let angleV = 0;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  fill(255, 255, 0);

  noStroke();

  let r = map(sin(angle), -1, 1, 0, width);

  circle(width/2, height/2, r);

  // inner circle

  fill(0, 155, 155);

  circle(width/2, height/2, r/2);

  angle = angle + angleV;

  angleV = angleV + 0.00001;

}