refactor: 提取 CloudExpansionModel 独立模块

- RadiusAt(t)/DensityAt(t)/TimeToReach(r) 封装在 CloudExpansionModel
- ComputeEffectiveRadius 简化为委托调用
- GaussianPuffDispersion 重复逻辑待后续统一

src/CounterDrone.Core/Algorithms/CloudExpansionModel.cs

@@ -0,0 +1,61 @@
+using System;
+using CounterDrone.Core.Models;
+
+namespace CounterDrone.Core.Algorithms
+{
+    /// <summary>云团膨胀模型——根据弹药和环境参数计算各阶段半径、密度、膨胀时间</summary>
+    public class CloudExpansionModel
+    {
+        private readonly AmmunitionSpec _ammo;
+        private readonly CombatScene _env;
+
+        public CloudExpansionModel(AmmunitionSpec ammo, CombatScene env)
+        {
+            _ammo = ammo;
+            _env = env;
+        }
+
+        /// <summary>Phase 1 爆轰初始半径 (m)</summary>
+        public float InitialRadius => 3.3f * (float)Math.Pow(Math.Max(0.01, (float)_ammo.BurstChargeKg), 0.32f);
+        public float TurbulentExpansionK => (float)_ammo.TurbulentExpansionK;
+
+        /// <summary>指定时刻湍流膨胀半径 R(t) = R₀ + k√t</summary>
+        public float RadiusAt(float elapsedSeconds)
+        {
+            if (elapsedSeconds <= 0) return InitialRadius;
+            bool inPhase3 = elapsedSeconds > 30f;
+            if (!inPhase3)
+                return InitialRadius + TurbulentExpansionK * (float)Math.Sqrt(elapsedSeconds);
+
+            // Phase 3: 高斯扩散
+            float windSpeed = (float)_env.WindSpeed;
+            float x = Math.Max(1f, windSpeed * (elapsedSeconds - 30f));
+            var cls = Kinematics.GetStabilityClass((WeatherType)_env.WeatherType, windSpeed);
+            float sY = Kinematics.SigmaY(cls, x);
+            float sZ = Kinematics.SigmaZ(cls, x);
+            float peakC = Kinematics.GaussianPeakConcentration((float)_ammo.SourceStrength, sY, sZ);
+            float effConc = (float)_ammo.EffectiveConcentration;
+            if (peakC <= effConc) return InitialRadius + TurbulentExpansionK * (float)Math.Sqrt(30f);
+            float sigma = (sY + sZ) / 2f;
+            float rPhase2 = InitialRadius + TurbulentExpansionK * (float)Math.Sqrt(30f);
+            return rPhase2 + sigma * (float)Math.Sqrt(2f * Math.Log(peakC / effConc));
+        }
+
+        /// <summary>指定时刻中心浓度</summary>
+        public float DensityAt(float elapsedSeconds)
+        {
+            float r = RadiusAt(elapsedSeconds);
+            float volume = (4f / 3f) * (float)Math.PI * r * r * r;
+            return volume > 0.001f ? (float)_ammo.SourceStrength / volume : (float)_ammo.CoreDensity;
+        }
+
+        /// <summary>达到指定半径所需时间 (s)</summary>
+        public float TimeToReach(float radius)
+        {
+            float r0 = InitialRadius;
+            if (radius <= r0) return 0;
+            float k = TurbulentExpansionK;
+            return (radius - r0) * (radius - r0) / (k * k);
+        }
+    }
+}

src/CounterDrone.Core/Algorithms/DefaultDefensePlanner.cs

@@ -349,41 +349,13 @@ namespace CounterDrone.Core.Algorithms
         private (float effectiveRadius, float expansionTime, float rPhase2) ComputeEffectiveRadius(
             DroneGroup threat, AmmunitionSpec ammo, CombatScene env)
         {
-            float totalFlightTime = threat.ArrivalTime * 2f;
-            float halfTime = totalFlightTime / 2f;
-            float windSpeed = (float)env.WindSpeed;
-            var weather = (WeatherType)env.WeatherType;
-            float avgSpeed = (float)threat.Target.TypicalSpeed / 3.6f;
-
-            // Phase 1 初始半径（基于爆发药 TNT 当量）
-            float r0 = 3.3f * (float)Math.Pow(Math.Max(0.01, (float)ammo.BurstChargeKg), 0.32);
-            float k = (float)ammo.TurbulentExpansionK;
-            float maxDur = (float)ammo.MaxDuration;
-
-            // Phase 2 湍流膨胀后的半径
-            float phase2Time = Math.Min(halfTime, 30f);
-            float turbulentRadius = r0 + k * (float)Math.Sqrt(Math.Max(0, phase2Time));
-
-            float expansionTime = (float)Math.Pow((turbulentRadius - r0) / Math.Max(k, 0.01f), 2);
-            float effectiveR = turbulentRadius;
-
-            // Phase 3 高斯扩散
-            if (halfTime > 30f)
-            {
-                float x = Math.Max(1f, windSpeed * (halfTime - 30f));
-                var cls = Kinematics.GetStabilityClass(weather, windSpeed);
-                float sY = Kinematics.SigmaY(cls, x);
-                float sZ = Kinematics.SigmaZ(cls, x);
-                float peakC = Kinematics.GaussianPeakConcentration((float)ammo.SourceStrength, sY, sZ);
-                float threshold = (float)ammo.EffectiveConcentration;
-                if (peakC > threshold)
-                {
-                    float sigma = (sY + sZ) / 2f;
-                    effectiveR = turbulentRadius + sigma * (float)Math.Sqrt(2f * Math.Log(peakC / threshold));
-                }
-            }
-
-            return (effectiveR, expansionTime, turbulentRadius);
+            var model = new CloudExpansionModel(ammo, env);
+            float tPhase2 = 30f;
+            float rPhase2 = model.RadiusAt(tPhase2);
+            float expansionTime = model.TimeToReach(rPhase2);
+            float halfTime = threat.ArrivalTime * 2f; // 总飞行时间的一半
+            float effectiveR = model.RadiusAt(halfTime);
+            return (effectiveR, expansionTime, rPhase2);
         }
 
         private int CalcRoundsNeeded(DroneGroup threat, AmmunitionSpec ammo,
@@ -399,14 +371,6 @@ namespace CounterDrone.Core.Algorithms
 
             return Math.Max(1,
                 (int)Math.Ceiling(requiredCoverage / spacing));
-
-            var aerosolType = (AerosolType)ammo.AerosolType;
-            float neededExposure = aerosolType == AerosolType.ActiveMaterial ? 2f : 6f;
-            float singleCoverage = neededExposure * avgSpeed;
-            float requiredCoverage = singleCoverage;
-
-            return Math.Max(1,
-                (int)Math.Ceiling((requiredCoverage - 2f * turbulentRadius) / spacing) + 1);
         }
 
         private float ComputeInterceptProbability(DroneGroup threat,