Amplitude Of Axial Force Research Articles

Force Characteristics of Centrifugal Pump as Turbine during Start-Up Process under Gas–Liquid Two-Phase Conditions

The start-up process of a centrifugal pump as turbine (PAT) under gas–liquid two-phase conditions was simulated based on Fluent, and the evolution mechanism of the internal flow field and the variation law of force characteristics were studied in its start-up process under gas–liquid two-phase conditions. The results show that the area with high gas phase concentration corresponds to a strong vortex at the beginning of the start-up. The vortex intensity in the impeller gradually decreases with an increase in rotational speed. The gas volume fraction of the blade suction surface is more significant than that of the blade pressure surface. The higher the inlet gas volume fraction (IGVF) is, the more severely the blade load will fluctuate during the start-up process. As the rotational speed increases, the fluctuation of the blade load gradually weakens, and the maximum load is distributed near the inner edge of the blade after the rotational speed is stable. The periodic unbalanced radial force is produced in the start-up process. From the pure liquid conditions to the gas–liquid two-phase conditions with increasing IGVF, the dominant frequency amplitude of radial force shows a similar trend of decreasing first but then increasing. After the rotational speed tends to be stable, the dominant frequency of radial force is equal to the rotational frequency of the blade. With the increase in rotational speed, the dominant frequency amplitude of axial force decreases gradually. The higher the IGVF, the greater the dominant frequency amplitude of axial force at the same time.

Dynamic Analysis of Axially Loaded Beams Partially Supported by an Elastic Foundation Under a Moving Harmonic Load

In this paper, a first-order shear deformable beam element is formulated and employed to study the dynamic behavior of beams partially resting on a Pasternak elastic foundation subjected to an axial force and a moving harmonic load. The beam element is derived by using the solution of differential equilibrium equations of a beam segment to interpolate the transverse displacement and rotation. The dynamic response of the beams is computed with the aid of the Newmark method. A parametric study is carried out to highlight the effects of the moving load parameters, the axial force amplitude, and the foundation support on the dynamic characteristics of the beams. The obtained result reveals that the axial force and the moving velocity have an important role in the dynamic behavior of the beams, and the influence of the axial force on the dynamic behavior of the beam is dependent on the excitation frequency.

Influence of Eccentricity on Hydrodynamic Characteristics of Nuclear Reactor Coolant Pump under Different Cavitation Conditions

In order to study the influence of eccentricity on hydrodynamic characteristics of nuclear reactor coolant pump under different cavitation conditions, five different schemes were obtained by analyzing and optimizing the existing structural schemes. Based on the RNG k-ε model (Renormalization Group with k-epsilon turbulence models) and two-fluid two-phase flow model, the unsteady numerical analysis and test verification of different designed schemes are carried out by using the flow field software ANSYS CFX. The results of research show that different eccentricities will affect the nuclear reactor coolant pump’s head under different cavitation conditions, and the corresponding head in the scheme with the eccentricity of 5mm under the fracture cavitation condition is lower than that of the other schemes. When the impeller rotates at a certain angle from the initial position under critical and severe cavitation conditions, the radial force acting on the rotor system will fluctuate greatly. Under the condition of fracture cavitation, the radial force changed periodically and the resultant force value is small. Compared to the original scheme, the peak value of radial force is 6° clockwise after eccentricity of the impeller appeared. With the aggravation of cavitation condition, the axial force value of impeller decreases, but the corresponding amplitude of the impeller increases. Under critical and severe cavitation conditions, the maximum axial force amplitude of the nuclear reactor coolant pump appears in the two times blade frequency, and in the broken cavitation condition, the maximum axial force amplitude appears at the shaft frequency. When the eccentricity is 20 mm, the axial force fluctuates most under critical and severe cavitation conditions, and when the eccentricity is 10 mm, the corresponding axial force is smaller than that of the original scheme. When the eccentricity is 5 mm, the axial force on the impeller is the smallest, but the amplitude is the largest under the condition of fracture cavitation.

Modal analysis and dynamic responses of a rotating Cartesian manipulator with generic payload and asymmetric load

Here, investigation to explore the effect of generic payload and externally applied asymmetric load on the calculation of modal parameters and dynamic performance of a rotating flexible manipulator under prismatic motion has been established. We thus have developed a dynamic model of a rotating Cartesian manipulator with a payload whose center of gravity doesn’t coincide with the point of attachment, to determine the modal parameters i.e., natural frequency and corresponding mode-shape. These modal parameters are then illustrated graphically upon varying parameters like offset parameters (i.e., offset mass, offset inertia, offset length), mass and stiffness of rotary actuator, and amplitude and frequency of asymmetric load. An investigation into the nonlinear dynamics of the system accounting of geometric nonlinearity has been executed while obtained results have been validated numerically within the permissible error at the assorted critical points in frequency characteristic curves. Current research further investigates the influences of offset parameters, mass and stiffness of the actuator, frequency and amplitude of axial force on the steady state responses for the primary and sub-harmonic resonance conditions to reveal the built-in saddle-node and pitchfork bifurcation due to which the system losses its structural stability. This work enables an insight into the modal characteristics and nonlinear behavior of a rotating-Cartesian manipulator with a generic payload under asymmetric axial force and prismatic motion.

