import java.awt.*; import java.awt.event.*; import java.applet.Applet; import java.awt.image.*; /** * Class NobleGas - calculates and displays movements of gas-atoms (kinetic gas theory) * created with BlueJ * * @author (Martin Lieberherr) * @version (29. April 2011) */ public class NobleGas extends Applet implements ActionListener, Runnable { // instance variables and attributes (all private) int nx = 800; // number of pixels in x-direction for picture int ny = 800; // number of pixels in y-direction for picture int n_atoms = 200; // number of atoms in simulation int max_n_atoms = 2000; // maximum number of atoms double temp = 300.0; // absolute temperature in Kelvin double e_min = (1.04e-2)*(1.6022e-19); // energy-minimum in Lennard-Jones potential in Joule (Argon gas) double r_min = 304.0e-12; // distance (m) for energy-minimum in Lennard-Jones potential (gaseous Argon) double r_atom = 71.0e-12; // radius of the atom (meter) (for collision and for display) (Argon) double kB = 1.381e-23; // Boltzmann-constant in J/K double m_atom = 39.95*(1.661e-27); // mass of the atoms (in kg) double v_thermal = Math.sqrt(kB*temp/m_atom); // thermal speed (in m/s, in one dimension!) double scale = 1.25e-11; // scale factor pixels*scale = real distances in meters double dt = 1.0e-15; // step size for numerical integration (seconds) boolean new_n_atoms = true; // true, if a new n_atom is entered boolean new_temp = true; // true, if a new temp is entered double x[] = new double[max_n_atoms]; // position of atoms in meters double y[] = new double[max_n_atoms]; double vx[] = new double[max_n_atoms]; // velocity of atoms in m/s double vy[] = new double[max_n_atoms]; double ax[] = new double[max_n_atoms]; // acceleration of atoms in m/s^2 double ay[] = new double[max_n_atoms]; double t_mean; // calculated mean temperature double e_pot; // calculated mean potential energy double r_near; // shortest distance bewteen any two atoms int n_paint; // number of time steps per frame displayed // attributes Label titleLabel; // holds a title and the author's name Label n_atomsLabel; // text "n_atoms: " TextField n_atomsField; // display / input n_atoms Label tempLabel; // text "T (K): " TextField tempField; // display/input temperature Label statusLine; // display messages / status Label diagnosticsLabel; // displays "Diagnostics:" Label meanTempLabel; // displays the mean temperature Label meanEpotLabel; // display the mean potential energy Label rNearLabel; // display the shortest distance between any two atoms Label stepsPerFrameLabel; // display the number of time-steps per frame in display Thread thread; // loop to numerically integrate the movement // buffered image for display of atoms BufferedImage BuffImage1 = new BufferedImage(nx, ny, BufferedImage.TYPE_INT_RGB); Graphics g1 = BuffImage1.createGraphics(); /** * Called by the browser or applet viewer to inform this Applet that it * has been loaded into the system. It is always called before the first * time that the start method is called. */ public void init() { setLayout(null); // for "hard" layout in pixels int xText = nx+20; // position of next element on window int yText = 30; // position of next element on window titleLabel = new Label("NobleGas (by Martin Lieberherr)"); titleLabel.setBounds(xText, yText, 260, 20);// setBounds(x_left, y_top, width, height) for display add(titleLabel); //added to ContentPane to the right of picture yText = yText+30; n_atomsLabel = new Label("n_atoms: "); n_atomsLabel.setBounds(xText, yText, 80, 20); // setBounds(x_left, y_top, width, height) for display add(n_atomsLabel); //added to ContentPane to the right of picture n_atomsField = new TextField(""+n_atoms); n_atomsField.setBounds(xText+80, yText, 180, 20); add(n_atomsField); n_atomsField.addActionListener(this); // ActionListener is called if "enter" is pressed in TextField yText = yText+30; tempLabel = new Label("T (K): "); tempLabel.setBounds(xText, yText, 80, 20); add(tempLabel); tempField = new TextField(""+temp); tempField.setBounds(xText+80, yText, 180, 20); add(tempField); tempField.addActionListener(this); yText = yText+40; statusLine = new Label("Status: running"); statusLine.setBounds(xText, yText, 260, 20); add(statusLine); yText = yText+60; diagnosticsLabel = new Label("Diagnostics:"); diagnosticsLabel.setBounds(xText, yText, 260, 20); add(diagnosticsLabel); yText = yText+30; meanTempLabel = new Label("mean temperature:"); meanTempLabel.setBounds(xText, yText, 260, 20); add(meanTempLabel); yText = yText+30; meanEpotLabel = new Label("mean Epot:"); meanEpotLabel.setBounds(xText, yText, 260, 20); add(meanEpotLabel); yText = yText+30; rNearLabel = new Label("nearest neighbor: "); rNearLabel.setBounds(xText, yText, 260, 20); add(rNearLabel); yText = yText+30; stepsPerFrameLabel = new Label("steps per frame: "); stepsPerFrameLabel.setBounds(xText, yText, 260, 20); add(stepsPerFrameLabel); thread = new Thread(this); // thread is a new thrad of this applet thread.start(); // start the thread } // end init () public void destroy() { thread = null; // set thread to zero if applet is stopped } /** update()-method for applet * (overridden to avoid flicker) * @param g the Grapics object for this applet */ public void update( Graphics g ) { //display buffered image with atoms g.drawImage( BuffImage1, 0, 0, null); } // end update() /** * Paint method for applet. * * @param g the Graphics object for this applet */ public void paint(Graphics g) { update( g ); } // end paint() /** * ActionListener Interface method. * Called when action events occur with registered components that * can fire action events. * @param ae the ActionEvent object created by the event */ public void actionPerformed(ActionEvent evt) { // if a value for n_atoms is entered if (evt.getSource() == n_atomsField) { try { n_atoms = (int) Double.parseDouble(n_atomsField.getText()); if ((n_atoms < 1) || (n_atoms > max_n_atoms)) { if (n_atoms < 1) { n_atoms = 1; n_atomsField.setText(""+n_atoms); statusLine.setText("n_atoms must be > 0!"); } if (n_atoms > max_n_atoms) { n_atoms = max_n_atoms; n_atomsField.setText(""+n_atoms); statusLine.setText("n_atoms must be <=" + max_n_atoms); } } else { n_atomsField.setText(""+n_atoms); statusLine.setText("Status: n_atoms changed to "+n_atoms); } new_n_atoms = true; } catch (NumberFormatException e) { statusLine.setText("n_atoms had wrong number format"); n_atomsField.setText(""+n_atoms); // System.exit(0); } repaint(); } // if a value for temp is entered if (evt.getSource() == tempField) { try { temp = Double.parseDouble(tempField.getText()); if (temp < 0) { temp = 0.0; tempField.setText(""+temp); statusLine.setText("temperature must be >= 0 !"); } else { tempField.setText(""+temp); statusLine.setText("Status: temp. changed to "+temp+" K"); } new_temp=true; } catch (NumberFormatException e) { statusLine.setText("temp. had wrong number format"); tempField.setText(""+temp); // System.exit(0); } repaint(); } } // end actionPerformed() /** * Returns information about this applet. * An applet should override this method to return a String containing * information about the author, version, and copyright of the Applet. * * @return a String representation of information about this Applet */ public String getAppletInfo() { // provide information about the applet return "Title:NobleGas \nAuthor: Martin Lieberherr \nkinetic gas theory \nApril 29th, 2011 "; } public void run(){ double xx, yy, rr, qq, c, cc, ccc, cccc; // temporary variables long t0; // System.currentTimeMillis() int k; // temporary variable try{ while (true) { // endless loop if (new_n_atoms) { // initialize and draw positions g1.setColor(Color.white); g1.fillRect(0,0,nx,ny); g1.setColor(Color.blue); rr = Math.ceil(Math.sqrt( n_atoms)); k = 0; make_startpositions: // a label for (int i=0; i < rr; i++) { // distribute atoms on a regular lattice with small scatter for (int j=0; j < rr ; j++) { x[k] = (19.9 + ((double) nx-40.0+Math.random())/rr*j)*scale; y[k] = ((double) ny-19.9 -((double) ny-40.0+Math.random())/rr*i)*scale; g1.fillOval( (int) ((x[k]-r_atom)/scale), (int) ((y[k]-r_atom)/scale), (int) (2.0*r_atom/scale), (int) (2.0*r_atom/scale)); k = k+1; if (k >= n_atoms) { break make_startpositions; } } } repaint(); new_n_atoms = false; new_temp = true; } if (new_temp) { // initialize velocities and accelerations of atoms v_thermal = Math.sqrt(kB*temp/m_atom); // for 1 degree of freedom! for (int i=0; i=2) { // calculate the inter-atomar forces and the net-accelerations for (int i=0; icccc) {qq=cccc;} // prevent instabilities for very small separations e_pot = e_pot + qq*qq-2*qq; // Lennard-Jones potentials (up to a constant factor) qq = cc*(qq*qq-qq)/rr; ax[j] = ax[j] +qq*xx; ax[i] = ax[i] -qq*xx; ay[j] = ay[j] +qq*yy; ay[i] = ay[i] -qq*yy; } } } } e_pot = e_pot*e_min/(n_atoms/2)/1.6022e-22; // energy per atom in milli-electonvolt e_pot = (double) Math.round(e_pot*100)/100; r_near = Math.sqrt(r_near); r_near = Math.round(r_near*1e12); // shortest distance in picometer // complete third step in velocity-Verlet t_mean = 0; for (int i=0; i= xx) { x[i] = xx; vx[i] = -vx[i]; //hard wall (elastic collision) } else if (x[i] < 0) { x[i] = 0; vx[i] = -vx[i]; } if (y[i] >= yy) { y[i] = yy; vy[i] = -vy[i]; // elastic reflection } else if (y[i] < 0) { y[i] = 0; vy[i] = -vy[i]; } } // draw new positions after 100 steps OR 10 milliseconds n_paint = n_paint+1; // number of temporal steps in simulation if ((n_paint>99) || (System.currentTimeMillis()-t0 > 20)) { g1.setColor(Color.white); g1.fillRect(0,0,nx,ny); g1.setColor(Color.blue); k = (int) Math.round(2.0*r_atom/scale); // diameter of atom in pixels for (int i=0; i