java - 抛射运动的实现

Question

我用 Java 创建了一个带有用户界面的抛射运动模拟。该程序允许用户输入初始值来计算物体的射弹。我当前没有设置任何内容来将射弹绘制到屏幕上。

我有一个单独的 spring 工作线程在后台处理模拟代码。

我还添加了碰撞检测，以便当物体撞击地面时它会反弹并继续这样做，直到循环退出。

我所使用的方程对于我想要实现的目标来说并不正确。

在以下初始条件下，输出数据的绘图结果如下:

Initial Conditions:
Angle: 30 degrees;
Initial Speed 8.66 m/s;
Height: 50 m;
Elasticity of object: .5 coefficient of restitution in the y direction;
Acceleration: -9.8 m/s^2;
No acceleration in the x direction

看来，一旦模拟开始，y就会变得越来越大，因此循环永远不会自行退出。

这是代码:

    //This class will handle all time consuming activities
class Simulation extends SwingWorker<Void, Void>
{
    //Execute time consuming task
    protected Void doInBackground() throws Exception 
    {
        FileWriter fstream = new FileWriter("output.txt");

        BufferedWriter out = new BufferedWriter(fstream);

        double angle = Double.valueOf(angleText.getText());
        double radians = angle * (Math.PI/180); 
        double vel = Double.valueOf(speedText.getText()); 
        double mass = Double.valueOf(massText.getText()); 
        double y = Double.valueOf(heightText.getText());
        double x = 0;
        double epX = Double.valueOf(epxText.getText());
        double epY = Double.valueOf(epyText.getText());
        double ax = Double.valueOf(accxText.getText());
        double ay = Double.valueOf(accyText.getText()); 

        int numBounces = 0;
        double deltaTime = .00000001; 
        double total_velocity = 0.0;
        double time = 0.0;

        String fs; 

        angle = angle * Math.PI / 180; 

        while(numBounces < 10)
        {
            //Increment Time
            time = time + deltaTime;

            //Calculate new values for velocity[x] and velocity[y]
            double vx = (vel*Math.cos(angle)) + ax*time;;
            double vy = (vel*Math.sin(angle)) + ay*time; 

            //Calculate new values for x and y
            x = x + vx*time;
            y = y + vy*time + .5*ay*(time*time); 

            System.out.format("%.3f\n", y); 

            fs = String.format("%f\t %f\t %f\t %f\t %f\t %f\t %f\t\n", ax, ay, x, y, vx, vy, time); 

            out.write(fs); 

            //If ball hits ground: y < 0
            if(y < 0)
            {
                numBounces++;

                System.out.println("Number of Bounces: " + numBounces); 

                //Why is this statement needed if the velocity in the y direction is already being reversed?
                vy = -vy - ay*time; //  vy = -vy - ay*time; 

                //Calculate angle
                angle = Math.atan(vy/vx);

                angle = angle * Math.PI / 180; 

                //Calculate total velocity
                total_velocity = Math.sqrt((vy*vy) + (vx*vx));

                //Velocity with elasticity factored in
                total_velocity = Math.sqrt((epY) * total_velocity);

                //New velocities for when ball makes next trip
                vy = total_velocity*Math.sin(angle); 
                vx = total_velocity*Math.cos(angle);

                out.write(fs); 

            }

            //Draw projectile

                //Thread.sleep(.00001); //Sleep for deltaTime - 10 nanoseconds or draw after n number of points
        }

        out.close(); 

        return null;
    }

    //SwingWorker lets you execute code on the event dispatching thread. Also allows you to update the GUI
    public void done()
    {
        try
        {               
            /*
            rangeText.setText(" " + x);
            heightTText.setText(" " + y); 
            timeText.setText(" " + time);
             */
        }

        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

可能的问题是什么？我的猜测是，这可能与角度有关。在以前版本的代码中，我没有考虑角度，它工作得很好。另外，我不确定是否必须设置 GUI 上的界限，以免永远继续下去。

我也有一个 NullPointerException。

Answer 1

我看到的第一个问题在这里:

//Calculate angle
angle = Math.atan(vy/vx);
angle = angle * Math.PI / 180; 

Math.atan 已返回一个以弧度为单位的值:

Returns the arc tangent of a value; the returned angle is in the range -pi/2 through pi/2.

因此，* Math.PI/180 不会给您带来任何好处。

第二个问题在这里:

//Calculate new values for velocity[x] and velocity[y]
double vx = (vel*Math.cos(angle)) + ax*time;;
double vy = (vel*Math.sin(angle)) + ay*time; 

每次通过循环，这些值都会重新初始化。由于 angle、ax、ay 和 time 在循环期间无法更改，这意味着您始终会得到相同的 vx 和(正)vy。 vy 应该随着每次循环而变小，更像是:

//Calculate initial values for velocity[x] and velocity[y]
double vx = (vel*Math.cos(angle)) + ax*time;
double vy = (vel*Math.sin(angle)) + ay*time; 

while(numBounces < 10) {
    //Increment Time
    time = time + deltaTime;

    //Calculate new values for x and y
    x = x + vx*time;
    y = y + vy*time + .5*ay*(time*time); 

    //Calculate new values for velocity[x] and velocity[y]
    vx += ax * time;
    vy += ay * time;