1DSIM — 1D Thermal Network Simulator

A high-performance 1D thermal network simulator with a compiled C++ solver core, Python REST API, interactive browser-based schematic editor, and a native Windows desktop CAD application — inspired by GT-ISE / GT-Suite.

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Features

🔬 Physics Engine (C++ Core)

Feature	Details
Heat Transfer Modes	Conduction · Convection · Radiation · Advective Fluid Flow
Fan / Pump Link	Exact analytical quadratic root — fan curve vs. system resistance
Fluid Media	Water · Glycol 50/50 · Engine Oil · Air · Mixture (0–100% glycol) · Custom
Custom Fluid	User-defined polynomial ρ(T) and cₚ(T) coefficients
Solvers	Explicit Euler · RK4 · Implicit Backward Euler (Newton iteration)
Steady State	Nonlinear Newton iteration with configurable tolerance
T-dependent props	All node capacities and link conductances support C(T), G(T)

🌐 Web Interface

• Drag-and-drop schematic canvas — nodes, orthogonal links, live temperature colour map
• Live transient simulation — animated flow chevrons during run
• Attribute Sheet — click any element to edit all parameters live
• Fan Matcher tab — Chart.js plot of fan curve vs. system resistance with operating point
• 4 built-in presets — Vehicle Cooling Loop · CPU Cooler · Li-Ion Battery Pack · Double-Pane Window
• Dynamic Variable sliders — adjust power, flow rate, ambient temperature during simulation
• CSV export — full time-history of all node temperatures

🖥️ Desktop Application

• Native Windows app using Dear ImGui + ImPlot + DirectX 11
• Physical Component Library — Place standard ICE cooling components directly on the canvas:
  • Engine Block, Radiator, Radiator Fan, Water Pump, Thermostat, Coolant Hose, Oil Cooler, Heater Core, Expansion Tank, and Ambient Air
  • Auto-compiles component/connection graphs into the flat solver representation
• Schematic editor with grid snap, zoom/pan, multi-select
• Full Attribute Sheet editing for all component types
• ImPlot Fan Matcher panel — fan & resistance curves with operating point marker
• Save/load .gtm JSON project files (backward compatible)
• Animated directional flow chevrons at 60 fps

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Project Structure

1DSIM/
├── src/
│   ├── core/               # C++ solver engine
│   │   ├── solver.h        # ThermalNode, ThermalLink, ThermalSystem API
│   │   ├── solver.cpp      # Physics: solvers, fluid properties, fan matching
│   │   └── bindings.cpp    # C-ABI DLL exports for Python ctypes
│   ├── wrapper/
│   │   └── thermal_solver.py   # Python ctypes wrapper
│   ├── gui/
│   │   ├── server.py           # Python HTTP REST server
│   │   └── web/
│   │       ├── index.html      # Browser schematic editor
│   │       ├── app.js          # Simulation logic, canvas rendering
│   │       └── style.css       # GT-Suite-inspired dark theme
│   └── desktop/
│       └── main.cpp            # Native ImGui + ImPlot application
├── tests/
│   ├── test_simulation.py      # Core solver tests (transient, steady, stiff)
│   └── test_media_simulation.py # Fluid media + fan link physics tests
├── thirdparty/
│   ├── imgui/                  # Dear ImGui (vendored)
│   ├── implot/                 # ImPlot (vendored)
│   └── json.hpp                # nlohmann/json single header
├── build.py                    # Build solver DLL (MSVC)
├── build_desktop.py            # Build thermal_sim.exe (MSVC + ImGui)
└── run.py                      # Launch web server shortcut

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Getting Started

Prerequisites

Tool	Version
Python	3.10+
MSVC (Visual Studio Build Tools)	2022
pytest	pip install pytest

1. Build the C++ Solver DLL

python build.py
# Outputs: src/core/solver.dll

2. Run the Web Interface

python run.py
# Opens http://localhost:8000 automatically

3. Build & Run the Desktop App

python build_desktop.py
# Outputs: thermal_sim.exe
./thermal_sim.exe

4. Run the Test Suite

pytest -v
# 9 tests, 0.000000% relative error on all physics checks

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Physics Reference

Fan / Pump Operating Point

The fan curve is modelled as a quadratic:

P_fan(v) = P_max − B·v²     where B = P_max / v_max²

The system resistance:

P_sys(v) = K·v² + R·v

Setting P_fan = P_sys and solving analytically:

v_oper = (−R + √(R² + 4(K + B)·P_max)) / (2(K + B))
Q_vol  = v_oper × A × 60000   [L/min]

Fluid Mixture Interpolation

ρ_mix(T)  = (1 − r)·ρ_water(T)  + r·ρ_glycol(T)
cₚ_mix(T) = (1 − r)·cₚ_water(T) + r·cₚ_glycol(T)

where r is the glycol volume fraction (0 = pure water, 1 = pure glycol).

Custom Fluid Polynomials

ρ(T)  = a₀ + a₁·T + a₂·T²   [kg/m³]
cₚ(T) = b₀ + b₁·T + b₂·T²   [J/(kg·K)]

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Test Results

All 9 tests pass with 0.000000% relative error against closed-form analytical solutions:

Test	Validates
test_fluid_capacities	ρ(T)·V·cₚ(T) for Water, Glycol, Oil, Air
test_fluid_advection	Upstream enthalpy transport in closed loop
test_mixture_fluid	Linear interpolation at 40% glycol fraction
test_custom_fluid	Polynomial ρ(T), cₚ(T) evaluation
test_fan_link	Quadratic root v_oper → advective heat rate
test_transient_cooling	RK4 exponential temperature decay
test_steady_state	Newton iteration convergence
test_stiff_system_implicit	Implicit Euler stiff system stability
test_temperature_dependence	Nonlinear C(T) during transient

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Built-in Presets

Preset	Nodes	Links	Description
Vehicle Cooling Loop	5	5	Engine → Jacket → Radiator → Ambient
CPU Cooler Assembly	4	3	Die → TIM → Heat Sink → Air
Li-Ion Battery Pack	10	12	4-cell array with serpentine coolant channels
Double-Pane Window	5	4	Indoor → Glass → Argon gap → Glass → Outdoor

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Tech Stack

Layer	Technology
Solver core	C++17 · MSVC
Python binding	ctypes
Web server	Python http.server
Web UI	Vanilla HTML/CSS/JS · Chart.js
Desktop UI	Dear ImGui · ImPlot · DirectX 11
Tests	pytest
JSON I/O	nlohmann/json

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License

MIT License — see LICENSE for details.

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Built to demonstrate real-world 1D thermal simulation competency for automotive and motorsport engineering applications.