive vein dilatation. Furthermore, our force balance approach allows us to identify that shear feedback occurs with a typical timescale and with a typical target shear rate that are not universal properties of the material but instead depend smoothly on the vein’s location within the network. In particular, the target shear rate is related to the vein’s hydrostatic pressure, which highlights the role of pressure in vascular adaptation in this context. Finally, since our derivation is based on force balance and fluid mechanics, we believe our approach can be extended, giving attention to specific differences, to describe vascular adaptation in other organisms.

Adaptive back-stepping Control of Electro-hydraulic Servo system of Steam Turbine

The parameters such as oil density and bulk elastic modulus of hydraulic oil in steam turbine electro-hydraulic servo system vary with ambient temperature, pressure, and other factors, and there are unmodeled dynamics in the system, so obtaining a satisfactory following effect is a challenging task for the electro-hydraulic servo(EHS) system. According to the principle of force balance and flow continuity, the mathematical model of a bilateral oil intake motor is established in this paper. On this basis, a back-stepping controller is designed, and an adaptive method is used to estimate uncertain parameters and disturbances. The designed control system is simulated and verified, and compared with the RBF control system after parameter optimization. The results show that the controller designed in this paper has good tracking performance and adaptability to uncertain parameters and external load disturbances.

Quantitative characterization of critical reservoir physical properties of tight oil charging in the third member of the Shahejie Formation in the Gaobei Slope of Nanpu Sag, Bohai Bay Basin

Unconventional petroleum occupies an important position in the world energy structure. Tight oil is an important field of unconventional oil and gas exploration and development, and the physical property condition of a tight oil reservoir is an important determinant of its commercial production. The application of different geological and engineering strategies to quantitative characterization of the aspect of hydrocarbon charge vis-à-vis reservoir physical properties is critical and essential to thoroughly understand the formation and accumulation mechanism and help in achieving the optimum producibility of tight oil resources. This study focuses on the tight oil of the third member of the Shahejie Formation (Es3) region in the Gaobei Slope of the Nanpu Sag. The upper and lower physical limits of charging were quantitatively deduced and explained characterized by a combination of geological analysis, analytical testing, and numerical simulation of force balance; the formation mechanism of the tight oil reservoir is primarily constrained by its permeability. The inversion phenomenon of oil and water in the tight oil Es3 reservoir occurs at a burial depth of 3900 m. The pore type of the reservoir is mainly primary in nature, with a positive correlation between the porosity and the permeability. The upper limit of tight oil charging is quantitatively characterized by porosity approximately equal to 10%, the corresponding permeability being 1 × 10−3 μm2. When the reservoir's physical properties exceed the upper limit of tight oil charging, the reservoir mainly develops a water layer. This is mainly caused by the boundary effect of tight reservoirs, where the pore throat radius corresponding to the critical physical property is equivalent to the boundary layer thickness of oil in the reservoir pore, making it difficult for boundary fluids to flow in the pore space at this time. On the other hand, based on comprehensive analysis of the minimum flow hole roar radius, the irreducible water saturation, and drilling result statistical methods, the lower limit of the tight oil charging in Es3 reservoir is characterized quantitatively by the porosity of about 2%–4%, wherein the pore throat radius is approximately equal to 0.04 μm. The lower limit of tight oil charging varies from one place to another, mainly attributed to factors such as interfacial tension, hydrocarbon generation dynamics, kerogen type, and basin temperature. The charging process of tight oil complies with the principle of force balance, whereas the pressure exerted the generated hydrocarbon is counterbalanced by the capillary force of the pore space.

Research on the Multi-Point Gravity Balance Method for the Large-Aperture Space Camera in the Imaging Quality Test

The large-aperture space camera needs gravity unloading in the ground imaging quality test. The multi-point gravity balance method is mainly applied to the object with symmetrical structure and regular mass distribution, such as the primary mirror of the space camera. There is no relevant research on whether large-aperture space cameras with large weight and low stiffness can be unloaded by a multi-point gravity balance system. Based on the equivalent statically determinate structure and the classical equation of force method, the load-solving method of a multi-point gravity balance system is studied. The mathematical model of a two-point unit and a three-point unit is established with the principle of force balance. The mathematical model of a gravity balance system is built with the unit-grouping principle. A 15-point gravity balance system of a large-aperture space camera is established. The displacements of the mirrors under the multi-point gravity balance system are much smaller than the displacements under the traditional support by the finite element analysis, which can realize the imaging quality test. The multi-point gravity balance method is effective on the space camera imaging quality test.

