Numerical coupling of fluid and structure in cardiac flow and devices

Numerical simulations are a powerful tool in investigation of flow and structure dynamics in biological systems and in the design of biomedical devices. Time-dependent fluid-structure interaction (FSI) problems in biological systems are often characterized by a periodic nature and relatively low Reynolds number. In order to solve the dynamics of the fluid and structure of coupled systems, different approaches may be used. Several parameters such as geometrical complexity, degree of displacement, convergence to steady periodicity, and the system stability may determine the coupling method. In the talk, four numerical studies of biological and implanted systems will be presented, each with a different FSI approach. The first study is of flow through mechanical heart valves, using finite-volume (FV) fluid solver coupled with an external structural solver using a weak coupling scheme for large displacements. The second study is of flow inside a pulsatile ventricular assist device with FV fluid solver coupled with finite-element (FE) structure solver using a strong staggered coupling assuming small displacements. The third study is of flow through vulnerable plaque in the coronary arteries, with FE solvers for both the fluid and structure domains, using a fully-coupled iterative scheme assuming small displacements. The fourth simulation is of an impedance pump using a direct FE coupling method for large displacements. In addition to the methodology, the applicative design and hemodynamic aspects of the cases will be discussed, including washout properties and risk for thrombosis. The results obtained from the studies will be compared to experimental analyses

Computational studies of resonance wave pumping in compliant tubes

The valveless impedance pump is a simple design that allows the producion or amplification of a flow without the requirement for valves or impellers. It is based on fluid-filled flexible tubing, connected to tubing of different impedances. Pumping is achieved by a periodic excitation at an off-centre position relative to the tube ends. This paper presents a comprehensive study of the fluid and structural dynamics in an impedance pump model using numerical simulations. An axisymmetric finite-element model of both the fluid and solid domains is used with direct coupling at the interface. By examining a wide range of parameters, the pump's resonance nature is described and the concept of resonance wave pumping is discussed. The main driving mechanism of the flow in the tube is the reflection of waves at the tube boundary and the wave dynamics in the passive tube. This concept is supported by three different analyses: (i) time-dependent pressure and flow wave dynamics along the tube, (ii) calculations of pressure–flow loop areas along the passive tube for a description of energy conversion, and (iii) an integral description of total work done by the pump on the fluid. It is shown that at some frequencies, the energy given to the system by the excitation is converted by the elastic tube to kinetic energy at the tube outlet, resulting in an efficient pumping mechanism and thus significantly higher flow rate. It is also shown that pumping can be achieved with any impedance mismatch at one boundary and that the outlet configuration does not necessarily need to be a tube

Experimental and Numerical Study of the Flow Dynamics in Treatment Approaches for Aortic Arch Aneurysms

Aortic arch aneurysm is a complex aortic pathology which affects one or more aortic arch vessels. In this chapter, we explore the hemodynamic behavior of the aortic arch in aneurysmatic and treated cases with three currently available treatment approaches: surgery graft, hybrid stent‐graft and chimney stent‐graft. The analysis included time‐dependent experimental and numerical models of aneurysmatic arch and of the surgery, hybrid and chimney endovascular techniques. Dimensions of the models are based on typical anatomy, and boundary conditions are based on typical physiological flow. Flexible and transparent experimental models were used on a mock circulation in vitro experimental system to allow both visualization and time‐dependent flow and pressure measurements. The simulations used computational fluid dynamics (CFD) methods to delineate the time‐dependent flow dynamics in the four geometric models. Results of velocity vectors, flow patterns, pressure and wall shear stress distributions are presented. Both the numerical and experimental results agree on the poor hemodynamics of the aortic arch aneurysm and present the hemodynamic advantages of the surgery technique, implying the possible advantage of fenestrated stent‐graft for the aortic arch. Out of the two minimally invasive procedures, the hybrid procedure clearly exhibits better hemodynamic performances. The chimney graft technique is based on off‐the‐shelf devices; thus, it is low in cost and requires less pre‐operation preparations. However, it is associated with higher risks for complications, such as endoleaks and stroke. This chapter may give some insight into the hemodynamic characteristics of the different procedures

