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This paper investigates the force features of inclined pipes under the action of waves and flows through both test and numerical simulation. Firstly, the wave and flow loads on inclined pipes were examined through tests in circulating water flumes. Next, the unsteady Reynolds-averaged Navier-Stokes (RANS) equations were adopted to numerically simulate the test conditions. Multiple factors were taken into consideration: immersion depth, inclination, flow rate, wave height, and cycle. The results show that, the wave and flow loads on the pipes both increase with wave height and flow rate. When the inclination β = 0°, the flow force is most rapid, conversely, it is most slow when the inclination β = 30°. Furthermore, when the pipe was immersed by 75%, the change of inclination directly affected the ratio of vertical force to horizontal force. For the pipes with different inclinations, the wave load increases basically at the same rate with the rising wave height. With the widening of the inclination, the wave and flow loads on the pipes become less sensitive to immersion depth, and the maximum loads remain near the free water surface.

Using a novel formulation based on flow force, we prove the existence of a global continuum of periodic traveling wave solutions to the irrotational water wave problem in finite depth where the flow force is held fixed, instead of fixing the mass flux. We further establish the limiting behaviour of solutions in this continuum where the flow force remains fixed throughout the continuum of the solutions. The global solutions, with a fixed flow force, show the possibility that a weak stagnation point can be approached at the surface, which is a characteristic of large amplitude irrotational water waves. The formulation is suitable for applications to numerical studies on water waves.

In this paper, we study steady two-dimensional periodic equatorial water waves of small amplitude which propagate over a flat bed and with a specified fixed mean-depth. In particular, we focus on irrotational flows and develop an equivalent formulation using flow force functions. The analysis is based on the local bifurcation theory due to Crandall-Rabinowitz.

The temperature-induced variation in operating force of flow control valves may result in performance degradation or even jam faults of fuel metering unit (FMU), which significantly affects the safety of aircrafts. In this work, an analytical modeling approach of temperature-sensitive operating-force of servo valve is proposed to investigate the temperature characteristics in varying temperature conditions. Considering the temperature effects, a new extended model of flow force is built and an analytical model of valve friction is also derived theoretically based on the dynamic clearance induced by thermal effects. The extremum condition of friction is obtained to analyze the characteristic-temperature points where jam faults occur easily. The numerical results show that flow force increases firstly and then decreases as temperature increases under a constant valve opening. The maximum friction of flow servo valve can be uniquely determined when the structural parameters and ambient temperature are given. The worst situation just happens at the characteristic-temperature points, which are linearly related to the axial temperature gradients of valve spool. Such evaluations may give an explanation for the temperature-induced jam faults of vulnerable valves and provide a reference for designers to determine a suitable working-temperature range of valves in practice.

The optimal parameters for the fluid-structure interaction analysis using the Smoothed Particle Hydrodynamics (SPH) for fluids and finite elements for structures, respectively, are explored, and the effectiveness of the simulations with those parameters is validated by solving several open surface fluid problems. For the optimization of the Equation of State (EOS) and the simulation parameters such as the time step, initial particle spacing, and smoothing length factor, a dam-break problem and deflection of an elastic plate is selected, and the least squares analysis is performed on the simulation results. With the optimal values of the pivotal parameters, the accuracy of the simulation is validated by calculating the exerted force on a moving solid column in the open surface fluid. Overall, the SPH-FEM coupled simulation is very effective to calculate the fluid-structure interaction. However, the relevant parameters should be carefully selected to obtain accurate results.

Ischemia which leads to heart attacks and strokes is one of the major causes of death in the world. Whether an occlusion occurs or not depends on the ability of a growing thrombus to resist flow forces exerted on its structure. This manuscript provides the first known in vivo measurement of how much stress a clot can withstand, before yielding to the surrounding blood flow. Namely, Lattice-Boltzmann Method flow simulations are performed based on 3D clot geometries, which are estimated from intravital microscopy images of laser-induced injuries in cremaster microvasculature of live mice. In addition to reporting the blood clot yield stresses, we also show that the thrombus “core” does not experience significant deformation, while its “shell” does. This indicates that the shell is more prone to embolization. Therefore, drugs should be designed to target the shell selectively, while leaving the core intact to minimize excessive bleeding. Finally, we laid down a foundation for a nondimensionalization procedure which unraveled a relationship between clot mechanics and biology. Hence, the proposed framework could ultimately lead to a unified theory of thrombogenesis, capable of explaining all clotting events. Thus, the findings presented herein will be beneficial to the understanding and treatment of heart attacks, strokes and hemophilia.