Force constraint-based approach to compute the position and orientation of parts assembled by multiple non-ideal planes

The occurrence of position and orientation deviations (PODs) during the assembly of rigid components, which is caused by non-ideal morphologies on the manufactured surface, directly affects the performance of the mechanical product. Moreover, the generated PODs are influenced by the deformation of the contact points because of the assembly force. Therefore, to control the product performance in the design stage, the PODs should be computed considering both the non-ideal morphologies of the mating surfaces as well as the forces acting on the assembly. However, most existing approaches to POD computation ignore the effects of the assembly force. Moreover, they often focus on assemblies with a single mating plane. To address this problem, a force constraint-based approach is proposed in this study, which considers both the non-ideal morphologies of multiple mating planes and the assembly forces. The principle of force balance is employed to determine whether the assembly is completed. Different tentative positions and orientations are determined according to the strategies of progressively approaching position and orientation, and recursion of degrees of freedom (DOFs). An unbalance indicator was established in this study to determine whether the force balance in the direction of each DOF is satisfied. As long as the force balance of all DOFs to be constrained is achieved, the assembly of parts is considered to be finalised, and the final PODs are acquired. Finally, the PODs of a typical assembly with multi-mating planes and the guiding accuracy of a sliding workbench are computed according to the non-ideal morphologies modelled from the perspective of manufacturing errors, thereby validating the proposed approach.

Negation of Equivalence Principle

According to the electric charge and the elastic coefficient of the object independent of the motion of the object, and based on the similar properties of the gravitational field and the electrostatic field, it is concluded that the gravitational mass of the object is a constant independent of the motion of the object. However, experimental results show that the inertial mass of the object is related to the motion of the object. Therefore, it is considered that the principle of equivalence is not satisfied. As the object moves at a low velocity, the principle of equivalence is approximately true, so it is concluded that the general theory of relativity is applicable to all space celestial bodies. When the object is moving at high velocity, the principle of equivalence is not satisfied, so the general theory of relativity is not the truth. According to the principle of force balance, it is concluded that the velocity V of the black hole must be zero. Under the necessary conditions of V = 0, the existence of the black hole cannot be deduced according to the general theory of relativity. Therefore, it is considered that the black hole does not exist in theory. It is also estimated that the density of black hole is more than one million times the neutron density. It is believed that the black hole can never be a real material existence. The principle of black hole observation published on April 10, 2019 was considered theoretically wrong against the common sense of physics. The photos of the black hole halo taken at eight observation points in the world are judged to be untrue.

An accurate and numerically efficient time-varying mesh stiffness model for modified straight bevel gear under load

Gear time-varying mesh stiffness (TVMS) plays an important role in the analysis accuracy of a gear transmission mechanism. In previous research, the TVMS of a modified straight bevel gear (SBG) was mainly obtained by the finite element method (FEM), whose computation time is usually long to ensure computational accuracy. By contrast, this work proposes a fast calculation method with high accuracy for the TVMS of a modified SBG. First, B-spline surfaces are introduced to reconstruct a modified SBG using discrete tooth surface points. Next, based on the tooth contact analysis and loaded tooth contact analysis, combined with energy conservation principle and infinitesimal method, a semi-analytical instantaneous single mesh stiffness (SMS) model for the modified SBG is derived. Then, using the additional deformation compatibility condition and principle of force balance, the calculation method of the TVMS of the modified SBG is obtained. Finally, a comparison of the mesh stiffness calculation results between the method of this study and that of FEM is completed. The results show that the semi-analytical TVMS model used in this study can be accurately and quickly solved.

Study on excitation and time-varying mesh characteristics of straight bevel gears considering modification and friction

An accurate and numerically efficient nonlinear coupled excitation model for straight bevel gears (SBG) with linear and point contact is proposed. This model incorporates stiffness, load distribution, and transmission error (TE) models. Considering root fillet and axial mesh force components, energy equivalence principle, accumulated integral potential energy method, and segment coupling theory, single mesh stiffness (SMS) models with and without coupling effect are proposed. On this basis, the formula for calculating SMS under the action of friction is given. Time-varying mesh stiffness (TVMS), load distribution, and TE models were established using the deformation compatibility condition and principle of force balance. The proposed model was verified by comparing the calculation results with those obtained using the finite element method (FEM). The semi-analytical TVMS model used in this study could be solved accurately and quickly. The meshing characteristics and changing rules of SBG under the influence of different modification methods, modification amounts, and friction coefficients were analyzed. This study is expected to help further enrich and develop gear stiffness theory and provide a theoretical tool for gear dynamics research.

