added gravity function for calculating local g updated config for faster testing and changed the symbols at physical pos

src/helper/gravity.js

@@ -0,0 +1,90 @@
+/**
+ * Gravity calculations based on WGS-84 ellipsoid model.
+ * Author: Rene de Ren (Waterschap Brabantse Delta)
+ * License: EUPL-1.2
+ */
+
+class Gravity {
+  constructor() {
+    // Standard (conventional) gravity at 45° latitude, sea level
+    this.g0 = 9.80665; // m/s²
+  }
+
+  /**
+   * Returns standard gravity (constant)
+   * @returns {number} gravity in m/s²
+   */
+  getStandardGravity() {
+    return this.g0;
+  }
+
+  /**
+   * Computes local gravity based on latitude and elevation.
+   * Formula: WGS-84 normal gravity (Somigliana)
+   * @param {number} latitudeDeg  Latitude in degrees (−90 → +90)
+   * @param {number} elevationM   Elevation above sea level [m]
+   * @returns {number} gravity in m/s²
+   */
+  getLocalGravity(latitudeDeg, elevationM = 0) {
+    const phi = (latitudeDeg * Math.PI) / 180;
+    const sinPhi = Math.sin(phi);
+    const sin2 = sinPhi * sinPhi;
+    const sin2_2phi = Math.sin(2 * phi) ** 2;
+
+    // WGS-84 normal gravity on the ellipsoid
+    const gSurface =
+      9.780327 * (1 + 0.0053024 * sin2 - 0.0000058 * sin2_2phi);
+
+    // Free-air correction for elevation (~ −3.086×10⁻⁶ m/s² per m)
+    const gLocal = gSurface - 3.086e-6 * elevationM;
+    return gLocal;
+  }
+
+  /**
+   * Calculates hydrostatic pressure difference (ΔP = ρ g h)
+   * @param {number} density     Fluid density [kg/m³]
+   * @param {number} heightM     Height difference [m]
+   * @param {number} latitudeDeg Latitude (for local g)
+   * @param {number} elevationM  Elevation (for local g)
+   * @returns {number} Pressure difference [Pa]
+   */
+  pressureHead(density, heightM, latitudeDeg = 45, elevationM = 0) {
+    const g = this.getLocalGravity(latitudeDeg, elevationM);
+    return density * g * heightM;
+  }
+
+  /**
+   * Calculates weight force (F = m g)
+   * @param {number} massKg      Mass [kg]
+   * @param {number} latitudeDeg Latitude (for local g)
+   * @param {number} elevationM  Elevation (for local g)
+   * @returns {number} Force [N]
+   */
+  weightForce(massKg, latitudeDeg = 45, elevationM = 0) {
+    const g = this.getLocalGravity(latitudeDeg, elevationM);
+    return massKg * g;
+  }
+}
+
+module.exports = new Gravity();
+
+
+/*
+const gravity = gravity;
+
+// Standard gravity
+console.log('g₀ =', gravity.getStandardGravity(), 'm/s²');
+
+// Local gravity (Breda ≈ 51.6° N, 3 m elevation)
+console.log('g @ Breda =', gravity.getLocalGravity(51.6, 3).toFixed(6), 'm/s²');
+
+// Head pressure for 5 m water column at Breda
+console.log(
+  'ΔP =',
+  gravity.pressureHead(1000, 5, 51.6, 3).toFixed(1),
+  'Pa'
+);
+
+// Weight of 1 kg mass at Breda
+console.log('Weight =', gravity.weightForce(1, 51.6, 3).toFixed(6), 'N');
+*/