Numerical simulation of two experiments for studying propeller exciting forces

ABSTRACTIn model tests, propellers are usually operated in nominal ship wake to measure exciting forces, and the incoming flow to propellers is different from that when the propeller is working right after the hull, which may lead to different results. Numerical methods were applied for simulations of two experiments: one is to simulate the propeller after a specially designed stern, and the nominal ship wake is set to the velocity inlet boundary, and free surface is considered; the other is to simulate the propeller right after the entire hull model. Results show that the amplitude of axial force of a single blade from the simulation of propeller after the stern is under-predicted, while the amplitudes of transverse and vertical forces of the whole propeller are over-predicted, but the differences are small. The amplitudes of fluctuating pressures on the hull surface predicted by the two approaches are basically the same.

Wind Tunnel Study on a Missile with Forward-Facing Cavity in Supersonic Flow

A forward-facing cavity will be composed of the components of a scramjet from inlet to combustion chamber which has a uncovered inlet before the separation of the booster. Longitudinal oscillations are generated within the cavity under some certain flow conditions. Strong oscillations may damage the components of the scramjet, or induce bow-shock oscillations which may cause unsteady loads on the missile and affect the performance of the aerodynamical characteristics. An experimental study of missile model with a scramjet was conducted in a transonic wind tunnel. The characteristics of cavity flow were researched by both the dynamic force measurement and the fluctuation pressure measurement. In the experiments the oscillations within the cavity and the bow-shock in front of the inlet interacted. The oscillations of cavity flow and bow-shock affected the fluctuation pressure and the aerodynamical characteristics of missile remarkably. The amplitude of axial force was higher than the normal force's. The RMS of the fluctuation pressure of some measured place inside the scramjet reached a quarter of the total pressure, and the amplitude of the fluctuation reached half of the total pressure. Those might threaten the safety of the structure of the scramjet.

Finite difference method for dynamic response analysis of anchorage system

Based on some assumptions, the dynamic analysis model of anchorage system is established. The dynamic governing equation is expressed as finite difference format and programmed by using MATLAB language. Compared with theoretical method, the finite difference method has been verified to be feasible by a case study. It is found that under seismic loading, the dynamic response of anchorage system is synchronously fluctuated with the seismic vibration. The change of displacement amplitude of material points is slight, and comparatively speaking, the displacement amplitude of the outside point is a little larger than that of the inside point, which shows amplification effect of surface. While the axial force amplitude transforms considerably from the inside to the outside. It increases first and reaches the peak value in the intersection between the anchoring section and free section, then decreases slowly in the free section. When considering damping effect of anchorage system, the finite difference method can reflect the time attenuation characteristic better, and the calculating result would be safer and more reasonable than the dynamic steady-state theoretical method. What is more, the finite difference method can be applied to the dynamic response analysis of harmonic and seismic random vibration for all kinds of anchor, and hence has a broad application prospect.

Axial force measurement for esophageal function testing

The esophagus serves to transport food and fluid from the pharynx to the stomach. Manometry has been the "golden standard" for the diagnosis of esophageal motility diseases for many decades. Hence, esophageal function is normally evaluated by means of manometry even though it reflects the squeeze force (force in radial direction) whereas the bolus moves along the length of esophagus in a distal direction. Force measurements in the longitudinal (axial) direction provide a more direct measure of esophageal transport function. The technique used to record axial force has developed from external force transducers over in-vivo strain gauges of various sizes to electrical impedance based measurements. The amplitude and duration of the axial force has been shown to be as reliable as manometry. Normal, as well as abnormal, manometric recordings occur with normal bolus transit, which have been documented using imaging modalities such as radiography and scintigraphy. This inconsistency using manometry has also been documented by axial force recordings. This underlines the lack of information when diagnostics are based on manometry alone. Increasing the volume of a bag mounted on a probe with combined axial force and manometry recordings showed that axial force amplitude increased by 130% in contrast to an increase of 30% using manometry. Using axial force in combination with manometry provides a more complete picture of esophageal motility, and the current paper outlines the advantages of using this method.

Simulation of piano strings and a soundboard by a large deformation theory

Three-dimensional finite element analyses of piano strings and a soundboard are presented in which a large deformation theory is adopted. In the large deformation theory, the momentum balance of a body is preserved in the course of the deformation and the changes of direction and amplitude of axial force due to deformation are taken into account. It is shown that the secondary partials appear in the spectrum of the velocity component in the axial direction as well as the transverse direction. A hammer is modeled by masses with springs and dashpots. Gap elements are employed to simulate the contact and detachment between the hammer model and a string. It is demonstrated that multiple reflections between hammer and agraffe can be reproduced by the method. Modeling of the interaction among strings, a bridge, and a soundboard is also discussed in which the crown and the preloading of the soundboard are taken into account.

A Study of the Estimation Method of Long-Term Distribution of Hot-Spot Stress Amplitude at Leg Nodes of Jack-up Rig

The method of practical fatigue strength analysis for the hot-spot parts around leg nodes of the Jack-up rigs is seemed to be behind the demand because of their unique operating systems and complicated mechanism of axial force occurrence in braces. In order to estimate the fatigue strength at leg nodes, the forced vibration analysis for irregular waves in short and long-term sea conditions is mandatory.In this paper, the method of the forced vibration analysis in the regular wave is developed for the irregular waves and the method to estimate the long-term distributions of axial force amplitude in braces is introduced by applying the simple formula in the previous paper. For the estimation, the probability of occurrence of wave incident angle, operating sea depths and whether the wedges are installed or not are considered.The fatigue strength at nodes can be estimated by the combinations of long-term distribution of hot-spot stress amplitudes calculated from axial force in braces and the S-N curve for the used material.