Dynamic modeling of reciprocating pump valves with considering the interaction effects between pump and pipeline

The components of a pump–pipeline system are coupled and interact with each other, but the dynamic analysis of reciprocating pump valves is usually executed without considering the effects of pipeline. In this article, a theoretical study is carried out to investigate the interaction effects between pump and pipeline on the motions of suction and discharge valves. Based on the principle of force balance and the law of mass and energy conservation, a new dynamic model of reciprocating pump valves is presented in order to obtain the motions of pump valve and the flow characteristics of pipeline simultaneously. The computational results are compared with the prior experimental data and the computational fluid dynamics simulation results to validate the proposed model, and good agreement is obtained. With the proposed model, the influences of piping parameters as well as the interaction effects on dynamic behaviors of pump valves and discharge flow rate are analyzed and discussed. It is found that the error between computational and prior experimental maximum valve lifts is less than 5%, and the proposed model has higher precision than the Adolph model in predicting the actual working characteristics of pump valves. The lift of pump valve and the flow rate in pipe are coupled with each other because the cylinder pressure and the leakage are directly related to the working load and the pressure drop of pipeline. The flow resistance of pipe could reduce the maximum value of valve lift but has slight influence on the lag time of valve opening. With the increasing of spring stiffness, the maximum value of valve lift decreases nonlinearly. The variation characteristics of flow rate versus pump operating speed relationships are significantly influenced by the flow resistance of pipeline, which means that the piping effects are significant and non-negligible for the pump design.

Design of a 3DOF XYZ Bi-Directional Motion Platform Based on Z-Shaped Flexure Hinges.

This paper presents a design of a 3DOF XYZ bi-directional motion platform based on Z-shaped flexure hinges. In the presented platform, bridge-type mechanisms and Z-shaped flexure hinges are adopted to amplify its output displacement. Bi-direction motion along the X-axis and Y-axis follows the famous differential moving principle , and the bi-directional motion along the Z-axis is realized by using the reverse arrangement of the Z-shaped flexure hinges along the X-axis and Y-axis. Statics analysis of the proposed platform is carried out by the energy method, compliance matrix method, and force balance principle. Meanwhile, the Lagrange method is used to analyze the dynamics of the platform. A series of simulations are conducted to demonstrate the effectiveness of the proposed design. The simulation results show that the average displacements of the platform in the XYZ-axis are μm, μm and μm, respectively.

Isogeometric analysis of cracks with peridynamics

Isogeometric analysis (IGA) is an important mesh-free method that provides the technique for the integration of computer-aided design and analysis. However, its formulation is based on classical continuum mechanics and is not suitable for crack propagation problems. The peridynamics (PD) theory is based on the non-local integral equation, which avoids the discontinuous problem of classical continuum mechanics and can solve the crack problems. In this paper, a coupling model of IGA and bond-based PD (IGA-PD) is proposed to provide the solution to crack problem of model with exact geometry. We prove that in the IGA-PD coupling model, the PD nodes can be constructed by using the control net from IGA. The implicit and explicit formulas of the PD model are combined with IGA formulations based on the force balance principle. Through setting the isogeometric model on the domain near the boundaries, the surface effect of the PD model can be relieved. The IGA-PD model fully utilizes the advantages of non-local continuum theory and improves the precision and computational efficiency in calculation of crack problems. The coupling method is straightforward and effective, and can be integrated within existing IGA codes. Examples of static problems and crack propagations are given to prove the effectiveness of the proposed method.