This study was done to investigate the effects of angle and spacing of Collar-rings (innovative attachments for scour reduction over the circular piers) on the flow-induced forces on the circular piers. To this end, three angles (0°, 15°and 30°) and three relatives spacing (2/3, 3/3, and 4/3 of pier diameter) for the Collar-rings, have been considered. The ratio of the Collar-rings thickness to pier diameter was considered as 0.15. To compare the Collar-rings and helical cable performance, a circular pier with helical cable (the angle of 15°and the cable–pier diameter ratio of 0.15, suggested by previous experiments) is also numerically simulated. Reynolds number of the flow around circular piers with Collar-rings and helical cable is set to be 9554. In comparison to a plain surface pier, the results show that Collar-rings with the relative spacing of 4/3 for each three desired angles (0°, 15°and 30°) can reduce the mean and fluctuation of pressure, drag and lift coefficients around circular piers. Among tested configurations of the Collar-rings, Collar-rings with the relative spacing of 4/3 and angle of 15°are the best configuration to reduce the flow forces (mean pressure 5%, pressure fluctuation 24%, mean drag 2%, drag fluctuation 55%, fluctuation of lift 19%) around the simulated circular pier. Nevertheless, the helical cable increases flow forces (mean pressure 12%, pressure fluctuation 34%, mean drag 22%, drag fluctuation 110%, fluctuation of lift 30%). In addition to the flow forces and scour control around the circular piers, this tool can be readily and economically installed on the existing circular piers.

A pressure safety valve (PSV) is widely used to open and relieve excess pressure from a pressure vessel/system. The rapid opening and reliable reclosing of a PSV are of great importance and are strongly determined by the coupling effect of the compressed spring and the fluid flow through the chamber region, which is mainly determined by the shape and the size of the disc and adjusting ring. In this paper, a multi-objective design optimization of a PSV is presented to trade-off the rapid opening and the reliable reclosing. The opening and reclosing operation is firstly estimated by comparing the spring force and the fluid forces, respectively, where flow force is obtained by using three-dimensional (3-D) steady CFD simulation. Then, radial basis function (RBF) models are developed to approximate the two objective functions. A multi-objective optimization algorithm is then utilized to search the optimal design. Additionally, a global sensitivity analysis (GSA) is carried out to identify the most important variables for the optimal design. The results show the influence of design variables on the opening and reclosing of the PSV, and give the optimal structure with desirable function. The analysis and optimization method used also shows a great potential to assist engineers in the preliminary design of PSVs, especially when the physical experiments are difficult to implement.

The proposed microstructural model of the functional-mechanical behavior of shape memory alloys (SMA) is aimed to describe reversible phase deformation, microplastic deformation due to accommodation of martensite and evolution of deformation defects. The internal variables of the model are volume fractions of the Bain's variants of martensite and measures of microplastic deformation associated with these variants. The proposed microplastic flow rule accounts for kinematic and isotropic hardening. The microplastic flow force and the back force characterizing the two modes of hardening are related to the densities of reversible and irreversible deformation defects. For the variation of the defect densities a special evolution equation is formulated. Model verification is carried out through simulation of the reversible and irreversible strain evolution under thermocycling across the interval of the phase transformations. It is shown that the model can describe a rather big irreversible strain in the first thermocycle and its fast decrease with the number of cycles.

This paper focuses on analyzing the characteristic of the flow forces acting on a large flowrate directional valve (1200L/min). The flow area of the notches on the spool is calculated and the mathematic model of the spool is presented. The change rule of the total steady flow force is obtained through numerical simulation. The nonlinear response of the spool valve is explained reasonably and the input forces needed to make this valve closing reliability are given out respectively. The results show that the total flow force promotes the spool movement at the beginning but suppresses it after the spool displacement reaches a certain value. Furthermore, the vibration is caused by the dynamic force balance acting on the spool, leading to the large input force to make sure the relative ports closed. It is proposed that each pair of ports of the large flowrate directional control valve should be designed to the same structure to weaken these problems.

Fenestrated endovascular aneurysm repair (f-EVAR) stent grafts offer an alternative treatment for conventional open heart surgery for patients with juxsta-renal Abdominal Aortic Aneurysms (AAA) that are unsuitable for the common infrarenal endovascular aneurysms repair (EVAR) procedure. The f-EVAR endograft includes branched stent grafts fixed to the aortic endograft main body via designated strengthened fenestrations. Repetitive stresses activated upon the endograft by the pulsatile flow might cause detachment or fracture of branching. Thus, investigation of the flow forces and stresses on the graft may help minimize complications and improve the endograft design. The present work investigates the flow and stress fields of the fenestrated endograft configuration using a fluid structure interaction (FSI) model in order to evaluate risks for graft fracture or detachments. The results show that the f-EVAR dramatically improves the aortic and iliac flow and that elevated cyclic stresses are found at the graft’s bifurcation and branches’ connections.

Recently,the band width of servo systems is required strictly to be broaden, consequently the fast response of spool valves which play important roles in the systems is also strongly required. In a spool valve, flow force is applied to the spool in its axial direction by the fluid, because of the change in the momentum of the fluid flowing through the valve chamber in that direction by the spool. This axial flow force, generally, tends to increase in high frequency region. There have been few published papers showing the experimental results of this force in frequency domain. In this research, axial flow forces are being measured under various conditions.