Edit in JSFiddle

<body>

<script src="https://cdn.plot.ly/plotly-latest.min.js"></script>

<div id="graph2" style="width: 600px; height: 400px;"></div>

<script>
        function arakawaMean(pte, fc, m_qd, pw, sigwy, b, j) {
            var sigsu = 0.068 * (pte ** 0.23) * (18.0 + fc) / (m_qd + 0.12) + 0.85 * (pw * sigwy) **0.5;
            return sigsu * b * j / 1000.0;
        }

        var fc    = 21.0
        var m_qd1 = 1.0
        var m_qd2 = 2.0
        var m_qd3 = 3.0
        var pw    = 0.008
        var sigwy = 295.0
        var b     = 600.0
        var j     = 700.0
        // pteを変えてみる
        var x = [
            0.05, 
            0.06,
            0.07,
            0.08,
            0.09,
            0.10,
            0.11,
            0.12
        ];
        var y1 = x.map(pte => arakawaMean(pte, fc, m_qd1, pw, sigwy, b, j));
        var y2 = x.map(pte => arakawaMean(pte, fc, m_qd2, pw, sigwy, b, j));
        var y3 = x.map(pte => arakawaMean(pte, fc, m_qd3, pw, sigwy, b, j));
        var data = [
            { name: 'M/Qd=1', x : x, y : y1},
            { name: 'M/Qd=2', x : x, y : y2},
            { name: 'M/Qd=3', x : x, y : y3}
        ];
        var layout = { title : '荒川Mean式', legend : { showlegend : true }, xaxis : { title : 'pte(%)'}, yaxis : { title : 'Qsu(kN)' } };
        Plotly.newPlot("graph2", data, layout);
</script>

</body>