Circumferential Cross Section Research Articles

A fluid-structure coupled transient mixed lubrication model for piston ring lubrication property analysis with CMFF method

The bore's circumferential cross-section is not always a perfect circle, due to manufacturing errors, installation, and the influence of high-temperature and high-pressure gas, especially for a cylinder liner of the two-stroke marine diesel engine. This non-axisymmetric feature significantly impacts the lubrication properties of the piston ring and cylinder liner tribo-pair. To study the tribology and lubrication properties of the tribo-pair, a fluid-structure coupled transient mixed lubrication model is developed, which incorporates the piston ring curved beam model and mixed lubrication model. The key challenge lies in integrating the interface contact issue between the piston ring and bore with the structural deformation, requiring a multi-scale modeling strategy. To address this challenge, a method of coupling mesh between the finite difference method and the finite element method (CMFF) is proposed. The approach achieves the requirement for a fine mesh for the interface contact solution while maintaining the accuracy of the curved beam model for the structural response of the piston ring. Based on the model, the lubrication performance and deformation behavior of the piston ring in an elliptical bore are comprehensively analyzed. The results are compared with those of the rigid ring model to explore the overall differences. Results reveal that the current model predicts the friction is mostly caused by asperity contact between solids at the top dead center, whereas the rigid ring model predicts viscous shearing of the lubricant. The discrepancy is mainly due to the reduction of the oil film thickness between the piston ring and the cylinder liner following the consideration of ring deformation. Moreover, the minimum clearance exhibited at the piston ring end gap demonstrates the thorough consideration of the local and global lubrication performance of piston rings in the proposed model. This is significant for the resolution of local friction and wear problems of piston rings in engineering applications. Based on the work, a new framework is established for the study of the coupled performance of piston ring dynamics and tribology.

Three-dimensional numerical study of the combined stroke swimmer

A three-dimensional (3D) numerical simulation was performed using a combined stroke swimmer (deformable sphere) in an incompressible fluid of an infinite domain. The time-dependent deformation of the swimmer surface was assumed independent of the circumferential cross section in the flow direction of the swimmer. The 3D numerical simulation is an extension of our previous study that considered an axisymmetric numerical simulation. In particular, different fluid viscosities were considered for the same stroke of the swimmer. The effect of the swimmer inertia was studied by gradually decreasing the fluid viscosity. When the fluid viscosity decreased, the mean velocity of the swimmer changed its direction between Re = 0.00189 and Re = 0.0103. There is a transition between Re = 0.0103 and Re = 9.90 from the axisymmetric to three-dimensional flow that exhibits planar symmetry.

A novel resistivity measurement method for a homogeneous cylinder shape based on the vdP configuration

The electrical resistivity method for a cylinder shape is an essential method for reflecting physical properties. However, the use of a nondestructive resistivity method with the circumferential cross-section arrangement for working components remains challenging. This paper provides a simple novel resistivity method for a cylinder shape based on the van der Pauw configuration, with four electrodes placed near the middle cross-section layer of shape. First, the theoretical solution formulae for the electrostatic potential function in the cylindrical coordinate system are derived. Then, the effect of the electrode and shape size is analysed. The results show that the electrode height is less than 1% of the cylinder height and the radian angle is less than 10°, where the electrode size effect on the correction factor (CF) can be ignored, and CF rarely depends on the cylinder shape. Finally, a prototype is designed, and the proposed method is verified in laboratory tests using geomaterials. The performance of the proposed method for fine soil at high moisture contents is found to be better than that at low moisture contents.

Simultaneous Temperature and Strain Sensing With Hybrid Resonator of Fiber Bragg Grating and Whispering Gallery Resonator

This study proposes a hybrid resonance structure of fiber Bragg grating (FBG) and whispering gallery resonator (WGR) in a single optical fiber to simultaneously measure temperature and strain. Bragg grating written in the fiber itself provides the first sensing signal in conjunction with the second signal produced by a whispering gallery mode (WGM) propagating along the circumferential cross-section of the FBG. Under changes in temperature and strain, variation in the refractive index or diameter (or length) of the fiber occurs, which also shifts the resonance frequency of each structure. Taking advantage of the difference in thermo- and strain-optic coefficients of FBG and WGR, such an integration of two different sensing techniques at an identical spot thus provides a $2\,\,{\times }\,\,2$ matrix to the characteristic equation of temperature–strain sensing that realizes a cross-sensitivity-free sensing with high accuracy. An uncertainty of ±1.91 °C and $\pm 36.2~{\mu \varepsilon }$ was achieved in the experimental verification.

Numerical Computation of Circumferential Waves in Cylindrical Curved Waveguides

We present a complex field general variational statement to study the waves propagating in the circumferential directions of cylindrical curved waveguides. A semi-analytical technique that has been applied on straight waveguides in the literature is reformulated to adapt to the circumferential directions and used for constructing the trial wavefunction in complex field. The method requires the waveguide to be analyzed to be geometrically and physically uniform along its circumferential axis; however, its circumferential cross-section can be arbitrarily complex. The formulation is verified using various examples, which were examined previously by other numerical or analytical solutions. Different cases were studied and comparisons with those published are also performed show the utility and advantages of present method.

104 Optimization of handheld Wand to Activate a Shape Memory Penile Prosthesis

We previously described a novel shape memory alloy penile prosthesis that could be activated using an external wand via magnetic induction, thus obviating the need for internal hydraulics, pumps and reservoirs found with inflatable penile prostheses. Optimally, this wand would be portable, battery-powered, quick and easy to use. Herein, we characterize the parameters required to optimize the external wand for touchless activation of this novel shape memory penile prosthesis. Using a commercially purchased external inductor (Miniductor II) with 1000Watt of maximum power, we measured the time of activation of the SMA prosthesis. We compared the time of activation of the existing design (fig 1b) vs an alternate design with circumferential cross section (fig 1c). Activation is reached when the Nitinol component of the prosthesis reaches the full activation temperature of 42C. The time of activation and temperatures were measured with the use of thermocouples on the spine of the prosthesis. Additional parameters examined included distance, angle and shape of the coils (ring or flat).

The reflection of guided waves from simple dents in pipes

Guided elastic waves have been anticipated as a rapid screening technique for pipe inspection. Dents occurring in pipes are a severe problem which may lead to the possibility of pipe failure. A study of the reflection characteristics of guided waves from dents of varying geometrical profile in pipes is investigated through experiments. Dented region is represented by a series of circumferential cross-sections and its geometric parameters are described by axial length and the maximum and minimum outer diameters. Both single and double sided dents are mechanically simulated in hollow aluminum pipes and then experimentally tested by exciting the longitudinal L(0,2) mode. A quantitative parameter, so-called deformation rate relating to the maximum and minimum outer diameters of the dents is defined to evaluate the effect of the extent of the deformation on the reflection. For both types of dents, it is shown that the reflection coefficients of the L(0,2) mode are all approximately a linear function of their respective deformation rates. Mode conversion occurs at the dents and reflections of the F(1,3) mode are identified. The results show that the amplitude of the reflected F(1,3) mode is generally higher when the dent has stronger non-axisymmetric features.

Prediction of Fully Plastic Collapse Stresses for Pipes With Two Circumferential Flaws

Fully plastic collapse stress for a single circumferential flaw on a pipe is evaluated by the limit load criteria in accordance with the JSME Code S NA-1-2004 and the ASME Code Section XI. However, multiple flaws such as stress corrosion cracking are frequently detected in the same circumferential cross section in a pipe. If the distance between adjacent flaws is short, the two flaws are combined as a single flaw in compliance with combination rules. If the two flaws separated by a large distance, it is not required to combine two flaws. However, there is no evaluation method for two separated flaws in a pipe in the JSME and ASME Codes. Plastic collapse stresses for pipes with two symmetrical circumferential flaws based on net-stress approach had been proposed by one of the authors. Bending tests were performed on Type 304 stainless steel pipes with two symmetrical circumferential flaws. Consequently, it was shown that the proposed method can predict well the plastic collapse stresses for pipes with two flaws. In addition, it is also shown that this method is appropriate to use in fitness-for-service procedures, and higher plastic collapse stresses are expected, compared with current prediction methods for pipes with two flaws.

A Generalized Method for Calculating Strain for a Circular Cross-Section Specimen Subject to Axial Force and Bending

Abstract A theoretical analysis was performed with multiple-point measurements of the bending strain distribution along the circumferential cross section of a cylindrical alignment cell. A simple and general equation for representing the maximum bending strain was developed to unify the expression of bending strain. Also, both the general equation for the net bending contributions, due, respectively, to the testing machine and the specimen and the equation for the general orientation angle after separation of the testing machine component and the specimen component are provided.

Stress Concentration Solution for a 2D Dent in an Internally Pressurized Cylinder

Dent imperfections in internally pressurized shells have a stress concentration effect. In cylindrical shells under internal pressure, such as pipelines, stress concentrations associated with dent imperfections can degrade in-service performance. A new semianalytical solution is developed for the stress concentration distribution present along the two-dimensional circumferential cross section of a cylinder under internal pressure containing a local dent-like imperfection. An equivalent load approach is used. Results are compared against finite-element results. For practical application, the stress concentration factor (SCF) present at the outer surface of the dent center is derived. Parametric studies with this expression show that long dent stress concentrations are primarily influenced by the dent depth-pipe thickness and the dent depth-pipe diameter ratios. Example cases show that SCF values between 10.0 and 20.0 are possible and that even shallow dent SCFs can be above 2.0.

A Closed-form Solution to Finite Bending of a Compressible Elastic-perfectly Plastic Rectangular Block

The self-consistent Eulerian rate-type elastoplastic model based on the logarithmic rate is used to study finite bending of a compressible elastic-perfectly plastic rectangular block. It is found that an explicit closed-form solution for this typical inhomogeneous finite deformation , mode may be available in a general case of compressible deformation with a stretch normal to the bending plane, where the maximum circumferential stretch at the outer surface serves as an Independent parameter. Expressions are given for the bending angle, the bending moment, the the outer and the inner radii, and the radii of the two moving elastic-plastic interfaces, etc. The exact stress distribution on any circumferential cross-section of the deformed block is accordingly determined.

Experimental Study of the Swirling Flow in the Volute of a Centrifugal Pump

Detailed three-dimensional velocity distributions, corresponding to design and off-design operation, were measured in two different circumferential cross sections of a volute by means of LDV. It is shown that the swirl has a forced vortex type velocity distribution and that the location of the swirl center changes with mass flow. The throughflow velocity distribution is primarily defined by the conservation of angular momentum. A strong interaction between the throughflow and swirl velocity is observed. Flow visualization in the tongue region reveals a reversal of the velocity at the volute inlet with increasing mass flow. The pressure drop between volute outlet and inlet at low mass flow pushes extra fluid through the tongue gap and increases the mass flow in the volute. The abrupt pressure rise at high mass flow results in local return flow perturbing the flow in the outlet pipe.

Thermal and hydraulic tests of test sections in the helium engineering demonstration loop

The helium engineering demonstration loop (HENDEL) has been constructed and operated to test the large-scale components of the high temperature engineering test reactor (HTTR) under simulated reactor operating conditions. The fuel stack test section (T 1) of HENDEL simulates the fuel stack of the HTTR core and is used to investigate thermal and hydraulic performance. Hot tests with 1000°C helium gas have been conducted using simulated fuel rods having uniform, exponential and cosine axial heat flux distributions. The test results agreed with previously proposed correlations, although the simulated fuel rods had various heat flux distributions and high heat flux rates. The in-core structure test section (T 2) also was installed in the HENDEL to verify the performance of the core bottom structure of the HTTR. The tests show that good performance was obtained. Examination of the thermal mixing characteristics indicated that mixing started at the location where the hot helium gas flowed into the hot plenum and that complete mixing was achieved during the downward flow in the outlet hot gas duct. The seal performance testing indicated no change of the leakage flow rate after 4000 hours of operation. The temperature of the metal portion of the structure was below 500°C and uniform around circumferential cross-sections due to the good performance of the thermal insulation blocks.

The effect of multiple circumferential through-wall cracks in the same cross-section on the fracture instability of a stainless steel pipe subject to bending deformation

This paper examines the fracture instability of a pipe, fabricated from a ductile material such as 304 stainless steel, in which a circumferential cross-section contains two symmetrically situated through-wall cracks, the pipe being subject to bending deformation. The theoretical analysis, which is based on the tearing modulus procedure, demonstrates the extent to which a multiple-cracked pipe has a greater tendency towards instability than a pipe containing a single through-wall crack.

Small bowel allografts: Sequence of histologic changes in acute and chronic rejection

Using a rat model of accessory small bowel transplantation, the histologic sequence of both acute and chronic rejection in intestinal allograft rejection has been defined. Histologically, all allografts were normal for the first 5 postoperative days. Allografts with caval venous drainage were subject to acute rejection. By 6 to 7 days postoperatively, plasma cells and lymphocytes infiltrated the lamina propria of these grafts (phase I). By 8 to 9 days postoperatively, the cellular infiltration intensified and was associated with villous blunting and scattered epithelial sloughing (phase II). By the 10th day, complete mucosal destruction developed, with heavy transmural infiltration by lymphocytes, plasma cells, and polymorphonuclear leukocytes (phase III). This histologic end point of acute graft rejection was accompanied by death of the host. Grafts with portal venous drainage underwent a similar, although less rapid, sequence of histologic changes (phase 16 to 9 days, phase II 10 to 13 days, phase III 13 or more days) resulting in graft fibrosis and encapsulation. Some variability was seen among different areas of a given circumferential cross section taken from grafts in phases I and II. Studying circumferential cross sections allowed correct classification into the appropriate phases.

IRIS — Internal rotary inspection system

IRIS is a new ultrasonic system for inspecting air‐cooled heat exchangers. It employs the conventional pulse echo technique for measuring the wall thickness, but uses a novel method for displaying the measurements. All of the measurements made during a complete scan, around the circumference of the tube, are displayed on an oscilloscope screen to produce a stationary, rectilinear picture of the circumferential cross section. Missed and false measurements are easily recognised and can be compensated for by extrapolation of the valid measurements. The novel display allows wall thicknesses to be measured, virtually down to zero in ideal circumstances.