Coupling approach of isogeometric analysis with non-ordinary state-based peridynamics

Isogeometric analysis (IGA) is an important mesh-free method for the integration of computer aided design (CAD) and computer aided engineering (CAE) but not suitable for crack propagation problems. A coupling model of IGA and non-ordinary state-based peridynamics (NOSB-PD) is proposed to solve crack initiation and propagation problems in IGA because peridynamics can deal with the discontinuities well. The NOSB-PD model is constructed from the control points of IGA model directly, and the stiffness of the NOSB-PD model is combined with the IGA model based on the force balance principle. This method relieves the boundary effect of NOSB-PD by setting the IGA model on the domain near boundaries. In addition, a precise volume correction algorithm is proposed in this study to correct the volume of NOSB-PD points at the boundary of horizon. Some examples of the dynamic simulation of crack propagation and the static simulation of a homogeneous square plate and a prenotched rectangular plate are given to prove the effectiveness of the proposed coupling method.

A novel lift-off diameter model for boiling bubbles in natural gas liquids transmission pipelines

The pipeline is a convenient and safe way to transport natural gas liquids (NGLs). However, the NGL is easy to boil due to the variations of pressures and temperatures along the pipeline. The bubble lift-off diameter is an essential parameter to calculate the mass and heat transfer rates between vapor and liquid phases for the NGL two-phase saturated boiling flow. This paper proposed a novel bubble lift-off diameter model based on the force-balance principle of bubbles, which considers the effects of the pressure, shear lift force, unstable drag force, surface tension, gravity force, buoyancy force, gas-phase density, bubble volume, bubble flow velocity, and bubble growth time on the bubble’s lift-off diameters at various pipe inclination angles. A total of 136 experimental data points are applied to validate the new model. Results demonstrate that the average relative deviation (ARD) between the experimental bubble’s lift-off diameters and calculated values based on the new model is in the range from 5.75% to 29.95%. In contrast, for horizontal and vertical pipes, the minimum ARDs of seven existing models (Fritz, Kocamustaf, Zeng, Lee, Situ, Hamzekhani, Chen models) are in the range from 19.42% to 42.58%, respectively. Moreover, the in-depth force analysis results reveal that the shear lift force, buoyancy force, drag force and surface tension force are dominant factors affecting the bubble lift-off diameters in inclined pipes. The new model provides an effective method to calculate the bubble lift-off diameter in the pipe at various inclination angles, overcoming the deficiencies of most existing models that only can be applied to either horizontal or vertical pipes.

Simplified Layer Model for Solid Particle Clusters in Product Oil Pipelines

Pipe corrosion caused by the pressure tests using water before starting the normal operation occurs often in Chinese product oil pipelines because of remaining water. To explore the migration of the corrosion impurities in the product oil pipelines, this study started from the force balance principle and considered the entire particle cluster as the research object. This paper established a one-dimensional migration model, and proposed the Froude number equality criterion to calculate the particle cluster length in the equilibrium state. The proposed criterion was verified by experiments. A loop was built to conduct the tests and obtain the migration velocities of the particle cluster from the non-equilibrium state to the equilibrium state in the pipeline. The proposed model was verified using the experimental data. Verification results demonstrate that the model can describe the development process from the non-equilibrium state to the equilibrium state of particle clusters after sudden external disturbance and accurately predict some important parameters, including the velocity of the particle cluster in the equilibrium state and the critical velocity that leads to the transition from fixed bed flow to moving bed flow. The model provides the theoretical basis and calculation method to remove corrosion impurities from product oil pipelines.

Determination of initial cable force of cantilever casting concrete arch bridge using stress balance and influence matrix methods

Cantilever casting concrete arch bridge using form traveller has a broad application prospect. However, it is difficult to obtain reasonable initial cable force in construction stage. In this study, stress balance and influence matrix methods were developed to determine the initial cable force of cantilever casting concrete arch bridge. The stress balance equation and influence matrix of arch rib critical section were established, and the buckle cable force range was determined by the allowable stress of arch rib critical section. Then a group of buckle cable forces were selected and substituted into the stress balance equation, and the reasonable initial buckle cable force was determined through iteration. Based on the principle of force balance, the initial anchor cable force was determined. In an engineering application example, it is shown that the stress balance and influence matrix methods for the determination of initial cable force are feasible and reliable. The initial cable forces of arch rib segments only need to be adjusted once in the corresponding construction process, which improves the working efficiency and reduces the construction risk. It is found that the methods have great advantages for determining initial cable force in cantilever casting construction process of concrete arch bridge.

