New Trends in Computational Solid Mechanics

Wednesday, 10/23/2002

Class ProgressVisualization: abstract concept (stress,2D, 3D), mechanical field

Atomistic Simulations:Stochastic simulations: random walk, Brownian movementMonte Carlo method (MC) EnsembleMolecular Dynamics (MD) Trajectory

Continuum Simulation:Material Point Method (MPM)

Multiscale simulationAdaptive Mesh Refinement/Coarsening; Renormalization

Finite Element Method (FEM);

Computational Solid Mechanics

Bio/IT/Nano

BiomedicalEngineering

InformationTechnology

Nanotechnology

Stress, strain, constitutive modelDefects, dislocationFractureSurface roughness

FEM, MPMMD, MC

Bio/IT/Nano

HeartThe heart is a muscular organ located just to the left of the breast bone (sternum). It is about the size of your fist, and this amazing muscle pumps 4300 gallons of blood a day. The heart has four chambers:

Atria. The top two chambers that receive blood from the body or lungs. Ventricles. The bottom two chambers. The right ventricle pumps blood to the lungs to pick up oxygen, The left ventricle pumps blood to the rest of the body and is the strongest chamber. Valves. There are four valves in the heart that help to direct blood flow.

Mechanical Heart Valve

• Structurally designed to last a lifetime

Most are constructed of pyrolytic carbon, a highly durable and biocompatible material

Excellent blood flow characteristics

Patient requires long-term anticoagulation therapy ("blood thinners", this medication actually slows the clotting process of blood)

Patient may hear the valve leaflets open and

close

Biocompatibility

Mechanical valves are recognized for their exceptional durability, but require life-long anticoagulation medication.

Stress distribution in Mechanical Heart Valve

Harsh environmentRoughness evolution

Platelet Coagulation

Platelets are the smallest corpuscular components of human blood (diameter 2-4µm) - the physiological number varies from 150,000 to 300,000/mm3 blood.

When reaching a damaged vessel, platelets release a chemical which sets up a change of events leading to the production of long, strand like threads called fibrin. Many fibrin threads join together to plug a vessel.

Flow Field Near Rough Surface

Turbulence

Blood clot

As the blood flows turbulently over the rough surface of the artificial heart, the blood begin falling on itself and clotting.

Shock Wave

Extracorporeal Shock Wave Lithotripsy (ESWL)

A shocking blow for kidney stones

Extracorporeal shock wave lithotripsy (ESWL) is a medical procedure used to break kidney stones into fragments small enough for natural elimination.

Kidney Stone

Some of the smaller kidney stones that are less than 5mm in diameter pass on along during urination. However, a larger stone that does not pass on out can block the urinary tract. If left untreated, the blockage may hamper the normal function of the kidney and may cause complete shutdown of the affected kidney in a few days.

Extracorporeal Shock Wave Lithotripsy

high-frequency sound waves to crush kidney stones into granules small enough to be passed in the urine

Noninvasive

Mechanism of Stone Fails

Evidence that the shock wave may lead to permanent damage to healthy tissue in the kidney.

Spallation

Spallation refers to large tensile stress that leading to stone failure probably by fatigue.

Cavitation

Cavitation occurs when the tensile stress of the shock wave is strong enough to make fluid rip apart. The nature of the shock wave in lithotripsy leads to a dramatic growth of the bubble followed by a subsequently violent collapse. The collapse leads to an probably surface damaging microjets.

Mechanical interaction of shock wave with renal calculi

After the application of 40 shock waves a stone phantom is fractured into two pieces. Here the fracture plane is oriented perpendicular to the wave propagation and exhibits a circular rings. The diameter of the stone phantom (magnesium oxide) is 15mm."