STRATEGI PEMASARAN PRODUK SAMPINGAN AYAM PADA UD. GEMILANG SEJAHTERA

Abstract The purpose of this study was to determine the marketing strategy of chicken byproducts at UD. Gemilang Sejahtera Jombang. This type of research is quantitative descriptive, which is to determine the company's owner's strategy in marketing chicken byproducts. The method used is unstructured interview techniques and documentation. Interviews were conducted to obtain information in the form of company activities related to sales development. While documentation is done to obtain quantitative data. From quantitative data is then processed using the basic accounting formula. The formula is used to find the number of sales, net income and inventory turnover ratios. The result of this research is that the strategy used by the company owners is to go directly to the large markets in the region. So customers can immediately find out the quality of the product from UD. Gemilang Sejahtera. And company owners use postpaid strategies that can make potential customers increasingly interested in UD products. Gemilang Sejahtera. For the sale of UD. Gemilang Sejahtera was able to sell products on January 27 for 84,062,500. With these sales the company got a profit of 26,651,500. whereas for the analysis of inventory turnover ratio on January 26, it was 11.48x and on January 27 it was 17.35x. The conclusion of the inventory turnover is inventory turnover on January 27, 2019 has increased and has a positive impact on company activity. This indicates that the company does not need to pay excessive product maintenance costs compared to the previous day

The Effect of Mechanical Circulatory Support on Blood Flow in the Ascending Aorta: A Combined Experimental and Computational Study

Percutaneous mechanical circulatory support (MCS) devices are designed for short-term treatment in cases of acute decompensated heart failure as a bridge to transplant or recovery. Some of the known complications of MCS treatments are related to their hemodynamics in the aorta. The current study investigates the effect of MCS on the aortic flow. The study uses combined experimental and numerical methods to delineate complex flow structures. Particle image velocimetry (PIV) is used to capture the vortical and turbulent flow characteristics in a glass model of the human aorta. Computational fluid dynamics (CFD) analyses are used to complete the 3D flow in the aorta. Three specific MCS configurations are examined: a suction pump with a counterclockwise (CCW) rotating impeller, a suction pump with a clockwise (CW) rotating impeller, and a discharge pump with a straight jet. These models were examined under varying flow rates (1–2.5 L/min). The results show that the pump configuration strongly influences the flow in the thoracic aorta. The rotating impeller of the suction pump induces a dominant swirling flow in the aorta. The swirling flow distributes the incoming jet and reduces the turbulent intensity near the aortic valve and in the aorta. In addition, at high flow rates, the local vortices formed near the pump are washed downstream toward the aortic arch. Specifically, an MCS device with a CCW rotating impeller induces a non-physiological CCW helical flow in the descending aorta (which is opposite to the natural helical flow), while CW swirl combines better with the natural helical flow

Early Gapping and Platoon Merging Strategies for Autonomous Vehicles using Local Controllers

Autonomous vehicle merging schemes require a central control or a complex communication system between the vehicles. We suggest an alternative local traffic control method based on distance sensors and roadside units which provides the vehicles with the desired gap profile without the need for vehicle-to-vehicle communication. The gap profile aims to open gaps between the vehicles before an upcoming junction. To explore the profiles’ governing parameters, 140,000 simulation cases with varying conditions were run. Results show that, for a speed limit of 100 km/h and high inlet density (of 1–1.5 s between vehicles), the best strategy with respect to flow and merging percentage (of ~90%) is to use early gapping and platoon merging using linear profiles with long stabilization sections (>0.6 km). Moreover, the gapping process should start when the vehicle ahead attains a velocity of 75 km/h. In this way, fluent traffic can be sustained without perpetuating upstream traffic jams