A Physics-Based Estimation of Mean Curvature Normal Vector for Triangulated Surfaces

In this note, we derive an approximation for the mean curvature normal vector on vertices of triangulated surface meshes from the Young-Laplace equation and the force balance principle. We then demonstrate that the approximation expression from our physics-based derivation is equivalent to the discrete Laplace-Beltrami operator approach in the literature. This work, in addition to providing an alternative expression to calculate the mean curvature normal vector, can be further extended to other mesh structures, including non-triangular and heterogeneous meshes.

Modeling analysis and experimental study for the friction of a ball screw

This paper aims to develop a new systematic creep analysis model to calculate the friction of a ball screw. In order to investigate the friction behavior better, a proper transformed coordinate system was established. Through the creep analysis and the principle of force balance, the creep parameters can be easily obtained, such as the vertical creep ratio, the horizontal creep ratio and the spin ratio acting on three contact areas. Based on roll contact theory, the ball screw friction can be predicted more accurately. The effectiveness of the creep analysis model is verified through experiments. Furthermore, the influence of the creep parameters on the ball screw friction and friction distribution will be discussed. The study not only provides a new perspective and approach for the study of ball screw friction, but also provides the theory basis for reasonably reducing the friction and improving the mechanical efficiency of a ball screw.

Simulation of diffusiophoresis force and the confinement effect of Janus particles with the continuum method

The Janus particle is a special class of colloidal particle that has different surface characteristics on its two hemispheres. In the microsystem field, an interesting application is the Janus particle's self-propulsion. Diffusiophoresis (DFP) provides one possible mechanism to explain this phenomenon. In this paper, we used the continuum model to simulate DFP and to study the confinement effect of Janus particles travelling on the substrate. In the experiment, we noticed a special quasi-1D motion, in which the DFP force is dominant and particles move at a constant velocity within a short interval approximately along a straight line. This enables us to adopt a reference frame to numerically study the distributions of the flow field and concentration field and hence to evaluate the different forces. Because the confinement effect has a great influence on the magnitude of forces, the gaps were calculated accurately according to the force balance principle. Meanwhile, the fitting coefficients to match the experimental and numerical results were suggested. This result may help us to get a better understanding of self-propulsion and is also beneficial for designing a DFP-based micro-device.

Quantitative regularity analysis of offset-vector sampling for seismic acquisition geometry

Symmetric acquisition geometry consisting of identical sampling of shots and receivers, can maintain the spatial continuity of the wavefield automatically, according to symmetric sampling theory. However, asymmetric geometry is often adopted in practical seismic exploration applications. Such geometry can cause uneven sampling and is necessary to be assessed for its sampling performance prior to acquisition. In conventional survey design, based on the common mid-point (CMP) analysis for a horizontally layered earth or common reflection point (CRP) analysis for a complex subsurface structure, the quality of acquisition geometry is generally judged by such bin properties as effective fold, offset scalar and azimuth distributions. However, these conventional approaches are limited by an incomplete understanding of the offset-vector sampling. Therefore, we propose a new method for quantitatively evaluating the continuity of offset-vector sampling including four spatial coordinates of shot and receiver. On the basis of physical potential energy and force-balance principle, it analyzes the regularity coefficient of offset-vector sampling as a whole using potential function model and takes into account fold, offset-scalar and azimuth distribution factors. The combination of regularity coefficients of every bin can produce spatial continuity distribution of offset-vector sampling. Similar to symmetric sampling, this approach emphasize the spatial relationships between adjacent bins rather than single bin attribute, since it aims to maintain the spatial continuity of the wavefield which allows the faithful reconstruction of the underlying continuous wavefield. Using this method, we can quantitatively compare spatial continuity distribution for different seismic acquisition geometries, and then choose the better acquisition scheme.

Structural Optimization Design and Experiment Investigation of Electric-Pneumatic Converter Device Based on the Principle of Nozzle Flapper

In this paper, a new electric-pneumatic convert device with piezoelectric composite disc as actuator is proposed. The new convert device break through traditional principle of force balance, which the parameters optimization to the whole air course and the structure of piezoelectric actuators were carried on by orthogonal experiment method. Experimental results show that the new device character is effected seriously by original installation site and has the characters of fast response, sensitive reaction, stable performance and meet the requirement of air pressure output between 0.02MPa and 0.1 MPa in industrial field with low voltage, which provides good basis of development of electric-pneumatic convert valve with new piezoelectric structure.