Problem 15.8 - Buckling & yield – Euler’s formula

Picture with a simple truss constructed from a steel pipe. The reuss has a base of a+b and a height of c. The load, P, is applied downwards a distance of a from the left end of the truss. The pipe has a cross section of a hollow cylinder made of an inner radius ri and an outer radius ro. [Problem adapted from © Kurt Gramoll CC BY NC-SA 4.0]

#| standalone: true
#| viewerHeight: 600
#| components: [viewer]

from shiny import App, render, ui, reactive
import random
import asyncio
import io
import math
import string
from datetime import datetime
from pathlib import Path

def generate_random_letters(length):
    # Generate a random string of letters of specified length
    return ''.join(random.choice(string.ascii_lowercase) for _ in range(length))  

problem_ID="617"
ri=reactive.Value("__")
ro=reactive.Value("__")
a=reactive.Value("__")
b=reactive.Value("__")
c=reactive.Value("__")
  
attempts=["Timestamp,Attempt,Answer,Feedback\n"]

app_ui = ui.page_fluid(
    ui.markdown("**Please enter your ID number from your instructor and click to generate your problem**"),
    ui.input_text("ID","", placeholder="Enter ID Number Here"),
    ui.input_action_button("generate_problem", "Generate Problem", class_="btn-primary"),
    ui.markdown("**Problem Statement**"),
    ui.output_ui("ui_problem_statement"),
    ui.input_text("answer","Your Answer in units of kip", placeholder="Please enter your answer"),
    ui.input_action_button("submit", "Submit Answer", class_="btn-primary"),
    ui.download_button("download", "Download File to Submit", class_="btn-success"),
)

def server(input, output, session):
    # Initialize a counter for attempts
    attempt_counter = reactive.Value(0)

    @output
    @render.ui
    def ui_problem_statement():
        return[ui.markdown(f"A simple truss is constructed from steel pipe with inner radius r<sub>i</sub> = {ri()} in. and outer radius r<sub>o</sub> = {ro()} in. If lengths a = {a()} ft, b = {b()} ft, and c = {c()} ft, determine the largest load F that may be applied before either member AB or BC buckles? Assume all joints are pin connected and E = 29,000 ksi.")]
    
    @reactive.Effect
    @reactive.event(input.generate_problem)
    def randomize_vars():
        random.seed(input.ID())
        ri.set(random.randrange(30,150,5)/100)
        ro.set(ri()+random.randrange(10,30,5)/100)
        a.set(random.randrange(10,30,1)/10)
        b.set(a()*2.5)
        c.set(a()*2)
        
    @reactive.Effect
    @reactive.event(input.submit)
    def _():
        attempt_counter.set(attempt_counter() + 1)  # Increment the attempt counter on each submission.
        I = math.pi*ro()**4/4-math.pi*ri()**4/4
        LAB = (c()**2+a()**2)**0.5
        LBC = (c()**2+b()**2)**0.5
        alpha = math.atan(a()/c())
        theta = math.atan(b()/c())
        Pcr1 = math.pi**2*29000000*I/((LBC*12)**2)
        Pcr2 = math.pi**2*29000000*I/((LAB*12)**2)
        PBC = (math.sin(theta)*math.cos(alpha)/math.sin(alpha)+math.cos(theta))*Pcr1
        PAB = (math.sin(theta)*math.cos(alpha)/math.sin(alpha)+math.cos(theta))*math.sin(alpha)/math.sin(theta)*Pcr2
        instr = min(PBC,PAB)/1000
        if math.isclose(float(input.answer()), instr, rel_tol=0.01):
            check = "*Correct*"
            correct_indicator = "JL"
        else:
            check = "*Not Correct.*"
            correct_indicator = "JG"

        # Generate random parts for the encoded attempt.
        random_start = generate_random_letters(4)
        random_middle = generate_random_letters(4)
        random_end = generate_random_letters(4)
        encoded_attempt = f"{random_start}{problem_ID}-{random_middle}{attempt_counter()}{correct_indicator}-{random_end}{input.ID()}"

        # Store the most recent encoded attempt in a reactive value so it persists across submissions
        session.encoded_attempt = reactive.Value(encoded_attempt)

        # Append the attempt data to the attempts list without the encoded attempt
        attempts.append(f"{datetime.now()}, {attempt_counter()}, {input.answer()}, {check}\n")

        # Show feedback to the user.
        feedback = ui.markdown(f"Your answer of {input.answer()} is {check}. For reference in debugging this, the calculated instructor answer is {instr}")
        m = ui.modal(
            feedback,
            title="Feedback",
            easy_close=True
        )
        ui.modal_show(m)

    @session.download(filename=lambda: f"Problem_Log-{problem_ID}-{input.ID()}.csv")
    async def download():
        # Start the CSV with the encoded attempt (without label)
        final_encoded = session.encoded_attempt() if session.encoded_attempt is not None else "No attempts"
        yield f"{final_encoded}\n\n"
        
        # Write the header for the remaining CSV data once
        yield "Timestamp,Attempt,Answer,Feedback\n"
        
        # Write the attempts data, ensure that the header from the attempts list is not written again
        for attempt in attempts[1:]:  # Skip the first element which is the header
            await asyncio.sleep(0.25)  # This delay may not be necessary; adjust as needed
            yield attempt

# App installation
app = App(app_ui, server)