Water Recuperation from Hydrogen Fuel Cell during Aerial Mission

A water recuperation system (WRS) from an open-cathode proton exchange membrane fuel cell (PEMFC) is designed to increase the energy density of hydrogen production by hydrolysis of metal hydrides. WRS may significantly reduce the water weight in the carried fuel. The design is based on circulating the humid air through the PEMFC stack in a closed dome. To ensure oxygen supply to the PEMFC, the WRS has a ventilation inlet and an exhaust outlet. The required conditions for ventilation flow are developed theoretically and examined experimentally in a WRS prototype with a commercial PEMFC at 20–100 W. The experimental system includeds a closed dome, an edge cooling system for the PEMFC, a controllable ventilation air inlet, and an exhaust port. The humid exhaust air was cooled down to the ambient temperature to improve vapor condensation. Results show high efficiency (80% recuperated water from prediction), with a potential to achieve gravimetric hydrogen storage capacity (GHSC) of >6 wt% at an ambient temperature of 27 °C. The described principle may be applied for small fixed-wing drones where the cold ambient air may be utilized both for providing oxygen supply and for thermal management of the PEMFC and the humid exhaust, thus allowing higher GHSC

Biomechanical Aspects of Closing Approaches in Postcarotid Endarterectomy

The carotid bifurcation tends to develop atherosclerotic stenoses which might interfere with cerebral blood supply. In cases of arterial blockage, the common clinical solution is to remove the plaque via carotid endarterectomy (CEA) surgery. Artery closure after surgery using primary closures along the cutting edge might lead to artery narrowing and restrict blood flow. An alternative approach is patch angioplasty which takes longer time and leads to more during-surgery complications. The present study uses numerical methods with fluid-structure interaction (FSI) to explore and compare the two solutions in terms of hemodynamics and stress and strain fields developed in the artery wall

A novel micro-reactor for hydrogen production from solid NaBH4 hydrolysis in a dual-cycle methodology

Hydrogen-based Fuel Cells (FCs) hold significant potential as energy conversion technologies. In a previous study, we presented a pump-based hydrogen generator (PHG) that utilizes a catalytic reaction between sodium borohydride (NaBH4) powder and water. The pump circulates the water solution through the powder chamber in a closed-loop reaction. The PHG demonstrated clear advantages over alternative hydrogen sources in terms of both safety and energy density. However, as operating time increases, the solution in the closed-loop PHG becomes saturated, causing the reaction rate to decline. This limitation can be overcome in cases where an external water source is available, such as marine vehicles, drones equipped with water recovery systems from their fuel cells, or systems located near pipelines. In such scenarios, introducing freshwater feeding and product emission offers intriguing possibilities for significantly enhancing the fuel's energy density and extending its effective operation time.Our current research introduces an innovative concept: a dual-cycle generator (DCG) that effectively overcomes the issue of solution saturation over time. It achieves this by combining solution circulation with freshwater feeding and product emission. Our study employed a DCG prototype to examine various operating modes and to demonstrate the effectiveness of this approach. The DCG achieved a calculated energy density for the fuel of 3868 Wh/kg, with 93% H2 extraction yield from the powder. Our findings reveal substantial improvements in terms of extended operation duration (81%), increased hydrogen flow rate (36%), enhanced energy density (33%), and improved H2 yield extraction from the powder (39%). This methodology holds promise for mobile applications or off-grid systems situated in proximity to a water source

Early Gapping and Platoon Merging Strategies for Autonomous Vehicles using Local Controllers

Autonomous vehicle merging schemes require a central control or a complex communication system between the vehicles. We suggest an alternative local traffic control method based on distance sensors and roadside units which provides the vehicles with the desired gap profile without the need for vehicle-to-vehicle communication. The gap profile aims to open gaps between the vehicles before an upcoming junction. To explore the profiles’ governing parameters, 140,000 simulation cases with varying conditions were run. Results show that, for a speed limit of 100 km/h and high inlet density (of 1–1.5 s between vehicles), the best strategy with respect to flow and merging percentage (of ~90%) is to use early gapping and platoon merging using linear profiles with long stabilization sections (>0.6 km). Moreover, the gapping process should start when the vehicle ahead attains a velocity of 75 km/h. In this way, fluent traffic can be sustained without perpetuating upstream traffic jams