shock hazard

Examples of shock hazard in the following topics:

• Humans and Electric Hazards

  • The hazards from electricity can be categorized into thermal and shock hazards.
  • There are two known categories of electrical hazards: thermal hazards and shock hazards.
  • A shock hazard occurs when electric current passes through a person.
  • This can prolong the shock indefinitely.
  • The lethality of an electric shock is dependent on several variables:

• Safety Precautions in the Household

  • Electrical safety systems and devices are designed and widely used to reduce the risks of thermal and shock hazards.
  • Electricity has two hazards.
  • A thermal hazard occurs in cases of electrical overheating.
  • A shock hazard occurs when an electric current passes through a person.
  • There are many systems and devices that prevent electrical hazards .

• Radiative Shocks

  • The opposite extreme is that the shock heats the gas sufficiently that radiative losses are important near the shock and the gas rapidly cools.
  • In this case we must abandon the conservation of energy flux through the shock (fourth equation of this chapter) and find another criterion to understand how the gas changes through the shock.
  • Just above the flux the flow enters the shock slightly supersonically and leaves subsonically.
  • The ratio of the energy flux entering the radiative shock to that leaving is given by
  • This yields a minimum energy ratio for the isothermal shock of

• Detonation Waves

  • The various points outline how the gas changes as it passes through the shock and burns.
  • In the case of a shock without a chemical change there is no minimum velocity jump.
  • This special situation often arises when the combustion itself creates the shock.
  • If the postshock gas is traveling subsonically relatively to the shock then the rarefaction wave will eventually catch up to the back of the shock reducing the flux through the shock by reducing the postshock pressure and shock velocity relative to the preshock gas until the minimum flux is achieved.
  • The point $E$ for example has a lower entropy than point $C$ so the gas cannot pass from $C$$C$to $E$ either immediately after the shock or through a subsequent shock.

• Non-relativistic Shocks

  • Let's stand in the frame of the shock.
  • What goes into the shock must come out of the shock.
  • The fluid enters the shock supersonically and leaves the shock subsonically.
  • It is not obvious from the expression but the post-shock temperature always exceeds the pre-shock value.
  • The velocity difference vanishes for small shocks and grows as the area of the box as the shock grows.

• Problems

  • Show that the entropy of the fluid increases as it passes through a shock.
  • Figure 12.5 shows shocked air heated to incandescence about two milliseconds after the detonation of a nuclear bomb.
  • Find the incoming and outgoing velocity of a relativistic shock in terms of the energy density and pressure on either side of the shock.

• Relativistic Shocks

  • We will look at relativistic shocks as an example of relativistic hydrodynamics.
  • In particular we will look at the relativistic jump conditions across the shock.
  • The particle flux must be conserved across the shock
  • where $V_1=1/n_{\mathrm{prop},1}$ and $U_1 = \gamma_1 v_1/c$is the spatial component of four-velocity of the flow before the shock and $\gamma_1=(1-v_1^2/c^2)^{-1/2}$.
  • Finally we can derive the equation of the shock adiabat, using the identity $\gamma^2 = 1 + U^2$, to yield

• Sonic Booms

  • A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound.
  • A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound.
  • They eventually merge into a single shock wave traveling at the speed of sound.
  • The shock waves radiate out from the sound source, and create a "Mach cone' .
  • An observer hears the boom when the shock wave, on the edges of the cone, crosses his or her location

• A Spherical Shock - The Sedov Solution

  • The velocity of the shock wave with respect to the undisturbed gas is
  • We would like to know the speed of the gas relative to the undisturbed gas after the shock has passed,
  • Behind the shock, the fluid is ideal so we can use the continuity, Euler and energy equations
  • The shock jump conditions give the boundary conditions for the solution,
  • Variation of the density, velocity and pressure behind the shock for the Sedov-Taylor blast wave

• B.12 Chapter 12

  • Show that the entropy of the fluid increases as it passes through a shock.
  • Specifically what is $P/\rho^\gamma$ on each side of the shock?
  • The value of $K$ increases across the shock for $\gamma>1$, therefore the entropy increases.
  • Find the incoming and outgoing velocity of a relativistic shock in terms of the energy density and pressure on either side of the shock.
  • Start with the equations found in the concept on "Relativistic Shocks," as well as: