Ureteral peristalsis can be considered as a series of waves on the ureteral wall, which transfers the urine along the ureter toward the bladder. The stones that form in the kidney and migrate to the ureter can create a substantial health problem due to the pain caused by interaction of the ureteral walls and stones during the peristaltic motion. Three-dimensional (3D) computational fluid dynamics (CFD) simulations were carried out using the commercial code ansys fluent to solve for the peristaltic movement of the ureter, with and without stones. The effect of stone size was considered through the investigation of varying obstructions of 5%, 15%, and 35% for fixed spherical stone shape. Also, an understanding of the effect of stone shape was obtained through separate CFD calculations of the peristaltic ureter with three different types of stones, a sphere, a cube, and a star, all at a fixed obstruction percentage of 15%. Velocity vectors, mass flow rates, pressure gradients, and wall shear stresses were analyzed along one bolus of urine during peristalsis of the ureteral wall to study the various effects. It was found that the increase in obstruction increased the backflow, pressure gradients, and wall shear stresses proximal to the stone. On the other hand, with regard to the stone shape study, while the cube-shaped stones resulted in the largest backflow, the star-shaped stone showed highest pressure gradient magnitudes. Interestingly, the change in stone shape did not have a significant effect on the wall shear stress at the obstruction level studied here.

Tire noise reduction is an important aspect of overall vehicle noise reduction. However, due to the complex nature of tire noise generation and correlation between various generation mechanisms, it is difficult to isolate, predict, and control tire noise. Air-related noise generation mechanisms in tires are tough to predict experimentally, resulting in the need for an accurate numerical model. Computational fluid dynamics (CFDs) is used here to propose a numerical tool capable of predicting air-pumping noise generation. Slot deformations are prescribed by custom functions instead of using structural solvers and the rotation of tire is represented by using mesh motion and deformation techniques. Near-field and far-field acoustic characteristics are predicted using fluid dynamic equations and acoustic models. The use of various spectral analysis tools show that the proposed model is capable of predicting the high frequency air-pumping noise while also predicting other air-related mechanisms such as pipe resonance, Helmholtz resonance, and rotational turbulence. This study is intended to provide an understanding of the various air-related noise generation mechanisms so that numerical models can be used in the future to predict tire acoustics economically and effectively.

Urine is transported from the kidney to the urinary bladder through the ureter by peristalsis and pressure gradients. The contractile force acting on the ureter wall has drawn considerable interest in the field of biomechanics. Backflow of urine from bladder to the kidney can occur due to failure of the ureterovesical (ureteral-bladder) junction or blockage in the ureter passage because of recurrent urinary tract infection and also due to formation of stone in kidney. To understand the nature of the flow as well as its effect on the ureter wall, two-way fluid-solid interaction (FSI) modeling of the ureter peristaltic flow at different pressure is required. A transient 2D axisymmetric numerical calculation of ureteral wall peristalsis and urine flow is performed with a fully-coupled monolithic solver using an arbitrary Lagrangian-Eulerian (ALE) method. The ureter is assumed to be a circular tube with successive compression waves traveling downstream. The incompressible Navier-Stokes equations are solved to calculate the laminar flow of urine. The ureter wall is modeled as a non-linear hyper-elastic, nearly incompressible material, by curve fitting the biaxial test data of a human ureter, obtained from literature. Displacement due to peristalsis on ureteral wall is created with a compressive force having a Gaussian bell-curve variation along the length of the ureter, and a certain wavelength specified according to the data found from previous studies. It is observed that, as the compression wave travels from the abdominal part of the ureter towards to the pelvis, it is more likely for urine reflux to occur due to the failure of the ureteropelvic junction rather than the ureterovesical junction.

Urine moves from the kidney to the bladder through the ureter. A series of compression waves facilitates this transport. Due to the highly concentrated mineral deposits in urine, stones are formed in the kidney and travel down through the urinary tract. While passing, a larger stone can get stuck and cause severe damage to ureter wall. Also, stones in the ureter obstructing the urine flow can cause pain and backflow of urine which in turn might require surgical intervention. The current study develops a 2D axisymmetric numerical model to gain an understanding of the ureter obstruction and its effects on the flow, which are critical in assessing the different treatment options. Transient computational analysis involving a two-way fully coupled fluid-structure interaction with the arbitrary Lagrangian-Eulerian method between the ureteral wall and urine flow is conducted with an obstruction in the ureter. The ureter wall is modeled as an anisotropic hyperelastic material, data of which, is based on biaxial tests on human ureter from previous literature, while the incompressible Navier-Stokes equations are solved to calculate urine flow. A finite element-based monolithic solver is used for the simulations here. The obstruction is placed in the fluid domain as a circular stone at the proximal part of the ureter. One of the objectives of this study is to quantify the effect of the ureteral obstruction. A sharp jump in pressure gradient and wall shear stress, as well as retrograde urine flow, is observed as a result of the obstruction.

The complex nature of the tire/road noise generation process makes it difficult to isolate and study each mechanism individually. This paper presents an experimental and numerical investigation of air-borne tire noise generation mechanisms for a realistic tire. Experimentally, a single slot is cut into the tire and the noise data are measured and studied. Air-borne noise is isolated by filling the slot with foam and comparing the resulting frequency spectra. Numerically, a previously developed computational fluid dynamics tire noise prediction model is employed to predict the air-borne noise for the same tire, under similar operating conditions. A direct comparison between the experimental and computational results is also presented in terms of pressure time traces and spectral characteristics. Comparisons indicate that the computational model is capable of predicting the noise generated by the air pockets in the tire. While providing a deeper understanding of the causes of air-borne noise, this paper also aims to demonstrate the use of a computational tool that can be used to obtain a reasonably accurate prediction of air-borne tire noise.